Influence of the physical and mechanical characteristics of sands on the hydraulic and biological behaviors of sand filters

摘要

Sand filters systems are widely used around the world for on-site and small communities wastewater treatment. Their treatment efficiency depends on several parameters like the media used, temperature, wastewater characteristics, hydraulic and organic loads. One of the most important design parameter in relation to treatment efficiency and sustainability (clogging phenomena) is the sand characteristics and its implementation. To precise the impact of sand implementation on hydraulic and biological behaviors, a study has been done in laboratory columns (surface 0.1 m~2) in relation to physical and mechanical characteristics of the sand. Two sands (d_(10) 0.42 and 0.8 mm) as well as two implementations (natural compaction and 100% proctor compaction) have been studied during 8 months fed with synthetic wastewater. The weight of the columns was followed continuously and it allowed the following of different parameters (media humidity, infiltration rate, drainage flow). Other parameters linked to biological activity (treatment efficiency (BOD5, COD, SS, nitrogen forms, etc.), oxygen content of the porous gas phase) were followed on a daily basis. The results give information on the importance of media implementation on treatment efficiency and gas and water transfers within the sand filter. Physical parameters, like particle size distribution, are not the only ones to be determinant on biological and hydraulic behaviors of sand filters. If sand compaction can be detrimental in terms of clogging for fine sands, it can be beneficial for coarser sands. This has to be known to avoid bad design and clogging risks.