Comparative Study of Two Standard Septic Tank Drain fields Using Different Sand with Recirculation for Nutrient Removal

摘要

On-site Wastewater Treatment System (OWTS) using a septic tank followed by arecirculating sand filter (RSF) with effluent discharged to an unlined standard drain fieldis a typical performance-based treatment facility for nutrient removal. The type ofeffluent distribution in the standard drain field systems include gravity systems, lowpressure dosed systems, drip irrigation systems, etc. The standard drain field that isconstructed by a series of parallel, underground, perforated pipes allows the septic tankeffluent to percolate into the surrounding soil in the vadose (unsaturated) zone wheremost of the residual nutrients may be assimilated. The inclusion of RSF may improve thenitrification to some extent so as to promote denitrification in the drain field. With suchdesign, most residual nutrients in wastewater are expected to be consumed as thewastewater passes through the soil. This author’s aim of this paper is to present theeffectivenss of RSF and a comparative study with these two different drain field sands fornutrient removal in vadose zone. They include astatula sand (i.e., citrus grove sand) andwashed building sand, popular in Central Florida for drain field use. The use of a geneidentification method is novel in supporting the biological removal. Research findingsshow that the performance of washed building sand and the astatula sand in terms ofultimate nutrient removal is about the same. Because astatula sand is less costly it canpossibly be considered for replacement of the more expensive washed building sand.