Last reviewed 10 July 2018
Avoiding waste generation and recycling waste are often seen as a holy grail. However, within the hierarchy of waste the importance of energy recovery should not be forgotten. Alan Field examines some key points to consider when looking at waste management options.
The hierarchy of waste is now an established approach and for most environment and facilities management professionals the drive towards avoidance, or prevention, of waste is well understood. Not only does understanding the hierarchy help minimise waste but it has other environmental benefits such as promoting reductions in greenhouse gas emissions, reducing energy consumption and encouraging green technologies throughout the waste management lifecycle.
The hierarchy of waste starts from what is the most desirable, to the least desirable, method of disposal. Recycling is often focused upon as the most desirable solution for waste that cannot be prevented in the first place (eg by better product design) or, alternatively, by the waste being diverted to other uses. (See Recycling, Reuse and Recovery topic).
Where recycling is not possible or available in certain areas many organisations now look at alternatives. Instead of accepting that some waste simply goes to landfill or to other non-productive uses, they are making targets towards nil to landfill. This is due largely to the environmental consequences of landfill and the increasing shortage of such sites and some organisations adopt this as part of their corporate social responsibility or marketing strategy. However, achieving nil to landfill can be difficult to achieve for certain waste streams (although recycling techniques, can and do evolve). So, we are left with what is usually seen as the next most desirable stage of the hierarchy of waste — recovery.
Energy recovery is an option not always fully understood. The basic principle is simple — the waste is processed in some way that produces energy that in turn, can be harnessed in a productive way, eg for sale to the National Grid. There are many different techniques, but either electricity or biogas is produced from the waste and there are some processes which recover energy indirectly, eg some technologies produce refuse derived fuel (RDF). RDF is a broad term for several different products and outcomes, but the RDF material produced from the waste can be used as fuel to generate energy.
The basis of all energy recovery is that the waste — that would have otherwise gone to landfill or other disposal — becomes a fuel used to generate productive energy. Without it, fuel would have to have been obtained from other sources — many of them being finite and polluting such as oil and natural gas. Recovery also conserves an equivalent need to draw on energy supplies derived from renewable sources, eg wind generation or hydroelectricity.
Of course, recovery is not entirely “free” energy. The lifecycle of recovery needs to be considered. For example, this could be the building and ongoing maintenance of the recovery facility, its own energy requirements, and any pollutants from the recovery process itself. For example, if incineration is being used to produce RDF then there will be some emissions to air, no matter how much scrubbing and other filtration is done before the emissions to air are released. It should be remembered that incineration is controversial — while some experts argue that even the most modern incineration techniques are still polluting, others would argue that this is no longer an issue. In any event, the environmental consequences of landfill might be even more undesirable than an element of controlled emissions to the air. So, there is no incontrovertibly right answer. An organisation needs to look at the recovery method being used and whether it meets its sustainability policies.
Where an organisation has set itself energy reduction targets, one decision that should be taken is whether electricity or biogas generated from recovered waste should be credited to the target. This is a question that is not always considered. Perhaps this is because many organisations see recycling, and the prevention of waste, as completely divorced from energy management. However, the recovered energy from waste is part of energy management and can be treated as such, even for organisations which purchase “green” energy.
It is true that it can be difficult to calculate exact figures of energy recovered as the efficiency of different recovery techniques can vary by the hour, eg with general waste incineration to produce combined heat and power (CHP) the efficiency is partly dependant on the right mix of waste and a continuous supply to feed the furnace to get the highest energy recovery. Yet average figures can be obtained based on the tonnage of waste produced by the organisation, which is then fed into the recovery process.
Crediting recovered energy against reduction targets should also be considered because it may encourage diversion of waste from landfill to recovery. While the hierarchy of waste implies there are clear cut demarcations between the different outcomes, this is sometimes not the case, because there may be borderline decisions as to treatment options. So, the producer of waste may need to go the extra mile, either in terms of cost or changing to a contractor who can offer a certain recovery option. A contribution to an organisation’s energy reduction targets may influence a decision towards a recovery option.
The way ahead
Where an organisation has a number of waste providers there is a need to ensure that all possible recycling, as well as recovery, options have been considered — even with hazardous or special waste streams there can be a wide range of possibilities to consider.
With general waste streams, there are many recovery options. For example, virtually all food waste can go through anaerobic digestion — basically a fermentation of organic matter to produce biogas – which can be sold to the National Grid or used for local electricity generation. However, this isn’t available in all parts of the country and there may need to be a certain volume of food waste generated. Alternatively, there are other schemes which, effectively, dry or desiccate the food waste so it can be incinerated, normally with other general waste. As another example, feminine hygiene waste — which is still often landfilled or incinerated without any energy recovery — can be processed in a similar way to produce a dry waste suitable for energy recovery incineration. These are just a few examples.
So, depending on the location of the waste streams and the contractor involved there may be more than a few recovery possibilities to consider.
The hierarchy of waste helps us understand how to deal with waste from the most desirable to the least desirable options.
While recycling is the preferred option over energy recovery, the latter is always preferred over landfill or other non-productive processing of waste.
Energy recovery is an option not always fully understood, yet it can contribute to energy reduction targets.
In broad terms, energy recovery means that electricity or biogas is generated from waste that cannot be viably be recycled.
Where an organisation has a nil to landfill target then energy recovery should always be considered if recycling is not a viable option.
Where multiple waste contractors are used, regularly review how effective they are at considering the best recycling or recovery options — smaller organisations may find it helpful to employ a specialist consultant to advise on trends and changing waste technologies.