Automated online coupling of robot-assisted single drop microextraction and liquid chromatography.

A high-throughput and innovative setup has been developed to automate the online integration of single drop microextraction (SDME), liquid chromatography (LC) and high-resolution mass spectrometry (QqToF). SDME and LC were online hyphenated for the first time. SDME was carried out by a lab-made cartesian robot actuating a 100 µL syringe, equipped with a three-way solenoid microvalve that allowed the online transference of the enriched extract to the chromatographic system, through a six-port switching valve. The complete method, including the synchronized robot action, valves, and the analytical instruments, was controlled by an Arduino Mega board. The merits of the proposed setup were demonstrated by the triazines determination in coconut water samples. The most relevant extraction parameters, such as drop size, exposure time, stirring effect, salt addition and pH were systematically investigated. Under optimized conditions (60 µL drop volume and 10 min extraction time), the LC-UV enrichment factors (EF) and the extraction recoveries (ER) ranged between 15.2-18.4 and 11.4-13.8%, respectively. Using the SDME-LC-MS setup, the linear range, detection limit (S/N = 3) and precision (RSD, n = 6 at 0.25 µg L-1 level of concentration) were 0.25-25 µg L-1, 0.10 µg L-1 and 16.8% for simazine; 0.25-25 µg L-1, 0.05 µg L-1 and 14.7% for atrazine; and 0.25-25 µg L-1, 0.05 µg L-1 and 18.5% for propazine, respectively. Although none of the analytes were detected in the evaluated commercial samples, the results indicate that the proposed online SDME-LC setup is a competitive analytical strategy for the determination of target organic compounds in complex matrices.

Removal of organic matter of electrodialysis reversal brine from a petroleum refinery wastewater reclamation plant by UV and UV/H202 process.

Direct (UV) and hydrogen peroxide-assisted (UV/H2O2) photolysis were investigated in bench-scale for removing the organic compounds present in the electrodialysis reversal (EDR) brine from a refinery wastewater reclamation plant. In the UV/H2O2 experiments, a COD:H2O2 molar ratios of 1:1, 1:2 and 1:3 were tested by recirculating the brine in the UV reactor for 120 min. Results showed a significant reduction in UVA254, whereas no reduction was observed for chemical oxygen demand (COD), in the UV process, suggesting great cleavage but limited mineralization of the organic matter. UV/H2O2 with C:H2O2 ratio of 1:3 exhibited high efficiency in removing the organic matter (COD removal of 92% with an electrical energy per removal order (EEO) value of 22 kW h m-3). Although the EDR brine has high salinity, no strong scavenging effect of •OH was found in the water matrix due to the high concentration of anions, especially chloride and bicarbonate. Finally, UV/H2O2 with C:H2O2 ratio of 1:3 and residence time of 120 min is an efficient alternative for organic matter removal of EDR brine from refinery wastewater reclamation plant showing total capital cost (CapEx) estimated at US$ 369,653.00 and total operational cost (OpEx), at US$ 1.772 per cubic meter of effluent.

Potential use of membrane bioreactor to treat petroleum refinery effluent: comprehension of dynamic of organic matter removal, fouling characteristics and membrane lifetime.

This study aims to evaluate membrane bioreactor (MBR) performance in a pilot scale to treat petroleum refinery effluent, and has been primarily focused on (1) investigation of dynamics of organic matter removal; (2) characterization of membrane fouling under real hazardous events; (3) evaluation of the effect of fouling on membrane lifetime; and (4) estimate the membrane lifetime. The results have shown that the MBR was able to effectively reduce COD, NH3-N, turbidity, color, phenol and toxicity, and bring them to the levels required to meet disposal and non-potable water reuse standards. The FTIR results showed that organic matter was removed by biological oxidation and/or retained by adsorption in the biological sludge, or retention in the UF membrane, and that SMP was produced during the treatment. In terms of membrane permeability, the results showed that soluble fraction of mixed liquor contributed significantly to membrane fouling. And finally, considering the concept of lifetime based on permeability decline, a membrane lifetime of 7 years is expected.

Removal of recalcitrant organic matter content in wastewater by means of AOPs aiming industrial water reuse.

