New Process Study on Biochemical Treatment of Crushed Coal Pressurized Gasification Wastewater

Author:Ji Qin Hong

Supervisor:zhang zhen jia


Degree Year:2016





Coal gasification wastewater is discharged mainly from the raw gas washing,condensing and purifying operations of the coal gasifier.The contaminants composition of coal gasification wastewater is related to gasifier physical configuration,operating conditions,coal type,and so on.The crushed coal pressurized gasification wastewater is hard to treat,due to the high concentration of pollutants in the wastewater.Currently,the integrated process of hydrolytic acidification + multistage A/O process is usually used for the treatment of coal gasification wastewater by the modern coal chemical industry.However,there are some shortcomings of this integrated process,such as low treatment efficiency,large amount of sludge,high energy consumption,etc.In this thesis,the effluent of phenol and ammonia recovery unit from fixed bed crushed-coal-pressurized gasifier was used as the research object.The Experimental analysis result of wastewater quality pointed out that the used coal gasification wastewater has the following characteristics,such as complex pollutants composition,high concentration of COD,phenol,ammonia nitrogen and poor biodegradability,etc.According to the characteristics of the wastewater quality,a new biochemical treatment process of anaerobic sludge bed + inner-circulating aerobic biofilm reactor + embedded denitrifying bacteria particles reactor + ozonation + embedded bacteria fluidized bed was put forward and used to treat the coal gasification wastewater.This laboratory research optimized the operation parameters of each treatment unit,investigated the pollutants removal efficiency of each treatment unit,and then the applicability of the new process for coal gasification wastewater treatment was done systematically deriving the understanding and evaluation of the system.Anaerobic sludge bed reactor is the core unit of the new biochemical treatment process,which plays a key role in improving the biodegradability of coal gasification wastewater,removing phenols and other toxic pollutants.This paper mainly studied the start-up method of anaerobic reactor for treating crushed coal pressurized gasification wastewater,pollutants removal efficiency of the increased load operation stage,and the analysis of the influencing factors.Under the condition of without diluted the coal gasification wastewater,used the municipal digested sludge as inoculation sludge,without added supplementary carbon source and gradually shorten the hydraulic retention time,the acclimatization period of anaerobic sludge was about 3 months.Under the operation condition of the shorter hydraulic retention time,increasing COD concentration of influent and increasing total phenols concentration of influent,the negative effect on the removal efficiency of pollutants of anaerobic reactor increased in turn.It was closely related with the increasing toxic pollutant concentration of phenolics,which inhibited the activity of anaerobic bacteria.During 300 days of continuous operation it was concluded that the anaerobic reactor could handle coal gasification wastewater with COD concentration 3300 mg/L and total phenols concentration 350 mg/L.In terms of impact load,anaerobic reactor could withstand COD concentration of influent increased by two times(in the range of 1500 mg/L-3300 mg/L),total phenols concentration of influent increased by 50%(in the range of 230 mg/L-350 mg/L).Under optimized conditions,the removal rate of COD,total phenol of anaerobic reactor reached 60% and 40%,respectively.Through the experiments it was revealed that the total phenols concentration in the influent was the key control parameter for the treatment of coal gasification wastewater by the anaerobic reactor,and the biogas production rate was an important evaluation index of the anaerobic reactor performance.Internal recycle aerobic biofilm reactor further removed the residual organic pollutants and ammonia nitrogen in the effluent of anaerobic reactor.Experimental results showed that,under the condition of aerobic reactor and anaerobic reactor started up almost at the same time,the acclimatization period of nitrifying bacteria was about 3 months.It was found that,there was nitrification inhibition phenomenon in the early stage operation of the aerobic reactor,which may be caused by the high organic load,high concentration of phenols and lack of alkalinity,and so on.The nitrification inhibition of aerobic reactor could be effectively relieved by means of wastewater pH adjustment,an increased in hydraulic retention time,a decrease in organic load,and so on.Experimental results showed that,pollutants in coal gasification wastewater could be effectively removed,and aerobic reactor also showed good ability in resisting the impact load.During the steady-state of aerobic reactor,the removal rate of COD,total phenols and ammonia nitrogen was more than 70%,80%,and 80%,respectively.The COD,total phenols and ammonia nitrogen in the effluent was less than 300 mg/L,30 mg/L,and 10 mg/L,respectively.For the removal of nitrate nitrogen and ammonia nitrogen of aerobic reactor effluent,the embedded bacteria technology was innovatively used for denitrification treatment unit and advanced treatment unit.The research results showed that nitrate nitrogen of coal gasification wastewater could be effectively removed by anaerobic sludge bed reactor with embedded denitrifying bacteria pellets,and also has some advantages such as short start-up period,stable operation.Under the optimal condition of operation parameters,the influent nitrate nitrogen concentration 160 mg/L and the effluent nitrate nitrogen conc.was less than 5 mg/L of denitrification reactor.The removal rate of nitrate nitrogen remained above 97%.To meet the wastewater discharge or reuse standard,the integrated process of ozonation-fluidized bed reactor with embedded nitrifying bacteria pellets was creatively used to removal residual refractory organic compound and ammonia nitrogen of denitrification reactor effluent.When ozonation-fluidized bed reactor was in steady-state,the average removal rate of COD,total phenols and ammonia nitrogen was 74.2%,100%,and 93.3%,respectively.The average COD,total phenols and ammonia nitrogen in the effluent was 52.7 mg/L,undetected and 0.28 mg/L,which meets national Integrated Wastewater Discharge Standard(GB8986-1996).The experimental results showed that the biologically pretreated coal gasification wastewater could be effectively treated by the combined process of ozonation-fluidized bed reactor with embedded nitrifying bacteria pellets.Laboratory studies broke through the new biochemical treatment process for crushed coal pressurized gasification wastewater,obtained the operation parameters and pollutant removal efficiency of each treatment unit,which provided the basis data for engineering design.Compared with the existing process,the new biochemical treatment process has the following advantages: high pollutants removal efficiency of anaerobic reactor,low sludge production,low energy consumption,etc.Among them,the COD removal rate of anaerobic reactor of the new biochemical treatment process reached 60%,however,the COD removal rate of existing process was only 5% to 25%.Based on theoretical calculation,the new biochemical treatment process could approximately reduce sludge production by 50%,which significantly reduced sludge treatment cost.Consequently,the studied new biochemical treatment process in this thesis was beneficial for the exploration and innovation of biochemical treatment of crushed coal pressurized gasification wastewater.