Biological method is the most commonly used method in leachate treatment. Because of its relatively low operating cost, high treatment efficiency and no secondary pollution caused by chemical sludge, it is widely used all over the world. The specific process forms of waste infiltration treatment devices include traditional activated sludge process, stabilization pond, biological turntable, anaerobic fixed membrane bioreactor and so on. Biological turntable is one of the so-called fixed growth system biofilm methods, which can effectively solve the sludge bulking problem of activated sludge method when used in conventional sewage treatment. Moreover, because of the large biomass and rich biological phases on the membrane, there are both aerobic microorganisms on the surface and anaerobic microorganisms on the inner layer, it has the advantages of resisting the impact load of water and water quality, and nitrifying bacteria with a long generation can also grow on the biofilm.
Pitea Leachate Treatment Plant adopts biological rotary table to treat landfill leachate, with a design scale of 5m3 /d, a surface area of 3m2 and an average design load of 4.8g[NH3-N/ (m2 d). The temperature of leachate entering the biological turntable is kept at about 2℃ by using landfill gas heating, and good treatment effect has been achieved. Experiments prove that; When the leachate after biological treatment is flocculated and precipitated (using iron salt or aluminum salt as flocculant), even when ρ(BOD5) is very low (<: 25mg/L), the removal rate of CODcr can still reach 5%. In the reaction process, the optimal pH value is 4.5 ~ 4.8 and 5. ~ 5.5 for iron salt and aluminum salt respectively, and the minimum dosage is between 25 ~ 5 g/m3.
The disadvantage of flocculation and sedimentation process is that it will produce a lot of chemical sludge; The pH value of the effluent is low and the salt content is high. The removal rate of ammonia nitrogen is low. Therefore, even if the flocculation and sedimentation process has considerable treatment efficiency, it should be carefully considered when selecting it. Reverse osmosis (RO) is often used in the post-treatment of leachate, because it can remove the dissolved organic matter with medium molecular weight. The early domestic experiments using cellulose acetate membrane show that the removal rate of CODcr can exceed 8%. Although there are membrane pollution problems in the operation process, RO is set as a post-treatment process after biological pretreatment or physicochemical method to remove the organic matter, colloid and suspended matter with low molecular weight, which can improve the treatment efficiency and the service life of the membrane [5]. According to Ehrig's research in 1989, the removal rate of CODcr, BOD5 and organic halogenated compounds (AOX) can reach 8qc by one-stage reverse osmosis process, but the removal rate of ammonia nitrogen and chloride ion needs at least two-stage reverse osmosis process to reach a higher level. At the same time, you can view more technical documents of China Sewage Treatment Engineering Network.
In a word, reverse osmosis technology has been used more and more because of its advantages of high efficiency, modularization and easy automatic control, but there are still some problems in its application in leachate treatment: the interception efficiency of small molecular weight substances (such as ammonia and small molecular organic halogenated compounds (AOX), etc.) is not satisfactory. High concentration of organic matter or inorganic settleable matter is easy to cause membrane pollution or scaling on the membrane surface. High energy consumption due to high operating pressure (3 ~ 5ba). The treatment of concentrated reverse osmosis solution is the biggest difficulty, and it is no longer desirable to reinject it into landfill, because the concentrated reverse osmosis solution has a high pollutant concentration and is a very dangerous waste. Evaporation and drying are often used, but the cost is very high.
Rochem's patented disc tube reverse osmosis system was used to treat primary leachate in the landfill in Britain. This treatment technology is Rochem's separation membrane system designed and produced by Winterton Landfill in South Humberside. Rochem's separation membrane system can remove heavy metals, SS, ammonia nitrogen, harmful and refractory organic substances, and the treated water quality meets strict discharge standards. Chemical oxidation process can completely eliminate pollutants, and will not produce chemical sludge in which pollutants formed in flocculation and precipitation process are concentrated. This process is often used for disinfection of wastewater, but rarely used for oxidation of organic matter, mainly due to the economic problems caused by high dosage of chemicals. For some organic pollutants that are difficult to control in leachate, chemical oxidation process can be considered.
Common chemical oxidants include chlorine, calcium hypochlorite, potassium permanganate and ozone. When calcium hypochlorite is used as oxidant, the removal rate of CODcr is less than 5%; When ozone is used as oxidant, there is no problem of excess sludge, and the removal rate of CODcr is not more than 5%. It is not very effective to use ozone as oxidant for acidic leachate containing a lot of organic acids, because organic acids are ozone-resistant, which requires a high dosage and a long contact time. Hydrogen peroxide is mainly used to remove odor because it can remove hydrogen sulfide. Generally, 1.5 ~ 3. parts of hydrogen peroxide should be added to each part of soluble sulfur. The research on the treatment of leachate by chemical oxidation is still in the laboratory stage, and the main problem is that the treatment cost is too high, but it is still of certain significance for the treatment of low-volume and low-content refractory leachate after the closure of the landfill site.