The Possible Roles of Wastewater Treatment Plants in Sector Coupling

Energy shifting in wastewater treatment using compressed oxygen from integrated hydrogen production

Integrating renewable hydrogen production via electrolysis with wastewater treatment is an opportunity to manage environmental resources more sustainably while providing a pathway to producing sustainable hydrogen at industrial scale. The synergies of integrating oxygen production from water electrolysis and oxygen use in wastewater treatment benefit both hydrogen production and wastewater industries. However, the understanding of the most suitable integrated process configuration and scale of renewable equipment is not known. A novel energy shifting process is proposed here using compressed and stored oxygen produced by water electrolysis and used in the activated sludge process, replacing traditional aeration in the wastewater treatment plant and eliminating the high energy consuming blowers supplying air to submerged fine bubble diffusers. In the proposed energy shifting process, excess oxygen produced by water electrolysis at times of peak renewable electricity production is stored and used for wastewater treatment at times of peak oxygen demand. Wastewater treatment data from the activated sludge process was used to calculate oxygen demand in 1-h intervals over a 24-h period, and the system response of the integrated plant was simulated at hourly intervals and equipment size determined according to an optimisation algorithm that balances oxygen and electricity supply and demand over a 24-h period. Sensitivity analysis of operational parameters is assessed and the case for replacing traditional WWTP aeration with newer technologies is quantified using a high efficiency oxygen transfer system such as a Speece cone as an example that is shown to be a prerequisite for the feasibility of the process. The results produced by this study provide valuable information to the hydrogen and wastewater industries on how an integrated plant could be configured. Besides the environmental advantages of sustainably produced hydrogen, using oxygen as a biochemical energy storage medium in this configuration means WWTP powered from renewable electricity becomes more viable reducing the industries reliance on fossil fuels.

Beyond Traditional Energy Sector Coupling: Conserving and Efficient Use of Local Resources

Decentralisation and sector coupling are becoming increasingly crucial for the decarbonisation of the energy system. Resources such as waste and water have high energy recovery potential and are required as inputs for various conversion technologies; however, waste and water have not yet been considered in sector coupling approaches but only in separate examinations. In this work, an open-source sector coupling optimisation model considering all of these resources and their utilisation is developed and applied in a test-bed in an Israeli city. Our investigations include an impact assessment of energy recovery and resource utilisation in the transition to a hydrogen economy, with regard to the inclusion of greywater and consideration of emissions. Additionally, sensitivity analyses are performed in order to assess the complexity level of energy recovery. The results demonstrate that waste and water energy recovery can provide high contributions to energy generation. Furthermore, greywater use can be vital to cover the water demands in scarcity periods, thus saving potable water and enabling the use of technology. Regarding the transition to hydrogen technologies, resource energy recovery and management have an even higher effect than in the original setup. However, without appropriate resource management, a reduction in emissions cannot be achieved. Furthermore, the sensitivity analyses indicate the existence of complex relationships between energy recovery technologies and other energy system operations.

Impact of a methane emission tax on circular economy scenarios in small wastewater treatment plants

This paper analyzes the impact of methane emissions taxation on the recovery of the investments required for implementing technologies that use biogas energy in small wastewater treatment plants (WWTPs) in Brazil. It is based on the hypothesis that the adoption of a national methane emission tax policy would encourage small WWTPs to become sustainable power plants. The procedure involved 173 anaerobic plants to analyze: (a) methane production; (b) available useful energy; (c) investments and avoided costs for implementing STHIL system (thermal drying sludge) and motor generator (electricity generation); (d) financial impact for two scenarios (C1: no emissions tax; C2: with tax). Positive environmental and financial results were observed for WWTPs, varying according to the period of time analyzed for both technologies. Investments must be made in cogeneration in anaerobic WWTPs for achieving satisfactory results. Taxation must not be viewed simply as a punitive instrument; on the contrary, it should be seen as a tool to encourage continuous process improvement. The circular economy may support the enlargement of the wastewater collection and treatment system, guaranteeing widespread sanitation conditions in urban areas. However, the actual implementation of a methane emission tax in Brazil still requires many rounds of discussion among sanitation companies, government, and civil society, to establish emission limits, and unit taxes, as well as to consolidate a carbon trade to follow through with this decision in the sanitation sector.

Wastewater Treatment Plants as Local Thermal Power Stations—Modifying Internal Heat Supply for Covering External Heat Demand

To counteract climate change, the application of renewable energy sources and their efficient use are of crucial importance. In this context, wastewater has also gained increased attention in recent years. For decades, wastewater treatment plants have applied the heat from digester gas combustion to supply internal demands. However, in the context of efficient energy use the question arises: can using high temperature heat for supplying low temperature demand still be considered the best option? This article presents an innovative approach to covering wastewater treatment plant (WWTP) internal demand with low temperature wastewater heat recovery, making thermal energy from digester gas combustion available for feed-in to a local high temperature district heating network. The presented feasibility study was carried out in an Austrian municipality and investigates the heat balance, the economic risk, climatic benefits and the social aspects of the suggested approach. The practical implementation of the novel approach was planned in two steps. First, the WWTP should be connected to the district heating network to enable the feed-in of excess heat. Second, the WWTP internal heat supply should be modified and based on wastewater heat recovery from the effluent. Due to the promising results of the feasibility study, the first step was realized in summer 2020. The second and final step was initiated in 2021.

