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The BIGHP Project

RIWIS (Rhode Island Wastewater Information System)

Onsite Systems Basics
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Property owner's guide

Wastewater Manager's Toolkit
Creating a management plan
Drafting an ordinance
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Using GIS for evaluation
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Treatment Technology: Single pass sand filter
Single pass sand filter technology has been used for over 100 years to treat both wastewater and drinking water supplies because they are quite effective in removing bacteria. The term “sand filter” refers to a biological and physical wastewater treatment component consisting of an underdrained bed of sand to which septic tank effluent is periodically applied. Wastewater is time dosed to the top of the filter bed and percolates down through the sand media where wastewater treatment occurs. Filtrate is collected in the underdrain at the base of the filter and then pressure dosed to a shallow narrow drainfield for final dispersal.
Cut-away view of the filter showing the PVC pipe distribution system, sand media in the foreground, and the over-lying 3 inches of crushed stone.

This image shows a completed filter, which is flush with the ground surface and covered by grass.

A treatment train containing a single pass sand filter
Wastewater flows through a building sewer (A) and enters into a two-compartment septic tank (B). Septic tank effluent is pressure dosed using a time dosed pump located in the second compartment of the tank. Effluent is distributed over the top of the sand filter (C), infiltrates the sand media flowing down to the base of the filter. Filtrate collects in a sump area in the middle of the filter, where a second pump is located. This pump pressure doses sand filter effluent to a shallow narrow drainfield (D) where additional treatment and final dispersal occurs.
Treatment performance observed for single pass sand filters in RI
% TN Reduction
Fecal Coliform
Coming Soon!
For more information on single pass sand filters:

Web Links:These media filters have been studied under various URI-lead projects, as well as by other onsite treatment testing facilities. The results of URI, NEOWTC projects can be found in various technical publications which will be online soon at www.uri.edu/ce/wq/OWT/Research/

Copyright 2006 URI Water Quality Program