Composting sludge from municipal waste treatment plants may help solve an urgent environmental problem, according to Dr. T. W. Edminster, administrator, USDA Agricultural Research Service.
Speaking before the recent meeting of the 1977 National Conference on Composting of Municipal Residues and Sludges, Edminister said composting would help dispose of ever-increasing piles of sludge in an environmentally safe way.
As waste treatment plants across the country come under more stringent regulation, the amount of sludge to be disposed of will increase from the present 5 million dry tons annually to over 10 million by 1985, he predicted.
Composted sludge can turn a minus into a plus, Edminster declared. It can be used as a fertilizer and soil conditioner on both agricultural and recreational land, benefiting both the farmer and the general public.
"There are problems in using uncomposted sludge on land. Some sludges contain excessive amounts of heavy metals and can be harmful to plants and people. Sludge also contains a variety of pathogens (disease organisms)
"However, composting takes care of most of the problems.However, composting takes care of most of the problems. It reduces sludge disposal costs, environment and health hazards and dilutes heavy metal content. The high temperature generated during composting kills most pathogens.
"Composting makes sludge not only safe, but odor-free, dry, easy to handle, transport and store.
The technique for composting sludge was developed by Agricultural Research Scientists at Beltsville.
Considerable research on composting sludge also has been done at the University of Maryland. The research team, headed by Dr. Francis R. Gouin, associate professor of horticulture, has developed a compost mix utilizing sewage sludge which has received clearance from the Federal Environmental Agency for use on nonfood crops by wholesale operators.
The mix contains sand, leaves and composted sludge in equal amounts. It is now being used by the Buckingham Forest Tree Nursery at Harmens, near the far southwest corner of the Baltimore-Washington International Airport. This nursery is operated by the Forest Service of the State Department of Natural Resources.
Another user is Arlington National Cemetry. Gouin says a survey of horticulture tradespeople in the Washington metropolitan area indicates a demand for at least 900 tons of composted sludge per day.
Agronomists at the University of Maryland have been attempting to develop guidelines for use of composted sludge on food crops.
Since 1972, Dr. A Morris Decker, professor of agronomy, has led a team in studying the effects of sewage sludge on crop yields, soil nutrient status and soil structure. After four years of cropping, yields of corn, soybeans and rye were all increased with the application of sewage sludge (compared to no fertilization).
They found that increases in soil temperature created higher death rates for disease-causing organisms but also greater uptake of heavy metals like zince, copper and cadmium.
Uptake of heavy metals can be lessened by maintaining soil pH near neutral. Leafy vegetables were found to be rapid absorbers of heavy metals. Grasses and grass-type crops like corn have a high tolerance for heavy metals without an adverse effect on product quality.