Algae and Phosphorus Removal from Sewage Lagoon Effluents by in situ Chemical Addition.

The purpose of this study is to develop methods for rapidly and economically increasing the capacity of complete retention andor intermittently discharging wastewater stabilization lagoons located at Corps of Engineers recreational sites through in situ application of chemical coagulating agents. Alum was chosen as the coagulant in this study because it is relatively inexpensive and readily available. Application and mixing techniques were optimized using a 14-ft boat and small outboard motor. Analyses were performed to determine treatment efficiencies for biochemical oxygen demand BOD5, chemical oxygen demand COD, suspended solids, total phosphates and orthophosphates. Algae enumerations were also performed. The study took place over an entire year with three coagulant applications performed to study the long-term effects of in situ alum addition. In situ alum addition consistently produced effluents with phosphate concentrations below 1.0 mgalum. Removal rates for BOD and COD were approximately 80 percent with suspended solids being removed at rates as high as 95 percent. Algae removal rates were as high as 95 percent. No adverse effects were seen in either lagoon performance or in spraying the effluents on vegetation as a result of alum addition. Sludge accumulations of 0.1 to 0.2 in. per chemical application were measured. Repeated applications of alum did not result in significant increases in the sludge thickness, and no long-term adverse effect on lagoon performance is expected.