Tertiary Treatment

REED BEDS FOR ADDITIONAL  BOD5 AND SUSPENDED SOLIDS REMOVAL

The most popular application of  reed beds within the Water Companies of England and Wales is  for further improvement of the quality of the effluent from a  sewage treatment works, whether this be a traditional trickling filter or a  small rotating biological contactor type package plant.  The two most important parameters  requiring improvement are  BOD5      and suspended solids.

The first purpose built tertiary treatment reed bed in the UK was built at Leek Wootton in Warwickshire in 1991 and it remains in use more than a decade later.

The two reed beds operate in parallel and treat the effluent from a trickling filter.

The works needs to meet a standard of 20mg/litre BOD5

and 30mg/litre suspended solids, and has done so every year since the reed beds were installed.

Over a four year period of intensive monitoring the reed bed performance can be summarised as follows:

BOD5  

Suspended Solids

Ammoniacal Nitrogen

Total Oxidised Nitrogen

Influent to reed bed

11 mg/l

19 mg/l

6.5 mg/l

25.3 mg/l

Effluent from reed bed

2 mg/l

5 mg/l

2.35 mg/l

11.1 mg/l

All figures are the averages of several samples.