Landfill leachate refers to the moisture contained in the garbage itself, the rain and snow water and other moisture entering the landfill, deducting the saturated water holding capacity of the garbage and the overlying soil, and through the garbage layer and the overburden soil and formed a high concentration of wastewater, in the treatment process, the various stages of the application of instruments is very extensive, related to flow, pressure, liquid level, temperature, analytical instruments of measurement and control products.
The water quality of landfill leachate is very complicated, and it usually contains high concentrations of organic matter, heavy metal salts, SS and ammonia nitrogen. Landfill leachate not only pollutes soil and surface water sources, but also causes pollution to groundwater, there have been many researches on the removal of CODCr from landfill leachate, and biological treatment is usually used, but the treatment effect is not very good and the operation cost is relatively high, the new process also needs to be upgraded and optimized instrumentation, Dawson to adapt to the process at each stage of the introduction of a wide range of measurement and control products with adaptability, in obtaining high measurement and control effect at the same time does not reduce the cost-effective.
The specific content of the five stages
1. The initial adjustment stage: the garbage is put into the landfill, the landfill stabilization stage enters the initial adjustment stage. In this stage, the easy-to-degrade components in the garbage rapidly react with the oxygen carried in the garbage to produce carbon dioxide (CO2) and water, and at the same time release some heat.
2. Transition Stage: at this stage, the oxygen in the landfill is exhausted, the anaerobic condition begins to form in the landfill, and the degradation of waste is from aerobic to facultative anaerobic. At this stage, nitrate and sulfate are reduced to nitrogen (N 2) and hydrogen sulfide (H 2s) respectively, and the pH of leachate begins to decrease.
3. Acidizing stage: when hydrogen gas (H2) is continuously produced in the landfill, it means that the stabilization of the landfill goes into the acidizing stage. At this stage, facultative and trans-anaerobic bacteria are the main microorganisms which play an important role in garbage degradation, the main component of landfill gas is carbon dioxide (CO2) , and the concentration of COD, VFA and metal ions in leachate continues to rise to reach the middle stage, large value, then gradually decline; PH continued to decline to a low value, then gradually increased.
4. Methane fermentation stage: when the content of H2 in landfill decreases to a low point, the landfill enters the methane fermentation stage, at which time methanogens convert organic acids and H2 into methane. Organic matter concentration, metal ion concentration and electrical conductivity decreased rapidly, BOD/COD and biodegradability decreased, while pH value began to rise.
5. Mature stage: when the biodegradable components in the landfill are basically degraded, the landfill will enter the mature stage. At this stage, most of the nutrients in the garbage have been removed with the leachate, only a small number of microorganisms can degrade some of the refractory substances in the garbage, the biodegradability of leachate decreased further, and BOD/COD was less than 0.1. But the leachate concentration is already low.