Abstract:
A study was carried out to compare the performances of different
substrates used in a laboratory scale subsurface flow constructed wetland systems to
treat gray water released from the university staff canteen. Three wooden boxes
with the dimensions of 60cm x 25cm x 25cm were fabricated and 15mm rock
aggregates, pebbles (15mm) and broken tiles (25mm) were used as substrates (which
were selected considering the availability) in each of the boxes. Each horizontal
subsurface flow bed was fed in a batch process with gray water with a flow rate of
20 litres per day. The retention time for each batch was maintained as 6 days. BOD,
COO, pH, conductivity, N03-, P043-, turbidity and temperature in the influent and
the effluent were monitored for every batch of waste water passed through the
systems and their removal efficiencies were determined. The highest removal
efficiencies of COD and, BOD,and P043- were 80%-90%and 60%- 80%, respectively
were recorded from broken tiles, while highest removal efficiency of N03-, of 60%-
90%, was recorded from aggregates. Removal of turbidity in all three tanks was
similar being between 60%- 90%. Hence, crushed aggregates and broken tiles are
found to be the best substrates, considering the removal efficiencies to treat gray
water.
