Initial Environment Examination (Part 4 of 4) Dynagreen Environmental Protection Group Company Limited Dynagreen Waste-To-Energy
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Initial Environment Examination (Part 4 of 4) Project Number: 46930-014 March 2017 Dynagreen Environmental Protection Group Company Limited Dynagreen Waste-to-Energy Project Bengbu Waste-to-Energy Plant (People’s Republic of China) Prepared by Dynagreen Environmental Protection Group Co., Ltd. This Initial Environment Examination is a document of the Borrower. The views expressed herein do not necessarily represent those of ADB's Board of Directors, Management, or staff, and may be preliminary in nature. Your attention is directed to the “Terms of Use” section of this website. In preparing any country program or strategy, financing any project, or by making any designation of or reference to a particular territory or geographic area in this document, the Asian Development Bank does not intend to make any judgments as to the legal or other status of any territory or area. removing and thoroughly breaking up the refractory macromolecular organics. For the large water circulation enables the uniform mixing of sewage, so the activated sludge has good dispersion, which greatly increases the specific surface area of activated sludge. The high dispersion of activated sludge in MBR is another reason to improve the effect of water treatment. This outdistances the larger group of bacteria formed by common biochemical method of water treatment technology; MBR has easy integration, easily realized automatic control and simple operate and manage; by abandoning the secondary clarifier, MBR areas decreases the area. After the effluent form MBR, it goes on with the NF process. NF is compact membrane, which is a kind of organic membrane. For MBR's COD is not up to standard, it needs further treatment. NF can further separate refractory organic matter and partial ammonia nitrogen, and further process desalination treatment. NF technology has good pass rate for monovalent ions, and higher retention rate of two valence ion. Therefore, the NF ion concentration of the solution is relatively low and easy to handle. To make the effluent meet the standard of reuse water, the RO process will further intercept chloride ions and concentration of dissolved solids in water. Summary comparison of 2 leachate treatment process plans is shown in Table 8.2-3. Table 8.2-3 Process analysis of comparison and selection Item Plan 1 Plan 2 Main process Anaerobic+aerobic+ultrafiltration+R Anaerobic+MBR+NF+RO flowchart O Process Biochemistry and New membrane bioreactor+Membrane principles materialization+RO Technology Inlet water quality Big anti-shock loading capability and Big anti-shock loading capability and small effects small inlet water quality effects inlet water quality effects Remove COD Good Better Remove NH High removal rate of NH Higher removal rate of NH Have some engineering and Technology of Have much engineering and operation operation experiences, and operating experiences, and operation and operation and management is experience management is simple. simple. Area Big Small Investment costs General General Operational costs High High Environmental Small impact on environment Small impact on environment benefits Finally comprehensive comparisons has been carried with respect to the the process characteristic, the adaptability of water quality fluctuation, treatment effect of pollutants, the investment and operating costs, etc., the second one has been chosen as optimal one. 8.2.3.2 Wastewater Treatment Process 1. Process Flow Chart High concentration wastewater treatment of the project uses “pretreatment+ABR+MBR+NF+RO” process. Process flow chart is shown as follows. Plant leachate Mechanical grating Methane treatment system Odor Adjusting tank Methane Torch flaming treatment Flocculent agents Overhaul Methane Incinerating Odor Coagulation Normal sedimentation tank operation Pre-treatment Reflux Reflux Filtration pool system Center heating pool Methane Anaerobic Methane Sludge processing system UASB anaerobic Sludge processing Sludge reactors system Odor Odor Odor Sludge pool MBR biological Supernat Odor processing system Nitrification pool Sludge e fluid Back-flo Denitrification pool sludge thickener pool wed First class A/O Dehydrat Odor Sludge Odor ed fluid sedimentation Sludge dewatering basin equipment Back-flo sludge wed Dehydrated sludge Nitrification pool Denitrification pool Garbage Back-flo sludge Second class A/O wed storing pit Excess Mud cake Odor UF ultrafiltration sludge burning system Concentrate Normal operation Concentrated Back-ejecta d solution solution NF nanofiltration incineration membrane system gathering tank Concentrate Concentrated solution processing system Odor treatment Incineratio RO reverse d solution osmosis membrane