3 research outputs found
Arsenic Waste Management: A Critical Review of Testing and Disposal of Arsenic-Bearing Solid Wastes Generated during Arsenic Removal from Drinking Water
Water treatment technologies for arsenic removal from groundwater
have been extensively studied due to widespread arsenic contamination
of drinking water sources. Central to the successful application of
arsenic water treatment systems is the consideration of appropriate
disposal methods for arsenic-bearing wastes generated during treatment.
However, specific recommendations for arsenic waste disposal are often
lacking or mentioned as an area for future research and the proper
disposal and stabilization of arsenic-bearing waste remains a barrier
to the successful implementation of arsenic removal technologies.
This review summarizes current disposal options for arsenic-bearing
wastes, including landfilling, stabilization, cow dung mixing, passive
aeration, pond disposal, and soil disposal. The findings from studies
that simulate these disposal conditions are included and compared
to results from shorter, regulatory tests. In many instances, short-term
leaching tests do not adequately address the range of conditions encountered
in disposal environments. Future research directions are highlighted
and include establishing regulatory test conditions that align with
actual disposal conditions and evaluating nonlandfill disposal options
for developing countries
Differential Resistance of Drinking Water Bacterial Populations to Monochloramine Disinfection.
The impact of monochloramine
disinfection on the complex bacterial
community structure in drinking water systems was investigated using
culture-dependent and culture-independent methods. Changes in viable
bacterial diversity were monitored using culture-independent methods
that distinguish between live and dead cells based on membrane integrity,
providing a highly conservative measure of viability. Samples were
collected from lab-scale and full-scale drinking water filters exposed
to monochloramine for a range of contact times. Culture-independent
detection of live cells was based on propidium monoazide (PMA) treatment
to selectively remove DNA from membrane-compromised cells. Quantitative
PCR (qPCR) and pyrosequencing of 16S rRNA genes was used to quantify
the DNA of live bacteria and characterize the bacterial communities,
respectively. The inactivation rate determined by the culture-independent
PMA-qPCR method (1.5-log removal at 664 mg·min/L) was lower than
the inactivation rate measured by the culture-based methods (4-log
removal at 66 mg·min/L). Moreover, drastic changes in the live
bacterial community structure were detected during monochloramine
disinfection using PMA-pyrosequencing, while the community structure
appeared to remain stable when pyrosequencing was performed on samples
that were not subject to PMA treatment. Genera that increased in relative
abundance during monochloramine treatment include <i>Legionella</i>, <i>Escherichia</i>, and <i>Geobacter</i> in
the lab-scale system and <i>Mycobacterium</i>, <i>Sphingomonas</i>, and <i>Coxiella</i> in the full-scale system. These results
demonstrate that bacterial populations in drinking water exhibit differential
resistance to monochloramine, and that the disinfection process selects
for resistant bacterial populations
Optimization of Arsenic Removal Water Treatment System through Characterization of Terminal Electron Accepting Processes
Terminal electron accepting process (TEAP) zones developed
when
a simulated groundwater containing dissolved oxygen (DO), nitrate,
arsenate, and sulfate was treated in a fixed-bed bioreactor system
consisting of two reactors (reactors A and B) in series. When the
reactors were operated with an empty bed contact time (EBCT) of 20
min each, DO-, nitrate-, sulfate-, and arsenate-reducing TEAP zones
were located within reactor A. As a consequence, sulfate reduction
and subsequent arsenic removal through arsenic sulfide precipitation
and/or arsenic adsorption on or coprecipitation with iron sulfides
occurred in reactor A. This resulted in the removal of arsenic-laden
solids during backwashing of reactor A. To minimize this by shifting
the sulfate-reducing zone to reactor B, the EBCT of reactor A was
sequentially lowered from 20 min to 15, 10, and 7 min. While 50 mg/L
(0.81 mM) nitrate was completely removed at all EBCTs, more than 90%
of 300 μg/L (4 μM) arsenic was removed with the total
EBCT as low as 27 min. Sulfate- and arsenate-reducing bacteria were
identified throughout the system through clone libraries and quantitative
PCR targeting the 16S rRNA, dissimilatory (bi)sulfite reductase (<i>dsrAB</i>), and dissimilatory arsenate reductase (<i>arrA</i>) genes. Results of reverse transcriptase (RT) qPCR of partial <i>dsrAB</i> (i.e., <i>dsrA</i>) and <i>arrA</i> transcripts corresponded with system performance. The RT qPCR results
indicated colocation of sulfate- and arsenate-reducing activities,
in the presence of iron(II), suggesting their importance in arsenic
removal