Constructed Wetlands to Turn Wastewater into Energy

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  • 2016/08/23     Dresden, Germany

    Image: istock/Veronica Bogaerts

    Image: istock/Veronica Bogaerts

    Reporting by Atiqah Fairuz Salleh, Communications and Advocacy

    A Nexus Approach towards water reuse can help improve food and energy security in Sub-Saharan Africa (SSA). Wastewater is rich in carbon and nutrients – by treating and recovering wastewater through linking cycles of water, waste, and energy, we capture the resources contained in it.

    “To overlook wastewater as an important resource is to overlook the potential to supply energy for households and irrigate and fertilise crops.”

    SSA relies overwhel­mingly on solid fuels for household energy needs. Often this leads to deforestation and environmental degrada­tion in many places. To continue meeting some of these needs without resulting in disastrous outcomes, renewable bioenergy sources can replace wood-based fuels. In the most recent UNU-FLORES policy brief Wastewater As a Resource: The Water-Waste-Energy Nexus in Sub-Saharan Africa, it is argued that wastewater can provide three fundamental resources: water, nutrients, and energy.

    “Humans produce about 12 m3 of water, 4.5 kg of nitrogen, and 0.6 kg of phosphorous per person per year. A community of 500 can irrigate about a hectare of agricultural land and fertilise five to seven hectares. Harvested plants from constructed wetlands for wastewater treatment can provide 12% of a village’s cooking fuel needs.”

    In particular, the policy brief outlines constructed wetlands as one low-technology alternative to treat wastewater and harvesting the wetland plants as an energy source. As visualised in the figure below, wetlands can be introduced to an ecosystem as the collection and treatment point of wastewater.

    In such a system, nutrients that would otherwise be released into surface water or groundwater can be captured and used in agricultural lands instead. This offsets the need for artificial fertilisers and improves the quality of ecosystems. Moreover, in SSA, where most peri-urban lands are supported only by rainfall, using treated wastewater offers the potential for the expansion of peri-urban agriculture.

    Threading together the components of the water-waste-energy nexus links resources to more than one use. This minimises losses of material and energy and maximises resource use impact, which can ultimately lead to sustainable development. Particularly in developing areas such as in SSA, it is crucial that implementation is not demanding. Low-technology systems such as constructed wetlands have low operation and maintenance needs.

    In a region where the population is ex­pected to double to 2.1 billion by 2050, the need for a sustainable solution to energy provision is real. Given the right technique, we can help improve human and ecosystem health.

    At the 2016 World Water Week in Stockholm this week, UNU-FLORES will be co-convening two seminars on wastewater use and will be launching the book Safe Use of Wastewater in Agriculture: Good Practice Examples at the United Nations University stand (#35) in the Exhibition area. Send your questions/queries/comments with the hashtag #4WastewaterReuse on Twitter and be part of the conversation!