Experimental Study On Domestic Sewage Treatment With Tidal Flow Bio-contact Oxidation

With the rapid development of urbanization and the improvement of living standard of urban residents in China,the amount of sewage will increase greatly.It is an important way to control the water pollution by on-site sewage treatment on decentralized domestic sewage in urban areas that sewage collection pipe network is not completely covered and in rural areas.Therefore,the selected decentralized sewage treatment technology should be not only appropriate to local environmental conditions,but also reasonable in technology and economy,finally determining a technology that can realize stable effluent quality,simple operation and management as well as low investment and operating cost.The bio-contact oxidation process,which has multiple advantages of activated sludge method and biofilm method,is widely used to treat the decentralized domestic sewage,but there is a problem that the aeration and water are not evenly distributed during the running process.For the reasons given above,in this paper,tidal flow bio-contact oxidation is proposed,and the tidal operation mode of"rapid influent-submerged-rapid drainage-empty"is used to make the sewage periodically infiltrate the filler.The phase of rapid influent is equivalent to the"high tide"process,so that the sewage flows through the filler.During the submerged phase the sewage contacts fully with the biofilm,as a result the organic matter is adsorbed by the biofilm.The phase of rapid drainage is equivalent to"low tide"process which can form a suction effect that induces air quickly into the reactor to provide oxygen for aerobic degradation of pollutants.During the empty phase,microbial organisms take in organic matter as the substrate that absorbed on biofilm before,with the aid of oxygen to efficiently degrade,at the same time the dissolved oxygen concentration difference in the reactor strengthen the natural diffusion of oxygen.During the tidal process,the pore of the filler is filled with air,so that the oxygen is evenly distributed in the reactor.When the water is fed again,the air in the pore of the filler is exhausted so that the sewage can fully contact with the biofilm.On the one hand the tidal process improves the oxygen transport capacity of the bio-contact oxidation reactor,and overcomes the problem that the aeration and water are not evenly distributed during the traditional bio-contact oxidation process.On the other hand the system is a low-cost operation process that does not need aeration,but a small amount of power to achieve the“tide”.The filler which produced by sludge incineration has the characteristics of high porosity,rough surface and easy attached by biofilm.It can meet the filler requirements of bio-contact oxidation method and meet the reclamation requirements of municipal sludge.The main contents and conclusions are as follows:?1?Natural biofilm formation was used to start tidal flow biological contact oxidation,under the conditions that environmental temperature was about 15²1?,the concentration of DO was more than 2mg/L and the ratio between submerged time and empty time was 1:3.On the 15th day,the removal rate of COD_cr was above 80%stably;on the 29th days,ammonia nitrogen removal rate achieved 91.9%.At this point,the COD_cr,ammonia removal effect is stable,which is the mark of biofilm formation.It is shown that the tidal flow bio-contact oxidation reactor with urban sludge regeneration filler can achieve faster biofilm formation at lower temperature.?2?In this study,the effects of different biological conditions on the removal of organic matter in domestic sewage were studied.The experimental result showed that the treated effluent quality of tidal flow bio-contact oxidation reactor was stable while the influent water quality fluctuated greatly,and the removal efficiency of COD_cr was high,turning out that the system had powerful resistance to impact load.The effect of tidal flow bio-contact oxidation reactor on the removal of organic matter in domestic sewage was investigated by comparing the different operating modes.The treatment effect in different ratios between submerged time and empty time was analyzed.When the ratio was 1:1,the COD_cr removal rate could reach85.4%,which was higher than that the ratio was 1:3,indicating that the larger ratio was more favorable for the removal of organic matter.The reason is that the larger ratio represents longer submerged time,thereby strengthening adsorption abilities of biofilm for pollutants;the experiment results of different treatment time showed that in the early processing cycle the degradation of COD_cr was the mainly function in the reactor,while the following paragraph was regeneration of biofilm.According to the treatment of water quality to select the appropriate treatment time can meet the requirements to remove COD_cr,but also make the biofilm fully regenerated,which is conducive to the next cycle of adsorption,so that makes the overall effect of the process better.?3?In order to realize the simultaneous denitrification of organic matter,the tidal and submerged area were set up in the tidal biological contact oxidation reactor to provide the denitrification condition.The experimental result showed that the removal efficiency of ammonia nitrogen was good.The average removal rate of the six conditions were more than72%,even up to 99.4%.During the experiment,the accumulation of nitric nitrogen was significantly lower than that of ammonia nitrogen,indicating that there was N loss in the removal of ammonia nitrogen,as well as synchronous nitrification-denitrification occurred in the reactor.Compared with the different submerged vacancy time ratio,it is found that the larger submerged vacancy time benefits to removal of ammonia nitrogen.When the temperature is lower than 15?,the nitrification reaction is obviously inhibited,and the removal efficiency of ammonia nitrogen is only 72.4%?C2?.The nitrification and denitrification intensity of biofilm showed that the tidal area in the upper part of the reactor was nitrification zone,and there was no obvious denitrification zone in the reactor.When the influent COD_cr was 175.9³86.8 mg/L and the ammonia nitrogen was 34.2⁵1.6 mg/L,the results showed that operation mode C1 could get better removal effect of both COD_cr and nitrogen,at this time the ratio between submerged time and empty time was 1:1,and the treatment time was 24h.?4?The characteristics of the biofilm were studied,and the mechanism of the tidal biological contact oxidation was revealed from the microbial perspective.By the microscopic observation of the biofilm,a large number of zoogloea and a variety of protozoa,metazoan and micro-animals were found,indicating that biofilm microbial morphology was rich.There are stable predator-prey relationships among bacteria,protozoa,metazoan on the biofilm,and a longer food chain is maintained.?5?The biofilm quantity and activity were determined by measuring the quantity of volatile biofilm and the microbial respiration rate.The biofilm quantity was 18.01 g/L by converting into MLSS and the respiration rate was 40.2 kgCO₂/kg_?biofilm?·d,indicating that the biofilm quantity was large and the activity was high.?6?In this study,Biolog-ECO method was used to analyze the metabolic characteristics of biofilm microbial carbon in the process of long-term operation of tidal bio-contact oxidation reactor,and the mechanism was further analyzed.The results show that the readily available carbon source composition of the biofilm microorganism in the bioreactor is basically the same as that of the domestic carbon source.Due to the rich readily available carbon source in the environment of microbial living environment,the biofilm microorganism growth and reproduction are fast,and the diversity and species are rich.