Study On The Bioclogging Mechanism Of Rapid Infiltration Land Treatment Systems

In recent years,with the rapid development of the rural economy,the discharge of rural domestic sewage has been increasing,which has worsened the environmental conditions in rural areas and directly threatened the living environment and physical health of farmers.Many domestic researches have been done on the treatment process of rural domestic sewage.Among them,the Rapid Infiltration Land Treatment System?RI System?is more suitable for its flexible process,low investment and low energy consumption for the treatment of domestic sewage in rural areas.But when coming to the engineering practice,it has been gradually found that clogging is a common problem which would greatly restrict the application of the RI system.In this study,a coupling model between the development of biological clogging and the filter bed sewage treatment efficiency in the intermittent sewage dosing mode was constructed by establishing the mathematical relationship between microbial growth and porosity variation.Combined the experimental data of study on the biological clogging of the filter bed,The established biological coupling model was verified.The evaluation value of the model shows that the coupled model based on the permeability-porosity mathematical formula proposed by Blazejewski has the best simulation performance and can better describe the evolution law of biological clogging in the rapid infiltration system.The theoretical research results of the model show that:The development of biological clogging could be accelerated by the increase in hydraulic loading rate?HLR?,influent sewage concentration or dosing frequency?DF?in the regular sewage dosing mode.And the influent wastewater concentration has the greatest impact for directly affecting the amount of organic matter that enters the filter bed.The second is the influence of HLR,and DF has the least effect on biological clogging,because it affects the growth of microorganisms indirectly by affecting the residence time of sewage in the filter bed.Under the adaptive sewage dosing mode,increasing the instantaneous hydraulic loading rate?instantaneous HLR?,influent sewage concentration or buried depth of the moisture monitoring point?SP?will also promote the growth of microorganisms.Among them,the concentration of influent sewage has the greatest impact on the development of biological clogging,followed by instantaneous HLR,and SP has the smallest impact on biological clogging because it affects the growth of microorganisms by adjusting the dosing frequency and the daily accumulated dosing time.Overall,the concentration of influent sewage is the main factor affecting the biological clogging of the filter bed.Pretreatment measures for sewage before dosing are necessary to slow down the development of clogging.While accelerating the development of clogging,the growth of microorganisms will also affect the removal effect of the filter bed on pollutants.For the COD,the increase of HLR or sewage concentration will cause the increase of effluent COD concentration,however,the increase of DF under constant HLR will reduce its effluent concentration.This is mainly due to the increase in the concentration of HLR or sewage,which increases the requirements for the efficiency of the sewage treatment of the filter bed.The increase of DF under the same HLR means the decrease of the instantaneous HLR,resulting in the increase of the residence time of the sewage in the filter bed,moreover,improves the efficiency of sewage treatment of the filter bed.The essential difference between the three is whether the increased microbial biomass under the influence of different factors can meet the demand for the removal of increased organic load;for NO₃^--N,the increase of HLR or sewage concentration will lead to the decreased of its effluent concentration,while the increase of DF will lead to an increase in the concentration of NO₃^--N in the effluent.The main reason is that increasing the concentration of HLR or sewage causes the amount of organic matter entering the filter bed to increase and promote the progress of denitrification.On the contrary,the increase of DF under fixed HLR means the decrease of instantaneous hydraulic load,which leads to the increase of the residence time of sewage in the filter bed.At the same time,the increasing of DF will raise the ratio of the growth and death time of microorganisms,which promotes the Growth,and in turn leads to an increase in NO₃^--N concentration of system effluent.In this paper,on the basis of exploring the evolution of biological clogging and the efficiency of filter bed sewage treatment,the dynamic relationship between the two processes is further studied.The results show that in the early stage of clogging,the removal efficiency of organic matter and NH₄-N by the filter bed gradually increases with the increase of microbial biomass,but when the microbial biomass increases to seriously clog the pores,the reduction of porosity will weaken the reoxygenation capacity of the filter bed by the atmosphere,leading to the corresponding gradual reduction of the removal capacity of NH₄-N.