Monoaromatics removal from polluted water through bioreactors-a review

Microbial remediation of petroleum-contaminated soil focused on the mechanism and microbial response: a review

The environmental pollution caused by petroleum hydrocarbons has received considerable attention in recent years. Microbial remediation has emerged as the preferred method for the degradation of petroleum hydrocarbons, which is experiencing rapid development driven by advancements in molecular biology. Herein, the capacity of different microorganisms used for crude oil bioremediation was reviewed. Moreover, factors influencing the effectiveness of microbial remediation were discussed. Microbial remediation methods, such as bioaugmentation, biostimulation, and bioventilation, are summarized in this review. Aerobic and anaerobic degradation mechanisms were reviewed to elucidate the metabolic pathways involved. The impacts of petroleum hydrocarbons on microorganisms and the environment were also revealed. A brief overview of synthetic biology and a unique perspective of technique combinations were presented to provide insight into research trends. The challenges and future outlook were also presented to stimulate contemplation of the mechanisms involved and the development of innovative techniques.

Superoleophilic conjugated microporous polymer nano-surfactants for realizing unprecedented fast recovery of volatile organic compounds

A pervaporation membrane with fast and selective permeation is key to improving the recovery efficiency of volatile organic compounds from water. Here, we synthesize a new type of nanofiller-conjugated microporous polymer (CMP) to fabricate polydimethylsiloxane (PDMS)-based mixed matrix membranes (MMMs) and explore their application in the recovery of organic solvents from water via pervaporation. Due to their good dispersibility in the dope solvent and compatibility with PDMS, uniform MMMs without discrete particle phases or aggregates are prepared. Interestingly, CMP nanosheets play a unique role as a nano-surfactant in enhancing both the sorption and diffusion coefficients, realizing unprecedented fast recovery of organic solvents from water. The total flux of the as-fabricated membranes can be enhanced from 74.8 to 406.2 kg μm-2 h-1 and the separation factor αethyl acetate/water is increased from 118.7 to 526.6 when using 5 wt% ethyl acetate aqueous solution as the feed at 50 °C. In addition, the CMP-incorporated PDMS membranes are also effective in recovering a wide range of organic compounds from water, including ethanol, acetone, tetrahydrofuran and acetonitrile.

Assessing the Biodegradation of BTEX and Stress Response in a Bio-Permeable Reactive Barrier Using Compound-Specific Isotope Analysis

By using compound-specific isotope analysis (CSIA) in combination with high-throughput sequencing analysis (HTS), we successfully evaluated the benzene and toluene biodegradation in a bio-permeable reactive barrier (bio-PRB) and the stress response of the microbial community. Under stress conditions, a greater decline in the biodegradation rate of BTEX was observed compared with the apparent removal rate. Both an increase in the influent concentration and the addition of trichloroethylene (TCE) inhibited benzene biodegradation, while toluene biodegradation was inhibited by TCE. Regarding the stress response, the relative abundance of the dominant bacterial community responsible for the biodegradation of BTEX increased with the influent concentration. However, the dominant bacterial community did not change, and its relative abundance was restored after the influent concentration decreased. On the contrary, the addition of TCE significantly changed the bacterial community, with Aminicenantes becoming the dominant phyla for co-metabolizing TCE and BTEX. Thus, TCE had a more significant influence on the bio-PRB than an increasing influent concentration, although these two stress conditions showed a similar degree of influence on the apparent removal rate of benzene and toluene. The present work not only provides a new method for accurately evaluating the biodegradation performance and microbial community in a bio-PRB, but also expands the application of compound-specific isotope analysis in the biological treatment of wastewater.

Conventional and high resolution chemical characterization to assess refinery effluent treatment performance

Refinery effluents represent an emission source of hydrocarbons (HCs) and other constituents to the environment. Thus, characterisation of effluent quality in terms of concentrations of key parameters relative to permitted standards is important and for total petroleum hydrocarbons (TPH), the specific composition of the HC mixture can affect its toxicity to aquatic organisms. Therefore, this study was designed to analyse TPH, benzene, toluene, ethyl benzene, xylenes (BTEX), polycyclic aromatic hydrocarbons (PAHs), (bio) chemical oxygen demand, total nitrogen, total suspended solids and selected metals before, and after, treatment steps to demonstrate removal efficiencies across 13 refineries with variable wastewater treatment systems. Final discharge concentrations of the measured parameters were by 97% within the so called Best Available Technique Associated Emission Levels (BAT-AELs). Further, TPH composition was characterised using high-resolution two-dimensional gas chromatography (GCxGC) analysis to understand the mass distribution by carbon number and specific chemical class. Measurements were compared to SimpleTreat model predictions for validation. SimpleTreat successfully predicted the shape of the effluent composition since it is essentially a removal constant applied to the influent composition. The predictions were of similar magnitude as, or were greater than, the effluent concentrations since SimpleTreat is based on typical performance and is intended to be conservative. This was especially true for aromatic constituents. Reduction in potential HC exposures also coincided with a decrease in predicted toxicity using a mechanistic oil toxicity model, PETROTOX. Overall, the results indicate that EU petroleum refineries are likely to achieve a high performance level regarding effluent treatment.

