Biodegradation of agricultural herbicides in sequencing batch reactors under aerobic or anaerobic conditions

Fate of pesticides in agricultural runoff treatment systems: Occurrence, impacts and technological progress

The levels of pesticides in air, water, and soil are gradually increasing due to its inappropriate management. In particular, agricultural runoff inflicts the damages on the ecosystem and human health at massive scale. Present study summarizes 70 studies in which investigations on removal or treatment of pesticides/insecticides/herbicides are reported. A bibliometric analysis was also done to understand the recent research trends through the analysis of 2218 publications. The specific objectives of this study are as follows: i) to inventorize the characteristics details of agriculture runoff and analyzing the occurrence and impacts of pesticides, ii) analyzing the role and interaction of pesticides in different environmental segments, iii) investigating the fate of pesticides in agriculture runoff treatment systems, iv) summarizing the experiences and findings of most commonly technology deployed for pesticides remediation in agriculture runoff including target pesticide(s), specifications, configuration of technological intervention. Among the reported technologies for pesticide treatment in agriculture runoff, constructed wetland was at the top followed by algal or photobioreactor. Among various advanced oxidation processes, photo Fenton method is mainly used for pesticides remediation such as triazine, methyl parathion, fenuron and diuron. Algal bioreactors are extensively used for a wide range of pesticides treatment including 2,4-Dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, alachlor, diuron, chlorpyrifos, endosulfan, and imidacloprid; especially at lower hydraulic retention time of 2-6 h. This study highlights that hybrid approaches can offers potential opportunities for effective removal of pesticides in a more viable manner.

The state-of-the-art development of photocatalysts for the degradation of persistent herbicides in wastewater

Herbicides are one of the most recurring pollutants in the aquatic system due to their widespread usage in the agriculture sector for weed control. Semiconductor-based photocatalysts have gained recognition due to their ability to degrade and mineralize pollutants into harmless by-products completely. Lately, many studies have been done to design photocatalysts with efficient separation of photogenerated charge carriers and enhanced light absorption. Photocatalyst engineering through doping with metal and non-metal elements and the formation of heterojunction are proven effective for minimizing the recombination of electron-hole pairs and enlarging the absorption in the visible light region. This review focuses on discussing and evaluating the recent progress in the types of photocatalysts and their performance in the remediation of herbicides in wastewater. The development of innovative hybrid technologies is also highlighted. The limitations and challenges of photocatalysis technology in the present literature have been identified, and future studies are recommended.

Optimizing anaerobic technology by using electrochemistry and membrane module for treating pesticide wastewater: Chemical oxygen demand components and fractions distribution, membrane fouling, effluent toxicity and economic analysis

Optimization in performance and membrane fouling of an electrochemical anaerobic membrane bioreactor (R1) for treating pesticide wastewater was investigated and compared with a conventional anaerobic membrane bioreactor (R2). The maximum COD removal efficiency of R2 was 80.1%, 80.0%, 67.4%, 61.1% with HRT of 96, 72, 48 and 24 h, which of R1 was enhanced to 84.7%, 84.3%, 82.0% and 66.3%. These results demonstrated that the optimum HRT of R1 was shortened to 48 h, which of R2 required 72 h. R1 reduced the contents of particulate and colloidal COD, and the fraction of COD converted to sludge was 5.0-8.2% lower than that of R2. The fouling rate was 0.99-1.44 kPa/d and reduced by 31.0%-38.5% compared with R2. Detoxification was enhanced by 7.8-47.7% with the assistance of bio-electrochemistry. Ultimately, ensuring similar performance, R1 achieved a 65.6% improvement in environmental benefit, a 26.3% and 38.9% reduction in unit capital and operating costs.

