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Decreasing effect and mechanism of moisture content of sludge biomass by granulation process a
a
b
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Xia Zhao , Hao Xu , Jimi Shen , Bo Yu & Xiaochun Wang
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College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, China b
State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China Accepted author version posted online: 29 Jun 2015.
Click for updates To cite this article: Xia Zhao, Hao Xu, Jimi Shen, Bo Yu & Xiaochun Wang (2015): Decreasing effect and mechanism of moisture content of sludge biomass by granulation process, Environmental Technology, DOI: 10.1080/09593330.2015.1066448 To link to this article: http://dx.doi.org/10.1080/09593330.2015.1066448
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Publisher: Taylor & Francis Journal: Environmental Technology DOI: 10.1080/09593330.2015.1066448
Decreasing effect and mechanism of moisture content of sludge biomass by granulation process Xia Zhao*1,a, Hao Xu1,b, Jimi Shen2,c, Bo Yu1,d, Xiaochun Wang2,e
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1. College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, China; 2. State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering,
[email protected], [email protected], [email protected], [email protected], e
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Abstract
[email protected]
Disposal of high volume of sludge significantly raises water treatment costs. A method for cultivating aerobic granules in a sequencing batch airlift bioreactor (SBAR) to significantly
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produce lower moisture content is described. Results indicate that optimization of settling time and control of the shear stresses acted on the granules. The diameter of the granule was within the
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range of 1.0 mm to 4.0 mm, and its sludge volume index (SVI) was stabilised at 40 mL·g-1 to 50 mL·g-1. Its specific gravity was increased by a factor of 0.0392, and specific oxygen uptake rate (SOUR) reached 60.126 mg·h- 1·g- 1. Moreover, the percentage of its moisture content in the
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a
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Harbin Institute of Technology, Harbin 150090, China
reactor ranged from 96.73% to 97.67%, and sludge volume was reduced to approximately 60%, greatly due to the presence of extracellular polymeric substances (EPS) in the granules, as well as ＋
changes in their hydrophobic protein content. The removal rate of COD and NH4 -N reaches up to 92.6% and 98%, respectively. The removal rates of and TP is over 85%. Therefore, aerobic granular sludge process illustrates a good biological activity. *Corresponding
author. Tel. +86-13993184112, E-mail: [email protected]
Keywords: Low moisture content, granulation, biomass, hydrophobicity, sequencing batch airlift bioreactor 1. Introduction Continuous growth of biomass with high water content (e.g., algae produced by water
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eutrophication and biological sludge produced by sewage treatment plants) is due to greater water
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pollution, caused by increasing industrialization and increased demand. These organic biomasses
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have the following characteristics: 1) They possess high water content (>98%).; 2) They contain
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improper management.; and 4) They require high energy consumption and special equipment for dehydration. Determining the best way to handle biomasses with high water content has attracted increasing attention from scholars[1]. Additionally, abundant excess sludge produced from biological sewage treatment often contains a considerable number of hazardous and noxious
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substances (e.g., parasitic ova, pathogenic microorganisms, and heavy metals), as well as unstable organics, which must be treated properly to avoid environmental contamination. However, the
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existing excess sludge treatment is inefficient and economically ineffective. For example, the capital expenditure for sludge treatment in Europe and America accounts for as high as 60% to 70% of the total capital expenditure of a sewage treatment plant[2,3].
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certain calorific value.; 3) They are difficult to process, resulting in secondary pollution upon
Research has shown that dehydration is an effective way to reduce sludge volume. When
sludge water content decreases from originally 95% to approximately 85%, 65%, and 20% through mechanical dehydration, volume is reduced to 1/3, 1/7, and 1/16 of the original volume, respectively. Lower volume of dehydrated sludge occupies a smaller storage area and is better suited for transportation and disposal. Sludge with excessive water content also loses nitrogen,
phosphorus, and potassium (N, P, and K) as inorganic salts during dehydration[4,5]. Thus, dehydration, known as the end treatment, is an important step in the biosafe disposal of biomasses with high water content (e.g., municipal sludge). However, it faces problems of heavy dehydration load and high energy consumption. As a result, to produce aerobic granular sludge (AGS)
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containing biomasses with low water content, this research describes the successful formation and
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stable properties of granular sludge cultured from active sludge. Total water content in the tested
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granular sludge was measured.
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most research on SBR startup with AGS focused on parameters influencing the granulation process[9], such as short settling time for the selection of fast-settling particles[6,10–12], high shear stress caused by aeration[13,14], and so on. Much longer periods, on the order of 60 days to 150 days, have been reported for the achievement of high N- and P-removal performances[15–17].
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Compared with conventionally activated flocs, AGS has a regular, dense, and strong physical structure, good settling ability, high biomass retention, and ability to withstand shock loading
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rate[18]. In addition, as a result of oxygen’s diffusion gradient, aerobic, anoxic, and anaerobic zones simultaneously exist in AGS[19]. The development of methods to facilitate the fast cultivation of high quality AGS is a current research hotspot in the area of water treatment
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AGS formation in a sequencing batch reactor was first reported in the late 1990s[6–8]. Initially,
technology because a solution to this obstacle is urgently needed[20]. In recent years, there are more and more researchers focusing on the study about aerobic granular sludge (AGS), for example, it was found that the ratio of flocculent sludge should be kept a low level so as to maintain the stable operation of the granular sludge reactor because of the kinetic superiority of flocculent sludge over granular sludge, rather than microbial competition[21]. The distribution of
extracellular polymeric substances (EPS), hydraulic shear parameters and reactor configuration have a important influence on the structural stability of AGS[22-24]. Moreover, the concentration of Cu2+ and carbon source also plays a key role in performance of AGS[25-26]. 2. Materials and Methods
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2.1 Experimental set-up
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A sequencing batch airlift reactor (SBAR) was used to culture AGS (Fig. 1). Its volume was
3.0 L and water changing rate per cycle was 50%. The downcomer’s internal diameter was 6.25
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placed at a distance of 1.2 cm from the bottom of the downcomer. Air was introduced by a fine bubble aerator at the bottom of the reactor at a superficial air velocity of 1.6 cm.s-1, while a mass
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flow controller controlled the airflow rate. The experiment was conducted at room temperature, and excess activated sludge in the municipal sewage treatment plant’s sludge thickener was used as inoculated sludge (14.61 g·L-1).
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2.2 Inoculated sludge and experimental wastewater
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Synthetic wastewater was used as test water. Then, appropriate amounts of MgSO4·7H2O,
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CaCl2, CuSO4·5H2O, MnCl2·2H2O, and ZnSO4·7H2O and essential microelements for microbial growth were added.
The inoculated sludge, presented as brown flocs, contained 1.88 L activated sludge, 14.61
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cm, while the riser’s height and internal diameter were 70 cm and 4 cm, respectively, and was
g·L-1 total mixed liquor suspended solids (MLSS), 7.84 g·L-1 mixed liquor volatile suspended solids (MLVSS), 0.54 MLVSS/MLSS, 54.07 mL· g- 1 sludge volume index (SVI), and 99.1%
water.
2.3 Analytical methods
Chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total phosphorus (TP), MLSS,
MLVSS, and SV30 were tested using national standards methods[9,27]. AGS’ humidity and density were tested using centrifugation[28], while SOUR was tested using an established method[29]. AGS’ sedimentation rate was tested using gravitational sedimentation[30], and the size distribution of granular sludge was tested by wet sieving[31]. The microbial morphology and
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biophase of granular sludge were observed using optical and scanning electron microscopes (SEM,
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HITACHI S-3400N/4700). EPS was extracted and analysed using an established method[32], and
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2.4 Granulation process
In the experiment that lasted for 2.5 months, the SBAR’s working volume was 2.9 L. The inflow chemical oxygen demand (COD) was 600 mg·L-1. The system operated for 10 cycles every
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day, wherein each cycle had 8 min of water feeding, 112 min to 130 min of aeration, 2 min to 20
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min of sedimentation, and 4 min of drainage. To maintain a high sludge concentration in the SBAR, sedimentation time was determined based on sludge settleability (Table 1). The whole
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experiment was conducted at room temperature (20±3 °C). Dissolved oxygen (DO) was fed using micropore aeration from the bottom of the SBAR. The upward gas velocity was maintained at 0.2
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spectrophotometer (JASCO, FP-6500).
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the three-dimensional excitation-emission matrix (EEM) was analysed using a fluorescence
m3·h-1 to 0.3 m3·h-1, and the DO in the water was maintained at 3 mg·L-1 to 4 mg·L-1. The SBAR’s water feeding, aeration, sedimentation, drainage, and standing (idling) were controlled automatically.