Direct analysis of aromatic pollutants using a HPLC-FLD/DAD method for monitoring biodegradation processes

Industrial discharges resulting in contaminated groundwater is a global environmental problem. For such contaminated groundwater cases, bioremediation is a cost efficient and environmentally friendly approach. The determination and quantification of these pollutants has gained great importance and researchers are currently seeking to develop labor extensive, accurate and reliable methods for evaluating their biodegradation process. In this study, a HPLC method was developed and optimized for the quantification of 11 industrial pollutants studied as two different mixtures: benzene, toluene, ethylbenzene, o, m/p-xylene, indane, indene, and naphthalene (mixture A) and benzene, monochlorobenzene, 1,2-dichlorobenzene, and 1,4-dichlorobenzene (mixture B). The method uses two different detectors: fluorescence detection and diode array. The fluorescence detector was used for mixture A to achieve lower quantification limits and to quantify separately o-xylene and indene due to them showing similar wavelength behaviors. The limit of detection was found to be between 2 and 70 μg L^-1 for mixture A and 290 μg L^-1 for mixture B. The limit of quantitation was between 6 and 210 μg L^-1 for mixture A and 980 μg L^-1 for mixture B, respectively. The novel part of this study is that aqueous samples can be directly measured with one-step sample preparation and it comes with other advantages such as low volumes of sampling from batch bottles and also avoidance of high cost, relative to other analytical techniques. Therefore, this analytical method aims to facilitate the quantification of various aromatic hydrocarbons in laboratory batch samples and can be used as a routine monitoring tool for biological degradation processes of these 11 prevalent contaminants.

In-depth investigation of Sodium percarbonate as oxidant of PAHs from soil contaminated with diesel oil

Sodium percarbonate (SPC, 2Na₂CO₃∙3H₂O₂), is a compound that can be used under multiple environmental applications. In this work, SPC was employed as oxidant in the treatment of soil contaminated with diesel oil. The soil samples were collected during the earthmoving stage of RNEST Oil Refinery (Petrobras), Brazil. Then, the samples were air-dried, mixed and characterized. Subsequently, raw soil was contaminated with diesel and treated by photo-Fenton reaction (H₂O₂/Fe²⁺/UV). SPC played a significant role in the generation of hydroxyl radicals under the catalytic effect of ferrous ions (Fe²⁺), hydrogen peroxide (H₂O₂) and radiation. These radicals provoked the photodegradation of polycyclic aromatic hydrocarbons (PAHs), in the soil remediation. A factorial design 3³ was carried out to assess the variables which most influenced the decrease in total organic carbon (TOC). The study was performed with the following variables: initial concentration of [H₂O₂] and [Fe²⁺], between 190.0 and 950.0 mmol L^-1 and 0.0-14.4 mmol L^-1, respectively. UV radiation was supplied from sunlight, blacklight lamps, and system without radiation. All experiments were performed with 5.0 g of contaminated soil in 50.0 mL of solution. The initial concentration of Fe²⁺ showed the statistically most significant effect. The oxidation efficiency evaluated in the best condition showed a decrease from 34,765 mg kg^-1 to 15,801 mg kg^-1 in TOC and from 85.750 mg kg^-1 to 20.770 mg kg^-1 in PAHs content. Moreover, the sums of low and high molecular weight polycyclic aromatic hydrocarbons (LMW-PAHs and HMW-PAHs) were 19.537 mg kg^-1 and 1.233 mg kg^-1, respectively. Both values are within the limits recommended by the United Sates Environmental Protection Agency (USEPA) and evidenced the satisfactory removal of PAHs from contaminated soil, being an alternative to classic oxidation protocols.

Biodegradation of selected hydrocarbons by novel bacterial strains isolated from contaminated Arabian Gulf sediment

Three strains of novel bacteria were isolated from oil-contaminated sediment from the Arabian Gulf (Brevibacillus brevis T2C2008, Proteus mirabilis T2A12001, and Rhodococcus quinshengi TA13008). The isolated strains were tested for their degrading efficacy of low and high molecular hydrocarbon (naphthalene and pyrene). The efficacy of the two-hydrocarbon degradation by the isolates bacterial was determined at a temperature of 25 °C and 37 °C and pH of 5.0 and 9.0. In inoculated media at 37 °C, Rhodococcus qinshengi fully metabolized naphthalene and degrade 56% of pyrene. Brevibacillus brevis break down over 80% of naphthalene at room temperatures (25 °C). However, it was found that P. mirabilis and R. qinshengi biodegraded nearly 94% of naphthalene in the incubated media. The capacity for pyrene and naphthalene degradation in varying pH and temperature conditions was shown to be significant in Rhodococcus qinshengi because of its mineralization exceeding 50% across the tested pH and temperature. This implies that the isolated strains are ideal for biodegradation of contaminated sediment with naphthalene and pyrene.

