Cross-Flow Filtration in Physical-Chemical Treatment of Municipal Sewage Effluents.

摘要

Cross-flow filtration was tested for separation of water from the effluent of primary or secondary treatment of municipal sewage,after addition of physical-chemical reagents. In this approach,the solution being filtered is pumped parallel to the filter,to slow buildup of flux-limiting filtercake. In most cases,the filtering surfaces were 1-inch fabric tubes,manufactured as fire-hose jackets. Results are presented as functions of pressure,water recovery,circulation velocity,additive concentration and other variables. With Fe(III),Al(III),or powdered activated carbon (PAC) added to Oak Ridge primary sewage effluent,filtrate was superior in quality to effluent from activated sludge secondary treatment,and compared favorably with reported characteristics of sewage treated with similar reagents when solids-liquid separation was accomplished by settling. Turbidities were usually well below 1 JTU,and bacteria were substantially removed. With Fe(III),filtrate total organic carbon (TOC) typically was 10to 15mg/l,and phosphate below 1mg/l. With PAC,TOC was lower,usually about 5mg/l,but phosphate removal was poor. With Fe(III) at about 0.001 M,average fluxes of about 6 m/d (150gpd/sq ft) appear attainable at 4.6 m/sec (15ft/sec) circulation velocity with 24-hour backwash intervals. On this basis,we estimate filtrate cost for a 3,800cum/d (10raised to the 6th power gpd) plant using Fe(III) of 12cents/cu m (46cent/kgal). There are reasonable possibilities of lower costs. Fluxes and product characteristics are similar when feed is activated sludge secondary effluent,except that TOC is lower.