Waste Technologies - Composting

Improving our waste management system is a key challenge that is currently engaging Ireland’s citizens and government. A primary goal in accordance with the EU Landfill Directive is to reduce our dependence on landfill in favour of more environmentally sound alternatives.

Biodegradable waste is broadly defined as waste which is capable of undergoing decomposition either in the presence of oxygen (aerobically) or in the absence of oxygen (anaerobically). It is also more commonly known as organic waste and includes materials such as putrescible food and garden wastes, paper, cardboard and, to a certain extent, wood and textiles. Under Council Directive 1999/31/EC on the landfill of waste, all Member States of the European Union are required to reduce their landfill of biodegradable municipal waste and to encourage measures aimed at the separate collection, recovery and recycling of biodegradable waste.

It is envisaged that such measures will contribute positively towards the reduction of methane gas produced at landfills and impact significantly on other adverse effects on the environment arising from the disposal of biodegradable municipal waste.

Changing Our Ways
The Policy Statement - Changing Our Ways - preceded the development of the Regional Waste Management Plans, setting a primary objective of reducing Ireland’s dependence on landfill in favour of an integrated system of recycling and recovery infrastructure.

Changing Our Ways provided national targets for municipal waste recycling and biological treatment and set the framework for regional waste management planning.

Key targets for 2013 -

Diverting BMW away from landfill will require a high level of source separation of food and garden waste, followed by biological treatment - either composting or anaerobic digestion. The aim of biological treatment is to produce a high quality, marketable product.

Home composting provides a way of reducing the amount of waste to be collected, thereby minimising the environmental impacts and costs associated with managing food and garden waste. Garden waste and food waste of vegetable origin are suitable for home composting. Garden waste from public parks and gardens should also preferably be composted on-site. International experience suggests that up to 10% of all household organic waste can be home composted and so diverted from landfill. To reach this level requires widespread participation.

What is composting?
The composting process may be defined as the controlled decomposition and stabilisation of organic materials such as vegetables, plant, food waste, garden waste, agricultural waste, etc. - under conditions that are predominantly aerobic and that allow the development of thermophilic temperatures as a result of biologically produced heat.

It results in a final product - referred to as compost - that has been sanitised and sterilised, is high in humic substances and can have a variety of uses. It is estimated that almost 50% of the total waste stream could be composted - it is nature's way of recycling and is an important way to recycle.

Composting is now employed as a treatment process for a wide range of organic materials such as municipal solid waste, sewage sludge and agricultural and industrial by-products. The current focus on composting is primarily due to the expected EU Directive on Biowaste and Sewage Sludge which, it is hoped, will lead to the diversion of organic material from landfill. The diversion of organic matter from landfill is necessary, principally because it can release greenhouse gases, which are a prime cause of global warming.

Ireland's record in this regard is not particularly good, compared to other EU countries, as can be seen in the figure below. In this country, 85% of biological municipal waste is sent to landfill - compared to 20% in Austria and 10% in the Netherlands. The Department of Environment, Heritage and Local Government has prepared a draft report on the National Strategy on Biodegradable waste (click here to see).

Composting systems / technologies
There are different types of composting technologies - from a simple back-yard operation, or home composting - to a more sophisticated operation using centralised facilities such as windrow or in-vessel composting.

Home composting
Home composting is becoming more popular as local authorities are willing to subsidise the cost of the compost bin. It is a system that is greatly favoured by the EU. However, it is not possible for everybody to undertake home composting, as not everybody has space to do so. Home composting can take from a couple of months - if conditions are optimum - to up to a year or two years - if conditions are not ideal. It is estimated that up to 10% of all household organic waste can be home composted and, thereby, diverted from landfill. However, widespread participation is necessary in order to reach this level

Windrow Composting
Composting carried out in the open, is known as windrow composting.

In-vessel Composting
In-vessel composting encompasses a wide range of techniques for the composting of organic material in an encapsulating environment. It is suitable for a wide range of organic waste materials - including food processing and catering waste. This is due to the enclosed nature of the process which can be controlled and monitored in order to develop a high enough temperature throughout the vessel for a sufficient amount of time to ensure the required level of pathogen kill. It also prevents vermin infestation.

