I read an article about the Biosolids Management at the Charlotte-Meckenburg McAlpine Creek WWTP recently. This 64 MGD plant utilizes biological P removal and then anaerobically digests the solids to make a class B biosolid for land application.

Their discharge limit for phosphorous is stated at 1067 lbs/day on a monthy average which would be a 2.0 mg/L P in the effluent. It would appear that their bio P removal is mostly a waste of treatment effort. I do not know what their influent P levels are but even without P removal treatment 40% would be removed just with activated sludge.

I would hope that they are looking into a procedure such as Ostara or some other chemical method to remove the phosphorous from the sludge dewatering centrate so that phosphorous removed during bio P will be kept out of the recycle to the head of the plant. Bio P should result in a discharge of 0.5 mg/L on a routine basis.

I think that Bio P removal and anaerobic digestion should have chemical sequestering of the P in the recycle stream as a requirement. This would help reduce phosphorous entering our waterways.