Abstract
Rapid urbanization in the developing world is one of the greatest challenges of the 21st century. Rates of urban poverty and food insecurity are increasing, whereas agricultural and urban water demand is exceeding supply leading to scarcity in many regions. Meanwhile, the speed of urban growth is outpacing the provision of water and sanitation infrastructure. This fact requires innovative interventions that could mitigate the negative impacts of urbanization. Urban agriculture is presented as one significant measure to increase the food self-reliance and improve the livelihood of urban inhabitants, particularly poor. Given that freshwater provision in cities of most developing countries is already below standard, covering the water requirements for urban agriculture has been extremely difficult. Greywater is seen as a good option for urban agriculture. Greywater is less polluted than blackwater, thereby; treatment of greywater to make it suitable for local-food production tends to be safer, easier and less controversial. This study developed and tested a new treatment method for greywater called the Drawer Compacted Sand Filter (DCSF). This is a modified sand filter design in which the sand filter is broken down into several layers approximately 10 cm high, each of which is placed in a movable drawer that is stacked vertically, with each drawer separated by 10 cm of space. This treatment unit is seeking to overcome the problems commonly found in traditional sand filter designs, such as clogging, emission of bad odours and need for a large land area to house the filter. The new design was proposed and developed to be suitable in urban communities and could produce good quality water that matches the requirements of food production in urban areas. The response of drawer sand filters to variable hydraulic and organic loading rates in terms of Biological Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), Total suspended Solid (TSS), pH, Electrical Conductivity (EC) and Escherichia coli (E. coli) reductions was tested in laboratory under controlled conditions. Hydraulic Loading Rate (HLR) was studied by increasing it stepwise from 72 to 142 L m-2 day-1 and Organic Loading Rate (OLR) was studied by increasing it from 24 to 30 g BOD5 m-2 day-1 while keeping the HLR constant at 142 L m-2 day-1. Each loading regime was applied for 110 days. Results showed that DCSF was able to remove > 90% of organic matter and Total Suspended Solids for all doses. No significant difference was noticed in terms of overall filter efficiency between different loads for all parameters. Significant reduction in BOD5 and COD (P<0. 05) was noticed after water drained through the third drawer in all tested loads. Based on the laboratory tests, nine pilot DCSF units were operated at different locations in Jordan during the period of 2011-2013. Composite water samples from the inlet and outlets of the DCSF over a period of 16 months were taken periodically and tested for BOD5, COD, TSS, pH, EC and E. coli. A socio-economic study was conducted to evaluate the validity and feasibility of the DCSF. The results showed that DCSF removed 78-96% of BOD5 and COD and 98% of TSS and up to 6 logs reduction in E. coli. The socio-economic study and the cost-benefit analysis showed that DCSF unit was a feasible and reliable treatment method for greywater with a very low land footprint and minimal maintenance requirements, thus making it suitable for a wide range of geographical settings.