Study On Treatment Of High Ammonia Nitrogen Wastewater By Aerobic Granular Sludge And Its Mechanism

Aerobic granular sludge (AGS) process is a new technology of wastewater treatment which uses aerobic granules instead of conventional activated floccular sludge. AGS possesses many advantages such as perfect settling properties, better separation ability, abundance of microorganisms, higher density and resistance to shock loading. In addition, nitrifying bacteria and denitrifying bacteria coexist in the granular sludge due to the coexistence of aerobic and anaerobic zones. Therefore it may have the potential for high-strength ammonium wastewater treatment. In this thesis, a preliminary study on granulation process was carried out, in which the physical and chemical property changes during granulation process, and the trial of treating high-strength ammonium wastewater and nitrogen removal mechanisms using the mature granules obtained under low-strength of ammonium wastewater were also studied.The experiments of AGS rapid cultivation and the impact of moderate-strength ammonium on aerobic granules were firstly conducted. The results indicated that mature and sharp edged AGS could be obtained in an SBR reactor through COD loading adjustment (reducing first, later keeping constant) in34days. After granulation, MLSS reached to10.8g/L with MLVSS of7.8g/L and SVI decreased by70%. The PN/PS ratio was first declining during granulation, then increased to>0.3on day65d after mature granules were formed. The increase of proteins in the AGS could lead to higher hydrophobicity of granules thus promote cell-cell attachment. The experiments also indicate that granules may break with the gradual increase of ammonium concentration in the reactor. It was interesting to find that the granules could be recovered when COD level increased. Mature granules were found to have some tolerance to moderate-strength ammonium wastewater.AGS had the potential for treating high-strength ammonium wastewater, and the higher the influent COD, the higher ammonium level that AGS could tolerate. The COD and TN removal rates were94%and60%, respectively when the influent COD was10000mg/L and ammonium nitrogen was2000mg-N/L. The mechanisms of nitrogen removal in this reactor may involve ammonium oxidation, denitrification of oxidation products such as nitrate/nitrite, simultaneous nitrification and denitrification (SND), as well as short-denitrification processes. During the SBR cycle tests DO was found to be a useful indicator to online monitoring the involved biological reactions, which is better for process optimization and by-products control compared to pH and ORP during the treatment of high-strength ammonium wastewaters.When treating high-strength ammonium wastewater, ammonium adsorption onto AGS can not be ignored. Under high ammonium levels, the adsorption reached equilibrium within20minutes, and the amount of adsorption increased with the increase of initial ammonium concentration. When the initial ammonium concentrations were600and2000mg-N/L,9%and16%of the initial ammonium were adsorbed by AGS, respectively. When the initial ammonium concentrations were200mg-N/L, ion exchange dominated the process accounting for64%of the total adsorption. Physical adsorption rather than ion exchange was the dominant process when the initial ammonium concentration increased to2000mg-N/L, and the latter only occupied9%. During the adsorption, little contribution could be attributed to biological utilization. Restated, physical adsorption was the major process for AGS under high-strength ammonium conditions.This paper is a feasibility test on AGS for high-strength ammonium wastewater treatment. The results obtained in this study could provide an experimental and scientific basis for the practical application of AGS in the treatment of high-strength ammonium wastewater.