The Norwegian State Pollution Control Authority introduced in 1986 a system for approval of wastewater treatment plants serving less than 35 persons. This system is based upon three approval classes and includes “real life” testing of the plants for a minimum period of six months. During the test period several factors (hydraulic capacity, sludge production, effluents concentrations etc.) are examined. The six types of plant that have been approved so far are described and the test results are presented and discussed. General experiences with the approval system are summarized, including effects of the mandatory service contract between manufacturer/supplier and the houseowner.

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