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Wattala Pradeshiya Sabha tackles degradable waste

Nandana Edirisinghe from NERD


R. Shanmugapriya, Zonal Manager,
Colombo Zone of WMA

The issue of waste management is a major problem faced by many local government bodies as dumping of collected solid waste has created health, social and environmental issues in Sri Lanka.

With the on-going development and programs to beautify the country, a proper mechanism to manage this waste has become an urgent requirement for Local bodies.

They are compelled to implement a sophisticated solution to address this issue especially in densely populated areas instead of just looking for dumping grounds.

Although there is a demand for a proper waste management system, lack of mechanisms to tackle this issue has put many of the local authorities in dilemma. At the same time, the lack of a system to address these issues has also put the costly efforts made by some institutes to waste.

The bio-gas generation plant in Dickowita in the Wattala area implemented by the National Engineering Research and Development (NERD) Centre initiated in 2002 under World Bank funding is one such project that did not yield the anticipated results.

It is considered to be the biggest-ever bio-gas plant by NERD to manage degradable waste collected from the Wattala Pradeshiya Sabha, the administration of the plant was shifted from pillar to post but is now under purview of the Waste Management Authority of the Western Provincial Council.

This plant has 16 digesters (tanks), each with a capacity of 40 metric tonnes to produce bio gas out of the market waste collected from the area. However, the absence of a proper mechanism to separate degradable waste to feed this plant, the NERD centre handed over the plant to the Wattala Pradeshiya Sabha for operational purposes.

The Wattala Pradeshiya Sabha handed it over to a private institute called Burns Environmental Technologies (Pvt) Ltd in 2004 due to operational problems and it is now abandoned for years since there was no proper mechanism to feed the plant with separated market waste.


Garbage being filled into garbage tanks

Digesters being filled with degradable waste.
Pic: Chinthaka Kumarasinghe

It was in such a backdrop under the directive of the Chief Minister of the Western Province and on the initiative taken by the Wattala Pradeshiya Sabha, Chairman Thiyagaratne de Alwis the bio-gas plant was taken under the Waste Management Authority of the WPC in July 2011", R. Shanmugapriya, Zonal Manager, Colombo Zone of WMA said explaining the present situation of the bio-gas plant.

The bio-gas plant is now gradually becoming operational as the required mechanisms are put in place to provide a permanent solution to the garbage issue in the Wattala Pradeshiya Sabha and the Wattala Urban Council.

Since it was abandoned the tanks were corroded and the automatic systems were not operational by the time WMA took over the project.

We had two objectives at the time we took over the project. We had to repair the tanks and had to create a mechanism to separate garbage at the site to make the plant operational, explaining the challenge faced by the WMA Shanmugapriya said.

Since it is operated as dry digesters it has to be fed with market and degradable waste and once the tank is full it has to be covered and sealed it with water. In a week it emanates methane gas under anaerobic digestion of the degradable waste and for three months it will generate bio-gas.

Microbes have to be introduced into the tanks and we use cow dung as the source of mechanisation bacteria. We get about a half feet layer of cow dung at the bottom of the tank before filling degradable waste into the tank, she added.

The Wattala Pradeshiya Saba and the Wattala Urban Council has initiated a (Green Basket); project to collect only separated degradable waste directly from households and bring it into the bio-gas plant.

The biggest problem faced by waste management is that people are not yet used to waste segregation in their homes. They dump waste without segregation and it is difficult to manage the waste. With the introduction of this Green Basket program this bio-gas plant is in the process of receiving the separated waste directly to the plant.

We started the green basket program from Alwis Town, Convent road and Hendala Road and distributed these baskets requesting them to put only degradable waste into these baskets. If polythene is put into these baskets we cannot make use of the degradable waste for bio-mechanisation as polythene is harmful to microbes.

We have set up committees and educated labourers about the mechanism. We visited the houses and handed over these garbage bins to the people. We deployed separate vehicles to collect these degradable waste", she said.

We started the program with 2,000 households and we have expanded it to 6,000. The entire Hendala area comprises about 15,000 houses. This year we hope to cover another 6,000 houses to bring the number to 12,000, she said.

The bio-gas plant needs eight metric tonnes of waste per day". We started the program with two metric tons and now we get four metric tonnes of garbage per day, she added.

The daily waste collection of the Wattala Pradeshiya Sabha is 35 metric tonnes while the daily collection of solid waste by the Wattala UC is 22 metric tonnes. The Wattala Pradeshiya Sabha provides six metric tonnes per day and the Urban Council provides two to three metric tonnes.

This will be a relief for the Wattala Pradeshiya Sabha and Wattala Urban Council which faced a difficult situation due to the non availability of a dumping site as the number of metric tonnes of degradable waste is reducing as the bio-gas plant is expanding its capacity by increasing the number of tanks with the support of the NERD Centre.

According to Nandana Edirisinghe, of NERD this bio-gas system is based on the NERD design of dry garbage.

Now the WMA is of the view that it is feasible to deviate from the dry batch system because it requires an open system for a longer time but a bad odour emanates. They request to convert it to a continuous system. The advantage of a continuous system is that it feeds the tanks daily and has a water seal. As a research project NERD undertook to convert two digesters to the continuous system, he said.

That is the project we have at present. We signed an MoU with WMA for another project to make use of the bio-gas to generate electricity. At the moment they are operating two or three digesters. We are trying to use our own engine and bring it here and fix it as a research to operate a chopping machine from the electricity that it generated by using the gas", he said.

The plant needs to chop vegetable waste and the chopping machine requires 11 kilo watts for this operation.

We want to see whether we can generate power and operate the chopping machine. Based on the results of that project the WMA will try to expand and generate its own power for lighting and other purposes.

That is the project we have undertaken at present".

We measure 50 to 55 percent of methane gas production from one tank and that is acceptable to generate power. We have to clean the gas emanating from the digesters, after removing the hydrogen sulphide", he said.

Initially, the plant needs 11 Kilowatts and we can increase it operating two to three digesters simultaneously. That is enough to generate power to operate the chopping machine. If it is successful we can fill all the digesters and generate power from the power generator and generating a maximum of 20 Kilo watt. Based on our research output the WMA will purchase a better generator to produce more electricity, he said.

According to Shamugapriya the WMA is thinking of modifying the plant further. At present we are operating only two digesters and at the end of August based on the research findings we are going to develop another three digesters, she said.

There is a huge demand for the collection of fish and meat waste. This can't be done on our own because they are nitrogen sources and good for bio-gas. But the problem is the odour. As the covers of these digesters are open it will emanate a bad odour. At present we are only concentrating on food and vegetable waste. Otherwise we can make use of the other degradable waste and increase the efficiency of the bio-gas production.

Almost 55 metric tonnes of waste is generated both from Wattala PS and Wattala UC area and out of that 60 per cent is degradable waste. In the future we will be able to get more than 30 metric tonnes of degradable waste both from Wattala UC and PS to develop this project and to cover the entire Wattala area. So daily we can use 30 metric tonnes of waste and the bio-gas plant can provide a solution for more than half of the garbage collected from Wattala area.

That covers the entire degradable waste in Wattala area and after that we have only polythene, plastic and other non degradable waste. This is not a problem and people can store them for weeks. If they start the segregation practice, waste is not a problem", she said.

The WMA has purchased a bail machine to crush plastic to be operated by the electricity generated from the plant. "So the WMA will also be able to accept the plastic and polythene also for this plant in future, she added.

The incinerator that is being installed at the plant will provide a solution for the waste collected from the area by making use of the gas produced from the plant, she said.

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