Elsevier

Bioresource Technology

Volume 243, November 2017, Pages 417-425
Bioresource Technology

Growing Chlorella vulgaris on thermophilic anaerobic digestion swine manure for nutrient removal and biomass production

https://doi.org/10.1016/j.biortech.2017.06.141Get rights and content

Highlights

  • Chlorella vulgaris grew well on minimally diluted pretreated swine manure.

  • Nutrients could be rapidly removed by C. vulgaris, particularly with bacteria.

  • Chemical compositions in C. vulgaris changed with the culture conditions.

  • The alga could be used as biodiesel feedstock if cultivated in PADSM.

  • The algal biomass produced could be used as animal feed.

Abstract

Liquid swine manure was subjected to thermophilic anaerobic digestion, ammonia stripping and centrifugation in order to increase the available carbon sources and decrease the ammonia concentration and turbidity. Chlorella vulgaris (UTEX 2714) was grown on minimally diluted (2×, 3× and 4×) autoclaved and non-autoclaved pretreated anaerobic digestion swine manure (PADSM) in a batch-culture system for 7 days. Results showed that C. vulgaris (UTEX 2714) grew best on 3× PADSM media, and effectively removed NH4+-N, TN, TP and COD by 98.5–99.8%, 49.2–55.4%, 20.0–29.7%, 31.2–34.0% and 99.8–99.9%, 67.4–70.8%, 49.3–54.4%, 73.6–78.7% in differently diluted autoclaved and non-autoclaved PADSM, respectively. Results of chemical compositions indicated that contents of pigment, carbohydrate, protein and lipid in C. vulgaris (UTEX 2714) changed with the culture conditions. Moreover, its fatty acid profiles suggested that this alga could be used as animal feed if cultivated in autoclaved PADSM or as good-quality biodiesel feedstock if cultivated in non-autoclaved PADSM.

Introduction

Microalgae technology has attracted considerable attention nowadays because of its potential as high impact feedstock for production of biofuel, high value pigments, nutraceuticals and therapeutic compounds (Lowrey et al., 2015). However, the high cost of microalgae cultivation limits its commercial applications. Nutrients and water are important cost factors, accounting for 10–20% of the total cultivation cost (Singh et al., 2011). Many animal manures have nutrient compositions similar to classic microalgae culture media and were found to support the growth of some microalgal strains well (Zhou et al., 2014). In addition to large amounts of nitrogen and phosphorous, volatile fatty acids (VFAs) such as acetic acid, propionic acid and butyric acid were also found in animal manures (Hu et al., 2013), and considered as potential soluble organic carbon substrates for microalgae cultivation (Hu et al., 2012). There is an increasing interest in using animal manures to grow microalgae because manures provide low cost nutrients and water, and at the same time manure based algae production is a cost effective tool for manure waste management.

Recently, researchers have demonstrated the feasibility of growing microalgae on swine manure (Ji et al., 2014, Luo et al., 2016, Nam et al., 2017). However, there are some major issues with the use of animal manures for microalgae cultivation, including (1) high turbidity due to the presence of solid particles; (2) high ammonia concentration; (3) low available carbon sources, most of which are locked in the insoluble organic compounds; and (4) lack of high performance microalgal strains capable of adapting to the environment of animal manures (Zhou et al., 2014). Some of these issues could be addressed through diluting the manures 20–100 times with water (Zhou et al., 2014); however, this requires a large quantity of freshwater. In addition, researchers have attempted to convert organic materials to usable carbon sources through anaerobic digestion (Hu et al., 2012), remove NH4+-N through aeration and air stripping (Liao et al., 1995, Min et al., 2014), and separate solid particles using centrifugation to reduce the turbidity (Hjorth et al., 2008).

In the light of above discussion, the aim of this work was to investigate processes enabling fast growth of a selected microalgal strain on swine manure with minimal dilution. The specific objectives were (1) to determine whether the pretreatment methods of liquid swine manure (LSM) were feasible and efficient; (2) to investigate if C. vulgaris could grow well in minimally diluted pretreated anaerobic digestion swine manure (PADSM); (3) to understand how the growth of C. vulgaris could be affected by the bacteria in PADSM; and (4) to study the nutrient removal efficiency, biomass production, chemical composition, and fatty acid profiles of C. vulgaris grown on PADSM. It is hoped that the results of this study could provide a scientific basis and support for microalgae cultivation using minimally diluted animal manures in large scale.

Section snippets

Swine manure collection, pretreatment and analysis

Liquid swine manure (LSM) was collected from the University of Minnesota Southern Research and Outreach Center (Waseca, Minnesota), and anaerobically digested at 55 °C for 16 days with activated sludge for biogas production, resulting in anaerobic digestion swine manure (ADSM). Then, ammonia was stripped from the ADSM at 55 °C for 2 h under a vacuum of 25 inch Hg (84.7 kPa), the solid particles were removed using the methods of natural precipitation and centrifugation (10,000g, 10 min) to decrease the

Physicochemical analysis

The physicochemical characteristics of PADSM before and after autoclave were listed in Table 1. After pretreated with the method of this study, concentrations of TN and TP were 463.0 and 400.8 mg/L, 113.3 and 116.6 mg/L in PADSM and autoclaved PADSM, respectively. The TN-to-TP ratio (N/P) of PADSM and autoclaved PADSM were 4.1:1 and 3.4:1, respectively, which were similar with the optimal N/P ratio for algae growth (Min et al., 2014). In addition, concentrations of NH4+-N in PADSM were 255.4 and

Conclusions

It was concluded that (1) C. vulgaris (UTEX 2714) grew best in 3× PADSM; (2) C. vulgaris (UTEX 2714) was capable of completely depleting NH4+-N, TN, TP and COD from PADSM, particularly when it was cultivated with bacteria; and (3) C. vulgaris (UTEX 2714) grown on autoclaved PADSM could be used as animal feed, while oil from this strain cultivated in non-autoclaved PADSM could be used as a good-quality biodiesel resource. Thus, an integrated process of LSM pretreatment and microalgae cultivation

Acknowledgements

This manuscript was supported in part by the Jiangsu Overseas Research and Training Program for University Prominent Young and Middle-aged Teachers and Presidents, the Jiangsu Provincial Natural Science Foundation of China (no. BY2015065-10), and the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative Citizen Commission on Minnesota Resources (LCCMR) and University of Minnesota Center for Biorefining.

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