This paper comes out from the need to provide an improvement in the current oil refinery wastewater treatment plant (WWTP) aiming to generate water for reuse. The wastewater was pretreated and collected in the WWTP after the biological treatment unit (bio-disks) followed by sand filtration. Ozonation (ozone concentration from 3.0-60 mgO3 L-1), UV (power lamp from 15 to 95 W), H2O2 (carbon:H2O2 molar ratio of 1:1, 1:2, and 1:4), and two advanced oxidation processes (UV/O3 and UV/H2O2) were investigated aiming to reduce the wastewater organic matter and generate water with suitable characteristics for the reverse osmosis operation and subsequent industrial reuse. Even after the biological and filtration treatments, the oil refinery wastewater still presented an appreciable amount of recalcitrant organic matter (TOC of 12-19 mgC L-1) and silt density index (SDI) higher than 4, which is considered high for subsequent reverse osmosis due to membrane fouling risks. Experiments using non combined processes (O3, H2O2, and UV only) showed a low degree of mineralization after 60 min of reaction, although the pretreatment with ozone had promoted the oxidation of aromatic compounds originally found in the real matrix, which suggests the formation of recalcitrant compounds. When the combined processes were applied, a considerable increase in the TOC removal was observed (max of 95 % for UV/O3 process, 55 W, 60 mgO3 L-1), likely due the presence of higher amounts of reactive species, specially hydroxyl radicals, confirming the important role of these species on the photochemical degradation of the wastewater compounds. A zero-order kinetic model was fitted to the experimental data and the rate constant values (k, mgC L-1 h-1) ranged from 4.8 < k UV/O3 < 11 ([O3]0 = 30-60 mg L-1), and 8.6 < k UV/H2O2 < 11 (C:H2O2 from 1:1 to 1:4). The minimum and maximum electrical energy per order (E EO) required for 60 min of treatment were calculated as 5.4 and 81 Wh L-1, respectively, for UV/O3 (15 W, 60 mgO3 L-1) and UV/H2O2 (95 W, 1C:1H2O2). Good results in terms of water conditioning for reverse osmosis operation were obtained using UV/H2O2 process with initial molar ratio of 1 C:2 H2O2 (UV lamp 55 W) and 1 C:4 H2O2 (UV lamp 95 W), and total organic carbon (TOC) removals of 62 % (SDI15 = 1.8) and 74 % (SDI15 = 2.0) were achieved, respectively, after 60 min. The treated wastewater followed to the reverse osmosis system, which operated with an adequate flux of permeate, was very efficient to remove salt and generate a permeate water with the required quality for industrial reuse.

Dilution standard addition calibration: A practical calibration strategy for multiresidue organic compounds determination.

Among calibration approaches for organic compounds determination in complex matrices, external calibration, based in solutions of the analytes in solvent or in blank matrix extracts, is the most applied approach. Although matrix matched calibration (MMC) can compensates the matrix effects, it does not compensate low recovery results. In this way, standard addition (SA) and procedural standard calibration (PSC) are usual alternatives, despite they generate more sample and/or matrix blanks consumption need, extra sample preparations and higher time and costs. Thus, the goal of this work was to establish a fast and efficient calibration approach, the diluted standard addition calibration (DSAC), based on successive dilutions of a spiked blank sample. In order to evaluate the proposed approach, solvent calibration (SC), MMC, PSC and DSAC were applied to evaluate recovery results of grape blank samples spiked with 66 pesticides. Samples were extracted with the acetate QuEChERS method and the compounds determined by ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Results indicated that low recovery results for some pesticides were compensated by both PSC and DSAC approaches. Considering recoveries from 70 to 120% with RSD <20% as adequate, DSAC presented 83%, 98% and 100% of compounds meeting this criteria for the spiking levels 10, 50 and 100µgkg(-1), respectively. PSC presented same results (83%, 98% and 100%), better than those obtained by MMC (79%, 95% and 97%) and by SC (62%, 70% and 79%). The DSAC strategy showed to be suitable for calibration of multiresidue determination methods, producing adequate results in terms of trueness and is easier and faster to perform than other approaches.