New requirements in relation to animal by-products have increased the impetus for in-vessel composting systems and, therefore, the use of this composting system is likely to increase.

One disadvantage of in-vessel composting is cost - which is much higher than windrow composting. Another factor which needs to be considered is that, after a short period in the vessel, the material has to be cured - and hence, extra space is required for the curing phase.

There are many types of equipment available for in-vessel composting and these are varied. It suffices to say that they all have their advantages and disadvantages and the choice of technology will depend on feedstock, scale of operation, location, etc.

Vermi-composting
This is the process of using worms and micro-organisms to turn waste, particularly kitchen waste, into compost - a dark humus which is rich in nutrients with a rich earthy smell. It can be used as a soil amendment or even as a component of a growing media.

Mechanical Biological Treatment
If the organic matter is largely stabilised - but contaminated and not suitable for use in agriculture - the final product may be used for landfill cover, soil conditioning, applications in forestry - or may be fed into another treatment process, such as incineration or gasification. The practicing of this process is likely to increase in the short or medium-term, as source separation is not very common in Ireland and in order to achieve the landfill directive targets of biodegradable municipal waste.

Testing
When composting is considered to be complete, the compost material must be analysed. Some of these tests are obligatory - for instance, the EPA has a set of tests which the composted material must pass before it can be released. These tests consist of plant nutrient levels, stability or maturity, levels of heavy metals, foreign materials such as plastic and glass and microbial tests for human pathogens - e.g. Salmonella in the compost. However, additional tests may be carried out - e.g. suitability for proposed use - this often includes a growing trial with plants.

Standards
A number of EU member states - including the UK - have established their own standards. There is a need for the development of standards for Irish composts. This should include minimum requirements for the process of composting, selection of input materials, quality of composted material and information labelling of the product. Cré - the Composting Association of Ireland - is presently working on these standards and, at this stage, compliance by the compost producer is likely to be voluntary.

Applications of Compost
If there is not enough emphasis placed on the end-use of the product derived from composting, there is a danger that Ireland will end up with huge amounts of finished compost material with no ultimate use. Though there are numerous usages of composted material, the following are some of the major applications.

Compost as a soil amendment and mulch
In this case, the compost can be mixed into the soil. This will increase the water holding capacity of sandy soil, improve the aeration of heavy clay soil and, thus, improve drainage. Compost also inoculates the soils with a vast number of microbes. These microbes are able to extract nutrients from the mineral part of the soil as well as from the organic material.

With the growing public demand to use less and less agricultural chemicals and an increase in using 'organic' methods of growing, it would be accurate to say that there will be an increased demand for composted material.

Other applications of compost as a soil amendment include the use on road side embankments, golf greens, sports fields, forestry, the manufacture of topsoil, nursery beds and back-fill for trees and shrubs. It can also be used as a mulch (ground cover to keep down weeds and hold moisture).

Growing media
Due to environmental concerns and the forthcoming EU Biowaste Directive, there is a big demand to reduce the quantity of peat being used in horticulture. One of the ways to achieve this is to dilute the peat with a suitable recycled material.

Research conducted at Bord na Mona Horticulture has shown that properly processed composted greenwaste can be used to dilute peat up to 30% without any significant decrease in the quality of the plants.

Composted material, by itself, cannot be used as a growing media except in very special circumstances.

Soil bioremediation
Compost bioremediation refers to the use of micro-organisms to break down contaminants in soil. Compost bioremediation has proven effective in degrading or altering many types of contaminants - such as chlorinated and non-chlorinated hydrocarbons, pesticides and explosives.

Compost biofilter
Compost biofilter is one of the most important biological processes used to treat waste gases and to control odour. The degradation activity derives from micro-organisms which live and develop in the media. Undesirable compounds in the gas are absorbed and degraded by the micro-organisms and high efficiency has been recorded for the reduction of VOCs.

