Performance evaluation and organic mass balance for treatment of high strength wastewater by anaerobic hybrid membrane bioreactor

The performance and chemical oxygen demand (COD) mass balance of a lab-scale anaerobic hybrid membrane bioreactor (An-HMBR), treating high strength wastewater, at mesophilic temperature, was investigated. Long-term (275 days) operation was carried out at various hydraulic retention times (HRTs), namely, 3, 2, 1, and 0.5 days corresponding to organic loading rate (OLR) of 1.06, 1.6, 3.2, and 6.4 kg COD/m(3)d, respectively. An-HMBR achieved, COD removal of 97-87% at HRT of 3-0.5 days, respectively. The study showed that polyurethane foam as attached growth media adsorbed mixed liquor suspended solids and thereby reduced the load on the membrane by 42%. During COD mass balance, an additional 4-5% of COD balance was achieved by consideration of COD conversion to biomass. The results suggest that unknown COD fraction varies between 33 and 37%, which was attributed to the loss of gaseous as well as oversaturation of dissolved methane. Consideration of oversaturation leads to a COD mass balance of over 95%.