Abstract |
High levels of phosphorus removal have been observed at the Baltimore Sewage Plant in the past. A six month study of the operating conditions and design parameters of tow parallel, 10 MGD activated sludge systems was conducted in an attempt to establish the mechanism by which the phosphate was removed. The following variables were used: suspended solids concentration, waste water flow, aeration basin mixing configuration, and dissolved oxygen levels. Both mixing and dissolved oxygen were shown to influence the process greatly. Contact stabilization or step aeration, as opposed to plug flow, caused sharp decreases in the removals, while low dissolved oxygen levels stimulated releases of phosphorus from the sludge. Operating conditions which enhance phosphate removal are standard conditions now at the Baltimore plant. Phosphate removal at Baltimore average 82%, compared with 15 to 20% removals for conventional activated sludge, and 9% in Baltimore's trickling filter. No cost analysis was undertaken, wince complete removal of the phosphorus involves removal from the sludge supernatant. Some of the parameters which may lead to enhanced phosphate removals have been demonstrated. However, the exact reaction or mechanism by which the removals proceed is still unknown, even though it was established that the calcium removed from the system was not principally by precipitation. (WRSIC abstract) |