Fixed-bed column recirculation system for investigation of sorption and biodegradation of organic pollutants in saturated sediment: a detailed design and development
© The Author(s) 2016
Received: 7 January 2016
Accepted: 13 October 2016
Published: 21 October 2016
Sorption and biodegradation are the primary processes of organic pollution remediation in aquatic and soil/sediment environments. While researchers have substantially reported their findings regarding these processes, little attention has been given to description of experimental apparatus. This technical paper aims to present the development and detailed design of a fixed-bed column recirculation (FBCR) system which has been widely applied to investigate sorption and biodegradation of organic pollutants in aquatic and/or sediment environments.
The FBCR system was developed and tested by three experiments investigating sorption and biodegradation of two herbicides (isoproturon and mecoprop) in different saturated materials (hydrofilt and river sediment). Efficiency of the FBCR system was assessed according to criteria i.e. reliability, leaking inhibition, reproducibility, practical of use and cost. The results indicated that the latest version (Version 4) of the FBCR system has been significantly improved and ready to extend to similar studies.
This system is therefore recommended to researchers who intend to investigate the remediation of organic pollutants in aquatic, soil and sediment environments.
Development of a FBCR system
In Version 1 (Fig. 3a), the body and the two end-caps were connected together by eight sets of plastic bolts and nuts (four at each end). The column was packed with Hydrofilt material (see the Additional file 1). The system worked properly without leakage at low internal pressure (due to large particle sizes of Hydrofilt, from 0.8 to 1.5 mm). However, once river sediment was packed in the column, internal pressure increased considerably due to fine particle size of the sediment (23 % silt and 76 % sand, Additional file 1: Table S2). This resulted in leakage and, in several cases once the plastic bolts were tightened, fracture was observed. Leakage was often found at the connection between the body and the end-cap. In addition, the cap and the body were easily broken once the plastic bolts were tightened in connecting these parts together.
Version 2 (Fig. 3b) was created to improve the shortcomings of Version 1. Two stainless steel clamps were made to house the body and the two end-caps by using four stainless steel studdings and wing nuts holding the clamps. This design improved the leakage problem and minimized incidences of breakage. However, this design was inconvenient for packing sediment material because the lower end-cap and the body were not fixed together once the upper end-cap was taken off for packing. Furthermore, manufacturing of the stainless steel clamps was costly.
In Version 3 (Fig. 3c), a number of improvements were applied. Two conical connections at the two ends of the column were designed to replace the clamp-connections used in Version 2. The two caps and body of the column were connected by the two conical joints (vaseline should be used at the connect contact in order to facilitate the disassembling step). The connection was strengthened by stainless steel springs (or rubber bands) and hooks surrounding four sides of the column. This design also improved the manipulation of packing material in the column, making it quicker and easier to use. The leakage problem was mostly prevented by the conical joint. After several tests, the advantages of this version were compared to the previous versions and noted in terms of its faster manufacture, easier manipulating and packing, and lower production cost. Experiencing the trials, however, it was observed that the lower conical cap was not really necessary and, as a consequence, further refinements were made resulting in the final version (Version 4).
Materials and methods for testing the FBCR system
River water and river sediment were collected at River Thames (Gatehampton, Reading, UK). Hydrofilt, a porous material used in water treatment, was purchased from Akdolit® Company. Herbicides isoproturon (IPU) (3-(4-isopropylphenyl)-1,1-dimethyl urea) and mecoprop (MCPP) (2-(4-chloro-o-tolyloxy) propaonic acid) were purchased from Sigma Aldrich, UK. Further information of these materials, their characteristics, and analytical procedure are presented in Additional file 1: Tables S1 and S2.
Three experiments were established to test the FBCR system.
Experiment 1: Testing IPU attenuation in Hydrofilt material with Version 1
Experiment 2: Testing IPU attenuation in river sediment with Version 3
River sediment (150 g) was packed in the columns. River water (1.5 L) was transferred to the reservoir of Version 3. The IPU stock solution was spiked in the reservoir to achieve final concentration of about 1050 μg L−1. The contaminated solution was recirculated through the column for 14 days. Aqueous samples were collected from the reservoir at every intervals. The samples were then analysed by the HPLC system to determine IPU concentration.
Experiment 3: Testing MCPP attenuation in river sediment with Version 4
River sediment (150 g) was packed in the columns. River water (1.5 L) was transferred to the reservoirs of Version 4 system. Two treatments (n = 3) were established: Treatment 1 with both sterilised river water and river sediment (autoclaved at 121 °C for 30 min); and Treatment 2 with both non-sterile river water and river sediment (the natural materials). The MCPP stock solution was spiked in the reservoirs to achieve the final concentration of about 100 μg L−1. The contaminated solution in the reservoir was recirculated through the column for 18 days. Aqueous samples were collected at every intervals. The samples were also analysed by HPLC to determine MCPP concentration.
Results and discussion
Sorption of IPU on Hydrofilt material (Experiment 1)
IPU concentration in the controlled treatment (without packing material) did not significantly decrease (p > 0.05) over 128 h of recirculation (Fig. 5). This indicated that IPU was not significantly lost by sorption to the wall of the apparatus or by evaporation. IPU concentrations in both Treatments 1 and 2 were observed as a biphasic model: (1) the rapid sorption phase occurred over the initial one-third day; and (2) the stable phase occurred over the remaining of 5 days. Over the rapid sorption phase, IPU concentration significantly decreased (15 %) in both Treatments 1 and 2. Stable phase indicated that the equilibrium state of IPU between the solid and liquid phases could be reached. Several isotherm sorption parameters of IPU on Hydrofilt were estimated i.e. the maximum sorption capacity of Hydrofilt to IPU (CS,max) to be 614 ± 71 µg kg−1 and the solid-water distribution coefficient (K d ) to be 6.28 ± 0.70 L kg−1.
Sorption and biodegradation of IPU in river water–river sediment system (Experiment 2)
Sorption and biodegradation of MCPP in river water–river sediment system (Experiment 3)
Observations from the three experiments indicated that the FBCR system is reliable and useful for investigation of sorption and biodegradation of organic pollutants in saturated sediment. This system was found to be efficient, reproducible, practical in terms of packing materials and leaking control, low cost and quick to assemble. In addition, unnecessary mistakes presented in this paper could be also helpful in terms of saving time and cost to reproduce this system. It is therefore recommended to researchers who intend to investigate sorption and biodegradation processes of organic pollutants in aquatic, soil and sediment environments.
The outcomes of this paper are a part of BST Ph.D. research. The research was implemented at the University of East Anglia, Norwich, UK under the supervision of Professor KH and Dr BR. All authors read and approved the final manuscript.
The authors would like to acknowledge the People’s Committee of Ho Chi Minh city (project CT300), Vietnam for funding this research with a PhD fellowship to Bao Son Trinh. Special thanks to Dr Michael Jones and his colleagues at Thames Water Utilities who helped with access to field sites to collect river water and sediment samples.
The authors declare that they have no competing interests.
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