Soil Infiltration Of The Sewage Treatment Process To Run Simulation Studies

Soil Infiltration Treatment (SIT) is a kind of in-situ wastewater treatment technique, making full use of animals, plants, microorganisms in soil and the physico-chemical characteristics of soil. The purpose of this thesis was to focus on the purification performance under different operation conditions through both field and laboratory experiments. The kinetics models were established according to the influence factors on carbon, nitrogen and phosphorus removals and their removal mechanisms. At last, the optimal parameter designs and operation conditions were proposed for the guarantee of effective performance.The results from field experiments showed that SIT systems became gradually maturation during the first 3 month start-up periods. The pretreatment process including solar energy aeration and sedimentation could remove less than 35.2 % of organics. All the final effluent CODs were less than 40 mg l^-1 under various conditions with accumulative COD removal rates ranged from 50.6 % to 75.8 %., on which water temperature was one of the important factors. The removal rates of total phosphorus, phenolic and phthalate pollutants could reach 57.7 %-100.0 %, 35.2 %-100.0 % and 36.4 %-59.6 %, respectively. And the effluent DOs were 1-3 times of the influent values with UV254 decreased by 13.5 %-67.2 %, which was in favor of the survival and procreation of hydrophilous creatures and the recovery of ecosystem.The results from laboratory experiments demonstrated that besides temperature, the constituent and physico-chemical characteristic of artificial soil, wastewater quality of the influent, hydraulic loading rate and effective depth of soil layer, etc. affected carbon, nitrogen and phosphorus removals. The characteristic of artificial soil was the most important factor on COD and TP removals, and the denitrification process was remarkably improved with the increase of C:N ratio in artificial soil. Wastewater quality was the most important factor on TN removal but the impact of it on COD and TP removals seemed rather less. So did the hydraulic loading rate. From the experiment results, an optimal hydraulic loading rate, 8.0×10^-2 m³ m^-2 d^-1 was obtained. The effective depth of soil layer of 0.50 m could be satisfied with COD removal, but not enough for denitrification and higher TP removal requirements. In addition, the removal of ammonia nitrogen was not affected by the above influence factors due to the large adsorption capability of soil matrix applied.The researches on pollutant removal mechanisms disclosed that COD removal consisted of abiological adsorption and biodegradation processes. The abiological process followed Temkin adsorption isothermal, and the proportion of biological COD removal occupied 57.7 %-71.9 %. The abiological and biological removals of ammonia nitrogen changed with the variance of influent concentration. Both accumulation and shortage of nitrite nitrogen could affect nitrification efficiency and the effluent nitrite concentrations should be controlled within 0.10 mg l^-1-0.25 mg l^-1 with the consideration of maintaining the sustainable operation of SIT. The results indicated that C:N ratio in artificial soil was the limiting factor on denitrification. And the static adsorption of TP followed Freundlich isothermal, in which Fe oxyhydroxide (Fe_o) content had a close relationship with TP removal rate.Based on Eckenfelder first order kinetic model, COD, TN and TP removal models were established by adding or modifying several influence factors, for example, temperature, hydraulic loading rate, influent concentration, effective depth of soil layer and the characteristic of artificial soil, etc. These models could be used to forecast the effluent COD, TN and TP concentrations from SIT systems, with the errors between simulated and experimental values less than 5 mg 1^-1,5.0 mg l^-1 and 0.15 mg l^-1, respectively. The results implied that COD removal rates were determined by the removal potential of SIT system. Besides, the simulation resutlts indicated that TN and TP effluent concentrations were significantly affected by hydraulic loading rate. Furthermore, the pollutant removal efficiencies of SIT systems could be remarkably improved by optimizing these key factors mentioned above.