Nanoparticles for Treatment of Chlorinated Organic Contaminants - Nanotechnologies for Water Environment Applications - page 105

cause the loss of one oxygen atom so that ClO 4 - become ClO 3 - , which is easier to be
reduced and less stable in aqueous solution.
NZVI was also tested for reduction of perchlorate in water or ion-exchange
brine. At an iron dosage of 1.8 g L -1 and at moderately elevated temperatures (90-95
°C), ~90% removal of perchlorate in both fresh water and a simulated ion-exchange
brine (NaCl = 6% (w/w)) was achieved within 7 h. Perchlorate was rapidly reduced to
chloride without accumulation of any intermediate products. Stabilized NZVI by starch
and carboxymethyl cellulose increased perchlorate degradation by 1.8- and 3.3-fold,
respectively, compared to that of non-stabilized NZVI particles. Interestingly, any
addition of a metal catalyst (Al, Cu, Co, Ni, Pd, or Re) did not show additional
improvement (Xiong et al., 2007).
ZVI was found to inhibit the growth of bacteria capable of reducing perchlorate
(Shrout et al., 2005). The addition of ZVI to the mixed bacterial culture showed
decreased rates of perchlorate reduction than that of the culture without the presence of
ZVI. According to the research, the addition of ZVI resulted in a pH increase, while the
precipitation of Fe minerals encapsulated the bacterial cells, but the negative effect of
ZVI was observed even in experiments where pH was kept constant.
Contradictorily, more recent studies demonstrated the capability of reducing
perchlorate by iron-supported microorganism cultures, which completely removed 65
mg/L of perchlorate in batch reactors in 8 days. Complete removal of perchlorate by
anaerobic bacteria was observed when iron was added (Son et al., 2006). The
combination of ZVI with perchlorate-reducing microorganisms resulted in perchlorate
removal from water (Yu et al., 2006). Perchlorate degradation rates were found to follow
Monod kinetics, with a normalized maximum utilization rate (r max ) of 9200 g g -1 (dry
wt) h -1 . Neutral pH conditions would provide the most suitable environment for
perchlorate reduction (Yu et al., 2006).
4.4.4 Application of NZVI in PCB Degradation
4.4.4.1 PCB Degradation by ZVI and NZVI
Application of ZVI for degrading PCBs was probably first studied by Chuan et
al. (Chuang et al., 1995), who reported that an aqueous mixture of PCBs consisting of
Aroclo 1221 and 1254 was completely reduced to biphenyl at temperature over 300 o C
when powdered irons were introduced. At such high temperature, most of PCBs were
degraded within 10 minutes. Yak et al. (Yak et al., 1999) confirmed the applicability of
microscale ZVI (100 mesh) in degrading Aroclor 1260 in subcritical water at 250 o C, 10
MPa within 10 hours. The higher chlorine-containing congeners were completely