Ultrafiltration meets discharge regulations and reduces waste pump-out

Domestic black and gray shipboard wastewaters when processed with tubular UF effectively meet marine discharge requirements as currently envisioned. Tubular UF processing of raw sewage and mixed wastewaters using 1 in. (2.5 cm) tubes does not require any pretreatment. Operating UF membranes at high processing temperatures reduces membrane fouling and increases membrane flux. Flux decline of UF membranes can be effectively recovered by cleaning with hypochlorite solution. The feasibility of utilizing UF in a shipboard environment still has to be proven. The January, 1980, regulations governing sewage discharge from marine vessels as established by the Environmental Protection Agency and to be enforced by the U.S. Coast Guard require that the effluent contain less than 150 mg/l suspended solids and less than 200 fecal coliform bacteria/100 ml. A 1 in. (2.5 cm) diameter noncellulosic tubular UF membrane system was evaluated with raw sewage as well as mixed wastes (raw sewage, laundry, shower, and gallery wastewaters). Rejection of fecal coliform bacteria and suspended solids was determined. In all cases the effluent quality satisfied forthcoming discharge regulations. No pretreatment of the wastewaters, such as coarse screening was necessary. Overall membrane performance was established in terms of flux and rejection. In all tests, treatment of the raw sewage resulted in higher fluxes than for the mixed wastes. Higher temperatures were found to improve significantly membrane performance without compromising rejection.