Issue 3 • March 2005

• Mechanical Biological Treatment• Anaerobic Digestion

• In Vessel Composting

• Thermal Treatment Technologies• Mass Burn Incineration• Fluidised Bed Incineration• Gasification• Pyrolysis

• Summary• Emissions• Products

• Residues

• Conclusions

Introducing Materials Resource Management

Summary of the options for dealingwith our rubbish

The purpose of this leaflet is to provide background information about a future waste managementservice referred to as the Materials Resource Management Service and to share lessons learnedfrom technical seminars concerning waste management technologies. It is the third in a series ofnewsletters.The first two summarised comments made at meetings of Community Interest Groups.These groups are an integral part of the County Council’s commitment to public consulta-tion concerning how our wastes are managed.

Introduction

There are approximately threequarters of a million people livingin West Sussex. Together, we pro-duce over 400,000 tonnes ofhousehold rubbish per annum.

The West Sussex Local Authorities arecommitted to waste prevention. The ‘RealNappy Initiative’ has received National awardsand, more recently, the Government has granted £2M torealise a major home composting initiative. There still remains much tobe completed in this area and our future proposals place waste prevention as the prime aim in ourservice requirements. We also aim to recycle and compost much of our rubbish and, to this end,we work with our private sector contractor Viridor, under the partnership of ‘Reclaim West Sussex’.Reclaim aims to increase our current recycling level from 24% to 45% by 2015.

The rubbish not recycled under ‘Reclaim’ is currently sent to landfill which is a disposal method thatis becoming increasingly expensive and is not considered a sustainable disposal option. In addition,the Government has set strict limits on the amounts of rubbish that can be landfilled. LocalAuthorities will face fines if they exceed these limits. Not achieving our landfill diversion targetswill be very costly to the community and this expenditure would put increased pressure on all ourother existing services. The County Council, together with the District and Borough Councils, islooking at other ways of handling our non-recycled wastes. There are a number of options thatinclude recovery of materials or energy that will help reduce our landfill requirements.

No decision has yet been made as to the type of treatment systems that are likely to be used and,to help in the decision-making process, two information days were held where providers of wastemanagement technologies were invited to describe their processes in general terms to electedmembers and officers.

Background

Levels of industrial, and domestic rubbish production have been steadily increasing inrecent years. In the past the preferred method of “end disposal” has been land-

fill but it is now recognised that this cannot continue at current levels andmore sustainable disposal methods need to be used.

No single treatment option, even reduction and recycling, is capableof dealing with all of our rubbish. Every disposal option has advan-tages and disadvantages, which gain or lose significance dependingupon the locality, the size of the treatment facility and the nature

of the rubbish being treated.

In 1998 the County Council, following extensive consultations with thepublic, made a strategic decision to create two contracts for dealing with

our rubbish.The first is the Recycling and Waste Handling Contract (known as‘Reclaim West Sussex’) which accepts rubbish delivered to it from either the District

and Borough Councils or from the public delivered to the Household Waste Recycling Sites (for-merly known as Civic Amenity Sites).This contract takes out materials for recycling and sends the remain-ing waste for disposal at landfill.

This disposal to landfill is not considered to be a sustainable disposal option and when considering theimplications of the Landfill Directive,which drastically restricts how much waste can be landfilled, its viabil-ity, both economically and environmentally, is becoming more limited. In recognition of this the CountyCouncil is looking to let a second contract that will reduce our dependence on landfill.The County Councilhas called this contract the Materials Resource Management Contract (MRMC).

One of the key intentions of developing the MRMC is to explore the disposal technologies available and toprovide the discovered information to the public.To this end The County Council has held two technicalinformation days where suppliers of technologies have been asked to present to elected members.

Both of the days started with an overview presentation followed by “Technical” presentations from systemsuppliers.The first of the days focussed on Mechanical and Biological Treatment whilst the second lookedat Thermal Treatments.

Exploring Options for Dealing with our Rubbish

Presentations were given on Mechanical Biological Treatment, Anaerobic Digestion and In VesselComposting.The main messages delivered by the presenters are outlined below.

Mechanical and Biological Treatment (MBT)

MBT plant, Leicester incorporating a Ball Millwhich pulverises rubbish ready for biological processing

MBT is a generic term for a series of processes that can be “bolted together” in a variety of waysto produce recyclates, compost and/or refuse derived fuel.The mechanical section of the processuses physical properties to recover some of the rubbish for recycling, for instance magnets to col-lect metal.The mechanical section may also process the rubbish to break itdown into smaller pieces ready for introduction to the biologicalprocess.The biological section relies on promoting or inhibitingbiological activity to break the rubbish down into its variouscomponents such as gas and compost. Alternatively it canbe used to help stabilise rubbish by reducing the watercontent. The resulting material is easier to handle andcan be readily processed into a fuel. The two most com-mon types of biological processing within MBT areAnaerobic Digestion and In Vessel Composting whichare described now in more detail.

MBT plant, Milan, Italy

This uses micro-organisms which operate inthe absence of oxygen, producing a mix-ture of carbon dioxide and methane,(known as biogas) and a stabilisedresidue.The process requires mixing thepre sorted “readily biodegradable” partof the waste (ie food, paper etc) withwater and bacteria and then keeping themixture which resembles a sludge in an oxy-gen free atmosphere for a period of approxi-mately 20 days.The biogas produced by the processcan be used as a fuel to generate heat and electricity.Theresidue (often referred to as a digestate) can be used as a fertilis-er which has been demonstrated to be suitable for agriculturaluse.

The process takes place in an enclosed vessel, which leadsto enhanced control of odour, gas emissionsand liquid effluents produced by theprocess.

