Effect of Organic Loading Rate for On-Site Treatment of Wastewater Using SubMBR

Abstract

Treatment of wastewater alone using submerged MBR and without energy requirement in permeate withdrawal was investigated. The effect of organic loading rate (OLR) was determined by monitoring organic matter removal, characteristics of organic matter, nitrogen and phosphorus, and permeate flux decline. Four lab-scale subMBR were operated at HRT of 4.5, 7, 12, and 24 hours giving a corresponding OLR of 6.9, 4.5, 2.6, and 1.3 kg_COD/m³-day, respectively. The wastewater supplied was obtained at the university's cafeteria with a COD range of 770–2050 mg/L. Regardless of high COD variations relatively stable permeates were obtained at OLR of 4.5, 2.6, and 1.3 kg_COD/m³-day with COD <40 mg/L. HRT of 4.5 hours was too short to degrade the high organic loading supplied to the system. This resulted to accumulation of organic matter inside the reactor and relatively high COD of permeate ranging from 40–70 mg/L. Furthermore, the accumulated organic matter inside each reactor was characterized. Increase in larger molecules (0.1–0.45 μm) was observed at OLR of 6.9 and 1.3 kg_COD/m³-day, but COD and biodegradability were high at OLR of 6.9 kg_COD/m³-day and low at OLR of 1.3 kg/m³ day. This indicated that the accumulated organic matter in a high OLR system was due to the undecomposed matter from the influent, while the ones accumulated in low OLR system was due to the microbial by-products. Nitrates and phosphates were low at high OLR due to frequent sludge withdrawal and high at low OLR since these are released during the decay of microorganisms. Severe fouling was observed in reactor at OLR of 6.9 kg_COD/m³-day, followed by the reactors at OLR of 4.5, 2.6, and 1.3 kg_COD/m³-day, respectively.