|Other Abstract||It is hard for any single wastewater treatment technology to meet all the requirements for different influent water quality and the effluent standards demands. Hence, the combination of multi-technologies probably is the natural answer to solve this problem. It is necessary to optimize these combination technologies so as to fulfill the treatment demands. The membrane bioreactor (MBR) technology, which has the advantages of small footprint, high treatment efficiency and easy management, was widely applied to high concentration and non-biodegraded wastewater. However, its low removal rates of nitrogen and phosphorus hinder its wide application in some circumstances. The constructed wetland (CW), which has the advantages of cheapness, high treatmenting efficiency of nitrogen and phosphorus, easy management and environmental friendship, was also widely applied in many fields. However, it has the disadvantage of large land areas and excessive sensitivity to the season or the temperature.
The integrated system of MBR and CW probably could make up for the shortages of the two technologies. It will have the good future with the advantages of both MBR and CW in the fields of treating and reusing the wastewater from the population centralized communities, colleges and factories. The integrated system of submerged membrane bioreactor and integrated vertical flow constructed wetland (SMBR-IVCW) was chosen as the typical representative. The research to this integrated system would be carried out from the three ways, and the results were as following:
Firstly, the operating conditions of SMBR unit were optimized. The membrane flux (JV), mixed liquid suspended solid (MLSS), aeration (Q), ratio of pumping time to break time (tr/ts), and ratio of up flow area to down flow area (Ar/Ad) were chosen as the easily manipulable parameters to carry on the orthogonal experiments of Five factors and Four levels as L16(45). The results showed that the optimal operational conditions were MLSS = 7g•L-1, JV = 10L•m-2•h-1, Q = 6 m3•h-1, tp/tb= 4 min/1 min, and Ar/Ad = 1.7 m2/m2. Under such conditions, the SMBR could achieve a double win of high removal efficiency and low membrane fouling. At the same time, it is found that the soluble extracellular polymer (EPSS) was the main substance on the foul membrane. There was a lined relationship between the ratio of protein concentrations to polysaccharid and the climbing velocity of trans-membrane pressure (TMP).
Secondly, on the basis of optimum operational conditions, SMBR-IVCW system was applied to treat the integrated wastewater with different concentrations. Under the influent condition with high, middle and low concentrations, eleven kinds of hydraulic condition combinations were designed, respectively. The results were as follow.
(1) Under the influent condition of high concentration wastewater, the best hydraulic loading conditions were 1000 L/d for SMBR and 375mm/d for IVCW. And the ideal total hydraulic retention time (HRT) was 19.22 hours. The concentrations of CODCr, TP and Ammonia in the final effluent from this system reached or exceeded the Class Ⅲ of the national environmental quality standards for surface water in China, while the concentrations of TN was less than 6 mg/L.
(2) Under the influent condition of middle concentration wastewater, the best hydraulic loadingconditions were 1000 L/d for SMBR and 375mm/d for IVCW. The concentrations of CODCr, TP and Ammonia in the final effluent from this system reached or exceed the Class Ⅲ of the national environmental quality standards for surface water in China, while the concentration of TN reached the Class Ⅴ.
(3) Under the influent condition of low concentration wastewater, the best hydraulic loading conditions were 1000 L/d for SMBR and 250mm/d for IVCW. The concentrations of CODCr, TP and Ammonia in the final effluent from this system reached or exceed the Class Ⅱ of the national environmental quality standards for surface water in China, while the concentration of TN reached the Class Ⅳ.
Thirdly, according to the problem of low purification in the winter potential in practical application, the differences of the integrated system arising from seasonal change were carried out to find the solution. The purification efficiency and running stability under different hydraulic conditions in growing season were studied some results were obtained.
(1) The comprehensive purification efficiencies and running stability were lower in the non-growing season than those in the growing season when SMBR-IVCW system was applied to treat the same influent in same hydraulic loading conditions. In the non-growing season, the burden of the membrane in solid-liquid separation increased, the formation of membrane fouling grew fast, and the running stability got low. While the removal rates to TN of IVCW was higher than those in the growing season.
(2) In the practical engineering, the difference of purification efficiency of SMBR-IVCW with the change of season was able to be avoided by regulating the combination mode and the hydraulic conditions matching to SMBR and IVCW each other. In the growing season, for high, middle and low concentration influent, the better hydraulic conditions were 1000L/d for SMBR and 375 mm/d for IVCW, 1000L/d for SMBR and 500 mm/d for IVCW, 1500L/d for SMBR and 500 mm/d for IVCW respectively. While in the non-growing season, for high, middle and low concentration influent, the better hydraulic conditions were 1000L/d for SMBR and 250 mm/d for IVCW, 1000L/d for SMBR and 375 mm/d for IVCW, 1000L/d for SMBR and 375 mm/d for IVCW, respectively.
In accordance with the practical requirement, the integrated system of SMBR-IVCW would reach the goal of high purification, high efficiency and low costs by many modes of combining SMBR and IVCW units such as in series, parallel and partial distributaries.|