Characteristics, key points and difficulties of leachate treatment technology in waste incineration plants
Release time：2024-09-30click：0
Leachate from garbage incineration plants mainly comes from the water held by the garbage itself, the liquid produced by the decomposition of garbage, and the rainwater brought in during the garbage collection and transportation process. Leachate from waste incineration plants has the characteristics of high ammonia nitrogen content, high concentration of organic pollutants, high salt content, complex components, and large fluctuations in water quality and quantity, making treatment difficult.
Characteristics of leachate from waste incineration plants
1. High concentration of organic pollutants and good biodegradability
The CODcr of the leachate from the waste incineration plant is as high as 20,000~60,000mg/L, and the BOD5 is 10,000~30,000mg/L, which is a high-concentration organic wastewater. Most of the organic compounds in the leachate are soluble organic matter. About 90% of the soluble organic carbon is composed of short-chain volatile fatty acids. The main components are acetic acid, propionic acid and butyric acid, followed by polycarboxylic and aromatic carboxyl groups. of griseoflavinase acid, so the biodegradability of the leachate is better.
2. High ammonia nitrogen concentration
The ammonia nitrogen concentration in the leachate can be as high as 1000~3000mg/L, and most of the nitrogen in the leachate exists in the form of ammonia nitrogen. , accounting for about 75% to 90% of total nitrogen.
3. High salt content
The salt content in leachate is usually as high as 10,000 mg/L or more. The use of membrane treatment will cause excessive osmotic pressure. Largely, the water production rate is too low. If only ordinary biochemical treatment is used, it will be difficult to start due to high salt content, low load, unstable operation, or even failure to operate.
4. Water quantity and quality fluctuate greatly
The amount of leachate produced is affected by the type of urban garbage collection and transportation system, the composition of garbage, rainfall, etc. factors influence. The daily output of leachate is approximately 5% to 40% of the garbage volume. The variation range of pollutant concentration also reaches 3 to 5 times.
Common technical routes for leachate treatment
1. Biochemical + oxidation + advanced treatment
The leachate has a high concentration of organic pollutants and good biodegradability. The biochemical treatment process is a thorough and economical process for treating high-concentration organic wastewater. It can greatly degrade organic pollutants under relatively economical conditions, and at the same time exert The effect of nitrogen and phosphorus removal saves the overall leachate treatment cost. Since the leachate also contains many difficult-to-degrade macromolecular organic matter, theAfter biochemical treatment technology, some "inert COD" that cannot be biodegraded and adsorbed will always remain. Engineering practice shows that using a variety of biochemical treatment processes can reduce the CODcr of leachate to less than 1000 mg/L, and the removal rate is very impressive. However, the effluent generally cannot directly meet the discharge standard requirements.
2. Biochemical + membrane process treatment
The leachate is further treated by membrane process after biochemical treatment. This is a commonly used leachate treatment method. The process water quality is good and can meet the standards of reused water. It also has high resistance to fluctuations in leachate water quality and water quantity, and has high operational stability. After membrane separation treatment, the effect of pollutants is obvious, and the separated effluent meets the corresponding national discharge standards. Moreover, membrane technology can operate continuously, has a high degree of mechanization, is easy to manage, and unstable water quality has less impact on the effect of membrane treatment.
3. Use membrane technology or evaporation treatment
The disc type reverse osmosis DTRO membrane has good anti-pollution and high membrane flux. With the characteristics of long service life, the front end of the disc type reverse osmosis DTRO membrane only needs to be protected by sand filtration to directly process the leachate. Even in the case of high turbidity, high SDI value, high salt content and high COD, it can be economical Effective and stable operation.
The MVC evaporation process for treating leachate has the advantages of fast start-up, low energy consumption, low concentration ratio, and small floor space. The problems in the evaporation process are: first, the condensate contains volatile hydrocarbons, volatile organic acids, ammonia and other pollutants, which require further treatment to reach the standard, and the treatment cost is relatively high; second, the COD in the leachate raw solution is relatively high When the reaction temperature is high, it is easy to foam in the reactor, which directly affects the quality of the effluent water and the concentration ratio. This can be solved by adding a defoaming agent, which is more expensive. Most of the ammonia nitrogen is transferred to the condensate. When ion exchange is used in the subsequent treatment, the frequency of resin replacement is high.