Treatment of petroleum refinery wastewater containing heavily polluting substances in an aerobic submerged fixed-bed reactor.

Petroleum refineries produce large amount of wastewaters, which often contain a wide range of different compounds. Some of these constituents may be recalcitrant and therefore difficult to be treated biologically. This study evaluated the capability of an aerobic submerged fixed-bed reactor (ASFBR) containing a corrugated PVC support material for biofilm attachment to treat a complex and high-strength organic wastewater coming from a petroleum refinery. The reactor operation was divided into five experimental runs which lasted more than 250 days. During the reactor operation, the applied volumetric organic load was varied within the range of 0.5-2.4 kgCOD.m(-3).d(-1). Despite the inherent fluctuations on the characteristics of the complex wastewater and the slight decrease in the reactor performance when the influent organic load was increased, the ASFBR showed good stability and allowed to reach chemical oxygen demand, dissolved organic carbon and total suspended solids removals up to 91%, 90% and 92%, respectively. Appreciable ammonium removal was obtained (around 90%). Some challenging aspects of reactor operation such as biofilm quantification and important biofilm constituents (e.g. polysaccharides (PS) and proteins (PT)) were also addressed in this work. Average PS/volatile attached solids (VAS) and PT/VAS ratios were around 6% and 50%, respectively. The support material promoted biofilm attachment without appreciable loss of solids and allowed long-term operation without clogging. Microscopic observations of the microbial community revealed great diversity of higher organisms, such as protozoa and rotifers, suggesting that toxic compounds found in the wastewater were possibly removed in the biofilm.

Color, organic matter and sulfate removal from textile effluents by anaerobic and aerobic processes.

An upflow anaerobic sludge blanket (UASB)-submerged aerated biofilter (SAB) system was evaluated to remove color and chemical oxygen demand (COD) from real textile effluent. The system was operated for 335 days in three phases (P-1, P-2, P-3) with total hydraulic retention time varying from 21 h to 14 h. The results showed that high sulfate levels (>300 mg SO4(2-)/L) impaired the dye reduction. The best color removal efficiencies of 30% and 96% for the UASB and the reactor system, respectively, were obtained in P-1; the SAB higher efficiency was associated with adsorption. The best COD removal efficiency of 71% for the reactor system was obtained in P-2. Precipitation of some material composed mostly of sulfur (98%) and some metals occurred in the UASB. However, the precipitated sulfur was again oxidized in the SAB. The system also showed an effective toxicity reduction in tests (Daphnia magna) with the treated effluent.

Characterization of a biosurfactant produced by Pseudomonas cepacia CCT6659 in the presence of industrial wastes and its application in the biodegradation of hydrophobic compounds in soil.

The bacterium Pseudomonas cepacia CCT6659 cultivated with 2% soybean waste frying oil and 2% corn steep liquor as substrates produced a biosurfactant with potential application in the bioremediation of soils. The biosurfactant was classified as an anionic biomolecule composed of 75% lipids and 25% carbohydrates. Characterization by proton nuclear magnetic resonance ((1)H and (13)C NMR) revealed the presence of carbonyl, olefinic and aliphatic groups, with typical spectra of lipids. Four sets of biodegradation experiments were carried out with soil contaminated by hydrophobic organic compounds amended with molasses in the presence of an indigenous consortium, as follows: Set 1-soil+bacterial cells; Set 2-soil+biosurfactant; Set 3-soil+bacterial cells+biosurfactant; and Set 4-soil without bacterial cells or biosurfactant (control). Significant oil biodegradation activity (83%) occurred in the first 10 days of the experiments when the biosurfactant and bacterial cells were used together (Set 3), while maximum degradation of the organic compounds (above 95%) was found in Sets 1-3 between 35 and 60 days. It is evident from the results that the biosurfactant alone and its producer species are both capable of promoting biodegradation to a large extent.

Removal of persistent organic pollutants in fish oils using short-path distillation with a working fluid.

