Abstract:
There is an increasing demand for better water quality in order to safeguard public
health, the social security and accomplish environmental integrity. It has been found
over the past couple of years that health hazards associated with heavy metal have been
on the rise, particularly the chronic health problems due to the ingestion or consumption
of even low doses of heavy metal-rich waters. Accumulation of such metals is reported
mainly due to non-treatment or poor treatment of industrial wastewaters. Lack of
tertiary treatment may have attributed to this growing problem and hence the
environmental pollution. Constructed wetlands have therefore received great attention in
the recent past as a tertiary treatment method or a polishing technique due to low
construction and operation costs, minimum maintenance and also as an environmental
friendly system. However, finding a low-cost sorbent material which can be used as an
alternative to activated carbon has been a problem for decades in wastewater treatment
industry, especially in developing countries. Therefore, the present study focuses on the
applicability of low-cost sorbent materials that can be used in constructed wetlands as a
filter medium. The focus was on four sorbent materials: tile, brick, saw dust and rice
husks, which were selected based on their local availability. Laboratory-scale
experiments were performed to investigate their maximum adsorption capacity and
removal efficiency with a synthetic Zinc solution. The Results revealed that tile material
has the highest adsorption capacity (47.6 mg/g) and removal efficiency, (98%) while
brick (37.0 mg/g, 86%), sawdust (20.4 mg/g, 80%) and rice husks (15.8 mg/g, 64%)
have relatively low adsorption capacities and removal efficiencies, respectively. The
percentage removal of Zinc by all the four sorbent materials increased with an increase
of contact time. The kinetics of adsorption were relatively fast for all tested low-cost
materials. The equilibrium data were correlated with both Langmuir and Freundlich
isotherms. Adsorption isotherms are well described by Langmuir isotherms. The
separation factor of equilibrium (RL) indicates favourable isotherms (0< RL >1) for all
tested materials. Characterization of four sorbent materials was done by undertaking
SEM, XRD and FTIR analyses. It can be concluded from the results that, the low-cost
sorbent materials that were tested can be an attractive substitute for activated carbon in
removing Zn from industrial wastewaters.
Keywords: adsorption isotherms, constructed wetlands, sorbent material, Zinc
