Specialist Group on Use of Macrophytes in Water Pollution ... - IWA

NUTRIENT RELEASE FROM INTEGRATED CONSTRUCTED WETLANDS
SEDIMENT
Yu Dong 1 , Birol Kayranli 1 , Miklas Scholz 1,2 , Devi Prasad Tumula 2 and Rory Harrington 3
1 Institute for Infrastructure and Environment, School of Engineering, The University of
Edinburgh, William Rankine Building, King’s Buildings, EH9 3JL, Edinburgh, UK
2 Civil Engineering <strong>Group</strong>, School of Computing, Science and Engineering, The University of
Salford, Newton Building, Salford M5 4WT, UK
3 Water and Planning Division, Department of Environment, Heritage and Local Government,
Waterford County Council, Ireland
Email: y.dong@ed.ac.uk
INTRODUCTION
Wetland sediments mainly comprise of organic matter from wastewater, dead plants and
minerals associated with soil erosion. Sediment may retain or release contaminants when
environmental conditions change.
METHODS
Five horizontal free surface flow constructed wetland mesocosms (Figure 1) were set up at
The University of Edinburgh to provide nutrient removal and/or accumulation within
integrated constructed wetland (ICW) sediment. The laboratory room temperature was
maintained at 15 ºC. Artificial light was provided by programmable controlled UV lights to
simulate diurnal sunshine. The mesocosms were constructed using polyvinyl chloride
drainage pipes with identical dimensions (height: 83 cm; diameter: 10 cm). Seven plastic taps
were evenly placed around the circumference of the pipe for subsequent sample collection.
The outlet valves were located at the centre of the bottom plate for each pipe. Outflow water
was collected with vinyl tubing of 1.2 cm internal diameter.
Of the five mesocosms (Figure 2), two were fed with farmyard runoff (mesocosms 1 and 2).
Three mesocosms (mesocosms 3, 4 and 5) were fed with pre-treated domestic wastewater.
Three planted experimental mesocosms (mesocosms 2, 3 and 4) were packed with four
successive layers of aggregates (from bottom to top): 50 mm of small gravel (1.2–5.0 mm),
50 mm of sand (0.6–1.2 mm), 250 mm of sodium bentonite clay (permeability of 10 -9 m/s)
and 350 mm of core sediment (incorporating plants if applicable). These systems were
flooded with inflow water up to the top. Core sediment samples were directly taken from the
surface of ICW site 11 (cell 1), which were applied for the treatment of farmyard runoff for
approximate ten years (Figure 3a). Further core sediment samples of domestic mesocosms
were extracted from the surface of ICW site 7 (cell 1), which were constructed to treat
domestic wastewater for approximate eight years (Figure 3b). Two control mesocosms
(mesocosms 1 and 5) were set up to ensure the same flow conditions and saturation ratios.
The soils and aggregates of the two control mesocosms (from bottom to top) contained 50
mm of small gavel (1.2–5.0 mm), 50 mm of sand (0.6–1.2 mm), and 600 mm of sodium
bentonite clay (permeability of 10 -9 m/s).
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IWA <strong>Specialist</strong> <strong>Group</strong> on Use of Macrophytes in Water Pollution Control: Newsletter No. 38 17