3. Results and discussions
3.1 Granulation of activated sludge
The SBAR operated for 2.5 months, and the morphological changes of the granular sludge are shown in Fig. 2. Inoculated sludge particles were initially tiny and appeared as brown flocs (Fig. 2a). The microeddy produced by the upflow in the SBAR drove granule collisions and shortened
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sedimentation time gradually, causing selection pressure for larger granules in the activated sludge.
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The physical properties of sludge flocs changed due to the scouring action of the hydraulic shear
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forces. After five days of domestication, the sludge flocs expanded and approximately 1 mm
granules, adhered to the edges of these crystal nuclei (Fig. 2b). When the aeration rate was
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increased from 0.2 m3·h-1 to 0.25 m3·h-1, the granules grew more quickly. The granule size increased to about 2 mm in 8 days, presenting as smooth white balls or irregular ovals. Within 14 days, the granule size increased from 3 mm to 6 mm, showing bright and smooth surfaces with
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few tiny flocs (Fig. 2c). Observations of AGS’ formation and maturation indicated that small granules were assembled from both small flocs and original granules that were then reassembled
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into large granules through collision and hydraulic shear forces[4]. The coexistence of different sizes of aerobic sludge granules and flocs in the SBAR indicates the presence of a dynamic equilibrium system[33]. In the following two months, the sludge granules shrank in size, expanded,
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irregular round brown crystal nuclei were observed. Cilia, generally observed in tiny milk white
and then shrank again, finally maintaining a diameter of 3 mm to 4 mm, compact structure, and clear yellow outlines. Moreover, crystal nuclei with an attached growth of cilia were observed in the centre of certain sludge granules (Fig. 2d). The microscopic microbial morphological variations in the granular sludge are shown in Figs. 2e to 2h. According to the microscopic observations, filamentous bacteria interconnect into a networked structure to form sludge crystal
nuclei that are enveloped again by filamentous bacteria. The outer and inner filamentous bacteria interconnect to form a stable network to capture free microorganisms in the water, finally forming mature granular sludge (Fig. 2g). Furthermore, the granular sludge contained rich microbiota, including abundant active metazoan-like worms (Fig. 2h).
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3.2 Characteristics of aerobic granular sludge with low moisture content
Particle size of aerobic sludge
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0.07 mm, which increased gradually with prolonged operation and shorter sedimentation time as
sludge granules.
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granular sludge began to be produced in the SBAR. Fig. 3 exhibits the size distribution of aerobic
In Fig. 3, granular sludge (1.0 mm to 4.0 mm) accounted for 80% of the observed particles.
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After the sludge granulation stage, larger floc sludge and granular sludge particles (>4.0 mm)
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accounted for only a small proportion of the particles. Granular sludge is easier to dehydrate.
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However, the specific surface area of sludge decreases with the expansion of granular sludge, impeding the transmission of substrate inside the granular sludge. The granular sludge expansion also restricts the DO diffusion significantly, thus reducing its metabolic activity. As a result,
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Research results demonstrated that the average granule size of inoculated activated sludge was
moderate granular sludge particle size is preferred to a large one. Fig. 4 reveals the positive correlation between the granular sludge’s settling velocity and size. Granular sludge particles of >1.0 mm in size accounted for 88% of the particles, and their setting velocity ranged from 64.2 cm·min-1 to 95.4 cm·min-1, indicating that during sludge granulation,
AGS can improve the SBAR’s sludge water separation efficiency.
The positive correlation between setting velocity and size of granular sludge in Fig. 4 can be expressed as: y = 8.2879x +23.9745
(1)
where: x——granule size (mm);
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y——granule setting velocity (m·h-1).
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Specific gravity of aerobic granules
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with higher specific gravity settles more quickly. In the SBAR, inoculated sludge’s specific
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gravity increased slowly by only a factor of 0.0392 in one month, which is caused mainly by the considerable spaces in granular sludge that decrease sludge mass, setting velocity, and biomass. Research results show that because no sludge granules formed in the SBAR during the early
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reaction, granular sludge’s specific gravity increased slowly in that phase. Within 14 days,
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influenced by filamentous bacteria, granular sludge was generated that quickly increased the sludge’s overall specific gravity; however, it remained relatively low. Other researchers have
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reported[20] that interparticle bridges (PAMs) within granular sludge can be generated quickly during the early reaction under the collaboration of airflow and hydraulic shear forces. This brings
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Microbial density in granular sludge is expressed using the sludge’s specific gravity. Sludge
about a sharp increase in the specific gravity of the granular sludge, followed by a smooth increase, and then a secondary quick increase. The sludge’s specific gravity increased gradually after the generation of granular sludge, indicating that increase in microbial density and decrease in water content had occurred in the sludge.
Moisture effects of aerobic granular sludge
Water content is one of the more important sludge parameters for development of optimal wastewater treatment outcomes. Conventionally activated sludge flocs generally contain at least 99% water[34]. Fig. 5 shows that the water content of common activated sludge reaches as high as 99.1%, whereas that of granular sludge ranges from 96.73% to 97.67%, indicating that sludge can
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be condensed by at least 60%. Interstitial, capillary, and internal water are the three main water
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forms in sludge. Among them, interstitial water accounts for 70% of the total water not directly
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combined with the sludge and can be easily separated from it. Granular sludge contains little
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proteins are hydrophobic, EPS’ protein content likely contributes to granular sludge’s low water content[35].
Effects of EPS content and hydrophobicity
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EPS content of aerobic granules cultivated in the SBAR was studied. As one of the main
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microbial products in activated sludge, EPS refers to the polymers secreted by bacteria. Polysaccharide (PS) and protein (PN) are the main components of EPS, accounting for 70% to
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80% of EPS content. In this paper, EPS and PN components in granular sludge and activated sludge systems during the aerobic stage were analysed using EEM (Fig. 6).
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interstitial water due to dense flora[20]. Considering that most amino acid components of EPS
Li discovered that EPS’ hydrophobic PN content is inversely proportional to the sludge water
content[35]. In Fig. 6, protein and soluble microbial products are the main fluorescent organics in sludge EPS. Fig. 6a shows that peak A’s fluorescence intensity increased significantly in the fluorescence spectrum of AGS’ EPS. This demonstrates that one category of organics represented by this peak correlates closely with granular microorganisms’ metabolism in the SBAR. A new peak (peak B) was observed at 270 nm to 280nm/300 nm to 310nm Ex/Em on the EEM spectrum
of EPS. According to the five fluorescence regions defined by Chen et al., peak B reflects the presence of one category of soluble microbial products (Region VI)[36]. Peak strength of peaks T1 and T2 (protein) on granular sludge’s EPS fluorescence spectrum increased significantly, as compared with that of activated sludge (Fig. 6a). This indicates that protein in granular sludge are
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mainly released from the EPS of granular microorganisms in the SBAR. In contrast,
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microorganisms in activated sludge secrete less EPS, thus releasing lower amounts of protein.
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Sheng and Yu et al. discovered two peaks (T1 and T2) on the EPS fluorescence spectrum of a
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Fig. 6a, at 225/350 nm Ex/Em and 280/350 nm Ex/Em, respectively. Two strong peaks and two weak peaks were found on the EPS fluorescence spectrum in this work as well. Hydrophobic PN and PS contents of EPS content’s aerobic granules were studied here to further characterize their EPS characteristics[38–40]. PN and PS compositions changing during
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the operation period of the SBAR reactor are shown in Fig. 7. First, EPS, a gel substrate with negative charges and high water content, can sequester
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microorganisms for a long time and help to develop interdependent microbial communities. Second, its PA cell wall reduces the cells’ effective critical potentials, thus resulting in its flocculation. Third, it enables some sludge surfaces to be hydrophobic because it contains some
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common activated sludge system [37]. Their positions align similarly to those of the two peaks in
hydrophobic substances (e.g., fat and protein). Fourth, it can be used as an interparticle bridge because it contains anionic groups that can bind with divalent cations[35]. All these properties confer a net positive effect to EPS on granular sludge’s formation and hydrophobicity. EPS PN content was always greater than PS content, indicating a predominance of PN over PS in the EPS. The fact that the ratio of PN to PS fluctuated in the range of 1.2 to 2.9 indicated that
the former was predominant in the granules of SBAR reactor. PN and PS contents correlated well with the granule formation rate, even though the latter fluctuated slightly after most granules formed, presumably due to biological consumption in the granules’ substrate limited core. Enhanced organic loading appeared to promote the cells to produce greater amounts of EPS.
