Abstract
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.
Highlights
Wastewater treatment using the activated sludge process requires large amounts of energy for removing the contained pollutants
There are various approaches which can assist in the achievement of zero CO2 emissions wastewater treatment plants (WWTPs) due to energy use, including: a) Increase of the energy efficiency in the plant, b) Utilizing the biogas produced from sludge digestion and increasing its yield with appropriate mixing with various other wastes having high organic content, c) Use of solar-PV technology, d) Use of wind power technology, e) Burning of the bio-solids produced for electricity generation, f) Use of high efficiency heat pumps utilizing the low enthalpy heat of the liquid wastes in the plant for the production of heat and cooling, and g) Offsetting CO2 emissions in the plant with carbon sequestration from tree plantations irrigated by the treated effluent
Annual electricity consumption in the sewage treatment plant of Chania has been estimated at 0.543 KWh/M3 and its current annual CO2 emissions due to grid electricity use at 0.33 kg CO2/M3
Summary
Wastewater treatment using the activated sludge process requires large amounts of energy for removing the contained pollutants. The authors have analyzed data from 1856 plants in 2009 and they have estimated an average energy consumption at 0.254 KWh/M3. They have reported that the aeration stage had a share of more than half the total energy consumption. The authors studied small scale WWTPs, estimating their overall energy consumption at 1.046 KWh/M3 They reported that the share of electricity consumption is approximately 50 % of the total energy use whilethe manual energy consumption is 32% of the total. The authors studied the energy consumption in twelve (12) Australian WWTPs using the activated sludge process They estimated that their electrical energy consumption varied from 0.323 KWh/M3 to 1.701 KWh/M3. The authors concluded that Australian WWTPs could improve their energy efficiency through self-supply systems, co-generation of heat and power from biogas. Maslon, 2017 analyzed the energy eer.ccsenet.org
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