Technical Focus and Difficulties
1. Accurately predict the design water volume and quality
< div> Accurately predicting the design water volume and water quality is the basis of engineering design. The daily production volume of leachate from the waste incineration plant should take into account factors such as the residence time of the garbage in the aggregate pit, the main components, and local rainfall. The leachate from the waste incineration plant should be considered. For water quantity and quality, please refer to the operating data of waste incineration plants in the same area.
At present, our country is vigorously promoting waste classification and promoting the construction of food waste treatment systems. The waste components entering the waste incineration plant will surelyCertain changes will occur, the proportion of food waste will gradually decrease, and the moisture content of the garbage will decrease as the proportion of food waste decreases. It is expected that the amount of leachate water produced by domestic waste entering the incineration plant will gradually decrease, and the concentration of pollutants will also show a downward trend.
2. Biochemical treatment
The COD of the leachate from the waste incineration plant is relatively high. If the aerobic process is directly used, the energy consumption of the aeration system will be too high. Therefore, the leachate raw solution should first pass through an anaerobic reactor to reduce the concentration of organic pollutants and then undergo aerobic treatment. The ammonia nitrogen concentration in the leachate is generally 500~2500mg/L, so the aerobic treatment unit should use a process with high denitrification load and good denitrification effect. Due to the complete interception of microorganisms by ultrafiltration in the membrane biochemical reactor (MBR), the mud age of the microorganisms reaches and far exceeds the time required for the growth of nitrifying microorganisms, and they can reproduce and aggregate to reach the concentration of nitrifying microorganisms required for complete nitrification, so that This enables complete nitrification of ammonia nitrogen in wastewater. Likewise, the extension of sludge age and the high concentration of microorganisms also greatly improve the removal of organic pollutants.
3. Selection of membrane system
The selection of membrane system is affected by the design effluent standard. When the effluent only needs to meet the requirements of the "domestic waste landfill" "Pollution Control Standard" (GB16889-2008), nanofiltration membranes can be given priority because the proportion of concentrated liquid is low, and due to the limited removal effect of nanofiltration on monovalent ions, the monovalent salt content in the concentrated liquid is small, and the concentrated liquid can After proper treatment, it is returned to the biochemical system, and there is no need to worry about the accumulation of monovalent salts.
When the effluent is not allowed to be discharged and needs to be reused and achieve "zero discharge", since the chloride ions in the nanofiltration effluent cannot meet the reuse water standard requirements, the membrane system should choose reverse osmosis Membrane or "nanofiltration + DTRO membrane" combined membrane technology. The effluent can meet the supplementary water standards for open circulating cooling water systems in the "Water Quality of Industrial Water for Recycling of Urban Sewage" (GB/T19923-2005) and the "Water Quality of Urban Miscellaneous Water for Recycling of Urban Sewage" (GB/T18920-2002). Cleaning, urban greening, and vehicle washing standards, the recycled water can be used to replenish the cooling system of the incineration plant and for road cleaning, vehicle washing, and greening irrigation in the factory area.
New ideas for concentrated liquid treatment
In recent years, the environmental protection requirements for new waste incineration plants have become increasingly higher. , many new waste incineration plants require leachate reuse after treatment and "zero discharge" requirements, and the design of leachate treatment systemsThe plan has put forward higher requirements. The clear liquid after membrane treatment of the leachate can meet the standards for reuse. At the same time, how to handle the concentrated liquid produced is the key to "zero discharge".
Domestic waste incineration fly ash must undergo necessary solidification and stabilization before it can be transported and processed. The fly ash stabilization treatment technology mainly includes melting, sintering, solidification, chemicals, etc. Generally, The solidification method is used while adding chelating agents to achieve fly ash stabilization. The fly ash solidification process requires water consumption. The leachate concentrate can be used as the water source for fly ash solidification. While saving water, it can achieve the control of heavy metal ions in the leachate concentrate. stabilization treatment.
Summary
At present, the membrane system treatment effect is obvious in leachate treatment, using disc type reverse osmosis DTRO Membranes are used to treat landfill leachate, with low operating costs and good water output.
With the complex composition of waste incineration plant leachate and extremely high concentration of pollutants, treatment is more difficult and treatment standards are constantly improving. The treatment of leachate should be considered from the entire waste incineration plant. Experts in the water treatment industry are also actively exploring more leachate treatment processes.
(Original title: Characteristics, key points and difficulties of leachate treatment technology in waste incineration plants)
