Design approach for the improvement of the economic and environmental performances of potable water supply

Triggered by the Kyoto Protocol and by the aggravation of freshwater scarcity, environmental impacts should soon become key decision criteria for the planning of potable water supply projects, especially when advanced systems such as seawater desalination are at stake. In order to foster the transition of the water industry towards sustainable practices, the present work proposes an integrated design approach dedicated to potable water supply that targets both economic and environmental objectives. At first, the current industrial practices (Chapter I) and the technical characteristics of potable water supply systems (Chapter II) are analyzed via the modeling of the process units used for potable water supply: pumping systems, conventional water treatment processes (e.g. clarification, filtration, disinfection) and advanced water treatment processes (e.g. membrane processes, thermal processes). Using the ISO 14040 standardized Life Cycle Assessment (LCA) method, Chapter III presents the development of a performance indicator that assesses the environmental impacts generated through all stages of the life cycle of potable water supply (i.e. from "cradle to grave"): from the construction of the potable water treatment plant, to its operation and decommissioning. This LCA-based indicator provides a holistic overview of all potential environmental impacts (e.g. green house gases (GHG) emissions, impacts on ecosystems and on human health). It allows to stress out the impact sources and the penalizing steps within potable water supply (Chapter IV): The production of electricity and chemicals required by the potable water treatment plant is highlighted to generate respectively 75% and 15% of the total impacts generated during the life cycle of potable water supply. Different potable water supply scenarios (e.g. potable water supply from ground water, from surface water, seawater desalination, water import from distant water resources) are benchmarked, in order to identify the best solutions as a function of the local context (e.g. type of electricity supply, topographic conditions, feed water quality). Based on the results of the environmental assessment, Chapter V proposes measures for the improvement of the industrial practices of the water sector, targeting energy and chemicals management, electricity sourcing and effluent disposal. Within the same perspective, Chapter VI details an optimization method for the design of the reverse osmosis (RO) membrane process, i.e. the key treatment process for desalination and wastewater reclamation. This method systematically synthesizes RO process configurations and evaluates their performances on economical (total annualized costs), technical (energy requirement, water conversion rate) and environmental criteria (GHG emissions). Evolutionary algorithms are then used to optimize the design of these configurations (process layout and operating conditions) and to identify those featuring the best trade-offs between economical costs and environmental impacts. As case study, the optimization method is applied on a brackish water reverse osmosis (BWRO) desalination project. The characteristics of the optimal BWRO process configurations are calculated as a function of the project constraints (e.g. economical and technical settings, minimum potable water quality), in order to illustrate how this method may support process engineers for the design of desalination plants.

Active façades : life cycle environmental impacts and savings of photovoltaic power plants integrated into the building envelope

