Creation of Zero Carbon Emissions Wastewater Treatment Plants - A Case Study in Crete, Greece

Wastewater treatment plants use energy intensive processes for removing pollutants, consuming large amounts of electricity and emitting greenhouse gases. The possibility of zeroing carbon emissions due to energy use in these plants has been investigated in the current work with reference to the municipal treatment plant of Chania on the island of Crete, Greece. The sewage treatment plant processes 19,400 M3 daily consuming 0.543 KWh per M3 or 3840 MWh annually. The use of locally available renewable energies has been proposed for electricity generation combined with co-generation of heat and power from the biogas already produced in the plant with sludge digestion. Installation of solar-PV systems and wind turbines in the plant could generate electricity, each equal to 25 % of the annual electricity consumption in the plant. Additionally, biogas use can cover all the heating needs in the plant and can generate electricity corresponding at 20% of the total annual grid electricity use. Creation of a tree plantation, irrigated by the treated effluent, of 118.4 hectares, has been proposed which could annually offset carbon emissions due to the remaining grid electricity use. Creation of the tree plantation will create additional benefits, due to existing land desertification in Crete, additionally to carbon sequestration. The size of the required solar-PV and wind turbine systems has been estimated at 640 KWp and 391 KW and their cost at 0.832 mil € and 0.430 mil € correspondingly. Current work indicates that the combined use of solar energy, wind energy, biogas and carbon sequestration with tree plantations could zero carbon emissions in the municipal sewage treatment plant of Chania, Crete.