Mechanistic insights into 2,4-D photoelectrocatalytic removal from water with TiO2 nanotubes under dark and solar light irradiation

Removal of recalcitrant pollutants from water is a major challenge, to which the photoelectrocatalytic processes may be a solution. Applied potential plays a key role in the photocatalytic activity of the semiconductor. This paper investigated the effect of applied potential on the photoelectrocatalytic oxidation of 2,4-Dichlorophenoxyacetic acid (2,4-D) with TiO₂ nanotubular anodes under solar light irradiation. The process was investigated at constant potentials in different regions of the polarization curve: the ohmic region, the saturation region and in the region of the Schottky barrier breakdown. PEC tests were performed in aqueous solutions of 2,4-D, and in the presence of methanol or formic acid, as scavengers of OH^• radicals and holes. Results showed the main mechanism is oxidation by OH^• radicals from water oxidation, while runs with hole scavenger revealed a second mechanism of direct oxidation by holes photogenerated at the electrode surface, with high removal rates due to current doubling effect.

Assessment of a fast method to predict the biochemical methane potential based on biodegradable COD obtained by fractionation respirometric tests

The biochemical methane potential test (BMP) is the most common analytical technique to predict the performance of anaerobic digesters. However, this assay is time-consuming (from 20 to over than 100 days) and consequently impractical when it is necessary to obtain a quick result. Several methods are available for faster BMP prediction but, unfortunately, there is still a lack of a clear alternative. Current aerobic tests underestimate the BMP of substrates since they only detect the easily biodegradable COD. In this context, the potential of COD fractionation respirometric assays, which allow the determination of the particulate slowly biodegradable fraction, was evaluated here as an alternative to early predict the BMP of substrates. Seven different origin waste streams were tested and the anaerobically biodegraded organic matter (COD_met) was compared with the different COD fractions. When considering adapted microorganisms, the appropriate operational conditions and the required biodegradation time, the differences between the COD_met, determined through BMP tests, and the biodegradable COD (COD_b) obtained by respirometry, were not significant (COD_met (57.8026 ± 21.2875) and COD_b (55.6491 ± 21.3417), t (5) = 0.189, p = 0.853). Therefore, results suggest that the BMP of a substrate might be early predicted from its COD_b in only few hours. This methodology was validated by the performance of an inter-laboratory studyconsidering four additional substrates.

Removal of ametryn and organic matter from wastewater using sequential anaerobic-aerobic batch reactor: A performance evaluation study

The present study was aimed to investigate biodegradation of 2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine (ametryn) in a laboratory-scale anaerobic sequential batch reactor (ASBR) and followed by aerobic post-treatment. Co-treatment of ametryn with starch is carried out at ambient environmental conditions. The treatment process lasted up to 150 days of operation at a constant hydraulic retention time (HRT) of 24 h and an organic loading rate (OLR) of 0.21-0.215 kg-COD/m³/d. Ametryn concentration of 4 and 6 mg/L was removed completely within 48-50 days of operation with chemical oxygen demand (COD) removal efficiencies >85% at optimum reactor conditions. Ametryn acted as a nutrient/carbon source rather causing toxicity and contributed to methane gas production and sludge granulation in the anaerobic reactor. Biotransformation products of ametryn to cyanuric acid, biuret, and their further conversion to ammonia nitrogen and CO₂ are monitored during the study. Adsorption of ametryn on to reactor sludge was negligible, sludge granulation, presence of ANAMMOX bacteria, and low MLVSS/MLSS ratio between 0.68 and 0.72. The study revealed that ametryn removal occurred mainly due to biodegradation and co-metabolism processes. Aerobic post-treatment of anaerobic effluent was able to remove COD up to 95%. The results of this study exhibit that anaerobic-aerobic treatment is feasible due to easy operation, economic, and highly efficient.

Environmental and health impacts of industrial wastewater effluents in Pakistan: a review

In developing countries, one of the most severe modern-day dilemmas is the management of industrial wastewater. In these countries, industrial wastewater effluents are directly discharged into the natural drain, a sewer system, an internal septic tank or a nearby field. Some of these industrial wastewater effluents are inadequately treated or untreated before being discharged. In recent years, in developing countries, urbanization and industrial activities have led to environmental deterioration. This paper was designed to review the health and environmental impacts of inadequately treated or untreated industrial wastewater effluents in Pakistan. The quality of industrial wastewater effluents is responsible for the degradation of the receiving water bodies. This is due to the reason that inadequately treated or untreated industrial wastewater effluents may cause eutrophication in the receiving water bodies and also form a favorable condition for toxin-producing waterborne pathogens. In order to comply with the wastewater guidelines and legislations, there is a need for proper treatment before discharge. In order to minimize the risk to the environment and public health, there is a need for proper treatment processes for industrial wastewater effluents. To achieve unpolluted discharge of industrial wastewater into the receiving water bodies, regular monitoring, proper and suitable treatment, careful planning and appropriate legislation are recommended.

