Establishment And Research On Mathematical Model Of Microalgae-Bacteria Symbionts In Livestock And Poultry Wastewater Treatment

The microalgae-bacteria symbiosis system has been used in the treatment technology of livestock and poultry wastewater due to its characteristics of efficiently removing pollutants such as nitrogen,phosphorus and COD in water.The research on the specific process and influencing factors of microalgae-bacteria symbionts in the treatment of livestock and poultry wastewater can provide theoretical support for optimizing and improving the efficiency and ability of microalgae-bacteria symbionts water treatment technology.The characteristics of complexity and high load of livestock and poultry wastewater have brought obvious limitations and influences on the application of wastewater treatment by microalgae-bacteria symbiosis process.The growth of microalgae and bacteria in response to the complex water quality environment and the change of pollutant removal situation is the theoretical basis for the study of the practical application of microalgae-bacteria symbiosis treatment process.Therefore,a mathematical model of a series of biochemical dynamic processes of microalgae and bacteria in the process of water treatment was constructed based on the study on the influence of microalgae-bacteria reactor on hydraulic load of livestock and poultry wastewater treatment.In this study,based on the known dynamic model of microalgae and bacteria,according to the practical application scenario of microalgae-bacteria technology,the influence of relevant dynamic environmental factors was described.The time discretization parameter was used to improve the model and the simulation test method of rate integration was carried out.The Monte-Carlo random simulation was used to analyze the sensitivity of some relatively sensitive parameters.It also evaluated the impact of input on model output,improved the accuracy of model application in the scene,and finally calibrated and validated the model through a continuous wastewater treatment cycle.In the process of studying the continuous treatment of livestock and poultry wastewater by microalgae-bacteria symbiotic system,the influence of different hydraulic residence times on the water treatment effect of microalgae-bacteria reactor and microbial growth status was taken as the research object.The research showed that microalgae-bacteria symbiotic system had a strong ability to adapt to the treatment of wastewater with higher hydraulic load.When the hydraulic residence time was 12h,18h and 24h,the removal effect of pollutants in the early stage of operation increased with the increase of the residence time,but the final removal effect of nutrients was little different with the gradual stabilization of the operating conditions of microorganisms in the microalgae-bacteria reactor.Meanwhile,the hydraulic load had a great impact on the growth of algal bacteria microorganisms.The final stable biomass of the three groups of reactors and the particle size of the bioflocs increased with the acceleration of the influent rate.Therefore,different hydraulic loads had significant effects on the final equilibrium state of the symbiotic system of microalgae and bacteria.On the basis of the study of microalgae-bacteria co-biological water treatment technology,the process dynamics mathematical model of the combined treatment of wastewater by microalgae and bacteria was constructed.According to the principle of microbial growth in the water treatment process and the biological process of pollutant removal,the changes in the reaction components were described.On the basis of Monod dynamics,light,temperature,p H,dissolved oxygen and other factors involved in the growth process of microalgae-bacteria were taken into account to establish the rate equation of biochemical dynamics process,and the econometric relationship between microbial growth and water quality change was designed based on the element composition of microalgae,heterotrophic bacteria,autotrophic bacteria and nutrients as the basis for mathematical model calculation and simulation,improving the description of the process and components in the model.Finally,the microalgae-bacteria symbiosis co-water treatment model was analyzed and verified,and the model rate integration was optimized by setting time discretization parameters to reduce the errors caused by ignoring time nodes of environmental and water quality factors in the model simulation.Then,the impact of Monte-Carlo simulation test parameters on the model output was analyzed.The sensitivity of model component output to parameter input was analyzed.The parameter test showed that the maximum specific growth rate of microalgae(μ_ALG)and the maximum specific growth rate of heterotrophic bacteria（μ_H）for example,the output results of corresponding model components in the simulation range of±5%,±10%and±20%were consistent with the actual situation.After continuous water treatment for one month,the model was calibrated and verified.The water quality changes predicted by the model and the growth of microalgae-bacteria symbiosis and microorganisms were in good agreement with the experimental values.