The use of greywater reduces the consumption of many resources and is an effective tool for achieving Sustainable Development Goals. In order to assess the rationality of its use as an alternative source of energy and water in buildings, a holistic literature review was carried out based on a bibliometric analysis of publications in these fields. The main bibliographic source was the Web of Science database. This review contributed to a better understanding of the analyzed research field. It also revealed trends in greywater energy recovery and recycling research, indicating that these are developing fields. In recent years, there has been a marked increase in the number of publications on the most popular ways of using greywater in buildings, with the territorial scope of research carried out in the greywater recycling domain being considerably larger than research on greywater energy recovery. The analysis revealed poor cooperation between different universities, especially in the field of greywater energy recovery. In light of previous literature reviews, some important research gaps and further proposals for future research were also identified. They concern, in particular, the simultaneous use of greywater as an alternative source of energy and water. Together with the findings of other researchers and people related to the subject matter, this review can contribute to the further development of greywater energy recovery systems and greywater recycling systems.

In recent years an increase of interest in usage of renewable energy sources as a substitution of fossil fuels is being noticeable. However, the waste heat potential, which can be used as an additional source of energy for heating water in buildings, is being omitted. The sources of this heat can be grey water discharged from such sanitary facilities as showers or washing machines. In response to this issue, we took on the task to define and analyze key factors affecting the development of DWHR (Drain Water Heat Recovery) systems using PESTLE (political, economic, social, technological, legal and environmental) analysis. The strengths and weaknesses of these systems were also identified. The studies were based on CFD (computational fluid dynamics) modeling tools. In the Autodesk Simulation CFD software environment, a DWHR unit was made, which was then analyzed for heat exchange efficiency. The obtained results were the basis for preparing the strategy for the development of Drain Water Heat Recovery systems. It was made using the SWOT/TOWS (strengths, weaknesses, opportunities and threats/threats, opportunities, weaknesses and strengths) method, which precisely orders information and allows presenting the project characteristic in readable way for a recipient. The results of the conducted analysis indicated the lack of acceptance on the part of potential users and the resulting need to promote the use of Drain Water Heat Recovery systems at residential level.

In order to identify the most effective variants for reducing flood risk in cities and to provide protection for water resources, an in-depth study was carried out. The research results allowed for the identification of sustainable drainage infrastructure solutions that should be used to increase the efficiency of traditional drainage systems. The most effective solution turned out to be the simultaneous use of low impact development facilities and stormwater flow control devices in drainage systems (Variant IV). Applicationof this variant (maximum discharge QOmax = 246.39 dm³/s) allowed for the reduction of the peak flow by as much as 86% in relation to those values that were established in the traditional drainage system (maximum discharge QOmax = 1807.62 dm³/s). The use of Variant IV allowed for a combination of the advantages of low impact development (LID) facilities and stormwater flow control devices in drainage systems while limiting their disadvantages. In practice, the flow of rainwater from the catchment area to the drainage system was limited, the share of green areas increased, and the drainage system retention capacity grew. The proposed approach for reducing the increasing flood risk in cities and providing protection for water resources provides a structured approach to long-term urban drainage system planning and land use guidelines.

The growing interest in the use of unconventional energy sources is a stimulus for the development of dedicated devices and technologies. Drain water heat recovery (DWHR) units can be an example of such devices. They allow the recovery of part of the heat energy deposited in grey water. This paper describes the results of research on the assessment of the financial profitability of the use of two horizontal heat exchanger solutions, taking into account the actual distribution of cold water temperature during the operating year in the plumbing and two operating regimes of the premises as the residential and service facilities. The analysis showed that the use of a horizontal heat exchanger with increased efficiency in a dwelling in a 15-year life cycle allowed for achieving more than twice as much savings (reaching up to EUR 1427) compared to a classic horizontal heat exchanger. At the same time, it was shown that the installation of this type of equipment was more profitable the greater the water consumption of the premises. The article also notes the impact of cold water temperature in the installation on the results of the analysis. It was featured that taking temperature on the basis of installation design recommendations led to significant distortions in the financial analysis. On the other hand, comparing the method of averaging the cold water temperature (daily, monthly and yearly), it was determined that averaging the temperature over the annual cycle was an acceptable simplification of the model. The research results presented in the paper have a practical aspect and may constitute guidelines for designers and potential investors. In addition, they can be an incentive to continue research on heat exchangers by other scientific centers, which on a global scale will increase the universality of their use.

This article is aimed at defining the impact of the direction and velocity of waves of rainfall as they pass over interconnected stormwater detention tank systems. The simulations were conducted for a real urban catchment area as part of the Storm Water Management Model (SWMM) 5.1 programme. The results permit us to conclude that the direction and velocity of a moving wave of rainfall have a significant influence on the required volumes of interconnected stormwater detention tank systems. By comparing the modelling test results for stationary rainfall and rainfall moving over the urban catchment area, it has been demonstrated that differences in the required volume of the detention tank located at the terminal section of a stormwater drainage system are inversely proportional to the adopted value of the diameter of the outfall channel for upstream storage reservoirs. In extreme cases, the differences may be up to several dozen percentage points. Furthermore, it has been proven that the arrangement of the stormwater detention tanks in relation to one another and the adopted diameter of the outfall channel are key factors in identifying the degree to which the detention tanks are hydraulically dependent on one another.

Wastewater has significant potential as a source of clean energy. This energy can be used both within external sewer networks and on the scale of individual residential buildings, and the use of shower heat exchangers appears to be the most reasonable solution. However, in the case of Poland, the problem is still the unwillingness of society to use this type of solution, caused mainly by the lack of space for the installation of vertical drain water heat recovery (DWHR) units and the low efficiency of horizontal units. In response to this issue, the efficiency of a new compact shower heat exchanger designed to be mounted below the shower tray, as well as its linear counterpart, was investigated under various operating conditions. In addition, the financial efficiency of using the compact DWHR unit with average water consumption for showering was evaluated. For this purpose, discount methods were used to estimate the financial efficiency of investments. The study showed that the compact shower heat exchanger has higher efficiency than its linear counterpart. Depending on the temperature of cold water and the flow rate of both media through the heat exchanger, it achieves efficiencies ranging from 22.43% to 31.82%, while the efficiency of the linear DWHR unit did not exceed 23.03% in the study. The financial analysis showed that its use is particularly beneficial when the building uses an electric hot water heater. The investment’s sensitivity to changes in the independent variables is small in this case, even with low water consumption per shower. The only exceptions are investment outlays. Therefore, the compact DWHR unit is a clean energy device, which in many cases is financially viable.