The Toxic Effect of Herbicidal Ionic Liquids on Biogas-Producing Microbial Community

The aim of the study was to evaluate the effect of herbicidal ionic liquids on the population changes of microorganisms used in a batch anaerobic digester. The influence of the following ionic liquids: benzalkonium (2,4-dichlorophenoxy)acetate (BA)(2,4-D), benzalkonium (4-chloro-2-methylphenoxy)acetate (BA)(MCPA), didecyldimethylammonium (2,4-dichlorophenoxy)acetate (DDA)(2,4-D), didecyldimethylammonium (4-chloro-2-methylphenoxy)acetate (DDA)(MCPA), as well as reference herbicides (4-chloro-2-methylphenoxy)acetic acid (MCPA) and (2,4-dichlorophenoxy)acetic acid (2,4-D) in the form of sodium salts on biogas production efficiency was investigated. The effective concentration (EC50) values were determined for all tested compounds. (MCPA)^- was the most toxic, with an EC50 value of 38.6⁻41.2 mg/L. The EC50 for 2,4-D was 55.7⁻59.8 mg/L. The addition of the test substances resulted in changes of the population structure of the microbiota which formed the fermentation pulp. The research was based on 16S rDNA analysis with the use of the Next Generation Sequencing method and the MiSeq platform (Illumina, San Diego, CA, USA). There was a significant decrease in bacteria belonging to Firmicutes and Archaea belonging to Euryarchaeota. A significant decrease of the biodiversity of the methane fermentation microbiota was also established, which was expressed by the decrease of the operational taxonomic units (OTUs) and the value of Shannon's entropy. In order to determine the functional potential of bacterial metapopulations based on the 16SrDNAprofile, the PICRUSt(Phylogenetic Investigation of Communities by Reconstruction of Unobserved States)tool was used, which allowed to determine the gene potency of microorganisms and their ability to biodegrade the herbicides. In the framework of the conducted analysis, no key genes related to the biodegradation of MCPA or 2,4-D were found, and the observed decrease of their content in the supernatant liquid was caused by their sorption on bacterial biomass.

Anaerobic degradation of 2,4-dichlorophenoxyacetic acid by Thauera sp. DKT

Thauera sp. strain DKT isolated from sediment utilized 2,4-dichlorophenoxyacetic acid (2,4D) and its relative compounds as sole carbon and energy sources under anaerobic conditions and used nitrate as an electron acceptor. The determination of 2,4D utilization at different concentrations showed that the utilization curve fitted well with the Edward model with the maximum degradation rate as 0.017 ± 0.002 mM/day. The supplementation of cosubstrates (glucose, acetate, sucrose, humate and succinate) increased the degradation rates of all tested chemical substrates in both liquid and sediment slurry media. Thauera sp. strain DKT transformed 2,4D to 2,4-dichlorophenol (2,4DCP) through reductive side-chain removal then dechlorinated 2,4DCP to 2-chlorophenol (2CP), 4-chlorophenol (4CP) and phenol before complete degradation. The relative degradation rates by the isolate in liquid media were: phenol > 2,4DCP > 2CP > 4CP > 2,4D ≈ 3CP. DKT augmentation in sediment slurry enhanced the degradation rates of 2,4D and chlorophenols. The anaerobic degradation rates in the slurry were significantly slower compared to the rates in liquid media.

