Wastewater Heat Recovery Research Articles

Improving Wastewater Heat Recovery Using Phase Change Material Heat Exchangers: A Numerical Study of Thermal Performance

ABSTRACTIndustrial processes often generate substantial amounts of wastewater with significant thermal energy content, which is typically discarded as waste. A promising approach to increase energy efficiency and advance sustainable resource management is waste water heat recovery. Utilizing a phase change material (PCM) to extract waste heat from wastewater and transfer it to cold water is an innovative method that separates the demand and supply of heat, while also integrating storage and transmission within a single heat exchanger (HE). A 3D numerical model of PCM‐based HE is developed and simulated. The thermal behavior of PCM and preheating of cold water are investigated in this study. In order to increase the thermal conductivity of the PCM, fins are strategically positioned. Around 71.13% of melting time is reduced by adding fins. Further, the 10° orientation of the fins is also numerically observed and it is found that it helps to improve natural circulation of molten PCM. Thus, melting time is reduced by 34% compared to the vertical fin. A 3.5°C–4.5°C temperature rise in cold water is obtained with the inclined fin, which is 14.28% higher than the vertical fin model.

The characteristics of heat exchanger for local utilization of wastewater heat under different operating conditions

RELEVANCE. The authors research the local utilization of wastewater heat (in close proximity to the place of their formation) based on a heat exchanger. To select rational characteristics of the heat exchanger and correctly assess the potential energy effect, it is necessary to take into account the influence of the operating conditions of the device (duration of individual use of the shower, mass flow of heated and heating water, temperature of heated water at the inlet to the heat exchanger, temperature of the flow at the moment the device is turned on).THE PURPOSE. The purpose of the work is to research the dependence of the efficiency of wastewater heat utilization on the operating conditions of the heat exchanger and to identify the parameters that have the greatest impact on the effect of energy-saving measures.METHODS. Based on a verified mathematical model of the thermal operation of a recovery heat exchanger, the temperature distribution inside the flows of the heated and heating water in time is calculated (from the moment of switching on until reaching a stationary operating mode). Based on the data obtained (the temperature of the heated water at the outlet of the heat exchanger at each point in time), the absolute and relative heat savings are determined under various operating conditions.RESULTS. The influence of the non-stationary phase of the heat exchanger operation on its energy efficiency is considered. For a specific heat exchanger configuration, the time required for the device to reach a steady state of thermal operation is determined. It was revealed that the greatest influence on the relative and absolute savings of thermal energy is exerted by such operating conditions as mass flow and temperature of heated water at the entrance to the heat exchanger. The temperature of the flow at the initial moment of time has the least influence on the energy effect.CONCLUSION. The operating conditions that have the greatest impact on the effect of local wastewater heat recovery are determined. The need to take these conditions into account when designing a heat exchanger and choosing its optimal parameters has been confirmed.

Economic–environmental trade-offs based support policy towards optimal planning of wastewater heat recovery

Wastewater heat, a promising alternative to traditional district heating and cooling sources, can be recovered using heat pumps and transmitted to surrounding buildings for winter heating and summer cooling. Despite its potential benefits, the policies to support wastewater heat recovery remain limited. This study provides support policies for local governments to encourage energy recovery in urban wastewater treatment plants, incorporating subsidies and renewable energy certificates. The local government aims to maximize the recovered energy, minimize the subsidy expenditure, and minimize the certificate price. Urban wastewater treatment plants seek to optimize producer profits under realistic planning constraints. This model was applied in Chengdu, China, which indicates that plants with a daily treatment scale exceeding 30,000 m3 can invest in heat recovery without support policies, achieving recovery ratios of only 27%–29%. As the calculated electricity charge accounts for about 90% of operating cost, the electricity price subsidy proves the most significant in improving the installed capacities, followed by renewable energy certificates, capital refunds, and tax reductions. Electricity prices and renewable energy certificates have combination and substitution effects. Further analysis shows that heat pump efficiencies have low sensitivity in project feasibility. Fluctuations in infrastructure costs have a minimal impact, while charges for heating and cooling services significantly influence feasibility. Lowering the available thermal energy ratio also affects project returns. The government can reduce risks in sensitive parameters by electricity price subsidies or renewable energy certificates.

