Research On The UCT Process For Municipal Wasterwater Treatment

At present, effluent of many water plants can not meet the Level 1 A standard in "the urban sewage treatment plant standards for discharge of water pollutants" (GB18918-2002). So they are faced with upgrade and improvement of the effluent quality standards. How to ensure the out effect of nitrogen and phosphorus and meet the national comprehensive emissions standards in every index has become a hot research issue for scholars.The UCT process is based on the traditional A2/O process, adding mixture returning from the anoxic reactor to the anaerobic reactor. Meanwhile,part sludge of sedimentation tank is reflowed to the anoxic reactor. The technology reduce content of NO₃- in the anaerobic reactor, preventing denitrification from affecting phosphorus release. Besides,mixture returning from the anoxic reactor to the anaerobic reactor ensures anaerobic circumstance of anaerobic reactor.As a result, the characteristics of the process improve phosphorus removal of A2/O.The test uses UTC process which belongs a kind of upflow reactors. The influent is from effluent of the first sedimentation tank of water plant in Taiyuan. The whole test mainly contains three stages. The first phase is inoculating and domesticating sludge.The sludge from water plant aerated by air pump is inoculated in the reactor. And then using municipal wastewater added some nutrient solution domesticates sludge. The procedure lasts 5 days until vorticella and infusorian appear in the sludge. Now, the phase finishes. The second stage is start-up and operation of reactors. In the phase, DO,HRT,reflux ratio of sludge and temperature and so on are changed in order to attain stable and good effect on treatment. The stage lasts 25 days. At the end of phase, the effluent except total phosphorus meets the requirement Level 1 A standard of the urban sewage discharge (GB18918-2002).However, total phosphorus achieves Level 1 B standard. The third stage is parameters analysis when the process operates stably. C/N ratio,SRT,HRT,reflux ratio of mixture and sludge etc are changed to study effect on UTC technology.In the third stage,firstly, the effect of influent C/N on the nitrogen and phosphorus removal was discussed. When the mean influent C/N ratio ranged among 1.4-2.9,the meanphosphorus removal efficiency was below 75% and the mean final effluent of PO₄³- was above 1mg/L, the mean nitrogen removal efficiency was 50% and the mean final effluent of TN was above 30mg/L.However wheninfluent C/N ratio increased up to 5.45, TP removal efficiency increased at 89.6% while the stable nitrogen removal efficiency increased at 89.2%. They all met the Level 1 A standard in "the urban sewage treatment plant standards for discharge of water pollutants" The C/N of themunicipal wastewater ranged among 4-7 in common.On the other hand, it can be found optimizing anoxic biological phosphorusremoval in the UCT system was dependent on some parameters:the internal return ratio, Sludge reflux ratio,sludge retention time (SRT) and Hydraulic Remain Time (HRT). The influent C/N ratio around 5, the SRT of 14 days, the internal return ratio of 200%, were determinedas optimal for the phosphorus and nitrogen removal in the system.The test results show that, UCT urban sewage disposed by UCT can make effluent of good water quality and meet the Level 1 A standard in "the urban sewage treatment plant standards for discharge of water pollutants" (GB18918-2002). Compared with the traditional A2/O technology, it can accommodate to low C/N ratio domestic sewage. When C/N ratio in influent is very low, so the UCT denitrifying phosphorus removal process has a good prospect for the municipal wastewater treatment.