Soil Infiltration Treatment Of The Feasibility Of The High Concentration Ammonia Wastewater And Process Optimization Studies

High-strength ammonia-nitrogen wastewater is a threat to the environment and human health if no treatment or partial treatment is taken, which will lead to the eutrophication of water body and induce the production of carcinogens. During soil infiltration treatment (SIT), a kind of ecological land treatment process, not only pollutants can be effectively removed from wastewater but also nitrogen and phosphorus in the wastewater can be utilized as nutrition for plants, resulting in the reclaimation of wastewater. Based on four different lab-scale SIT systems, this thesis focused on the purification performance of two-stage SIT systems when treating high-strength ammonia-nitrogen wastewater. Different ratios of raw wastewater were supplemented as additional carbon source to the 2nd stage SIT columns and it was also discussed about the effect of an anoxic reactor settled between the two SIT columns.The preliminary study on four different combined processes (single SIT, SBR+SIT, single SIT with recirculation, and SIT with additional carbon source and recirculation) indicated that all of the combined SIT processes exhibited high removal performance of COD, NH3-N and TP, and sufficient carbon source was necessary for stable TN removal. Although no better performance was observed for TN removal, the effluent TN level was more stable through SIT process with additional carbon source and recirculation, probably resulting from the addition of carbon source.Two-stage SIT system showed excellent removals of COD, NH3-N and TP. When influent COD, NH3-N and TP concentrations were 861.2～1686.3,168.00～292.48 and 10.26～20.50 mg l-1 respectively, all the removal rates were greater than 90%. As for TN removal:(1) during the first month of operation, the two-stage SIT systems with different adding ratios of raw wastewater exhibited perfect TN removals, which were 92.39%, 93.68%,92.93%, and 98.19%, respectively; (2) with the operation going on, all the TN removal rates decreased partly due to the changes of soil condition, temperature and pollutant concentrations in the influent; (3) a significant correlation was found between TN removal capacity and influent COD/TN ratio for the 2nd stage columns, and the drop of temperature might have detrimental influence on their TN removal performance. In addition, the anoxic reactor settled between the two stages of SIT systems, in which NO3-N could be denitrified in a relatively short time, was observed to have 45.3% of TN removal with final effluent TN decreased (less than 80 mg I-1) and other pollutants removals enhanced.Finally, the primary benefits of two-stage SIT systems were simply assessed and compared with single-stage systems from both economic and environmental aspects, which might provide some implications and reference for the practice of two-stage SIT systems.