Two fish oils, varying in origin, species and catching season, were decontaminated in a commercial scale short-path distillation equipment, aided by a working fluid (distilled ethyl esters of marine fatty acids). The processing conditions for the two oils varied by different processing temperature and pressure in the distillation column. The concentration of total cholesterol, vitamin E (alpha-tocopherol), vitamin A and vitamin D were reduced due to the decontamination process with the highest loss for the treatment with the highest temperature and lowest pressure (i.e. highest vacuum). Peroxide value (PV) and anisidine value (AV) were slightly reduced, and the content of the essential fatty acids EPA and DHA were reduced marginally. PCDD/PCDF, dl-PCB and ndl-PCB were efficiently removed with the highest efficiency for the treatment with the highest temperature (PCDD/PCDF, 76-96%; dl-PCB, 89-99%; ndl-PCB, 91-99%). For the treatment with the lowest temperature, the congeners were removed to varying degree, and there seemed to be a correlation between decontamination and the degree of chlorine substitution. Brominated flame retardants (PBDE) and chlorinated pesticides were only analysed in one of the oils (with highest process temperature). The overall decontamination efficiency was very high (PBDE, >86%, chlorinated pesticides, >89%). The short-path distillation, with working fluid, removes a broad group of persistent organic pollutants from fish oil efficiently with only minor negative effect on nutritionally important compounds.

Determination of some organic contaminants in water samples by solid-phase extraction and liquid chromatography-tandem mass spectrometry.

Independent methods for determination of organic contaminants such as pharmaceuticals and pesticides in drinking water samples, using SPE as the extraction technique and LC-MS/MS in the MRM mode with electrospray ionization, were developed and validated. Different SPE sorbents were evaluated, including lab-made fluorinated and phenyl and commercial Oasis HLB and C18, with the commercial phases being more suitable for the target compounds. Recoveries in the range of 70-120% were obtained for all target compounds, with the exception for paracetamol (acetaminophen), and precision values (inter-day and intra-day), expressed in terms of relative standard deviations (RSD), lower than 20% were obtained for all target compounds. Quantification limits were in the range of 0.006-0.208 µg L(-1) and the methods developed were successfully applied for the analysis of drinking water samples, detecting some pharmaceuticals and pesticides, but at concentration levels lower than the MRL.

Characterization of the volatile profile of Brazilian Merlot wines through comprehensive two dimensional gas chromatography time-of-flight mass spectrometric detection.

Wine aroma is an important characteristic and may be related to certain specific parameters, such as raw material and production process. The complexity of Merlot wine aroma was considered suitable for comprehensive two-dimensional gas chromatography (GC×GC), as this technique offers superior performance when compared to one-dimensional gas chromatography (1D-GC). The profile of volatile compounds of Merlot wine was, for the first time, qualitatively analyzed by HS-SPME-GC×GC with a time-of-flight mass spectrometric detector (TOFMS), resulting in 179 compounds tentatively identified by comparison of experimental GC×GC retention indices and mass spectra with literature 1D-GC data and 155 compounds tentatively identified only by mass spectra comparison. A set of GC×GC experimental retention indices was also, for the first time, presented for a specific inverse set of columns. Esters were present in higher number (94), followed by alcohols (80), ketones (29), acids (29), aldehydes (23), terpenes (23), lactones (16), furans (14), sulfur compounds (9), phenols (7), pyrroles (5), C13-norisoprenoids (3), and pyrans (2). GC×GC/TOFMS parameters were improved and optimal conditions were: a polar (polyethylene glycol)/medium polar (50% phenyl 50% dimethyl arylene siloxane) column set, oven temperature offset of 10 °C, 7s as modulation period and 1.4s of hot pulse duration. Co-elutions came up to 138 compounds in 1D and some of them were resolved in 2D. Among the co-eluted compounds, thirty-three volatiles co-eluted in both 1D and 2D and their tentative identification was possible only due to spectral deconvolution. Some compounds that might have important contribution to aroma notes were included in these superimposed peaks. Structurally organized distribution of compounds in the 2D space was observed for esters, aldehydes and ketones, alcohols, thiols, lactones, acids and also inside subgroups, as occurred with esters and alcohols. The Fischer Ratio was useful for establishing the analytes responsible for the main differences between Merlot and non-Merlot wines. Differentiation among Merlot wines and wines of other grape varieties were mainly perceived through the following components: ethyl dodecanoate, 1-hexanol, ethyl nonanoate, ethyl hexanoate, ethyl decanoate, dehydro-2-methyl-3(2H)thiophenone, 3-methyl butanoic acid, ethyl tetradecanoate, methyl octanoate, 1,4 butanediol, and 6-methyloctan-1-ol.

