Australia’s first major thermal hydrolysis process plant is the latest high-profile project awarded to Cambi AS of Norway.
In November 2004, the City of Brisbane, Australia, through its Brisbane Water Enviro Alliance (BWEA) partnership, awarded Cambi AS the first major Thermal Hydrolysis Process (THP) plant in Australia as part of the Oxley Creek wastewater treatment plant upgrade.
The Brisbane THP and digestion plant will be able to treat more than 10,000 dry tonnes per year of extended aeration sludge. BWEA has been converting their plants to biological nutrient removal (BNR) so the sludge from these plants is extremely difficult to digest and dewater.
The Cambi process typically doubles digester capacity, reduces sludge volume by increasing biogas production and dewaterability, while converting sludge to a low odour soil conditioner. Several technologies could increase digestion rates in anaerobic digesters by disintegration and hydrolysis, but none have the same dramatic effect that the Cambi THP process has on dewaterability. Other technologies have also been ineffective in improving digestion of difficult sludges. In one Cambi project built in 2000 in Næstved, Denmark, the rate of digestion and dewatering of extended aeration activated sludge after THP was shown to have nearly doubled from 30% volatile solids (VS)/organic matter destruction and 16% total dry solids (TDS) cake to more than 55% VS destruction and 30% TDS cake solids.
Thermal hydrolysis of sludge cake reduces sludge viscosity, resulting in increased digester loading rates by feeding sludge at 10% to12% TDS, as compared with 4%-6% in non-hydrolysed sludge. Because the sludge is solubulised by THP, digestion takes place rapidly with loadings of up to 6 kg VS/m3/day being routine. The digesters therefore will have doubled solids loading capacity at the existing volume and hydraulic retention time because of the high TDS% feed.
The new Cambi plant at Oxley Creek will have three major benefits. First, the combination of solids reduction in the digesters combined with a well-dewatered cake (>30% cake solids) will significantly reduce sludge volume. Second, the plant will be a net producer of green electricity from biogas. The Brisbane City Council claimed that Cambi would save at least 2,000 truck movements a year and produce an estimated Au$0.5 million per annum of green electricity. Third, the digested product will be a low odour, class A material that could be blended with other materials such as composted green waste, or soils to make a high-grade soil conditioner. Cambi digested cake is so well digested that it is more like soil than normal digested cake when dewatered.
A Cambi THP plant was installed at Aberdeen (Scotland), which treats 16,000 raw dry tonnes of sludge per year from the Grampian region (600,000 PE). This area is famous for beef (Aberdeen Angus) and malting barley for whiskey production. The operators of the plant, Grampian Water Services, owned by Yorkshire Water, are extremely pleased with the uptake of the product in this conservative farming area. Since starting production in 2001, no odour complaints have been received from its application on grassland and arable land, and growth results have been impressive.
The combination of high dry solids digestion, high VS reduction and low volume of pasteurised cake has been the key to Cambi winning contracts in recent years. In addition to the Brisbane Water contract, the company signed contracts in Brussels, Belgium; Kapusciska, Poland; and Chertsey, UK within the past two years. Cambi also signed a contract in 2004 for the design of the Ecopro project in Norway, which is for digestion of up to 45,000 tonnes per year of biowaste (from separate garbage collection), sludge, dairy wastes and animal by-products category 2&3.
Author’s Note
Keith Panter, Ebcor Ltd, UK. For more information visit www.cambi.com or contact Cambi at [email protected]