Promoting degradation of 2,4-dichlorophenoxyacetic acid with fermentative effluents from hydrogen-producing reactor

This research aims to identifying the potential effect of using a hydrogen-producing reactor's effluent as an enrichment amendment for enhancing the degradation rates of 2,4-dichlorophenoxyacetic acid (2,4-D) during the bioremediation of contaminated paddy soils. The results showed that addition of the effluents to 2,4-D- degrading enrichment culture enhanced (up to 1.3-fold) the degradation rate constant of 2,4-D. The enhancement effect most probably resulted from the co-metabolic degradation of 2,4-D facilitated by volatile fatty acids (e.g., acetate, propionate, and butyrate) in the effluents which served as the beneficial substrates. Results from DNA sequencing analysis showed that the effluent additions shifted the bacterial community composition in the enrichment culture. Dechloromonas and Clostridium were two dominant bacterial genera involved in 2,4-D degradation. The findings will make a substantial contribution to remediation of soils contaminated with 2,4-D.

Biodegradation of wastewater in alternating aerobic-anoxic lab scale pilot plant by Alcaligenes sp. S3 isolated from agricultural field

The isolated microbial Alcaligenes sp. S₃ from the agricultural field was used for the biodegradation of synthetic wastewater containing atrazine. This study was conducted in an alternating aerobic-anoxic lab scale pilot plant. The performance of continuously operated pilot plant was evaluated in three different phases with varying atrazine concentration. The best performance of plant was observed in phase-II. The atrazine (200 mg/L) having COD value 1356 mg/L was used with varying flow rate and 90.56% COD removal was obtained at a flow rate of 300 mL/h on 122th day of operation. The effect of process parameter like pH and DO on the performance of the reactor was studied. The GC-MS analysis was investigated, and urea was found the intermediate/metabolites of atrazine biodegradation. The kinetic parameters such as half saturation rate constant (Ks) 106.80 mg/L; maximum specific growth rate (μ_max) 0.208 per day and inhibition constant (Ki) 374.91 mg/L were evaluated by Andrew-Haldane model.

Modelling aerobic biodegradation of atrazine and 2,4-dichlorophenoxy acetic acid by mixed-cultures

The aim of this work was to study and to model the biodegradation of atrazine and 2,4-dichlorophenoxy acetic acid by aerobic mixed cultures. Slow removal rates were observed when biodegrading atrazine, in spite of the initial concentrations. However, high removal rates were obtained when biodegrading 2,4-D, removing up to 100mg/L in about 2months. Regarding the 2,4-D it must be highlighted that a lag phase appears, being its length proportional to the initial 2,4-D concentration. The biodegradation trends were fitted to a Monod based model and the value of the main parameters determined. In the case of atrazine they were µ_max: 0.011 1/d and Y: 0.53g/g and in the case of 2,4-D µ_max: 0.071 1/d and Y: 0.44g/g, indicating the higher persistence of atrazine. Once finished the experiments the microbial population was characterized being the major genus Pseudomonas when treating atrazine and Rhodococcus when treating 2,4-D.

Enhanced anaerobic degradability of highly polluted pesticides-bearing wastewater under thermophilic conditions

This work presents a sustainable and cost-competitive solution for hardly biodegradable pesticides-bearing wastewater treatment in an anaerobic expanded granular sludge bed (EGSB) reactor at mesophilic (35°C) and thermophilic (55°C). The reactor was operated in continuous mode during 160days, achieving an average COD removal of 33 and 44% under mesophilic and thermophilic conditions, respectively. The increase of temperature improved the biomass activity and the production of methane by 35%. Around 96% of pesticides identified in raw wastewater were not detected in both mesophilic and thermophilic effluents. A dramatic selection of the microbial population in anaerobic granules was caused by the presence of pesticides, which also changed significantly when the temperature was increased. Pesticides caused a significant inhibition on methanogenesis, especially over acetoclastic methanogens. Aerobic biodegradability tests of the resulting anaerobic effluents revealed that aerobic post-treatment is also a feasible and effective option, yielding more than 60% COD reduction.

Assessment of pesticides removal using two-stage Integrated Aerobic Treatment Plant (IATP) by Bacillus sp. isolated from agricultural field

The biodegradation of synthetic wastewater containing Atrazine, Malathion and Parathion was studied in two stage Integrated Aerobic Treatment Plant using Bacillus sp. (consortia) isolated from agricultural field. The influent stream containing these pesticides with initial COD of 1232mg/L were fed to first reactor and treated effluent of first reactor was fed to second reactor. The maximum removal of pesticides in IATP was found to be greater than 90%. The various process parameters such as pH, DO, Redox potential and BOD₅/COD were monitored during the treatment. The degradation of pesticides and its metabolites in the treated effluent were confirmed by GC-MS. Kinetic parameters such as first order rate constant (K_obs), cell yield (Y_X/C) and decay coefficients (K_dp) were evaluated and found to be 0.00425 per hr, 0.696mg of COD/mg MLSS and 0.0010 per hr respectively. This integrated process was found more effective than physico-chemical treatment of pesticides.

