Guide to waste disposal techniques and terminology.
Waste is a growing issue in the UK and across the world, with growing demands on
resources and land, finding both economical and sustainable methods of disposing of
our waste.
Waste disposal methods vary widely, depending upon the area and type of material.
Some methods are well developed and have be used for many years others are
developing to meet the need for different solutions. With new technology constantly
being introduced and older methods refined, there can be some confusion over what
is involved in each process, which I will try to alleviate.
There five main methods of waste disposal;- Landfill, Incineration, Resource
recovery, biological treatment and thermal treatment.
Landfill is the best known and most common form of disposal in the UK, although
with the diminishing availability of suitable sites and pressure from regulators the
role of Landfill is diminishing. There have been issues with older poorly managed
sites regarding vermin, wind blown litter and the contamination of water sources.
Modern landfill sites are designed to minimise their adverse environmental impact,
with systems in place to ensure the stability of the land form and prevent
contamination of water supplies. Many sites now capture the gasses released
through the decomposition of waste, some burn the collected gas to generate
electricity, but even those that just flare the gas (burn without energy recovery) are
reducing their environmental impact as Methane is a more potent greenhouse gas
than Carbon Dioxide.
Due to the relatively low cost of landfill it can be argued that it has encouraged a
wasteful culture and that by increasing the cost of waste disposal, we will be
encouraged to lead less wasteful lives. Some people have speculated that landfill site
may be mined in the future as resource that are common today and are frequently
thrown away become scarce.
Incineration is another very common waste disposal method, in its simplest form an
incinerator is a furnace where waste is burned at very high temperatures.
Incinerators are often perceived to be dirty and polluting, a reputation based on the
experience some have had with older incinerators, modern incinerators incorporate
pollution mitigation equipment greatly reducing there impacts. As waste is
combusted considerable amounts of energy are released in waste to energy plants
this energy is harnessed to generate electricity and to produce hot water. The
electricity produced is fed into the local grid, the hot water produced can be used in
district heating schemes, providing heat to the local community, this is common
place in Denmark, but unfortunately as we do not have the necessary infrastructure
to support district heating, waste to energy plants are restricted to power
generation.
Incineration has the advantage of greatly reducing the overall volume of solid waste,
but it does transfer the pollution from the land into the air and adds Carbon dioxide
to the atmosphere. Waste to energy with effective controls over emissions could help
to make the most of the resources we have by extracting the embedded energy.
Resource recovery covers any method that removes usable materials from the waste
stream, more commonly referred to as recycling. Resource recovery requires the
waste to be separated by either the producer or by the processor, separation and
sorting can be by hand or by machine. Most municipal recycling schemes require
householders to carry out a pre-sort of our waste, only placing those materials that
the authority can recycle into the recycling container , some schemes carryout a
further sort at the kerb side with others separating the various components of the
recycling stream at a central depot either by hand or machine. Mechanical separation
relies the differing properties of each component within the waste stream, such as
using magnets to remover Ferris metals, the process Known as Mechanical and
Biological Treatment or MBT is a combination of Mechanical sorting to remover the
Recyclable materials followed by some form of biological treatment of the remaining
organic content.
Recycling not only recovers reusable materials for reuse, but has the added
environmental benefit of reducing the need for the use of virgin materials and
therefore the environmental impact associated with the extraction and processing of
these materials. It usually requires less energy, water and other resources to recycle
materials than to produce new ones. For example recycling steel saves about 95% of
the energy used to refine virgin ore and every ton of Aluminium recycled saves 5
tons of Bauxite being mined. It is important that we assist in the process by ensuring
that all of the materials we are sending to be recycled are clean and that we only
place those items that our authorities do recycle into the containers as contamination
leads to a greater use of energy and therefore a greater environmental impact.
Biological treatment can be separated into aerobic decomposition and anaerobic
digestion methods. Aerobic decomposition is the process that takes place in any
domestic compost heap, with the organic waste being broken down by various
organisms in the presence of oxygen. Anaerobic digestion makes use of micro
organisms to breakdown waste in an enclosed environment without the presence of
oxygen, anaerobic digestion has been in use for may years as part of sewage
treatment, it is only been recently explored as a possible solution to domestic
organic waste. With anaerobic digestion the waste is reduced into Biogas which can
be burned to produce electricity (it is often used as a heat source in the digestion
process), a stable organic solid, and a liquid that is rich in nutrients.
Both of these processes turn organic waste into usable products but the quality of
which is highly dependent on the material going and strict control over
contamination needs to be maintained. Composting has the advantage that the
general public can do this at home but its efficiency is dependent upon the prevailing
weather conditions.
Lastly thermal treatment of waste covers any method that uses heat at the core of
the process, incineration is a thermal treatment method, others being Pyrolysis and
Gasification. Pyrolysis is the chemical decomposition of organic materials in the
absence of oxygen, Pyrolysis has three products, a solid residue that can be further
refined, a gas and liquid oil both of which can be burnt to produce energy or further
refined into usable products. Gasification can be used to convert plastic rich waste
into a gas for use as a fuel, this process has been in use for many years converting
carbon rich solids and liquids into gas, an example would be the production of Town
gas in the 19th century from coal.
Both of these techniques are relative new when applied to waste treatment, and
therefore carry the extra risk associated with new technologies, but both could have
a role to play in waste management.
With all of these methods of waste management there are impacts and products that
need to be considered. Some require the input of significant amounts of energy
others require the careful monitoring of the waste stream to prevent contamination
of end products.