Experimental Study On The Treatment Of Small Town Domestic Sewage By MBBR Wetland Combined System

In order to realize the sustainable development of our country’s economy and ensure the improvement of residents’living quality,we should use reasonable and effective methods to control water pollution,increase energy-saving and emission reduction efforts,upgrade the level of urban sewage treatment,and improve the quality of urban environment,to realize the sustainable development of our country's economy.In view of the particularity of sewage in small towns,a treatment system suitable for sewage treatment in small towns is developed according to local conditions and has advantages of economy and high efficiency.In this paper,the experiment of“MBBR+constructed wetland”combined system treating domestic sewage of small towns was analyzed and studied.The experiment is divided into three stages,the first stage is to study the start-up and stable operation of the combined system,the second stage is to study the influence factors of the combined system,and the third stage is to study the removal of pollutants under adverse circumstances.With a view to providing reference for the upgrading of wastewater treatment standards and the selection of wastewater treatment processes in small and medium-sized cities and towns,the following conclusions are drawn through the study:（1）During the experiment,the integrative equipment and the horizontal subsurface flow constructed wetland start up at the same time,the natural film-forming method is adopted for the packing of the aerobic tank of the integrative equipment,and the natural enrichment method is adopted for the constructed wetland.At the temperature of20～28°C,the process of biofilm formation was fast,and the removal efficiency of COD and NH₄⁺-N was stable after the start-up of 2～3 weeks.The concentration of TN effluent is less than 8 mg/l,COD,NH₄⁺-N and TP can reach the IV standard of surface water after 4～5 weeks of operation of constructed wetland.The removal efficiency of COD,NH₄⁺-N and TP by the integrated equipment is remarkable after stable operation at 22～28°C,and the removal contribution rate of COD,NH₄⁺-N and TP is over 90%,and the removal contribution rate of TN is over 80%.（2）At room temperature through the combination of different factors in the operation of the system analysis.When the HRT is 5 H,8 H,10 H,12 h,the HRT is 8 H,it is the most economical and efficient to remove the pollutants.Through the experimental analysis of the pollutant removal effect of the combined system under different filling rates,it was determined that the optimal filling rate of the combined system was 30%,which could obtain more stable and efficient removal effect than the activated sludge process.The effect of dissolved oxygen on the combined system is mainly reflected in the aerobic nitrification stage of the integrated equipment.The most suitable concentration of dissolved oxygen in the combined system is 3 mg/l.（3）Under low temperature condition,the water temperature of the integrated equipment is 6～12°C,the water temperature of the constructed wetland is 4～12°C,the influent concentration is higher than the influent concentration at normal temperature,but the influent concentration is still low.The removal of COD,NH₄⁺-N and TP all exceed the first grade a standard of the urban Sewage Treatment pollutant discharge standard（GB8918-2002）and can reach the grade IV discharge of surface water.Under low temperature operation,the integrated equipment in the combined system plays a major role in pollutant removal,low temperature suppresses plant growth in the constructed wetland,small rainfall,small runoff and little effect on wastewater treatment,the effluent will not be adversely affected and further sewage treatment can be carried out.（4）In summer,the temperature of biochemical pool is 32～38°C,and the water temperature of constructed wetland is 32～40°C.In summer,the concentration of influent is low,and the average removal rate of four indexes is 93.7%,98.5%,93.7%and 91.4%,respectively.The constructed wetland is in a good state of removal,which makes the combined system more effective in wastewater treatment.Both the constructed wetland and the integrated equipment can show their respective advantages,and the combined system is more effective in wastewater removal at different temperatures,discharge up to standard.