Thai starch producer sets global environmental benchmark transforming wastewater into green energy for internal use as well as for sale to local grid

Global Water Engineering partnered with Chokyuenyong Industrial in Thailand to reduce the effluent pollution levels at the latter’s cassava processing plant while using biogas generated from the effluent treatment to power the plant’s boilers and also produce electricity. Chockyuenyong Industrial uses GWE’s anaerobic technology with the capacity to treat 3,200 m3/day of effluent generated from processing 1,200 tonnes of cassava roots every day. The technology was installed by Retech Energy, the local agent of GWE.

Plant overview

GWE CEO Jean Pierre Ombregt praised the installation as an international benchmark achieving top environmental standards in wastewater treatment while generating green power and carbon credit profits. GWE has successfully built and commissioned more than 75 biogas utilisation systems for clients worldwide.

Commissioned and refined over the past three years, the Chockyuenyong installation’s key benefits are as follows:

* Cut the COD pollution level of influent wastewater from 22,500 ml/l (14,525mg/l Biochemical Oxygen Demand, BOD O2) to less than 1125 mg/l, resulting in substantially cleaner discharges to treatment ponds and ultimately the environment (and in the process, achieving dramatic reduction in odour)

View of the two scrubbers used to remove H2S in the biogas before it is sent to fuel the gensets

* Supplies up to 2.7MW of locally produced ‘green’ electricity annually to the provincial power grid, which serves areas distant from major generating sources

* Produces up to 34,000 Nm3 of bio gas, which is used to power the boilers and heating equipment used in cassava drying and processing and also generate electricity for the large amounts of rotating equipment used in the process, saving the equivalent of up to 21,000 litres/day of fuel oil.

* Generates carbon credits under the United Nations’ Framework Convention on Climate Change, through which the company earns valuable internationally tradeable CER certificates, representing the right to emit one tonne of carbon dioxide or carbon dioxide equivalent.

“Chokyeunyong’s achievement has implications for a broad range of primary processing industries and particularly for cassava-producing countries that turn this relatively low-cost raw material into high-value starch for domestic and international markets,” said Ombregt.

The granular sludge taken from the methane reactor, which constitutes the heart of the system. The sludge converts the pollutants in the wastewater into biogas.

The UN’s Food and Agriculture organisation estimates that each year, some 60 million tonnes of starch are extracted from a wide range of cereal, root and tuber crops for use in a staggering variety of products: as stabilisers in soups and frozen food, coating on pills and paper, adhesives on stamps and plywood, as stiffening agent in textiles, raw material for making ethanol, in non-food products, such as pharmaceuticals and thermobioplastics and even as binder in concrete.

Ombregt continued: “Thailand, as the world’s largest exporter of starch, is well placed to show leadership in how to achieve progress in an environmentally friendly manner. Our client, with excellent guidance from Retech Energy’s team led by Managing Director Hans Westphal, has achieved results that now serves as an international model of how to get the process right.”

Chokyeunyong’s process involves an equalisation basin (total volume 1600m3) with submerged agitators, degasifying basin with agitator (24m3) in-line pH adjustment, NaOH storage tank (25m3) UASB methane reactor (active volume 4,800m3) and biogas flare (standby, for use if required). The technology is installed above-ground for simplicity and ease of maintenance.

The wastewater’s organic content (COD) is digested by bacteria in a closed reactor, degrading the compounds and converting them into valuable biogas and clean effluent. The biogas in the plant’s thermal oil boiler, saving money that would otherwise be spent on bunker oil.

“Food product processing plants such as Chokyeunyong’s depend extensively on electrically powered rotating equipment, so it is very wise to have an almost infinite fuel source that provides a hedge against rising oil prices and which can also be sold back into the grid,” said Ombregt.

Tawatchai Yuenyong, President, Chokyeunyong Industrial with the generator sets that return power to the grid

Chokyeunyong Industrial President Tawatchai Yuenyong said his company’s investment has been justified in terms of the environmental and financial results and enhanced its standing in the local community as a “good neighbor” “Our investment programme has had a very happy ending,” he said.

Results achieved at Chokyeunyong can be even further improved by converting also its solid wastes (residual pulp from the roots, after starch extraction) into biogas as well, using GWE’s RAPTOR treatment system for solid organic residues. RAPTOR stands for Rapid Transformation of Organic Residues. “It’s a powerful liquid-state anaerobic digestion process which consists of enhanced pre-treatment followed by multi-step biological fermentation to optimise conversion of almost any organic residue or energy crop into biogas, valuable electricity or heat,” said Ombregt.

For further information, contact Marc Eeckhaut, Executive Vice President, Sales and Marketing, Global Water Engineering, mail(at)globalwe.com