Research On The Operation Mechanism And Efficiency Of A Small Vertical Deep Water Reactor (VDR)

With the rapid development of China's economy,more and more attention has been paid to sewage treatment,and the collection and treatment of urban sewage has been perfected,but the problem of domestic sewage in villages and towns has not been paid enough attention.By the end of 2020,more than 70%of the administrative villages in Shandong Province have no perfect sewage treatment system,and the sewage treatment facilities that have been built generally have problems in operation and management.Rural sewage pollution is wide and scattered,water quality and quantity vary greatly in different regions,and the fluctuation of discharged water quantity makes it more difficult to treat rural sewage.In view of the above problems,this paper proposes a new process for decentralized domestic sewage treatment in rural areas.A vertical AO biological method is used to treat the discharged domestic sewage,and a air lift device is used to reflux the sludge.The process is defined as a Vertical deepwater reactor(VDR).This paper studies the start-up operation effect and treatment efficiency of VDR device.The device has the characteristics of high treatment efficiency,convenient operation and management,small occupied area,strong adaptability to the fluctuation of sewage quality and water quantity,and is suitable for small-scale sewage in villages and towns.(1)The small test of VDR was carried out,and the design,installation and preliminary operation of the pilot test were completed.The results show that when the aeration rate is 150 L/h and the inflow rate is 3 L/h,the flow rate of air lift is 212 L/h and the reflux ratio is 70:1.The removal efficiency of small test is preliminarily studied,and the average removal rates of NH₃-N,TN,TP and COD are 99%,20.4%,38.2%and 84.2%respectively.According to the small test data of VDR,the medium test device of VDR is optimized and designed.(2)Study on the effect of stripping reflux in VDR pilot plant.The application effect of stripping reflux was investigated.The results showed that when the aeration rate was 1200 L/h and the inflow rate was 200 L/h,the stripping reflux flow rate was550 L/h,the gas-water ratio was 6:1 and the reflux ratio was 2.75:1.In small-scale sewage treatment equipment,especially in deep-water reactors requiring high aeration rate,the stripping device could replace the traditional pump reflux system to save energy consumption.(3)Study on quick start-up and removal efficiency of VDR pilot plant.After inoculation with 200 L sludge,the sludge concentration increased from 2683 mg/L to8390mg/L within 5 days,and the sludge concentration increased rapidly.During the start-up,the removal efficiency of VDR device was tested,and the average removal rates of NH₃-N,TN,TP and COD reached 99%,38.7%,80.7%and 87.9%respectively.After optimization,the removal efficiency of TN and TP in VDR pilot plant was significantly higher than that in small test,among which TP removal rate increased by 42.5%and TN removal rate increased by 18.3%.With the addition of carbon source,the effluent TN decreased to less than 15 mg/L,and the TN removal rate increased to 68%,which was stable for a long time.(4)Study on VDR removal efficiency under different reflux ratios.In order to further explore the operation mechanism of VDR pilot plant,the effects of different reflux ratios(1.75,2.75,3.5)on dissolved oxygen,TP,TN,ammonia nitrogen and COD were investigated.When the reflux ratio increases,the removal efficiency of ammonia nitrogen and COD increases,the removal efficiency of TN and TP decreases slightly,and the optimal aeration rate is 1200 L/h.(5)Study on sludge characteristics of VDR pilot plant.The higher rising gas velocity is the key to the formation of aerobic granular sludge,and the rising velocity of gas in VDR pilot plant is 0.17 cm/s.The sludge in the main reaction zone of pilot plant was screened with 0.6 mm sieve,and it was found that there was a small amount of granular sludge,the highest proportion of which was only 8%,and the generated granular sludge was loose,which indicated that the higher gas ascending velocity in VDR is beneficial to the formation of granular sludge.(6)Adaptability research of VDR pilot plant.According to the characteristics of large fluctuation of wastewater quality and quantity in villages and towns,the adaptability of VDR pilot plant to the changes of influent conditions and external environment was investigated.The adaptability under three conditions of increasing organic load,low temperature environment in winter and industrial sewage was mainly investigated,and compared with the removal effect of sewage treatment plant,ammonia nitrogen in the effluent of the plant was lower than that of water plant,and the removal rate was very stable compared with that of water plant,which indicated that VDR plant had strong adaptability.