Community composting facilities are an emerging system at European level - where local communities can become involved in the management of their own wastes, whilst implementing the proximity principle and increasing awareness of waste recycling practices within their own community.

In Ireland a number of initiatives have been undertaken - for example at an urban apartment complex and as part of the Ballymun redevelopment project in Dublin. Other examples of where community composting might be applied include -

• in relation to tidy-towns schemes
• local composting of green waste from public open spaces
• in residential housing estates - or
• in industrial estates where groups of companies pool their resources.

Interaction with farming in relation to green waste composting and vermi-composting schemes may also be considered.

Capturing organic waste from commerce is required in order to meet the target for 2009. Food waste from larger enterprises should be collected in separate containers. The following commercial enterprises are particularly relevant:

• Hospitality Sector – Hotels, Restaurants, B&B;’s, etc.
• Canteen Kitchens – in major companies and institutions
• Retail Sector - Supermarkets, Fruit and Vegetable Shops, Food Sector retails outlets
• Businesses and Offices with kitchen/ canteen facilities.

The Environmental Protection Agency essentially has already adopted the treatment standards being promoted in the technical working documents associated with the proposed European Community Initiative on the Biological Treatment of Biodegradable Waste.

The principal treatment methods to be developed and controlled under the initiative are -

Biological treatment of BMW can be successfully carried out in tandem with other waste streams, such as agricultural wastes, organic industrial wastes, fisheries residues, etc. Co-treatment can provide economies of scale and encourage investment in the development of modern recovery plants.

Health effects of composting
There are minimal effects on the health of people working at compost plants - or to the general public near composting plants - if certain precautions are taken. However, one area of concern is bioaerosols. Gaseous emissions from composting piles can include bioaerosols (fungi, bacteria, actinomycetes) and fine dust.

At present, there are few studies on the health effects of composting from which any quantitative indication of risk can be derived. A report has been prepared by Cré - partly funded by the EPA -which deals with the risks associated with bioaerosols. Odour from compost plants can sometimes be a nuisance if the composting is not done properly - but if the pile is well aerated, it should not be a problem.

Markets
A Report entitled - “Assessments and Evaluation of Outlets of Compost Produced from Municipal Waste” (click here) - was published in 2002 by the EPA (ERTDI programme, under the 2000-2006 National Development Plan). This report contains a series of strategic recommendations in support of sustainable markets for compost. The Report recommends adopting a ‘Hierarchy’ for compost utilisation, aiming for high quality product linked to a high revenue market. It also identifies a range of potential market outlets for compost and outlines a possible scenario for what quantity of waste could be sold to each market.

Development of Horticultural, Agricultural and Forestry Markets Use of compost in conventional agriculture is a vast potential market, where even a small degree of penetration will create a significant and stable demand for compost. Developing farmer confidence and know-how in relation to compost is, therefore, essential.

A Quality Assurance Scheme is a market-oriented step that goes beyond the adoption of National Compost Quality Standards. The aim is to prove to potential buyers that the product has been independently verified as coming from a process that has produced a bona-fide and high quality material that will deliver the purpose it is intended for. Experience shows that market-driven quality schemes can have a positive impact on collection and treatment of organic waste as well as the end-product itself.

The EPA report identified a need for market plan preparation by existing and new composting facility operators. A guidance note in this regard would be a useful tool for the industry and it is recommended that the industry should lead the implementation of this initiative which is essentially designed for its members.

High levels of awareness and motivation towards composting will benefit source separation schemes and, ultimately, lead to better quality compost products in greater volumes. Better awareness will also help expand the market for compost. Responsibility for improving public awareness in relation to compost and composting is a shared responsibility.

Composting is a very economical way of treating organic waste. Not only is the volume decreased by up to half of the original volume, but also, a range of products can be developed. Public authorities and the public sector should encourage the use of compost. Public funds should be made available to develop new products from composts. In addition, the environmental standards should be similar to an 'average' European country - rather than being unrealistically stringent - which would impede composting in the Irish context.