Rapid degradation of 2,4-dichlorophenoxyacetic acid facilitated by acetate under methanogenic condition

Acetate can be used as an electron donor to stimulate 2,4-dichlorophenoxyacetic acid (2,4-D), which has not been determined under methanogenic condition. This study applied high-throughput sequencing and methanogenic inhibition approaches to investigate the 2,4-D degradation process using the enrichments obtained from paddy soil. Acetate addition significantly promoted 2,4-D degradation, which was 5-fold higher than in the acetate-unsupplemented enrichments in terms of the 2,4-D degradation rate constant. Dechloromonas and Pseudomonas were the dominant 2,4-D degraders. Methanogenic inhibition experiments indicated that the 2,4-D degradation was independent of methanogenesis. It was proposed that the accelerated 2,4-D degradation in the acetate-supplemented enrichment involved an unusual interaction, where members of the acetate oxidizers primarily oxidized acetate and produced H₂. H₂ was utilized by the 2,4-D degraders to degrade 2,4-D, but also partially consumed by the hydrogenotrophic methanogens to produce methane. The findings presented here provide a new strategy for the remediation of 2,4-D-polluted soils.

Effect of W doping level on TiO2 on the photocatalytic degradation of Diuron

In the present study, three compositions of W-doped titania nano-photocatalyst are synthesized via the sol-gel method. The powders obtained were characterized by X-ray diffraction, Raman spectroscopy and UV-visible diffuse reflectance spectroscopy. The photocatalytic performances of the different photocatalysts are tested with respect to the degradation of Diuron in water solutions under simulated solar light and visible light irradiation. The W_0.03Ti_0.97O₂ catalyst exhibits better photoactivity than the pure TiO₂ even under simulated solar light and visible light. This improvement in activity was attributed to photoelectron/hole separation efficiency.

Evaluation of a sequencing batch reactor sewage treatment rig for investigating the fate of radioactively labelled pharmaceuticals: Case study of propranolol

Pharmaceuticals are frequently detected in the aquatic environment, and have potentially damaging effects. Effluents from sewage treatment plants (STPs) are major sources of these substances. The use of sequencing batch reactor (SBR) STPs, involving cycling between aerobic and anoxic conditions to promote nitrification and denitrification, is increasing but these have yet to be understood in terms of removal of pharmaceutical residues. This study reports on the development of a laboratory rig to simulate a SBR. The rig was used to investigate the fate of radiolabelled propranolol. This is a commonly prescribed beta blocker, but with unresolved fate in STPs. The SBR rig (4.5 L) was operated on an 8 h batch cycle with settled sewage. Effective treatment was demonstrated, with clearly distinct treatment phases and evidence of nitrogen removal. Radiolabelled (14)C-propranolol was dosed into both single (closed) and continuous (flow-through) simulations over 13 SBR cycles. Radioactivity in CO2 off-gas, biomass and liquid was monitored, along with the characteristics of the sewage. This allowed apparent rate constants and coefficients for biodegradation and solid:water partitioning to be determined. Extrapolation from off-gas radioactivity measurements in the single dose 4-d study suggested that propranolol fell outside the definitions of being readily biodegradable (DegT50 = 9.1 d; 60% biodegradation at 12.0 d). During continuous dosing, 63-72% of propranolol was removed in the rig, but less than 4% of dose recovered as (14)CO2, suggesting that biodegradation was a minor process (Kbiol(M) L kg d(-1) = 22-49) and that adsorption onto solids dominated, giving rise to accumulations within biomass during the 17 d solid retention time in the SBR. Estimations of adsorption isotherm coefficients were different depending on which of three generally accepted denominators representing sorption sites was used (mixed liquor suspended solids, reactor COD or mass of waste activated sludge). With further development and evaluation, the rig developed for simulating SBR processes has potential to be used for informing better environmental risk assessments for those pharmaceuticals showing ambiguous results in field fate studies.