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Such positive relationship between EPS content and organic loading level was probably because
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the higher level of organic loading induced the microorganisms to have greater biological activity
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and then to secrete more metabolic products.
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AGS’ settling characteristics can be represented by SVI and SV30. In Fig. 8, sludge settleability and SVI were relatively lower during the early adaptive stage. However, with the progression of granulation, SV30 and SVI increased gradually and settleability recovered to a
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certain extent. SVI increased to the peak (92.13 mL·g-1) in 34 days, implying that sludge in the
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SBAR was expanded with poorer settleability. Such sludge expansion can be controlled effectively by adjusting the aeration rate. Subsequently, SV30 and SVI decreased to about 15% and 40 mL·g-1
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to 50 mL·g-1 respectively, accompanied by improved settleability.
SOUR of aerobic granular
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Settling properties of aerobic granular with low moisture content
In biological treatment technology, SOUR is an important evaluation index of microbial
metabolic activity. Therefore, SOUR and the microbial metabolic activity of AGS in SBAR were tested and analysed here. MLSS was first measured to analyse DO variation. AGS’ SOUR was calculated according to MLVSS, reaction time (t), and DO variation (Equation 2). The SOUR curve at different times is presented in Fig. 9.
SOUR = (DO0 - DOt) / (t ×MLVSS)
(2)
In SOUR equation (Equation 2), DO0 is the initial DO (mg·L-1), DOt is the endpoint DO (mg·L-1), and t is the test time (min). According to Fig. 9 and Equation 2, AGS had a higher SOUR that showed that the microbial metabolic activity was good, resulting in lower sludge yield.
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The SOUR value achieved a relative stability (60.13 mg·h- 1·g- 1) after 35 days, reflecting the
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desired properties (specific gravity, water content, settleability, and microbial activity) of the
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cultivated AGS.
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observed. With the increase of sludge temperature and age, microbial decomposition intensifies, thus decreasing sludge yield and volume (Table 2).
3.3 Morphological characteristics of granular sludge with low moisture content
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The effect of the morphological structure in AGS’ microbial populations on water content was
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explored through the observation of sludge morphology and microbial morphology during granulation. The SEM in Fig. 10a shows that AGS generated in the SBAR contains many spaces,
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and only few bacilli exist between numerous filamentous substances. According to the granulation and experimental results, shear forces can influence granular sludge properties (e.g., settleability
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Furthermore, distinct sludge reduction, which is related to the sludge yield coefficient, was
and microbial activity) by condensing the granules. Therefore, stable granular sludge in the SBAR promotes greater stability of the biological treatment system. Furthermore, with dense flora but little interstitial water, the resulting granular sludge has low water content. During the late experimental stage, abundant filamentous bacteria were generated on AGS’ surface. Their branches grew and extended into surrounding areas quickly. In Fig. 10b, filamentous bacterial branches with obvious diaphragm and sheathes can be observed clearly on
granular sludge surfaces. The granular sludge profile presents three obvious layers (Fig. 10c), representing a stable aerobic, anoxic-aerobic, and anaerobic zones[41]. This structure promotes improved dephosphoralization[9], as compared with that of traditional activated sludge[36]. Moreover, it provides a good environment for microbial coexistence, allowing filamentous
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bacteria to assist in the formation of compact microbial community observed in granular sludge,
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which concentrates internal microorganisms and leaves a small space for interstitial water. Hence,
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granular sludge has a significantly lower water content when compared with activated sludge.
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total apparent microbial yield coefficient. AGS has a compact structure and special aerobic-anaerobic zone that provides microorganisms with an aerobic-anaerobic alternating environment[42,43].
3.4 Biological degradation efficiency of aerobic granules process
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The removal of conventional pollutants is shown in Table 3. Since the microorganisms did not fully adapt to sewage concentration and the change living
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environment, the treatment effect was not stable in the initial start-up of reactor, so that the effluent COD was higher and the removal rate of it was less than 60%. With the accumulation of biomass in the reactor and the adaptive improvement of microorganism to the influent substrate,
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Aerobic and anaerobic zones can affect microbial growth in granular sludge by decreasing the
the removal rate was on the rise. After that, the removal of COD decreased due to the morphologic change of AGS. It was found that the removal decrease of COD was associated with the reduction of the biomass of AGS, and connected with the morphologic change of sludge, there maybe existed sludge bulking in reactor[44]. With the gradual granulation of sludge, the removal effect of COD was stable gradually and it could keep above 90%. The removal rate of TN and NH4+-N
was about 91% and 98%, respectively. The removal of TP fluctuated greatly, however, the removal rate of it could reached above 85% after the aerobic granular sludge was mature. 4. Conclusions The SBAR can be used to quickly cultivate AGS, resulting in granular sludge production with
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a significantly lower water content than activated sludge. Because the water content of generated
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granular sludge ranges from 96.73% to 97.67%, a great opportunity is offered for sludge reduction.
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Granule size mainly varies between 1.0 mm to 4.0 mm and SVI varies between 40 mL·g-1 to 50
0.0392, reflecting a higher density of microorganisms. The SOUR (O2) values reached 60.13mg·h·g- 1. Thus, granular sludge exhibits better microbial activity and settleability than activated
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sludge. The removal rate of COD and NH4 -N reaches up to 92.6% and 98%, respectively. The removal rates of and TP is over 85%.
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AGS’ surface is partially hydrophobic because its EPS contains some hydrophobic substances (e.g., fat and protein), demonstrating that PN content in EPS plays an important role in AGS’ low
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water content. Meanwhile, EPS can be used as an interparticle bridge because it has anionic groups that can bind with divalent cations, which confirms its positive effect in the granular sludge’s formation and hydrophobicity.
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mL·g-1. As activated sludge is converted to granular sludge, the specific gravity increased by
A compact microbial community structure forms in AGS, because of the presence of numerous
filamentous bacteria interspersed with few bacilli. This community leaves only a small space for interstitial water, such that AGS has low water content when compared with activated sludge. AGS has a special aerobic-anaerobic zone that provides microorganisms with an aerobic-anaerobic alternating environment.
Acknowledgments
This study was financially supported by the Creative Research Groups of China Foundation (Grants No. 51121062) and State Key Laboratory of Urban Water Resource and Environment (Harbin Institute of Technology) (2014TS03) and excellent Young Teachers in Lanzhou
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[1]Li WD. The discussion about gasification technology of high-moisture-content biomass and
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coal. Silicon Valley 2013; 17: 143-145 [In Chinese].
[2]Low EU., Chase HA. Reducing production of excess biomass during wastewater treatment. Water Res. 1999; 33: 1119-1132.
[3]Liang P, Huang X, Qian Y. Research progress on sludge reduction technologies.Techniques
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and Equipment for Environmental Pollution Control 2003; 4 (1): 44-52 [In Chinese].
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[4]Zhang WC. The exploration about improvement of sludge drying characteristics methods through ultrasonic treatment. College of environmental science and engineering. Tianjin: Tianjin university; 2006 [In Chinese].
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[5]Shen SM. The discussion about desiccation of high-moisture-content mash. Pharmaceutical & Engineering Design 2005; 26 (2): 5-7 [In Chinese].
[6]Beun JJ, Hendriks A, Van Loosdrecht MCM, Morgenroth, E, Wilderer, PA, Heijnen, JJ.
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Downloaded by [FU Berlin] at 23:08 05 July 2015
References
rip
Project for Creative and Entrepreneurship of China (No. 1210731150).
t
University of Technology Training Project (1005ZCX016) and the College Students Training
Aerobic granulation in sequencing batch reactor. Water Res. 1999; 33: 2283-2290.
[7]Dangcong P, Bernet N, Delgenes JP, Moletta R. Aerobic granular sludge-a case report. Water Res. 1999; 33: 890-893. [8]Morgenroth E, Sherden T, van Loosdrecht MCM, Heijnen JJ, Wilderer PA. Aerobic granular sludge in a sequencing batch reactor. Water Res. 1997; 31: 3191-3194. [9]Lochmatter S, Gonzalez GG, Holliger C. Optimized aeration strategies for nitrogen and phosphorus removal with aerobic granular sludge. Water Res. 2013; 47: 6187-6197.
