Typical solid waste utilisation and disposal technologies
01 Landfill disposal
Sanitary landfill: waste is isolated from groundwater through a multi-layer impermeable system (clay + HDPE membrane), compacted in layers and covered with soil. Leachate is collected, treated and discharged, and biogas (methane-based) is recycled or burned through a conduit system.
Anaerobic landfill: anaerobic microorganisms are used to decompose organic matter and produce biogas under confined conditions, but long-term monitoring of impermeability is required.
Advantages
Low cost: initial investment and operating costs are relatively low; wide range of treatment: can accommodate a wide range of waste types (inert waste, non-recyclables, etc.); simple technology: no complex equipment is required and operation and management are relatively easy.
Disadvantages
Large land area: consumes a lot of land resources, difficult to choose a site (needs to be far away from residential areas and water sources); long-term pollution risk: leachate may leak and pollute groundwater, methane emissions exacerbate the greenhouse effect; waste of resources: waste resource utilisation has not been realised, continuous monitoring is required after the landfill is closed; hazardous wastes are expensive to treat in rigid landfill sites.
Types of solid waste that can be treated: inert waste such as construction waste (concrete, masonry, slag), glass, ceramic fragments; non-recyclables such as incineration ash, stabilised hazardous waste (e.g., solidified fly ash).
02 Composting
Aerobic composting: under ventilated conditions, thermophilic bacteria (e.g. Bacillus) decompose organic matter, and the temperature rises to 60°C to kill pathogens and produce humus.
Anaerobic fermentation: methanogenic bacteria in a closed reactor convert the organic matter into biogas (60% CH₄) and the residue is used as organic fertiliser.
Advantages
High resourcing rate: organic waste is converted into humus fertiliser; low carbon and environmental protection: reduces methane emissions from landfill, replaces chemical fertiliser to reduce carbon emissions from agriculture; wide range of application: can treat kitchen waste, garden waste, livestock and poultry manure, etc.
Disadvantages
High pre-treatment requirements: plastic, glass and other impurities need to be removed, municipal sludge may contain heavy metals (need to be tested); long cycle: aerobic composting takes 20-30 days, anaerobic fermentation takes more than 15 days; odour problems: ammonia, hydrogen sulphide and other malodorous gases require additional deodorisation facilities.
Types of solid waste that can be processed: organic waste such as kitchen waste (fruit and vegetable residues, leftovers), agricultural waste (straw, animal manure, mushroom sludge), garden waste (fallen leaves, pruned branches); sludge from municipal sewage treatment plants (heavy metal content needs to be tested).
03 Incineration
Incineration is high-temperature oxidation: in the incinerator at 850~1200℃, organic matter decomposes into CO₂ and H₂O, and the heat is used to generate electricity or heat. The exhaust gas is subject to semi-dry deacidification (lime slurry spraying), activated carbon adsorption of dioxins, and bag filtering to remove fly ash.
Advantages
Volume and weight reduction: volume reduction of more than 90%, weight reduction of 70% to 80%; energy recovery: waste heat for power generation or heat supply, replacing fossil fuels; rapid harmlessness: high temperature and complete inactivation of pathogens (e.g. medical waste).
Disadvantages
High cost: Hundreds of millions of dollars of investment are needed to build incineration plants, and the tail gas treatment system is expensive; Secondary pollution: Fly ash contains heavy metals and dioxins, and needs to be disposed of as hazardous waste; NOx and SO₂ emissions need to be strictly controlled; Public resistance: the ‘neighbourhood effect’ is significant, and residents are worried about the health risks.
Types of treatable solid waste: high calorific value waste such as waste plastics, waste rubber (tyres), waste oil, medical waste (infectious, pathological); mixed domestic waste; industrial waste such as textile waste, waste wood, chemical residues, etc.
04 Pyrolysis and gasification
Pyrolysis(anoxic cracking): organic matter decomposes into pyrolysis oil (which can be refined as fuel), carbon black (industrial filler), and gas (H₂, CO) at 400~800℃. For example, waste tyre pyrolysis can recover 45% carbon black and 35% fuel oil.
