Among the many issues facing modern society, energy and waste are of growing importance. Increasing the cost of energy to both the industrial and domestic consumer is a well understood economic regulator. We know from recent history that increasing the price of fuel may have an immediate impact – consumption gradually begins to rise as a result of necessity or complicacy.

However, technology offers innovative ways to achieve more permanent measures to achieve energy reduction and generation efficiencies. Of particular interest are the technology developments that harness the resources of the waste mountain to achieve these objectives. Unfortunately this cannot be achieved without a different kind of economic regulator, which has the effect of revaluing the raw materials that form the basic feed stock for the process technology.

Again, this is not a new mechanism. For instance, the increased cost of mining coal in the UK to fuel power stations led to imports of cheaper foreign mined coal. Another factor that came into play was the regulator driver. Once air emission standards were tightened, driving the need for desulphurisation and other gaseous abatement technology, gas-fired power stations took on a new relative economic value.

Technology drive

We are now seeing a re-evaluation of waste processing technology driven by the landfill tax escalator. While this has the effect of making landfill less attractive, the upside is that it makes waste process technologies more attractive. As the landfill tax rises, the range of alternative technologies increases and those processes which until now have not been able to compete in the recovery and recycling market are beginning to enjoy a new relative economic value.

The recovery and recycling industry is on the verge of a massive investment programme estimated at £11B. The question is which of the currently available technologies will emerge as the market leader in this new market place. Already we have seen a reduction in the number of landfill sites from 3,400 in 1994 to less than 2000 today with a decrease in the proportion of municipal waste sent to landfill.

Incineration still dominates the alternative technology although the new generation of plants are now promoted as waste-to-energy plants. Unfortunately, the public has yet to appreciate how current emission standards have made incineration a much more environmentally friendly technology. Recovery of energy-from-waste both in the form of heat and electricity adds to the attraction of the new generation of plants and places a new value on the waste as a energy source. It leaves a residual ash for which other uses can be put, although landfill remains the current end-use.

One high-temperature alternative process to incineration is gasification. Turning waste into a gaseous product, which can then be used as a fuel, on the face of things has a relatively greener image than mass burn technologies. The technique has been used in other industries for many years but its application in the waste-to-energy market has brought with it new challengers. Managing the by-products of combustion requires further consideration. Perhaps investment in full-scale demonstration plants will be needed before the full environmental and economic benefits can be quantified.

Benefits of anaerobic digestion

Anaerobic digestion of organic waste is already an established route for the generation of a gaseous fuel. Unlike gasification, the energy product from this process is methane. This has to be regarded as an intermediate product that is suitable for gas boilers, gas engines or CHP units and thereby can be converted into electrical and or heat energy.

In this process the feedstock takes on a different value. The calorific value of the gas will be dependent on the ratio of CO2 to methane in the emerging biogas. This in turn will be influenced by the chemical composition of the material passing though the process. However, the process is becoming increasingly attractive for the processing of food waste and farm waste.

Pre-treatment techniques using MBT will improve the feedstock quality making them essential units within a modern process flow system. Enhancement techniques are in the market place which enhance the gas production by pre-conditioning the feedstock prior to entering the reactor. The effect is to increase the gas yield per unit of weight processed.

Unearthing potential

Work is under way to quantify the potential of various wastes to respond to anaerobic treatment. Pre-blending of wastes offers further potential in maximising the advantages of the process for wastes, which have a singularly low gas yield. Anaerobic digestion has the advantage of not only producing an energy source, but also the liquid/semisolid material exiting the process has a value as a soil conditioner/fertiliser.

Once again, we see how the role of regulation can influence the economics of a process. Anaerobic treatment of sewage sludge has been around for many years. But current regulations place restrictions on the use of the processed material on the traditional agricultural land outlet to provide a barrier against metals and pathogens contaminating the soil or entering the human food chain.

Paul Lowe is director of Aqua Enviro

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