Experiment Study And Anayslis On Modified Step-feed A/O Process Treatmenting Domestic Sewage

Step-feed A/O process has been widespread concerned in the domestic and foreign water treatment field because of its high nitrogen removal and carbon source utilization.In this paper, actual sewage is treated in continuous water modificated step-feed A/O process and investigated the effect of the system to the major pollutants removal efficiency. Experimental study of modificated step-feed A/O process in two conditions:the main factors affecting the pollutant removal efficiency of steady water system and mechanism of pollutant removal on the best condition; pollution removal effect and coping strategies of non-steady water system.This study last one year, getting the major findings:(1) The optimal operating conditions of the steady modificated step-feed A/O process: sludge recycle ration of75%, sludge age of15d, water flow distribution of20%:35%:35%:10%, aeration rate of0.2m3/h (aerobic area DO:0.8-1.5mg/L), when hydraulic retention time is8.7h, the water pollutant indicators in this condition are able to meet "the urban sewage treatment plant emissions standards "(GB18918-2002) in A level standard.(2) On the optimal operating conditions, adding30%fillers in aerobic area of Steady water system can reduce hydraulic retention time,when hydraulic retention time is6h, ammoniacal nitrogen, total nitrogen and COD can meet "the urban sewage treatment plant emissions standards "(GB18918-2002) A level standard.(3) Steady modificated step-feed A/O process has highly carbon source utilization in the optimal conditions, influent carbon source of66%is utilized in the anoxic and anaerobic area and17%in aerobic area. The carbon source utilization of the first, second and third paragraphs is42%,31%and10%, first paragraph>second paragraph> third paragraph, the system for the carbon source utilization along the drop in participation.(4) On the best conditions, Steady water system has high level of nitrification, can reach more than75%in each paragraph, ammonia nitrogen removl rate is first paragraph> second paragraph> third paragraph. Denitrification ability of the system was the first paragraph> second paragraph> third paragraph and nitrate-nitrogen in return sludge is removed in preconditioning anoxic area. The phenomenon of simultaneous nitrification and denitrification is found in the aerobic area, and first paragraph> second paragraph> third paragraph.(5) Dissolved oxygen of aerobic area in the Steady water system aerobic rises step by step, associated with the influent distribution and sludge concentration gradient.Because of the dissolved oxygen from aerobic area and weakening of denitrification,ORP of anoxic area rises step by step. pH in aerobic area is elevated due to denitrification phosphorus removal and denitrification. When sludge recycle ration is fixedness, the sludge concentration in the reactor is progressively reduced because of the stepwise dilution of step feed.(6) On the best conditions,the water pollutant indicators of non-steady water system are not stable.The pollutant removal efficiency of the system is fluctuated depending on fluctuations in influent load of pollutants.50%non-steady water system is more visible, DO, pH, ORP and other test parameters are volatile.(7) The variable aeration rate can effectively reduce influence of non-steady state for the water system, COD, ammoniacal nitrogen and total nitrogen can meet "the urban sewage treatment plant emissions standards "(GB18918-2002) a level standard.This paper provide theoretical basis for the practical application of modificated step-feed A/O process, which is highly nitrogen and phosphorus removel.This system has a broad prospect, economic benefit, remarkable environmental benefit whether for constructing or reforming a zsewage treatment plant.