Commentary: The energy sector should care about wastewater
Today is World Toilet Day, an opportunity to raise awareness about the global sanitation crisis. About 4.5 billion people around the world still lack access to safely managed sanitation and 80% of the world’s wastewater is released untreated.
Two of the targets under the Sustainable Development Goal dedicated to water (SDG 6) — providing sanitation for all (target 6.2) and halving the proportion of untreated wastewater (target 6.3) — seek to address these challenges. But meeting these targets could put significant upward pressure on energy demand.
The links between energy and water run deep, which explains why the IEA is looking at the issue. New analysis in this year’s World Energy Outlook (WEO) shows that today’s water sector, which includes the collection and treatment of wastewater, accounts for 4% of total global electricity consumption. Wastewater treatment alone represents roughly a quarter of the water sector’s electricity consumption. Additionally, some estimates have put the sector’s share of total greenhouse gas emissions at 3%. However, there are also significant opportunities to produce energy by harnessing the embedded energy in wastewater, as our analysis in 2016 emphasized.
The urban technology challenge
In urban areas, where almost 2.3 billion people still lack access to safely managed sanitation, this year’s WEO examinedthree potential pathways for urban municipal wastewater management to achieve sustainable development goals. They provide an illustration of how technology and policy choices can influence the additional electricity needed:
- If cities follow today’s typical technology blueprint for centralised wastewater capacity, electricity consumption could increase by over 680 TWh over the period to 2030.
- If cities instead deploy a range of economically viable energy efficiency technologies in all new wastewater facilities, as is done in our Sustainable Development Scenario (see left-hand side of the Figure below), the increase in electricity consumption could be reduced by roughly 10%. This pathway also sees higher rates of energy recovery; 30% of the electricity needed to meet the targets could be generated from the wastewater itself, compared to just 6% if the current blueprint for wastewater management is used.
- A third possibility, at the frontier of today’s technology, is to build energy-neutral or even energy-positive facilities (right-hand side of the Figure). On this pathway, electricity consumption would increase by less than 460 TWh thanks to additional energy-efficiency measures while the installation of energy recovery for biogas and high-efficiency combined heat and power units would enable utilities to generate over 50% more electricity than they need.
"Business as usual" equals the amount of electricity consumed (less 60 TWh from energy recovery) from municipal wastewater treatment excluding SDG 6 in 2030 in the SDS. "Sustainable Development Scenario" equals the total electricity consumption from urban municipal wastewater treatment plants in the SDS if SDG 6 were achieved. "Energy neutral/positive case" is equal to the total electricity consumption from urban municipal wastewater treatment plants in the SDS if all new capacity built to achieve SDG 6 was energy neutral or energy-positive. The negative values indicate that more energy is generated than needed and can be sold.
Improving process efficiency and harnessing the embedded energy in wastewater will not happen on its own. Appropriate financing, water-quality regulations, pricing mechanisms for water and electricity, land availability, and developing natural gas infrastructure so that utilities can offload excess biogas, would also be needed.
Rural wastewater solutions
In rural areas, providing for the other 2.2 billion people without access to safely managed sanitation continues to rely on more decentralised technologies and solutions in our projections, most of which do not require energy. However, the safe collection, disposal and treatment of waste present both a challenge and an opportunity. Using anaerobic digesters to generate biogas from the collected waste, and then consuming this biogas for household energy needs, could reduce indoor air pollution, help prevent deforestation, save time spent – typically by women – on collecting solid biomass, and contribute towards the achievement of SDG 7.1.2 (clean cooking for all).
To date, barriers related to cost, scale, installation and maintenance have limited efforts to scale up the use of anaerobic digesters. However, the opportunity to make progress on two SDGs at once (SDG 6 and SDG 7) could provide an incentive to speed up progress and remove barriers to deployment. If waste from all those who lack access to safely managed sanitation in rural areas today was captured and digested, the biogas potential could be roughly 20-50 billion cubic metres (bcm). This could be enough to provide a clean cooking fuel to around 60-180 million households.
Energy and water: the need for integrated thinking
Clearly, energy plays an important role in reaching SDG 6 targets on sanitation and wastewater and there are a range of potential synergies between SDGs 6 and 7. However, thinking about water in an integrated way will be essential to capitalize on these co-benefits and avoid future stresses on both sides of the energy-water nexus.
This is one of the reasons why WEO 2018 added a water dimension to the Sustainable Development Scenario, to assess what the implications of meeting SDG 6 are for the energy sector, and what policymakers need to do to hit multiple goals with an integrated and coherent policy approach.