Appl Microbiol Biotechnol DOI 10.1007/s00253-015-6537-x
ENVIRONMENTAL BIOTECHNOLOGY
Nutrient removal and biogas upgrading by integrating freshwater algae cultivation with piggery anaerobic digestate liquid treatment Jie Xu 1 & Yongjun Zhao 1 & Guohua Zhao 1 & Hui Zhang 1,2
Received: 27 January 2015 / Revised: 10 March 2015 / Accepted: 12 March 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract An integrated approach that combined freshwater microalgae Scenedesmus obliquus (FACHB-31) cultivation with piggery anaerobic digestate liquid treatment was investigated in this study. The characteristics of algal growth, biogas production, and nutrient removal were examined using photobioreactor bags (PBRbs) to cultivate S. obliquus (FACHB-31) in digestate with various digestate dilutions (the concentration levels of 3200, 2200, 1600, 1200, 800, and 400 mg L−1 chemical oxygen demand (COD)) during 7day period. The effects of the level of pollutants on nutrient removal efficiency and CO2 removal process were investigated to select the optimum system for effectively upgrade biogas and simultaneously reduce the nutrient content in digestate. The treatment performance displayed that average removal rates of COD, total nitrogen (TN), total phosphorous (TP), and CO2 were 61.58–75.29, 58.39–74.63, 70.09–88.79, and 54.26–73.81 %, respectively. All the strains grew well under any the dilution treatments. With increased initial nutrient concentration to a certain range, the CO4 content (v/v) of raw biogas increased. Differences in the biogas enrichment of S. obliquus (FACHB-31) in all treatments mainly resulted from variations in biomass productivity and CO2 uptake. Notably, the diluted digestate sample of 1600 mg L−1 COD provided an optimal nutrient concentration for S. obliquus
* Yongjun Zhao [email protected] 1
College of Biological Chemical Science and Engineering, Jiaxing University, Jiaxing 314001, People’s Republic of China
2
Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, People’s Republic of China
(FACHB-31) cultivation, where the advantageous nutrient and CO2 removals, as well as the highest productivities of biomass and biogas upgrading, were revealed. Results showed that microalgal biomass production offered real opportunities to address issues such as CO2 sequestration, wastewater treatment, and biogas production.
Keywords Biogas enrichment . Microalgae . Nutrient removal . Piggery wastewater . Scenedesmus obliquus
Introduction Nutrient pollution from the anaerobic digestion process of animal wastewaters becomes an increasingly severe problem if disposed inappropriately (Zhu et al. 2013). Biogas production through anaerobic digestion has previously expanded worldwide because of the support of specific legislative tools aimed at increasing biogas production in different economic sectors (Franchino et al. 2013). One limitation of biogas production through anaerobic digestion is that the amount of nutrients in the digestate is insignificantly reduced and crude biogas must be upgraded before use (Zhao et al. 2013). Biological treatment of these wastewaters and crude biogas is a preferable solution to agricultural nutrient and energy management to attain sustainable development. Recently, the potential value of microalgae has been proposed for simultaneous digestate removal and upgrade (Yan and Zheng 2013). A possible option to reduce production costs is to use waste CO2 as source of carbon and wastewater as source of nutrients (see Pittman et al. (2011) for a review). Developing strategies for renewable and sustainable energy is a promising approach to avoid further aggravating the energy crisis and to increase global energy reserves (Lam and Lee 2012).
Appl Microbiol Biotechnol
Several studies have tested freshwater algae for digestate treatment. The results do not involve biogas upgrading but are promising. Zhu et al. (2013) and Yang et al. (2011) have studied the biomass growth and nutrient removal of the green algae Chlorella zofingiensis and Neochloris oleoabundans. The results of this study show that using microalgae may be appropriate to remove the main nutrients in digestate. The utilization of digestate as carbon and nutrient source can enhance microalgal growth reducing costs and environmental impacts (Uggetti et al. 2014). Microalgal growth is affected by the contents of organic matter and nutrients in anaerobic effluent, as well as the presence of other heterotrophic microorganisms (Serejo et al. 2015). Some researches about the integration of digestate treatment and biogas upgrading via microalgae culture systems currently exist (Yan and Zheng 2014; Zhao et al. 2013). Cultivating Chlorella sp. in digestate produces a maximum methane (CH4) content (v/v) of 92.16 %, while removing about 85– 88 % chemical oxygen demand (COD), 78–83 % total nitrogen (TN), and 73–80 % total phosphorus (TP) from wastewater (Yan and Zheng 2014). Nonetheless, few documents are available about the potential of combining microalgae cultivation in anaerobic digestate, such as piggery anaerobic digestate, with microalgae-based biogas upgrading. This combination is especially important because biogas enrichment by coupling with microalgae production appears to be highly economically convenient in conjunction with wastewater treatment only (Samori et al. 2013). Additionally, diluting the original piggery anaerobic digestate is necessary when the nutrient concentrations are high, but the optimal dilution ratio for biogastargeted microalgae production is still unclear. This study aims to measure digestate nutrient reduction, biogas upgrading, biogas CO2 removal, and microalgal biomass cultivation for value-added energy applications. Thus, this study investigates an integrated approach, which combines the cultivation of the green microalgae Scenedesmus obliquus with piggery anaerobic digestate. In summary, the objectives of this study are as follows: (1) to determine an optimal digestate dilution ratio for microalgal biomass cultivation, (2) to evaluate the main nutrient removal abilities, and (3) to specify the productivities of biomass and biogas upgrading.
