This thesis for the first time reports the fate and behaviour of herbicides mecoprop (MCPP) and isoproturon (IPU) in the hyporheic zone of a river bank. Two laboratory studies based on fixed-bed circulation and 14Crespirometry were developed to investigate the attenuation of the two herbicides in riverbank filtration (RBF), a means of pre-treatment of drinking water obtained from bank-side boreholes. The first laboratory study investigated the sorption and biodegradation of MCPP and IPU (100 μg L-1) in a river water (RW)-riverbed sediment (RS) system with materials obtained from a site on the River Thames at Gatehampton, England. Using a fixed-bed circulation method, approximately 18-20 % of the herbicides were removed by sorption, with the remainder removed by a high rate of biodegradation during 14 circulating days. The RS-borne microorganisms played a primary role in the biodegradation process of these herbicides, while the RW-borne microorganisms contributed very little. In addition, after a period of incubation (by 18 circulation days with IPU) the RS-borne microorganisms were able to immediately mineralise 14C-IPU (29.4 % 14CO2) while the RW-borne microorganisms were not competent to do so (1.6 % 14CO2). The second laboratory study investigated catabolic insights into IPU degradation in river water (RW), groundwater (GW) and riverbed sediment (RS). Very low maximum levels of mineralisation of IPU were observed in RW (0.4 % 14CO2) and GW (1.2 % 14CO2) while very high maximum level of mineralisation of IPU was obtained in RS (14.5 % 14CO2). Furthermore, the catabolic competence with respect to IPU was enhanced with increasing the IPU-dosed concentrations (ranging 1 – 100 μg L-1) in RS microcosm. By plotting the maximum mineralisation levels versus the residual IPU concentration (after various periods of incubation), a logarithm linear relation between the maximum mineralisation levels and IPU concentrations was obtained. This relationship suggested that higher mineralisation levels are achieved for higher IPU concentrations. Nonetheless, the catabolic activity not only was not significantly enhanced (p > 0.05) after a period of incubation (0 – 10 days) but also was greatly decreased (p < 0.05) after 30 incubation days. Based upon the experimental results, to remove the herbicides from 1 L of RW contaminated with MCPP and IPU (up to 100 μg L-1), a required volume of RS (bulk density of 1.25 ± 0.02 g cm-1 and porosity of 50.6 %) was determined to be 0.027 m3. Extent in a RBF context, it is suggested that a bank-side borehole with a capacity of 16 x 106 L day-1 and 25 % river-fed water could be protected from the river-borne herbicide pollution (up to 100 μg L-1) if the borehole is located at a minimum distance (path length) of 400 m from the river with the thickness of a RS layer to be 6 m. Collectively, the herbicides MCPP and IPU were completely degraded in a hyporheic zone of a river bank. Microorganisms originated from RS played a pivotal role in the degradation. This demonstrated that RBF is potentially a highly efficient pre-treatment method which can totally remove herbicide pollution in river. Hence, bank-side boreholes which are mainly or partly fed by induced RW may be benefit from this natural attenuation process.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:569320 |
| Date | January 2010 |
| Creators | Bao Son, Trinh |
| Publisher | University of East Anglia |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ueaeprints.uea.ac.uk/10592/ |
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