Rotating disk sorbent extraction for pre-concentration of chromogenic organic compounds and direct determination by solid phase spectrophotometry.

A novel and very simple microextraction approach for pre-concentration and direct solid phase spectrophotometric measurement has been developed for the determination of chromogenic analytes. The model analyte to assess this approach was the chromophore malachite green (MG). The analyte was extracted from water samples onto a small rotating disk made of Teflon containing a sorbent phase of polydimethylsiloxane (PDMS) on one of its surfaces. We refer to the extraction procedure as rotating disk sorptive extraction (RDSE). After extraction, the sorbent phase with the concentrated analyte was separated from the Teflon disk and used directly for MG determination by solid phase spectrophotometry at 624 nm, without the necessity of a desorption step. Chemical and extraction variables such as concentration of sodium sulfate, pH, disk rotational velocity, extraction time, and temperature were studied in order to establish the best conditions for extraction. Under optimum conditions, the extraction of MG was carried out in 18 min and 90 min, for sample volumes of 100mL or 1000 mL, respectively. The detection limit, based on three times the standard deviation of the blank phase (3σ(b)), was 1.4 µg L⁻¹ and the repeatability, expressed as relative standard deviation (RSD), for 20 µg L⁻¹ MG was 8.1%. This study also applied the method to real samples, obtaining quantitative recovery (mean recovery of 99.3%). The PDMS phases could be reused after desorbing the MG into methanol for 3h. Replacement of the PDMS film onto the disk is very easy and low cost.

Validation of a mutant of the pore-forming toxin sticholysin-I for the construction of proteinase-activated immunotoxins.

The use of pore-forming toxins from sea anemones (actinoporins) in the construction of immunotoxins (ITs) against tumour cells is an alternative for cancer therapy. However, the main disadvantage of actinoporin-based ITs obtained so far has been the poor cellular specificity associated with the toxin's ability to bind and exert its activity in almost any cell membrane. Our final goal is the construction of tumour proteinase-activated ITs using a cysteine mutant at the membrane binding region of sticholysin-I (StI), a cytolysin isolated from the sea anemone Stichodactyla helianthus. The mutant and the ligand moiety would be linked by proteinase-sensitive peptides through the StI cysteine residue blocking the toxin binding region and hence the IT non-specific killing activity. To accomplish this objective the first step was to obtain the mutant StI W111C, and to evaluate the impact of mutating tryptophan 111 by cysteine on the toxin pore-forming capacity. After proteolysis of the cleavage sequence, a short peptide would remain attached to the toxin. The next step was to evaluate whether this mutant is able to form pores even with a residual peptide linked to cysteine 111. In this work we demonstrated that (i) StI W111C shows pore-forming capacity in a nanomolar range, although it is 8-fold less active than the wild-type recombinant StI, corroborating the previously reported importance of residue 111 for the binding of StI to membranes, and (ii) the mutant is able to form pores even with a residual seven-residue peptide linked to cysteine 111. In addition, it was demonstrated that binding of a large molecule to cysteine 111 renders an inactive toxin that is no longer able to bind to the membrane. These results validate the mutant StI W111C for its use in the construction of tumour proteinase-activated ITs.

Degradation of a mixture of pollutants in water using the UV/H2O2 process.

