Wisconsin Department of Natural Resources
Proposed WCR Sample WWTP effluent and sludge for bioavailable phosphorus
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This is a request to fund a Tier III investigation of WPDES management actions pertaining to the phosphorus contnet of municipal sludge. Research on alum treatment in lakes suggests that phosphorus/alum complexes are unlikely to be broken in the natural aquatic environment. This means that phosphorus leaving treatment plants that is complexed to alum would be biologically inert. WWTPs treating phosphorus with alum report that they need to add a final filtration step to attain low levels of P removal because adding more chemical does not help. This suggests that the effluent leaving the final settling basins contains some component of biologically inert alum complexed phosphorus. Similarly, a significant fraction of phosphorus applied to agricultural fields may be complexed with alum and therefore unavailable to both agricultural crops and aquatic plants, should it be transported to aquatic systems.
This proposal is phased over two years. During the first year, minimal sampling would occur to initially investigate the relationships. This would involve a single effluent sample from 2 WWTPs treating with alum, one sample from a WWTP treating with ferric chloride and one WWTP treating biologically. Seven municipal sludges would be sampled including 2 treating with alum, two with ferric chloride, two biologically and one with no phosphorus limit. Also, one sample of solid, daily haul dairy manure would be analyzed along with one sample of liquid dairy manure. If these samples indicate that adjustment of regulations for biologically available phosphorus shows promise, a follow-up project proposal will be submitted next year to define the variability of the relationships and include additional facilities.
Develop an analytical technique for effluent phosphorus which reflects the biologically relevant fraction instead of the total. If this inert portion is a significant component of the total phosphorus in effluent, this could make attainment of a restrictive phosphorus limit possible without adding final filtration. Significant economic savings could result and perhaps some of the opposition to establishing a phosphorus standard would diminish.ining to regulation of phosphorus. The relationship between phosphorus forms in sludge; total, that available to crops and that available in the aquatic system, will be quantified so that proper regulations can be applied. For example the Snap Plus model could to be adjusted to account for this relationship where sludge is applied to land.
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