Excellent performance of cobalt-impregnated activated carbon in peroxymonosulfate activation for acid orange 7 oxidation
Environ Sci Pollut Res
Excellent performance of cobalt-impregnated activated carbon in peroxymonosulfate activation for acid orange 7 oxidation
Tianyin Huang 0 1 2
Jiabin Chen 0 1 2
Zhongming Wang 0 1 2
Xin Guo 0 1 2
John C. Crittenden 0 1 2
0 Brook Byers Institute for Sustainable Systems and the School of Civil and Environmental Engineering, Georgia Institute of Technology , Atlanta, GA 30332 , USA
1 School of Environmental Science and Engineering, Suzhou University of Science and Technology , Suzhou 215001 , People's Republic of China
2 Responsible editor: Vítor Pais Vilar
3 John C. Crittenden
Cobalt-impregnated activated carbon (GAC/Co) was used to produce sulfate radical (SO4·−) from peroxymonosulfate (PMS) in aqueous solution (hereafter called PMS activation). We evaluated its effectiveness by examining the degradation of orange acid 7 (AO7). GAC/Co exhibited high activity to activate PMS to degrade AO7. The degradation efficiency of AO7 increased with increasing dosage of GAC/Co or PMS and elevated temperatures. pH 8 was most favorable for the degradation of AO7 by GAC/Co-activated PMS. The radical quenching experiments indicated that the reactions most likely took place both in the bulk solution and on the surface of GAC/Co. We found that SO4·− played a dominant role in AO7 degradation. Sodium chloride (NaCl) which presents in most dye wastewater had a significant impact on AO7 degradation. Low dosages (<0.4 M) of NaCl showed a slight inhibitory effect, whereas high dosages (0.8 M) increased the reaction rate. HOCl was confirmed as the main contributor for accelerating AO7 degradation with high concentration of NaCl. In a continuous-flow reaction with an empty-bed contact time of 1.35 min, AO7 was not detected in the effluent for 0 to 18.72 L of treated influent volume (156 h) and 85% removal efficiency was still observed after 40.32 L of treated volume (336 h). Finally, the azo bond and the naphthalene structure in AO7 were destroyed and the degradation pathway was proposed.
Peroxymonosulfate; Orange acid 7; Activated carbon; Cobalt; Chloride
Introduction
Recently, dye wastewater generated from textile, printing,
leather, food, and pharmaceutical industries have attracted
worldwide concern due to their large concentrations in
wastewaters and their environmental risk
(Bakheet et al. 2013; Yang
et al. 2011)
. Azo dyes, characterized by azo bonds (−N=N–),
are the most widely utilized colorants, accounting for 50% of
all commercial dyes
(Azam and Hamid 2006; Garcia-Segura
et al. 2013)
. Azo dyes are extremely stable because they are
designed to be resistant to water, weather, detergent, and
biodegradation during the production
(Cai et al. 2014b)
.
The occurrence of azo dyes in the environment is
undesirable not only because of their color but also because they are
persistent, toxic, and carcinogenic
(Cai et al. 2014a; Peng et al.
2008)
. Thus, it is imperative to treat the azo dye wastewater
before discharge into the receiving waters. However, the
conventional wastewater treatment methods are inefficient to
degrade the azo dyes
(Cai et al. 2014b; Grčić et al. 2012)
.
Alternative treatment methods for azo dyes include
electrochemical treatment
(Brillas and Martinez-Huitle 2015)
,
ozonation
(Szpyrkowicz et al. 2001)
, photo-catalysis
(Han et al.
2009)
, and Fenton or Fenton-like reactions
(Szpyrkowicz
et al. 2001; Zhang et al. 2013a)
.
Currently, sulfate radical (SO4·−)-based advanced oxidation
processes (SR-AOPs) have demonstrated great promise in the
degradation of the recalcitrant pollutants
(Qian et al. 2016;
Zhang et al. 2015a, b)
. SO4·− is known as a strong oxidant
possessing a high redox potential (2.5–3.1 V) but more selective
than hydroxyl radical (HO·) over a wide pH range
(Chen et al.
2016a; Qian et al. 2015)
. SO4·− can be generated from the
peroxymonosulfate (PMS) when activated by UV
(Guan et al.
2011; He et al. 2014; Zhang et al. 2015b)
, heat
(Antoniou
et al. 2010; Chen et al. 2016b; Gao et al. 2016; Yang et al.
2010)
, or transition metal ions
(Anipsitakis and Dioniou 2004;
Chan and Chu 2009)
. UV irradiation and thermal activation are
not cost efficient due to the high-energy input. By contrast,
transition metal ions are cost-effective activators for PMS due
to their natural abundance and low-energy input. Among the
transition metal ions, cobalt (Co) is considered the most
effective activator for PMS
(Anipsitakis and Dioniou 2004; Nfodzo
and Choi 2011)
. Co(II)-activated PMS has been widely used to
degrade phenolic compounds
(Zhang et al. 2009)
, dyes
(Wang
et al. 2011)
, and other recalcitrant contaminants (Mahdi Ahmed
et al. 2012). Nonetheless, Co is regarded as a priority
contaminant in water, because Co has a potential health risk (e.g.,
asthma, pneumonia, and other lung problems)
(Shukla et al. 2010)
.
To restrict the discharge of Co(II) into the water, heterogeneous
activation of PMS with Co was preferred because when Co(II)
is impregn (...truncated)