Filtration performance of ceramic membrane for the recovery of volatile fatty acids from liquid organic sludge

This research focused on the filtration performance of a membrane-coupled fermenter system for dissolved organics recovery from liquid organic sludge. Over the range 0.1–5 µm, the magnitude of total membrane resistance (Rt) is ranged as follows in the order: 0.1 µm>0.2 µm>0.5 µm>1 µm>2 µm>5 µm. The cake layer resistance (Rc) occupied about 68–88% of total resistance. The decline of permeation flux was mainly attributed to Rc, which was formed by a strong deposition from physicochemical interactions of solids on the membrane surface. Higher suspended solids concentration of suspension caused lower permeation flux. However, there was not a proportional relation beyond a certain SS concentration. The cross-flow velocity on the membrane surface was faster, which resulted in higher permeation flux and also more efficiency with low transmembrane pressure. The appropriate pH of suspension was in the range of 5.0 to 6.0 for dissolved organics recovery as well as permeation flux. It is possible for bacteria to be separated perfectly with 0.1 µm and 0.2 µm membrane pore sizes. Based on experimental results, optimal membrane pore size for the recovery is believed to be around 1 µm.

Based on the results obtained in the present study, the main conclusions can be summarized as follows: The magnitude of total membrane resistance (Rt) of various filters ranges as follows in the order: 0.1 µm > 0.2 µm > 0.5 µm > 1 µm > 2 µm > 5 µm. The cake layer resistance (Rc) was about 68% to 88% of Rt. High SS concentration of suspension caused low permeation flux. The cross-flow velocity on the membrane surface was faster, which resulted in higher permeation flux and was also more efficient with low-pressure operation. The appropriate pH range of suspension was over the range of 5.0–6.0 for organic materials recovery as well as the permeation flux. TOC recovery ratio was almost the same with [1] A.D. Bailey, G.S. Hansford and P.L. Dold, The enhancement of upflow anaerobic sludge bed reactor performance using crossflow microfiltration, Water Res., 28(2) (1994) 291–295. [2] S. Ghosh, K. Buoy, L. Dressel, T. Miller, G. Wilcox and D. Loos, Pilot-and full-scale two-phase anaerobic digestion of municipal sludge, Water Environ. Res., 67(2) (1995) 206–214. [3] C. Yanagi, M. Sato and Y. Takahara, Treatment of wheat starch wastewater by membrane combined two phase methane fermentation system, Desalination, 98 (1994) 161–170. [4] A. Fakhru Al-Razi, Ultrafiltration membrane separation for anaerobic wastewater treatment, Water Sci. Tech., 30(12) (1994) 321–327. [5] H. Aya and K. Namiki, Anaerobic digestion of sewage sludge by membrane separated biofermenter, J. JSWE, 15(3) (1992) 187–194 [in Japanese]. [6] W. Ghyoot and W. Verstraete, Anaerobic digestion of primary sludge from chemical pre-precipitation, Proc. 8th International Conf. on Anaerobic Digestion, 1 (1997) 315–322. [7] P. Elefsiniotis and W.K. Oldham, Effect of HRT on acidogenic digestion of primary sludge, J. Environ. Engn., 120(3) (1994) 645–660. [8] APHA, AWWA, WEF, Standard Methods for the Examination of Water and Wastewater, 1998. [9] M.H. Al-Malack and G.K. Anderson, Crossflow microfiltration with dynamic membranes, Water Res. 31(8) (1997) 1969–1979.