Bio-Augmentation of Cupriavidus sp. CY-1 into 2,4-D Contaminated Soil: Microbial Community Analysis by Culture Dependent and Independent Techniques

In the present study, a 2,4-dichlorophenoxyacetic acid (2,4-D) degrading bacterial strain CY-1 was isolated from the forest soil. Based on physiological, biochemical and 16S rRNA gene sequence analysis it was identified as Cupriavidus sp. CY-1. Further 2,4-D degradation experiments at different concentrations (200 to 800 mg l^-1) were carried out using CY-1. Effect of NaCl and KNO₃ on 2,4-D degradation was also evaluated. Degradation of 2,4-D and the metabolites produced during degradation process were analyzed using high pressure liquid chromatography (HPLC) and GC-MS respectively. The amount of chloride ions produced during the 2,4-D degradation were analyzed by Ion chromatography (IC) and it is stoichiometric with 2,4-D dechlorination. Furthermore two different types of soils collected from two different sources were used for 2,4-D degradation studies. The isolated strain CY-1 was bio-augmented into 2,4-D contaminated soils to analyze its degradation ability. Culture independent methods like denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP), and culture dependent methods like colony forming units (CFU) and most probable number (MPN) were used to analyze the survivability of strain CY-1 in contaminated soil. Results of T-RFLP were coincident with the DGGE analysis. From the DGGE, T-RFLP, MPN and HPLC results it was concluded that strain CY-1 effectively degraded 2,4-D without disturbing the ecosystem of soil indigenous microorganisms.

Microbial degradation of herbicides

Herbicides remain the most effective, efficient and economical way to control weeds; and its market continues to grow even with the plethora of generic products. With the development of herbicide-tolerant crops, use of herbicides is increasing around the world that has resulted in severe contamination of the environment. The strategies are now being developed to clean these substances in an economical and eco-friendly manner. In this review, an attempt has been made to pool all the available literature on the biodegradation of key herbicides, clodinafop propargyl, 2,4-dichlorophenoxyacetic acid, atrazine, metolachlor, diuron, glyphosate, imazapyr, pendimethalin and paraquat under the following objectives: (1) to highlight the general characteristic and mode of action, (2) to enlist toxicity in animals, (3) to pool microorganisms capable of degrading herbicides, (4) to discuss the assessment of herbicides degradation by efficient microbes, (5) to highlight biodegradation pathways, (6) to discuss the molecular basis of degradation, (7) to enlist the products of herbicides under degradation process, (8) to highlight the factors effecting biodegradation of herbicides and (9) to discuss the future aspects of herbicides degradation. This review may be useful in developing safer and economic microbiological methods for cleanup of soil and water contaminated with such compounds.

Strategies to evaluate biodegradability: application to chlorinated herbicides

The biodegradability of nitrochlorinated (diuron and atrazine) and chlorophenoxy herbicides (2,4-D and MCPA) has been studied through several bioassays using different testing times and biomass/substrate ratios. A fast biodegradability test using unacclimated activated sludge yielded no biodegradation of the herbicides in 24 h. The inherent biodegradability test gave degradation percentages of around 20-30% for the nitrochlorinated herbicides and almost complete removal of the chlorophenoxy compounds. Long-term biodegradability assays were performed using sequencing batch reactor (SBR) and sequencing batch membrane bioreactor (SB-MBR). Fixed concentrations of each herbicide below the corresponding EC50 value for activated sludge were used (30 mg L(-1) for diuron and atrazine and 50 mg L(-1) for 2,4-D and MCPA). No signs of herbicide degradation appeared before 35 days in the case of diuron and atrazine and 21 days for 2,4-D, whereas MCPA was partially degraded since the early stages. Around 25-36% degradation of the nitrochlorinated herbicides and 53-77% of the chlorophenoxy ones was achieved after 180 and 135 days, respectively, in SBR, whereas complete disappearance of 2,4-D was reached after 80 days in SB-MBR.

