Optimization Scheme On Perfusion PRBs In Situ Carbon Injection Bioremediation For Nitrate Contamination Of Groundwater

In situ carbon injection bioremediation technology for removing nitrate fromgroundwater is a promising and economically effective technique, and carbon sourceinjection optimization can also reduce the cost of groundwater remediation and wellinstallation at the most, which minimizes the management cost. In this paper, thegroundwater polluted by nitrate in a landfill site in Beijing was taken as a researchobject, a biological coupling Monod solute transport model (RT3D) was taken basingon perfusion PRBs in situ bioremediation technology, which can simulate theconcentration changes of the nitrate, carbon source and denitrifying bacteria in thegroundwater after injecting carbon source (ethanol), and can integrally quantify thepollution plume of different periods using MATLAB software at the same time. Basedon Monod kinetics reaction simulation, genetic algorithm (GA) and simulatedannealing (SA) were used to optimize the scheme of18alternative wells and in situbioremediation system in remediation area for groundwater nitrate pollution plume.The paper draws the following conclusion:(1) Different method of carbon source injection for simulation results show thatunder the condition of constant carbon source injection volume, increasing theconcentration of carbon source (the total amount of carbon source rises) can increasethe removal rate of nitrate per unit mass of single well and utilization rate of carbonsource, while the nitrate removal rate per unit mass of carbon source in double-wellfirst increased and then decreased. Under the circumstance of adding carbon sourcescontinously, the longer the length of injecting time, the more likely it is that theremoval rate of nitrate per unit mass of carbon source and utilization rate of carbonsource in single well and double well will drop.When the carbon source was inputintermittently,(the total amount of carbon source unchanged) the removal rate ofnitrate per unit mass of carbon source and utilization rate of carbon source in singlewell and double well wouldn’t vary with the change of time interval.(2)The results of optimization show that, both GA and SA optimizationconditions can reach the desired results, which means that the concentration of nitrate can be reduced to10mg/L after100days injecting carbon source with50mg/L. Thetotal carbon injection volume of well5,7and9optimized from GA are separately2.5m3/d,1.5m3/d and1.3m3/d; and well5,7and9optimized from SA are separately2.2m3/d,1.4m3/d and1.5m3/d.The total mass removal rates of biodegradable nitrateafter100days are90.78%and84.51%respectively.(3)The results of optimization show that, carbon injection wells should bearranged in triangular forms, and the upstream volume of carbon source injecting isgreater than the others. Comparing the two optimization algorithms of in situbioremediation shows that the treatment cost of SA is1.46%lower than that of GA,and SA has stronger convergence with smaller volatility, but longer computing time.