High-strength greywater treatment in compact hybrid filter systems with alternative substrates

Four parallel pilot-scale experimental filter systems were established in 2009 in order to study the treatment capacity of hydrated oil shale ash (an industrial by-product) and Filtralite (R) in compact highly loaded filter systems in order to reduce BOD and COD values and nutrient concentration in household greywater. The systems were tested at two different hydraulic loading rates over a nearly two-year period. All the Filtralite (R) systems performed significantly better than the oil shale ash system, showing a median COD reduction of 83-88%, whereas the system with 4-10 mm crushed Filtralite (R) performed significantly better than others filled with Filtralite (R). The oil shale ash system clearly outperformed the Filtralite (R) systems, with a median reduction of TP in the oil shale ash filter system of 89%, achieving a median effluent concentration of 0.55 mg P L-1 compared to the respective 40-44% and 2.9-3.3 mg P L-1 for Filtralite (R) systems. The median outflow pH values of the Filtralite (R) systems and oil shale ash system were similar to 8.5 and similar to 9, respectively. It was also noticeable that most of the organic matter, TSS and even TN and TP was removed in vertical flow (VF) filters. When operating the filter systems under similar to 2.5 times higher loading rates, there were no significant differences between the removal efficiencies regarding the organic matter, TSS and TN removal, although the fluctuations of pollutant content in inflow were more distinctly reflected in the outflow values and concentrations. The study serves as a good basis for the development of a low-tech compact filter system for greywater treatment. (C) 2012 Elsevier B.V. All rights reserved.