Energy Flexibility Chances for the Wastewater Treatment Plant of the Benchmark Simulation Model 1

Future energy systems must mainly generate electricity from renewable resources. To deal with the fluctuating availability of wind and solar power, new versatile electricity markets and sustainable solutions concentrating on energy flexibility are needed. In this research, we investigated the potential of energy flexibility achieved through demand-side response for the wastewater treatment plant of the Benchmark Simulation Model 1. First, seven control strategies were simulated and assessed. Next, the flexibility calls were identified, two energy flexibility scenarios were defined and incorporated into the model, and the control strategies were evaluated anew. In this research, the effluent ammonia concentration needed to be maintained within the limits for as long as possible. Strategy 5, which controlled ammonia in Tank 5 at a low value and did not control any nitrate in Tank 2, of Scenario 1, which was characterized by an undetermined on/off aeration cycle, was then found to be the best. Although this control strategy led to high total energy consumption, the percentage of time during which aeration was nearly suspended was one of the highest. This work proposes a methodology that will be useful to plant operators who should soon reduce energy consumption during spikes in electricity prices.

Energetic Potential for Biological Methanation in Anaerobic Sewage Sludge Digesters in Austria

Biological methanation as a method of sector coupling between electric and gas grids is expected to be an integral part of the green energy change. Wastewater treatment plants (WWTPs) involving anaerobic digestion (AD) allow existing infrastructure to operate as energy conversion plants, to close carbon cycles and to generate long-term storable energy in the form of biomethane. Therefore, municipal raw sludge and additional organic residuals (co-substrates) are converted into biogas. Hydrogen is added to convert the carbon dioxide in the biogas into methane via biological methanation (BM). In this study, the energy amount that is convertible via BM in municipal digesters in Austria was calculated. The amount of energy, which can be transformed from electric surplus energy into biomethane, was assessed. Operational data from lab-scale digesters were combined with data from 28 Austrian full-scale wastewater treatment plants with AD. They represent 9.2 Mio population equivalents (PE), or 68% of Austria’s municipal AD capacity for WWTPs > 50,000 PE (in sum, 13.6 Mio PE). Energy flows for BM including water electrolysis and anaerobic digestion were created on a countrywide basis. It was found that 2.9–4.4% (220–327 GWh·y−1) of Austria’s yearly renewable electricity production (7470 GWh·y−1) can be transformed into biomethane via BM in municipal digesters.

Disruption Potential Assessment of the Power-to-Methane Technology

Power-to-methane (P2M) technology is expected to have a great impact on the future of the global energy sector. Despite the growing amount of related research, its potential disruptive impact has not been assessed yet. This could significantly influence investment decisions regarding the implementation of the P2M technology. Based on a two-year-long empirical research, the paper focuses on exploring the P2M technology deployment potential in different commercial environments. Results are interpreted within the theoretical framework of disruptiveness. It is concluded that P2M has unique attributes because of renewable gas production, grid balancing, and combined long-term energy storage with decarbonization, which represent substantial innovation. Nevertheless, empirical data suggest that the largest P2M plants can be deployed at industrial facilities where CO2 can be sourced from flue gas. Therefore, a significant decrease of carbon capture technology related costs could enable the disruption potential of the P2M technology in the future, along with further growth of renewable energy production, decarbonization incentives, and significant support of the regulatory environment.

Evaluating Spatial Interdependencies of Sector Coupling Using Spatiotemporal Modelling

In light of global warming and the energy turn, sector coupling has gained increasing interest in recent years, from both the scientific community and politics. In the following article it is hypothesized that efficient multifaceted sector coupling solutions depend on detailed spatial and temporal characteristics of energy demand and supply. Hence, spatiotemporal modelling is used as a methodology of integrated spatial and energy planning, in order to determine favourable sector coupling strategies at the local level. A case study evaluation was carried out for both central and decentral renewable energy sources. Considering the high temporal resolutions of energy demand and supply, the results revealed a feasible operation of a district heating network in the central areas of the case study municipalities. Additionally, building integrated solar energy technologies are capable of providing large amount of excess energy that could serve other demand sectors, such as the mobility sector, or could be used for Power-to-X solutions. It is suggested that sector coupling strategies require spatial considerations and high temporal comparisons, in order to be reasonably integrated in spatial and urban planning.

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

Power-to-methane technology (P2M) deployment at wastewater treatment plants (WWTPs) for seasonal energy storage might land on the agenda of decision-makers across EU countries, since large WWTPs produce a notable volume of biogas that could be injected into the natural gas grid with remarkable storage capacities. Because of the recent rapid increase of local photovoltaics (PV), it is essential to explore the role of WWTPs in energy storage and the conditions under which this potential can be realized. This study integrates a techno-economic assessment of P2M technology with commercial/investment attractiveness of seasonal energy storage at large WWTPs. Findings show that a standardized 1 MWel P2M technology would fit with most potential sites. This is in line with the current technology readiness level of P2M, but increasing electricity prices and limited financial resources of WWTPs would decrease the commercial attractiveness of P2M technology deployment. Based on a Hungarian case study, public funding, biomethane feed-in tariff and minimized or compensated surplus electricity sourcing costs are essential to realize the energy storage potential at WWTPs.

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

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.