[10]McSwain BS, Irvine RL, Wilderer PA. Effect of intermittent feeding on aerobic granule structure. Water Sci. Technol. 2004a; 49: 19-25. [11]McSwain BS, Irvine RL, Wilderer PA. The influence of settling time on the formation of aerobic granules. Water Sci. Technol. 2004b; 50: 195-202. [12]Qin L, Liu Y, Tay JH. Effect of settling time on aerobic granulation in sequencing batch reactor. Biochem. Eng. J. 2004; 21: 47-52.
rip
and granular sludge. Water Res. 2002; 36: 1653-1665.
t
[13]Liu Y, Tay JH. The essential role of hydrodynamic shear force in the formation of biofilm
[14]Tay JH, Liu, QS, Liu Y. The effect of upflow air velocity on the structure of aerobic granules
us c
[15]Gonzalez GG, Holliger C. Dynamics of microbial community structure and enhanced biological phosphorus removal of propionate- and acetate-cultivated aerobic granules. Appl.
M an
Environ. Microbiol. 2011; 77: 8041-8051.
[16]de Kreuk MK, Heijnen, JJ, van Loosdrecht, MCM. Simultaneous COD, nitrogen, and phosphate removal by aerobic granular sludge. Biotechnol. Bioeng. 2005; 90: 761-769. [17]Xavier JB, De Kreuk MK, Picioreanu C, Van Loosdrecht MCM. Multi-scale
d
individual-based model of microbial and by conversion dynamics in aerobic granular sludge.
pt e
Environ. Sci. Technol. 2007; 41: 6410-6417. [18]Lin, YM, Liu, Y and Tay JH. Development and characteristics ofphosphorus – accumulating
ce
microbial granules in sequencing batch reactors. Appl. Microbiol. Biotechnol. 2003; 62: 430-435.
[19]De Kreuk MK and De Bruin LMM. Aerobic Granule Reactor Technology. London, IWA
Ac
Downloaded by [FU Berlin] at 23:08 05 July 2015
cultivated in a sequencing batch reactor. Water Sci. Technol. 2004; 49: 35-40.
Publishing; 2004.
[20]Yi C, Zhan HH, Chen JD, Cheng JG. Characteristics of aerobic granular sludge in a whisk-sequencing batch reactor (WSBR). Acta Scientia Circumstantiae 2011; 31: 268-275 [In Chinese]. [21]Liu YQ, Tay JH. The competition between flocculent sludge and aerobic granules during the long-term operation period of granular sludge sequencing batch reactor. Environ. Technol. 2012; 33: 2619-2626. [22]Chen H, Zhou SH, Li TH. Impact of extracellular polymeric substances on the settlement
ability of aerobic granular sludge. Environ. Technol. 2010; 31: 1601-1612. [23]Zhu L, Zhou JH, Yu HT, Xu XY. Optimization of hydraulic shear parameters and reactor configuration in the aerobic granular sludge process. Environ. Technol. 2015; 36: 1605-1611. [24]Zhao X, Chen ZL, Shen JM, Wang XC. Performance of aerobic granular sludge in different bioreactors. Environ. Technol. 2014; 35: 938-944. [25]Zheng XY, Wang XN, Huang X, Chen Q, Chen W, He YJ. Effects of Cu2+ on morphological
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structure, functional groups, and elemental composition of aerobic granular sludge. Environ.
rip
Technol. 2013; 34: 219-224.
[26]Lashkarizadeh M, Yuan Q, Oleszkiewicz JA. Influence of carbon source on nutrient removal
us c
Technol. 2015; 1-26.
[27]National Environmental Protection Bureau. 2002(in Chinese), Water and Waste Water
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Monitoring and Analysis. 4th ed. Beijing: China Environmental Science Press 96-220. [28]Zhu JR, Liu CX. Cultivation and physic-chemical characteristics of granular activated sludge in alternation of anaerobic/aerobic process. Environ. Sci. 1999; 20: 39-41. [29]Xu YT, Shi JL, Zhang M. The Microbial Engineering of Pollution Control. Beijing:
d
Chemical Industry Press 2002; 231-233.
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[30]Wang F, Yang FL, Zhang XW, Liu YH. Characteristics of aerobic granular sludge under different organics. China Water & Wastewater 2004; 20: 46-48 [In Chinese].
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[31]Laguna A, Ouattara A, Gonzalez RO, Baron O, Famá G, Mamouni E, Guiot S, Monroy O, Macarie H. A simple and low cost technique for determining the granulometry of up flow anaerobic sludge blanket reactor sludge. Water Sci. Technol. 1991; 40: 1-8.
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Downloaded by [FU Berlin] at 23:08 05 July 2015
performance and physical-chemical characteristics of aerobic granular sludge. Environ.
[32]Adav SS, Lee DJ, Show KY, Tay JH. Aerobic granular sludge: Recent advance. Biotechnol Adv. 2008; 26: 411-423.
[33]Shen XX, Li XM, Yang Q, Zeng GM, Xu WX, Liao Q, Zheng Y. 2007. Acceleration of the formation of aerobic granules in SBR by inoculating mature aerobic granules. Environmental Science 2007; 28: 2467-2472 [In Chinese]. [34]Zhang ZJ. Drainage Engineering (Rudin). 3rd ed. Beijing: China Building Industry Press 1996; 296-303 [In Chinese]. [35]Li Y., 2008. The change about the EPS of sludge and its influence to operation of reactor in
MBR. Tianjin: Tianjin University; 2008 [In Chinese]. [36]Chen GH. Saby S, Djafer M, Mo HK. New approaches to minimize excess sludge in activated sludge systems. Wat .Sci .Tech. 2001; 44: 203-208. [37]Sheng GP, Yu HQ. Characterization of extracellular polymeric substances of aerobic and anaerobic sludge using three-dimensional excitation and emission matrix fluorescence spectroscopy. Water Res. 2006; 40 (6), 1233-1239.
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aerobic sludge blanket reactor. Journal of Appl Microbiol. 91(1), 168-175.
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[38]Tay JH, Liu Q.S., Liu Y, 2001. Microscopic observation of aerobic granulation in sequential
[39]Zhang LL, Feng XX, Zhu NW, Chen JM. Role of extracellular protein in the formation and
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[40]Chen MY, Lee DJ, Tay JH. Distribution of extracellular polymeric substances in aerobic granules. Appl. Microbiol. Biotechnol. 2007; 73: 1463-1469.
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[41]Wang C, Zheng XY. Effect of shear stress on morphology, structure and microbial activity of aerobic granules. Environmental Science 2008; 29: 2235-2241 [In Chinese]. [42]Wang JL, Zhang ZJ, Wu WW. Research advances in aerobic granular sludge[J]. Acta Scientiae Circumstantiae, 2009; 29: 449-473 [In Chinese].
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[43]Tay JH, Ivanov V, Pan S, Tay STL. Specific layers in aerobically grown microbial granules.
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Letters in Applied Microbiology 2002; 34: 254-257. [44]Zhao X, Zhao YL, Chen ZL, Jiang F, Luo HM, Feng HX. Control of filamentous sludge
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bulking in aerobic granular sludge SBR process. China Water & Wastewater 2012; 28(3): 15-19 [In Chinese].
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stability of aerobic granules. Enz. Microbiol. Technol. 2007; 41: 551-557.
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Fig. 1 –Schematic diagram of SBAR.
Fig. 2–Photographs and micrographs of aerobic granules in the reactor during different phase:
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Fig. 3 –Size distribution of the aerobic granules
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(a)inoculated sludge, (b)five days, (c)fourteen days, (d)forty-five days, (e)seed sludge, (f)granular sludge, (g)sludge nuclei and (h)Microbial phase.
Fig. 4 –Relation between granules diameter and settling velocity.
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Fig. 5 –Moisture content with time.
b
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Fig. 8 –SVI of granular sludge.
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Fig.7 –Changes in protein (PN) and polysaccharide (PS) in aerobic granules during granulation.
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Fig. 9 –SOUR change with time.
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Table 1 Operation in granulation of activated sludge 1
3
5
7
9
Effluent /min
4
4
4
4
4
Settling /min Aeration /min
20 112
14 118
8 124
3 129
2 130
Influent /min
8
8
8
8
8
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Sludge yield coefficient (gVSS/gBOD5)
Reduction effect (%)
Activated sludge Aerobic granular sludge
0.6～0.8 0.15
75
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Process
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Influent (mg/L) 600 52 5.6 60 172
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COD ＋ NH4 -N TP TN TOC
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Table 3 The removal of conventional pollutants in granulation process
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Table 2 Comparison of sludge reduction technologies
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Operation / d
Effluent (mg/L) 44.4 1.04 0.84 5.4 14.62
Removal efficiency (%) 92.6 98 85 91 91.5
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Decreasing effect and mechanism of moisture content of sludge biomass by granulation process a
a
b
a
Xia Zhao , Hao Xu , Jimi Shen , Bo Yu & Xiaochun Wang
b
a
College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, China b
State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China Accepted author version posted online: 29 Jun 2015.
