Influence of iron precipitated condition and light intensity on microalgae activated sludge based wastewater...

The indigenous microalgae-activated sludge (MAAS) process during remediation of municipal wastewater was investigated by studying the influence of iron flocculation step and light intensity. In addition, availability of total phosphorous (P) and photosynthetic activity was examined in fed-batch and batch mode under northern climatic conditions and limited lighting. This was followed by a semi-continuous operation with 4 d of hydraulic retention time and mean cell residence time of 6.75 d in a photo-bioreactor (PBR) with varying P availability. The fed-batch condition showed that P concentrations of 3-4 mg L^-1 were effective for photosynthetic chl. a development in iron flocculated conditions. In the PBR, the oxygen evolution rate increased with increase in the concentration of MAAS (from 258 to 573 mg TSS L^-1) at higher surface photosynthetic active radiation (250 and 500 μmol m^-2 s^-1). Additionally, the rate approached a saturation phase at low MAAS (110 mg L^-1) with higher light intensities. Semi-continuous operation with luxury P uptake and effective P condition showed stable average total nitrogen removal of 88 and 92% respectively, with residual concentrations of 3.77 and 2.21 mg L^-1. The corresponding average P removal was 68 and 59% with residual concentrations of 2.32 and 1.75 mg L^-1. The semi-continuous operation produced a rapidly settleable MAAS under iron flocculated condition with a settling velocity of 92-106 m h^-1 and sludge volume index of 31-43 ml g^-1 in the studied cases.