Research On Domestic Wastewater Treatment By Double Upflow Anaerobic Sludge Blanket And Anaerobic Filter Coupled With Constructed Wetland

As an ecological technology system, constructed wetland (CW) becomes more and more attractive in the field of treating and reusing decentralized domestic wastewater. However, the CW technique has the deficiencies of occupying large land area and low removal efficiency of nitrogen and phosphorus. This has impeded its deep application in the domestic wastewater treatment in some extent. Therefore it is necessary to strengthen the pre-treatment technology before the application of CW technique. Coupling of primary technique with CW is the hot issue in the field of ecological wastewater treatment because of the prominent character of the low energy consumption and equip ability. The development of high speed anaerobic technology has made the anaerobic technology possible to treat the low organic concentration wastewater (COD＜1000mg·L-1). Further, it can provide the theoretical basis in developing a new ecological wastewater treatment system with the short flow, low energy and high efficiency. Based on this analysis, the present work coupled the double upflow anaerobic sludge blanket and anaerobic filter (dUBF) with CW (dUBF-CW), and designed a new decentralized domestic wastewater treatment technology for the first time.Firstly a new anaerobic-dUBF technique is designed as the primary treatment equipment in the wastewater ecological treatment system. The dUBF is improved based on the two-staged anaerobic technology and UBF equipment, and is used to treat domestic wastewater in low temperature condition(＜20℃). In order to improve the removal efficiency of COD and shorten the start-up time, the sludge circumfluence equipment which based on EGSB is added in dUBF. The work time of sludge circumfluence equipment in dUBF could be controlled. The experiment shows that the dUBF can start quickly in the low temperature under the suitable control condition of the sludge circumfluence. When the operating time of the sludge circumfluence equipment at the first and second stages in dUBF is 5 seconds after stopping 2 hours and 10 seconds after stopping 1 hour, the removal efficiency of COD and SS is more than 60% and 80%, respectively.At the same time, two simulative wetland systems, i.e. the subsurface flow constructed wetland (SSCW) and integrate vertical flow constructed wetland (IVCW), are designed. The two systems are independently operated between SSCW and IVCW. The treating result of the domestic wastewater shows that, the removal efficiency of COD and NH4+-N meets the first standard of domestic wastewater effluence (GB8978-1996), and the TP removal ability also accord with the second standard of GB8978-1996. Because of the better oxygen transmission condition, the IVCW possesses the higher removal efficiencies than those of the SSCW for all the contaminations.Then the industrial byproduct, i.e. water-granulated slag of blast-furnace (WGS), is firstly used as the medium of CW to probe into its effect on removing phosphorus in domestic wastewater. The phosphorus variation mechanism in different CW medium is further explored. The langmuir isotherms adsorption analyses of the experiment show that the phosphorus adsorption capacity of WGS, sand and steel slag is 3333 mg·kg-1,270mg·kg-1, 12500mg·kg-1; the phosphorus desorption ratio of WGS, sand and steel slag is 0.68%,7.59% and 2.15%, respectively. It can be seen that the WGS not only possesses the high phosphorus adsorption capacity and low phosphorus desorption ratio, but also moderates the pH value. Thus WGS can be fairly suitable for a sort of medium in CW. The removal mechanism of WGS on phosphorus is revealed. It is found that WGS contains rich alumina and calcium oxide, and the corresponding absorption position is very active to the phosphorus in the waste water. The chemical and physical absorptions are the critical reasons which lead to the high removal efficiency of WGS on phosphorus.Furthermore, the method of strengthened nitrogen removal efficiency of CW is investigated, and the corresponding biological mechanism is explored. It is found that, the addition of biological medium in the surface of new CW can obviously shorten the start-up time of the CW system and improve the nitrogen removal efficiency. Comparing with the control check(without biological medium), NH4+-N removal efficiency of biological medium added CW system increases by 17%. When the CW operation becomes stable, the bacterial morphology tends to be mature. At this time, the sufficiency nitrogen removal efficiency of CW can be kept even without the biological medium.At last, the dUBF is coupled with the CW, and a new domestic wastewater treating technique is proposed. The coupled technique is integrally optimized through continuous operation test. It is found that when the respective HRT at the dUBF and CW stages is 4 hours and 1 day, the removal efficiency of either COD or SS meets the first standard of domestic wastewater effluence (GB8978-1996), and the TP removal accords with the second standard of GB8978-1996. The removal efficiency of NH4+-N followed by the SSCW and IVCW post-treatments meets the first and second standard of GB8978-1996, respectively.