Elsevier

Bioresource Technology

Volume 192, September 2015, Pages 382-388
Bioresource Technology

Cultivation of Chlorella sp. using raw dairy wastewater for nutrient removal and biodiesel production: Characteristics comparison of indoor bench-scale and outdoor pilot-scale cultures

https://doi.org/10.1016/j.biortech.2015.05.094Get rights and content

Highlights

  • Chlorella sp. was successfully cultivated in raw dairy wastewater outdoors.

  • Nutrients were efficiently removed in outdoor pilot-scale cultures.

  • 110 mg L−1 day−1 of biomass was achieved in outdoor pilot-scale cultures.

  • Scale up of Chlorella sp. production using raw dairy wastewater is possible.

Abstract

The biomass productivity and nutrient removal capacity of simultaneous Chlorella sp. cultivation for biodiesel production and nutrient removal in raw dairy wastewater (RDW) in indoor bench-scale and outdoor pilot-scale photobioreactors were compared. Results from the current work show that maximum biomass productivity in indoor bench-scale cultures can reach 260 mg L−1 day−1, compared to that of 110 mg L−1 day−1 in outdoor pilot-scale cultures. Maximum chemical oxygen demand (COD), total nitrogen (TN), and total phosphorous (TP) removal rate obtained in indoor conditions was 88.38, 38.34, and 2.03 mg L−1 day−1, respectively, this compared to 41.31, 6.58, and 2.74 mg L−1 day−1, respectively, for outdoor conditions. Finally, dominant fatty acids determined to be C16/C18 in outdoor pilot-scale cultures indicated great potential for scale up of Chlorella sp. cultivation in RDW for high quality biodiesel production coupling with RDW treatment.

Introduction

Inappropriate discharge of livestock effluent with high concentration of nitrogen and phosphorous as well as high turbidity not only cause environment pollution but also waste lots of valuable nutrients which have substantially positive impacts on agricultural development. Biological treatment, such as anaerobic digestion is conventionally employed for aquaculture wastewater treatment (Rico et al., 2011, Deng et al., 2012). However, COD, TN and TP concentration in the effluents from anaerobic digestion facilities are still higher than the allowable discharge limits in China. Therefore, further treatment process is required to reduce COD, TN and TP to an acceptable level. In general, aerobic treatment processes, such as active sludge systems, involve an oxygen supply with an energy demand and extra sludge generation. High consumption of fossil fuels in industry and transportation sectors accelerate energy depletion and emit substantial quantities of greenhouse gases (GHG) into the atmosphere. Under these scenarios, the development of renewable energy is regarded as a promising approach to avoid further aggravation of the energy crisis and global climate change (Lam et al., 2012). Microalgae based biofuels, such as biodiesel, have great potential to be employed as a supplement to conventional fuel. Furthermore, oleaginous microalgae has further advantage as a biofuel feedstock compared to food crops, since microalgae biomass has a much shorter growth circle time, higher lipid content and can be cultivated in abandon land and wastewater. Therefore, using microalgae as algal based biodiesel feedstock has great potential in raw material assurance for biodiesel production and can avoid competition of limited arable land and fresh water. Finally, high culture medium cost and complicated production processes are still the most prominent bottlenecks that hinder commercialization of algal based biodiesel production. Thus, cultivation of microalgae in nutrient rich wastewater, such as aquaculture wastewater, makes it possible recover nutrients through microalgae assimilation and produce microalgae biomass economically.