Numerical investigation of coupled heat transfer and flow characteristics in helical coil heat exchanger for mine water waste heat recovery

To efficiently recover waste heat from mine water, this study numerically investigates the flow and heat transfer performance of a tube-shell coupled helical coil heat exchanger (HCHE), under high Reynolds number conditions. The effects of inlet water temperature, mass flow rate (m), tube diameter (d), and helix pitch (P) on the tube side, shell side, and overall performance are analyzed. Performance metrics include friction factor (f), Nusselt number (Nu), overall heat transfer coefficient (U), heat transfer rate, and the Performance Evaluation Criteria (PEC) number. Specifically, this study focuses on detailed observation and analysis of the shell-side flow and temperature fields. Findings reveal that enlarging d from 30 mm to 50 mm results in a 32.55% decrease in U, whereas increasing P from 50 mm to 200 mm boosts U by 8.02%. The highest PEC number of HCHE is 2.43, observed in conditions of P = 50 mm, d = 30 mm, and mc = 4 × 103 kg/h. Correlations for fc, Nuc, and Nush are proposed based on simulation results. This study provides a theoretical basis for the design and structural optimization of HCHE in the mine water waste heat recovery applications.

A Modeling Analysis of Wastewater Heat Recovery Effects on Wastewater Treatment Plant Nitrification

A global shift towards renewable energy production, driven primarily by the challenges posed by climate change, is currently underway. In this context, the utilization of heat recovery from municipal wastewater emerges as a promising green technology. Notably, the advantage of implementing energy recovery in sewers, as opposed to wastewater treatment plants (WWTPs), lies in the higher temperature of the wastewater and its proximity to potential heat users. Despite these benefits, concerns arise regarding the potential adverse effects on biological wastewater treatment processes downstream of the heat recovery section, particularly during colder seasons. This paper seeks to assess the impact of a heat recovery system along the sewer network on the efficiency of biological wastewater treatment processes. The methodology involves a modeling analysis of a real sewage network in Italy. Under typical northern Italy climate conditions, the results demonstrate the feasibility of heat recovery in sewers for WWTPs designed with a sludge residence time under aerobic conditions (SRTaer) greater than 13 days. In such cases, the nitrification process remains relatively unaffected. However, for lower SRTaer values, a case-specific feasibility assessment is recommended to evaluate the overall process efficiency comprehensively.

A new evaluation framework for the assessment of wastewater heat recovery potential coupled with wastewater reuse

Abstract The integration of wastewater heat recovery (WWHR) and wastewater reuse offers a numerous advantage, making its application possible in various sectors. Nevertheless, this concept faced challenges to the identification of appropriate location. Existing research lacks comprehensive evaluation methods that encompass a various factor for effective decision-making. This study introduces a new evaluation framework that involves different aspects, including thermal energy potential and spatial distribution analysis. The novelty of this research lies in its unique focus on the combination of WWHR and wastewater reuse. Moreover, it introduces a structured evaluation framework that considers multiple criteria and expert opinions, enhancing decision-making precision. Multi-criteria decision analysis (MCDA) was applied to select assessment criteria, which were categorized into three aspects: water–energy supplier, water–energy consumers, and water–energy station. The relative importance of criteria was determined using the analytical hierarchical process (AHP). The results of the AHP highlight significance of factors: treated wastewater flow rate; treated wastewater temperature; water–energy supply distance, and type of water–energy consumer. These factors were assigned weight values of 0.297, 0.186, 0.123, and 0.096, respectively. It is emphasizing their influence in the decision-making process that potential locations depend on the water–energy supplier and water–energy consumer as supply and demand sources.

