Wastewater dams a ‘ticking time bomb’
02 September 2020 | Web Article Number: ME202020363
PIETERMARITZBURG-based water and wastewater solutions company Talbot is helping companies in the agro-processing sector to put a new face on decades old passive biological wastewater treatment systems.
According to Technical Director Grahame Thompson, the aim is to help them avert a potentially disastrous collapse and achieve environmental compliance without having to invest significant capital in the construction of new facilities.
“These dams, also referred to as anaerobic lagoons, are commonly used by agro-processors in rural settings as they enable wastewater treatment at low cost. Furthermore, land is typically readily available and minimal operator input is required,” says Talbot Technical Director Grahame Thompson.
The trouble with these facilities, he said, is that they are usually situated in obscure parts of an operation, the consequence being that neglect – often over decades – results in them becoming ticking time bombs.
“All may seem calm on the surface but with little or any form of pre-treatment, solids build up may result in a gradual reduction in freeboard and the eventual collapse of the treatment system.”
Talbot, which provides water and wastewater solutions across multiple sectors in Africa, was asked by a major player in the sugar industry to investigate a lasting solution for a decades old 20 000m3 treatment dam. Almost 50% of the dam was silted up by solids largely comprising sugarcane ash.
“We came back with a proposal that not only provides a rapid resolution to the customer’s dilemma, but is relatively simple to execute at low cost,” said Thompson.
The project involves the removal of around 15 000 tonnes of sludge, the relining of the dam to guard against groundwater seepage and splitting the facility into anaerobic and aerobic compartments for high efficiency treatment.
“At the same time, we are investigating an improved upstream solids handling system to bring about a significant reduction of solids entering the dam. This will result in the increased longevity of the facility, improved performance and lower maintenance costs.”
Anaerobic treatment in the first compartment will remove the bulk of pollutants and is able to handle a variation of flow rates and pollutant loads.
Water will then flow into an aerobic activated sludge system where low-speed surface aerators will assist with the biological degradation of organic contaminants before a clarifier separates biomass from wastewater prior to discharge. The clarifier is to be constructed from concrete and includes a rotating bridge for the conveyance of settled sludge for removal.
“The fact that the anaerobic and aeration dams will be constructed within the existing dam footprint significantly reduces the project cost,” Thompson said, adding that this intervention provides an example of how budget constrained companies can meet environmental limits for the safe release of purified wastewater without breaking the bank.