Gianluca Cattaneo, Angela Clua Longas

Aim and approach used Increased energy supply from photovoltaics is a main priority in the “Energy Strategy 2050”. Within the joint research project "Next generation photovoltaics" funded by the Swiss National Science Foundation, we analysed different options for the enhanced integration of photovoltaic technologies into the envelope of Swiss buildings (BIPV). The PV modules for building integration are using novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC) with adaptions to improve the visual acceptance. In a joint effort of product developers, architects and scientists, this project aimed at providing pathways for the wide-scale use of BIPV façade solutions, and developing integrated designs based on emerging high-efficiency module technologies to improve the visual aspect and acceptance of PV systems installed in Switzerland. These so-called active façades incorporating BIPV modules to generate electricity can provide a significant contribution to the energy transition away from fossil and nuclear fuels. We compared the environmental impacts of different façade construction systems with and without SHJ-PSC BIPV modules with improved visual design, using a prospective life cycle assessment with a time horizon of 2025. The comparison includes a conventional brick and roughcast façade, a timber frame façade, and the Advanced Active Façade (AAF), which integrates SHJ-PSC BIPV modules in a low embodied impact façade substructure. In addition, we compared the environmental impacts caused by the construction of the above described façades with the environmental impacts saved due to the electricity produced by BIPV modules incorporated into the AAF. 2. Scientific innovation and relevance Our research focuses on the combined expertise of life cycle thinking, PV module development and façade design. The major scientific innovations are: 1) the prospective life cycle assessment of novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC); 2) the comparison of different façade construction systems and their environmental impacts; 3) the quantification of the saved environmental impacts arising from the electricity generated by the active façade; and 4) the visual adjustments of PV modules to improve their acceptance. The main advantage of integrating PV into building façades is the large available area, which can be limited on rooftops. In order to reach the market penetration for PV required for the energy transition, PV modules must be integrated into façades as well as into rooftops. 3. Results and conclusions An equilibrium must be achieved among different technical and aesthetic issues when integrating energy generation systems into the building envelope, especially into the façade for its public condition and exposure. Based on these prerequisites, the research team has developed the AAF which combines passive and active energy design strategies while meeting contemporary architectural requirements. This façade design is based on low-embodied-energy construction principles, it is defined by a non-loadbearing wood-panel substructure and it integrates a double layer of natural insulation: cellulose and wood-fibre. In addition, its design incorporates an opaque SHJ-PSC BIPV façade-cladding following contemporary façade design trends. (Figure 1). The use of photovoltaic modules integrated into the façade cladding or roof will increase the environmental impact of the building envelope, compared to using conventional construction materials. The environmental impacts of the AAF using PV modules are two to four times higher compared to a conventional façade. The PV modules cause the highest share of greenhouse gas emissions of the AAF with about 375 kg CO2-eq per square meter (see Figure 2). The additional materials required to build the AAF including exterior panels, insulation and other materials cause about 75 kg CO2-eq per square meter of façade. The brick and timber frame façades cause greenhouse gas emissions around 200 and 100 kg CO2-eq, respectively. If the greenhouse gas emissions caused by the PV module is excluded this will result in a reduction between 25 and 125 kg CO2-eq per square meter of façade. However, the environmental impacts of the AAF are significantly reduced if the whole life cycle is considered due to the PV electricity produced by the building. Therefore, we calculated the saved greenhouse gas emissions due to the electricity produced by the advanced active façade and fed to the European electricity grid using the greenhouse gas emissions caused by the current European electricity mix as reference. These calculated savings due to the electricity produced by the BIPV are about 4 times higher than the impacts of the advanced active façade. Incorporating BIPV panels into building’s façades will cause net savings of about 1700 kg CO2-eq per square meter over the whole life cycle of BIPV façades, while simultaneously saving up to 125 kg CO2-eq per square meter of façade for the reduced material demand to build the façade (see Figure 3). We performed this analysis for 16 different environmental impacts according to the recommended midpoints by the Joint Research Council of the European Commission. The results were comparable to greenhouse gas emissions with the net saved environmental impacts being many times higher for all the environmental impacts analysed except mineral resource use caused by the indium used in the novel SHJ-PSC tandem module (see Figure 4). To conclude, the use of PV modules in AAF can reduce the greenhouse gas emissions per square meter of façade between 25 and 60 % if the production of the PV module and its produced electricity are excluded. If the production and life cycle of the PV modules are included into the analysis the AAF will cause net greenhouse gas savings up to four times higher than the production of the AAF itself. The results for environmental impacts other than greenhouse gases were similar except for mineral resource depletion. Overall, the building integration of photovoltaic modules as AAF will reduce the environmental impacts of the building while simultaneously providing a visually appealing building envelope.

