Wastewater Biogas to Energy

Overview
The organic matter in raw wastewater contains almost 10 times the energy needed to treat it. Some wastewater treatment works (WWTW) can produce up to 100% of the energy they need to operate, though more typically 60% of operational energy can be produced. Biogas is typically used to meet on site power and thermal energy needs. Export of gas to local industrial users, power producers or for use as a municipal vehicle fleet fuel is also possible. In a wastewater treatment works (WWTW) biogas is produced when sludge decomposes in the absence of oxygen, in digesters. This process is referred to as Anaerobic Digestion. South Africa was one of the first countries in the world to utilise digesters as part of sludge management at WWTW. Digesters at WWTW were, however, not built to capture and use the biogas produced, but rather to assist in sludge management. In most cases, digesters can actually be refurbished to allow for biogas collection.
Biogas (a methane-rich natural gas) derived from anaerobic digestion and captured at WWTW plants provides a renewable energy source which can be used for electricity, heat and biofuel production. At the same time the sludge is stabilized and its dry matter content is reduced. This sludge, or digestate (remaining solid matter after the gas has been removed), contains valuable chemical nutrients such as nitrogen and potassium, and can be used as an organic fertilizer.