Consulting Engineers MBB, which operate and manage the Lower Blyde River Water Distribution (LBRWD) pipeline, is working with the University of Pretoria to research the presence of a bacterium known as biofilm, which has been found in the pipeline.

“Biofilm is a natural bacterium that grows on the inside of a wide range of pipelines through the oxidation of a variety of minerals which occur naturally in water – in this case, low concentrations of manganese and iron dissolved in water,” explains MBB Consulting Engineers project manager Org van Rensburg.

The research project has been conducted in the LBRWD network, which supplies untreated pressurised water to 109 farmers who have about 8 000 ha under irrigation.

The network includes the Hoedspruit Air Force Base, the town of Hoedspruit and other smaller primary users. Since its inception in 2003, MBB has oper- ated, maintained and adminis- tered this 120 km pipeline net-work.

Biofilm has exceeded researchers’ expectations, with growth of up to 4 mm on the inside of pipes, which range from 1,5 m to 250 mm.

“Comparisons between hydraulic models and measurements in the field have confirmed that the actual energy loss is significantly higher than what original theory implied. An investigation was launched to find the culprit, which was discovered to be a gellike biofilm growing inside the pipe.

Van Rensburg notes that the bacterium is not harmful to the environment. The water quality is still exceptionally good. “Live- stock and people have drunk the water from the pipeline for many years without ill effects, although, as untreated water, it is not recommended for human consumption.”

MBB has constructed two experimental rigs – one at the beginning of the system and the other at the lower end, which have been operational since late 2010. Research began soon after construction was completed.

The rigs facilitate the collection of samples and enable researchers to ascertain variance in the behaviour, growth and die-off of biofilm in different flow conditions.

“The results of the first research project have shown that biofilm growth spikes are seasonal. During rainfall, when additional material is washed into the Blyderivierspoort dam, growth intensifies.

“The investigation also found that bacteria increase substantially in the pipeline’s downstream section, owing to the sloughing off of biofilm upstream. The research discovered that flow velocity has an impact on biofilm accumulation and that turbulent and laminar flow regimes influence growth rates,” he says.

Currently, a three-month experiment is being conducted, where ozone gas is injected into the test rigs as a possible solution to the problem.

Funding has been granted to conduct further research to measure velocity losses in the pipeline network and this is scheduled to begin in early 2013.