Navigating the energy-from-waste land

Simon Bimpson and Marcel Goemans of environmental engineers MWH, discuss the steps to delivering effective and efficient waste infrastructure.

One of the most significant challenges facing local authorities today is how to divert biodegradable and recyclable municipal waste away from landfill while still providing an affordable and deliverable waste management solution. Driven by environmental, legislative and economic pressures, the European and UK preference is to manage waste as far up the hierarchy as possible, with resource recovery ranking higher than landfill but below prevention, reuse and recycling.

In responding to this challenge, local authorities must consider a bewildering variety of waste management options, technologies and strategies. However, knowing which technology or combination of technologies to opt for can be minefield that few local authorities have the time or resources to navigate.

While it goes without saying that there is no “one size fits all” approach to waste management, there are a number of initial steps that local authorities should take to inform decisions about residual waste infrastructure.

Prioritising objectives from the outset is very important. For example, are carbon footprint and resource efficiency the main drivers, and how far will timescales and budget also impact decisions? What is required as output – heat, power or a specific product such as refuse derived fuel (RDF) and/or compost? In setting the priorities, it should be recognised that the markets for these outputs are volatile and changing, hence a degree of flexibility should be built into the specification.

Before residual waste treatment options can be evaluated, local authorities should also use waste flow modelling to provide a clear idea as to how much residual waste will arise, where it will arise and when. Modelling future municipal waste tonnages and composition should include an evaluation of local population growth and demographic, housing growth and the impact of national and local waste minimisation initiatives.

In addition, consideration will need to be given to the (preresidual treatment) recycling rate likely to be achieved by the local authority and whether other activities (e.g. the operation of a MRF or composting facility) might be integrated with the residual waste management function.

After determining future waste growth and recycling rates, the local authority will be in a position to model the profile of residual waste arising over the period of the project – normally 25 to 30 years.

There are four main types of technology typically considered for the treatment of residual waste: incineration (also referred to as energy-from-waste or EfW), mechanical biological treatment (MBT), mechanical heat treatment (MHT) and advanced thermal treatment (ATT).

While some of these technologies are already established practice in the UK or overseas, others are yet to be commercially tested for municipal waste treatment. They also vary in the extent to which they recover value from the waste stream. The two main sources of value are: materials which can be reprocessed; and energy recovery through a thermal and/or biological treatment process. To maximise energy recovery, local authorities should explore the potential for combined heat and power applications.

Energy recovery should be assessed by reference to the overall efficiency of the process – including collection, sorting and the level of pre-treatment required – as well as the efficiency of the chosen residual waste treatment technology. To only measure the efficiency of the plant in terms of converting waste inputs into energy outputs (i.e. heat and power) is not accurate.

When comparing the different technology options or combinations, therefore, it is useful to apply a standard set of evaluation criteria.

At a very basic level, these should cover: the extent of diversion of municipal solid waste from landfill; the degree of value recovery either through additional recycling delivered by the technology or through energy recovery (heat and power); emissions or overall environmental impact; the flexibility of the system in responding to variances in the tonnage and composition of the waste; commercial risk; deliverability, including issues in relation to securing planning for the facility and funding for the project as a whole; and full economic cost.

The UK has a long way to go before it catches up with some of its European neighbours in its ability to reclaim heat and power from waste material it is not able to recycle. But there is no doubt we are making progress. In taking advantage of the funding and range of sophisticated technologies available, the UK is in a far better position to reduce its reliance on landfill and, more importantly, its
greenhouse gas emissions.