Biogas Upgrades Cut Energy Costs in South Africa

Client: Johannesburg Water
Location: Johannesburg, South Africa

Facing a steep increase in energy costs, Johannesburg Water is upgrading the sludge handling and digestion facilities at its five wastewater treatment plants. The new high-performance digestion facilities will significantly offset energy costs at the plants – as much as 55% at one plant.

Project Outcomes and Benefits

  • High performance mesophilic anaerobic digestion including pre-thickening as well as mixed and heated anaerobic digesters with biogas collection and storage facilities at five wastewater treatment plants will significantly reduce energy costs.
  • A biological sludge cell lysis (cell destruction) installation on the thickened waste activated sludge streams will maximize methane production from the WAS constituent of the combined sludge.
  • Upgrades provide for the cleaning of the biogas to adequately condition it to manufacturer’s specifications for use in co-generation engines or turbines.
  • Upgrades provide for generation of electrical power by means of co-generation methane gas engines or turbines
  • Upgrades provide for the recovery of heat from the coolant train of the power generating equipment to be used for digester heating purposes and in future from the exhaust heat to assist in drying applications of the dewatered sludge.

JW Northern Wastewater Treatment Works (450 Ml/d, South Africa's biggest BNR Plant)

PSTs and Bioreactor at the JW Driefontein Wastewater Treatment Works (currently 35 Ml/d, upgrade (expansion) to 55 Ml/d currently underway)

New anaerobic digesters at the Driefontein Wastewater Treatment Works

Waste biogas flare with new sludge drying / composting beds in the background, Driefontein Wastewater Treatment Works

New heat exchanger and sludge macerator/pump combination at anaerobic digester, Driefontein Wastewater Treatment Works

Johannesburg Water (JW) has embarked on a major capital investment program to upgrade and expand their wastewater treatment works (WWTPs). The upgrading of the sludge handling and digestion facilities at the different works is an important part of the current capital investment program. Hazen & Sawyer, as sub-consultant to Golder Associates, is providing review and support at various stages of the design and bidding processes, with focus on the more innovative aspects of the project.

JW has opted to implement high performance mesophilic anaerobic digestion including pre-thickening as well as mixed and heated anaerobic digesters with biogas collection and storage facilities at their WWTPs. Increased biogas production is a benefit associated with the implementation of high performance digestion facilities.

The electrical power cost in South Africa is set to increase substantially based on the need to finance new power stations. The first such power tariff increase has already taken place and substantial above inflation rate increases are expected in the next years. It is anticipated that power cost will increase by 100% (double) over the period 2009 – 2014 and triple over the period 2009 – 2018. This development places substantial strain on the operating budgets for the different JW WWTPs.

A Biogas-to-Energy Project can soften the impact of increasing power costs, and an attractive business case exists for a Biogas to Energy project based on pay back of capital invested over a short period of time as well as long term savings in electrical power costs, especially in light of the anticipated rapid increase in power costs. Further, a Biogas-to-Energy project will showcase JW’s commitment to renewable energy, and renewable energy is fast becoming a necessity in South Africa. JW has therefore decided to implement Biogas-to-Energy installations at five of their WWTPs.

The key features of the Biogas-to-Energy installations include:

  • A biological sludge cell lysis (cell destruction) installation on the thickened waste activated sludge (WAS) streams to maximize methane production from the WAS constituent of the combined sludge.
  • Cleaning of the biogas to adequately condition it to manufacturer’s specifications for use in co-generation engines or turbines.
  • Generation of electrical power by means of co-generation methane gas engines or turbines.

The Biogas-to-Energy installations will provide for the recovery of heat from the coolant train of the power generating equipment to be used for digester heating purposes and in future from the exhaust heat to assist in drying applications of the dewatered sludge. All existing methane fired boilers will be kept functional and they will serve as a backup system for the heating of digesters.

For more information on this project, or to discuss a similar project in your area, contact

C. Michael Bullard, P.E. at mbullard@hazenandsawyer.com