Table 1 Characteristics of original and autoclaved piggery digestate used in the experiments (means±SD)
Material and methods Microalgae strain and pre-culture conditions The microalgae S. obliquus (FACHB-31) were obtained from the stock cultures in our laboratory; these microalgae were proven as highly biogas-tolerant and fast-growing and were grown in BG11 medium. BG11 culture media were selected and prepared for growing the microalgal strains. The composition of BG11 medium is as follows: 1.5 g NaNO3, 0.04 g K2HPO4 · 3H2O, 0.2 g KH2PO4 · 3H2O, 0.0005 g EDTA, 0.005 g Fe ammonium citrate, 0.005 g citric acid, 0.02 g Na2CO3, and 1 mL of trace metal solution per liter of medium (pH 7.0). The trace metal solution is composed 2.85 g H3BO3, 1.8 g MnCl2 ·4H2O, 0.02 g ZnSO4 ·7H2O, 0.08 g CuSO4 · 5H2O, 0.08 g CoCl2 ·6H2O, and 0.05 g Na2MoO4 ·2H2O per liter of medium (Tansakul et al. 2006). The initial pH of the medium was adjusted to 6.9. The stock culture conditions were as follows: cool white fluorescent light on three sides of the photobioreactors (400 L), light intensity of 200 μmol m−2 s−1, temperature of 25±1 °C, and 12-h light– dark cycle, and the media were artificially and intermittently shaken thrice a day. Piggery wastewater Piggery wastewater was obtained from an anaerobic digestion reactor in a livestock wastewater treatment plant of Jiaxing pig farm, Zhejiang, China. Pretreatment was performed via sedimentation and filtration using a filter cloth to remove large non-soluble particulate solids. After filtration, the wastewater was autoclaved for 20 min at 121 °C, after which the liquid was stored at 4 °C for 2 days for any visible particulate solids to settle, and supernatant was used to study the microalgae growth. The characteristics of the raw and autoclaved wastewater are shown in Table 1. Raw biogas Raw biogas was obtained from the same place where piggery wastewater was collected. Biogas was pretreated via chemical absorption to decrease the H2S concentration to
ENVIRONMENTAL BIOTECHNOLOGY
Nutrient removal and biogas upgrading by integrating freshwater algae cultivation with piggery anaerobic digestate liquid treatment Jie Xu 1 & Yongjun Zhao 1 & Guohua Zhao 1 & Hui Zhang 1,2
Received: 27 January 2015 / Revised: 10 March 2015 / Accepted: 12 March 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract An integrated approach that combined freshwater microalgae Scenedesmus obliquus (FACHB-31) cultivation with piggery anaerobic digestate liquid treatment was investigated in this study. The characteristics of algal growth, biogas production, and nutrient removal were examined using photobioreactor bags (PBRbs) to cultivate S. obliquus (FACHB-31) in digestate with various digestate dilutions (the concentration levels of 3200, 2200, 1600, 1200, 800, and 400 mg L−1 chemical oxygen demand (COD)) during 7day period. The effects of the level of pollutants on nutrient removal efficiency and CO2 removal process were investigated to select the optimum system for effectively upgrade biogas and simultaneously reduce the nutrient content in digestate. The treatment performance displayed that average removal rates of COD, total nitrogen (TN), total phosphorous (TP), and CO2 were 61.58–75.29, 58.39–74.63, 70.09–88.79, and 54.26–73.81 %, respectively. All the strains grew well under any the dilution treatments. With increased initial nutrient concentration to a certain range, the CO4 content (v/v) of raw biogas increased. Differences in the biogas enrichment of S. obliquus (FACHB-31) in all treatments mainly resulted from variations in biomass productivity and CO2 uptake. Notably, the diluted digestate sample of 1600 mg L−1 COD provided an optimal nutrient concentration for S. obliquus
* Yongjun Zhao [email protected] 1
College of Biological Chemical Science and Engineering, Jiaxing University, Jiaxing 314001, People’s Republic of China
2
Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, People’s Republic of China
(FACHB-31) cultivation, where the advantageous nutrient and CO2 removals, as well as the highest productivities of biomass and biogas upgrading, were revealed. Results showed that microalgal biomass production offered real opportunities to address issues such as CO2 sequestration, wastewater treatment, and biogas production.