Anaerobic digestion has beenaround for many years andis commonly used to treatsewage sludge with goodeffect. The price obtainedfrom electricity sales is akey factor in determiningthe financial viability of ananaerobic digestion plant.

Anaerobic DigestionAD plant, Leicester

AD plant, Munster, Germany

This is a process mainly used for the controlled compost-ing of garden wastes. Unlike anaerobic digestion this sys-tem processes waste using micro organisms in the pres-ence of air to speed up the rate at which the biodegrade-able fraction of the rubbish decomposes. It is carried out in avessel whilst air is passed through the material. The rubbish ismechanically pre treated and uses micro-organisms to break downthe organic materials in the presence of oxygen to produce carbon dioxide, water and a stabilisedcompost or humus. A high temperature of approximately 60ºC is maintained for an extended peri-od of time in order to eliminate undesirable bacteria such that the compost can be safely used asa soil conditioner.

A type of In Vessel Composting can also be used to rapidly stabilise rubbish and remove approxi-mately 20% of the moisture content. This process involves pretreating the waste using some crude

shredding device. The shredded material is then processed in acontainer by circulating air through the waste and captur-

ing the moisture content. After a week or so thematerial is very dry and more easily managed to

enable the non – combustible fraction to beseparated leaving a material which can be

further shredded foruse as a fuel.

In Vessel Composting

MBT plant, Germany

In Vessel Composting

Thermal Treatment Technologies

Presenters outlined the Mass Burn, Fluidised Bed, Pyrolysis andGasification processes and the key messages are given below.

Mass Burn Incineration

This is the most commonly used method of reducing disposalto landfill where the rubbish is simply burnt on a grate in thepresence of air, generally with no pre-processing. The heatproduced is used to produce steam which is subsequently usedto generate electricity.

Fluidised Bed Incineration

These burn rubbish on a bed of sand which is pre-heated and made fluid by blowing hot air throughit. Rubbish which has been pulverised and sorted is poured onto the bed and combusts.The bot-tom ash (the heavy non-combustible fraction, eg, glass, ceramics etc) for disposal at the end of theprocess is approximately 10-15%, (by weight) of the initial volume of material for combustion.

Energy can be recovered from the thermal processing and the efficiencies are generally consideredhigher than those in a mass burn grate. However, this efficiency needs to be balanced against theenergy required to prepare the fuel which involves a process to pulverise and sort the rubbish.

Chineham, Hampshire – Mass Burn Incinerator

Prepared rubbish (in the form of pulverised pre-sorted fuel) is converted to gas by partial oxida-tion under the application of heat.The rubbish is transformed into minerals, metals and fuel gas.Thevolume of this gas is considerably less than the volume of incinerator exhaust gas.This reduces thecost and size of the flue gas cleaning equipment.

Gasification

This is the process by which rubbish (pre-treated as with gasification) is thermally broken down inthe absence of air. The products formed include combustible char usually of low calorific value,combustible gases, a mixture of oils and tars as well as a liquid effluent. The products formeddepend very much on the rubbish being treated and the external temperature that is applied.Higher temperatures usually produce gases andlower temperatures usually produce liquidfuels. It is common for these systemsto be followed by a gasificationprocess where the carbonresidues are combusted withthe fuel gas.

Pyrolysis

Pyrolysis Plant Burgau, Germany

A summary of the two days of presentations was given by an independent technical consultant who,in order to visualise waste processes, suggested that we can consider any of the technologies as a“black box”. They all follow a similar process pattern in that they accept rubbish, carry out somekind of processing and produce emissions, residues, losses and products.

Summary

These are the treated gaseous emissions that arise from the processes such as methane, carbondioxide and carbon monoxide which occur either from combustion or by the breaking down oforganic material.These emissions are very tightly controlled and the amounts that are permitted tobe released to the atmosphere are regulated by the Environment Agency.

Emissions

This covers such materials as metals, plastics, stone etc that are recovered from the rubbish streamas part of the process and can be passed on for further use or sold to a market.

Products:- Materials

EmissionsLosses

• Materials

Products:-

• Compost

• Energy / RDF

Residues

Rubbish

Products:- Compost

Heat created by the combustion of rubbish or the methaneproduced from anaerobic digestion, is converted intoelectricity via steam driven turbines that are similarto that of a conventional power station. Theelectricity can be sold to the National Grid, usedto power the process or a combination of both.Heat can be sold to local factories or, wherepossible, used for district heating systems.

Products:- Energy

Dependent on the process this can vary in quality from a soil conditioner used simply to improvesoil, to a high grade compost which in itself can be used to grow plants.

These are generally in the form of solids which can include ash arising from combustion or nonprocessable materials from biological systems eg contaminated plastics.

Residues

When considering any solution there are key points that need to be kept in mind:

• Treatment is needed to provide diversion from landfill to meet legislative targets and costreduction

• All the processes could provide a solution for landfill reduction but sorting is required forobtaining the additional recycling

• All the systems require development of new or improved markets for the products to min-imise the need for landfill

The overall conclusion is, however, that no one type of technology can provide the ultimate solu-tion to dealing with our rubbish and therefore an acceptable integrated solution is needed toachieve the aims of the West Sussex Residents.

Conclusions

This is one of a series of leaflets to keep you informed.

If you require further details about any of theinformation in this newsletter or if you would

like to receive any previous or future issues thenplease contact the Project Manager on (01243)753570 or email at: mrmc@westsussex.gov.uk

For further information:

Materials Resource Management ContractWastes Management Services

County Hall, Chichester,West Sussex. PO19 1RE

www.westsussex.gov.uk

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West Sussex PO19 1RH,telephone 01243 777544 or email Env.dev@westsussex.gov.uk