Minimizing land requirement and evaporation in small wastewater treatment systems

Water supplies in the Middle East arid climate are a scarce commodity making treated wastewater an economically attractive source for increasing the limited existing water resources for agricultural purposes. In order to minimize water losses with the corresponding increased salinity and to reduce land demand, an integrated system based mainly on high-rate semi-intensive treatment units is being tested and demonstrated. The units include an upflow anaerobic sludge blanket (UASB) reactor and vertical and horizontal flow wetlands. The units are characterized by simple and low-cost maintenance with minimal energy input. Three years of pilot plant results from the combined system are presented in this paper. The results show a high organic removal rate for the combined system: 140 g COD/m2/day for the scheme, which included a UASB reactor followed by two PAVB units and subsurface horizontal flow CW. Even higher rates of 900 g COD/m2/day were achieved for the same scheme by replacing the final CWL with another PAVB unit. These high rates allow for a small treatment plant footprint equivalent to 0.13-0.9 m2 per person, assuming 125 g COD per person per day.