Operation of a circular economy, energy, environmental system at a wastewater treatment plant

Abstract

Decarbonising economies and improving environment can be enhanced through circular economy, energy, and environmental systems integrating electricity, water, and gas utilities. Hydrogen production can facilitate intermittent renewable electricity through reduced curtailment of electricity in periods of over production. Positioning an electrolyser at a wastewater treatment plant with existing sludge digesters offers significant advantages over stand-alone facilities. This paper proposes co-locating electrolysis and biological methanation technologies at a wastewater treatment plant. Electrolysis can produce oxygen for use in pure or enhanced oxygen aeration, offering a 40% reduction in emissions and power demand at the treatment facility. The hydrogen may be used in a novel biological methanation system, upgrading carbon dioxide (CO 2 ) in biogas from sludge digestion, yielding a 54% increase in biomethane production. A 10MW electrolyser operating at 80% capacity would be capable of supplying the oxygen demand for a 426,400 population equivalent wastewater treatment plant, producing 8,500 tDS/a of sludge. Digesting the sludge could generate 1,409,000 m 3 CH 4 /a and 776,000 m 3 CO 2 /a. Upgrading the CO 2 to methane would consume 22.2% of the electrolyser generated hydrogen and capture 1.534 ktCO 2 e/a. Hydrogen and methane are viable advanced transport fuels that can be utilised in decarbonising heavy transport. In the proposed circular economy, energy, and environment system, sufficient fuel would be generated annually for 94 compressed biomethane gas (CBG) heavy goods vehicles (HGV) and 296 compressed hydrogen gas fuel cell (CHG) HGVs. Replacement of the equivalent number of diesel HGVs would offset approximately 16.1 ktCO 2 e/a. • Curtailed electricity from a 144 MW offshore wind farm can supply a 10MW electrolyser • A 10 MW electrolyser can supply O 2 to a 426,400 person wastewater treatment facility • Only 22% of the H 2 is required for methanation of biogas from sludge digestion • Pure O 2 aeration can result in a 40% reduction in emissions at the treatment facility • Excess H 2 and biomethane could together fuel 390 heavy goods vehicles