Disposal and energy recovery
Once recyclables have been removed from waste, any residual materials need to be disposed of or otherwise utilised. This has traditionally been achieved by deposition into landfill but to meet EU landfill targets the amount (and type) of material going to landfill has reduced significantly and been diverted into that produce energy and/or other products.
Landfill involves burying waste in quarries. The main health and safety risks to workers at landfill sites include:
- fire and explosion caused by uncontrolled ignition of landfill gas (largely methane) generated during decomposition;
- exposure to landfill gas
- transport hazards caused by heavy earth-moving plant and vehicles.
- Vehicles and edge protection
Incineration and Energy from Waste
A smaller quantity of waste is incinerated, the preferred option for disposing of some hazardous wastes. For example, clinical and chemical wastes require exposure to high temperatures to reduce or remove the hazards they pose. You should carry out a risk assessment for handling and disposing of fly-ash following incineration and implement suitable control measures. Precautions should be taken to prevent ash from becoming airborne and subsequently inhaled, so far as is reasonably practicable.
Energy can be recovered from a range of organic feedstocks (biomass) by modern processing plants to generate electricity. This makes it an attractive prospect as at the same time as diverting waste material from landfill it provides economic and environmental benefits.
Due to the technical nature of the processes and the composition of the feedstock there are a number of additional hazards associated with these processes. In additional to general health and safety requirements consideration of the following legislation may be required:
- Dangerous Substances and Explosive Atmosphere Regulations 2002 (DSEAR)
- Pressure Systems Safety Regulations 2000
- Confined Spaces Regulations 1997
- Electricity at Work Regulations 1989
- Control of Substances Hazardous to Health Regulations 2002 (COSHH)
Biomass is a generic term for forestry and plant material, agricultural crops, food and garden waste and the biodegradable or combustible fractions of municipal waste. It can be used as a fuel or an energy source. It can be converted into heat, electricity, liquid and gaseous fuels or feedstock for the chemical industry.
Sources of biomass include specifically grown crops such as oil seed rape, agricultural by-products, waste wood, animal waste such as slurry, food processing waste and biodegradable or combustible fractions of municipal waste.
All biomass energy generation technologies require the feedstock material to be pre-processed into a suitable form e.g. sorted (Mechanical Biological Treatment (MBT)), shredded, pulped or pelleted etc. depending on the needs of the particular process.
A wide range of solid biomass crops, agricultural and industrial waste can be turned into wood chips, fuel pellets or briquettes for use as energy feedstocks.
Anaerobic Digestion (AD)
The term ‘anaerobic digestion’ refers to a natural biological process which converts organic matter such as commercial and household food waste, garden waste and farm slurry, into energy.
There are two main types of anaerobic digestion called thermophilic and mesophilic – the primary difference between them is the temperatures reached in the process. Thermophilic processes reach temperatures of up to 60C and mesophilic normally runs at about 35-40C.
AD sites also have to comply with the Animal By Products Regulations so a mesophilic site would also have a pasteurisation unit to make sure the end product is safe.
The main products resulting from anaerobic digestion are biogas (a mixture of mainly methane and carbon dioxide), which is very similar to natural gas, and digestate (liquid and solid fractions). The biogas can be used to generate surplus heat and electricity, or compressed for use as a biofuel. The material left over at the end of the process (digestate) is rich in nutrients and it can be used on land as fertiliser or soil improver (liquid fraction) or further processed in composting operations (solid fraction).
This is a very diverse sector and rapidly growing with multiple technologies being developed on a range of scales, from the small scale farm processing animal manure through to large industrial scale premises processing sewage sludge, and municipal waste. Further information is available from:
- Anaerobic Digestion and Biogas Association (ADBA)
- Renewable Energy Association (REA)
- Department for Environment Food and Rural Affairs (defra)
- Waste Resource Action Programme (WRAP)