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Turning industrial waste into compost

A successful environmental-protection and resource-conservation project in Brazil

by Winfried Schmidt

Citrus farmers in the Vale do Cai region of Porto Alegre's hinterland who switched to ecofarming have set up their own company that is developing a method of turning organic waste from the region into compost by aerobic fermentation. The compost is to be distributed among the shareholders. Consultancy is being provided to the farmers via a GTZ-supported scheme.

Composting residues from the food industry is an economically viable approach to disposal and supplies ecofarmers with low-cost fertiliser for their citrus crops. The GTZ-assisted project in Brazil has succeeded in combining environmental protection with economic interests. The author describes how these successful measures took root.

Most foods consumed and exported by Brazil are produced and processed by the agro-industries in the Federal State of Rio Grande do Sul. Enormous dumps of organic waste are scattered over the State.

Enforcing stricter waste disposal legislation is not an easy task because the authorities are having difficulties in setting limits and ensuring that they are adhered to. Nor has it yet been possible to break the waste producers' resistance to disposing of the residues using the latest technology as this entails very high costs for them.

Problematic organic industrial waste

The state environmental authority FEPAM has set up a hazardous waste cadastre with the assistance of Technical Cooperation funds in which 383 large, medium and small-scale food and leather processing industries are registered in greater Porto Alegre alone. In most of these industries, organic waste from the production process is not being disposed of in an environmentally sound manner.

For example, TANAC and SETA, the producers of organic leather tanning agents, generate some 500,000 tons of acacia bark, a residue from tannin extraction, each year and dump it near the factory grounds. In one very serious case a dump was even established along a riverside in the outskirts of Montenegro without sealing the foundations, and since 1990 the urban groundwater there has been contaminated with lignin.

The state environmental authority FEPAM has declared the bark extract dump a contaminated site. Since 1995 operators wishing to prolong their operating licences have had to guarantee that residues from ongoing production be disposed of according to the latest state of the art and in the long term undertake to rehabilitate any contaminated sites generated in earlier production years.


The Vale do Cai region in Porto Alegre's immediate hinterland is a traditional citrus fruit growing area. Full time and part time farmers cultivate average cropping areas of 5 hectares, growing mandarines, lemons and oranges using conventional methods. The PRORENDA project, an assistance programme of German Technical Co-operation, is promoting small farmers in the Harmonia region. It gave the first impulses for setting up co-operatives and organising marketing in 1990.

In this context a group of mostly young citrus farmers decided to turn to eco-farming and gradually switched over their fruit plantations to less aggressive cropping methods without using mineral fertilisers and pesticides. They quickly realised that for the new farming system to be sustainable, artificial fertiliser must be replaced by high quality organic compost.

A parallel survey revealed that large volumes of organic residues from the agro-industries were dumped in the region. Pilot tests demonstrated that the residues could be transformed into organic compost without this requiring any large-scale technical input.

Organic waste composting project

The conditions were a favourable launching pad for the ECOCITRUS concept. Industries, for their part, were faced with the problem of coping with the new regulations to rehabilitate their contaminated sites and organise appropriate disposal paths for everyday production waste. A group of committed ecofarmers on the other hand, was working to obtain approval to use these waste products as raw material for their composting process.

The ECOCITRUS group established itself as a company with the goal of turning organic waste from the region into compost by aerobic fermentation. The articles of association underlined the company's non-profit-making goals. The final product - the compost - is to be distributed amongst the share-holders, enabling them to save the high costs for mineral fertiliser.

The organic products obtained are expected to be an impulse for the market. Initial surveys indicate that organic citrus fruits fetch a high price on the Porto Alegre and Sao Paulo markets.

The group rented a 3.4 hectare site. The 20 shareholders levelled and compacted the ground themselves, built a collecting tank for the surface water and a sealed basin for the liquid fruit pulp, a component of the composting process. To date, the company associates have covered the operating costs by a monthly membership fee of 150 Real (approx. DM 230).

The GTZ-assisted "Environmental and Resource Protection FEPAM" project provided consultancy to the farmers during the experimental phase. Long-term and shortterm experts gave technical assistance on designing the plantsite and optimising the composting process.

The composting process

The chief ingredients of the compost (expressed as m³ per year) are: 50,000 m³ acacia bark, 6,000 m³ ash, 4,000 m³ charcoal, 3,000 m³ fruit pulp from orange juice manufacturing and 2,000 m³ paunch contents and other slaughterhouse waste. The organic wastes are moistened with the fruit pulp, mixed and deposited in 1.5 m high triangular stocks. Although the addition of fruit pulp with pH-value 5 hinders the composting process at the beginning, this problem is remedied by adding ash from burned acacia wood. The alkaline ash raises the pH-value to 6-7, which is suitable for composting. Absorptive charcoal binds any unpleasant odours generated when mixing the raw materials and during the composting process itself. Thanks to the high proportion of bark sufficient structural material is available, the oxygen supply is adequate and surplus heat is ventilated from the centre of the stock.

These two processes (oxygen supply and heat removal) are vital to composting and are supported by perforated plastic pipes sunk vertically into the stock. Once prepared, the stocks are covered with a layer of acacia bark to stop any unpleasant odours from escaping and to protect the composting material from drying out or becoming too wet depending on the weather. When the stock content is turned over, the moisture content can be regulated, if necessary, by adding water from the rain collection tanks. The rotting process takes 6 - 9 months depending on the season.

Promising results

The first results are very promising. The quality control of the initial compost series gave the following values: moisture content 40 %, organic content 40%, C/N ratio 10/1, nitrogen content 2%. The pure organic compost obtained does not contain heavy metals or other pollutants.

ECOCITRUS is presently tackling the problem of reducing the turn-around time of the material in the compost yard and ensuring that the high volumes of material are processed better and more efficiently. 21,000 tons of organic compost have been produced to date-enough to provide organic fertiliser for 400 hectares of citrus plantations.