Abstract |
Two years of plant scale studies indicated metal addition was an effective effluent polishing technique at this conventional wastewater treatment plant. Effluent phosphorus (P), five-day BOD and suspended solids were reduced to 0.5, 5, and 7 mg/l respectively. Aluminum sulfate was more effective than ferric chloride. Alum addition ahead of the final clarifier proved the best arrangement. An optimum mole ratio (metal/phosphorus) 1.6 developed; this ratio shows moles of aluminum fed per mole of incoming total phosphorus. Chemical costs, of which one-third was for transportation, were 5 cents per 1,000 gallons of flow treated, or 36 cents per pound of phosphorus removed when in the 96 percent reduction range. Chemical addition doubled the volume of digested sludge but dewatering on sand beds took half as long as previous conventional operations. During this demonstration the treatment system received some 1.6 mgd of typical domestic discharge, essentially its design loading. Hydraulic loading on clarifiers was minimized by drastic reduction of recirculation flows. (Author) |