Study On Opposite Folded Plate Anaerobic Reactor In Treatment Of Low Concentration Sewage

With the demands of quantity and quality for water are increasing rapidly and a lot of wastewater treatment processes are difficult to be used abroad, the situation of water pollution is aggravating at a startling speed. Therefore, how to enhance the efficiency and to reduce consumption is the key to solve these problems. And the key to enhance the efficiency is to promote mass transfer efficiency of water treatment process and improve the biomass of system under the condition of keeping higher activity of microorganism. The transfer-reaction kinetics and how to enhance microorganism biomass of system were studied deeply during exploring high efficient opposite folded plate anaerobic reactor (OFPHAR). Base on the mass transfer mechanism and two-double integrated staged multi-phase anaerobe (TSMPA), the theories of high efficient OFPHAR were put forward as follow: 1) It should focus on enhance mass transfer of OFPHAR achieve high efficient. Namely, the fluid of swift water and tiny whirlpool come from kinetics of the process which make the mass transfer better; 2) based on the TSMPA theories, the system was designed as together with the multi-phase anaerobe of compartments longitudinally down reactor, the two-double phase of sludge-biomembrane in every compartment could maintain high biomass concentration. By take two meatures as above, the COD removal efficience of system was enhanced markedly.For purpose of enhancing mass transfer in the system, the reactor was modified with the structure characteristic of opposite folded plate. This structure characteristic of reactor can change water power characteristic and improve the term of mass transfer in the reactor to increase bio-reaction velocity; and the system with the characteristic of multi-phase anaerobe of compartments longitudinally down reactor and two-double phase of sludge- biomembrane in every compartment. This characteristic of reactor can improve the biomass concentration in the system. Under the condition of keeping higher activity of microorganism, the higher mass transfer and biomass would improve the organic matters removal efficiently.In order to verify that high efficient hydrolysis-acidogenosis phase can feed good water quality to following aerobic treatment and enhance the high removal efficience of all the process, the opposite folded plate hydrolysis and acidification-A2O integrative reactor was designed by this research. The characteristic of hybrid actived sludge-contact oxidation in aerobic tank at A2O stage maybe enhance removal efficiency markedly.The results of 30 months'laboratory-scale and pilot-scale experiment indicatied that the efficacy of OFPHAR and following aerobic treatment were high efficient. The results and conclusions are shown as followed:By taking hydraulic meature, plenty of turbulent current and diverse scale whirling current generated in the system, which enhances mass-transfer efficiency markedly. And the system buffered with Na2CO3 can fortified wastewater alkalinity and prevent from pH decreasing because VFAs accumulation was avoided, which can enhance the activity of microorganism. As mass-transfer efficiency was enhanced markedly and the system pH value was controlled at 4.8-6.27, the high efficient hydrolysis and acidification was achieved with higher organic removal efficiency and rate. At this phase, the optimal COD concentration is 450～900mg/L and optimal HRT was 4h. Under the optimal condition, the average SCOD removal rate of hydrolysis and acidification phase was 43%±4%. Under the condition that COD concentration was 500mg/L and optimal HRT was 8h, the average SCOD removal rate of two-phase anaerobic digestion was 88.9%. The COD removal efficiency was still 75.8% at low temperature of 10℃. The results of this study indicated that the effect of temperature on pollutant removal efficiency isn't remarkable and it is feasible to apply this OFPAR to treat low concentration sewage at psychrophilic temperature in north China. As a result, an pilot-scale opposite folded plate hybrid anaerobic reactor (OFPHAR) was designed and applied to treat low concentration sewage.In order to accelerate the speed of starte up reactor, 1#, 2# and 3# OFPHARs were applied to start-up study. Therefore, the anaerobic sludge-fly ash (the ratio of anaerobic sludge to fly ash was 10: 1) was added into system as inoculation sludge. The results indicated that the OFPARs have been started up when them have been running 50 days and the efficacy of follow running was enhanced under the condition that inoculated with anaerobic sludge being mixed with fly ash. Based on the results of trial, the mechanism of fly ash enhancement efficacy of start-up and follow running phase of OFPHAR can be due to larger specific surface area and porosity of fly ash. And the results of following trial at short HRT indicating that the optimal particles of fly ash to enhancement efficacy of OFPAR was 20~83μm. The reason that fly ash optimal particles ranged 20~83μm is it has larger specific area and isn't easy to coagulate as mass.When the HRT≥6h and the sludge retention time (SRT) was controlled 120 days, the pilot-scale opposite folded plate hybrid anaerobic reactor (OFPHAR) was Two-phase Anaerobic