Study On Construction And Operation Performance Of A Pilot-scale Biofilm Reactor With Microbubble Aeration

Aeration is the basic process for aerobic biological wastewater treatment processes, and accounts for the main power consumption in wastewater treatment plants. Microbubble could enhance oxygen mass transfer and is supposed to be able to provide potential advantage for high oxygen utilization, efficient pollutants removal and energy-saving. In this study, the biofilm reactors with microbubble aeration(MB) and conventional bubble aeration(CB) were operated simultaneously to investigate their performances and biofilm characteristics. Furthermore, different microbubble generators, reactor types and filler types were compared for determination of the pilot-scale system. Then the pilot-scale biofilm reactor with microbubble aeration was designed, constructed and operated. The performance of the pilot-scale system was investigated during start-up and stable operation, including pollutants removal, oxygen utilization and biofilm characteristics.The results indicated that the average removal efficiencies of COD, NH4+-N and TN were 90.3%, 92.7% and 43.4% in MB reactor during start-up and stable operation, respectively. The corresponding removal efficiencies in CB reactor were 79.4%, 86.3% and 29.3%, respectively. MB reactor presented more efficient performance of contaminant removal than CB reactor. In addition, the oxygen utilization efficiency in MB reactor reached 94.3%, which was much higher than that in CB reactor. Faster biofilm formation and larger biofilm biomass were achieved in MB reactor, compared with CB reactor. Moreover, the biofilm formed in MB reactor showed higher VSS/SS ratio and lower EPS content. These results demonstrated that biofilm formation was enhanced by microbubble aeration in MB reactor, which contained more active biomass.The porous fiber carrier showed obvious advantages for start-up and contaminant removal, compared with ring carrier and rubber particulate carrier. The biofilm biomass reached 1.4g/L in the reactor filled with porous fiber carrier during stable operation, and the average removal efficiencies of COD, NH4+-N and TN were 93.7%, 58.87% and 50.83%, which was more efficient than the reactors filled with other two types of carriers. When OHR microbubble generator was used for microbubble aeration, the contaminant removal capacity and energy consumption of the biofilm reactor were more efficient than that using SPG membrane for microbubble aeration. Therefore, the OHR microbubble generator and a fixed bed biofilm reactor filled with porous fibrous carrier was determined to be involved in the pilot system.After the stable operation of the pilot system, the average COD effluent concentration, removal rate and organic loading rate were 136.9mg·L-1, 64%, 0.8kg·(m3·d)-1when the HRT was 6h. When the HRT decreased to 2h, the average COD effluent concentration, removal rate and organic loading rate were154.34mg/L, 64.27%, and 3.12kg·(m3·d)-1. The ammonia nitrogen and total nitrogen removal rate were also relatively low. However, the oxygen utilization reached 96% when the HRT was 2h. The study on biofilm reactor with OHR microbubble aeration treating sewage was still in the initial stage, which should be improved further, to increase sewage treatment efficiency and support the future application of OHR microbubble aeration.