Atrazine Removal Efficiency Research Articles

Evaluation of kenaf fibers as moving bed biofilm carriers in algal membrane photobioreactor

In this lab-scale study, the feasibility of using kenaf fibers as moving bed biofilm carriers in hybrid microalgal membrane photobioreactors (HMPBR) in organic matter and atrazine elimination from real secondary effluent was evaluated. For evaluating the kinetics of biofilm substrate consumption, an experimental model was proposed. Inoculation of wastewater samples with free carriers resulted in the greater removal of target pollutants. Removal efficiency of atrazine and chemical oxygen demand (COD) increased to 27% and 16%, with respect to the control, respectively. The total biomass accumulation in HMPBR exceeded 5g/L, and the microalgae tended to aggregate and attached to biofilm carriers. The removal efficiency of HMPBR improved significantly via inoculation of kenaf fiber carriers with bioremediation microalgal strains (p < 0.01). A lower stabilization ratio (VSS/TSS) was also recorded. The biomass in HMPBR included more lipids and carbohydrates. The results revealed that kenaf fibers could improve and upgrade the biological activity of different wastewater treatment applications, considering the great potential of biofilm carriers and their effluent quality.

Simultaneous removal of atrazine and organic matter from wastewater using anaerobic moving bed biofilm reactor: A performance analysis

In this study, an anaerobic moving bed biofilm reactor (AMBBR) was designed to biodegrade atrazine under mesophilic (32 °C) condition and then it was evaluated for approximately 1 year. After biofilm formation, acclimation, and enrichment of microbial population within the bioreactor, the effect of various operation conditions such as changes in the concentration of influent atrazine and sucrose, hydraulic retention time (HRT), and salinity on the removal of atrazine and chemical oxygen demand (COD) were studied. In optimum conditions, the maximum removal efficiency of atrazine and COD was 60.5% and 97.4%, respectively. Various models were developed to predict the performance of atrazine removal as a function of HRT during continuous digestion. Also, coefficients kinetics was studied and the maximum atrazine removal rate was determined by Stover - Kincannon model (rmax = 0.223 kgATZ/m3d). Increasing salinity up to 20 g/L NaCl in influent flow could inhibit atrazine biodegradation process strongly in the AMBBR reactor; whereas, the reactor could tolerate the concentrations less than 20 g/L easily. Results showed that AMBBR is feasible, easy, affordable, so suitable process for efficiently biodegrading toxic chlorinated organic compounds such as atrazine. There was no accumulation of atrazine in the biofilm and the loss of atrazine in the control reactor was negligible; this shows that atrazine removal mechanism in this system was due to co-metabolism.

The removal of COD and NH3-N from atrazine production wastewater treatment using UV/O3: experimental investigation and kinetic modeling.

In this study, a UV/O3 hybrid advanced oxidation system was used to remove chemical oxygen demand (COD), ammonia nitrogen (NH3-N), and atrazine (ATZ) from ATZ production wastewater. The removal of COD and NH3-N, under different UV and O3 conditions, was found to follow pseudo-first-order kinetics with rate constants ranging from 0.0001-0.0048 and 0.0015-0.0056min-1, respectively. The removal efficiency of ATZ was over 95% after 180min treatment, regardless the level of UV power. A kinetic model was further proposed to simulate the removal processes and to quantify the individual roles and contributions of photolysis, direct O3 oxidation, and hydroxyl radical (OH·) induced oxidation. The experimental and kinetic modeling results agreed reasonably well with deviations of 12.2 and 13.1% for the removal of COD and NH3-N, respectively. Photolysis contributed appreciably to the degradation of ATZ, while OH· played a dominant role for the removal of both COD and NH3-N, especially in alkaline environments. This study provides insights into the treatment of ATZ containing wastewater using UV/O3 and broadens the knowledge of kinetics of ozone-based advanced oxidation processes.

