As sludge volumes continue to rise across South Africa’s water, wastewater and industrial sectors, organisations are shifting from purely disposal-based practices towards approaches that focus on value recovery.

EnviroServ’s national Haztech and inland southern commercial manager, Hugh Khumalo, outlines how the company is advancing sludge management practices.

Sludge remains one of the most complex waste streams in the water and industrial sectors. Its composition varies widely – from organic hydrocarbon sludge to inorganic, mineral-rich residues – each with different densities, viscosities and odour characteristics. These factors influence how sludge is removed, transported and treated.

“Sludges are managed and transported using a range of methods. In some cases, sealed tankers are used instead of tippers, and additional treatment processes – such as odour-control measures – may be required, with certain sludges ultimately needing incineration,” explains Khumalo.

Before any treatment or disposal route is considered, EnviroServ conducts a detailed assessment through its accredited laboratory working alongside the company’s alternatives team and hazmat specialists. Samples are analysed to determine whether sludge should be stabilised, dewatered, incinerated or landfilled. “These departments work together to determine the safest and most responsible solution before any proposal is presented to a customer,” says Khumalo.

EnviroServ uses several treatment technologies depending on the classification of the sludge and prevailing legislation. Treatment at EnviroServ’s Holfontein Waste Management Facility range from ash blending to more technical applications using lime, ferro-sulphate or specialist stabilisers for difficult waste streams. Wherever possible, alternatives to landfill are prioritised. Holfontein is South Africa’s largest hazardous waste management facility. It is engineered to safely take Type 1 to Type 4 wastes, and is equipped with treatment processes capable of treating even Type 0 materials before disposal.

Dewatering

Transporting sludge carries inherent risks. EnviroServ selects sealed tankers or RoRo bullet tankers where necessary and uses advanced digital systems for route planning, manifest control and compliance with UN/TREM requirements. These UN-aligned Transport Emergency (TREM) protocols ensure that drivers have the hazard information and emergency actions needed to move dangerous goods safely and transparently.

A major focus area in recent years has been reducing the transport and disposal of water-rich sludge. EnviroServ has developed a sludge dewatering system in partnership with a specialist supplier. This system extracts sludge from dams, dewaters it, and returns low-solids water to the client’s process.

“This approach significantly reduces the number of trucks on national roads, lowers carbon emissions and ensures that prohibited liquid wastes do not reach landfill,” notes Khumalo.

In one project, belt presses were used to extract sewage sludge from an overloaded treatment dam, helping the client restore capacity and avoid compliance issues.

More customers are embracing the idea of sludge as a resource. Hydrocarbon sludge has been trialled successfully in brickmaking, where it contributes to kiln firing and final product strength. Treated sewage sludge from water treatment plants is being used as lawn-dressing material. High-calorific sludges are blended for alternative fuel use in cement kilns, reducing reliance on coal, while alumina-rich fractions are reclaimed for refractory lining, ceramics and other high-temperature applications. These initiatives support broader (environmental, social and governance) ESG goals and strengthen participation in the circular economy.

Several projects highlight the value of this approach. At one of EnviroServ’s petrochemical clients, dam dewatering yielded significant disposal savings, while pond harvesting helped prevent wet sludge from reaching landfill. Hydrocarbon and alumina-rich sludges have also been supplied to cement producers for fuel blending and raw material use.

Khumalo believes that the next decade will see sludge increasingly recognised as a feedstock rather than a liability. “Clients are investing more in alternatives and research. With tighter landfill restrictions ahead, solutions like dewatering, sludge blending and waste-to-energy will become standard practice. The public and private sectors will need to partner and invest in infrastructure to support this transition.”

Sludge management is no longer merely an operational requirement but a strategic opportunity. Through rigorous assessment, flexible treatment technologies, and a strong focus on circular-economy value, EnviroServ is helping industries move beyond disposal towards sustainable resource recovery.