『Abstract
Groundwater contamination by nitrates is a worldwide problem,
but to date there have been no effective measures to purify contaminated
groundwater. If a denitrifying system can be constructed in aquifers,
it will be able to purify groundwater in situ. This purifying
system should also be maintenance free. The purpose of our work
is to construct a maintenance-free denitrification system for
in situ groundwater purification. This paper presents the result
of a basic study on a maintenance-free denitrification system
using biodegradable plastic and iron powder. A biodegradable plastic
(polylactic acid, PLA) and iron powder were used as detergents,
and the nitrate-contaminated groundwater was injected from the
bottom of a packed silica sand column filled with a mixture of
the detergents. laboratory experiments were carried out, varying
factors such as molecular weight of the biodegradable plastic
and mixing ratio of the detergents. Water that permeated through
the purification column was sampled to determine the decrease
in nitrate concentration. The experimental results suggest that
a combination of PLA and iron powder seems effective for denitrification,
and that the rate of the PLA degradation is closely related to
the molecular weight of the PLA and iron powder content. In this
case iron powder acts as accelerator in denitrification. It is
concluded that a maintenance-free denitrification system can be
built, using PLA and iron powder as detergents. The proposed system
may also be used in a wide range of nitrate contamination conditions,
adjusting the molecular weight of the PLA and the mixing ratio
of the detergents.
Keywords: Nitrate contamination; Denitrification; Biodegradable
plastic; Groundwater; Polylactic acid』
1. Introduction
2. materials and test methods
2.1. Materials
2.2. Organisms
2.3. Experimental setup
2.4. Analysis
3. Results and discussion
3.1. Quality of water that permeated through iron powder-filled
column
3.2. Quality of water that permeated through PLA (Mw=5,000)
and iron powder-filled column
3.3. Quality of water that permeated through column filled with
blended PLA and iron powder
3.4. Relationships between PLA and iron powder
4. Conclusions
References