Application of Fe(II)/peroxymonosulfate for improving ultrafiltration membrane performance in surface water treatment: Comparison with coagulation and ozonation

Coagulation and ozonation have been widely used as pretreatments for ultrafiltration (UF) membrane in drinking water treatment. While beneficial, coagulation or ozonation alone is unable to both efficiently control membrane fouling and product water quality in many cases. Thus, in this study an emerging alternative of ferrous iron/peroxymonosulfate (Fe(II)/PMS), which can act as both an oxidant and a coagulant was employed prior to UF for treatment of natural surface water, and compared with conventional coagulation and ozonation. The results showed that the Fe(II)/PMS-UF system exhibited the best performance for dissolved organic carbon removal, likely due to the dual functions of coagulation and oxidation in the single process. The fluorescent and UV-absorbing organic components were more susceptible to ozonation than Fe(II)/PMS treatment. Fe(II)/PMS and ozonation pretreatments significantly increased the removal efficiency of atrazine, p-chloronitrobenzene and sulfamethazine by 12–76% and 50–94%, respectively, whereas coagulation exerted a minor influence. The Fe(II)/PMS pretreatment also showed the best performance for the reduction of both reversible and irreversible membrane fouling, and the performance was hardly affected by membrane pore size and surface hydrophobicity. In addition, the characterization of hydraulic irreversible organic foulants confirmed its effectiveness. These results demonstrate the potential advantages of applying Fe(II)/PMS as a pretreatment for UF to simultaneously control membrane fouling and improve the permeate quality.

Photocatalytic degradation of atrazine herbicide with Illuminated Fe+3-TiO2 Nanoparticles

BackgroundAtrazine is a herbicide that is widely used to control broadleaf and grassy weeds for growing many crops especially in maize production. It is a frequently detected herbicide in many groundwater resources. This study aimed to assess the feasibility of using ultraviolet radiation UV and fortified nanoparticles of titanium dioxide (TiO2) doped with trivalent iron to remove atrazine from aqueous phase and determin the removal efficiency under the optimal conditions.ResultsThe results of this study demonstrated that the maximum atrazine removal rate was at pH = 11 in the presence of Fe+ 3-TiO2 catalyst =25 mg/L and the initial concentration of atrazine equal to 10 mg/L. As the reaction time increased, the removal rate of herbicide increased as well. Atrazine removal rate was enhanced by the effect of UV radiation on catalyst activation in Fe+3-TiO2/UV process. It was also revealed that pH has no significant effect on atrazine removal efficiency (p > 0.05).ConclusionBased on the data obtained in this study, atrazine removal efficiency was increased by increasing pH, initial atrazine concentration, catalyst, and contact time. The results also showed Fe+3-TiO2/UV process was an appropriate method to reduce atrazine in contaminated water resources. In conclusion, Fe+3-TiO2/UV process may enhance the rate of atrazine reduction in highly polluted water resources (more than 99%).

Rapid biodegradation of atrazine by Ensifer sp. strain and its degradation genes

A bacterial strain (CX-T) capable of utilizing atrazine as a nitrogen source for growth was isolated from an industrial soil sample via enrichment culture. The isolate was identified as an Ensifer sp. which can metabolize atrazine (100 mg L−1) completely within 30 h in a liquid culture medium. Factors such as temperature, pH and the shaker speed were analyzed with regard to their effect on atrazine degradation in liquid medium. It was found that atrazine removal efficiency varied significantly depending on temperature (mean degradation efficiency: 54.30% at 25 °C, 99.71% at 30 °C and 84.7% at 35 °C, P<0.01) and is optimal under neutral to acidic conditions (pH 5, 91.54%; pH 7, 99.71%; pH 9, 91.71%, P<0.01), as well as low shaker speeds (100 rpm (99.38%) and 180 rpm (99.71%) P<0.01). Additionally through Polymerase Chain Reaction (PCR), degradation genes atzA, atzB, atzC, atzD, atzE and atzF were amplified successfully using highly conserved primers, while trzN and trzD were not detected. We propose these unique genes enabled the CX-T strain to mineralize atrazine, supported by the observation of its growth in the cyanuric acid medium. We conclude CX-T could be a useful bioremediation tool for atrazine polluted soils.

Operation Performance of a Bioaugmented Membrane-aerated Biofilm Reactor Treating Atrazine Wastewater