Click for updates To cite this article: Xia Zhao, Hao Xu, Jimi Shen, Bo Yu & Xiaochun Wang (2015): Decreasing effect and mechanism of moisture content of sludge biomass by granulation process, Environmental Technology, DOI: 10.1080/09593330.2015.1066448 To link to this article: http://dx.doi.org/10.1080/09593330.2015.1066448
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Publisher: Taylor & Francis Journal: Environmental Technology DOI: 10.1080/09593330.2015.1066448
Decreasing effect and mechanism of moisture content of sludge biomass by granulation process Xia Zhao*1,a, Hao Xu1,b, Jimi Shen2,c, Bo Yu1,d, Xiaochun Wang2,e
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1. College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, China; 2. State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering,
[email protected], [email protected], [email protected], [email protected], e
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Abstract
[email protected]
Disposal of high volume of sludge significantly raises water treatment costs. A method for cultivating aerobic granules in a sequencing batch airlift bioreactor (SBAR) to significantly
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produce lower moisture content is described. Results indicate that optimization of settling time and control of the shear stresses acted on the granules. The diameter of the granule was within the
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range of 1.0 mm to 4.0 mm, and its sludge volume index (SVI) was stabilised at 40 mL·g-1 to 50 mL·g-1. Its specific gravity was increased by a factor of 0.0392, and specific oxygen uptake rate (SOUR) reached 60.126 mg·h- 1·g- 1. Moreover, the percentage of its moisture content in the
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a
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Harbin Institute of Technology, Harbin 150090, China
reactor ranged from 96.73% to 97.67%, and sludge volume was reduced to approximately 60%, greatly due to the presence of extracellular polymeric substances (EPS) in the granules, as well as ＋
changes in their hydrophobic protein content. The removal rate of COD and NH4 -N reaches up to 92.6% and 98%, respectively. The removal rates of and TP is over 85%. Therefore, aerobic granular sludge process illustrates a good biological activity. *Corresponding
author. Tel. +86-13993184112, E-mail: [email protected]
Keywords: Low moisture content, granulation, biomass, hydrophobicity, sequencing batch airlift bioreactor 1. Introduction Continuous growth of biomass with high water content (e.g., algae produced by water
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eutrophication and biological sludge produced by sewage treatment plants) is due to greater water
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pollution, caused by increasing industrialization and increased demand. These organic biomasses
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have the following characteristics: 1) They possess high water content (>98%).; 2) They contain
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improper management.; and 4) They require high energy consumption and special equipment for dehydration. Determining the best way to handle biomasses with high water content has attracted increasing attention from scholars[1]. Additionally, abundant excess sludge produced from biological sewage treatment often contains a considerable number of hazardous and noxious
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substances (e.g., parasitic ova, pathogenic microorganisms, and heavy metals), as well as unstable organics, which must be treated properly to avoid environmental contamination. However, the
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existing excess sludge treatment is inefficient and economically ineffective. For example, the capital expenditure for sludge treatment in Europe and America accounts for as high as 60% to 70% of the total capital expenditure of a sewage treatment plant[2,3].
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certain calorific value.; 3) They are difficult to process, resulting in secondary pollution upon
Research has shown that dehydration is an effective way to reduce sludge volume. When
sludge water content decreases from originally 95% to approximately 85%, 65%, and 20% through mechanical dehydration, volume is reduced to 1/3, 1/7, and 1/16 of the original volume, respectively. Lower volume of dehydrated sludge occupies a smaller storage area and is better suited for transportation and disposal. Sludge with excessive water content also loses nitrogen,
phosphorus, and potassium (N, P, and K) as inorganic salts during dehydration[4,5]. Thus, dehydration, known as the end treatment, is an important step in the biosafe disposal of biomasses with high water content (e.g., municipal sludge). However, it faces problems of heavy dehydration load and high energy consumption. As a result, to produce aerobic granular sludge (AGS)
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containing biomasses with low water content, this research describes the successful formation and
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stable properties of granular sludge cultured from active sludge. Total water content in the tested
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granular sludge was measured.
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most research on SBR startup with AGS focused on parameters influencing the granulation process[9], such as short settling time for the selection of fast-settling particles[6,10–12], high shear stress caused by aeration[13,14], and so on. Much longer periods, on the order of 60 days to 150 days, have been reported for the achievement of high N- and P-removal performances[15–17].
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Compared with conventionally activated flocs, AGS has a regular, dense, and strong physical structure, good settling ability, high biomass retention, and ability to withstand shock loading
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rate[18]. In addition, as a result of oxygen’s diffusion gradient, aerobic, anoxic, and anaerobic zones simultaneously exist in AGS[19]. The development of methods to facilitate the fast cultivation of high quality AGS is a current research hotspot in the area of water treatment
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AGS formation in a sequencing batch reactor was first reported in the late 1990s[6–8]. Initially,
technology because a solution to this obstacle is urgently needed[20]. In recent years, there are more and more researchers focusing on the study about aerobic granular sludge (AGS), for example, it was found that the ratio of flocculent sludge should be kept a low level so as to maintain the stable operation of the granular sludge reactor because of the kinetic superiority of flocculent sludge over granular sludge, rather than microbial competition[21]. The distribution of
extracellular polymeric substances (EPS), hydraulic shear parameters and reactor configuration have a important influence on the structural stability of AGS[22-24]. Moreover, the concentration of Cu2+ and carbon source also plays a key role in performance of AGS[25-26]. 2. Materials and Methods
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2.1 Experimental set-up
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A sequencing batch airlift reactor (SBAR) was used to culture AGS (Fig. 1). Its volume was
3.0 L and water changing rate per cycle was 50%. The downcomer’s internal diameter was 6.25
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placed at a distance of 1.2 cm from the bottom of the downcomer. Air was introduced by a fine bubble aerator at the bottom of the reactor at a superficial air velocity of 1.6 cm.s-1, while a mass
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flow controller controlled the airflow rate. The experiment was conducted at room temperature, and excess activated sludge in the municipal sewage treatment plant’s sludge thickener was used as inoculated sludge (14.61 g·L-1).
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2.2 Inoculated sludge and experimental wastewater
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Synthetic wastewater was used as test water. Then, appropriate amounts of MgSO4·7H2O,
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CaCl2, CuSO4·5H2O, MnCl2·2H2O, and ZnSO4·7H2O and essential microelements for microbial growth were added.
The inoculated sludge, presented as brown flocs, contained 1.88 L activated sludge, 14.61
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cm, while the riser’s height and internal diameter were 70 cm and 4 cm, respectively, and was
g·L-1 total mixed liquor suspended solids (MLSS), 7.84 g·L-1 mixed liquor volatile suspended solids (MLVSS), 0.54 MLVSS/MLSS, 54.07 mL· g- 1 sludge volume index (SVI), and 99.1%
water.
2.3 Analytical methods
Chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total phosphorus (TP), MLSS,
MLVSS, and SV30 were tested using national standards methods[9,27]. AGS’ humidity and density were tested using centrifugation[28], while SOUR was tested using an established method[29]. AGS’ sedimentation rate was tested using gravitational sedimentation[30], and the size distribution of granular sludge was tested by wet sieving[31]. The microbial morphology and
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biophase of granular sludge were observed using optical and scanning electron microscopes (SEM,
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HITACHI S-3400N/4700). EPS was extracted and analysed using an established method[32], and
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2.4 Granulation process
In the experiment that lasted for 2.5 months, the SBAR’s working volume was 2.9 L. The inflow chemical oxygen demand (COD) was 600 mg·L-1. The system operated for 10 cycles every
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day, wherein each cycle had 8 min of water feeding, 112 min to 130 min of aeration, 2 min to 20
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min of sedimentation, and 4 min of drainage. To maintain a high sludge concentration in the SBAR, sedimentation time was determined based on sludge settleability (Table 1). The whole
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experiment was conducted at room temperature (20±3 °C). Dissolved oxygen (DO) was fed using micropore aeration from the bottom of the SBAR. The upward gas velocity was maintained at 0.2
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spectrophotometer (JASCO, FP-6500).
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the three-dimensional excitation-emission matrix (EEM) was analysed using a fluorescence
m3·h-1 to 0.3 m3·h-1, and the DO in the water was maintained at 3 mg·L-1 to 4 mg·L-1. The SBAR’s water feeding, aeration, sedimentation, drainage, and standing (idling) were controlled automatically.