Gasification(partial oxidation): by passing a limited amount of oxygen, the organic matter is converted into syngas (CO+H₂) at more than 1,000°C, which is used for power generation or as a chemical raw material.
Advantages
High energy conversion: pyrolysis oil and syngas can replace fossil fuels (e.g. waste tyre pyrolysis oil has a calorific value of ≈ diesel); Controlled pollution: anoxic environment reduces the generation of dioxins (50%-90% compared to incineration); Variety of outputs: Carbon black can be used as a filler for rubber, syngas can be used to produce methanol or hydrogen.
Disadvantages
Technical complexity: precise temperature control (±10°C), anti-coking, high equipment maintenance costs; poor economics: treatment costs of about 500-800 RMB/tonne, relying on government subsidies; difficult to process products: pyrolysis oil containing sulphur needs to be refined, and the purity of carbon black affects the market.
Types of solid wastes that can be treated: organic polymer wastes such as waste tyres (pyrolysis to generate carbon black and fuel oil), waste plastics (PP/PE/PVC pyrolysis to make oil), biomass (straw, woodchip gasification to make syngas); oil sludge and slag, and other oil-containing sludges (pyrolysis to recover the oil).
05 Biological treatment
Anaerobic digestion: two-stage reaction (hydrolysis and acidification → methane production), 1 tonne of kitchen waste can produce 120m³ biogas.
Biodegradable plastics: using Pseudomonas aeruginosa to secrete esterase to break down PLA into lactic acid, requiring specific temperature and humidity conditions.
Advantages
Green and low carbon: anaerobic digestion produces biogas (CH₄ can replace natural gas), reducing greenhouse gas emissions; use of by-products: biogas residue is used as organic fertiliser, and biogas can be used for farmland irrigation (heavy metals need to be dealt with); low energy consumption: aerobic composting only needs to be turned over to supply oxygen, and energy consumption is lower than that of mechanical treatment.
Disadvantages
Long cycle time: anaerobic digestion takes 15-30 days, continuous feeding requirement is high; sensitive conditions: fluctuations in temperature, pH, carbon/nitrogen ratio are easy to inhibit the activity of microorganisms (e.g. pH<6.5 inhibits methanogens); pre-treatment is stringent: crushing to particle size<5cm, high oil and grease wastes (e.g. kitchen wastes) need to be degreased and pre-treated.
Types of solid waste that can be treated: anaerobic digestion can treat kitchen waste, livestock and poultry manure, food processing waste (biogas production); aerobic composting can treat garden waste, agricultural straw, municipal sludge (need to adjust the ratio of carbon and nitrogen); biodegradation can treat compostable plastics (PLA/PHA), organic contaminated soil (bioremediation).
06 Curing/Stabilisation
Cement curing: mix hazardous waste (e.g. leaded sludge) with silicate cement to form a lattice to encapsulate heavy metals.
Pharmaceutical stabilisation: add chelating agent to chelate and solidify fly ash, sulphide (Na₂S) to generate insoluble sulphide precipitation of heavy metals. The picture below shows the use of chelating agents to solidify the powdered fly ash into granular form and bagging it for landfill.
Advantages
Hazardous waste harmlessness: heavy metals are encapsulated or chemically immobilised (e.g. lead leaching concentration
Disadvantages
Enlargement effect: 10% to 50% volume increase after adding curing agent, subsequent disposal cost increases; Long-term risk: Acidic environment may destroy the solid structure (e.g., corrosion of cement at pH<4); Higher cost: Treatment fee for pharmaceutical stabilisation is about 300~500 RMB/tonne, higher than that of ordinary landfill.
Types of solid wastes that can be treated: hazardous wastes such as heavy metal-containing wastes (lead storage battery slag, electroplating sludge), radioactive wastes (special curing agents are required), incineration fly ash (dioxin+heavy metal composite contamination); contaminated soils and so on.