The treatment of leachate from garbage should be combined with its characteristics, usually using a combination process of "pretreatment+biological treatment+deep treatment", and some scenarios require post-treatment (such as concentrated liquid and sludge treatment).
1. Preprocessing stage
The purpose is to remove large particle impurities, regulate water quality and quantity, and create stable conditions for subsequent treatment.
Grille/sieve: Remove large impurities such as garbage fragments and plastic bags to avoid blocking subsequent equipment.
Regulating tank: By stirring or aerating to homogenize water quality (such as COD and ammonia nitrogen fluctuations) and water quantity (such as differences between rainy and dry seasons), it reduces the impact on subsequent processes.
Coagulation precipitation/air flotation: Adding coagulants (such as PAC, PAM) to coagulate colloids and suspended solids, or separating them through air flotation, can remove 30% -50% of SS and some COD, reducing subsequent loads.
2. Biological treatment stage (core link)
The key to reducing the pollution load of leachate is to use microorganisms to degrade biodegradable pollutants such as organic matter and ammonia nitrogen.
anaerobic biological treatment
Suitable for high concentration COD (such as young leachate), organic matter is decomposed into biogas (mainly methane) and small molecular substances by anaerobic microorganisms.
Common technologies: UASB (Upflow Anaerobic Sludge Bed), UBF (Anaerobic Composite Bed), Anaerobic Membrane Bioreactor (AnMBR).
Advantages: Low energy consumption, recyclable biogas (energy conversion); Disadvantages: Poor removal of ammonia nitrogen and decreased efficiency at low temperatures.
aerobic biological treatment
Mainly remove residual organic matter and ammonia nitrogen (through nitrification denitrification process).
Common techniques:
MBR (Membrane Bioreactor): Combining a bioreactor tank with an ultrafiltration membrane, it intercepts microorganisms and pollutants, resulting in good effluent quality (COD can be reduced to below 100 mg/L) and strong impact resistance. It is currently the mainstream technology.
SBR (sequencing batch reactor): Through periodic inflow, reaction, and sedimentation, the operating parameters can be flexibly adjusted, making it suitable for small and medium-sized treatment.
Nitrification denitrification process: specifically designed for high ammonia nitrogen, it removes ammonia nitrogen through aerobic nitrification (ammonia → nitrate) and anoxic denitrification (nitrate → nitrogen), requiring control of alkalinity and dissolved oxygen (DO).
Combination process: In practice, the combination of "anaerobic+aerobic" (such as "UASB+MBR") is often used, which first reduces high COD through anaerobic treatment, and then removes residual pollutants and ammonia nitrogen through aerobic treatment, balancing efficiency and cost.
3. Deep processing stage
After biological treatment, there are still residues of recalcitrant organic matter, salts, heavy metals, etc., which need to be deeply treated to meet emission standards or reused.
Membrane separation technology:
NF (nanofiltration): intercepts small molecule organic matter and some salts, and has good removal of COD and chromaticity.
RO (reverse osmosis): intercepts almost all pollutants (including ions), and the effluent can meet the emission standards of the "Pollution Control Standards for Landfills" (GB 16889-2008), and even be reused (such as site flushing and greening).
Disadvantages: It produces concentrated solution (with extremely high pollutant concentration, requiring separate treatment), the membrane is prone to fouling, and the operating cost is high.
Such as Fenton oxidation (Fe ² ⁺+H ₂ O ₂ → hydroxyl radicals) and ozone oxidation, which decompose difficult to degrade organic matter (such as humus) through strong oxidation, are often used in conjunction with membrane technology (such as "MBR+ozone+RO").
Adsorption method: Activated carbon, zeolite, etc. are used to adsorb residual organic matter, but the cost is high and the adsorbent needs to be regenerated.
4. Post processing
Sludge treatment: The sludge produced by biological treatment and pretreatment contains heavy metals and pathogens, and needs to be dehydrated (plate and frame pressure filtration) before being buried or incinerated.
Concentrated liquid treatment: The concentrated liquid produced by membrane separation (accounting for 10% -30% of the influent) is a difficult problem in the industry, and commonly used treatment methods include:
Evaporative crystallization: Water is evaporated and reused, and the residue is buried (high energy consumption).
Advanced oxidation+solidification: After oxidation, it is mixed with cement and solidified for landfill.
Recharge landfill site: Utilize garbage layer to adsorb and degrade (controlling salt accumulation).
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