Mother nature as sludge thickener

Shows how modifying the process to direct filtration and letting seasonal changes do the rest solved compliance and growth problems for the Lake Ontario Filtration Plant in upstate New York. By combining an unconventional backwash system that relies on natural freezing and thawing cycles to dewater alum sludge with an innovative filtration system using water from Lake Ontario, the water treatment plant has been significantly upgraded. The new process, which complies with new state discharge regulations, has doubled the facility's capability with minimal capital expenditures. Direct filtration is the coagulation and filtration of raw waters without the flocculation and subsequent settling steps. The process depends upon the formation of a pinpoint filterable floc instead of a large settleable floc used in conventional processes. This results in substantial reduction in alum feed and elimination of settling aids and/or floc weighting agents, and ultimately in a reduction in the amount of sludge produced. Observation of the sludge delivered to the freezing/thawing beds led to the conclusion that regardless of the pumped sludge's concentration, it separated into sludge and clear supernatant. The operating sequence evolved to the following: plugging a bed drain line by inserting plugs in holes drilled at different levels inmore » the upturned drainline; filling the bed and letting it stand at least overnight (the hose was moved to the next bed to maintain continuity of pumping); removing the plugs and decanting the clear supernatant to the lagoons.« less