Currently, wastewater is still a major burden worldwide as it costs money to be processed and then safely released into the environment. However, wastewater can be a sustainable resource of energy if wastewater-to-energy projects are implemented successfully. Many opportunities exist in waste-water to renewable energy projects, according to the Water Research Commission (WRC). The potential energy in wastewater today in the US is between 15gw and 20GW.One large nuclear power plant can put out 1GW of energy.
According to Sean Power, head of wastewater projects at SSI Engineers and Environmental Consultants, methane gas can be captured in the wastewater-to-energy process rather than being released into the atmosphere, thus reducing greenhouse gas emissions.” He points out that the noxious effect of methane gas released into the atmosphere is equivalent to approximately 20 times that of carbon dioxide when allowed to escape to the atmosphere. He explains that currently large amounts of methane are being released from landfills where methane gas is not captured. This of course has a negative impact on the environment. In addition to generating electricity and reducing pollution, wastewater can also be used in fertiliser production or for producing secondary products. Taking all the benefits into account, investing in wastewater projects could become economically feasible.
According to the WRC, anaerobic digestion (AD) is the most commonly recognized technology for organic sludge stabilization and has been applied to wastewater of different characteristics in both small- and large-scale projects. AD is a series of processes in which micro-organisms break down biodegradable material in the absence of oxygen to stabilize waste and/or to release energy. AD is suitable for use with domestic sewerage as well as in the industrial and agricultural sectors. Another emerging technology, microbial fuel cells (MFC), can operate with dilute wastewater streams to produce electricity directly. MFC’s are suited to applications in remote or rural sites with no infrastructure. The new technology can now produce 10 to 50 more times the electricity, by volume, more than most other approaches using microbial fuel cells, and 100 times more electricity than some.
WRC points out that the integration of technologies may be required to realize the maximum energy-from-wastewater potential instead of using single wastewater stream technology which may not be suitable for achieving efficient energy recovery.
Electricity production from waste-water faces a number of challenges which need to be overcome:
- Maintenance of the technology can be problematic with the absence of suitably trained staff
- Waste water management is controlled mainly by municipal engineers and is a function of the local government whereas energy technology is managed by mechanical, electrical and process engineers, and is the function of the national government. The challenge is to work across these disciplines that have different mandates and objectives. The various disciplines need to come together in order to formulate something that both treats wastewater effectively and generates electricity in a cost-effective manner.
- Overcoming the division of powers between the different spheres of government
- Technology can be expensive in terms of capital outlay and skills needed for maintenance (especially for imports). Government grants and policies will help to promote this renewable energy
Dr André van Niekerk, a director at Golder Associates says that waste water-to-energy projects can be implemented successfully, if enough attention is paid to technological, commercial and operational aspects.
If governments and industries are committed to finding more sustainable methods of dealing with wastewater, the possibilities should be thoroughly investigated and harnessed as opportunities to reach carbon emission and renewable goals, as well as energy sustainability.