Performance evaluation of the Worms subsurface flow constructed wetland for treating black water using insitu and exsitu analytical methods

Abstract

This paper evaluates the performance of a subsurface flow constructed wetland at Worms Germany used for the treatment of black and grey water from a non-residential facility. Snap black water samples from four wells made up of a clarifying unit, an activated carbon unit and an aeration unit were analysed insitu using the HACH HQ40d multimeter and exsitu using Sensafe water metals check strips for preliminary metal detection onsite. HACH bar code reagents, a HACH Digital Reactor Block 200 (DRB200) and a HACH DR 3900 Spectrophotometer were subsequently used for the analysis of lead (Pb), chromium (Cr), cadmium (Cd), biochemical oxygen demand (BOD), Chemical Oxygen demand (COD), Ammonium (NH 4 -N) and Nitrate (NO 3 -N) in the lab. The removal efficiency for the constructed wetland was in the order BOD > Cr > COD > NH 4 -N > NO 3 -N > Pb. The 57.90% removal efficiency of COD for the constructed wetland was due to the higher fractions of inert COD which constitutes a part black water. This makes the use of the BOD/COD ratios of 0.69 and 0.5 for wells 1 and 4 an unreliable index for the determination of amenability of COD in black water with regards to microbial activity at the wetland at Worms. The pH range of 7.2–8.4 of the blackwater is conducive for the growth microbes necessary for the breakdown of organic matter in the black water. Further investigation including plant and sediment analysis over different seasons has to be undertaken if the efficiency of the constructed wetland for nutrients and metals removal is to be optimized.