Reuse of Grey water in Peri-urban areas in Dar es Salaam, Tanzania : Minor Field Study
The purpose of this thesis is to understand and analyse the issues of grey water generation and disposal in peri-urban areas of Dar es Salaam in Tanzania and to propose a suitable solution to which includes designing a treatment system for grey water (water from shower, washing and kitchen). The purification will eliminate the sanitation issues that are brought by exposing untreated grey water to the environment as well save freshwater. This will be implemented with regard to local conditions in Dar es Salaam, Tanzania.
Water-borne and vector-borne diseases are mainly brought by untreated grey water, which sadly enough causes thousands of death cases every year in Tanzania. The year between 2004- 2005, 154551 cases of dysentery were reported with 170 deaths. It was also reported, 863488 cases of typhoid with 1167 deaths and last but not least 12923 cases of cholera from with 350 deaths. Deaths that were caused by diarrhoea were also reported, whereby, 90 % of them are children.
According to the interviews that were conducted, people would not want to recycle the grey water for example for washing due to socio-cultural context where water is considered dirty even after treatment. They had difficulties in believing that the same dirty grey water can be purified and reused again for various domestic activities.
The conducted characterisation of grey water showed the tested grey water has relatively high levels of BOD, basic pH, higher than average values of TSS, relatively low levels of DO, increased salinity and average level of FC. The analyses were performed on the most polluted grey water from every source. The volume of household produced grey water varies strongly, depending on socio-economic situation of the household and type of access to water supply. From estimation, the volume varies approximately between 60 -160 l/day and household for a low income household.
Living wall was proposed as grey water treatment system, because of its suitability to the peri-urban settlement and tropical climate. The system consists of concrete boxes placed over each other, filled with inner porous material and planted with plants. The system purifies grey water as it percolates through it and at the same time provides a vertical space for growing plants.
The plants for the treatment system were chosen to Typha latifolia and Scirpus species. The plants are growing in Tanzania and are being used for wastewater treatment purposes. The plants are tolerant to increased salinity and can grow in alkaline soil.
The cleaning effectiveness of the system was not tested, but only roughly estimated with help of values from a similar treatment system build in Gotland, Sweden.
Hence, the reuse of grey water in this geographical location suits best for irrigation in rural and peri-urban areas with potential for agriculture as well as groundwater recharge in the peri-urban and urban areas. Recharging groundwater with treated grey water has a potential to be observed as an indirect and long term reuse of the water as it reconnects in the hydrological cycle.
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