3. Results and discussions
3.1 Granulation of activated sludge
The SBAR operated for 2.5 months, and the morphological changes of the granular sludge are shown in Fig. 2. Inoculated sludge particles were initially tiny and appeared as brown flocs (Fig. 2a). The microeddy produced by the upflow in the SBAR drove granule collisions and shortened
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sedimentation time gradually, causing selection pressure for larger granules in the activated sludge.
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The physical properties of sludge flocs changed due to the scouring action of the hydraulic shear
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forces. After five days of domestication, the sludge flocs expanded and approximately 1 mm
granules, adhered to the edges of these crystal nuclei (Fig. 2b). When the aeration rate was
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increased from 0.2 m3·h-1 to 0.25 m3·h-1, the granules grew more quickly. The granule size increased to about 2 mm in 8 days, presenting as smooth white balls or irregular ovals. Within 14 days, the granule size increased from 3 mm to 6 mm, showing bright and smooth surfaces with
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few tiny flocs (Fig. 2c). Observations of AGS’ formation and maturation indicated that small granules were assembled from both small flocs and original granules that were then reassembled
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into large granules through collision and hydraulic shear forces[4]. The coexistence of different sizes of aerobic sludge granules and flocs in the SBAR indicates the presence of a dynamic equilibrium system[33]. In the following two months, the sludge granules shrank in size, expanded,
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irregular round brown crystal nuclei were observed. Cilia, generally observed in tiny milk white
and then shrank again, finally maintaining a diameter of 3 mm to 4 mm, compact structure, and clear yellow outlines. Moreover, crystal nuclei with an attached growth of cilia were observed in the centre of certain sludge granules (Fig. 2d). The microscopic microbial morphological variations in the granular sludge are shown in Figs. 2e to 2h. According to the microscopic observations, filamentous bacteria interconnect into a networked structure to form sludge crystal
nuclei that are enveloped again by filamentous bacteria. The outer and inner filamentous bacteria interconnect to form a stable network to capture free microorganisms in the water, finally forming mature granular sludge (Fig. 2g). Furthermore, the granular sludge contained rich microbiota, including abundant active metazoan-like worms (Fig. 2h).
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3.2 Characteristics of aerobic granular sludge with low moisture content
Particle size of aerobic sludge
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0.07 mm, which increased gradually with prolonged operation and shorter sedimentation time as
sludge granules.
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granular sludge began to be produced in the SBAR. Fig. 3 exhibits the size distribution of aerobic
In Fig. 3, granular sludge (1.0 mm to 4.0 mm) accounted for 80% of the observed particles.
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After the sludge granulation stage, larger floc sludge and granular sludge particles (>4.0 mm)
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accounted for only a small proportion of the particles. Granular sludge is easier to dehydrate.
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However, the specific surface area of sludge decreases with the expansion of granular sludge, impeding the transmission of substrate inside the granular sludge. The granular sludge expansion also restricts the DO diffusion significantly, thus reducing its metabolic activity. As a result,
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Research results demonstrated that the average granule size of inoculated activated sludge was
moderate granular sludge particle size is preferred to a large one. Fig. 4 reveals the positive correlation between the granular sludge’s settling velocity and size. Granular sludge particles of >1.0 mm in size accounted for 88% of the particles, and their setting velocity ranged from 64.2 cm·min-1 to 95.4 cm·min-1, indicating that during sludge granulation,
AGS can improve the SBAR’s sludge water separation efficiency.
The positive correlation between setting velocity and size of granular sludge in Fig. 4 can be expressed as: y = 8.2879x +23.9745
(1)
where: x——granule size (mm);
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y——granule setting velocity (m·h-1).
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Specific gravity of aerobic granules
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with higher specific gravity settles more quickly. In the SBAR, inoculated sludge’s specific
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gravity increased slowly by only a factor of 0.0392 in one month, which is caused mainly by the considerable spaces in granular sludge that decrease sludge mass, setting velocity, and biomass. Research results show that because no sludge granules formed in the SBAR during the early
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reaction, granular sludge’s specific gravity increased slowly in that phase. Within 14 days,
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influenced by filamentous bacteria, granular sludge was generated that quickly increased the sludge’s overall specific gravity; however, it remained relatively low. Other researchers have
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reported[20] that interparticle bridges (PAMs) within granular sludge can be generated quickly during the early reaction under the collaboration of airflow and hydraulic shear forces. This brings
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Microbial density in granular sludge is expressed using the sludge’s specific gravity. Sludge
about a sharp increase in the specific gravity of the granular sludge, followed by a smooth increase, and then a secondary quick increase. The sludge’s specific gravity increased gradually after the generation of granular sludge, indicating that increase in microbial density and decrease in water content had occurred in the sludge.
Moisture effects of aerobic granular sludge
Water content is one of the more important sludge parameters for development of optimal wastewater treatment outcomes. Conventionally activated sludge flocs generally contain at least 99% water[34]. Fig. 5 shows that the water content of common activated sludge reaches as high as 99.1%, whereas that of granular sludge ranges from 96.73% to 97.67%, indicating that sludge can
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be condensed by at least 60%. Interstitial, capillary, and internal water are the three main water
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forms in sludge. Among them, interstitial water accounts for 70% of the total water not directly
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combined with the sludge and can be easily separated from it. Granular sludge contains little
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proteins are hydrophobic, EPS’ protein content likely contributes to granular sludge’s low water content[35].
Effects of EPS content and hydrophobicity
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EPS content of aerobic granules cultivated in the SBAR was studied. As one of the main
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microbial products in activated sludge, EPS refers to the polymers secreted by bacteria. Polysaccharide (PS) and protein (PN) are the main components of EPS, accounting for 70% to
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80% of EPS content. In this paper, EPS and PN components in granular sludge and activated sludge systems during the aerobic stage were analysed using EEM (Fig. 6).
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interstitial water due to dense flora[20]. Considering that most amino acid components of EPS
Li discovered that EPS’ hydrophobic PN content is inversely proportional to the sludge water
content[35]. In Fig. 6, protein and soluble microbial products are the main fluorescent organics in sludge EPS. Fig. 6a shows that peak A’s fluorescence intensity increased significantly in the fluorescence spectrum of AGS’ EPS. This demonstrates that one category of organics represented by this peak correlates closely with granular microorganisms’ metabolism in the SBAR. A new peak (peak B) was observed at 270 nm to 280nm/300 nm to 310nm Ex/Em on the EEM spectrum
of EPS. According to the five fluorescence regions defined by Chen et al., peak B reflects the presence of one category of soluble microbial products (Region VI)[36]. Peak strength of peaks T1 and T2 (protein) on granular sludge’s EPS fluorescence spectrum increased significantly, as compared with that of activated sludge (Fig. 6a). This indicates that protein in granular sludge are
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mainly released from the EPS of granular microorganisms in the SBAR. In contrast,
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microorganisms in activated sludge secrete less EPS, thus releasing lower amounts of protein.
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Sheng and Yu et al. discovered two peaks (T1 and T2) on the EPS fluorescence spectrum of a
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Fig. 6a, at 225/350 nm Ex/Em and 280/350 nm Ex/Em, respectively. Two strong peaks and two weak peaks were found on the EPS fluorescence spectrum in this work as well. Hydrophobic PN and PS contents of EPS content’s aerobic granules were studied here to further characterize their EPS characteristics[38–40]. PN and PS compositions changing during
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the operation period of the SBAR reactor are shown in Fig. 7. First, EPS, a gel substrate with negative charges and high water content, can sequester
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microorganisms for a long time and help to develop interdependent microbial communities. Second, its PA cell wall reduces the cells’ effective critical potentials, thus resulting in its flocculation. Third, it enables some sludge surfaces to be hydrophobic because it contains some
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common activated sludge system [37]. Their positions align similarly to those of the two peaks in
hydrophobic substances (e.g., fat and protein). Fourth, it can be used as an interparticle bridge because it contains anionic groups that can bind with divalent cations[35]. All these properties confer a net positive effect to EPS on granular sludge’s formation and hydrophobicity. EPS PN content was always greater than PS content, indicating a predominance of PN over PS in the EPS. The fact that the ratio of PN to PS fluctuated in the range of 1.2 to 2.9 indicated that
the former was predominant in the granules of SBAR reactor. PN and PS contents correlated well with the granule formation rate, even though the latter fluctuated slightly after most granules formed, presumably due to biological consumption in the granules’ substrate limited core. Enhanced organic loading appeared to promote the cells to produce greater amounts of EPS.