Experimental characterization of a spiral heat exchanger for waste water heat recovery from partially filled sewage pipes

This paper focuses on the experimental characterization of horizontal, spiral heat exchangers used for heat recovery from sewage pipes. Such non-intrusive heat exchanger configurations are appealing for this application, but they often exhibit reduced heat exchange performances compared to more compact designs. To compare the performance of this configuration with that of an ideal counter-flow heat exchanger, a representative test setup was constructed. As the sewer pipes are generally not completely filled, tests were conducted using three different fillings (100%, 50%, 33%) and a filling parameter z was introduced in the heat transfer equations. Correction factors to be applied in the Logarithmic Mean Temperature Difference (LMTD) design method for this specific spiral configuration were derived from the test results. It was found that the filling of the sewer pipe has minimal impact on the correction factor, which ranges between 0.78 and 0.83. The average value of 0.81 is recommended for design purposes.

Design and Long-Term Performance of a Pilot Wastewater Heat Recovery System in a Commercial Kitchen in the Tourism Sector

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.

Unleashing wastewater heat Recovery's potential in smart building systems: Grey wolf-assisted optimization aided by artificial neural networks

This article presents an innovative and efficient way to address residential dwellings' substantial heating needs. The primary objective is to utilize the heat from wastewater to enhance energy efficiency through a control framework based on predetermined rules. This framework aims to increase the incoming air temperature at the air handling unit. A thorough evaluation is carried out to analyze all aspects of the proposed system compared to an identical system that does not incorporate the wastewater heat recovery process. The practicality of the concept is assessed for a residential building located in Beijing, China, employing the TRNSYS software. The most optimal operating condition is achieved via the grey wolf optimizer and TOPSIS decision-making approach equipped with the artificial neural network using MATLAB. Then, the proposed system's performance under optimal conditions is compared with similar works in the literature. According to the results, compared to the conventional system, a higher performance efficiency of 6 % and lower levelized cost of heating of 15.6 $/MWh is obtained by implementing the wastewater heat recovery process. The parametric study results also demonstrate a conflicting change in techno-economic and environmental indicators when altering the primary decision variables, highlighting the necessity for multi-criteria optimization. What stands out from the optimization outcomes is that the grey wolf method increases the efficiency and CO2 saving by around 5.2 and 531.2 kg/year while reducing the levelized cost of heating by about 13.6 $/MWh, respectively. The optimization results reveal that this condition is attained by raising the heat exchanger's effectiveness and the number of residences and decreasing the wastewater temperature. According to the scatter distribution of key parameters, the energy wheel effectiveness has low sensitivity, and the optimal points of tank volume are distributed within the range of 3 m3 and 4 m3.

Reducing the Energy and Environmental Impact of Commercial Kitchen Water Use: Assessment of Wastewater Heat Recovery in a Grease Interceptor and Its Impact on Fat, Oil, and Grease Removal Capabilities

Reducing the Energy and Environmental Impact of Commercial Kitchen Water Use: Assessment of Wastewater Heat Recovery in a Grease Interceptor and Its Impact on Fat, Oil, and Grease Removal Capabilities

Is on-property heat and greywater recovery a sustainable option? A quantitative and qualitative assessment up to 2050

This article deals with ongoing attempts to recover heat and greywater at property level, based on an in-depth study of Stockholm, Sweden. We explore different socio-technical development paths from now up until 2050 using a novel combination of on-property technology case-studies, actor studies and system-level scenario evaluation, based on Artificial Neural Networks modelling. Our results show that the more conservative scenarios work in favour of large-scale actors while the more radical scenarios benefit the property owners. However, in the radical scenarios we identify disruptive effects on a system level due to disturbance on wastewater treatment plants, where incoming wastewater can be critically low for up to 120 days per year. At the same time, net energy savings are relatively modest (7.5% of heat demand) and economic gains for property owners small or uncertain. Current policies at EU and national level around energy-efficient buildings risk being counter-productive in cases when they push property owners to install wastewater heat recovery technology which, in places like Stockholm, can create suboptimal outcomes at the system level.

