Waste disposal plant a long success at gheensboro.
In July 1961, Greensboro put into service a modern waste disposal plant. The new installation replaced an activated sludge plant that had been built in 1938 and had become overloaded: the activated sludge process had to be discontinued because of a strong textile waste. The engineering firm of Hazen and Sawyer, was engaged to design the plant that could handle both domestic and industrial wastes on Greensboro’s north aide at least until 1985. Design criteria and data on equipment and costs are included in the article under review along with a description of the treatment.
The Greensboro plant is designed to treat an average flow of 18 mgd with peaks up to 45 mgd. Parameters for maximum blochemical oxygon demand(BOD) and suspended solids(SS) loading are 45,000 and 20,500 lb per day, respectively. Although the plant was expected to treat 5 mgd of waste from a nearby textile mill, the mill built its own disposal plant and withdrew from Greensboro's system after construction was under way. As a result, the city now has a plant adequate to treat sewage beyond the scheduled 1985.
Included in the design and construction are all existing structures in good mechanical condition. Also incorporated are maximum flexibility and versatility to make it possible to cope with the changing character of the waste.
FILTRATION, AERATION EQUIPMENT.
Plow entering the plant, passes through two sets of screens. The first screen in handraked in order to protoot the mechanical screens that follow. Grit is removed in either of two aerated grit chambers and trucked to a nearby landfill.
The primary settling tanks, which have been operating very well, are equipped with sludge and soum removing mechanisms. Based on the present flow of approximately 8,3 mgd, the detentiоn time is slightly more than 4 hr.
The roughing filters provide a total volume of 5,8 acre-ft and are presently operated in parallel. Although greater efficiency may toe obtained with series operation, the power required does not justify the change. The aeration tank readily takes up the slack created by parallel operation. Design BOD reduction through the filters is 50 percent. The maximum monthly average obtained thus far, however, has been only 32 percent reduction while the annual average is about 25 percent. The loading on the filter is 50 lb of BOD per 1000 ou ft and the growth is excellent.
The aeration basins consist of four tanks (8 bays), only two of which are being used. They provide a detention time of 5,2 hr. The efficiency of the aeration tanks, including final settling, varies between 85 and 90 percent and is not affected by temperature. The BOD loading in the aeration is approximately 32 lb per 1000 оu ft.
The real river pollution problem is not the rare discharge of untreated sewage, but the discharge of large-scale industrial effluent. The direct effect of toxic metals accounts for about 1000 fishless, foul-smelling miles of river in this country,and many more where fish and other life struggle for existence under severe conditions. There are also indirect effects like the destruction of food organisms that support fish life, setting off a chain reaction changing the ecological balance in a river.
But some of the worst effects are produced by metals such as zinc, copper, nickel, lead and chromium derived from industrial processes. In addition to high toxicity to fish they are harmful to aerobic sewage treatment and anaerobic sludge digestion. Also temperature rises tend to increase the effectiveness of poisons, though with phenols and cyanides toxicity increases at low temperature .