Home > How sweet it is: Cane processors profit with green energy and environmental benefits - Global Water Engineering - July 2013

How sweet it is: Cane processors profit with green energy and environmental benefits - Global Water Engineering - July 2013

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article image United Farmer and Industry plant commissioning by GWE

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Advanced anaerobic technologies from Global Water Engineering, represented in Australasia by CST Wastewater Solutions are helping a global leader in the production of green energy from food and agribusiness wastewater, achieve high returns of biogas from sugarcane.

Grown worldwide in more than 90 countries with a worldwide harvest exceeding 1.6 billion tons, sugarcane has historically not been suited to biogas production because the vast amounts of water used in its processing are too weak in their organic carbon concentration to yield profitable amounts of methane.

According to Global Water Engineering (GWE), the industry has progressively used less water in recent years, increasing its waste stream concentrations to levels where it can be very successfully exploited for biogas and produce less effluent pollution through the latest anaerobic technologies.

GWE President and CEO Mr Jean Pierre Ombregt explains that the use of less water can produce major environmental benefits in the cane industry, where the size of a processing plant bears little relation to the huge amount of waste water it has traditionally produced. Instead of having a series of huge anaerobic and aerobic lagoons impacting the environment, effluent can be treated in contained anaerobic reactors where biogas is extracted and influent waste water is cleaned of most of its impurities without release to the environment.

GWE’s technology has been installed in more than 300 anaerobic waste water plants globally, including by CST Wastewater Solutions at the new Bluetongue Brewery in NSW where it simultaneously cleans process water to high discharge standards while producing biogas to fuel boilers.

The biogas can also be used to generate green electricity for sale to the local grid or other factories consuming fossil fuel. Many of the plants utilising biogas in this way achieve payback of plant costs in two years or less as they permanently reduce the amount of fossil fuel used and generate continuous environmental gains and financial savings.

One of the latest cane sugar mills to use GWE anaerobic technology incorporating its ANUBIX B reactor is the United Farmer and Industry mill at Khon Kaen in Thailand. The cane sugar plant has a capacity of 3500m³/day of waste water containing 22750kg/day COD (Chemical Oxygen Demand) of natural origin that can be broken down into biogas by anaerobic bacteria.

The process employed at United Farmer and Industry comprises of influent screen, equalisation, pH control, anaerobic treatment, biogas flare and two-stage biogas sweetening (Bio-Sulfurix followed by activated carbon filtration).

Biogas production is currently building to 9000 Nm³ a day (75% CH4), which will be used as fuel in several factory steam boilers.

Waste water effluent levels have also benefitted substantially, with a minimum of 85% removal of COD being achieved (to a maximum 975 mg/l COD, produced from influent with 6500 mg/l COD, or 3250 mg/l BOD5 - Biochemical Oxygen Demand).

GWE’s ANUBIX B medium-to-high loading rate UASB (Upflow Anaerobic Sludge Bed) reactor employed at the plant is typically used for most low-to-medium strength mainly soluble carbohydrate containing effluents. The effluent COD reduction achieved at United Farmer and Industry is excellent by cane industry standards, while in broader food and beverage industry service such technology has attained up to 99% COD removal efficiencies.

In addition to substantial environmental benefits from cleaner water being treated in reactor tanks rather than lagoons, the United Farmers Plant achieves a supply of green energy that delivers energy savings virtually in perpetuity, says Mr Ombregt.

Existing GWE anaerobic technologies of the type employed at United Farmer and Industry typically produce enough green energy to pay for the cost of their installation in typically one or two years.

According to Managing Director of CST Wastewater Solutions, Mr Michael Bambridge, the reactors reduce the need for huge lagoons with their associated odour, land use and environmental leaching issues.

The advanced anaerobic technology such as that installed at United Farmer and Industry is strongly applicable to any factory or process with one or more digestible solid waste streams. Plants such as breweries, fruit, food waste, agro industries, and energy crops including corn and cane used for ethanol can easily employ anaerobic wastewater treatment systems to generate energy, opening the door to environmental and production efficiency gains.

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 environmentally challenging settling lagoons.

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