Study On The Influence Of Low Temperature And Low Carbon To Simultaneous Nitrification And Denitrification

In order to meet the generalize of the activated-sludge wastewater treatment process of towns in cold places, more research must be done on the the activated-sludge process under low temperature and low carbon resource. A new process should be developed which is feasible for low temperature and low carbonaceous wastewater, and also has chraracteristics such as energy-saving, simply running, highly efficient, and so on. This article is a most important part of the technology report of the demonstrated wastewater treatment projects in Kangding. This project is one of the construction ministry demonstrated wastewater treatment projects in western towns. The Orbal process has been choosed as the treatment process in Kangding wastewater treatment plant. Now simultaneous nitrification and denitrification(SND) has been found in Orbal process. SND can be used and strengthened to save carbonaceous, reduce oxygen demand, reduce the size of reactors. Its nitrogen removal capacity is above 80%. The sewage temperature in winter of Kangding is less than 10℃, and the carbonaceous influent is not enough too. So the study was conducted on the impact of low temperature and low carbonaceous on SND. The result can supply references to the design and running for wastewater treatment plants in cold places. The study focus on: (1)the impact on SND when the sewage temperature is cooling; (2)Finding out the most efficient treatment group by SND under low temperature(4℃～6℃) and low carbonaceous; (3)oberaving and analyzing the phenomenon occuing in experiment. The experimental results indicated that: under group SRT=25d,HRT=12hr,DO=0～0.5mg/L, at temperature 23.5～6℃, there is a little impact on the removal rate of organaics and TP, a strong impact on TN. As the temperature over 8℃, the nitrogen removal rate more thran 65%. As it dropped to 8℃or low thran 8℃, the activity of microorganism decreased largely, then nitrogen rate was reduced shrarply under 16% . At temperature 4～6℃the optimal control parameters were that SRT equals to 20 days, HRT equals to 12 days and DO is between 0.5mg/L and 1.0mg/L. To improve HRT benefited removal rate increasing. However when BOD loading under 0.04kgBOD/(kgMLSS·d), bulking sludge happened easily. After adding extracarbon the removal rate of TN improved largely. So one of the key reason limiting the nitrogen removal rate is the low carbonaceous(BOD/TN=1.77). In addition, it was found that mifamentous bulking happened with low organic loadings, also when sewage temperature decreased shrarply or kept temperature at 4℃long, viscous bulking happened. So for good running in wastewater treatment plants when water temperature decreased shrarply or at temperature 4℃long time, SV30 and SVI should be monitored carefully and the setting condition in clarifier should be oberaved carefully too.