Pay more attention to the public account: environmental protection water treatment
Landfill leachate is a kind of black or yellow-brown wastewater with a foul odor produced during the stacking of municipal solid waste in landfills.
The leachate contains a large amount of organic and inorganic matter, including various refractory organic compounds (such as various aromatic compounds and humus, etc.), inorganic salts (such as ammonia, carbonate and sulfate, etc.) and metal ions (such as chromium, lead and copper).
Among them, the most typical feature of landfill leachate is the high content of pollutants, and most of them contain biological toxicity.
Leachate typically accounts for 35%-50% of landfill volume (by weight) and pollutant concentrations can vary by up to 5 times.
There are three main sources: the moisture contained in the garbage itself, the infiltration of surface water or groundwater, and the moisture produced by the degradation of organic matter in the garbage.
Difficulties in the treatment of landfill leachate
1. High ammonia nitrogen and high COD
The COD in landfill leachate can reach up to 90,000 mg/L, and the ammonia nitrogen is generally more than 2000 mg/L.
Traditional treatment processes, especially the core biological treatment process, are generally effective in removing ammonia nitrogen from leachate, but they are not ideal for the removal of total nitrogen.
2. Complex composition, high concentration and high salinity
The landfill leachate has high salinity and complex composition, containing more than 10 kinds of dissolved ions, heavy metals and organic pollutants. Some metal ions have a high concentration, such as iron, zinc, lead, and calcium ions, which will have a serious inhibitory effect on the biological treatment process.
It has a high content of organic matter and contains a large amount of toxic and macromolecular organic matter. A single physicochemical or biochemical process cannot achieve the standard discharge, and a combination of physicochemical and biochemical treatment processes must be used for treatment.
3. The water quantity and quality vary greatly
The water quality of landfill leachate varies greatly, and the yield varies seasonally, and the rainy season is significantly greater than that in the dry season. The quality and quantity of leachate in different seasons and different field ages vary greatly, which brings challenges to the selection and operation of treatment processes.
4. High cost of carbon source/nutrients
Methanol and glucose are commonly used as carbon sources for the biochemical treatment of landfill leachate, and their cost is much higher than that of composite carbon sources. In addition, many enterprises use nanofiltration or reverse osmosis-based membrane treatment processes as the final advanced treatment, resulting in high leachate treatment costs for a long time.
5. High emission standards
The state has high wastewater discharge standards for the landfill leachate industry, and higher discharge standards for areas prone to serious environmental pollution problems.
6. The treatment process is complex and the treatment cost is high.
At present, in order to achieve the standard discharge, in addition to the combined process, the membrane treatment process based on nanofiltration or reverse osmosis is often used as the final advanced treatment, resulting in the high cost of leachate treatment for a long time.
Landfill leachate treatment process and selection
(1)WSB+SBR+CMF+R
Analysis of process characteristics:
The process is more complex;
The amount of residual sludge is small;
There are 20%~28% of the concentrate to be treated;
The treatment capacity is susceptible to the influence of TDS and temperature in the water;
The membrane life is generally 2-3 years.
（2）MBR＋NF/RO
Analysis of process characteristics:
The MBR process mainly plays a nitrifying effect on NH3-N, with limited denitrification ability, high nitrate concentration and high dissolved oxygen concentration in the effluent.
There is a start-up stage of biochemical biological inoculation and acclimation, so it is not appropriate to start and stop the equipment at any time, and the maintenance of the equipment is difficult;
The system control requirements are high, BOD, COD and NH3-N mainly rely on biochemical process removal, and ammonia can be effectively removed when the biochemical treatment effect is good.
The sludge has high concentration, strong stability, low viscosity, easy dehydration, and is not easy to spoil.
(3) Pretreatment + two-stage DTRO disc tube reverse osmosis process
Analysis of process characteristics:
DTRO membrane stacks are susceptible to clogging and contamination, with high backwash strength and short membrane service life.
There are 20%~25% concentrate to be treated;
The water yield is easily affected by the conductivity, TDS and temperature in the water, and the system is easy to be unstable.
There is a problem of accumulation of ammonia nitrogen and salt, which needs to be treated in a follow-up process;
The cost is on the high side.
(4) Pretreatment + MVC evaporation + ion exchange + ammonium crystallization recovery
Analysis of process characteristics:
The process is simple, the degree of automation is high, the processing process and effect are stable, and the management is convenient, which can save labor input;
The equipment is prone to scaling and corrosion;
There is concentrate produced;
High electricity consumption;
High investment.
(5) Pretreatment + A/O system + advanced oxidation + BAF
Analysis of process characteristics:
The effluent quality is good and stable to meet the standard;
Low operating costs;
No concentrate is generated;
The treatment process is less affected by the environment.
In summary, the treatment process and management costs are shown in the following figure: