Experimental Study On Treatment Of Domestic Sewage By Pre - Denitrification Two - Stage Soil Filtration System

With the discharge of domestic wastewater, the environment is increasingly damaged by the high concentration of nitrogen in water. As an in situ disposal technology, soil aquifer treatment (SAT) are commonly used in distributed domestic sewage, however, the result of denitrification is not satisfying. Therefore, this study mainly focuses on reinforcing the ability of denitrification in SAT system.In order to simulate SAT, the artificial soil column was applied in the experiment. Four different combination of the packing and four crafts were carried out to investigate their effect on decontaminating the wastewater. Consequently, the efficacy of wastewater treatment of two-stages SAT with pre-denitrification was studied, In the meantime, the theory in organic matter and total nitrogen removal was analyzed, as well as the discussion on the main factors. Moreover, the derivation of the kinetic model as to the denitrification system was also conducted.Four different kinds of SAT craft were investigated to purify wastewater, including single stage system, cyclic single-stage system, two stage system with divided-flow, and cyclic two stage system. It can be concluded that the removal of CODCr, NH4+-N and TN in all three combined crafts were superior to the single stage system. In the stage of nitrification and dinitrification, the supply of sufficient oxygen and carbon sources was necessary to obtain preferable removal of TN. The removal rate of TN in cyclic two stage system was better than other treatment, and its ability was enhanced with optimized craft.For the SAT system, the removal rate of CODCr and NH4+-N was reduced by the rise in hydraulic loading. As to TN, the removal gained an increase prior to decrease. Under the hydraulic loading of0.08m3/(m2·d), the removal rate of CODCr, NH4+-N and TN were increased up to91.73%,95.32%and74.91%, respectively, reaching the best efficacy. As the reflux ratio increased, the dissipations of CODcr and NH4+-N were increased, whereas the removal rate of TN declined after the increase. Thus the flux ratio of150%appeared to be the optimum condition, where the removal rate of CODCr, NH4+-N and TN were increased to95.18%,97.68%and78.21%. With the increasing load of organic matters and ammonia nitrogen, the denitrification ability of the two stage SAT system coupled with pre-denitrification was decreased, contrarily, there was little effect on the removal of organic matters. The removal of CODCr and NH4+-N mainly occurred in the second soil column, while the TN was eliminated by the first soil column.For the two-stages soil aquifer treatment system with pre-denitrification, the kinetic model of denitrification in the first soil column, based on Eckenfelder model, was illustrated as follows:Se/S0=e-KH/qn with n of0.8957and K of0.5211.