| The inverted high rate activated sludge process(R-HRAS)is an efficient carbon source recovery wastewater treatment process that is improved on the basis of the high rate activated sludge process(HRAS).The main body of the process is composed of an adsorption tank followed by a sedimentation tank.The particulate organic carbon(pCOD)in the influent is first precipitated and recovered in the pre sedimentation tank,and the remaining colloidal organic carbon(cCOD)and dissolved organic carbon(sCOD)are selectively adsorbed and stored in the post adsorption tank.This design of carbon source classification and recovery breaks the bottleneck of low efficiency in cCOD and sCOD recovery in conventional HRAS processes.In the small-scale R-HRAS process experiment in the early stage,the COD recovery rate reached 49.2±4.1%,which significantly improves the carbon source recovery efficiency of the R-HRAS process compared to the traditional HRAS process with a COD recovery rate of 20-40%.At present,research on the R-HRAS process is only in the laboratory stage.In order to accelerate the comprehensive promotion and application of the process,it is urgent to expand the research scale and explore the performance of the process under long-term outdoor operation.Against this background,this study conducted a pilot scale R-HRAS experiment at a university town sewage treatment plant in Linyi City,Shandong Province.The designed daily treatment capacity was 30m3,and the influent was low-carbon source raw water from the sewage treatment plant(COD concentration 121.96～190.67mg/L).The total operating time was one year and zero April.During this period,in-depth research was conducted on the process start-up stage,long-term operational performance of the process,and the impact of seasonal factors on process performance.From a practical perspective,the operational performance of R-HRAS as a carbon source recovery sewage treatment process was evaluated in the application process.The specific chapter content and conclusions are as follows:(1)The role of the start-up stage of the R-HRAS process is to adapt the inoculated sludge to the operating conditions of the process,while the hydraulic retention time(HRT)and sludge retention time(SRT)become key parameters for adjustment during the start-up stage due to their impact on sludge load.The order of parameter adjustment has a significant impact on the success rate and start-up time of the process.Currently,there is no in-depth research on the start-up process of the R-HRAS process.In Chapter 3,three start-up schemes were designed to explore the performance of HRT and SRT in different adjustment sequences during process start-up:Scheme 1(R1)was HRT regulation followed by SRT regulation,Scheme 2(R2)was SRT regulation followed by HRT regulation,and Scheme 3(R3)was HRT and SRT regulation simultaneously.The results show that in terms of startup time,R3(42d)>R1(51d)>R2(infeasible),the average decrease in parameter regulation R1(13.95%)>R3(9.58%),and the actual operational difficulty R3>R1.Analysis of experimental results:Compared to R1,the increase in sludge load in each stage of the alternating reduction of HRT and SRT in R3 is relatively small.After calculation,the load shows a slow upward trend between 0.3 and 1.2 KgCOD/(m3 · d),allowing the sludge to fully adapt to the slowly changing growth environment while gradually possessing the unique characteristics of R-HRAS process sludge(small and loose sludge flocs,multiple surface adsorption points are conducive to carbon source recovery),In order to achieve the standard of parameter adjustment faster,R3 not only has a fast startup speed but also a small decrease in parameter adjustment with high stability.However,due to frequent parameter adjustments,the difficulty of operation correspondingly increases.R2 first regulates SRT through sludge discharge,but at this time,due to the low carbon source characteristics of the influent.it is difficult for nutrients to maintain the normal renewal of sludge in the system during the initial start-up.Finally,the sludge concentration in the adsorption tank rapidly decreases and the start-up fails.(2)Chapter 4 provides an overall evaluation of the long-term operational performance of the process.COD removal and recovery:the removal rate of the process for total chemical oxygen demand(tCOD)is 54.7±5.4%,in which the removal rates of pCOD,cCOD and sCOD are 70.5 ± 3.2%,21 ± 3.8%and 50.8 ±4.6%respectively.The process for COD recovery is 45.9 ± 7.4%,mineralization rate is 13.9± 4.1%,and loss rate is 40.2 ± 4.2%.Compared with the existing pilot scale HRAS process,the COD removal rate is 51.2%,and the recovery rate is 21.3%[1],The R-HRAS process has significant advantages in COD removal and recovery.Further analysis shows that in the removal of pCOD,the pre sedimentation tank plays a major role,with a removal contribution of 84.8 ± 1.5%.For the difficult to remove cCOD and sCOD,the removal contribution is mainly concentrated in the post adsorption tank,with 68.3 ± 4.2%and 98.9±0.6%,respectively.This indicates that the process characteristic of "carbon source classification and recovery" is correct;In terms of nitrogen and phosphorus pollutant removal,the NH3-N removal rate is 6.9 ±1.7%,the TN removal rate is 5.9± 1.1%,and the TP removal rate is 15.6± 1.5%;The total energy consumption during the process operation is 0.078(kWh/m3),of which the pump energy consumption is 0.012(kWh/m3),the aeration energy consumption is 0.066(kWh/m3),the energy neutralization rate is 228%,and the carbon neutrality rate can reach 84.8%,which belongs to the low energy consumption carbon source recovery sewage treatment process.(3)Existing research has shown that microorganisms have the best biological activity in sewage treatment processes at 20-30℃.The research stage is divided into a normal temperature stage(water temperature>20℃)and a low temperature stage(water temperature<20℃)based on the inlet temperature.On this basis,the influence of seasonal factors(water temperature and water quality)on the process is studied.The normal temperature stage has the characteristics of low influent concentration and high sewage temperature,while the low temperature stage is the opposite.Under the combined action of multiple factors,the process exhibits a superior pollutant removal effect in the room temperature operation stage compared to the low temperature stage.The removal effect of tCOD in the room temperature stage is 2.89%higher than that in the low temperature stage.This advantage is mainly attributed to the increase in microbial activity and the movement rate of pollutant molecules in the sewage at higher temperatures during the room temperature stage,which accelerates the process of settling pCOD in the pre sedimentation tank at a physical level,The removal efficiency of other forms of COD is similar at different stages.In terms of COD recovery rate,the process COD recovery rate at room temperature stage is about 49.6%,and at low temperature stage,the process COD recovery rate is about 44.1%.This is because at room temperature stage,when the inlet temperature is high and the carbon source concentration is low,there are more opportunities for pollutant molecules in the adsorption tank to come into contact with EPS,making the ability of microbial molecules to capture carbon sources better than at low temperature stage.In terms of nitrogen and phosphorus removal rate,because Nitrifying bacteria are affected by temperature,ammonia nitrogen removal shows the characteristics of low removal rate in high and low temperature stages at normal temperature,and total nitrogen removal capacity is negatively correlated with temperature(p<0.05).The process has little impact on total phosphorus removal effect due to seasonal changes.The focus of subsequent research should be on the development of corresponding nitrogen and phosphorus recovery coupling process;In terms of energy consumption,there is a positive correlation between the unit power consumption and the influent concentration during operation.The unit power consumption of sewage treatment fluctuates between 0.762 and 0.823kWh/m3.The energy consumption of the aeration system in the low temperature stage with high influent concentration and low sewage temperature is still the focus of green operation optimization.In actual operation and promotion,investment in main power consumption equipment such as lift pumps and submersible pumps should be increased,and low energy consumption equipment should be purchased,Reasonably adjust the operation mode of the aeration system based on water quality indicators and water temperature to minimize energy consumption during operation. |
PDF Full Text Request