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by B. F. A. Basnayake

The University of Peradeniya has developed a unique system for composting Municipal Solid Waste (MSW). Called the Inclined Step Grate (ISG) composting unit, it works at high temperature to ensure sanitary compost of very high quality.

The quality of compost has been tested and recognised not only by the academic and scientific community but also by leading enterprises in marketing and usage of compost. The pilot and demonstration composting unit at Meewathura, funded by the Urban Development Authority (UDA), the World Bank (MEIP) project and a private company, handles wastes from three local authorities: Udunuwara, Yatinuwara and Gangawatakorale in the Central Province.

tipping charges

The tipping charges for handling and disposal of wastes is presently Rs. 150/tonne, the capacity being 6 tonnes of wastes per day, producing 25 tonnes of compost per month.

The University of Peradeniya, recognising the gravity of the problem of urban solid waste disposal, established a Solid Waste Management Research Unit (SWMRU) in the Department of Agricultural Engineering, Faculty of Agriculture, to continuously support the development of technologies in managing MSW. The SWMRU is self-sustaining while paying for labour on contract.

However, the pilot plant was set up to generate adequate capital for maintaining and undertaking further research since depreciation of the unit is not accounted for in the process.

The Colombo Municipal Council (CMC) currently pays a tipping of Rs. 550/tonnes of waste, whereas the ISG system requires Rs. 350/tonne. Furthermore, it is an ecologically balanced system compared to others. The University of Peradeniya has decided to grant licences for this technology to any firm or local authority willing to undertake integrated MSW management projects.

Most of the MSW compost projects in the world have failed due to the poor quality of the compost. In many of the projects the concept has been to get rid of the waste as quickly as possible and therefore the proponents have resorted to using accelerators/effective microorganisms EM).

degradation rate

The degradation rate is too rapid with these specific types of microbes, leaving too little carbon in the made compost and leading to destruction of soil properties when applied.

Tropical soils in particular require large quantities of organic matter for sustaining agricultural production and thus the Faculty of Agriculture has put more effort into producing a MSW compost of high quality to the required sanitary standards.

Composting alone is not enough. For integrated solid waste management, the approach is to maximise resource use of local authorities, re-use, recycling including composting, recovery of material, energy generation through anaerobic digestion (biogas) while using incineration requiring final disposal in landfills for certain types of waste and finally, ensuring adequate sanitary landfill capacity.

waste generation

The waste generation rates change throughout the year as well as from place to place and none of the available technologies alone (without integrated MSW management) are able to cope efficiently with large quantities of waste generated seasonally. It is also important to consider socio-economic aspects of the waste generators so that an appropriate participatory approach could be introduced as part of this integration.

There will always be some waste that needs final disposal. Ash from incineration requires secure landfills because it is very hazardous when reactive. A maximum of 20 per cent of polythene could be recycled since it is a by-product of petroleum. Market forces will determine the percentage that could be recycled.

After a study by a selected number of Asian National Research Institutes (NRIs) - from Tongji University in China, Anna University in Chennai, the University of Peradeniya in Sri Lanka and Kasetsart University in Thailand, coordinated by the Asian Institute of Technology (AIT) with technical and financial support from the Swedish International Development Agency (Sida) a project was launched in April 2001 titled "Solid Waste Landfill Management in Asia" under the Asian Regional Research Programme on Environmental Technology. Each of the NRIs concentrates on one or two major technical issues.

The SWMRU of the University of Peradeniya along with the AIT, is entrusted with the task of developing technologies for 'landfill pre-treatment', whereas the Anna University NRI specialises in landfill mining and the other NRIs deal with yet other aspects.

Sida is providing required laboratory equipment, funds for research students, consumables for fabrication of devices, equipment and laboratory chemicals, etc. Also, Sida and AIT have emphasised the need for knowledge and technologies developed to be transferable since this is a regional project and recognised the need for basic research in the initial stage of the project while developing the required technologies. Therefore a kinetics study of microbial decomposition of organic matter was required while landfill pre-treatment, composting and biogas technologies were being developed.

Interestingly, the kinetics study is leading to a better understanding of biochemical transformations including plant growth. It could be a powerful tool to predict yield of a plant at the initial stage of its growth, better effluent treatment, optimism of bioreactors, etc. The findings have led to optimisation of composting conditions for rapid stabilisation of wastes while safeguarding the carbon content and producing both larger quantities and higher quality of MSW compost.

The pre-treatment study at Peradeniya is also examining the possibilities of achieving high compaction of remaining non-biodegradable wastes like polythene prior to landfill.

At a later stage more advanced feasible technologies for managing these wastes and landfill mining could take place. The AIT and Sida review the performance of each NRI quarterly, providing expert guidance for research while allowing flexibility for invention of new methods and technologies by individual researchers.

study conducted

In a study conducted in three local authorities in Sri Lanka in order to identify locations for landfills, it was confirmed that it is still difficult to site a common landfill without the support of all the relevant Government Authorities and the local communities.

The findings were published at the last Congress of The Postgraduate Institute of Agriculture (PGIA) held in November 2002. The response is positive and the study is being continued so that a common policy could be formulated.

The Japan International Cooperation Agency (JICA) team, at present engaged in improving the manage of MSW in Sri Lanka, has the same vision as the AIT - Sida project and joint efforts are being made for public awareness and for development of plausible solutions.

(The writer is a Senior Lecturer in Energy and Waste Management, Department of Agricultural Engineering, Faculty of Agriculture, University of Peradeniya)

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