Potential and problems related to reuse of water in households

Abstract: There is a growing demand in society for the introduction of decentralised sanitary reuse systems and the main reason for this is that centralised urban sanitation systems are expensive and resource-intensive. A second is water shortage and one way to reduce the need for freshwater is to reuse wastewater on-site. One possibility for recycling is to use grey wastewater or rainwater for non-potable purposes. Very little is currently known of the presence of xenobiotic organic compounds (XOCs) in these water fractions. Knowledge of the type of constituents present, concentration ranges and of any potential risk they may pose are all-important issues when discussing local handling e.g. on-site reuse as well as discharge into receiving water.We are exposed to thousands of compounds in our daily life as over one hundred thousand compounds are on the market in the European Union, with 30,000 being used in volumes of over 1 ton per annum. Pharmaceuticals, household chemicals, personal care products, clothing, foodstuffs, additives, building materials, cars, industry, combustion and incineration are a few examples of the sources of chemical compounds in our environment.The objective of the study is to develop a methodology for identifying compounds that might pose a threat in connection with the use of non-potable water in households or with discharges into the environment, with the focus on XOCs; and in addition to test the method in two different cases. The methodology used was to apply a number of different methods: research of literature, empirical studies incl. chemical analyses; specifically developed analysis methods; toxicity measurements, hazard and problem identification, and risk assessments. The battery of methods was applied to two selected cases, namely grey wastewater and collected rainwater.It can be concluded that previous knowledge about the characteristics of grey wastewater (physical, chemical and biological constituents) is limited. The focus has been on the content of oxygen-consuming compounds, nutrients and micro-organisms, while information about the presence and levels of specific XOCs is very limited. It was also found that grey wastewater from different sources has different characteristics, which illustrates the need for different types of treatment before any recycling of the water.XOCs that potentially are present in grey wastewater were listed based on information available on chemical products, consumption statistics and chemical databases as well as information on XOCs in wastewater. The list reached 900 different compounds and compounds groups. 201 different XOCs were identified in grey wastewater from bathrooms (showers and handbasins) by chemical analyses. Several fragrances such as citronellol, coumarin and hexyl cinnamic aldehyde were identified as well as some preservatives e.g. parabens and triclosan. The measurements also showed that bioactive chemicals (pharmaceuticals) were present, as well as unexpected compounds not directly derived from household chemicals e.g. flame retardants and drugs. The presence among others of detergents, softeners and preservatives was confirmed.In an investigation of consumption of household chemicals in multi-family accommodation, 92 different household chemicals and personal care products were recorded. The inhabitants’ average weekly consumption of chemicals was about 40 g per person. The inventory of household chemicals and personal care products listed registered a total of 290 chemical constituents. It was shown that it is possible to track the potentially toxic compounds used in households and which may present a problem, e.g. in relation to infiltration of grey wastewater. However, the observations made in this study illustrate that an inventory of the use of household chemicals, although detailed and carefully carried out, cannot represent a full characterisation of the compounds actually present in grey wastewater.In toxicity testing some types of grey wastewater (kitchen and laundry effluents) were found to be toxic to willow trees and freshwater green algae. The toxicity of the laundry effluent may be related to the toxicity of the detergents used.A total of 39 compounds out of the 201 found to be present in the grey wastewater from bathrooms were listed as potentially problematic pollutants in environmental hazard identification, based on the inherent properties; persistence, bioaccumulation and toxicity. A large number of the compounds were also found to be health hazardous. An environmental risk assessment of the 201 compounds revealed that five compounds constitute a risk if discharged into surface water or into a soil bed.For collected rainwater a large number of organic, inorganic, and microbiological constituents were found to be present. The data showed that there was significant variation between different sites due to different climate, urban environment, and land use. It was established that the majority of the studies focus on run-off from roads and roofs, as well as on unspecific stormwater. The number of constituents that were identified and quantified in collected rainwater is, however, probably only a fraction of those constituents that could be present, as a limited search of potential sources and their contribution resulted in a list of several hundreds of individual compounds.Hazard identification based on environmental and health hazards revealed that the number of pollutants, which constitute a potential hazard with respect to the use of collected rainwater, is high. However, there was no evidence of any adverse effects on willows caused by three samples of collected rainwater.Both health and environmental hazard identification were hampered by the lack of data on the identified compounds. However, the methodology used was found to be able to identify constituents that may constitute a problem both from constituents found to be observed or potentially present in the water fraction or from constituents detected in chemical analyses. The methodology can be refined and applied to other scenarios and could be extended to provide a realistic risk management tool.

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