The EU Directive 2018/2001 recognized wastewater as a renewable heat source. Wastewater from domestic, industrial and commercial developments maintains considerable amounts of thermal energy after discharging into the sewer system. It is possible to recover this heat by using technologies like heat exchangers and heat pumps; and to reuse it to satisfy heating demands. This paper presents a review of the literature on wastewater heat recovery (WWHR) and its potential at different scales within the sewer system, including the component level, building level, sewer pipe network level, and wastewater treatment plant (WWTP) level. A systematic review is provided of the benefits and challenges of WWHR across each of these levels taking into consideration technical, economic and environmental aspects. This study analyzes important attributes of WWHR such as temperature and flow dynamics of the sewer system, impacts of WWHR on the environment, and legal regulations involved. Existing gaps in the WWHR field are also identified. It is concluded that WWHR has a significant potential to supply clean energy at a scale ranging from buildings to large communities and districts. Further attention to WWHR is needed from the research community, policymakers and other stakeholders to realize the full potential of this valuable renewable heat source.

This paper assesses the performance of waste heat recovery from commercial kitchen wastewater in practice. A pilot study of heat recovery from the kitchen at Penrhyn Castle, a tourist attraction in North Wales (UK), is outlined. The pilot heat recovery site was designed and installed, comprising a heat exchanger, recirculation pumps, buffer tank and an extensive temperature/flow monitoring system for performance monitoring of the waste heat recovery system. Continuous monitoring was conducted for a period of 8 months, covering the 2022 tourist season. The recovered heat from the kitchen wastewater preheats the incoming cold freshwater supply and consequently reduces the amount of energy consumed for subsequent water heating. Retrofitting the pilot heat recovery system to the kitchen drains resulted in a heat saving of 240 kWh per month on average, a reduction of 928.8 kg CO₂e per year, and a payback period for the investment costs of approximately two years, depending on the cost of energy supply. The presented results illustrate the potential of this form of renewable heat in reducing the carbon footprint of water heating activities in buildings and the hospitality sector.

This paper aims to bridge the gap in the detailed modelling of flow and sediment process interactions in sewers through the development of a computational fluid dynamics (CFD) model. It draws on previous models developed for surface water sediment transport in the OpenFOAM CFD framework and builds on them to improve their suitability for sewer sediment processes. Three distinct sediment processes, suspended sediment transport, bedload transport, and deposited bed morphology, are incorporated into a free surface flow solver, interFoam. This sewer sediment model, called SewerSedFoam, models the impacts of sediment deposition and erosion on flow velocity by using dynamic mesh deformation to capture the movement of the deposited bed and its morphology. Further, three sediment classes, two suspended and one bedload sediment, can be modelled along with some bed stabilization and consolidation effects during deposition and erosion, respectively. The functionality of the overall model in modelling sewer sediment deposition and erosion is promising, although the validation of a large magnitude sediment erosion event has been limited by the availability of granular data in existing case studies.

Research involving multistakeholder collaborative partnerships is growing, as both academia and funding agencies align their objectives with societal challenges and undertake research in the context of application. In particular, the UN sustainable development goals mandate green process innovation research that transcends disciplinary boundaries. Responding to this opportunity, this article explores the question: how can researchers, as societal stakeholders, collaborate in the design and implementation of a green process innovation research initiative and produce actionable research-based contributions to knowledge? Drawing upon our shared experience of realizing green process innovation, we describe and conceptualize the collaborative inquiry process, reflecting on the interplay of modes of knowledge production and the complementarity of researchers’ roles. We conclude by noting how researchers collaborating in a green process innovation initiative can shape the environment in which Transdisciplinary research (TDR) develops and play different roles enabling breadth and diversity of interaction, depth of disciplinary integration, and production of different types of knowledge.

To achieve net-zero targets globally, industrial decarbonisation is a major priority. This paper examines lost energy resources in a wastewater treatment plant (WWTP) and the deployment of novel wastewater heat recovery (WWHR) technology in the food and beverage processing industry. Four industrial WWTPs were monitored in Ireland to quantify the available embedded energy. Post monitoring, WWHR technology was developed to be integrated within existing infrastructure without compromising the primary function, and evaluated in real operating conditions. On average, 1.11–2.55 GWh/a of embedded energy was measured within the wastewater. The direct WWHR pilot plant resulted in a projected recovery rate of 10.89 MWh/a, leading to substantial economic savings and emission reductions. Incorporating a water-to-water heat pump incurred energy savings of 13.5 MWh/a. Nationally, the energy recovery potential was assessed to be 82.1 GWh/a in Ireland and 476.9 GWh/a in the UK. A large proportion of the energy embedded in this wastewater remains to be recovered and, based on the monitoring campaign, could amount to 118.5 TWh/a and 20.4 TWh/a for the UK and Ireland, respectively. WWHR could serve a prominent role in increasing operational energy efficiency of manufacturing processes by enacting energy, economic and emission savings, thus leading to industrial decarbonisation.