A hydrophobic SPG (shirasu porous glass) membrane-aerated biofilm reactor (MABR) with genetically engineered microorganism (GEM) biofilm formed on the SPG membrane surface was applied to treat atrazine wastewater. The contaminant removal performance and its influencing factors were investigated during the stable operation of this MABR. The results indicated that the oxygen supply capacity could be increased in the SPG membrane aeration when the membrane pore size and the aeration pressure increased, which could improve the performance of COD and atrazine removals. The maximum oxygen supply capacity of hydrophobic SPG membrane with pore size of 1.5 μm was estimated to be about 22.4 g·(m2·d)-1 at aeration pressure of 70 kPa. When aeration pressure was 70 kPa and hydraulic retention time (HRT) was 1.5 h, the average COD removal efficiency was 80.1% and the average organic loading rate removed was 1.86 kg·(m3·d)-1in the MABR with 1.5 μm hydrophobic SPG membrane. Under the same operating conditions, the average atrazine removal efficiency was 62.5% and the average atrazine loading rate removed was 0.18 kg·(m3·d)-1. The COD and atrazine removal efficiencies decreased significantly at further shortened HRT and increased influent organic loading rate. DO concentration showed more significant influence on atrazine removal. The simplex genetically engineered microorganism biofilm turned into complex microbial community gradually during MABR operation, but the GEM cells could still reside in the biofilm well. Therefore, the efficient atrazine removal by GEM bioaugmentation could be maintained.

Erratum to: Biodegradation of a commercial mixture of the herbicides atrazine and S-metolachlor in a multi-channel packed biofilm reactor.

Atrazine and S-metolachlor are two of the most widely used herbicides for agricultural purposes; consequently, residues of both compounds and their metabolites had been detected in ground and superficial waters. Unlike atrazine, the complete degradation of metolachlor has not been achieved. Hence, the purpose of this research is to study the biodegradation of a commercial mixture of atrazine and S-metolachlor in a prototype of a multi-channel packed-bed-biofilm reactor (MC-PBR) designed with the aim of solving the problems of pressure drop and oxygen transfer, typically found on this type of bioreactors. Because the removal efficiency of the herbicides was increased when Candida tropicalis was added to the original microbial community isolated, the reactor was inoculated with this enriched community. The operational conditions tested in batch and continuous mode did not affect the removal efficiency of atrazine; however, this was not the case for S-metolachlor. The removal rates and efficiencies showed a notable variation along the MC-PBR operation.

Degradation of atrazine by a novel Fenton-like process and assessment the influence on the treated soil

This is the premier study reporting the remediation of atrazine contaminated soil with steel converter slag (SCS) catalyzed Fenton-like process. The effects of various operating parameters, such as SCS loads and H2O2 concentrations were evaluated with respect to the removal efficiency of atrazine. Results show the optimal SCS load and H2O2 concentration were 80gkg−1 and 10%, respectably. The graded modified Fenton’s oxidation with a 3-time addition of 10% H2O2 was able to remove 93.7% of total atrazine in the contaminated soil and maintain soil temperature within 50°C. In contrast to traditional Fenton treatment, a slight pH increase has been observed due to the addition of SCS. More importantly, experiment conducted at natural conditions with SCS gave the similar atrazine removal to the experiments with the other catalysts (e.g., FeSO4 and Fe2O3). One thing should be noted that after the treatment, dissolved organic carbon (DOC) content increased to 1.206gkg−1 from an initial value of 0.339gkg−1.

Biodegradation of a commercial mixture of the herbicides atrazine and S-metolachlor in a multi-channel packed biofilm reactor.

Atrazine and S-metolachlor are two of the most widely used herbicides for agricultural purposes; consequently, residues of both compounds and their metabolites had been detected in ground and superficial waters. Unlike atrazine, the complete degradation of metolachlor has not been achieved. Hence, the purpose of this research is to study the biodegradation of a commercial mixture of atrazine and S-metolachlor in a prototype of a multi-channel packed-bed-biofilm reactor (MC-PBR) designed with the aim of solving the problems of pressure drop and oxygen transfer, typically found on this type of bioreactors.Because the removal efficiency of the herbicides was increased when Candida tropicalis was added to the original microbial community isolated, the reactor was inoculated with this enriched community. The operational conditions tested in batch and continuous mode did not affect the removal efficiency of atrazine; however, this was not the case for S-metolachlor. The removal rates and efficiencies showed a notable variation along the MC-PBR operation.

