Effects of Hydraulic Loading Rate and Filter Length on the Performance of Lateral Flow Sand Filters for On-Site Wastewater Treatment

Abstract

On-site treatment of residential wastewater is important for rural and remote regions where centralized wastewater treatment may not be feasible. Sand filtration is a proven method for secondary treatment of septic tank effluent (STE) and can be an economical option where soil conditions do not favor the installation of a typical disposal field. This study investigates the hydraulics and treatment performance of eight lateral flow sand filters (LFSFs) receiving domestic STE at the Bio-Environmental Engineering Centre (BEEC) in Truro, Nova Scotia, Canada. The main objectives of this study were to evaluate the long-term treatment performance associated with the LFSFs and to investigate the effects of filter length and wastewater loading on performance. Previous research conducted at the BEEC indicated that current technical guidelines used in Nova Scotia for the design of LFSFs may be conservative and that the design of these systems could be optimized. The hydraulics and treatment performance associated with: (1) two shortened length filters (5.5 m versus 8 m standard length), and (2) six standard length filters receiving double the recommended hydraulic loading rate were evaluated. Results were compared to the previously documented performance of standard length filters operating at the recommended loading rate. Filters included fine (