Harmless treatment of leachate from household waste

Product Description

Landfill leachate accumulation liquid refers to the highly polluting liquid that can not be treated in time due to the damage of landfill seepage control system, overload of treatment facilities, extreme weather (such as rainstorm), etc. Its composition is complex, containing high concentrations of COD (up to tens of thousands of mg/L), ammonia nitrogen (thousands of mg/L), heavy metals, recalcitrant organic matter (such as humic acid), and pathogens. If leaked, it will seriously pollute soil, groundwater, and surface water. Therefore, emergency response needs to focus on "rapid pollution control, risk reduction, and temporary compliance", while balancing timeliness and safety.

Final harmless treatment of leachate from garbage

Leachate from garbage is a high concentration organic wastewater generated by rainwater erosion and self degradation during the process of landfilling or storage. It has the characteristics of high COD concentration (up to tens of thousands of mg/L), high ammonia nitrogen concentration (thousands of mg/L), high salt content, and complex composition (containing difficult to degrade substances such as heavy metals and polycyclic aromatic hydrocarbons), making it extremely difficult to treat. The final harmless treatment needs to go through the full process control of "pretreatment → biological treatment → deep treatment → tail water/by-product disposal".

1. Preprocessing: Reduce load and ensure subsequent processing efficiency

The core of pretreatment is to remove suspended solids, regulate water quality and quantity, and avoid subsequent equipment blockage or impact. Common techniques include:

Grille/sieve: remove large floating objects (such as plastic and tree branches);

Sedimentation tank (coagulation sedimentation): By adding coagulants such as PAC (polyaluminum chloride) and PAM (polyacrylamide), suspended solids (SS) and some colloidal substances are removed;

Anaerobic acidification: Under anaerobic conditions, complex organic matter is decomposed into small molecule organic acids, improving the biodegradability of subsequent biological treatments while reducing some COD.

2. Biological treatment: Degradation of core pollutants (organic matter, ammonia nitrogen)

Biological treatment is the core process of using microorganisms (bacteria, archaea, etc.) to degrade organic matter and nitrogen, which is divided into anaerobic treatment and aerobic treatment:

Anaerobic treatment: suitable for the degradation of high concentration COD, typical technologies such as UASB (Upflow Anaerobic Sludge Bed) and IC (Internal Circulation Anaerobic Reactor) can remove 50% -80% of COD and produce biogas (which can be recycled);

Aerobic treatment: Degradation of residual organic matter and ammonia nitrogen, commonly used techniques include:

SBR (sequencing batch reactor): achieves synchronous removal of organic matter and nitrogen through periodic aeration and sedimentation;

MBR (Membrane Bioreactor): Combining bioreactors with ultrafiltration membranes, membrane separation can intercept microorganisms and large molecule pollutants, with extremely low effluent SS and COD and ammonia nitrogen removal rates of over 90%. It is currently one of the mainstream technologies;

Short range nitrification denitrification: By controlling dissolved oxygen, the conversion of ammonia nitrogen → nitrite → nitrogen is achieved, resulting in efficient denitrification.

3. Deep processing: Remove residual difficult to degrade substances and meet emission standards

After biological treatment, residual recalcitrant organic compounds, salts, heavy metals, etc. need to be removed through deep treatment:

Membrane separation technology: Nanofiltration (NF) can intercept small molecule organic matter and some salt, while reverse osmosis (RO) can remove over 95% of salt and pollutants, making it a core technology for meeting standards;

Advanced Oxidation technologies, such as Fenton oxidation (H ₂ O ₂+Fe ² ⁺) and ozone oxidation, generate hydroxyl radicals (· OH) to oxidize recalcitrant organic compounds (such as pesticides and polycyclic aromatic hydrocarbons);

Activated carbon adsorption: adsorbs residual color, odor, and trace organic matter.

4. Final disposal of tailwater and by-products

Tail water: After deep treatment, it needs to meet national standards such as the "Pollution Control Standards for Landfill Sites for Domestic Waste" (GB 16889-2008) (such as COD ≤ 100 mg/L, ammonia nitrogen ≤ 25 mg/L), and can be reused (for landfill watering, greening irrigation) or discharged into municipal Sewage Treatment plants for further treatment (in accordance with takeover standards);

Membrane concentrated water: The concentrated water generated by RO/NF (containing high salt content and high concentration pollutants) is a difficult point to treat and needs to be disposed of separately

Evaporative crystallization: Water is evaporated through evaporation (condensate is reused), and crystalline salts are disposed of as hazardous waste;

Advanced oxidation+solidification: After oxidation, it is mixed with solidifying agents such as cement to form stable blocks, which are then sent to hazardous waste landfills;

Sludge: The sludge generated by biological treatment needs to be dehydrated (plate and frame pressure filtration), stabilized (lime conditioning or anaerobic digestion), and reach the "Sludge Disposal for Mixed Landfill Use in Urban Sewage Treatment Plants" (GB/T 23485-2009) before entering the sanitary landfill for disposal.