Case Studies

According to the Knowledge Product (KP) studies commissioned by the Department of Environmental Affairs (DEA), open windrow composting (OWC) takes place in the open air in large, elongated, uniform long, pyramid shaped ‘piles’ of waste known as windrows. The waste feedstock is mechanically shredded and placed into long windrows on a solid, non-permeable surface. Water may be added, depending on the moisture content of the waste. The windrows are turned regularly, either with a wheeled loader or by a specialist windrow turner machine (pulled along by a tractor / dedicated vehicle). The windrows are turned several times during the composting process, which involves the biodegradation of organic wastes by microbes in the presence of oxygen. The whole process takes approximately twelve to sixteen weeks. Use was made of the manual provided by GreenCape and approved by the Western Cape Department of Economic Development and Tourism, ‘Towards integrated municipal waste management: technical guide for technology identification and screening for integrated waste management planning’.

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Technology restrictions

• OWC is a process that can take up to 16 weeks depending on the climate
• The technology requires mechanical treatment to remove contaminants
• Compost turned by mechanical means should not be practised in close proximity to settlements in case of odour / bio-aerosol issues

Main licence requirements for OWC CLICK HERE [Insert link to legislation table] Advantages:

• open windrow composting is a relatively low capital waste treatment process
• saleable product
• land application when convenient
• improves nutrient qualities of soil

Disadvantages:

• Availability of green waste depends on the weather conditions.
• A separate collection system is required for green/organic waste. There can be respiratory/ health issues such as respiratory fungal infections, for example Aspergillosis (an infection caused by a common type of fungus or mould), irritation of the mucosal membranes, skin diseases) associated with bio-aerosols from turning compost, and some odour issues. Bio-aerosols are particles of microbial, plant or animal origin and may be called organic dust. They can include live or dead bacteria, fungi, viruses, particles that cause allergies.
• High use of water during dry periods.

Case Studies

Mechanical Composting of Municipal Waste in Cape Town, South Africa

Read more: (www.wasteplan.co.za/) With a population of about 3.7 million, Cape Town is one of the three largest cities in South Africa. It is a commercial and industrial centre with both processing and manufacturing industries. The average living standard is high and the rate of unemployment low compared to other areas in the country. In the area around Cape Town the agricultural sector is well developed with considerable export of fruit. International demand for organic products has increased awareness of the advantages of using compost and hands-on-knowledge about how to produce it in the agricultural sector. It has also stimulated research in the field at universities. The Cape Peninsula has a Mediterranean climate with mild winters with an average minimum temperature of around 7°C, and hot and dry summers. Most of the city's annual rainfall occurs in wintertime, but due to the mountainous topography of the city, rainfall can vary dramatically for specific areas. The valleys and coastal plains average 500 millimetres of rain per annum, while mountain areas can average as much as 1 500 millimetres per annum. The Peninsula gets frequent strong winds from the southeast. The warm climate is favourable for composting all year round, but the hot and windy summer weather puts high demands on water supply for the compost. A mechanical composting plant, RADNOR, located in Bellville, was in service for many years but was eventually discontinued as the product was expensive to produce and was never used by the wine and fruit farmers in the region. Instead, it was used as daily cover on the Vissershok and other City landfills. The City of Cape Town has one operational open windrow compost plant. Bellville South compost plant is located in Sacks Circle and produces compost for sale. In 2011 the City of Cape Town opened its Kraaifontein Integrated Waste Management Facility. The facility consists of four components: a public drop-off facility, a household waste transfer station, a recycling/material recovery facility and a green waste (plants) chipping facility. The household waste transfer facility has a daily capacity of 960 tonnes, which means this facility can direct 960 tonnes of household waste to the municipal landfill per day. The project is successful with the exception of the pyrolysis (high temperature decomposition) plant which ran as a pilot project and was discontinued. The plant has been taken over by a private company that wants to restart the operation. The green waste area is an outside area where garden waste is chipped with a grinding machine. Residents are allowed to drop off three 1.3 ton loads of garden waste each day. The chipped waste is sent to a facility at another location where it is turned into compost. There are a number of private initiatives using the green waste stream, such as Reliance Composting and WastePlan which operate composting operations.  

Gromor (Pty) Ltd in KwaZulu-Natal, RSA

Read more: (http://www.gromor.co.za/3.Gromor-Compost-and-Fertilizer.htm) Gromor and Farmyard Organics use industrial waste streams from agri-business to produce a variety of compost and growing mediums thus diverting these wastes from landfills. Situated at Cato Ridge in KwaZulu-Natal, Gromor, previously trading as National Plant Food, was founded in the 1960s to handle Rainbow's chicken litter as part of the input. Now trading as Gromor (PTY) LTD it  supplies quality organic-based products containing macro and micro nutrients catering for the retail, wholesale, nursery and agricultural markets. With more than 40 years of experience in the organic industry Gromor recently acquired Farmyard Organics. (http://www.farmyardorganics.co.za/compost/) Compost piles, KwaZulu-Natal Farmyard Organics, Cramond  

Turfnet Diepsloot Composting in Gauteng, RSA

Read more: (http://www.turfgreen.co.za/p/458462/compost) Windrow Compost Turfnet uses a base of all organic materials derived from garden refuse to produce compost, which is a soil amendment material and not a fertiliser. Landscapers deliver their garden refuse to the company’s site at no cost. The refuse, which consists of leaves, flowers, grass and branches, is sorted into piles of green matter and wood. The green-matter piles are hosed down with nutrient-rich water to aid in the decomposition of the material, which is left for 45 days before a ratio of carbon to nitrogen of 20:1 is achieved. Once the material pile reaches its peak stage of decomposition, it is aerated by an industrial turner. Turning the pile is essential to prevent the build-up of harmful ammonia which would inhibit microbial activity. If the green waste were to be disposed of in a landfill, it would biodegrade anaerobically resulting in emissions of strong greenhouse gases such as methane into the atmosphere. If the green waste is composted aerobically it results in the emission of carbon dioxide which has less greenhouse gas effect than methane. The aerobic bacteria used in the composting cycle are bred on site in a static compost system consisting of several alternate layers of grass and manure. The bacteria bred in the system are put back into the compost. If the compost does have an odour, it should be an earthy, pleasant smell. However, if decomposition becomes anaerobic from excess feedstock added under wet conditions, it will begin to smell like ammonia. Turfnet also specialises in vermicompost, which consists mostly of worm casts, compost and decayed organic matter. The worm cast or vermicast is the end product of the breakdown of organic matter by earthworms. Vermicompost is an excellent, nutrient-rich organic soil conditioner that contains water-soluble nutrients and bacteria. The company uses two methods to farm vermicompost.

• The first uses a shallow bin containing bedding material and compost for the worms to live in. Vegetables, which are grown on site, are fed to the worms.
• The second method, uses the American box model, which acts as a raised bed or flow-through system. The worms are fed across the top of the bed. An inch of castingsis harvested from below by pulling a breaker bar across a large mesh screen that forms the base of the bed.

The worms are surface dwellers, and will constantly move towards the new food source. The flow-through system eliminates the need to separate worms from castings before packaging. One ton of vermicompost is sold for R2 000, however, one handful of vermicompost can be spread over a large area because of the high nutrient content. The company employs 12 workers who ensure that all the material dumped on site goes to use. Tree cuttings are used to create bird nesting logs and feeders, while the perimeter wall of the recycling centre has been created out of large stones collected from the garden refuse and around the site. Rainwater is collected and fed through a settlement tank, which is then used to supply the piles of green matter with water.