Removal of trace organic micropollutants by drinking water biological filters

The long-term removal of 34 trace organic micropollutants (<1 μg L(-1)) was evaluated and modeled in drinking water biological filters with sand media from a full-scale plant. The micropollutants included pesticides, pharmaceuticals, and personal care products, some of which are endocrine disrupting chemicals, and represent a wide range of uses, chemical structures, adsorbabilities, and biodegradabilities. Micropollutant removal ranged from no measurable removal (<15%) for 13 compounds to removal below the detection limit and followed one of four trends over the one year study period: steady state removal throughout, increasing removal to steady state (acclimation), decreasing removal, or no removal (recalcitrant). Removals for all 19 nonrecalcitrant compounds followed first-order kinetics when at steady state with increased removal at longer empty bed contact times (EBCT). Rate constants were calculated, 0.02-0.37 min(-1), and used in a pseudo-first-order rate model with the EBCT to predict removals in laboratory biofilters at a different EBCT and influent conditions. Drinking water biofiltration has the potential to be an effective process for the control of many trace organic contaminants and a pseudo-first-order model can serve as an appropriate method for approximating performance.

Toxicity removal efficiency of decentralised sequencing batch reactor and ultra-filtration membrane bioreactors

As a consequence of the Water Framework Directive and Marine Strategy Framework Directive, there is now more focus on discharges from wastewater treatment plants both to transitional and marine-coastal waters. The constraint to encourage sustainable water policy to prevent water deterioration and reduce or stop discharges has entailed new requirements for existing wastewater treatment plants in the form of advanced wastewater treatment technologies as further suggested by the Integrated Pollution and Prevention Control Bureau. A whole toolbox of physico-chemical and ecotoxicological parameters to investigate commercial and mixed domestic and industrial discharges was considered to check the efficiency of an Activated-Sludge Sequencing Batch Reactor (AS-SBR) and two Ultra-Filtration Membrane Biological Reactors (UF-MBRs) on a small scale decentralised basis. All discharges were conveyed into Venice lagoon (Italy), one of the widest impacted Mediterranean transitional environment. The UF-MBRs were able to provide good quality effluents potentially suitable for non-potable reuse, as well as reducing specific inorganic micro-pollutants concentration (e.g. metals). Conversely, the AS-SBR showed unpredictable and discontinuous removal abilities.

Reduction of oxidative stress by bioaugmented strain Pseudomonas sp. HF-1 and selection of potential biomarkers in sequencing batch reactor treating tobacco wastewater

Oxidative stress induced by toxic pollutants is generally responsible for the poor performance of many sequencing batch reactors (SBRs) treating organic wastewater. In this study, the oxidative stress in two SBR systems that dealt with tobacco wastewater was monitored by measuring four popular biomarkers (superoxide dismutase, SOD; catalase, CAT; glutathione, GSH; and malondialdehyde, MDA). In the non-BA (non-bio-augmented) system, more intense oxidative stress was induced by a higher concentration of nicotine in tobacco wastewater, and excessive oxidative stress was induced by 250 mg/l of nicotine at the final stage. However, when a nicotine-degrading bacterial strain Pseudomonas sp. HF-1 was added to the BA (bio-augmented) system, the oxidative stress was significantly reduced compared to the non-BA system (p < 0.01).These results suggested that the oxidative stress was mainly induced by nicotine in the SBR treatment of tobacco wastewater, and that bioaugmentation with strain HF-1 would be a potential strategy to reduce the oxidative stress and thereby improve the performance in SBRs. Additionally, the positive correlation between the nicotine content and CAT, GSH and MDA activity in both systems implied that these parameters can be used as biomarkers for reflecting the performance of SBR treatment of tobacco wastewater, and in monitoring nicotine environmental pollution.