equipment n system Odor treatment equipment Odor treatment Membrane depth system processing system Picture 8.2-4 High concentration wastewater treatment process 2. Process Instruction (1) Pretreatment When leachate passes through the grille, impurities of large particles and suspended substances will be removed and sent to the garbage pit. There is a by-pass connected to the grille. If there are not many impurities or sewages, the sewages can be directly sent to the regulating pool by the by-pass to reduce the risk of the spillover of odor of the grille. The water pump pumps the leachate from the regulating pool. There is a pipe mixer in the pipe. The suspended substances can be partly removed by adding coagulant. Sludge collection bucket is set at the bottom of the primary sedimentation basin. The solids and the suspended substances that are easy to precipitate will subside to the sludge collection bucket. Then the sludges will be sent to the dewatering equipment by the sludge pump for dehydrating and incineration. The effluent from sedimentation basin will be sent to UASB anaerobic pool after the filtration through 3mm basket filter and 1mm pipeline filter. The function of the regulating pool is to equalize the quality and quantity in favor of the stable operation of the follow-up biochemical processing system. The project’s regulating pool is designed according to the quantity of leachate stored in 7 days. After the degradation of sludges through the anaerobic regulating pool, 15%~30% will be removed by the water inflow COD. When the solids and the suspended substances that is easy to precipitate, 5%~15% are removed after the treatment of primary sedimentation basin. (2) UASB anaerobic reactor The anaerobic reactor adopted by the project is UASB anaerobic reactor which was developed in the 1980s. At present, this technology has been applied successfully in sewage treatment in every industry with many advantages, such as high capacity of treatment, low investment and area with stable operation. The UASB reactor includes: water inflow and distribution system, pool body of the reactor and three-phase separator. The sewages are lifted through the pump into the bottom of the reactor, flowing upward with a certain flow rate. The methane of large amounts produced by anaerobic process can stir the sewages so that they can be mixed with sludges and organic matter can be absorbed and decomposed. The methane can be discharged through the gas-collecting chamber of the three-phase separator which is on the upper part of the anaerobic reactor. So the sewages containing suspended sludges will enter the settlement zone of three-phase separator. The sludges with good performance of precipitation return to the main body of the reactor and the sewages with a few light sludges are expelled from the top of the reactor. The anaerobic reactor features that it can granulate the sludges in the reactor and the sludges can have good performance of sedimentation and high activity of producing methane. In result, the concentration of sludges in the reactor is higher and the age of that longer. COD volume load is considerably increased and good contact between mud and water is reached. Because of the high COD load, the production of methane is high, which will lead to the expansion and fluidization of the sludges. The effect of mass transfer will be intensified so that the mud can have full access to the water. The effluents treated by the anaerobic reactor are sent to the MBR system for further treatment. The methane is drawn to the garbage pit through pipeline by induced draught fan. The designed removal rate of COD by UASB can achieve more that 70%. (3) MBR The combination of the leachate of MBR treatment and the reflux of nitrification pool (achieved by the reflux of UF concentrated solution) comes into denitrification reactor and mixes fully with denitrifying sludges with the help of under liquid agitator. Because of the nitrification of highly active aerobic microorganism, reflux of nitrification pool makes oxidation of ammonia nitrogen and organic nitrogen become nitrate and nitrite, which restores to nitrogen under the effect of denitrification sludge in denitrification reactor anaerobic environment, so that denitrification can be achieved. The effluents of the denitrification pool enter directly into nitrification pool. Activated sludge, wastewater and air are fully mixed and moves in circles in the reaction tank. The organic matter including carbon, nitrogen and phosphorus element in the sewages is effectively removed and oxidation of ammonia nitrogen and organic nitrogen is transormed into nitrate and nitrite through the effect of highly active aerobic microorganism. The jet aeration is adopted in the nitrification reactor pool. The air needed is self absorbed by jet aeration equipment. The mud water treated by the