Multimillion yearly benefits flow to early adopters of green energy from wastewater

Early adopters of anaerobic technology used to convert wastewater into green energy are now reaping millions of dollars a year in benefits by replacing fossil fuel, producing less pollution as a result, and achieving much cleaner effluent water into the bargain.

A major producer of native tapioca starch, sweeteners and modified starch in Thailand, for example, uses GWE anaerobic technology within its wastewater plant to produce up to 70,000 Nm³ (normal cubic metres) a day of biogas at 70% methane (CH₄). This corresponds to approximately 43,750 kg per day of heavy fuel oil, worth around $12.27 million a year (assuming a plant running 330 days a year at full capacity and a heavy fuel oil price of 0.83c US per litre).

Operating with a capacity of 6000 m³ a day of wastewater, containing 150,000 kg COD, the Corn Products International plant, commissioned in 2007, also achieves high effluent purification levels of more than 95%, reducing COD loads from 25,000 mg/L COD influent to 1250 mg/L effluent.

Anaerobic technologies such as those applied in this Corn Products International plant generate extensive benefits.

“Anaerobic technology is particularly brilliant for food, beverage and agro industry applications, such as this installation,” says Global Water Engineering CEO Jean Pierre Ombregt.

“While generating green energy from wastewater doesn’t get as much attention as other green technologies - such as wind power, for example - early adopters such as this plant are reaping benefits year after year.”

“The energy yield from the anaerobic digestion of the starch factory’s wastewater is more or less equal to the fuel demand for the mill’s production, making the factory just about self sufficient for its fuel energy needs. The biogas is used in four factory steam boilers, replacing heavy fuel oil.”

“The savings in such projects are permanent and ongoing, while the cost of typical installations can be repaid within a couple of years, sometimes even a year.”

Anaerobic digestion is a biological process whereby bacteria break down organic material into more basic compounds without requiring oxygen as a component of the process. Modern anaerobic processes concentrate the process in environmentally harmonious closed reactors, operated under ideal temperature and process control to optimise waste consumption and, in the process, generate large quantities of CH₄ from the organic materials in the wastewater.

“The quantities of methane produced can diminish or even completely replace the use of fossil fuels in the production process,” says Ombregt. “One tonne of COD (chemical oxygen demand) digested anaerobically generates 350 Nm³ of methane, equivalent to approximately 312 litres of fuel oil, or about 1400 kWh of green electricity.”

As a result of their efficiency, anaerobic digestion facilities have been recognised by the United Nations Development Programme as one of the most useful decentralised sources of energy supply, as they are less capital intensive than large power plants. They can also benefit local communities by providing local energy supplies and eliminate the need for large and often smelly and environmentally challenging anaerobic lagoons.

“Most industries have not realised the potential of this green energy cash cow,” says Ombregt. “They have mainly been focusing on treating their effluent to meet local discharge standards at the lowest possible investment costs. By doing so, wastewater treatment installations have only generated additional operating costs and have never been seen as revenue generators.

“However, applying anaerobic wastewater treatment sheds a whole different light on the cost structure of wastewater treatment infrastructure. It can now actually become a substantial additional source of income for many factories and processing plants throughout the world, including the food, beverage and agro industry and other primary product processing.”