Integration of algae-based sewage treatment with anaerobic digestion of the bacterial-algal biomass and biogas upgrading.

The domestic sewage treatment performance of an integrated anoxic-aerobic photobioreactor with biomass settling and recycling, coupled with anaerobic digestion of the produced bacterial-algal biomass and biogas upgrading in the photobioreactor was investigated. Hydraulic retention time in the photobioreactor initially was 4 days (stage I and II) and then reduced to 2.5 days (stage III). The integrated system supported high total organic carbon removals of 98.9 ± 1.1% regardless of the operational stage. A high total nitrogen removal of 90.8 ± 8.0% was recorded in the integrated system during the three operational stages, while total phosphorus removals accounted for 68.4 ± 20.1%, 68.3 ± 20.8% and 53.4 ± 25.0% in stages I, II and III, respectively. Biogas upgrading in the absorption column exhibited maximum removals of CO and HS of 74.7 ± 3.0% and 99.0 ± 2.8%, respectively. Biomass settling and recycling resulted in overall improvement of biomass settleability.