PHOSPHORUS REMOVAL IN PONDS

The municipal lagoon treatment systems which remove phosphorus by chem ical addition are the subject of this special study. The objectives of this study were to determine the degree of success of lagoon treatmen t systems in removing phosphorus and to identify any operational probl ems. fn order to obtain basic data for this study, thirty-two lagoon t reatment systems in Michigan and Minnesota were investigated. Chemical s typically used for phosphorus removal include metal salts such as al uminium sulfate (alum), ferrous and ferric chloride, lime, and various polymers. The overall experience with these lagoon systems is that th e technology, in its various configurations, has been working very wel l. Of the thirty-two lagoon treatment facilities reviewed, only two fa cilities were having problems meeting consistently the effluent phosph orus limits. Generally, the permitted effluent phosphorus limit is 1 m g/l. The influent phosphorus concentrations varied between 0.5 and 15 mg/l. Alum and ferric chloride applications produced consistently high quality effluents while Lime applications were not as effective in re moving phosphorus. None of these lagoon treatment systems experienced problems with build-up of sludges to levels which affected the effluen t concentrations. Accumulated amounts were an inch or less per year, c onsistent with solids build-up in the primary lagoon cells.