The use of laboratory sand, soil and crushed-glass filter columns for polishing domestic-strength synthetic wastewater that has undergone secondary treatment

Abstract

The aim of this study was to examine the performance of intermittently loaded, 150 mm-diameter stratified filter columns of 2 depths (0.65 and 0.375 m) comprising different media – sand, crushed glass and soil – in polishing the effluent from a laboratory horizontal flow biofilm reactor (HFBR) treating synthetic domestic-strength wastewater. The HFBR has been successfully used to remove organic carbon and ammonium-nitrogen (NH₄-N) from domestic wastewater. In this treatment method, wastewater is allowed to flow over and back along a stack of polyvinyl chloride (PVC) sheets. Biofilms on the sheets reduce organic carbon, suspended matter, and nutrients in the wastewater, but to achieve the quality of a septic tank system, additional treatment is required. In all filters, at a hydraulic loading rate of 100 L m⁻² d⁻¹, 40-65% of chemical oxygen demand (COD) and practically 100% of total suspended solids (TSS) were removed, nitrification was complete, and bacterial numbers were reduced by over 80%, with best removals achieved in the soil filters (93%). Soil polishing filters with the depth of 0.65 m performed best in terms of organic carbon, total nitrogen (Tot-N) and bacterial removal. Data from this preliminary study are useful in the design of treatment systems to polish secondary wastewaters with similar water quality characteristics.

Keywords:

• Wastewater treatment
• horizontal flow biofilm reactor (HFBR)
• intermittent filtration
• soil
• sand
• glass

Acknowledgments

This research was supported by a student fellowship from the College of Engineering and Informatics, NUI Galway. The authors acknowledge the support of the late Dr. John Mulqueen, NUI Galway; Mr. Michael Coughlan, Dept. of Microbiology, NUI Galway; Messrs. Gerry Hynes and Peter Fahy, and Ms. Mary O'Brien, Civil Engineering, NUI Galway.