Study On Biological Clogging Model Of Particle Packing Biofilter

Humified packing biofilter which is invented through facusing on the technical characteristics of rural domestic sewage treatment has the characteristics of not discharging excess sludge during the stable operation process.In other words,it does not need backwash to maintain the stable permeability of humified packing.But there is no suitable theoretical system to give a scientific explanation for this phenomenon.According to initial speculation,it is closely related to the law of microorganism growth and decay and the evolution law of permeability.At the same time,although the humified packing has outstanding performance in anti-clogging,the risk of clogging still exists during the long-term operation,the characteristic relationship between the law of microorganism growth and decay and evolution law of permeability needs to be mainly studied in the optimization and improvement process.Based on glass beads biofilter,the distribution characteristics of permeability coefficient,microbial biomass and substrate concentration in time and space are studied,and the permeability's evolution law of the particle packing biofilter is analyzed in this study.On the basis of the works above,substrate convective diffusion and degradation model,the microorganism growth and decay model,the porosity variation model and the permeability variation model are established respectively,then the biological clogging model of one dimension steady flow is established through combining the four models above.Combined the experimental data of study on the permeability 's evolution law of the particle packing biofilter,the biological clogging model is verified and corrected.Finally,the biological clogging model is applied to study the permeability's evolution law of the intermittent particle packing biofilter.The results show that:The relative permeability coefficient of each layer decreases gradually with time and the distribution of decreasing rate is gradient.Along the direction of seepage flow,the substrate is continuously adsorbed and degraded by microorganisms,and its concentration reduces gradually,the microorganism's growth rate decreases slowly,so that the relative porosity reduces gradually,finally it leads to the different distribution of the permeability coefficient's decreasing rate in time and space.It is showed that,in the upper layer the substrate concentration is high,the microorganism's growth rate is fast,the relative permeability coefficient decreases rapidly,the clogging occurs firstly.In the middle and lower layer,microorganism grows slowly due to the lack of sufficient substrate's supply and the relative permeability coefficient decreases gradually.By studying the influence rate,it is found that the influence rate of the 0-5cm layer on the variation of the total packing layer's permeability increases gradually,and it eventually closes to 1.The clogging of total packing layer is mainly caused by the clogging of 0-5cm packing layer.The relationship between the variation of the permeability coefficient and the variation of the porosity is related to the particle packing's size.The macroscopic model which just considering the effect of porosity's variation on the permeability coefficient is not suitable for simulating the variation of the permeability coefficient of particle packing with different particle size.Aiming at three different particle packings with size of 0.45-0.7mm,0.7-1.0mm,1.0-1.2mm.The biological clogging model ?,?,?which is suitable for the corresponding particle size are established through combining substrate convective diffusion and degradation model,the microorganism growth and decay model,the porosity variation model and the permeability variation model.It reflects the characteristic relationship between the law of microorganism growth and decay and the evolution law of the permeability at the same influent substrate concentration.Based on the experimental data of study on the permeability's evolution law of the particle packing biofilter,the verification reveals that the method which is established by adopting infinitesimal method,Darcy's law and biological clogging model for solving the permeability coefficient of the total packing layer is feasible.The biological clogging model ?,biological clogging model ? and modified biological clogging model? can simulate the dynamic variation process of the particle packing's permeability.The simulation results of the intermittent particle packing biofilter show that,with the degradation of substrate by microorganism,the substrate's concentration decreases along the depth of the packing and the decreasing rate increases gradually.Most of the substrate is degraded by microorganism in the upper packing layer.The microbial biomass decreases along the depth of the packing,microorganism's growth rate of the upper packing layer is rapid due to the high substrate concentration,microorganism's growth rate of the middle and lower packing layer is slow due to the low substrate's concentration.The variation of permeability coefficient is affected by the amount of microbial accumulation,the permeability coefficient of the upper layer decreases rapidly,and the permeability coefficient of the middle and lower layer decreases slowly.In the late stage,the microorganisms turn into the endogenous respiration period due to the lack of substrate's supply,and the decreasing of microbial biomass leads to the recovery of the permeability coefficient.When the influent substrate 's concentration is 200mg/L,the relative permeability coefficient of the intermittent particle packing biofilter decreases more slowly and its stable running time is 2.3 times that of the continuous particle packing biofilter.By comparing with the microorganism net specific growth rate in two kinds of running modes,it is found that the intermittent operation has the advantage of limiting the total growth of microorganism and its ability to resist shock loading is strong.Reseachs above show that the biological clogging model of particle packing biofilter can simulate the characteristic relationship between the microorganism growth and decay's law and the permeability's evolution law,and can provide important theoretical support for interpretation of anti-clogging mechanism and application of particle packing biofilter technology.