Simultaneous nitrate (N), phosphate (P), and COD removal was investigated in photobioreactors containing both algae and bacteria. The reactors were operated in the semi-batch mode with a hydraulic retention time of 2 days. Reactors were operated in two phases, (1) with 33 % biomass recycle and (2) with no biomass recycle. In both phases, more than 90 % of N and P and 80 % of COD present in synthetic wastewaters with initial N and P concentrations of up to 110 and 25 mg/L, respectively, and initial COD of 45 mg/L could be removed. Biomass growth in reactors did not increase with the increase in initial N and P concentration in either phase. However, biomass growth was slightly more in reactors operated with no biomass recycle. In both phases, N and P uptake was greater in reactors with greater initial N and P concentrations. Also in all cases, N and P uptake in the reactors was far in excess of the stoichiometric requirements for the observed biomass growth. This "luxury uptake" of nitrogen and phosphorus by biomass was responsible for excellent nitrogen and phosphorus removal as observed. However, based on the results of this study, no advantage of biomass recycling could be demonstrated.
Simultaneous nitrate (N), n>an class="Chemical">phosphate (P), and COD removal was investigated in photobioreactors containing both algae and bacteria. The reactors were operated in the semi-batch mode with a hydraulic retention time of 2 days. Reactors were operated in two phases, (1) with 33 % biomass recycle and (2) with no biomass recycle. In both phases, more than 90 % of N and P and 80 % of COD present in synthetic wastewaters with initial N and P concentrations of up to 110 and 25 mg/L, respectively, and initial COD of 45 mg/L could be removed. Biomass growth in reactors did not increase with the increase in initial N and P concentration in either phase. However, biomass growth was slightly more in reactors operated with no biomass recycle. In both phases, N and P uptake was greater in reactors with greater initial N and P concentrations. Also in all cases, N and P uptake in the reactors was far in excess of the stoichiometric requirements for the observed biomass growth. This "luxury uptake" of nitrogen and phosphorus by biomass was responsible for excellent nitrogen and phosphorus removal as observed. However, based on the results of this study, no advantage of biomass recycling could be demonstrated.