HOW LOW CAN YOU GO? CAN EBPR PLUS FILTRATION MEET PART-PER-BILLION PHOSPHORUS LIMITS?

摘要

Over a period of six months, a full-scale Enhanced Biological Phosphorus Removal(EBPR) pilot project was conducted at the Durham Advanced Wastewater TreatmentFacility in Tigard, Oregon. To supplement an insufficient supply of readilybiodegradable carbon, two existing gravity thickeners were retrofitted to serve asstatic fermenter/thickeners. The goals of the study were to determine the optimumoperating conditions for both the aeration basins and fermenter/thickeners, determineappropriate design criteria for the fermenter/thickeners to use in an upcoming plantexpansion, and to reduce chemical and solids processing costs. Despite frequentprocess changes during the pilot project, the secondary treatment process was ableto consistently meet low effluent ortho phosphorus levels - the average secondaryeffluent ortho phosphorus concentration was under 0.2 mg/L, with concentrationsfalling below 0.1 mg/l 50% of the time. Savings in chemical consumption realizedduring the pilot project were more than US$90,000, and projected system-wide annualsavings are over US$200,000. Much of the success can be linked to the additionalvolatile fatty acids generated by the fermentation process. High primary effluentdissolved oxygen due to excessive surface turbulence in the split-box downstream ofthe clarifier was identified as the major inhibitor to EBPR.