Nanomaterials for Environmental Burden Reduction, Waste Treatment and Non-Point Source Pollution Control - Nanotechnologies for Water Environment Applications - page 460

Different approaches have been proposed and used to remove NO 3- from groundwater,
such as membrane separation (MS), ion exchange (IE), and biological denitrification.
However, both MS and IE processes are not selective for NO 3 - removal and they are
expensive. The biological denitrification process removes NO 3 - selectively but produces
small amounts of wastes. In a heterotrophic biological denitrification process, external
organic carbon (e.g., methanol, acetate) usually is added, which requires precise control
of the process so that a low BOD (biochemical oxygen demand) in the effluent can be
achieved. However, NO 3 - removal efficiency with heterotrophic denitrification under
field conditions varies tremendously, because of temporal and spatial variations in
population of denitrifying microorganisms and carbon content.
A catalytic reduction process has been developed to selectively remove NO 3 -
from groundwater associated with agricultural communities. Palladium (Pd), platinum
(Pt), and rhodium (Rh) on carbon (5-10%) as catalysts were used to remove nitrate by
the catalytic reduction process (Reddy and Lin, 2000). The supported Pd-Cu/gamma-
Al 2 O 3 catalyst was prepared for reduction of nitrate and nitrite in water (Gao et al.,
2004). The catalytic selective reduction is a promising method for the removal of nitrate,
especially for the small-scale application in the rural area. If these catalysts are nano-
sized, the nitrate removal rate would be greatly increased. Zero-valent iron (ZVI) has a
high reactivity for removal of nitrate (Joo and Chang, 2006). The nitrate reduction of
ZVI is mainly affected by pH and the size of ZVI particles. Usually, microscale ZVI
converts nitrate to ammonia (Huang et al., 2003; Huang and Zhang, 2005), but nano-
scale ZVI (NZVI) converts nitrate to N 2 gas with much higher reactivity (Choe et al.,
2000; Chen et al., 2004; Wang et al., 2006). In order to increase reactivity and
flexibility for nitrate removal., NZVI is further supported on micro-scale exfoliated
graphite (Zhang et al., 2006). Recently, NZVI reduction and microbial reduction are
combined to reduce nitrate (Shin and Cha, 2008). Pd/Fe bimetallic nanoparticles were
also used for in situ removal and degradation of nitrate. Over 99% of nitrate was
removed even only 0.05 wt% of nanoscale Pd/Fe bimetal was injected (Yang et al.,
2008).
The nanofiltration membrane technique is another efficient approach to remove
nitrate (Santafe-Moros et al., 2005a) for obtaining drinking water from waters with
nitrate ion concentrations between 50 and 150 mg·L -1 (Santafe-Moros et al., 2005b;
Santafe-Moros et al., 2007). The Santafe-Moros group has studied and compared the
nitrate removal efficiencies of three commercial nanofiltration membranes, that is,
NF90, NF270 (Dow-FilmTec) and ESNA1-LF (Hydranautics). The van der Bruggen
group has also investigated the membranes NF70, NF45, UTC-20 and UTC-60, and
discussed the economical side of the implementation of the nanofiltration technique (van
der Bruggen et al., 2001). The most influential factors include pH, co-existing ions, and
nitrate concentrations (Choi et al., 2001; Diawara et al., 2005). Recently, many
technologies with nanomaterials being involved have been developed, such as the