Constructed Wetlands for Resource Recovery in Developing Countries

Avellán, T. and Gremillion, P., 2019. Renewable and Sustainable Energy Reviews

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Abstract

Constructed wetlands (CW) are effective in treating wastewater, particularly in settings that require low tech-nology and low maintenance as operational constraints. Biomass harvested from CW can be used as a renewableenergy source and treated effluent can provide irrigation for agricultural uses. Biomass yields for four selectedwetland plants in CW, namelyPhragmitesspp.,Typhaspp.,A. donax,andC. papyrus, ranged from an average ofabout 1500g of dry mass per square meter (g/m2) forTyphaspp., up to 6000g/m2forA.donax. The energy yieldfor direct combustion of these plants occupied a narrow range, averaging about 18 megajoules per kilogram ofdry mass (MJ/kg) for all plant types, a comparable amount toAcacia spp. Methane yields varied from about170–360L of methane (normalised to standard conditions) per kilogram of dry mass (LN/kg). 1m2of CWplanted withA. donaxcan produce on average 110MJ through direct combustion or 1660L of methane frombiogas production. In a village of 200 people the biomass from a CW planted withTyphaspp. can reduce cookingfuel needs by 4–55% and therefore save up to 12ha of forest per year. The water footprint of these plants wasmeasured as the percent loss in water in the CW from evapotranspiration (ET). Under a fixed set of assumptionson climate and operation, the water used through ET, the CW could deliver from 64% to 76% of the influentwater for subsequent use. In summary, CW have the potential to offset energy and irrigation needs at scalesranging from small communities to peri-urban areas. Constructed wetlands used to treat wastewater have thepotential to provide a sustainable bioenergy source without placing burdens on water resources or displacingother food or energy crops.

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