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Such positive relationship between EPS content and organic loading level was probably because
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the higher level of organic loading induced the microorganisms to have greater biological activity
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and then to secrete more metabolic products.
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AGS’ settling characteristics can be represented by SVI and SV30. In Fig. 8, sludge settleability and SVI were relatively lower during the early adaptive stage. However, with the progression of granulation, SV30 and SVI increased gradually and settleability recovered to a
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certain extent. SVI increased to the peak (92.13 mL·g-1) in 34 days, implying that sludge in the
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SBAR was expanded with poorer settleability. Such sludge expansion can be controlled effectively by adjusting the aeration rate. Subsequently, SV30 and SVI decreased to about 15% and 40 mL·g-1
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to 50 mL·g-1 respectively, accompanied by improved settleability.
SOUR of aerobic granular
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Settling properties of aerobic granular with low moisture content
In biological treatment technology, SOUR is an important evaluation index of microbial
metabolic activity. Therefore, SOUR and the microbial metabolic activity of AGS in SBAR were tested and analysed here. MLSS was first measured to analyse DO variation. AGS’ SOUR was calculated according to MLVSS, reaction time (t), and DO variation (Equation 2). The SOUR curve at different times is presented in Fig. 9.
SOUR = (DO0 - DOt) / (t ×MLVSS)
(2)
In SOUR equation (Equation 2), DO0 is the initial DO (mg·L-1), DOt is the endpoint DO (mg·L-1), and t is the test time (min). According to Fig. 9 and Equation 2, AGS had a higher SOUR that showed that the microbial metabolic activity was good, resulting in lower sludge yield.
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The SOUR value achieved a relative stability (60.13 mg·h- 1·g- 1) after 35 days, reflecting the
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desired properties (specific gravity, water content, settleability, and microbial activity) of the
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cultivated AGS.
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observed. With the increase of sludge temperature and age, microbial decomposition intensifies, thus decreasing sludge yield and volume (Table 2).
3.3 Morphological characteristics of granular sludge with low moisture content
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The effect of the morphological structure in AGS’ microbial populations on water content was
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explored through the observation of sludge morphology and microbial morphology during granulation. The SEM in Fig. 10a shows that AGS generated in the SBAR contains many spaces,
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and only few bacilli exist between numerous filamentous substances. According to the granulation and experimental results, shear forces can influence granular sludge properties (e.g., settleability
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Furthermore, distinct sludge reduction, which is related to the sludge yield coefficient, was
and microbial activity) by condensing the granules. Therefore, stable granular sludge in the SBAR promotes greater stability of the biological treatment system. Furthermore, with dense flora but little interstitial water, the resulting granular sludge has low water content. During the late experimental stage, abundant filamentous bacteria were generated on AGS’ surface. Their branches grew and extended into surrounding areas quickly. In Fig. 10b, filamentous bacterial branches with obvious diaphragm and sheathes can be observed clearly on
granular sludge surfaces. The granular sludge profile presents three obvious layers (Fig. 10c), representing a stable aerobic, anoxic-aerobic, and anaerobic zones[41]. This structure promotes improved dephosphoralization[9], as compared with that of traditional activated sludge[36]. Moreover, it provides a good environment for microbial coexistence, allowing filamentous
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bacteria to assist in the formation of compact microbial community observed in granular sludge,
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which concentrates internal microorganisms and leaves a small space for interstitial water. Hence,
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granular sludge has a significantly lower water content when compared with activated sludge.
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total apparent microbial yield coefficient. AGS has a compact structure and special aerobic-anaerobic zone that provides microorganisms with an aerobic-anaerobic alternating environment[42,43].
3.4 Biological degradation efficiency of aerobic granules process
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The removal of conventional pollutants is shown in Table 3. Since the microorganisms did not fully adapt to sewage concentration and the change living
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environment, the treatment effect was not stable in the initial start-up of reactor, so that the effluent COD was higher and the removal rate of it was less than 60%. With the accumulation of biomass in the reactor and the adaptive improvement of microorganism to the influent substrate,
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Aerobic and anaerobic zones can affect microbial growth in granular sludge by decreasing the
the removal rate was on the rise. After that, the removal of COD decreased due to the morphologic change of AGS. It was found that the removal decrease of COD was associated with the reduction of the biomass of AGS, and connected with the morphologic change of sludge, there maybe existed sludge bulking in reactor[44]. With the gradual granulation of sludge, the removal effect of COD was stable gradually and it could keep above 90%. The removal rate of TN and NH4+-N
was about 91% and 98%, respectively. The removal of TP fluctuated greatly, however, the removal rate of it could reached above 85% after the aerobic granular sludge was mature. 4. Conclusions The SBAR can be used to quickly cultivate AGS, resulting in granular sludge production with
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a significantly lower water content than activated sludge. Because the water content of generated
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granular sludge ranges from 96.73% to 97.67%, a great opportunity is offered for sludge reduction.
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Granule size mainly varies between 1.0 mm to 4.0 mm and SVI varies between 40 mL·g-1 to 50
0.0392, reflecting a higher density of microorganisms. The SOUR (O2) values reached 60.13mg·h·g- 1. Thus, granular sludge exhibits better microbial activity and settleability than activated
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1
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sludge. The removal rate of COD and NH4 -N reaches up to 92.6% and 98%, respectively. The removal rates of and TP is over 85%.
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AGS’ surface is partially hydrophobic because its EPS contains some hydrophobic substances (e.g., fat and protein), demonstrating that PN content in EPS plays an important role in AGS’ low
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water content. Meanwhile, EPS can be used as an interparticle bridge because it has anionic groups that can bind with divalent cations, which confirms its positive effect in the granular sludge’s formation and hydrophobicity.
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mL·g-1. As activated sludge is converted to granular sludge, the specific gravity increased by
A compact microbial community structure forms in AGS, because of the presence of numerous
filamentous bacteria interspersed with few bacilli. This community leaves only a small space for interstitial water, such that AGS has low water content when compared with activated sludge. AGS has a special aerobic-anaerobic zone that provides microorganisms with an aerobic-anaerobic alternating environment.
Acknowledgments
This study was financially supported by the Creative Research Groups of China Foundation (Grants No. 51121062) and State Key Laboratory of Urban Water Resource and Environment (Harbin Institute of Technology) (2014TS03) and excellent Young Teachers in Lanzhou
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[1]Li WD. The discussion about gasification technology of high-moisture-content biomass and
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coal. Silicon Valley 2013; 17: 143-145 [In Chinese].
[2]Low EU., Chase HA. Reducing production of excess biomass during wastewater treatment. Water Res. 1999; 33: 1119-1132.
[3]Liang P, Huang X, Qian Y. Research progress on sludge reduction technologies.Techniques
d
and Equipment for Environmental Pollution Control 2003; 4 (1): 44-52 [In Chinese].
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[4]Zhang WC. The exploration about improvement of sludge drying characteristics methods through ultrasonic treatment. College of environmental science and engineering. Tianjin: Tianjin university; 2006 [In Chinese].
ce
[5]Shen SM. The discussion about desiccation of high-moisture-content mash. Pharmaceutical & Engineering Design 2005; 26 (2): 5-7 [In Chinese].
[6]Beun JJ, Hendriks A, Van Loosdrecht MCM, Morgenroth, E, Wilderer, PA, Heijnen, JJ.
Ac
Downloaded by [FU Berlin] at 23:08 05 July 2015
References
rip
Project for Creative and Entrepreneurship of China (No. 1210731150).
t
University of Technology Training Project (1005ZCX016) and the College Students Training
Aerobic granulation in sequencing batch reactor. Water Res. 1999; 33: 2283-2290.
[7]Dangcong P, Bernet N, Delgenes JP, Moletta R. Aerobic granular sludge-a case report. Water Res. 1999; 33: 890-893. [8]Morgenroth E, Sherden T, van Loosdrecht MCM, Heijnen JJ, Wilderer PA. Aerobic granular sludge in a sequencing batch reactor. Water Res. 1997; 31: 3191-3194. [9]Lochmatter S, Gonzalez GG, Holliger C. Optimized aeration strategies for nitrogen and phosphorus removal with aerobic granular sludge. Water Res. 2013; 47: 6187-6197.
