Phosphorus is known to have a deleterious effect (eutrophication) on receiving bodies of water and is typically the limiting nutrient for algae growth in lakes and streams. The algae blooms reduce the recreational value of the lake, cause odors and consume dissolved oxygen during decomposition. Low dissolved oxygen levels stress higher aquatic life forms and in extreme cases cause fish kill. While there are many sources of phosphorus in water bodies, the contribution of soaps, detergents, and other phosphorus compounds in wastewater effluent cannot be ignored.
OPTAER® Wastewater Treatment Facilities can be equipped with chemical addition systems prior to the final settling cells to bind and settle phosphorus.
Where lagoons discharge into especially sensitive receiving streams, phosphorus removal to lower levels may be required. A filtration system following the lagoon further removes chemical floc formed in the lagoons while additional chemical may be added to a contact chamber upstream of the filter to achieve lower effluent Total Phosphorus (TP) levels.
A Ferric Chloride addition system can be used in combination with a gravity sand filter to achieve high levels of phosphorus removal. The system includes a serpentine contact chamber, which leads into an upflow gravity sand filter. In the filter, phosphorus is removed from the effluent by adsorption to the hydrous ferric oxide coated filter media. Rejected solids are recycled to the primary cell of the OPTAER® wastewater treatment lagoon where the precipitated phosphorus and iron settle out.
Alum addition in ponds with adequate settling time can reduce TP levels to 1 mg/l. Adding filtration after the settling ponds with secondary Alum addition can reduce TP levels to levels as low as 0.5 mg/l.
A gravity sand filter equipped with a ferric addition system following an OPTAER® lagoon process can achieve effluent total phosphorus levels of less than 0.02 mg/l. Filter reject is generally returned to the lagoon. Settling cells are typically designed to provide 10 to 20 years of sludge storage prior to de-sludging.