Enviro-engineering improves North End Lake's water quality

Enviro-friendly microbiological sanitisers, as well as reed and gabion stormwater filter ponds, will work naturally at the city's urban watering hole to keep pollutants at bay. AfriCoast Consulting Engineers environmental sector manager Clement Ofori, who conceptualised the system, has been involved with the project since the Nelson Mandela Bay Municipality first commissioned the lake area's clean-up in the approach to the 2010 FIFA World Cup.

"North End Lake had received little attention and consequently deteriorated into a polluted and smelly environment prior to the construction of Nelson Mandela Bay Stadium. The general perception at that time was that neighbouring industries were responsible for discharging chemical pollutants into the water, but our studies revealed that the offensive matter was rather organic, with nutrient and bacteriological contamination coming mostly from the ageing local sewer network.

"Faecal coliform levels were high (in excess of 200,000 counts per 100ml), along with prolific algal blooms and high turbidity levels. These conditions impaired the safe recreational use of the water and undermined the environmental, social and economic values of the lake."

The area needed a quick fix, but stakeholders agreed that the approach should be environmentally friendly.

"Aside from the need to improve the environmental quality of the lake and its precinct, there are fish, birds, otters and other life to consider. AfriCoast's recommendation of a unique biotechnology, which involved dosing the lake with efficient microbes (a cocktail of positive micro-organisms that out-compete the offensive ones) to quickly clear the odour and turbidity problems, was unanimously accepted," Ofori said.

Pioneering project

It was a pioneering move, since this non-toxic approach, which originated in Japan, had been used only once before in South Africa, in the successful rehabilitation of Johannesburg's Zoo Lake. A secure hot house was set up at nearby Rhino Plastics premises, where the microbes were activated with molasses and warm water before being added to the lake.

"We did the application in May, about a month before 2010 World Cup kick-off. Within a week the smell had vanished and the water quality had improved; within four weeks the clarity of the water had improved significantly. Plus, we achieved a sustained reduction in coliform levels for three to four months after application."

Reclaiming the lake

The scenic lake has since begun to reclaim its place as a playground for water sports, picnickers and fishermen. The NMBM, together with Mandela Bay Stadium curators Access Management, aims to develop the lake into a world class freshwater sports facility that will complement the neighbouring arena. AfriCoast was tasked with compiling and implementing the Catchment Management Plan that would guide the effective management of the lake and its precinct in the long term.

AfriCoast's extensive scientific, technical and operational expertise enabled Ofori and his team to design a multi-pronged, 'green' and sustainable plan: firstly, tackling the catchment to control pollutants at the source, secondly the pre-impoundment management of material in transit, and lastly treatment of the lake water and sediment, which is where the bioremediation with efficient microbes will again be employed.

"North End Lake has two main sub-catchments: the Korsten Dry Lake, from which about 42% of the water comes. The other 60% comes from domestic, commercial and industrial sources. We have discovered 27 stormwater drains diffusing into the lake, and the diffused nature of the sources of pollutants make it difficult to manage. However, we have transformed the Korsten Dry Lake, which had become a dump site, and fenced the area to prohibit further dumping," he said.

Increase in property value

Aside from the recreational and ecological appeal of improving this public space, the project is also increasing surrounding property values and will stimulate commercial activity in the area.

"Local communities have been instrumental in the lake's rehabilitation, including the surrounding businesses and industries, recreational users like the EC Power Boat Club, EC Bass Fresh Water Fishing Club and the PE Rowing Club, as well as the ward councillors and relevant government agencies."

"We also engaged with the Botany and Zoology divisions of Nelson Mandela Metropolitan University (NMMU), with students assisting us with, amongst others, a sediment analysis to estimate the level of contamination."

Ofori said an urban lake is one of the most difficult water bodies to manage because of the constraint in flow and circulation, and also because of the small amount of fresh water entering to dilute pollutant concentrates.

"It was essential to be innovative in our pre-lake management. We opted for natural filters like reeds, activated charcoal and gabions. The system is intended to hold back pollutants, slow down the in-flow and diffuse it through the natural reed filter before it reaches the lake."

Job creation

Construction of the stormwater gabion filter ponds is currently underway at four points around the lake. The multi-million rand project is planned for completion before December. Four SMMEs have been appointed for the work, creating approximately 35 job opportunities. The periphery of the lake and the ponds is cleaned manually, creating a further eight to 10 jobs.

"There has been a significant improvement in water quality and the general conditions around the lake since our involvement, but the water is not yet totally safe for swimming," Ofori advised. "Our target is to achieve and sustain average coliform levels of less than 1000 counts per 100ml within the next 12 months, which is the standard for intermediate contact recreation.

"Yes, chemical treatment would be quicker, but damaging in the long-term and we all want to do this the environmentally friendly way. The lake will take time to heal properly - it has been polluted for more than 25 years. We want to promote green life, devoid of toxic additives, so my persuasion is to allow nature the time it needs."