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Tropentag, September 19 - 21, 2016 in Vienna, Austria

"Solidarity in a competing world - fair use of resources"

Strength and Disintegration Characteristics of Compost Pellets from Urban Waste in Sri Lanka

Lakshika Hettiarachchi1, Johannes Paul2, Sudarshana Fernando2, Nilanthi Jayathilake2, Sanja Gunewardena1, Felix Grau3,2

1Moratuwa University Sri Lanka, Dept. of Chemical & Process Engineering, Sri Lanka
2International Water Management Institute (IWMI), Resource Recovery and Reuse (RRR), Sri Lanka
3University of Applied Sciences Osnabrueck, Fac. of Agricultural Sciences and Landscape Architecture, Germany


Recovering resources from urban organic wastes can serve agricultural production as well as provide cost savings through volume reduction. However, in both liquid and solid waste management, the magnitude of planned resource recovery so far remains restricted in low-income countries, although the agricultural value of both resources is well recognised.
In Sri Lanka, urban waste composting is well known, but marketing is poor and so is Word-of-Mouth promotion as standard compost receives limited attention from farmers.
To address this issue, the IWMI implemented a resource recovery treatment project based on co-composting of nutrient rich fecal sludge and organic municipal solid wastes. The project looks at the safe production of co-compost, compost blending and pelletizing, its agricultural application, and the economic viability of the whole process. This paper summarises results on the pelletizing process which makes compost transport, storage and application easier, and also allows to influence nutrient release.
Pelletizing increases the density of the compost material by 30%. In general, compost-pelletizing process consists of compost drying and pulverisation prior to pelletisation. This research confirmed that the above two steps can be successfully eliminated while reducing energy consumption and process cost.
With the right pressure and humidity, compost pellets can also be produced without binding agent. However, binding agents can increase pellet strength, as compared to pellets without binders. Most importantly, pellets without binding agent did not disintegrate in immersed water for a testing period of one month. Rice flour binder added by 3 % was able to achieve a quick pellet disintegration within 3 days. Evidence proved that careful selection of binding agent could control the time for disintegration while enabling the production of a tailor made fertiliser for crop type, depending on the crop nutrient demand. In addition, “roller and die” pelletizer appears more suitable in compost pelletizing, compared to ‘extruder' models.
This research is supported by the German Ministry for Economic Cooperation and Development (BMZ) through GIZ/CIM.

Keywords: Co-composting, pelletisation, resource and nutrients recovery, urban waste

Contact Address: Johannes Paul, International Water Management Institute (IWMI), Resource Recovery and Reuse (RRR), 127 Sunhil Mawatha Pelawatta, Battamarulla, Colombo, Sri Lanka, e-mail: j.paul@cgiar.org

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