Reusable magnetic microspheres for efficient removal of atrazine in aqueous media

Abstract In this study, a magnetic hypercrosslinked microsphere (Q150) was prepared and used for organic micropollutants (OMPs) removal. Q150 has a high surface area (1103.6 m2/g) with a narrow particle size distribution (10–30 μm). The high saturation magnetization (9.6 emu/g) of Q150 demonstrates its excellent separation ability. The adsorption behaviors of a typical OMPs, atrazine, were studied and a commercial powdered activated carbon, 1240AC, was selected as comparison. Q150 and 1240AC both displayed fast adsorption kinetics, and the adsorption followed a pseudo-second-order equation (R2 > 0.99). Q150 exhibited a slightly larger adsorption capacity (107.1 mg/g) for atrazine than 1240AC (101.8 mg/g). The most cost-effective adsorbent dose was 0.06 g/L at an initial atrazine concentration of 20 μg/L, resulting in an atrazine removal efficiency that was higher than 99.5%. Q150 could treat 600 ml more of the atrazine solution than 1240AC in a single batch before reaching a breakthrough point (3 μg/L). In the presence of dissolved organic matter (DOM), the water treatment volume of Q150 decreased by 29.2%, which is less than that observed for 1240AC (47.6%). 1240AC completely lost its adsorption capability after 3 adsorption–desorption cycles, whereas Q150 maintained approximately 50% of the initial adsorption capacity after 6 repeated uses. NDMP (magnetic anion exchange resin) pretreatment removed 45.2% of DOM, which improved the atrazine treatment capability of Q150 by 20.8% and enhanced the reusability.

Atrazine dissipation and its impact on the microbial communities and community level physiological profiles in a microcosm simulating the biomixture of on-farm biopurification system

The effects of repeated atrazine application (40mg a.i.kg−1) on its degradation, microbial communities and enzyme activities were studied in a peat based biomixture composed by straw, soil and peat in the volumetric proportions of 2:1:1 that can be used in on-farm biopurification system. Atrazine removal efficiency was high (96%, 78% and 96%) after each atrazine application and did not show a lag phase. Microbial enzyme activities were reduced significantly with atrazine application but rapidly recovered. Microbial diversity obtained by BiologEcoplate™ was similar after the first and second atrazine application. However, an inhibitory effect was observed after the third application. After each atrazine application, culturable fungi were reduced, but rapidly recovered without significant changes in culturable bacteria and actinomycetes compared to the control. Denaturing gradient gel electrophoresis (DGGE) patterns demonstrated that microbial community structure remained relatively stable in time when compared to the controls. In conclusion, our results demonstrated that after successive ATZ applications, the peat based biomixture had a good degradation capacity. Moreover, microbiological assays demonstrated the robustness of the peat based biomixture from a microbiological point of view to support pesticide degradation.

Study of the Bioremediation of Atrazine under Variable Carbon and Nitrogen Sources by Mixed Bacterial Consortium Isolated from Corn Field Soil in Fars Province of Iran

Atrazine herbicide that is widely used in corn production is frequently detected in water resources. The main objectives of this research were focused on assessing the effects of carbon and nitrogen sources on atrazine biodegradation by mixed bacterial consortium and by evaluating the feasibility of using mixed bacterial consortium in soil culture. Shiraz corn field soil with a long history of atrazine application has been explored for their potential of atrazine biodegradation. The influence of different carbon compounds and the effect of nitrogen sources and a different pH (5.5–8.5) on atrazine removal efficiency by mixed bacterial consortium in liquid culture were investigated. Sodium citrate and sucrose had the highest atrazine biodegradation rate (87.22%) among different carbon sources. Atrazine biodegradation rate decreased more quickly by the addition of urea (26.76%) compared to ammonium nitrate. Based on the data obtained in this study, pH of 7.0 is optimum for atrazine biodegradation. After 30 days of incubation, the percent of atrazine reduction rates were significantly enhanced in the inoculated soils (60.5%) as compared to uninoculated control soils (12%) at the soil moisture content of 25%. In conclusion, bioaugmentation of soil with mixed bacterial consortium may enhance the rate of atrazine degradation in a highly polluted soil.

Removal of atrazine by nanoscale zero valent iron supported on organobentonite

The organobentonite (CTMA-Bent) was prepared from Na +-saturated bentonite (Na-Bent) by intercalation with cetyltrimethylammonium bromide (CTMA), and used as a carrier of nanoscale zero valent iron (NZVI) for the removal of atrazine. The NZVI/CTMA-Bent composite was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), and good dispersion of nanoscale iron particles on the carrier was observed. The removal efficiency of atrazine by this composite was compared with that by commercial iron powder and NZVI itself. For both treatments by NZVI and NZVI/CTMA-Bent, the removal efficiency increased as the pH of the solution decreased, and the removal percentage of atrazine by NZVI/CTMA-Bent reached 63.5% at initial pH = 5.0 after 120 min. It is not only much higher than that (26.6%) by NZVI containing the same amount of iron, but also superior to the sum (32.1%) of reduction by NZVI plus adsorption by CTMA-Bent (5.5%). Besides, the NZVI/CTMA-Bent has a good long-term stability, and the carrier CTMA-Bent could prevent the iron ions (the byproduct of dechlorination) from leaching into the solution.

