Besides being the largest single source of carbon emissions, coal power plants also consume enough water to meet the needs of a billion people. In a world where half the population may face water shortages, and that will continue to rely on burning coal for years to come, there is a pressing need for both cutting emissions and improving water-use efficiency.
Coupling coal power plants with wastewater treatment plants could be a “win-win collaboration” that tackles both problems, researchers suggest in a new Nature Sustainability paper. Their analysis shows that using sewage sludge and reclaimed water from municipal water treatment as alternative fuel and water source in power plants could reduce emissions from water treatment plants in China by a third.
This infrastructure symbiosis would save two-thirds of freshwater that China’s coal power sector consumes, and an average of 7.5 billion CNY (a little over $1 billion USD) annually. Plus, it would be a way to use the massive amounts of sludge that water treatments plants produce. “Our results demonstrate how infrastructure systems can be developed more sustainably in China, and our approach can be applied around the world,” they write.
Coal-fired plants consume water for mining coal and to producing electricity. Over 40 percent of the world’s 8,359 coal plants are in areas under water stress. Meanwhile, hundreds of new plants are being built or are proposed, mostly in China, and a quarter to half of these will also be in water-stressed regions.
On the other hand, only 20 percent of treated wastewater is reused in China. And wastewater treatment plants there produce about 8 million metric tons of sludge. Research has shown that this sludge can be burned effectively with coal in power plants. Around 30 pilot projects have also tested this sludge co-combustion in China.
Yet, no study has examined how coal and wastewater infrastructure can benefit from each other. So Denise Mauzerall of Princeton University, Lyujun Chen of Tsinghua University and their colleagues created a geological database of coal-fired power plants and municipal wastewater treatment plants across China. They used modelling and life-cycle assessment to assess how best the two sectors could be linked together for sludge and water reuse.
The assessment showed that symbiosis between the two sectors could reduce wastewater treatment emissions by 8.6 million tons of carbon dioxide equivalent every year. And it would save over 3 billion cubic meters of freshwater.
The emissions and freshwater savings were highest in provinces where power plants and water-treatment plants were closer in proximity. Because sludge would be transported via trucks rather than pipeline, more power plants could reuse sludge than wastewater.
The results show that building future coal plants near wastewater treatment plants would maximize economic and environmental benefits. The researchers hope that policymakers can use these results for making sustainable infrastructure development decisions.
Source: Yang Guo et al. Benefits of infrastructure symbiosis between coal power and wastewater treatment . Nature Sustainability, 2022.
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