Waste Water Heat Recovery Systems types and applications: Comprehensive review, critical analysis, and potential recommendations

One of the most effective ways to deal with the effects of the current global energy crisis is to reduce energy consumption and rely energy management strategies. As a result, waste heat/energy recovery might be a helpful option for decreasing energy costs and environmental effect. It entails finding a practical way to apply any engineering system’s wasted heat where the percentage of wasted heat is too high in global. In this context, waste hot water is a rich source of wasted energy that, if recovered, can significantly cut down on the amount of electricity used worldwide. Within this framework, the present research paper provides a thorough analysis of Waste Water Heat Recovery Systems (WWHRS) in terms of performance, design, tools and applications. In addition, it is highlighting the key elements associated with WWHRS, including the wastewater sources and approaches used in the literature for waste water heat recovery. Moreover, the present paper demonstrates the effect of the heat recovery from the drain waste water on economically and discuss the technical barriers to using WWHRS. It will be demonstrated that the feasibility of recovering heat from waste water could decrease significantly the cost of energy consumption for residential or industrial application. In addition, the main tools that are used for heat recovery systems is the heat exchanger where various types are used and the thermal performance are strongly affected by the choice of heat exchangers. Moreover, based on the literature review, it is shown that the methods of studying the thermal performance of the heat recovery system are experimental and/or numerical and in some cases the study is performed analytically. Finally, all discussed and presented studies demonstrate that the WWHRS has a significant benefits and could be considered for new residential construction.

Renewable energy of wastewater heat recovery.

Wastewater heat recovery (HR) is one of the renewable energy sources. The associated harmful environmental, health, and social effects of traditional biomass, fossil fuel, and other polluted sources have enhanced the growing interest in the search for an alternate cleaner energy source globally. The major objective of this study is to develop a model to assess the impacts of wastewater flow (WF), the temperature of wastewater (TW), and internal temperature in sewer pipes (TA) on the performance of HR. Sanitary sewer networks in Karbala city of Iraq were chosen as a case study in the present research. Statistical and physically based models such as the storm water management model (SWMM), multiple-linear regression (MLR), and structural equation model (SEM) were used for this purpose. The model outputs were analyzed to assess the performance of HR in the context of changing WF, TW, and TA. The results showed that the total amount of HR from wastewater in Karbala city center during the 70 days was 136,000 Mw. The study clearly showed that WF in Karbala played a major role in HR. Basically, the heat from wastewater is CO2-free and represents a significant opportunity for the energy transition in the heating market.

Physical Separation: Reuse Pollutants and Thermal Energy from Water

Conventional sewage treatment based on biological and chemical methods have made historical contributions to humans. However, it breaks the biogeochemical cycles of carbon, nitrogen, and phosphorus and cannot remove hazardous materials including viruses and nano/microplastics. Therefore, we rethought the conceptual revolution of principles of sewage treatment in the 1890s, that is, “the replacement of a philosophy that saw sewage purification as the prevention of decomposition with one that tried to facilitate the biological processes that destroy sewage naturally”. We proposed a promising sewage treatment system based on physical separation, which mainly consists of the source separators and the insoluble-pollutants separators, soluble-pollutants separators, and the wastewater heat recovery devices in wastewater treatment plants. By using the promising system, the carbon in wastewater will be recovered by sending biosolids directly into the soil after removing the hazardous materials and organic toxicity. The nitrogen and phosphorus in wastewater will be sent back into the soil or be used for hydroponics rather than be mineralized. The thermal energy in wastewater will be recovered and reused, and the hazardous materials will be removed. As a result, the promising system will turn the wastewater treatment system with high resource and thermal energy waste and high energy consumption into a no-chemicals, green factory. At present, nonetheless, it is still urgent to develop more advanced insoluble-pollutants separators and soluble-pollutants separators with high separation efficiency and low energy consumption, especially volume separators. Because the volume separators (e.g., functionalized sand filters) have the potential for replacing the surface separators (e.g., membranes).

