Treatment of combined sewer overflows at small wastewater treatment works by constructed reed beds

The performance of constructed reed beds is illustrated by examination of results of surveys from a sewage treatment works with storm treatment reed beds and another sire with a combined storm and tertiary treatment reed bed. During surveys of the first system the average hydraulic loads were between 25 and 40 cm d(-1) and removals of between 6.7 to 15.4 g m(-2) d BOD5, 17.7 to 38.6 g m(-2) d TSS, 0.43 to 0.99 g m(-2) d NH4N and 0.63 to 0.76 g m(-2) d TON were observed. A survey during a storm at the combined storm and tertiary treatment reed bed showed a hydraulic loading of 98 cm d(-1) in the first 24 hr and removals of 12.6 g m(-2) d BOD5, 29.9 g m(-2) d TSS, 0.49 g m(-1) d NH4N and a small increase in TON. The sustainability of the high rate of removal during storm events is ascribed to the longer intervals in which loadings are much lower. Samples taken by the regulator from the time of commissioning of 20 sites with combined; storm and tertiary treatment reed beds, up to the end of May 1998 are examined. Three of these had operational problems not associated with storm treatment. The aggregate data for the remaining 17 sites (n = 906 to 911) illustrate a level of performance matching that of sites with tertiary treatment systems, with averages of 2.2 mg l(-1) BOD5, 3.0 mg l(-1) TSS, 1.25 mg l(-1) NH4N and 12.2 mg 1-' TON. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.