Biogas from faeces

In one application of the Ecological Sanitation (EcoSan) strategy, concentrated black-water (faeces and water) is processed to generate biogas for cooking meals to feed over 1,000 students staying in two rural secondary school hostels in Kuching Division.


one application of the Ecological Sanitation (EcoSan) strategy, concentrated black-water (faeces and water) is processed to generate biogas for cooking meals to feed over 1,000 students staying in two rural secondary school hostels in Kuching Division.
IT may not conjure up the most pleasing of images but a technology under the Ecological Sanitation (EcoSan) concept has been developed in Sarawak to produce biogas from human waste for the purpose of cooking.


In one application of the Ecological Sanitation (EcoSan) strategy, concentrated black-water (faeces and water) is processed to generate biogas for cooking meals to feed over 1,000 students staying in two rural secondary school hostels in Kuching Division.

State environment advisor Datuk Dr James Dawos Mamit said a research team from Universiti Malaysia Sarawak (Unimas), led by him and Professor Lau Seng, has established EcoSan systems in two local rural secondary schools — SMK Padawan, about 50km south of Kuching City and SMK Tebakang, about 80km southeast of Kuching City.

“These are our pilot projects and the first in Malaysia so far,” he added.

According to Dawos, an EcoSan concept looks at the entire system, consisting of social and natural components in consideration of spatial and temporal material flows.

In practice, a frequently applied EcoSan strategy is to separate faeces, urine and grey water, thereby minimising the volume of valuable drinking water needed to flush away excreta.

It enables an almost complete recovery of all nutrients, trace elements and energy contained in household wastewater and organic waste, and their application to any array of uses.

He said an essential step in the process is the appropriate treatment and handling of materials during the entire treatment and re-use process to ensure sufficient sanitisation of the excrement and the protection of public health.

Dawos, who is Mambong MP, revealed the projects in the two schools had modified toilets to accommodate one flushing a day to reduce water usage and make the black-water more concentrated for better production of biogas.

According to him, the model of Closed-Canal Toilet (CCT) generates only about 500 litres of black-water (faeces and water) a day from about 150 students where as in normal household flush toilets in Malaysia, the volume of black-water generated is about 20 litres per person per day.

“The CCT system is able to reduce water usage by about 12 to16 litres per person per day or 20 to 40 per cent less.

“This process entails three benefits — substantial saving of water, reduction in wastewater quantity and allowing the concentrated wastewater to generate biogas.”

Dawos said the biogas reactor, also known as digester, is a dome-shaped device, constructed at SMK Padawan from bricks with a capacity of 30 cubic metres while in SMK Tebakang, two reactors of similar capacity are constructed.

He explained the reactors received the black-water from the CCT and initiate the anaerobic digestion of the organic matter.

Since the black-water was still too low in organic matter, he said, the addition of the organic matter from food waste and spent cooking-oil and grease made the process more efficient.

The methane-rich gas produced is used for supplementing Liquefied Petroleum Gas (LPG) in the school kitchen, he added.

It is estimated that 500 litres of black-water a day from 150 students in SMK Padawan can produce about 70 cubic metres of biogas.

In SMK Tebakang, 300 students can generate about 135 cubic metres of biogas daily. It is estimated that both schools can save about RM1,750 to RM2,100 per month from reduction in the use of LPG.

Dawos said EcoSan released digested organic waste from the biogas reactor to the expansion chamber free of foul odour.

This process, he added, provided three benefits — efficient treatment of black-water, production of biogas for cooking and treatment of solid kitchen wastes.

He explained that sludge released from the biogas reactor was retained initially in the expansion chamber and then discharged into a sand filter where the remaining undigestable solids are separated from the liquid and where drying under direct sunlight takes place.

Drying kills most of the bacteria as the built-up heat can reach 70 degrees celsius. The liquid portion from the sand filter is collected in a container and is rich in nutrients.

“It is thus suitable for direct use as a liquid fertiliser in the schools’ gardens while the dry sludge is collected from the sand filter, and used as compost mixture, or directly for soil conditioning or mulching material for plants.”

“The benefits derived from this process are production of organic fertiliser from the liquid and solid sludge as well as protection of receiving streams from contamination, thereby preventing eutrophication and providing of better hygiene.”

The project’s total cost at SMK Padawan is about RM210,000 with financial contributions from Rotary Club International (RM140,000) and a federal government grant (RM200,000) while that at SMK Tebakang is about RM280,000 with a financial grant from the state government.

Dawos said total costs of both projects were incurred only in capital expenditure and labour. The remaining sum from the SMK Padawan project is used for further research on the two EcoSan projects.

According to Dawos, the school authorities handle maintenance and management of their systems.

“Maintenance cost is very low. Since the systems in the two schools became operational in November 2007, there hasn’t been any maintenance at all.”

He said the biogas generated daily by EcoSan is used for cooking meals to feed over 1,000 students staying in the schools’ hostels.

“Thus, a saving of RM1,750 to RM2,100 per month from purchasing LPG is proof of EcoSan success in rural Sarawak.”

Dawos pointed out that the exhausted organic waste, used as fertiliser in the school gardens, was another benefit.

“Over the long term, the capital costs of setting up EcoSan will be recouped by savings from LPG.”

He said the most efficient use of biogas is for cooking.

“This gas burns with a blue flame without any odour. It can also help illuminate a house through biogas mantle lamps.”

EcoSan works on the principle that urine and faeces are not simply waste products of the human digestion process but rather, an asset that, if properly managed, can contribute to better health and food production and reduce pollution.

EcoSan latrines store and prepare faeces for use in agriculture by encouraging the formation of humus with the addition of wood ash and/or soil, allowing the application of urine as fertiliser, in case urine is separated, and removing faeces and urine from the immediate environment, thereby contributing to better health.

They are dry systems that make contamination of groundwater extremely unlikely.