Laboratory Studies On Ammonia-Nitrogen In-situ Remediation In Vadose Zone At Non-formal Landfill Area

The ammonium-nitrogen absorption ability of experimental medium, the optimal reaction condition for nitrification and the ammonium-nitrogen removal kinetics were investigated in laboratory experiment. An enhanced biological technique for removing ammonium with the characters of combination of more water content increased in unsaturated zone and enhanced bio-venting was accordingly raised after a series of tests.Results showed that adsorption isotherm can be excellently described by Langmuir isotherm model for ammonium adsorption at 25 oС(R2>0.9). The maximum adsorption capacities of ammonium on experimental medium are up to 0.526 mg/g at 25 oС. The medium in unsaturated zone on interest area has an excellent capability of ammonium absorption and thus preventing the site from ammonium pollution. Meanwhile, these results indicated that the ammonium content in unsaturated zone on interest area was relatively high and a critical pollution event would happen if ammonium release with the change of environmental conditions. Additionally, the ammonium solution of 200mg/L was used for dynamic absorption test on experimental medium. The results showed that the dynamic absorption capability on ammonium was up to 0.151 mg/g, which was a few less than the static absorption capability (0.225 mg/g) under the same conditions.During the process of ammonium-nitrogen removal in unsaturated zone, both the soil moisture and aerobic environment were the most essential influencing factors of the nitrification. The usage of circumscribed strain had not obvious effect on ammonia nitrogen nitrification, but it could reduce the accumulation of nitrite. All strains engaging in the soil nitrification universally exist in nature, and simply cultivated which has fatal significance on remediation of ammonia nitrogen pollution in practical sites remediation. Ammonium-nitrogen adsorbed in unsaturated zone soil can transform to nitrate-nitrogen totally if only under suitable condition, therefore complete nitrogen removal would be achieved with the subsequent further treatment process, like denitrification.Column experiments showed that volatilization, adsorption/desorption and nitrification processes all had important effects on spatial distribution characteristics of ammonium-nitrogen. Under the condition mentioned in this essay, the nitrification process started from the 5th or 6th day, and the removal efficiency of ammonium could reach 50~70% in the reaction of more than 20 days. The way of bio-venting also has significant effect on ammonia nitrogen contamination. Low ventilation rate might lead to low nitrification reaction rate, incomplete reaction and accumulation of intermediate product like nitrite, while high ventilation rate might result in water evaporation, therefore inhibiting growth of microorganism and thus reaction rate. Therefore, determinations of optimal ventilation mode and ventilation rate are still the vital questions of the sequent research in future.