system. The trial results indicated that the optimal HRT was 6h at (25±2)℃, and the corresponding removal rates of COD, TN and TP removal rates were 78.58%, 35.15%, 39.17% respectively. The optimal anaerobic section rate and the optimal influent COD concentration were respectively 45%~65% and 150~800mg/L. Under HRT=6h, the effect of temperature on OFPHAR was investigated. The COD, TN and TP removal rates were 64.37%, 20.72%, 23.65%, while the specific mathane production capacity decreased to 1.85 mL(gVSS·h)-1 at (7±1)℃. Simultaneously, there was no effect of temperature on the distribution of acidogenic phase and methane phase. The trial results indicated that low temperature had adverse effect on the removal rates of COD, TN and TP and methanogen activity, while the removal efficacy and methanogen activity still could maintain high level. So, it is feasible to apply the proposed OFPHAR to treat low concentration and low temperature sewage in north China.When the HRT < 6h and the sludge retention time (SRT)≥200 days, the OFPHAR)was acidogenic phase system. The trial results indicated that the optimal HRT was 4h at (25±2)℃, and the corresponding removal rates of COD, TP and TN removal rates were52.24%, 22.28%, 25.77% respectively. The optimal influent COD concentration was 150~800mg/L. The trial results indicated that low temperature had adverse effect on the removal rates of COD, TP and TN, while the removal efficacy and the acidogenic efficacy still could maintain high level. The bio-degradability of wastewater was improved markedly and the following aerobic treatment was fed good water quality after the wastewater was treated by acidogenic phase system even at low temperature. So, it is feasible to apply the proposed OFPHAR to treat low concentration and low temperature sewage in north China.According to trial results, the high efficiencies of proposed OFPHAR can be due to high mass-transfer efficiency and two-double integrated staged multi-phase anaerobe (TSMPA): 1) The biochemical reaction and the removal efficacy would be enhanced markedly because hydraulic condition is modified and resulted in higher mass transfer efficiency by the characteristic structure of OFPHAR. 2) The two-double phase of sludge-biomembrane in every compartment integrated staged multi-phase anaerobe of compartments longitudinally down reactor are advantaged to maintain higher biomass concentration and enhance acidogenic and methanogenic activity, which would enhance the removal efficacy of bioreactor.Opposite folded plate hydrolysis and acidification-A2O integrative reactor was designed to treat low strength sewage. The results of 10 months indicated that the optimal hydraulic retention time (HRT) was 8h (the HRT of hydrolysis and acidification stage was 4h, and the HRT of A2O stage was 4h); the sludge retention time (SRT) of active sludge was 15 days; the optimal influent COD concentration was 240~600mg/L; the optimal mixed-liquor return ratio (R) - sludge return ratio (r) was 250%-100%. Under these conditions, the COD, TN and TP removal rate were 96.34%, 62.37% and 82.08% at (25±2)℃, respectively. When the temperature decreased to 7℃, the COD, TN and TP removal rate decreased to 86.35%, 50.25% and 65.68%. Based on the results of trial, the mechanisms of higher integrative reactor efficacy in treatment of low strength sewage were owed to high efficient mass-transfer of opposite folded plate at hydrolysis and acidification stage and the hybrid actived sludge-contact oxidation in aerobic tank at A2O stage. So, it is feasible to apply the proposed opposite folded plate hydrolysis and acidification-A2O integrative reactor to treat low concentration and low temperature sewage in north China.According to trial results, the high efficiency of proposed opposite folded plate hydrolysis and acidification-A2O integrative reactor can be due to high mass-transfer efficiency of acidogenic phase and the hybrid actived sludge-contact oxidation in aerobic tank at A2O stage. High mass-transfer efficiency of acidogenic phase was explained as above. The high efficiency of A2O stage can be due to the high biomass concentration and high oxygen radical absorption capacity and transfer efficiency, which would enhance the removal efficacy of COD, TN and TP at A2O stage markedly.When the OFPHAR was applied to treat wastewater as partial wastewater treatment system, the energy saving and consumption reduction could be evaluated as follow: The capital cost is saved 2.4%. According as the COD removal rate f hydrolysis and acidification stage is 40%, the energy of fan drive can be saved over 40%. Based on the energy cost of fan drive is 60% as all operation cost, the operation cost would be saved 24%. According as the excess sludge yield is decreased of 20%, and the treatment cost of excess sludge is 30% as all operation cost, the operaton cost of excess sludge treatment would be saved 6%. So, the saving in energy and consumption amount to 32.4%.All in all, the study of OFPHAR and following aerobic are application value. The bio-reactor with low construction, cost and energy requirements would enjoy widely application , which is continually demanded by both the policy makers and the general public in north China. The economic benefit, social benefit and environmental benefit are markedly.