Primary producer transforming waste into green energy

Clean water and green energy technology from Global Water Engineering (GWE) has been used by Chokyuenyong Industrial in Thailand to cut effluent COD pollution levels at its cassava production plant by more than 95%. The gas from its wastewater has also been extracted to power its boilers and generate electricity for its own use and to sell back to the provincial grid.

Processing 1200 tonnes of cassava roots a day, Chokyuenyong Industrial uses GWE anaerobic technology with a capacity of 3200 m³ effluent a day. Commissioned and refined over the past three years, the Chokyuenyong installation:

• Cut the Chemical Oxygen Demand (COD) pollution level of influent wastewater from 22,500 mL/L (14,525 mg/L biochemical oxygen demand, BOD O₂) to less than 1125 mg/L, resulting in cleaner discharges to treatment ponds (and in the process dramatically reducing odour from typical ponds);
• Returns up to 2.7 MW of electricity a year to a provincial power grid, PEA;
• Saves the equivalent of up to 21,000 L a day of fuel oil by producing up to 34,000 Nm³ of bio gas, which is used to power the boilers and heating equipment used extensively in cassava drying and processing and to generate electricity for the large amounts of rotating equipment used in processing;
• Generates carbon credits under the United Nations’ Framework Convention on Climate Change, through which it earns internationally tradeable CER certificates, representing the right to emit one tonne of carbon dioxide or carbon dioxide equivalent.

Chokyuenyong’s process involves an equalisation basin (total volume 1600 m³) with submerged agitators, degasifying basin with agitator (24 m³) inline pH adjustment, NaOH storage tank (25 m³) UASB methane reactor (active volume 4800 m³) and biogas flare (standby, for use if required). The technology is all above ground for simplicity and ease of maintenance.

GWE’s anaerobic treatment significantly reduces the plant’s carbon footprint by avoiding the release of methane gas into the atmosphere. The wastewater passes through several pre-treatment steps before entering a GWE methane reactor in which the wastewater’s organic content (COD) is digested by bacteria in a closed reactor, degrading the compounds and converting them into valuable biogas and cleaned effluent. Biogas from the process is collected and re-used as renewable fuel in the plant’s thermal oil boiler, saving money that would otherwise be spent on bunker oil. Chokyuenyong’s excess biogas is used in electrical power generation.

Results achieved at Chokyuenyong can be even further improved by also converting 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, says GWE.