Anaerobic Co-digestion of Chlorella vulgaris and Dairy Whey for Enhanced Methane Production

The anaerobic digestion process is an additional step that can be implemented at wastewater treatment facilities for the production of biogas (i.e. methane) that can be used to generate energy and significantly reduce the facility\u27s energy cost. An emerging area of interest with anaerobic digestion is the inclusion of high-strength degradable organic waste (in addition to wastewater solids) that can lead to increased methane production by methanogens. Chlorella vulgaris (C. vulgaris), a species of green microalgae, is ubiquitous green alga often present at water-water treatment plants. I investigated its usefulness in an existing wastewater treatment process. Two investigations were conducted, the first to investigate the biomass growth potential of C. vulgaris in wastewater (primary clarifier and secondary clarifier effluents) and associated nutrient (ammonia and phosphorus) uptake, and the second to investigate the potential for methanogens to produce methane-rich biogas from anaerobic co-digestion of C. vulgaris with dairy whey. I hypothesized that (1) C. vulgaris would grow well in both wastewater effluents, but achieve the greatest total biomass production when cultured in primary clarifier effluent; and (2) including C. vulgaris in the anaerobic digestion of wastewater solids and dairy whey (i.e. co-digestion) would result in the production of biogas volumes greater than that produced from the digestion of only wastewater solids and only dairy whey. A growth experiment was conducted to measure algal biomass growth in primary and secondary clarifier effluents, and an anaerobic digestion trial was conducted to measure biogas volume and composition (% of methane). Both hypothesis were supported by the results. The most biomass production was observed in primary clarifier wastewater effluent (605 mg/L). The highest volumes (827 ml) and methane concentrations (56.8%) were obtained from anaerobic co-digestion of 32 ml (48% feed ratio) C. vulgaris (15 mg/L volatile solids) with 32 ml (48% feed ratio) of dairy whey (~1000 mg/L volatile solids). The data from the anaerobic digestion experiment was used to calculate potential savings at an existing wastewater treatment facility. The results indicated that including C. vulgaris in the anaerobic co-digestion of wastewater solids and a high-strength organic feedstock (i.e. dairy whey) could result in significant financial savings to wastewater treatment systems with anaerobic digesters. Further site-specific studies are needed to determine more accurately what the maximum digester loading rates of Chlorella and dairy whey (or other high-organic strength feedstocks) are, and subsequent methane production and energy savings