Advanced Wastewater Treatment to Eliminate Organic Micropollutants in Wastewater Treatment Plants in Combination with Energy-Efficient Electrolysis at WWTP Mainz

Abstract

To achieve the Paris climate protection goals there is an urgent need for action in the energy sector. Innovative concepts in the fields of short-term flexibility, long-term energy storage and energy conversion are required to defossilize all sectors by 2040. Water management is already involved in this field with biogas production and power generation and partly with using flexibility options. However, further steps are possible. Additionally, from a water management perspective, the elimination of organic micropollutants (OMP) is increasingly important. In this feasibility study a concept is presented, reacting to energy surplus and deficits from the energy grid and thus providing the needed long-term storage in combination with the elimination of OMP in municipal wastewater treatment plants (WWTPs). The concept is based on the operation of an electrolyzer, driven by local power production on the plant (photovoltaic (PV), combined heat and power plant (CHP)-units) as well as renewable energy from the grid (to offer system service: automatic frequency restoration reserve (aFRR)), to produce hydrogen and oxygen. Hydrogen is fed into the local gas grid and oxygen used for micropollutant removal via upgrading it to ozone. The feasibility of such a concept was examined for the WWTP in Mainz (Germany). It has been shown that despite partially unfavorable boundary conditions concerning renewable surplus energy in the grid, implementing electrolysis operated with regenerative energy in combination with micropollutant removal using ozonation and activated carbon filter is a reasonable and sustainable option for both, the climate and water protection.

Pathways to Water Sector Decarbonization, Carbon Capture and Utilization

“…A combination of two or more sludge management technologies (e.g. AD and incineration) is a very common practice at energy efficient plants such as the Mainz WRRF (Gretzschel et al, 2020) and Hamburg's Köhlbrandhöft WRRF (Mills et al, 2014;Laurich, 2011). The implementation of both AD with biogas utilization and biosolids incineration with electricity generation at the WRRFs in Texas led to an estimated 83% reduction in electricity consumption (Stillwell et al, 2010).…”

Seasonal Energy Storage Potential Assessment of WWTPs with Power-to-Methane Technology

“…The calculation of P2G plant capacity on the basis of built-in CHP capacity of WWTPs: After executing the substitution, the calculated capacity is: (9) Although P P2G is more than two times higher than P P2G , due to the constraints of site conditions the authors justified P2G potential at a lower value than P P2G . In accordance with the information collected onsite and all the datasets provided by WWTP site managers, a P2G plant with 1 MW el electrolyzer capacity could be fit to the WWTPs with the load exceeding 100,000 PE in general, because…”

“…Schäfer et al [8] pointed out that WWTPs have notable synergy potential in sector coupling, for example, hydrogen and methane can be produced at WWTPs (with P2G technologies), and the oxygen (as the byproduct of the electrolysis) can be used to enhance purification processes. Gretzschel et al [9] focused on power-to-hydrogen (P2H) technology and the elimination of organic micropollutants at WWTPs, considering the possibility of offering system service, as well: automatic frequency restoration reserve (aFRR), which can provide short-term flexibility for network operators. Ceballos-Escalera et al [10] examined the energy storage attributes of a prototype with a bioelectrochemical system for electromethanogenesis (EMG-BES) at a WWTP, which is an emerging technology in the P2M segment besides chemical and biological methanation.…”

Techno-Economic Assessment of PEM Electrolysis for O2 Supply in Activated Sludge Systems—A Simulation Study Based on the BSM2 Wastewater Treatment Plant

“…O 2 is required in WWTPs by microorganisms in biological treatment steps and can also be transformed into ozone (O 3 ) to be used for disinfection, micropollutant removal, and/or sludge conditioning through ozonation [7,8]. Gretzschel et al [11] have carried out a feasibility study on the use of O 3 produced from electrolysis O 2 for micropollutant removal at a WWTP in Mainz, Germany. There, surplus energy coming from an on-site PV plant is used to operate a 1.25 MW alkaline water electrolyser to supply the 465,206 kg•a −1 of O 2 needed for the ozonation process.…”