ASABE Technical Library - Abstract
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A WASTEWATER SYSTEM FOR HIGH SHRINK-SWELLING CLAYS
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 701P0104, . (doi: 10.13031/2013.15782)Authors: B. N. Pour
Keywords: Shrink-swell clays; raised bed; drip systems; drip irrigation; textile filter; wet soils; high water table; N-sensitive environment; P-sensitive environment; N removal; P removal; Vertisols; Vertic
Clayey soils with high shrink swell properties present a serious challenge for a workable onsite
wastewater treatment system. A system was designed to test its workability on such sites. The
treatment train following a septic tank consisted of a recirculating trickling textile filter
pretreatment unit followed by drip irrigation on a raised bed constructed from imported soil
material. The bed was seeded with grass.
Four systems were installed for single-family residences on black clays of southwestern
Oregon in Jackson County. The systems, which are still operational, were monitored at various
treatment units during the years 2001-2002. Results indicate almost complete removal of
organics, bacteria, nitrogen (N), and phosphorus (P) at the end-point, the base of the raised-bed
native-soil surface. The treated effluent appeared to be fully assimilated into the natural
environment.
The concept appears to be workable for most limiting sites without a need for surface discharge.
The system can be designed with many different aerobic pre-treatment units. Various soil
materials can be used to construct a raised bed. The base and height of the bed can be varied to
achieve the required loading rate and vertical separation to the saturated soil zone. The design is
worth considering for small and community onsite systems in clayey soils, a high water table, or
in areas that are N or P sensitive.