Case studies on preliminary treatment facilities at marine outfalls

As with many coastal discharges, the search for a suitable primary treatment system has long been accepted as a first stage treatment of both municipal and industrial wastewater. Over the last decade, milliscreening has almost become the best alternative method among the conventional systems applicable to marine outfall treatment. This paper, summarizes three case studies using milliscreening equipment with variable bar spacings on treatment facilities at marine outfalls. The best solution was achieved at Poverty Bay in New Zealand where the bar spacing was 1 mm. The other two applications were attempted in United Kingdom. The milliscreens of 10 mm at Tonyrefail and 5 mm at Wooler were not able to meet the required performance. In regard of these studies, it is recommended that finer screens with bar spacing of less than 5 mm are likely to provide adequate performance when used to screen marine outfalls.