Sago starch factory effluent: salvaging a potential pollutant

The Sago Palm (Metroxylon sagu) grows well with minimum care in swamp and peat areas otherwise inhabitable for most other crops. It has a high starch yield: one palm may yield between 150 to 300 kg of starch.

Sarawak exports up to 40,000 tons sago a-year and the effluent (sago starch factory wastewater) resulting from sago debarking and processing are often discharged to nearby rivers. This inevitably contributes to river pollution. A typical sago mill consumes about 1,000 logs per day, generating a minimum of 400 tons of slurry effluent which contains about 5% solids (20 tons).

The Biochemistry Laboratory at the Faculty of Resource Science and Technology, UNIMAS under the supervision of Professor Dr Kopli Bujang has for the past couple of years been working on exploiting the potential of the sago waste solids in the slurry effluent, looking at the possible generation of biofuel.

Although the use of sago starch is a clear possibility, the production of biofuel from a food source doest not seems appropriate especially when one is looking at the rising prices of food supply around the world. The group, therefore, have put their focus on using the sago waste solids. This not only shift the reliance away from the sago starch but also minimise the effects of environmental pollution from the sago factories.

To begin with, the research group has successfully established a complete bench-plant in campus, in preparation for the pilot-plants which are currently being constructed at Kotobuki (Japan) and Malaysia under the supervision of a Malaysian private company.

The parameters are currently being set to increase the filtration efficiency of the slurry effluent to carve the possibility of harvesting the sago fibres for production of fermentable sugars in a continuous pilot-scale level. Using an in-house modified enzymatic process, initials attempts were able to extract 20-25% of fermentable sugars from sago fibres. At the conservative conversion of 20%, it is possible to produce a minimum of 4 tons/day of fermentable sugars from the slurry effluent produce in a typical sago mill.

Two units of hydrolysers and one unit of rotating vacuum pump filter for continuous filtration of the sago effluent have been developed and constructed to enable the efficient hydrolysis of sago fibres at the pilot-scale level. These will make a convenient attachment to the pilot-plant for a maximum production of biofuel and other by-products.

One of the other by-products currently investigated is the alga Spirulina culture on the filtered sago effluent. Standard parameters have been established to allow for the culture to be harvested after 10 to 20 days. The final objective is to market this product as a source of protein and organic health supplements, adding further commercial value to a potential pollutant.