| Random disposal of rural decentralized domestic sewage has seriously threatened rural environment. Development of new technologies which are suitable for local decentralized domestic sewage treatment is the key way out. Based on the Scientific and Technical Innovative Program "the Applicable Technology and Demonstration of Treatment for Rural Decentralized Sewage" in Chongming Ecological Island which supported by Science and Technology Commission of Shanghai Municipality in 2007 (Grant No.07dz 12408), the quantity and quality for rural decentralized sewage were investigated in Qianwei village and both the pilot-scale combined biological purification tank-enhanced ecological floating raft (CBPT-EEFR) and the lab-scale experimental facility about the microorganism were constructed. After the build-up of experimental facilities, following subjects were studied:start-up of combined biological purification tank (CBPT); the removal efficiencies and mechanism of pollutants from rural decentralized sewage in the CBPT; the contrast of removal efficiencies of pollutants between the enhanced ecological floating raft (EEFR) and general floating raft (GFR); the enhanced basis of EEFR; the removal efficiencies and mechanism of pollutants in the EEFR; the performance measurement of the preponderant strains in the CBPT at the optimized conditions and their identifications; the ecological characters and functions of microorganisms in the EEFR; the total treatment effects by CBPT-EEFR system and its applicability on economy and technology.The quantity per person in rural area of Chongming-Island basin was 95L/d. And about 40～45% sewage could be collected through pipe network system corresponding to 40L/d per person. The pilot-scale craftwork of CBPT-EEFR located at Qianwei Village in Chongming-Island. The process consisted of the septic tank, the combined biological purification tank and the enhanced ecological floating raft in series. The biomembrane in the CBPT were cultivated and domesticated by precoating treatment with aerobic activated sludge under 0.5m3/d flow rate and 25.7℃average water temperature. After about 10-day cultivation and domestication, biomembrane in the CBPT were hanged successfully. The removal effect of COD was obvious by the CBPT with removal rate 69.29% in summer,60.22% in autumn, 45.82% in winter and 59.45% in spring, respectively. From on-way distribution analysis, the first-stage purification tank's removal contribution was high. And the ratio of removal contribution among the first-stage, the second-stage and the third-stage purification tank was 5:3:2 on the whole. The removal rate of TN was bad by the CBPT. But due to the high TN influent concentration, the removal volume of TN was kept high at low removal rate. The second-stage purification tank's removal contribution was high. And the ratio of removal contribution among the first-stage, the second-stage and the third-stage purification tank was 3:5:2 on the whole. The removal effect of TP was good by the CBPT with removal rate 37.74% in summer, 33.58% in autumn,28.95% in winter and 32.36% in spring, respectively. Both the first-stage and the second-stage purification tank's removal contribution were high. And the ratio of removal contribution among the first-stage, the second-stage and the third-stage purification tank was 4:4:2 on the whole.Firstly, through planting different hydrophytes in the EEFR, it could achieve to converge of hydrophytes in different seasons. Secondly, fiber padding was embedded among the hydrophytes for adhering biomembrane. Because of these, the synergy between hydrophytes and microorganisms was enhanced and the concentration and amount of microorganisms were increased. So the removal rates of pollutants by EEFR were better than GFR. Zizania caduciflora Hand was used as floating raft's hydrophytes at the first experimental stage. The average removal rates of COD, NH4+-N, TP and SS were 37.33%,74.54%,45.95% and 50.99% in GFR, relatively, and 51.11%,79.32%,64.14% and 82.15% in EEFR, relatively. In order to satisfy converge of hydrophytes in different seasons, floating raft's hydrophytes were chosen as Oenanthe javanica which was kryophilous at the second experimental stage in low temperature and Nymphaea tetragona Georgi which likes warm at the third experimental stage in moderate temperature. And as results shown, both of them kept good removal effect of pollutants. The on-way distribution analysis of pollutants in the EEFR showed that there were different characters at different pollutants. The concentration of COD, TN, NH4+-N and TP decreased along the raft. Regarding to COD and TP, the first-stage raft's removal contribution were high, and the third-stage raft to TN. NH4+-N was discrepant in different seasons which the second-stage raft's was high in winter and the first-stage and second-stage raft's was high. The concentration of SS decreased firstly, and then increased, at last decreased. And the first-stage raft's removal contribution was high. The concentration of N03--N and NO2--N increased firstly, and then decreased. And the third-stage raft's removal contribution was high for N03--N, and the forth-stage for NO2--N.Water samples collected from CBPT was concentrated and separated after cultivated in broth bouillon and N/P obligate media. Three kinds of preponderant strains were sieved from the vessels. They were named as A-1, B-5 and C-2. After the performance measurement of the preponderant strains in the CBPT at the optimized conditions, the removal effects of TN and TP were bad for each strain individually. But with the compound proportion of 1:1:1 for the three strains, the removal rate of TN in 4d was 87.4% and TP in 7d 57.9% by the compound strains. The logarithmic test was carried out to optimize degradation conditions in logarithmic growth phase, and at the optimize conditions, the removal rate of TN and TP in 14d was 97% and 63%, relatively for the simulative rural decentralized sewage. By chromatography of ions and standard detecting method under the optimal biodegradation conditions, the preponderant strains were confirmed to be Proteus mirabilis, Pseudomonas Medocina, Bacillus subtilis by gene sequencing. From the analysis of 16S rDNA gene sequencing, the homologies of Proteus mirabilis were 99%,98% for Pseudomonas Medocina, and 98% for Bacillus subtilis.Enzyme activity, bacteria, and microbial biomass were monitored in the EEFR. The results showed that enzyme activity, bacteria, and microbial biomass decreased along with flow direction. The concentrations of these in July were more than other months. The proteinase activities, urease activities and dehydrogenase activities increased from the upper layer to the bottom layer, and this was opposite for phosphatase activities. The bacteria population was similar from the upper layer to the bottom layer. The microbial carbon and nitrogen were increased from the upper layer to the bottom layer, and this was opposite for microbial phosphorus. From on-way distribution analysis, the variations of proteinase activities and urease activities were irrelevant to the removal contribution of TN. The variations of phosphatase activities and dehydrogenase activities were relevant to the removal contribution of TP and COD. Taken as a whole, proteinase activities and phosphatase activities were relevant to the total removal rate of TN and TP, and urease activities and dehydrogenase activities were irrelevant to the total removal rate of TN and COD. That is to say, enzyme activity or bacteria or microbial biomass resulted from multifarious factors of the EEFR, such as the hydrophytes in different seasons, fiber padding and microorganisms. So it is too simple to select one parameter as index of organic matter or nitrogen of phosphorus removal of the EEFR.In summary, CBPT-EEFR system can effectively remove COD, TN, NH4+-N and TP from rural decentralized sewage with the average removal rate 79.59%,61.06%, 72.14% and 77.14%, relatively. The effluent concentration of NO3--N, NO2--N, PO43--P and SS were 1.533mg/L,0.442mg/L,0.36mg/L and 27.3mg/L, relatively. The effluent concentration of COD could get the Municipal Wastewater Treatment Plant 1 A Standard, TN and TP for the Municipal Wastewater Treatment Plant 1 B Standard, NH4+-N and SS for the Municipal Wastewater Treatment Plant 2 Standard. From the applicability on economy and technology of CBPT-EEFR system, the running cost was much lower. At the same time, CBPT-EEFR system exhibited the advantages of steady effluent, hard to be jammed, simple operation and as well as high viability. It also meets with the economic and technical situation of rural areas. So it is an ecological and applicable craftwork for rural decentralized sewage and has large potential in wide spreading in rural areas.
|
PDF Full Text Request