PILOT-SCALE TESTING FOR TOTAL NITROGEN REMOVAL FROM CENTRATE

摘要

Anaerobically digested sludge that is dewatered using centrifuges produces centrate,rnan ammonia-rich liquor which is normally treated with the raw wastewater. Whilerncentrate represents a very small portion of the total plant flow rate, it can be equivalentrnto 20 percent of the plant抯 nitrogen load. Hence, if the wastewater treatmentrnprocesses are not designed to accommodate centrate, an activated sludge systemrncan be stressed by the recycle of centrate. The presence of this highly concentrated,rnwarm, ammonia-rich, low-flow centrate stream provides the opportunity to costeffectivelyrnnitrify the centrate prior to returning it to the plant抯 liquid treatment stream.rnSubsequent denitrification in the biological reactors can produce almost completernremoval of nitrogen from the centrate.rnBecause centrate is typically low in BOD, conventional biological nitrogen removal ofrncentrate might require the addition of methanol as a carbon source for denitrification.rnAlternately, the BOD in the raw wastewater or primary clarified effluent could potentiallyrnbe used as a carbon source for the denitrification of centrate; this, however, wouldrndeplete BOD as a carbon source for use in denitrification of the sewage itself.rnA pilot plant was constructed and is currently in operation at New York City抯 WardsrnIsland Water Pollution Control Plant. The objective of the pilot plant study is to evaluaternthe process feasibility of centrate nitrification using dedicated nitrification reactors andrnsubsequent endogenous denitrification of the nitrified centrate in the RAS reaerationrnbasin of the existing secondary biological treatment process. Testing thus far hasrnshown that the proposed process provides reliable and complete nitrification andrndenitrification of centrate. Nitrification rates of up to 0.6 lb NH_3-N/lb VSS-day havernbeen observed. Denitrification rate testing results exhibited Monod kinetics with arnmaximum rate of about 0.16 lb NO_x-N/lb VSS-day.