Combined Water System Research Articles

The third route: A techno-economic evaluation of extreme water and wastewater decentralization

Water systems need to become more locally robust and sustainable in view of increased population demands and supply uncertainties. Decentralized treatment is often assumed to have the potential to improve the technical, environmental, and economic performance of current technologies. The techno-economic feasibility of implementing independent building-scale decentralized systems combining rainwater harvesting, potable water production, and wastewater treatment and recycling was assessed for six main types of buildings ranging from single-family dwellings to high-rise buildings. Five different treatment layouts were evaluated under five different climatic conditions for each type of building. The layouts considered varying levels of source separation (i.e., black, grey, yellow, brown, and combined wastewater) using the corresponding toilet types (vacuum, urine-diverting, and conventional) and the appropriate pipes and pumping requirements. Our results indicate that the proposed layouts could satisfy 100% of the water demand for the three smallest buildings in all but the aridest climate conditions. For the three larger buildings, rainwater would offset annual water needs by approximately 74 to 100%. A comprehensive economic analysis considering CapEx and OpEx indicated that the cost of installing on-site water harvesting and recycling systems would increase the overall construction cost of multi-family buildings by around 6% and single-family dwellings by about 12%, with relatively low space requirements. For buildings or combined water systems with more than 300 people, the estimated total price of on-site water provision (including harvesting, treatment, recycling, and monitoring) ranged from $1.5/m3 to $2.7/m,3 which is considerably less than the typical tariffs collected by utilities in the United States and Western Europe. Where buildings can avoid the need to connect to centralized supplies for potable water and sewage disposal, water costs could be even lower. Urine-diversion has the potential to yield the least expensive solution but is the least well developed and had higher uncertainty in the cost analysis. More mature layouts (e.g., membrane bioreactors) exhibited less cost uncertainty and were economically competitive. Our analysis indicates that existing technologies can be used to create economically viable systems that greatly reduce demands on centralized utilities and, under some conditions, eliminate the need for centralized water supply or sewage collection.

A combined-water-system approach for tackling water scarcity: application to the Permilovo groundwater basin, Russia

The suitability of a combined water system (CWS) is assessed for meeting drinking-water demand for the city of Arkhangelsk (northwestern Russian Federation), instead of using the polluted surface water of the Northern Dvina River. An appropriate aquifer system (Permilovo groundwater basin) was found and explored in the 1980s, and there were plans then to operate an abstraction scheme using traditional pumping methods. However, the 1980s planned water system was abandoned due to projected impermissible stream depletion such that complete interception of the cone of depression with the riverbed would cause the riverbed to become dry. The design of a CWS is now offered as an approach to addressing this environmental problem. Several sets of major pumping wells associated with the CWS are located on the banks of Vaymuga River and induce infiltration from the stream. The deficiency of the stream flow in dry seasons is compensated for by pumping from aquifer storage. A numerical model was constructed using MODFLOW-2000. The results of the simulation showed the efficiency of the compensation pumping. The streamflow depletion caused by the CWS is equal to the minimum permissible stream flow and is lower than the depletion projected by the abandoned plan. Application of the CWS in the Permilovo groundwater basin makes it possible to meet water demands during water-limited periods and to avoid environmental problems.

The dependence of stream depletion by seasonal pumping on various hydraulic characteristics and engineering factors

Compensation pumping is used to alleviate deficiencies in streamflow discharge during dry seasons. Short-term groundwater pumping can use aquifer storage instead of catchment-zone water until the drawdown reaches the edge of the stream. The capacitance is a complex, dimensionless parameter of an aquifer system that defines the delayed effect on streamflow when there is groundwater pumping. This parameter is a function of aquifer hydraulic characteristics, pumping time, and distance between the well and stream edge; the latter can involve stream leakance and vertical leakance of an associated aquitard. Three typical hydraulic cases of combined water systems (major catchment-zone wells close to the stream and compensation pumping wells) were classified depending on their capacitance structure (i.e. the relationship between surface water and groundwater): (1) perfect hydraulic connection between the stream and aquifer; (2) imperfect hydraulic connection between the stream and aquifer; and (3) essentially imperfect hydraulic connection between the stream and the underlying confined aquifer. The impact of various hydraulic characteristics and engineering factors on stream depletion was examined by conceptual and numerical modeling. To predict the suitability and efficiency of a combined water system application, regression tests were undertaken on unit stream depletion and capacitance, and power dependencies were defined.