Special Report No. 73-02: An Analysis of the Performance of Activated Sludge and Aerated Stabilization Basin Systems in Controlling the Release of Suspended Solids in Treated Mill

The attached special report summarizes the findings of an NCASI staff study of the current operational performance of forty-four (44) activated sludge and aerated stabilization basin treatment systems with respect to discharge of suspended solids.  The report contains a compilation showing the type of treatment process employed the existence in the case of aerated stabilization basin systems of post-aeration storage facilities with some sedimentation capability, average suspended solids levels on a per ton basis, and their statistical variability. The report then proceeds to analyze the performance of all forty-four (44) systems against the provisions of the Effluent Limitation Guidance (a) originally distributed by EPA in June 1972 for use by EPA Regional Offices in preparing discharge permits under the EPA-CE-Refuse Act Permit Program (RAPP) and (b) more recently in use for preparation of EPA-NPDES discharge permits under the 1972 water pollution control legislation. The report notes that almost universally those mills currently employing the "best practicable control technology currently available" discharge more suspended solids than called for in Schedule B of the above mentioned Effluent Limitation Guidance. This finding leads to the conclusion that the original formulation of suspended solids discharge allowances was developed at EPA from an inadequate data base