The effect of upper mesophilic temperature and feed-to-seed ratio on batch anaerobic digestion systems

This study investigated the effect of upper mesophilic temperature and feed-to-seed (F/S) ratio on anaerobic digestion using four 3.5 L batch-scale reactors. Initially, eight F/S ratios, ranging from 10/90 to 90/10, were explored at 37 degrees C, using a mixture of primary and secondary municipal sludge as feed. It was observed that the systems with low F/S ratios (40/60 and below) showed a stable performance while those with high ratios (50/50 and above) experienced the effect of organic overloading indicated by reduced removal of volatile solids (VS) in the feed, a drop in pH, volatile fatty acid (VFA) accumulation during the first 10 days of operation, and total gas production markedly lower than the corresponding theoretical values. Subsequently, the effect of temperature, in the 37 to 49 degrees C range, was studied at an F/S ratio of 20/80. Results revealed that an increase in temperature between 37 and 43 degrees C had a rather minimal effect on the process, with the exception of a moderate increase in total gas production. A further rise in the temperature in the 45 to 49 degrees C range however appeared to trigger an adverse effect evidenced by enhanced percent VSS reduction (possibly the result of cell lysis), VFA accumulation and an increase in the non-VFA total organic carbon (TOC) content. Therefore, it can be concluded that an operating temperature in the 37 to 43 degrees C range resulted in a stable and satisfactory reactor performance.

Bioaugmentation with the nicotine-degrading bacterium Pseudomonas sp. HF-1 in a sequencing batch reactor treating tobacco wastewater: degradation study and analysis of its mechanisms

The highly effective nicotine-degrading bacterium Pseudomonas sp. HF-1 was augmented in an SBR system that is used to treat tobacco wastewater. Compared to the non-bioaugmented (non-BA) system, the bioaugmented (BA) system exhibited considerably stronger pollution disposal abilities, with 100% nicotine degradation and more than 84% chemical oxygen demand (COD) removal within 12h. Nicotine degradation had a significant effect on COD removal in SBRs (r=0.928, p<0.01). The mechanisms of bioaugmentation were systematically investigated using a combination of polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) and a toxicity assay (protein carbonyl (PC) and DNA-protein crosslinking (DPC)). DGGE fingerprint profiles showed that the number of bands and the Shannon-Wiener index decreased at a nicotine load of 250mg/L compared to a 40-130mg/L nicotine load in the non-BA system. However, a stepwise increase in the Shannon-Wiener index was found during all periods in the BA system. A comparison of sequences excised from DGGE gels demonstrated significant differences in the dominant microbial species between the two SBRs. This result suggested that bioaugmentation of strain HF-1 could select cooperators for treating complicated tobacco wastewater. The PC content and the DPC coefficient increased significantly at levels higher than 80mg/L in the non-BA system; nevertheless, no increase was observed in the BA system during the stepwise nicotine load. This indicated that bioaugmentation of strain HF-1 resulted in the maintenance of high treatment activity by minimizing the nicotine toxicity for other microbes in the BA system. In conclusion, the rapid nicotine degradation of strain HF-1 performed a vital function in SBR by influencing the microbial community structure, dynamics and activity of the activated sludge system.

Diuron biodegradation in activated sludge batch reactors under aerobic and anoxic conditions

Diuron biodegradation was studied in activated sludge reactors and the impacts of aerobic and anoxic conditions, presence of supplemental substrate and biomass acclimatization on its removal were investigated. Diuron and three known metabolites, namely DCPMU (1-(3,4-dichlorophenyl)-3-methylurea), DCPU (1-3,4-dichlorophenylurea) and DCA (3,4-dichloroaniline), were extracted by solid-phase extraction (dissolved phase) or sonication (particulate phase) and determined using High Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD). During the experiments only a minor part of these compounds was associated with the suspended solids. Under aerobic conditions, almost 60% of Diuron was biodegraded, while its major metabolite was DCA. The existence of anoxic conditions increased Diuron biodegradation to more than 95%, while the major metabolite was DCPU. Mass balance calculation showed that a significant fraction of Diuron is mineralized or biotransformed to other unknown metabolites. The presence of low concentrations of supplemental substrate did not affect Diuron biodegradation, whereas the acclimatization of biomass slightly accelerated its elimination under anoxic conditions. Calculation of half-lives showed that under aerobic conditions DCPMU, DCPU and DCA are biodegraded much faster than the parent compound. In the future, the sequential use of anoxic and aerobic conditions could provide sufficient removal of Diuron and its metabolites from runoff waters.