Near zero energy wastewater treatment plants for the Greek islands

Abstract

Conventional wastewater treatment is an energy-intensive process, requiring electric energy of about 1.1–2.4 MJ/m3, being higher in plants with relatively small hydraulic capacity (<5,000 m3/d). Solar energy can be used to supply electric energy, particularly for the Greek islands; however, the huge energy demand of the wastewater treatment is a drawback for the use of photovoltaic energy, due to the additional capital cost and electricity storage requirements during the night. Here, a novel approach for wastewater treatment is proposed, based on enhanced primary solids removal, by the use of advanced sieving and filtration processes, utilizing a proprietary rotary fabric belt microscreen followed by a proprietary continuous backwash upflow media filter. Raw municipal wastewater treated with the above process results in about 80–90% reduction in TSS and 60–70% reduction in BOD5. The overall electrical power requirements for a novel configuration plant with hydraulic capacity of 1,000 m3/d (typical capacity for small settlements in the Aegean islands) have been calculated to about 10 kW, as compared to over 25 kW for a conventional activated sludge system with the same capacity.