Simulation study on comparison of algal treatment to conventional biological processes for greywater treatment

Abstract

The reuse of greywater is a promising strategy to preserve fresh water resources for future generations. The main objective of the present study is to simulate three different biological treatment technologies (high rate algal pond (HRP), conventional activated sludge (AS) treatment and rotating biological contactors (RBC)) at varying pollutant loadings (low, medium and high-strength polluted greywater) and, then, compare the treatment efficiency of HRP treatment with both RBCs and AS process. All of the adopted technologies were found to produce effluents with satisfactory quality. RBC achieved higher removal of nitrate and phosphorus compared to the conventional AS treatment process, whereas sensitivity analyses reveal that the AS process reached the steady state condition faster than the RBC process. The removal efficiency for AS process was 100% for biochemical oxygen demand, while the total suspended solids and Escherichia coli concentrations were lower than 5 mg L−1 and 0.001 MPN 100-mL−1, respectively. Algal ponds treatment is effective but highly variable. However, it had additional benefits such as CO2 assimilation and biomass production. The treatment efficiency of algal system depended mainly on the mass concentrations of algae and flow rates. Algae mass concentration of 700 g m−3 and flow rate of 40 m3 d−1 achieved complete removal of the SBOD. The influence of operational parameters on the production of algal biomass was investigated and the higher CO2 fixation efficiency was achieved with the fraction of photoperiod as 0.8 and mass concentration of algae 1000 g m−3.