Treatment of high strength industrial wastewater using extended aeration-immersed microfiltration (EAM) process

Fully submerged laboratory scale hollow fiber microfiltration module was used to treat a food industry wastewater in Malaysia. Permeate extraction was carried out continuously under a suction pressure not exceeding 0.9 bar. The module is aerated from beneath the microfiltration module to provide the crossflow effect and the oxygen requirement for the biological process. Active sludge from activated sludge plant at the factory was used in the start-up with a food/microorganisms (F/M) ratio of about 0.6, which later reduced further with time to 0.13 subject to the increase in the mixed liquor suspended solids (MLSS) and the permeate extraction rate. Primary effluent with chemical oxygen demand (COD) ranged between 1500 and 3000 mg/l was used in the study. MLSS of over 5500 mg/l were reached after nearly three month of filtration run. Permeate COD and turbidity reduction of over 97% and 99% respectively, were achieved. Dark streaks that formed on the inner side of the membrane surface are responsible for the declining permeate turbidity in the second month of operation since the membrane nominal size remains relatively unchanged.

The EAM process was able to reduce the feed turbidity and COD by over 99 and 97%, respectively. A three month operation without instituting cleaning of the membrane resulted in the increase in the permeate turbidity during part of the second month of operation, attributed to the growth on the inner surface of the membrane. MLSS of 5500 mg/l was achieved at the end of the three months operation period, without having any sludge wastage. Cleaning with 4% NaOH was adequate to return the permeate quality back to below 3 NTU.