Keywords Biogas enrichment . Microalgae . Nutrient removal . Piggery wastewater . Scenedesmus obliquus
Introduction Nutrient pollution from the anaerobic digestion process of animal wastewaters becomes an increasingly severe problem if disposed inappropriately (Zhu et al. 2013). Biogas production through anaerobic digestion has previously expanded worldwide because of the support of specific legislative tools aimed at increasing biogas production in different economic sectors (Franchino et al. 2013). One limitation of biogas production through anaerobic digestion is that the amount of nutrients in the digestate is insignificantly reduced and crude biogas must be upgraded before use (Zhao et al. 2013). Biological treatment of these wastewaters and crude biogas is a preferable solution to agricultural nutrient and energy management to attain sustainable development. Recently, the potential value of microalgae has been proposed for simultaneous digestate removal and upgrade (Yan and Zheng 2013). A possible option to reduce production costs is to use waste CO2 as source of carbon and wastewater as source of nutrients (see Pittman et al. (2011) for a review). Developing strategies for renewable and sustainable energy is a promising approach to avoid further aggravating the energy crisis and to increase global energy reserves (Lam and Lee 2012).
Appl Microbiol Biotechnol
Several studies have tested freshwater algae for digestate treatment. The results do not involve biogas upgrading but are promising. Zhu et al. (2013) and Yang et al. (2011) have studied the biomass growth and nutrient removal of the green algae Chlorella zofingiensis and Neochloris oleoabundans. The results of this study show that using microalgae may be appropriate to remove the main nutrients in digestate. The utilization of digestate as carbon and nutrient source can enhance microalgal growth reducing costs and environmental impacts (Uggetti et al. 2014). Microalgal growth is affected by the contents of organic matter and nutrients in anaerobic effluent, as well as the presence of other heterotrophic microorganisms (Serejo et al. 2015). Some researches about the integration of digestate treatment and biogas upgrading via microalgae culture systems currently exist (Yan and Zheng 2014; Zhao et al. 2013). Cultivating Chlorella sp. in digestate produces a maximum methane (CH4) content (v/v) of 92.16 %, while removing about 85– 88 % chemical oxygen demand (COD), 78–83 % total nitrogen (TN), and 73–80 % total phosphorus (TP) from wastewater (Yan and Zheng 2014). Nonetheless, few documents are available about the potential of combining microalgae cultivation in anaerobic digestate, such as piggery anaerobic digestate, with microalgae-based biogas upgrading. This combination is especially important because biogas enrichment by coupling with microalgae production appears to be highly economically convenient in conjunction with wastewater treatment only (Samori et al. 2013). Additionally, diluting the original piggery anaerobic digestate is necessary when the nutrient concentrations are high, but the optimal dilution ratio for biogastargeted microalgae production is still unclear. This study aims to measure digestate nutrient reduction, biogas upgrading, biogas CO2 removal, and microalgal biomass cultivation for value-added energy applications. Thus, this study investigates an integrated approach, which combines the cultivation of the green microalgae Scenedesmus obliquus with piggery anaerobic digestate. In summary, the objectives of this study are as follows: (1) to determine an optimal digestate dilution ratio for microalgal biomass cultivation, (2) to evaluate the main nutrient removal abilities, and (3) to specify the productivities of biomass and biogas upgrading.
Table 1 Characteristics of original and autoclaved piggery digestate used in the experiments (means±SD)
Material and methods Microalgae strain and pre-culture conditions The microalgae S. obliquus (FACHB-31) were obtained from the stock cultures in our laboratory; these microalgae were proven as highly biogas-tolerant and fast-growing and were grown in BG11 medium. BG11 culture media were selected and prepared for growing the microalgal strains. The composition of BG11 medium is as follows: 1.5 g NaNO3, 0.04 g K2HPO4 · 3H2O, 0.2 g KH2PO4 · 3H2O, 0.0005 g EDTA, 0.005 g Fe ammonium citrate, 0.005 g citric acid, 0.02 g Na2CO3, and 1 mL of trace metal solution per liter of medium (pH 7.0). The trace metal solution is composed 2.85 g H3BO3, 1.8 g MnCl2 ·4H2O, 0.02 g ZnSO4 ·7H2O, 0.08 g CuSO4 · 5H2O, 0.08 g CoCl2 ·6H2O, and 0.05 g Na2MoO4 ·2H2O per liter of medium (Tansakul et al. 2006). The initial pH of the medium was adjusted to 6.9. The stock culture conditions were as follows: cool white fluorescent light on three sides of the photobioreactors (400 L), light intensity of 200 μmol m−2 s−1, temperature of 25±1 °C, and 12-h light– dark cycle, and the media were artificially and intermittently shaken thrice a day. Piggery wastewater Piggery wastewater was obtained from an anaerobic digestion reactor in a livestock wastewater treatment plant of Jiaxing pig farm, Zhejiang, China. Pretreatment was performed via sedimentation and filtration using a filter cloth to remove large non-soluble particulate solids. After filtration, the wastewater was autoclaved for 20 min at 121 °C, after which the liquid was stored at 4 °C for 2 days for any visible particulate solids to settle, and supernatant was used to study the microalgae growth. The characteristics of the raw and autoclaved wastewater are shown in Table 1. Raw biogas Raw biogas was obtained from the same place where piggery wastewater was collected. Biogas was pretreated via chemical absorption to decrease the H2S concentration to