Determination of the optimal heat exchanger configuration for wastewater heat recovery

The work aims to increase the efficiency of the hot water supply system based on local recovery of the heat of wastewater generated in the shower room for preheating cold water. The work uses mathematical modeling of the thermal operation of the heat exchanger under study. Physical modeling of the heat exchange process between media flows in a heat exchanger was carried out (experimental test). Temperatures of media flows were measured. The temperature distribution inside media flows was compared experimentally with data obtained analytically. In conclusion, an analysis and generalization of the results obtained is made. The result of the research was a designed recovery heat exchanger. Data were obtained on the thermal inertia of the device, i.e., about the required time for the device to achieve a stationary thermal regime from the moment it is turned on. Data were obtained on the potential energy effect from introducing a recovery heat exchanger, taking into account its thermal inertia. The number of showers required to pay off the heat exchanger was calculated. Data were obtained on the influence of changes in the geometric and operating parameters of the heat exchanger on the efficiency of wastewater thermal energy utilization. A methodology for designing a heat exchanger for specific operating conditions was developed. The developed method for designing a recovery heat exchanger allows one to determine the optimal configuration of the device under particular operating conditions and mode of use of the heat exchanger, taking into account its thermal inertia. It is planned to continue the work by assessing the energy and economic effect of using local wastewater heat recovery within the heat supply system of a separate settlement/region.

Energy, environmental and economic assessment of wastewater heat recovery systems in hotel buildings

Wastewater heat pump system has been extensively researched due to its benefits in terms of energy conservation and environmental preservation. Most of these studies, however, use R134a or R22 as refrigerants, which are being phased out. This research selects the transcritical CO2 heat pump for wastewater heat recovery, the model is built in TRNSYS software, and the energy, environment, and economy analyses of the three systems are examined. The results reveal that the regenerative heat pump system (RHPS) can save 76.67% more energy than the regenerative boiler system (RBS). The RHPS has a larger initial investment than the RBS, but the yearly carbon dioxide emission is reduced by 33.99 tons, and the life cycle cost is lowered by 1452.55 thousand CNY. Furthermore, RHPS can reach the peak of the annual average cost difference earlier with the support of government policy, and the annual average cost difference has increased by around 21–29% more than that without the subsidies. This research will help to promote the combination and implementation of the transcritical CO2 heat pump in wastewater heat recovery technology.

Geographically Weighted Regression-Based Predictions of Water–Soil–Energy Nexus Solutions in Île-de-France

Due to global urbanization, urban areas are encountering many environmental, social, and economic challenges. Different solutions have been proposed and implemented, such as nature-based solutions and green and blue infrastructure. Taking into consideration exogenous factors that are associated with these solutions is a crucial question to assess their possible effects. This study examines the possible explanatory factors and their evolution until the year 2054 of several solutions in the Île-de-France region: wastewater heat-recovery, surface geothermal energy, and heat-mitigation capacities of zones. This investigation is performed by a series of statistical models, namely the ordinary least squares (OLS) and the geographically weighted regressions (GWR), integrated within a geographic information system. The main driving factors were identified as land use/land cover and population distribution. The results show that GWR models capture a large part of spatial autocorrelation. Apropos of prediction results, areas with low, medium, and high potential for implementing specific solutions are determined. Furthermore, the implementation capacities of solutions are compared with the demand depicted as the need for slowing down the effects of surface urban heat islands and the dependence on fossil energy. Moreover, the heat mitigation capacities are not at all times distinctively linked to human activities. Further investigations are needed to discover the remaining possible reasons, particularly air quality, water, vegetation, and climate change.

