The Technology Of Waste Activated Sludge Fermentation Coupling With Denitrification

At present, due to the low C/N ratio and less useful carbon source in wastewater,most of the wastewater treatment plants （WWTP） facing the problem of lackingcarbon source for nitrogen removal. To ensure the nitrogen removal efficiency, hugeamount of outside carbon source were dosed additionally, but this will undoubtedlyincrease the cost of sewage treatment and cause more extra sludge production. Further,since the amounts of sludge produced by the wastewater were relatively large, it’streating will also greatly increase the cost of wastewater treatment（accounting for20%-50%）, thus how to dispose the excess sludge economically and effectively hasbecome one of the urgent problem in WWTP. In order to solve the above two mainissues, the sludge Anaerobic Fermentation coupling with Denitrification（SAFD）system was put forward in this paper, exploit the inner carbon source and use it fornitrogen removal, in this way also can achieve a certain degree sludge reduction. fourkinds of WAS SAFD systems including batched nitrate type, batched nitrite type,continuous nitrate type and continuous nitrite type, were established. In this theory theconstructon, mechanism, influencing factors and process applications of SAFDsystem were mainly studied. The major innovative results obtained are introduced asfollows.In order to study the influence of electron acceptor concentration on SAFDsystems in short term, two kinds of the batched SAFD systems including batchednitrate type and batched nitrite type were established. For batched nitrite type SAFDsystem, from the perspective of dentirification, the400mg/L NO₂--N system have thebest denitirfication performence, the total NO₂--N degradation amount and the nitriteremoval amount per unit of volatile suspended solid（VSS） reduction were the largestamong all the systems, while in the point of sludge reduction,200mg/L NO₂--Nsystem showed the best sludge reduction capacity. For batched nitrate type SAFDsystem, it performed less effective denitrification compared to batched nitrite typeSAFD system, the nitrate type system with concentration of200mg/L exhibited thebetter denitrification capacity and sludge reduction capability than others, when usingthe nitrate as the electron acceptor, reducing the dosage or decrease the frequency ofdosing should be considered.To study the effects of different electron acceptors （NO₂--N and NO₃^--N） onSAFD system denitrification capacity, fermentation and acid producing capability and sludge reduction ability, long-term batch SAFD systems were builded. In this system,using the NO₂--N as the electron acceptor can achieve better dentrificationperformance than NO₃^--N electron acceptor, anammox reaction was found in theNO₂--N system, denitrificaiton coupling with anmomox reaction was realized in thisreactor, performed great nitrogen removal efficiency. Further, in NO₂--N systemspolysaccharides and protein production were significantly higher than NO₃^--N system,exhibited stronger sludge fermentation ability. Additionally, NO₂--N systems showedgreat sludge reduction capacity, with more than60%of VSS reduction.Build the continuous nitrate type SAFD system to deal with the actualwastewater, the main technology for the process is “pre-UASB+A/O” system. In thestable stage of this process, NH4+-N, NO₂--N and NO₃^--N can total removed from thewastewater, with almost100%removal efficiency, suggested the whole system have astrong nitrification and denitrification abilit. Besides, there was no WAS discharge inthe system, but dosed extra excess sludge for fermentation, the concentration of SS inthe whole system was not obviously increased which suggested a significant sludgereduction. Enhancement of the UASB denitrification ability and strengthen the A/Osystem nitrification capacity were the key points to maintain this system nitrogenremoval.Build the continuous nitrite type SAFD system dealing with high ammoniawastewater with the process of “A/O+rear-UASB” system. In the UASB reactor canrealize the sludge fermentation, dentrification and anammox reaction,simultaneously,the advantages of this combination performed high nitrogen removal efficiency.Further, this system has no WAS discharge also suggested a significant sludgereduction. In addition, the realize of fenitrification and anommox reaction in UASBsystem and the short-cut nitrification in A/O system were the key to improve thesystem nitrogen removal ability.