Alga-based dairy wastewater treatment scheme: Candidates screening, process advancement, and economic analysis

Abstract

The common means of wastewater pre-treatment is impractical in large-scale wastewater treatment plants (WWTP). There is still a lack of suitable microalgae to treat raw dairy wastewater (DWW) with high organic matter concentration. For screening more diverse microalgae to treat raw DWW, the growth characteristics and metabolite production of ten algal strains cultured in undiluted DWW were studied in this paper, among which three were able to tolerate excessive chemical oxygen demand (COD) concentration and yielded high biomass concentration. Under the condition of 25 ± 1 °C and 55 μmol/m2/s, the most suitable strain were Scenedesmus SDEC-13, Chlorella pyrenoidosa SDEC-35, and Chlorella vulgaris SDEC-34, all of which had biomass concentrations above 1.2 g/L and protein contents above 45%. Based on the feasibility of cultivating microalgae with raw DWW, an alternative alga-based WWTP strategy was provided for the first time. The most important modification was the construction of the photobioreactor (PBR) to replace hydrolytic upflow sludge bed (HUSB) reactor and remove anaerobic-aerobic (AO) pond. The dairy WWTP with a PBR unit (1.68 × 104 m3) will yield a biomass production of 1.44 × 106 kg/year while capturing 2.59 × 106 kg CO2/year. Through carbon comparison and economic analysis, we believe that the use of microalgal PBRs for the treatment of wastewater from dairy plants presents a cost-effective and environmentally friendly alternative for the future. And future research should focus on pilot scale photobioreactor in the natural environment and large-scale treatment of dairy wastewater.