This paper presents a literature review of the quality of greywater generated in different, especially developing, countries, constituents found in greywater, some treatment systems, natural materials for treatment, some reuse strategies and public perception regarding greywater reuse. The review shows that generation rates are mostly influenced by lifestyle, types of fixtures used and climatic conditions. Contaminants found in greywater are largely associated with the type of detergent used and influenced by other household practices. Many of the treatment systems reviewed were unable to provide total treatment as each system has its unique strength in removing a group of targeted pollutants. The review revealed that some naturally occurring materials such as Moringa oleifera, sawdust, can be used to remove targeted pollutants in greywater. The study further showed that user perceptions towards greywater treatment and reuse were only favourable towards non-potable purposes, mostly due to perceived contamination or lack of trust in the level of treatment offered by the treatment system.
There is a considerable body of knowledge about the way people perceive risks using heuristics and qualitative characteristics, and about how risk information should be communicated to the public. However, little is known about the way people use the perception of known risks (associated risks) to judge an unknown risk. In a first, qualitative study, six different risks were discussed in in-depth interviews and focus group interviews. The interviews showed that risk associations played a prominent role in forming risk perceptions. Associated risks were often mentioned spontaneously. Second, a survey study was conducted to confirm the importance of risk associations quantitatively. This study investigated whether people related unknown risks to known risks. This was indeed confirmed. Furthermore, some insight was gained into how and why people form risk associations. Results showed that the semantic category of the unknown risks was more important in forming associations than the perceived level of risk or specific risk characteristics. These findings were in line with the semantic network theory. Based on these two studies, we recommend using the mental models approach in developing new risk communications.
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