Use of low cost adsorbents to treat industrial wastewater
Date
2010-07-28T12:43:29Z
Authors
Musapatika, Evans Tongesai
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Advanced wastewater treatment techniques, such as adsorption, are economically and
environmentally essential in the removal of non-biodegradable toxic compounds from
industrial wastewater. The present study focuses on the use of low cost adsorbents
prepared from pine sawdust, coal fly ash and sugarcane bagasse to adsorb recalcitrant
compounds such as heavy metals, phenol and direct dyes from synthetic wastewater.
Carbonization of the adsorbents was done using a muffle furnace whereas a fluidized
bed reactor was used to prepare steam activated sawdust. Both batch and column tests
were performed to investigate the use of these alternative adsorbents as potential
replacements for the current costly commercial adsorbents. A 23 full-factorial design
with four centre points and response surface methodology were used to study the
interactive effect of the operating conditions on the adsorption capacity of sawdust
and coal fly ash. In addition, the performance of the low cost adsorbents was
compared with that of commercial activated carbon (CAC). The maximum adsorption
capacities were determined and correlated with the physicochemical properties of the
adsorbents.
Adsorption capacity was found to vary with initial concentration, adsorbent dose and
pH. An increase in pH led to a significant increase in heavy metal removal suggesting
the involvement of ion exchange mechanism. In column studies, breakthrough times
increased with an increase in bed height and aspect ratio. Conversely, breakthrough
times decreased with an increase in initial concentration. Overall, commercial
activated carbon was found to be superior; however, sawdust and coal fly ash showed
potential as alternative adsorbents for the removal of heavy metals and phenol from
petrochemical wastewater. Additionally, the trend followed by the maximum
monolayer adsorption capacities, qmax for the four adsorbents used to treat
petrochemical wastewater was in agreement with the specific surface area of the
adsorbents i.e adsorbents with high specific surface area had high qmax values with a
few exceptions. Amongst the low cost adsorbent, steam activated sawdust (SAS) was
superior and coal fly ash had the lowest adsorption capacities. Also, the highest
adsorbed contaminant by steam activated sawdust was Fe (15.385 mg/g). It has been
shown that the performance of steam activated sawdust was comparable to that of
commercial activated carbon in the removal of Pb and Ni. Nevertheless, sugarcane
bagasse proved to be a better adsorbent than coal fly ash in the uptake of direct red
dyes from textile wastewater. Direct red 80 (DR 80) was the highest adsorbed dye by
both sugarcane bagasse (6.536 mg/g) and coal fly ash (1.560 mg/g).
Equilibrium data for metal removal conformed well to the Freundlich isotherm
whereas phenol and direct dye removal complied with the Langmuir adsorption
isotherm model. Kinetic data were fitted to Lagergren first-order, pseudo secondorder
and the intraparticle diffusion models. Thus, kinetic parameters, rate constants,
equilibrium adsorption capacities and related correlation coefficients, for each kinetic
model were calculated and discussed. Consequently, the adsorption of cobalt
followed pseudo second order kinetics suggesting chemisorption for all the tested
adsorbents. Also, results suggested that intraparticle diffusion was not the only step
controlling the overall adsorption process of cobalt. Results presented here can help
to design an appropriate environmental management strategy to minimize the adverse
impacts caused by industrial wastewater.