The degradation reaction of a simple mixture of pollutants (dichloroacetic acid + formic acid) employing H2O2 and UVC radiation (253.7 nm) has been studied in a well-mixed reactor which operates inside a recycling system. The aim of this work is to develop a systematic methodology for treating degradation of mixtures of pollutants, starting from a rather manageable system to more complex aggregates. In this contribution, the effects of different variables such as hydrogen peroxide/pollutant mixture initial concentration ratio, pH and incident radiation at the reactor wall were studied. The results show that the best degrading conditions are: pH = 3.5 and hydrogen peroxide concentrations from 3.9 to 11.8 mM (134-400 mg/L), for initial concentrations of 1.10 and 0.39 mM for formic acid and dichoroacetic acid respectively (50 mg/L for both pollutants). The influence of the incident radiation at the reactor wall on the degradation rates of the mixture is significant. In addition to this, it has been shown that in the employed aqueous solution no stable reaction intermediates are formed. On this basis, a complete reaction scheme for the mixture is proposed that is suitable for a reaction kinetics mathematical modeling of the mixture and further studies of increasing complexity.

Influence of feed time and sulfate load on the organic and sulfate removal in an ASBR.

The removal of sulfate and organic matter was assessed in an ASBR, which treated wastewater containing 500 mg CODL(-1) (3 g CODL(-1)d(-1)) in 8h-cycles at 30 degrees C. The wastewater was enriched with sulfate at [COD/SO(4)(2-)] ratios of 1.34, 0.67 and 0.34 (8.8,4.5 and 2.2 gSO(4)(2-)L(-1)d(-1)). For each COD/[SO(4)(2-)] ratio fill times used were: 10 min (batch), 3 and 6h (fed-batch), achieving sulfate reduction of 30%, 72% and 72% (COD/[SO(4)(2-)] of 1.34); 25%, 58% and 55% (COD/[SO(4)(2-)] of 0.67) and 23%, 37% and 27% (COD/[SO(4)(2-)] of 0.34), respectively, and organic matter removal of 87%, 68% and 80% (COD/[SO(4)(2-)] of 1.34); 78%, 75% and 69% (COD/[SO(4)(2-)] of 0.67) and 85%, 84% and 83% (COD/[SO(4)(2-)] of 0.34), respectively. The results showed that fed-batch operation improved sulfate reduction, whereas organic matter removals were similar for batch and fed-batch operation. In addition, increase in sulfate loading in the fed-batch operation improved organic matter removal.

A new thermally immobilized fluorinated stationary phase for RP-HPLC.

A new fluorinated stationary phase was prepared through thermal immobilization of poly(methyl-3,3,3-trifluoropropylsiloxane) onto 5 microm Kromasil silica particles. The best conditions of immobilization time and temperature were determined through a central composite design and response surface methodologies. Physical-chemical characterization using solid-state (29)Si NMR measurements, infrared spectroscopy and elemental analysis showed that the immobilization process was effective to promote a coating of the support that corresponds to a monolayer of polymer. The stationary phase presents selectivity for positional isomers and good peak shape for basic compounds.

Enhanced extraction yields and mobile phase separations by solvent mixtures for the analysis of metabolites in Annona muricata L. leaves.

The effects of five extraction solvents and their mixtures on the yield of metabolites in crude and fractionated extracts of Annona muricata L. leaves were investigated by direct comparison. Extraction media were prepared using simplex centroid mixtures of ethanol, ethyl acetate, dichloromethane, acetone, and chloroform. The effects of the mobile phase solvent strength and the analysis wavelength on the chromatographic separation were also investigated. Solvent mixtures rather than pure solvents were found to be the most efficient extractors for the different fractions. The results indicated that the mobile phase composed of methanol/acetonitrile/water (26:27:47 v/v/v) was most suitable for the basic fraction analysis at 254 nm, whereas the mobile phase composed of methanol/acetonitrile/water (35:35:30 v/v/v) was the most adequate for the organic fraction analysis at 254 nm. The results indicated that the chromatographic profiles and number of peaks were affected by the mobile phase strength and analysis wavelength.

Microwave-assisted digestion procedures for biological samples with diluted nitric acid: identification of reaction products.

