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Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 200-206 in On-Site Wastewater Treatment, Proc. Ninth Natl. Symp. on Individual and Small Community Sewage Systems (11-14 March 2001, Fort Worth, Texas, USA), ed. K. Mancl., St. Joseph, Mich. ASAE  701P0009.(doi:10.13031/2013.6028)
Authors:   A. Heistad, P. D. Jenssen, A. S. Frydenlund
Keywords:   Sewage treatment, Wastewater infiltration, Till soil, Pretreatment, Distribution system

Glacial till, often with poor hydraulic conductivity or a topography that limits the use of traditional wastewater soil infiltration systems (WSIS), is the dominant soil type in Norway. A newly developed combined distribution and pretreatment unit overcomes some of the soil limitations and extends the use of WSIS. The new system, which may be used in any soil type, allows easy access to the infiltrative surface and is thus superior to traditional gravel filled trenches regarding monitoring and maintenance of WSIS. The new system is based on high head pumping of septic tank effluent to one or several units filled with lightweight clay aggregates (LWA). Each unit is directly connected to the pump by a small diameter pipe, and one small pump can serve several units. The wastewater is dosed through a single tangential/fullconical (TF)-nozzle that distributes the water evenly over the 2.3m 2 surface of the pretreatment filter. The filter medium can easily be replaced, and the nozzle can be refitted by hand. The wastewater is distributed to the different units using a hydrosplitter, or for larger or more advanced systems, using solenoid valves controlled by a timer or a programmable logic controller (PLC). The use of a PLC makes individual loading rates and dosing frequencies possible. It is also possible to adjust the loading to soil moisture conditions or groundwater levels beneath or adjacent to the unit. The even distribution assures good utilization of the LWA filter media, and a significant reduction in BOD, SS, number of coliforms as well as nitrification is achieved. Higher soil acceptance rates for wastewater are therfore possible.

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