TREATMENT OF NIGHT SOIL SEWAGE

PURPOSE:To improve the quality of treated water without decreasing the liquid permeation rate of a reverse osmosis membrane by subjecting night soil sewage to a biological treatment then adding an acid thereto to adjust the pH thereof then subjecting the sewage to a sepn. treatment with the reverse osmosis membrane. CONSTITUTION:The night soil sewage is subjected to the biological treatment and thereafter the acid is added thereto to adjust the pH thereof to 4.8-6.5 to suppress both of the flocculation of org. materials and the precipitation of scale. The sewage is then subjected to the sepn. treatment with the reverse osmosis membrane. A so-called 'loose' reverse osmosis membrane having a salt removal rate as low as 10-60% is preferable as the above-mentioned reverse osmosis membrane. The liquid permeation rate of the reverse osmosis membrane is thus increased and the treatment with a high concn. is made possible while the osmotic pressure of the concd. liquid is prevented. Since the permeation rate of org. COD components is the same as the permeation rate of the reverse osmosis membrane having a high removal rate, the treated water having excellent quality is obtd.