Energy, Cost, and Carbon Footprint Analysis of a Solar-Powered Mixer in a Facultative Lagoon for Wastewater Treatment

Lagoon treatment is common in small communities and/or rural areas where land is available. Mixing is the energy driver for this kind of treatment. Mixing could re-suspend the settled solids and oxidize matters at the surface in contact with atmosphere air. Traditionally, the mixer for lagoon treatment is mechanical mixer that gets power from grid. Recently, with the decreasing price of photovoltaic batteries, the solar powered mixers are posed to replace the traditional grid-powered mechanical mixers. As the aeration process is the most energy intensive process, transitioning the mixers off-grid means that the energy demand will be sharply reduced, which in turn reduces the process energy importation. In this research we studied the comparative scenarios of an existing grid-powered mechanical mixer and a solar-powered mixer. Testing campaign was conducted to monitor the water quality, energy consumption and carbon emission changes to evaluate the feasibility to use off-grid solar-powered mixer in lagoon treatment. In each test, water quality was tested in field to guarantee the performance of the solar-powered mixer. The energy usage was recorded with the electrical energy monitor by the wastewater treatment utility. The result shows that after the replacement, both energy usage and cost have a significant reduction, the energy usage having decreased by 70% and the cost by 47%. Additionally, carbon-equivalent emission from electricity importation dropped by 64%, with an effect on the overall carbon emissions (i.e., including all other contributions from the process) decreasing from 3.5% to 1.3%. The studied solar-powered mixer is adequate to replace the existing mechanical mixer and is an energy and carbon-emission conservation alternative.