Energy saving for an air conditioning system applied in a thin-film-transistor liquid-crystal display (TFT LCD) high-tech fabrication plant (Fab)

Data collected from this research is used to calculate energy consumption of the thin-film-transistor liquid-crystal display (TFT LCD) air-conditioning system. These results are then used to determine how much energy can be saved and proposes to reduce the energy consumption of the chiller component of the air conditioning system. Analysis based on factory operation data collected in the past indicates that process machine operation accounts for 45% of total energy usage. In addition to the power consumption of the factory system, compressed dry air CDA accounted for 22% of the total energy consumption. The high temperature chiller accounted for 7% and ranks second, while third is FFU power consumption, accounting for 6%. When evaluating the feasibility of energy conservation, it is necessary to collect operating parameters and evaluate the operating efficiency of the equipment to identify potential changes to effect energy conservation. According to preliminary analysis of distribution and operation data, it is found that the current filter used in the fan filter frame (FFU) responsible for the clean room circulation is a traditional high-efficiency filter made of glass fiber. Glass fiber filters can be replaced with PTFE filters, offering potential energy savings associated with lower pressure drop. The factory does not add CDA cooling water waste heat recovery and utilization in the warm water system. After the addition of this recovery system, the cooling water temperature will increase by 0.6 °C and the estimated electric boiler energy saving is 1.86%.If the new generation high-efficiency chiller were installed, under typical operating conditions where the load is between 70% and 90%, annual efficiency is expected to be between 0.423 kW/RT and 0.412 kW/RT, which is expected to save 2.6% when compared with older generation chiller technology.; If two sets of the original chillers are replaced with one chiller in constant use and one in standby configuration, the annual efficiency is 0.4 kW/RT, saving 5.4%. Replacing a configuration of four sets with three in constant use and one in standby configuration, the annual efficiency is 0.388 kW/RT, saving 8.3%.

Optimizing wastewater heat recovery systems in textile dyeing processes using pinch analysis

• An optimal WWHR system for textile dyeing was developed using a two-step approach. • The two-step approach comprises the scenario definition and pinch analysis. • The cost-optimal WWHR system lowered the energy usage by 28.64% and TAC by 73.65%. • The PBP of the optimal WWHR system was 4.32 y. Textile manufacturing discharges large amounts of wastewater containing significant amounts of thermal energy. The textile dyeing process consists of several complex processes with different operating times, temperatures, and water usage. The absence of a suitable wastewater heat recovery (WWHR) system requires a large amount of energy for heating fresh water and cooling wastewater. Therefore, recovering wastewater while satisfying the operating conditions of each process is crucial. Herein, we suggest an optimal design for WWHR systems to maximize the energy efficiency in the textile dyeing process using pinch analysis by a novel two-step approach. First, the scenarios for all feasible WWHR methods were defined, and the WWHR systems were designed accordingly by integrating a heat pump and heat exchanger. Second, the heat exchanger network of the developed WWHR systems was modified based on pinch analysis to maximize the waste-heat recovery efficiency. Finally, to derive the cost-optimal WWHR system, a techno-economic analysis was conducted. The total annualized cost (TAC), based on the capital and operating cost, was determined based on current and potential future economies. The proposed energy-saving measures reduced the TAC by 28.6% and obtained a payback period of up to 4.3 y.

Evaluation of increased electricity production when cooling solar panels

A municipal housing company located in the south of Sweden has energy renovated several buildings with a total of 380 apartments to meet today’s energy standards. Several energy efficient technologies and solutions were implemented and the energy consumption for these buildings were lowered by 50%. One of the buildings functions as a demonstration building for innovative solutions such as low temperature district heating, waste water heat recovery, and solar photovoltaic and thermal (PVT) panels. The solar PVT panels are cooled down with the main purpose to increase the electricity production. The cooling medium for these panels is circulated through two bedrock boreholes to dissipate the collected heat. The heat from the boreholes is then used for an electric heat pump to produce heat to send to the local district heating company. The electricity produced is primarily used in the building. The objective of this paper is to assess the electricity production from real-life outdoor Photovoltaic-thermal (PVT) plant. The plant was installed on the roof top of an energy renovated multi-family apartment building located in the south of Sweden. The cooling of the panels were turned on and off to assess if the electricity production would increase or not. The electricity production did not increase when the cooling was applied. The temperature measuring equipment which was installed at the wrong position and was supposed to measure the temperature at the back of the PVT is needed to compare the efficiency of the PVT plant and draw further conclusions.