"Rotary vacuum precoat filtration was investigated as a means for dewatering sludge produced by the neutralization of mine drainage at four locations in Pennsylvania during 1969 and 1970. The process used at these sites consisted of neutralization, aeration, sedimentation, and filtration. The alkalies investigated were limestone, limestone with hydrated lime, calcined magnesite, partially and fully calcined dolomite, and hydrated lime. Filter aids tested included HYFLO SUPER-CEL, CELITE 501, CELITE 503, and CELITE 545. Work at the first three locations indicated that limestone and hydrated lime were the preferred alkalies and the CELITE 501 was the preferred filter aid. A more extensive program was conducted at the fourth site. A 27 run factorial experiment was conducted investigating the effect of flow rate, limestone feed level, aeration level, and sludge recirculation on equipment operation and on process cost. The significant variables affecting process cost were found to be sludge solids content, the filtration rate, and sludge recirculation. A detailed economic analysis of the process is included in the report." -- Abstract from Input transaction form, final, unnumbered page.