Highly Influent Nitrogen Concentration Wastewater Treatment CAST Process Debugging And Operation Study

Eutrophication problem is more and more serious nowadays because of Nitrogen and Phosphorus excessive discharge. With the enhancement of environment protect consciousness and GB18918-2002 implement, no matter new-build Wastewater Treatment Plants or existing ones, are facing the challenge of depth Nitrogen and Phosphorus removal problem. CAST Process is a modified SBR wastewater treatment process with the function of Nitrogen and Phosphorus removal, which has been widely used in our country. Due to many merits such as little floor space,no need for preliminary and secondary sedimentation tanks,low cost of capital construction and operation , preventing sludge bulking effectively and convenient operation and management, It has a broad marketing prospect.In order to promote the investigation development of CAST process,especially highly influent Nitrogen CAST Process's production and operation testing research, a series production tests were carried out in Lijiatuo WWTP as the experimental field, from sludge cultivation and domestication, CAST process debugging, to operation optimization. Characteristics and problems of each pollutants removed by CAST process was studied in a year round continuum production tests. Based on pollutants removal characteristics research, research emphasis were put on optimizing several vital operation controls parameters and each affection factors'function rules study. According to these tests which had mentioned above, the reasonable operation patterns for high temperature period and low temperature period CAST running was found which were fit for present influent wastewater quality and quantity. Based on analysis prophase operation condition and data, especially Nitrogen removal rule and affection factors analysis, a new operation pattern was put forward, which can adapt to the future condition when influent wastewater quantity and Nitrogen removal pressure increased with the wastewater pipelines consummate. As the meanwhile, ORP change rules and its affection factors, its indication function during Nitrogen removal process has been elementarily studied.During the CAST process debugging in Lijiatuo WWTP, four operation patterns has been taken used. A: Influent/Aeration 2h—Settle 1h—Decant1h; B: Influent 2h—Aeration 2h—Settle 1h—Decant1h; C: Influent 1h—Influent/Aeration 2h—Slight Aeration 1h—Settle 1h—Decant1h; D: Influent/Aeration 3h—Settle 2h—Decant1h; According to the practical operation effect, select the C operation pattern for low temperature period operation pattern. Optimize its control parameters, the result shows it can reach the best effects when DO during aeration period is at the level of 2.0~3.0 mg/L, slight aeration period below 0.5 mg/L, MLSS 3500~4000mg/L, correspondingly, SRT 15~20d, recycle ratio 30%, average Nitrogen removal rate is nearly 75%. Select A pattern as the high temperature period operation pattern. and optimize its control parameters, when DO is at the level of 3.0~4.0 mg/L, MLSS 5000~6000mg/L, SRT 12~16d, recycle ratio 20%, the system's treatment effects reach the best.After analyzing whole year running data of 2008, conclusions as follow is found out. In CAST process's Nitrogen removal designing, N/MLSS has better below 0.04gN/gMLSS.d, overpass the level, Nitrogen removal effect is declined quickly. When carry out CAST debugging, especially the influent is with a high N/MLSS, it has better attaching more importance to operation pattern select. It can prevent the weakness and depressing the Nitrogen removal pressure which bring by high N/MLSS. When SRT is about 15d, the system's Nitrogen removal effect is best.In order to solve the problem when influent wastewater quantity and Nitrogen removal pressure increases, bring forward a new method which is DO Step-Control during optimizing simultaneous nitrification and denitrification (SND) effect research. The tests'result indicates that Nitrogen removal effect is better than normal when DO Step-Control is taken use in operation no matter whether it is under the low temperature period condition or high temperature period condition. Nitrogen removal rate increases 10%~15%, and mostly effluent TN concentration is below 15mg/L.When carry out the pilot study for researching the role of ORP making during the Nitrogen removal process, the study emphases is put on the relationship between ORP, CODCr, NH3-N and NOX—N during denitrification process. And the results indicate that influent wastewater quality makes an important role in affecting ORP. Linearity pertinency between ORP and logarithm of CODCr,NH3-N concentration product and NOX—N concentration ratio is preferable, R2=0.9146.Based on double factoes Nitrogen removal model and influent conditions, puting out CAST Nitrogen removal model and test by practical operation datas, the results shows that it matches with the actual situation well. The model can be used to guide control parameters setting, Nitrogen removal effect and effluent quality forecast.