2019

Impacts of irrigation with industrial treated wastewater on soil properties

Pascal Boivin, André Mermoud

Wastewater reuse in agriculture is a widespread practice in developing countries, especially in urban areas where water shortage and poverty encourage people to use that marginal resource. Raw or treated wastewaters are used by farmers, but even treated wastewaters frequently do not meet WHO and FAO standards for irrigation water. Such practices may lead to health hazards, relatively well documented in the literature and to environmental damages. Adverse environmental impacts such as soil degradation and groundwater contamination are frequently associated with the use of wastewater from industrial sources. Previous studies have demonstrated that wastewater irrigation may decrease soil hydraulic conductivity and infiltration rate. Nevertheless, the effects on soil structural and chemical behaviors have been little studied so far and need further investigations. The impacts of irrigation with alkaline and sodic industrial wastewater previously treated in microphyte ponds on soil physical and chemical properties were studied downstream the sewage treatment plant of Kossodo in Ouagadougou, on plots cropped with eggplants. Plots irrigated with fresh water and non cropped, non irrigated plots were used as controls. Different soil properties were characterized: pore volumes determined by using shrinkage analysis, pH and electrical conductivity of water extracts, and major soluble and exchangeable cations (Ca, Mg, K, and Na). Organic matter characterization was performed by means of three dimensional fluorescence spectra analysis to determine its origin and evolution on irrigated soils. Plots irrigated with wastewater showed important structural damages, especially in the subsurface horizon where the soil pore network collapsed dramatically, resulting in a compact impermeable layer. Fluorescence spectra revealed that the organic matter contained in the wastewater was largely dissolved due to a sharp soil pH increase, resulting in black alkali formation at the surface: the soil became sodic, with an exchange complex dominated by sodium, whereas plots irrigated with fresh water kept properties comparable to that of non irrigated plots. Such a rapid soil sodication was seldom reported so far. The study emphasizes the need to carefully examine irrigation water quality and particularly calcite residual alkalinity and suggests that shrinkage analysis could be used to monitor the physical changes of soil properties upon sodication. Inadequate wastewater quality is likely to cause deep and irreversible damages to irrigated soils. (C) 2013 Elsevier B.V. All rights reserved.

Elsevier Science Bv2013

Inactivation of waterborne viruses by ozone: Kinetics and mechanisms

Camille Wolf

The growing world population, in conjunction with climate change, cases the global water de-mand to increase. It is, therefore, crucial to protect existing water resources from chemical pollution and contamination by pathogens. An increasingly popular strategy to meet increased water demand is pota-ble water reuse, which uses wastewater effluent as the water source and treats it to such an extent that it is safe to drink. However, this practise may encompass risks for human health if the treatment train does not ensure a sufficient removal of chemical and microbial contaminants. In the context of both wa-ter and wastewater treatment, ozonation has emerged as an efficient treatment method for the control of pathogens, the abatement of organic micropollutants, and the removal of taste and odor compounds. Despite its popularity, information on the inactivation of waterborne viruses by ozone is scarce. The aim of this thesis was to investigate the kinetics and mechanisms of inactivation of water-borne viruses by ozone. In a first step, the inactivation kinetics of a suite of human viruses and commonly used surrogates (bacteriophages) were determined in well-controlled buffer systems. To this end, we developed a method to control O3 decay in batch reactors. This allowed us to measure virus inactivation as a function of low ozone exposures. The resulting inactivation rate constant (kO3-virus) differed between the virus species studied, but all kO3-virus fell within a narrow range of 105-106 M-1s-1. These high inactivation rate constant indicate that ozone is efficient to inactivate waterborne virus. Increases in temperature and pH resulted in an increased kO3-virus, though the effect was relatively minor. To determine if more complex, natural water matrices influence virus inactivation by ozone, we investigated the virucidal efficacy of ozone in two surface waters and a secondary wastewater effluent. While inactivation kinetics as a function of ozone exposure initially corresponded well to those observed in buffer solutions, the inactivation curve tailed off at higher ozone exposures. Furthermore, because it is not possible to measure virus inactivation during water treatment in real-time, we tested different if âeasy-to-measureâ proxies can be used to track virus inactivation. We determined that the applied specif-ic ozone dose, the reduction in UV254, or the abatement of carbamazepine all correlated to virus inactiva-tion, though some proxy-inactivation relationships were not universal but depended on the water type. The proxies were validated in a pilot-scale ozonation reactor treating Lake Zurich water, and were found to provide good estimates of virus inactivation. Finally, an immunostaining assay was developed to observe how ozonation affects crucial steps in the life cycle of echovirus 11, a representative of the Enterovirus genus. Specifically, we investigated if ozone alters the ability of the virus to enter the host cells, and if it prevents the viral genome from replicating. Preliminary results indicate a loss of internalization after ozone treatment as well as genome replication. In conclusion, this thesis provides new information on the efficacy and mechanisms of ozone as an inacti-vating treatment for waterborne viruses, and it delivers tools to monitor virus inactivation during water and wastewater treatment in real-time.

EPFL2019