Nitrogen Removal Of CAST Process In Tuyou Qi Sewage Treatment Station

CAST biological treatment is used by Tuyou Qi sewage treatment plant, the finaleffluent in addition to ammonia nitrogen was satisfactory with the first-B-standard ofChinese Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002). The study aimed at the substandard ammonia nitrogen concentration problemof Tuyou Qi sewage treatment plant comprehensively investigated at working performanceof CAST, and investigated the operating effects of different operating conditions. Afteranalysing the reasons of the substandard ammonia nitrogen concentration of Tuyou Qisewage treatment plant, effluent ammonia nitrogen concentration reached dischargestandard through scene debugging.By the data analysis and the test at the sewage treatment station from January2012toAugust2013, it was found that the into water of Tuyou Qi sewage treatment plant wasabout6000m3/d, it run three cycles a day and stop running at night, and water aeration ofeach cycle was3h, precipitation was40min, drainage was40min. Average effluent COD,BOD5, ammonia nitrogen, SS, TP were respectively59mg/L,13mg/L,35mg/L,28mg/L,1.9mg/L, other indicators can meet the standard in addition to the ammonia nitrogen that ismuch higher than drainage standard. Through the study of sludge in biological pool, it wasfound that sludge concentration and the content of inorganic particles were high, sludgeactivity is poor, and the amount and type of microorganisms were small. The main causesof limiting nitrogen removal were as follows: firstly, sludge concentration was high, thevalue of SVI was40or so, MLVSS/MLSS was below0.5, inorganic compounds in sludgewas high, sludge activity was too low; secondly, flocculation tank sludge discharged intocoarse grid, and entered biological pond along with the water, then it influenced the sludgeactivity of biological pond; thirdly, C/N ratio is somewhat low; fourthly, it leaded microbesto consumption their own nutrients and made its decomposition because it was idle in theevening.In order to determine the influence on account of operating conditions, aeration time, DO, reflux ratio, water drainage ratio were studied by using small CAST test-bed. Whenthe water aeration is3h, the precipitation of drainage is2h, dissolved oxygen is3mg/L,water drainage ratio is1/3, reflux ratio is50%, the water quality is best, ammonia is2.62mg/L, removal rate is95%. It shows that the designed operating parameters of Tuyou Qisewage treatment plant are reasonable.After analysing the reasons of the substandard ammonia nitrogen concentration ofTuyou Qi sewage treatment plant, two kinds of measures to solve the problem of lowammonia nitrogen removal rate are adopted, one is that the flocculation sludge in theflocculating settling basin is discharged into the sludge thickener by modifying the pipeline,rather than in coarse screen; the other is to develop the sludge activity by adding nitrifyingbacteria, denitrifying bacteria and sodium bicarbonate in the CAST reaction pool. Throughthe debugging of the denitrification system, ammonia nitrogen is under10mg/L, removalrate is over80%, ammonia nitrogen is satisfactory with the first-B-standard of ChineseDischarge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002).