Dissolved nutrients and atrazine removal by column-scale monophasic and biphasic rain garden model systems

Rain gardens are bioretention systems that have the potential to reduce peak runoff flow and improve water quality in a natural and aesthetically pleasing manner. We compared hydraulic performance and removal efficiencies of nutrients and atrazine in a monophasic rain garden design versus a biphasic design at a column-scale using simulated runoff. The biphasic rain garden was designed to increase retention time and removal efficiency of runoff pollutants by creating a sequence of water saturated to unsaturated conditions. We also evaluated the effect of C substrate availability on pollutant removal efficiency in the biphasic rain garden. Five simulated runoff events with various concentrations of runoff pollutants (i.e. nitrate, phosphate, and atrazine) were applied to the monophasic and biphasic rain gardens once every 5d. Hydraulic performance was consistent over the five simulated runoff events. Peak flow was reduced by approximately 56% for the monophasic design and 80% for the biphasic design. Both rain garden systems showed excellent removal efficiency of phosphate (89–100%) and atrazine (84–100%). However, significantly (p<0.001) higher removal of nitrate was observed in the biphasic (42–63%) compared to the monophasic rain garden (29–39%). Addition of C substrate in the form of glucose increased removal efficiency of nitrate significantly (p<0.001), achieving up to 87% removal at a treatment C/N ratio of 2.0. This study demonstrates the importance of retention time, environmental conditions (i.e. saturated/unsaturated conditions), and availability of C substrate for bioremediation of pollutants, especially nitrates, in rain gardens.

A feasibility study of immobilized and free mixed culture bioaugmentation for treating atrazine in infiltrate

A feasibility study of phosphorylated-polyvinyl alcohol immobilized and free mixed bacterial culture bioaugmentation for removing atrazine in agricultural infiltrate was conducted utilizing a sand column setup. The effects of bacterial cell loading and infiltration rate on atrazine degradation were investigated by short-term tests in which the amount of synthetic infiltrate fed through was five times of the void volume (five pore volumes) of the sand column. In addition, the loss of the inoculated atrazine-degrading cultures and the change of bacterial community were determined. Selected tests were continued for monitoring a long-term performance of the system (50 pore volumes of the sand column). The results indicated that the inoculated cells removed 42–80% of the atrazine. The infiltration rate and cell loading significantly affected the atrazine removal. In the short-term tests, the immobilized and free cells provided similar atrazine removal; however, leaching of the free cells was much greater than that of the immobilized cells. For the long-term performance, only the immobilized cells provided consistent atrazine removal efficiency throughout the test. Both immobilized and free cell systems exhibited a significant change in bacterial community structure during the atrazine degradation experiments. The infiltration rate was a significant factor for the change.

Kinetics of atrazine biodegradation by suspended and immobilized mixed microbial cells cultivated in continuous systems

AbstractBACKGROUND: Using a suspended or immobilized microbial community obtained through chemostat selection from agricultural soils formerly treated with triazinic herbicides, the atrazine biodegradation kinetics in continuous aerobic reaction systems was studied.RESULTS: When microbial cells were continuously cultivated on atrazine as the sole nitrogen and carbon source, atrazine removal efficiencies ηATZ near to 100% were reached, although accumulation of metabolic byproducts was detected. The fluidized‐bed biofilm reactor allowed atrazine removal rates RV, ATZ higher than that permitted by suspended cell cultures with similar removal efficiencies. In this system, the highest volumetric removal rate was obtained (RV, ATZ = 12.2 mg L−1 h−1), with herbicide removal efficiencies ηATZ near 100% and reduced accumulation of byproducts.CONCLUSIONS: With the operational conditions probed in continuous suspended‐cell culture, increasing the C:N ratio in the inflowing medium resulted in higher cell growth yields but not in better atrazine removal rates. Kinetic results showed that for similar working conditions higher RV, ATZ values and reduced amounts of degradation byproducts of recalcitrant organic compounds could be expected with multi‐stage biofilm reactors. Copyright © 2009 Society of Chemical Industry

