A Pilot-scale Study On Nitrogen Removal Characteristics And Operation Control Of BICT Biological Process

Nitrogen and phosphorus can not be effectively removed simultaneously in current BNR (biological nutrient removal) processes. In order to solve the problem, the pilot-scale study on new wastewater treatment process—BICT process in the dissertation is carded on. In the BICT process, different micro-organisms are intensified in different reactors with two sludge systerm, so the conflicts between them caused by different metabolism conditions are reduced, thereby the N,P can be removed effectively and steadily.The wastewater of Suzhou New Ditrict Wastewater Treatment Plant is used and the the capability of the pilot-scale B!CT process is 4.8m³/d (water input ratio 1/3 ),7.2m³/d (water input ratio 1/2) in the study. The main content of the study is: establish the operation index of separate biofilm zone(HRT,temperature etc.),the nitrification rate and fuction of the part to improve the BICT's removal effect; establish the denitrification rate and study the various influencing factors to denitrification; establish the feasible operation control conditon of the process(main reactor's SRT,water input ratio,returned flow ratio,main reactor's operational mode etc.).Experiment indicates, Nitrogen is removed mainly through three methods in the system: Nitrification and Denitrification,Simultaneous Nitrification and Denitrification (SND),Assimilation. The main form is Nitrification and Denitrification, and the efficiency of several mechanism respective is about 70%,10%,20% in the condition of the pilot-scale study. Nitrification is enhanced due to the separate biofilm zone, and the average nitrification rate constant of 0.39h^-1 is obtained by at the same time. Favorable denitrification is obtained in the main reactor because the main reactor's operation mode and the returned flow ratio are set up suitably, and the average denitrification rate constant is 0.0116 mgTN.(mgVSS.h)^-1. The nitrification is influenced remarkably by temperature,organic load,returned flow ratio. The denitrification is influenced remarkably by DO,organism's amount and form,denitrifying bacteria's amount.Study also indicates, The operation condition recommended for practical application in the pilot-scale study is: main reactor's SRT 5d,water input ratio1/2,returned flow ratio 150%,main reactor's operational mode: first aeration(30min) /anoxic mixing(60min) / second aeration (60min)/settling-discharge-idle(90min). And the feeding time is 60min, distributing in the whole first aeration phase and the first 30min of anoxic mixing phase. The system's removal efficiency in the recommend condition is steady and effective, the average removal efficiency of COD,TN,TP is all above 80%, and the efflunt is near or better than the first grade discharge standard.