Currently, there is a great deal of research looking to integrate microalgae cultivation and wastewater treatment (including municipal sewage, brewery wastewater, and dairy industry wastewater, etc.) (Van den Hende et al., 2014a, Kothari et al., 2012, Ramos Tercero et al., 2014, Farooq et al., 2013). Cultivation of microalgae in dairy wastewater (DW) has also received increased attention. Huo et al. (2012) evaluated the feasibility of cultivation Chlorella zofingiensis in DW in bench-scale outdoor ponds with pH regulation by CO2 and acetic acid, and achieved a maximum TP and TN removal percentage of 97.5% and 51.7% in 5 days, respectively. Chen et al. (2012) concluded that non-filamentous green algae (Chlorella and Scenedesmus) were able to tolerate high nutrient loading of chemically pre-treated anaerobic digestion during long term continuous cultivation in outdoor raceway ponds. Van den Hende et al. (2014b) found that aquaculture wastewater could be remedied by microalgal bacteria flocs in sequencing reactors through photosynthetic aeration with a COD, TN and TP removal rate of 65, 9.8 and 1.56 mg L−1 day−1, respectively. Ding et al. (2014) cultivated microalgae in DW without sterilization and obtained a maximum biomass concentration of 0.86 g L−1 in 20% DW, NH3-N, TP and COD removal ratio of 83.20–99.26%, 89.92–91.97% and 84.18–89.70% in 5%, 10%, and 20% RDW, respectively, in an 8-day indoor lab-scale experiment.

The literature available on the combination of nutrient removal and microalgae cultivation in RDW (without sterilization, disinfection or chemical pre-treatment) in outdoor pilot-scale photobioreactors is limited. In addition, reports on microalgae cultivation process without aeration pure CO2, addition of other carbon source or pH adjustment are also rare. This is especially important, since the development of economically favorable production processes is imperative in facilitating the industrial-scale production of microalgae biomass for algal based biodiesel (Samori et al., 2013). Finally, it is necessary to ascertain the growth characteristic and nutrient removal capacity difference between indoor bench-scale and outdoor pilot-scale cultures for guidance of cost-effective microalgae based biodiesel commercialization, however, information from the literature is currently lacking.

The objectives of this study are to: (1) evaluate the feasibility of simultaneous treatment of RDW and production microalgae based biodiesel at an outdoor pilot-scale site without disinfection, chemical pre-treatment, extra carbon source addition or pH control; (2) elucidate the distinction between indoor bench-scale and outdoor pilot-scale cultivation in microalgae growth characteristic and pollutant removal efficiency; (3) compare the fatty acid composition of indoor bench-scale and outdoor pilot-scale cultures and assess the scale-up potential of Chlorella sp. cultivation in RDW in outdoor photobioreactors.

Section snippets

Materials

The Chlorella sp. strain was obtained from Guangzhou Institute of Energy Conversion (GIEC), Chinese Academic of Sciences (CAS). The RDW was collected from the floor flushing effluent discharge point of a local dairy farm breeding about one thousand dairy cattle, close to the Demonstration Base of Energy Microalgae Cultivation, GIEC, CAS, in Foshan, China. The RDW was settled by gravity overnight and subsequently filtered through gauze before use. The physico-chemical parameters of RDW were

Biomass growth and productivity

The variations of biomass concentration throughout the culture period are illustrated in Fig. 1. It is easily to see that the Chlorella sp. is able to quickly adapt to the RDW in the indoor bench-scale conditions with the two tested initial inoculation concentration. Dramatic increase of biomass concentration was observed after 1 day growth, and sustained buildup of this value could also be observed in the remaining culture time. Finally, the maximum biomass concentration reached 2.25 g L−1 and

Conclusions

This study has clearly demonstrated the differences of integrating nutrient removal from RDW and biodiesel production in both indoor bench-scale and outdoor pilot-scale conditions. The fatty acid profiles of biomass suggesting that simultaneously remediation of RDW and production Chlorella sp. biomass in outdoor pilot-scale facilities is a feasible process for biodiesel production. The optimal culture conditions still required further investigation, however, for maximum FAMEs productivity in

Acknowledgements

The authors gratefully thank Dr. William Nock of University of Southampton for a proof-reading of English. This research was supported by Grants from the National Natural Science Foundation of China (Grant No. 51476177) and the CAS-Foshan cooperation project (2012HY100415), providing partial financial support, are also greatly acknowledged. The authors would also like to thank the two anonymous reviewers for their helpful comments and suggestions that greatly improved the manuscript.

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