Microwave-assisted sample preparation using diluted nitric acid solutions is an alternative procedure for digesting organic samples. The efficiency of this procedure depends on the chemical properties of the samples and in this work it was evaluated by the determination of crude protein amount, fat and original carbon. Soybeans grains, bovine blood, bovine muscle and bovine viscera were digested in a cavity-microwave oven using oxidant mixtures in different acid concentrations. The digestion efficiency was evaluated based on the determination of residual carbon content and element recoveries using inductively coupled plasma optical emission spectrometry (ICP OES). In order to determine the main residual organic compounds, the digests were characterized by nuclear magnetic resonance ((1)H NMR). Subsequently, studies concerning separation of nitrobenzoic acid isomers were performed by ion pair reversed phase liquid chromatography using a C18 stationary phase, water:acetonitrile:methanol (75:20:5, v/v/v)+0.05% (v/v) TFA as mobile phase and ultraviolet detection at 254 nm. Sample preparation based on diluted acids proved to be feasible and a recommendable alternative for organic sample digestion, reducing both the reagent volumes and the variability of the residues as a result of the process of decomposition. It was shown that biological matrices containing amino acids, proteins and lipids in their composition produced nitrobenzoic acid isomers and other organic compounds after cleavage of chemical bonds.

AnSBBR applied to organic matter and sulfate removal: interaction effect between feed strategy and COD/sulfate ratio.

A mechanically stirred anaerobic sequencing batch reactor containing anaerobic biomass immobilized on polyurethane foam cubes, treating low-strength synthetic wastewater (500 mg COD L(-1)), was operated under different operational conditions to assess the removal of organic matter and sulfate. These conditions were related to fill time, defined by the following feed strategies: batch mode of 10 min, fed-batch mode of 3 h and fed-batch mode of 6 h, and COD/[SO(4)(2-)] ratios of 1.34, 0.67, and 0.34 defined by organic matter concentration of 500 mg COD L(-1) and sulfate concentrations of 373, 746, and 1,493 mg SO(4)(2-) L(-1) in the influent. Thus, nine assays were performed to investigate the influence of each of these parameters, as well as the interaction effect, on the performance of the system. The reactor operated with agitation of 400 rpm, total volume of 4.0 L, and treated 2.0 L synthetic wastewater in 8-h cycles at 30 +/- 1 degrees C. During all assays, the reactor showed operational stability in relation to the monitored variables such as COD, sulfate, sulfide, sulfite, volatile acids, bicarbonate alkalinity, and solids, thus demonstrating the potential to apply this technology to the combined removal of organic matter and sulfate. In general, the results showed that the 3-h fed-batch operation with a COD/[SO(4)(2-)] ratio of 0.34 presented the best conditions for organic matter removal (89%). The best efficiency for sulfate removal (71%) was accomplished during the assay with a COD/[SO(4)(2-)] ratio of 1.34 and a fill time of 6 h. It was also observed that as fill time and sulfate concentration in the influent increased, the ratio between removed sulfate load and removed organic load also increased. However, it should be pointed out that the aim of this study was not to optimize the removal of organic matter and sulfate, but rather to analyze the behavior of the reactor during the different feed strategies and applied COD/[SO(4)(2-)] ratios, and mainly to analyze the interaction effect, an aspect that has not yet been explored in the literature for batch reactors.

Comparative performance evaluation of full-scale anaerobic and aerobic wastewater treatment processes in Brazil.

This article evaluates and compares the actual behavior of 166 full-scale anaerobic and aerobic wastewater treatment plants in operation in Brazil, providing information on the performance of the processes in terms of the quality of the generated effluent and the removal efficiency achieved. The observed results of effluent concentrations and removal efficiencies of the constituents BOD, COD, TSS (total suspended solids), TN (total nitrogen), TP (total phosphorus) and FC (faecal or thermotolerant coliforms) have been compared with the typical expected performance reported in the literature. The treatment technologies selected for study were: (a) predominantly anaerobic: (i) septic tank + anaerobic filter (ST + AF), (ii) UASB reactor without post-treatment (UASB) and (iii) UASB reactor followed by several post-treatment processes (UASB + POST); (b) predominantly aerobic: (iv) facultative pond (FP), (v) anaerobic pond followed by facultative pond (AP + FP) and (vi) activated sludge (AS). The results, confirmed by statistical tests, showed that, in general, the best performance was achieved by AS, but closely followed by UASB reactor, when operating with any kind of post-treatment. The effluent quality of the anaerobic processes ST + AF and UASB reactor without post-treatment was very similar to the one presented by facultative pond, a simpler aerobic process, regarding organic matter.