The Anammox Activity Enhancement By Low Intensity Ultrasound And Co-immobilized With Partial Nitrifying Sludge For Autotrophic Nitrogen Removal

Single-stage autotrophic nitrogen removal process with partial nitrification-anaerobic ammonium oxidation (anammox) is that ammonium is transformed into dinitrogen gas completed by ammonia oxidizing bacteria (AOB) and anammox bacteria in a single reactor. The process has great potential to treat low C/N ratio, ammonia-rich wastewater. According to reports,26sewage treatment plants have established the single stage equipments based on nitritation and anammox reaction. But, the currently running single-stage reactors face some questions, for example, bacteria grow slowly, and the sludge is easy to wash out, and reactor stability is poor. These factors have induced that the single-stage autotrophic nitrogen removal process has a long startup time, which limit the application of the technology.We firstly cultivated anammox bacteria and strengthened its activity by ultrasound. Second, the mass transfer performance of the polyvinyl alcohol (PVA) entrapment carrier was improved by adding sodium bicarbonate (SB) or sodium alginate (SA). Third, the partial nitrifying and anammox biomass was co-immobilized with PVA_SA material and a single-stage autotropic nitrogen removal reactor was started up. We studied the suitable conditions of single stage autotrophic nitrogen removal system. We also investigated nitrogen removal performance in reactor and the effects of the operation conditions on the single-stage autotrophic nitrogen removal. Lastly, we investigated bacterial morphology, distribution and proliferation by SEM experiment, and investigated bacterial abundance by FISH experiment. The dissertation has made some innovative research results:(1) Anammox sludge was effectively enriched from conventional activated sludge using an up-flow composite-bed biofilm reactor. On day362, both of the influent ammonia and nitrite concentrations increased to270mg N/L, the total nitrogen (TN) removal rate reached1.85kg N/m3/d. During the stable running stage, the average TN removal efficiency was over85%.(2) Anammox microbial consortium activity was improved by exerting ultrasound field. Anammox activity was significantly improved when the ultrasound field strength was in the scope of0.1～0.4W/cm2. Anammox activity was enhanced by25.5%at the optimal ultrasonic intensity of0.3W/cm2and irradiation time of4min. (3) The mass transfer performance of the PVA carrier is relatively poor, which affect the transfer of nutrients, metabolites and oxygen. The mass transfer capabilities of PVA hydrogel carriers can be improved by adding SA or SB, and the carriers formed by adding SA, SB were called PVA_SA carrier, PVA_SB carrier, respectively. The mass transfer of PVA_SA and PVA_SB gel carriers increased by29%and38%than traditional PVA carriers. The ammonia oxidizing activities of partial nitrifying sludge entrapped by PVA_SA material and PVA_SB material improved by30%and44%than traditional PVA carriers, respectively.(4) A single-stage autotrophic nitrogen removal process using co-immobilizing AOB and anammox biomass was started up with a gas-lifted reacor. It was running for175days, and the ammonia removal capacity was stable. The maximum TN removal rate reached1.66kg N/m3/d. During the stable running stage, the average TN removal efficiency was77%. From these results, it can be summed up that Co-immobilizing technology is suitable for single stage autotrophic nitrogen removal process.SEM showed that bacteria had a greater increase observed on day81than that of day1. FISH showed AOB existed around the anammox bacteria, and anammox bacteria and AOB accounted for45%,40%of the total bacteria. This indicates that, the AOB and anammox bacteria have colonized, grew and proliferated in the carriers.