| The OCO reactor was first developed by Degremont Puritek A/S Company (Denmark), and was named because the shape of the reactor is similar to the letters of the alphabet "OCO" Anaerobic zone, anoxic zone and aerobic zone were designed in one reactor within a small space which offered an appropriate condition for biological removals of nitrogen, phosphorus and COD at a lower cost, and an easy implementation of online monitor and automatic control. The OCO process was widely used in many European countries including Denmark, France, and Sweden and so on. However, there has been little documentation of the operation parameters about the OCO process, and little field application was built on the basis of the process in China. Currently, the overwhelming advantages of the integrated OCO process in municipal wastewater treatment have attracted many researchers in China who are dedicated to the modification of integrated OCO process.Based on a comparative study for the early series of integral OCO process, a novel sewage treatment process, the integral OCO process with two side-ditch separators was designed. The hydraulic mixing characteristic and the effect of operating factors on sewage treatment efficiencies in the integral OCO reactor were investigated, the kinetics equations and prediction model by BP neural network methods were developed.The integrated OCO processes from the first generation to fourth generation reactor (integral side-ditch OCO reactor with biofilm and activated sludge, integrated OCD reactor with central island separator, integrated OCO reactor with central island separator, integral side-ditch OCO reactor) were developed by author as described in this study.. The design parameters, characteristics of these processes were described systematically, the performances on the removals of nitrogen and phosphorus were summarized, and the advantages and limitations were discussed concluding in the design of a novel reactor—the integrated OCO process with two side-ditch separators.Based on the pulse sampling method, hydraulic mixing characteristics test was conducted in the integrated OCO process with two side-ditch separators. A proportion of86.8%for the completely-mixed flow and another proportion of13.2%for the plug-flow were proven quantitatively by the combination of the function E (t) for the retention time distribution in the reactor. By using the continuous sampling method, the reactor was run in the whole completely-mixed flow and the local plug-flow, which were shown by the hydraulic model constructed on the basis of the law of mass conservation. These results were consistent with the theoretical assumptions and showed water flow characteristics in the reactor meet the design idea.The effect of dissolved oxygen (DO), hydraulic retention time (HRT), influent CODcr/TN mass ratio (C/N ratio), CODcr/TP mass ratio (C/P ratio) and sludge retention time (SRT) on treatment efficiencies by this process in domestic sewage were analyzed. The optimal operating parameters were listed as follows:DO concentration in aerobic was about2.0mg/L, and those in the anoxic zone and the anaerobic zone were lower than0.5mg/L and0.1mg/L, respectively; SRT was approximately12d, HRT was approximately12h (influent flow rate of20L/h), the C/N ratio was near8:1and the C/P ratio was approximately50:1. The stable operation results show that the integrated OCO process with two side-ditch separators has good removal efficiencies of COD, NHU+-N, TN and TP for60days, their removal rates were95%,99%,81%and90%, respectively.Based on kinetic analysis for removals of COD, NH4+-N, TN in the integral OCO reactor with two side-ditch separators, kinetic equations were built and kinetic constants were calculated suitable for removals of COD, NH4+-N, TN. The effluent water quality prediction model was constructed by BP neural network methods and used to predict sewage treatment efficiencies in the integral OCO process. The prediction results match with experimental data.Preliminary research for pilot experiment (expanded4times) was carried out in the integral OCO process with two side-ditch separators. Proportion of80.6%for the completely-mixed flow and another proportion of19.4%for the plug-flow were proved by hydraulic characteristics test in this reactor, and liquid flow patterns performance was the whole completely-mixed flow and the local plug-flow. This integral OCO reactor was used as trial operating research to treat domestic wastewater. When the preliminary research results showed:DO concentration in aerobic was near2.0mg/L, SRT was12d, HRT was12h, the C/N ratio was approximately8:1and the CODcr/TP mass ratio (C/P ratio) was near50:1, the good efficiencies for wastewater treatment by the pilot integral OCO reactor were achieved: the removal rates of COD, NH4+-N, TN and TP were94%,99%,81%and93%, respectively.The integral OCO process with two side-ditch separators is suitable to remove pollutants such as carbon, nitrogen and phosphorus from domestic wastewater without any auxiliary chemical reagents. This study can provide a theoretical basis for application of this integral OCO process in China. |
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