50 Years - 50 Stories: The Chocolate Factory (and the Upflow Anaerobic Sludge Blanket!)

"During the commissioning, Cadbury let me use the lab on Sundays for testing; chocolates everywhere one looked which was quite a distraction (they had no issues with me thieving some). As I was regarded as a local, I could purchase 5kg of chocolate seconds, which I did regularly and took home in my suitcase"

- Geoff Parker, Project Manager for Cadbury's Claremont WWTP (Tasmania).

The Cadbury chocolate factory on the Derwent River in Claremont, a northern suburb of Hobart, Tasmania, was a very popular destination for many travellers, with its factory tours being legendary for mums and kids in particular. The factory had minimal treatment of its liquid waste product, which had been discharged into the river for around 80 years.. (much to the delight of the local fish population?)

In the early 1990s, legislation was introduced which resulted in a general move for industries in the Hobart area to cease river discharge and treat their liquid waste to a standard acceptable for further treatment by the closest sewage treatment plant (STP). Hence Cadbury was one of the factories to recognise the need to install a wastewater treatment plant.

It was generally accepted that anaerobic treatment for high strength waste – in this instance substances such as milk, sugars, cocoa – had several advantages over aerobic treatment, including flexibility of operation (granular sludge can be dormant for months, unlike aerobic sludge), minimal power requirements, and relatively small footprint. As well, it was considered likely that the effluent quality from a UASB plant would be sufficient to meet inflow pollutant limits applicable to the nearest sewage treatment plant without the need for aerobic polishing (which was the case). Interestingly, the adjacent STP was the Cameron Bay plant which had been upgraded by Aquatec Maxcon.

At the time, Aquatec Maxcon had successfully installed the Paques BV designed UASB (Upflow Anaerobic Sludge Blanket) for Golden Circle cannery in Brisbane, and was in the early stages of developing a large Paques UASB plant at the CUB Yatala brewery mid-way between Brisbane and the Gold Coast, when Roger Locke of Hobart consultants Scott and Furphy in conjunction with Cadbury chief engineer Keith Wells approached Aquatec Maxcon to discuss a staged WWTP development. This led to the design and construction of a primary treatment facility including a Balance Tank and DAF unit (dissolved air flotation), with a small volume of the DAF overflow stream being diverted to a Paques anaerobic pilot plant. Upon the completion of successful pilot testing, Cadbury management sought pricing and performance guarantees for a full scale plant. The programme timing from initial primary treatment discussions and design, to commissioning of the secondary treatment UASB occurred over several years.

Being an anaerobic plant with associated generation of methane, AM had installed a gas flare, which was used by Keith Wells to demonstrate to management that when the flare was quite active it essentially represented increased production costs due to wasted milk/sugars/cocoa; i.e. lost profit. The result was that waste streams were more closely monitored and treatment plant inflow was reduced. Cadbury, later, designed and installed a hot water system which utilised the methane as a gas fuel, to further reduce costs.

The UASB process plant readily met all requirements for Cadbury needs; with Aquatec Maxcon soon after becoming the successful tenderer for the supply of the smaller UASB plant for Mars Confectionary at Ballarat.

Story submitted by Geoff Parker, Project Manager