| Author | Anawat Pinisakul |
| Call Number | AIT Diss no.EV-02-03 |
| Subject(s) | Water--Pollution
Water--Purification
|
| Note | A dissertation submitted in partial fulfil~ment of the reqqirements for the degree of Doctor
of Technical Science.
Inter-University Program on Environmental Toxicology, Technology and Management, Asian Institute of Technology; Chulabhorn Research Institute and Mahidol University
|
| Publisher | Asian Institute of Technology |
| Abstract | This research was conducted to investigate the efficiency, chemical reactions and
mechanisms of arsenic (As) removal from a contaminated water by using the electrochemical
treatment (ECT) process. For a synthetic As-contaminated water, within the
following operating conditions : initial As-concentration of 0.5-5 mg/L, area of electrode
plate/volume ofECT reactor of 0.02 cm2/cm3, 0.1 M KCl, electrical gradient of200 volt/m
and initial pH higher than 3, the laboratory-scale ECT reactors operating in batch mode
were able to reduce As to be within 0.01 mg/L in 15-20 min, making the treated water
suitable for use in shrimp culture. For a contaminated groundwater containing As about
0.135-1.072 mg/L, the batch ECT reactors were effective in reducing the As to be within
0.01 mg/Lin 5 min. The Cr salt was found to yield better As removal efficiencies than the
N03- salt because, chemically, N03- ions interfere with the production of OH- and
Fe(OH)3, the compound mainly responsible for As removal.
A first-order reaction model for As removal, incorporating parameters such as area of
electrode plate/volume of ECT reactor, conductivity and electrical gradient, was developed
which was found feasible in predicting As removal efficiency by the ECT process.
The continuous ECT reactor was found to be equally effective in treating the Ascontaminated
water, but due to the continuous As input, it required longer operation time
than that of the batch operation. However; because of the continuous mixing condition, it
required less power and electi'ode consumptions than those of the batch reactors in
achieving the same As removal efficiency.
The ECT sludge characteristics were analyzed by X-ray fluorescence (XRF) and X-ray
diffractometric (XRD) methods. The results revealed maghemite (Fe203) and angellelite
(Fe<iAs20 11) to be the major compounds present in the precipitated ECT sludge generated
from both in the synthetic water and contaminated groundwater. The percent Fe203 and
Fe<iAs20 11 (as As20 3) contents of the dried ECT sludge were 98.29% and 0.26% for the
synthetic As-contaminated water and 90-95% and 0.07-0.14% for the contaminated
groundwater, respectively. A mass balance analysis of the As removal in the ECT process
revealed the follows : As incorporation in and adsorption on the ECT sludge, 73.3 ± 14.6%;
As conversion to arsine (AsH3) gas, 10.6 ± 4.3%; As adsorption on the electrode plates and
reactor walls, 0.4 ± 0.4%; As residual in the supernatant, 0.3 ± 0.1 % and As unaccounted
for, 15 .4 ± 11.2%. From the adsorption/desorption experiments and Freundlich isotherm
analysis, the ECT sludge was found to possess less As adsorption capacity than other
absorbents, such as activated carbon and rice husk, but it appeared to have strong
adsorptive bond and less As desorption potential.
The operation cost of the ECT process in treating the As-contaminated water was
calculated to be slightly lower than that of the chemical precipitation process using FeCh
as coagulant. This lower cost was probably due to the high efficiency of the ECT reactions
in producing that ECT sludge that was effective in removing the As compounds by
adsorption and incorporation in the ECT sludge. Overall, the ECT process was found to be
a feasible technology in treating the As-contaminated groundwater in southern Thailand
and the treated effluent was found to have characteristics suitable for use in low-salinity
shrimp culture, and, based on literature data, should not cause toxicity to the slu·imps or
create serious environmental impact to the nearby environment. |
| Year | 2002 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EEM) |
| Chairperson(s) | Chongrak Polprasert; |
| Examination Committee(s) | Preeda Parkpian;
Jutamaad Satayavivad;
Gupta, Ashim Das;Yamamoto, Kazuo; |
| Scholarship Donor(s) | Post-Graduate Education, Training and Research
Program in Environmental Science, Technology and
Management under Higher Education Development
Project of the Ministry of University Affairs; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2002 |
