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August 2004

Feature

 

Biofouling: An affordable solution to an expensive problem

Sophia Dower

Prof Eugene Cloete and the RotoscopeIn May this year, a major brewery in southern Africa was the first to test the abilities of a new biofilm monitoring and treatment system - one that looks set to save industrial water users hundreds of thousands of rands in production and running costs.

Developed at the University of Pretoria, the Rotoscope is a uniquely South African answer to a problem that costs global industry several billion Euros a year. The system is designed to monitor and treat the formation of unwanted biofilm - the accumulation of bacteria, proteins, algal material and fungi that causes the deterioration in the microbiological quality of treated water.

The corrosion and weathering caused by this biofilm can lead to considerable damage, ranging from contamination of pharmaceutical or microelectronic products, to reduced efficacy of heat exchangers, unexpected corrosion of stainless steel and premature destruction of mineral materials.

In a nutshell, the Rotoscope aims to provide an affordable on-line, real-time, non-destructive method to monitor biofilm. And at roughly a tenth of the price of similar high-end systems, it holds huge promise for local companies who want to improve the price and quality of their products. Once commercialised, it could also capture a substantial slice of the somewhat under-served overseas market.

According to local company BTC Products & Services, who have been licensed to manufacture and market the Rotoscope, there are only two other commercial units currently available. Both sell for around 40 000 each, and are bought almost exclusively by large utility companies.

BTC owner, Hugh Mitchell, says that the first three Rotoscope prototypes will be installed at the brewery in PE by mid-May, and five to 10 units will be under evaluation by June. The units will be used in the brewery's pasteuriser, and to measure biofilm formation in a pipeline carrying re-treated effluent.

"This 'test' phase will determine the robustness of the unit as well as the value and practicality of the data and information it generates," he explains.

"We have secured funding from the Department of Trade and Industry, as well as the support of three major organisations, for the commercialisation process. We hope to sell the first two commercial units to our technology transfer partners in the USA and in England."

This success follows more than two years of internally-funded development by Rotoscope inventors Professor Eugene Cloete (head of the Department of Microbiology and Plant Pathology at the University of Pretoria) and Professor Fanie van Vuuren (from the Department of Civil and Biosystems Engineering).

"I have been studying biofouling and biocorrosion for the past 10 years and one major challenge has always been monitoring the adhesion of bacteria to surfaces exposed to water and the adverse effects that go along with this," explains Prof Cloete. "What became clear was that there was no affordable on-line real time non-destructive method to monitor biofilms."

Biofilm: a difficult customer

So what is biofouling, and what makes it such a tricky - and widespread - problem?

Prof Cloete explains that when water-borne bacteria congregate in sufficient numbers they form a film on the surface of pipes, tanks and indeed any piece of equipment. This "biofilm" is a living organism which consists of mainly water, bacteria, suspended solids, corrosion products, algae, yeasts /molds, protozoa and molluscs.

Biofilm is typically found wherever liquid and a solid surface interface, such as in heat exchangers, cooling towers, municipal water storage and the food and beverage industry. To prevent contamination of water and related products, biofilm development must be monitored and treated continuously by taking water samples and measuring plate counts to determine the level of microbiological contamination. "Even the most efficient organisation work on the principle that if these samples are clear then the whole production will be clear from microbiological contamination," says Prof Cloete.
This is extremely costly, which means most companies are restricted to intermittent testing and treatment. 

"However, this film has been found even in water that has been tested and shown to have very low microbiological counts when water samples are plated out. Therefore product loss still occurs as a result of microbiological contamination, even though quality control samples show little evidence thereof."

BTC's Hugh Mitchell adds that currently, biofilm management is based on decisions made from the results obtained from bulk water samples - even though research shows there is little correlation between planktonic bacteria (floating in water) and sessile (attached to surface) bacteria of the same type.

"Any strategy that incorporates antifouling technologies will be therefore more cost-effective if the extent of the biofilm can be monitored online and in real time, without destroying the biomass formation," he says.

Most monitoring techniques rely on the removal of biomass from the system in the form of coupons that have been exposed to the fluid for a given period. These samples are then sent away and analysed, which is time-consuming and require skilled personnel.

"Usually biofilm is only detected after it has already caused economic losses," says Mitchell. "Current treatment techniques are also problematic, as many are based on the assumption that if one kills the organisms in the bulk water, one will prevent the formation of biofilm. However, biofilms are resistant to many non-oxidising biocides re-growth of biofilm is inevitable. This often leads to significant overuse of poorly selected disinfectants or biocides, which raises costs and creates environmental concerns."

Enter the Rotoscope

Besides real-time, online monitoring of biofilm, the Rotoscope automatically releases a dose of biocide used to disperse the biofilm, whenever a threshold level is reached.

The device has a rotating plastic wheel that is half submerged in water flowing from a slipstream of the main process water. Biofilm forms on the disc and is measured by green and/or infrared light reflecting off the white surface. The frequency of measurement can be varied, from every five minutes to every 120 minutes and/or be continuous.

"It is a proactive system, in that biofilm forms in the Rotoscope before it forms on mild or stainless steel," explains Prof Cloete. "This means that appropriate dosages of biocide can be released before biofilm becomes a serious problem in any system." 

Simply put the Rotoscope is immediate, effective, non-destructive, continuous and affordable.

The technology has been patented in South Africa, with international patents pending. Each unit is expected to sell for between R35 000 and R50 000, and the most significant applications are expected to be in industrial water systems like paper mills, cooling towers, brewery pasteurisers, water utilities, water distribution pipelines and heat exchangers.


More information:

Hugh Mitchell, BTC Products, Tel(011) 794 9193/ 9239
Prof Eugene Cloete, University of Pretoria, Tel (012) 420 3265

Article courtesy of the Water Wheel.

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