[10]McSwain BS, Irvine RL, Wilderer PA. Effect of intermittent feeding on aerobic granule structure. Water Sci. Technol. 2004a; 49: 19-25. [11]McSwain BS, Irvine RL, Wilderer PA. The influence of settling time on the formation of aerobic granules. Water Sci. Technol. 2004b; 50: 195-202. [12]Qin L, Liu Y, Tay JH. Effect of settling time on aerobic granulation in sequencing batch reactor. Biochem. Eng. J. 2004; 21: 47-52.
rip
and granular sludge. Water Res. 2002; 36: 1653-1665.
t
[13]Liu Y, Tay JH. The essential role of hydrodynamic shear force in the formation of biofilm
[14]Tay JH, Liu, QS, Liu Y. The effect of upflow air velocity on the structure of aerobic granules
us c
[15]Gonzalez GG, Holliger C. Dynamics of microbial community structure and enhanced biological phosphorus removal of propionate- and acetate-cultivated aerobic granules. Appl.
M an
Environ. Microbiol. 2011; 77: 8041-8051.
[16]de Kreuk MK, Heijnen, JJ, van Loosdrecht, MCM. Simultaneous COD, nitrogen, and phosphate removal by aerobic granular sludge. Biotechnol. Bioeng. 2005; 90: 761-769. [17]Xavier JB, De Kreuk MK, Picioreanu C, Van Loosdrecht MCM. Multi-scale
d
individual-based model of microbial and by conversion dynamics in aerobic granular sludge.
pt e
Environ. Sci. Technol. 2007; 41: 6410-6417. [18]Lin, YM, Liu, Y and Tay JH. Development and characteristics ofphosphorus – accumulating
ce
microbial granules in sequencing batch reactors. Appl. Microbiol. Biotechnol. 2003; 62: 430-435.
[19]De Kreuk MK and De Bruin LMM. Aerobic Granule Reactor Technology. London, IWA
Ac
Downloaded by [FU Berlin] at 23:08 05 July 2015
cultivated in a sequencing batch reactor. Water Sci. Technol. 2004; 49: 35-40.
Publishing; 2004.
[20]Yi C, Zhan HH, Chen JD, Cheng JG. Characteristics of aerobic granular sludge in a whisk-sequencing batch reactor (WSBR). Acta Scientia Circumstantiae 2011; 31: 268-275 [In Chinese]. [21]Liu YQ, Tay JH. The competition between flocculent sludge and aerobic granules during the long-term operation period of granular sludge sequencing batch reactor. Environ. Technol. 2012; 33: 2619-2626. [22]Chen H, Zhou SH, Li TH. Impact of extracellular polymeric substances on the settlement
ability of aerobic granular sludge. Environ. Technol. 2010; 31: 1601-1612. [23]Zhu L, Zhou JH, Yu HT, Xu XY. Optimization of hydraulic shear parameters and reactor configuration in the aerobic granular sludge process. Environ. Technol. 2015; 36: 1605-1611. [24]Zhao X, Chen ZL, Shen JM, Wang XC. Performance of aerobic granular sludge in different bioreactors. Environ. Technol. 2014; 35: 938-944. [25]Zheng XY, Wang XN, Huang X, Chen Q, Chen W, He YJ. Effects of Cu2+ on morphological
t
structure, functional groups, and elemental composition of aerobic granular sludge. Environ.
rip
Technol. 2013; 34: 219-224.
[26]Lashkarizadeh M, Yuan Q, Oleszkiewicz JA. Influence of carbon source on nutrient removal
us c
Technol. 2015; 1-26.
[27]National Environmental Protection Bureau. 2002(in Chinese), Water and Waste Water
M an
Monitoring and Analysis. 4th ed. Beijing: China Environmental Science Press 96-220. [28]Zhu JR, Liu CX. Cultivation and physic-chemical characteristics of granular activated sludge in alternation of anaerobic/aerobic process. Environ. Sci. 1999; 20: 39-41. [29]Xu YT, Shi JL, Zhang M. The Microbial Engineering of Pollution Control. Beijing:
d
Chemical Industry Press 2002; 231-233.
pt e
[30]Wang F, Yang FL, Zhang XW, Liu YH. Characteristics of aerobic granular sludge under different organics. China Water & Wastewater 2004; 20: 46-48 [In Chinese].
ce
[31]Laguna A, Ouattara A, Gonzalez RO, Baron O, Famá G, Mamouni E, Guiot S, Monroy O, Macarie H. A simple and low cost technique for determining the granulometry of up flow anaerobic sludge blanket reactor sludge. Water Sci. Technol. 1991; 40: 1-8.
Ac
Downloaded by [FU Berlin] at 23:08 05 July 2015
performance and physical-chemical characteristics of aerobic granular sludge. Environ.
[32]Adav SS, Lee DJ, Show KY, Tay JH. Aerobic granular sludge: Recent advance. Biotechnol Adv. 2008; 26: 411-423.
[33]Shen XX, Li XM, Yang Q, Zeng GM, Xu WX, Liao Q, Zheng Y. 2007. Acceleration of the formation of aerobic granules in SBR by inoculating mature aerobic granules. Environmental Science 2007; 28: 2467-2472 [In Chinese]. [34]Zhang ZJ. Drainage Engineering (Rudin). 3rd ed. Beijing: China Building Industry Press 1996; 296-303 [In Chinese]. [35]Li Y., 2008. The change about the EPS of sludge and its influence to operation of reactor in
MBR. Tianjin: Tianjin University; 2008 [In Chinese]. [36]Chen GH. Saby S, Djafer M, Mo HK. New approaches to minimize excess sludge in activated sludge systems. Wat .Sci .Tech. 2001; 44: 203-208. [37]Sheng GP, Yu HQ. Characterization of extracellular polymeric substances of aerobic and anaerobic sludge using three-dimensional excitation and emission matrix fluorescence spectroscopy. Water Res. 2006; 40 (6), 1233-1239.
rip
aerobic sludge blanket reactor. Journal of Appl Microbiol. 91(1), 168-175.
t
[38]Tay JH, Liu Q.S., Liu Y, 2001. Microscopic observation of aerobic granulation in sequential
[39]Zhang LL, Feng XX, Zhu NW, Chen JM. Role of extracellular protein in the formation and
us c
[40]Chen MY, Lee DJ, Tay JH. Distribution of extracellular polymeric substances in aerobic granules. Appl. Microbiol. Biotechnol. 2007; 73: 1463-1469.
M an
[41]Wang C, Zheng XY. Effect of shear stress on morphology, structure and microbial activity of aerobic granules. Environmental Science 2008; 29: 2235-2241 [In Chinese]. [42]Wang JL, Zhang ZJ, Wu WW. Research advances in aerobic granular sludge[J]. Acta Scientiae Circumstantiae, 2009; 29: 449-473 [In Chinese].
d
[43]Tay JH, Ivanov V, Pan S, Tay STL. Specific layers in aerobically grown microbial granules.
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Letters in Applied Microbiology 2002; 34: 254-257. [44]Zhao X, Zhao YL, Chen ZL, Jiang F, Luo HM, Feng HX. Control of filamentous sludge
ce
bulking in aerobic granular sludge SBR process. China Water & Wastewater 2012; 28(3): 15-19 [In Chinese].
Ac
Downloaded by [FU Berlin] at 23:08 05 July 2015
stability of aerobic granules. Enz. Microbiol. Technol. 2007; 41: 551-557.
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Fig. 1 –Schematic diagram of SBAR.
Fig. 2–Photographs and micrographs of aerobic granules in the reactor during different phase:
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Fig. 3 –Size distribution of the aerobic granules
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(a)inoculated sludge, (b)five days, (c)fourteen days, (d)forty-five days, (e)seed sludge, (f)granular sludge, (g)sludge nuclei and (h)Microbial phase.
Fig. 4 –Relation between granules diameter and settling velocity.
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a
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Fig. 5 –Moisture content with time.
b
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Fig. 8 –SVI of granular sludge.
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Fig.7 –Changes in protein (PN) and polysaccharide (PS) in aerobic granules during granulation.
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Fig. 9 –SOUR change with time.
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Table 1 Operation in granulation of activated sludge 1
3
5
7
9
Effluent /min
4
4
4
4
4
Settling /min Aeration /min
20 112
14 118
8 124
3 129
2 130
Influent /min
8
8
8
8
8
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Sludge yield coefficient (gVSS/gBOD5)
Reduction effect (%)
Activated sludge Aerobic granular sludge
0.6～0.8 0.15
75
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Process
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Influent (mg/L) 600 52 5.6 60 172
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COD ＋ NH4 -N TP TN TOC
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Table 3 The removal of conventional pollutants in granulation process
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Table 2 Comparison of sludge reduction technologies
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Operation / d
Effluent (mg/L) 44.4 1.04 0.84 5.4 14.62
Removal efficiency (%) 92.6 98 85 91 91.5