Treatability of atrazine in a simulated DEPHANOX process

In this study a simulated DEPHANOX process was used, including anaerobic/anoxic and oxic phases. An upflow anaerobic sludge blanket reactor (UASB), an anoxic sludge blanket reactor (UANSB) and a completely stirred tank reactor (CSTR) were used, sequentially. The atrazine, chemical oxygen demand (COD) removal efficiencies, methane and nitrogen (N2) gas productions and volatile fatty acid (VFA) concentrations were monitored to assess the stability and the performance of anaerobic/anoxic and oxic reactors. The produced intermetabolites were Diaminochloroatrazine(DACT), Desethylatrazine(DEA), Deisopropylatrazine(DIA) urea, ammonia, aromatic amines, Cl− 1 and NO3-N. For maximum atrazine and COD removal efficiencies (86% and 82%, respectively) the optimum atrazine concentrations were between 30-80 mg L− 1. The methane gas percentage varied between 40 and 68% while no N2 production was observed in the anaerobic UASB reactor; 6–10 mg L− 1 of urea, 4–21 mg L− 1 of ammonia, 8–10 mg L− 1 of aromatic amine and 4–6 mg L of Cl− 1 were detected during anaerobic atrazine degradation. 25–45% N2 gas production was observed in the anoxic reactor while the methane gas production was 1–5%. In the aerobic phase COD and atrazine were removed with removal efficiencies of 98% and 99% for initial atrazine concentrations of 0.3 mg L− 1 and 2.5 mg L− 1, respectively.

Atrazine remediation in agricultural infiltrate by bioaugmented polyvinyl alcohol immobilized and free Agrobacterium radiobacter J14a

Bench-scale sand column breakthrough experiments were conducted to examine atrazine remediation in agricultural infiltrate by Agrobacterium radiobacter J14a (J14a) immobilized in phosphorylated-polyvinyl alcohol compared to free J14a cells. The effects of cell loading and infiltration rate on atrazine degradation and the loss of J14a were investigated. Four sets of experiments, i) tracers, ii) immobilized dead cells, iii) immobilized cells, and iv) free cells, were performed. The atrazine bioremediation at the cell loadings of 300, 600, and 900 mg dry cells l(-1) and the infiltration rates of 1, 3, and 6 cm d(-1) were tested for 5 column pore volumes (PV). The atrazine breakthrough results indicated that the immobilized dead cells significantly retarded atrazine transport. The atrazine removal efficiencies at the infiltration rates of 1, 3, and 6 cm d(-1) were 100%, 80-97%, and 50-70% respectively. Atrazine remediation capacity for the immobilized cells was not significantly different from the free cells. Both infiltration rate and cell loading significantly affected atrazine removal for both cell systems. The bacterial loss from the immobilized cell system was 10 to 100 times less than that from the free cell system. For long-term tests at 50 PV, the immobilized cell system provided consistent atrazine removal efficiency while the atrazine removal by the free cells declined gradually because of the cell loss.

Atrazine removal in agricultural infiltrate by bioaugmented polyvinyl alcohol immobilized and free Agrobacterium radiobacter J14a: A sand column study

Bench-scale sand column breakthrough experiments were conducted to examine atrazine removal in agricultural infiltrate by Agrobacterium radiobacter J14a (J14a) immobilized in phosphorylated-polyvinyl alcohol compared to free J14a cells. The effects of cell loading and infiltration rate on atrazine degradation and the loss of J14a were investigated. Four sets of experiments, (i) tracers, (ii) immobilized dead cells, (iii) immobilized cells, and (iv) free cells, were performed. The atrazine biodegradation at the cell loadings of 300, 600, and 900 mg dry cells L −1 and the infiltration rates of 1, 3, and 6 cm d −1 were tested for 5 column pore volumes (PV). The atrazine breakthrough results indicated that the immobilized dead cells significantly retarded atrazine transport. The atrazine removal efficiencies at the infiltration rates of 1, 3, and 6 cm d −1 were 100%, 80–97%, and 50–70%, respectively. Atrazine degradation capacity for the immobilized cells was not significantly different from the free cells. Both infiltration rate and cell loading significantly affected atrazine removal for both cell systems. The bacterial loss from the immobilized cell system was 10–100 times less than that from the free cell system. For long-term tests at 50 PV, the immobilized cell system provided consistent atrazine removal efficiency while the atrazine removal by the free cells declined gradually because of the cell loss.