Bioelectrochemical degradation of monoaromatic compounds: Current advances and challenges

Monoaromatic compounds (MACs) are typical refractory organic pollutants which are existing widely in various environments. Biodegradation strategies are benign while the key issue is the sustainable supply of electron acceptors/donors. Bioelectrochemical system (BES) shows great potential in this field for providing continuous electrons for MACs degradation. Phenol and BTEX (Benzene, Toluene, Ethylbenzene and Xylenes) can utilize anode to enhance oxidative degradation, while chlorophenols, nitrobenzene and antibiotic chloramphenicol (CAP) can be efficiently reduced to less-toxic products by the cathode. However, there still have several aspects need to be improved including the scale, electricity output and MACs degradation efficiency of BES. This review provides a comprehensive summary on the BES degradation of MACs, and discusses the advantages, future challenges and perspectives for BES development. Instead of traditional expensive dual-chamber configurations for MACs degradation, new single-chamber membrane-less reactors are cost-effective and the hydrogen generated from cathodes may promote the anode degradation. Electrode materials are the key to improve BES performance, approaches to increase the biofilm enrichment and conductivity of materials have been discussed, including surface modification as well as composition of carbon and metal-based materials. Besides, the development and introduction of functional microbes and redox mediators, participation of sulfur/hydrogen cycling may further enhance the BES versatility. Some critical parameters, such as the applied voltage and conductivity, can also affect the BES performance, which shouldn't be overlooked. Moreover, sequential cathode-anode cascaded mode is a promising strategy for MACs complete mineralization.

Pollution, Toxicity and Carcinogenicity of Organic Dyes and their Catalytic Bio-Remediation

Water pollution due to waste effluents of the textile industry is seriously causing various health problems in humans. Water pollution with pathogenic bacteria, especially Escherichia coli (E. coli) and other microbes is due to the mixing of fecal material with drinking water, industrial and domestic sewage, pasture and agricultural runoff. Among the chemical pollutants, organic dyes due to toxic nature, are one of the major contaminants of industrial wastewater. Adequate sanitation services and drinking quality water would eliminate 200 million cases of diarrhea, which results in 2.1 million less deaths caused by diarrheal disease due to E. coli each year. Nanotechnology is an excellent platform as compared to conventional treatment methods of water treatment and remediation from microorganisms and organic dyes. In the current study, toxicity and carcinogenicity of the organic dyes have been studied as well as the remediation/inactivation of dyes and microorganism has been discussed. Remediation by biological, physical and chemical methods has been reviewed critically. A physical process like adsorption is cost-effective, but can't degrade dyes. Biological methods were considered to be ecofriendly and cost-effective. Microbiological degradation of dyes is cost-effective, eco-friendly and alternative to the chemical reduction. Besides, certain enzymes especially horseradish peroxidase are used as versatile catalysts in a number of industrial processes. Moreover, this document has been prepared by gathering recent research works related to the dyes and microbial pollution elimination from water sources by using heterogeneous photocatalysts, metal nanoparticles catalysts, metal oxides and enzymes.

Determination of Monoaromatic Hydrocarbons in Water Samples by Nano-Liquid Chromatography using a Composite Carbon Nanotubes- Lauryl Polymethacrylate Capillary Monolithic Column

Background:

This work reports a green analytical method for the determination of organic environmental pollutants using nano-liquid chromatography with a self-made column for rapid, sensitive, inexpensive and efficient analysis of BTX pollutants in water. The applications of monolithic nanoscale columns for quantitative analysis of environmental real samples are very limited in the literature.

Methods:

A capillary column containing a composite of multi-walled carbon nanotubes incorporated into a lauryl methacrylate-co-ethylene dimethacrylate porous monolithic polymer was fabricated for the determination of BTX pollutants in real water samples.

Results:

Baseline separation was accomplished at 0.4 µL/min flow rate with UV-detection set at 208 nm. Under the optimum conditions, the calibration curves were validated over the range of 1.0-500 µg/L with R2 more than 0.9992. The detection limits of benzene, toluene, o-xylene and m/p-xylene were 0.25, 0.05, 0.075 and 0.05 µg/L, respectively. After a simple extraction process with a theoretical preconcentration factor equal to 200, the recovery values in Milli-Q, tap and sea water samples were found to be ranged from 84.85 to 97.84% with %RSD less than 7.5. Furthermore, we reported a comparison between our prepared composite column with a commercial C18 silica based column which is the most used in such analytical field. Each column demonstrated its advantages from different analytical aspects.

Conclusion:

The application of monolithic columns and nano-scale LC for routine analysis of environmental samples is very promising as the use of monolithic capillary columns offers several advantages over conventional scale particulate packed columns.

Engineered bacterial biofloc formation enhancing phenol removal and cell tolerance

A microbial floc consisting of a community of microbes embedded in extracellular polymeric substances matrix can provide microbial resistances to toxic chemicals and harsh environments. Phenol is a toxic environmental pollutant and a typical lignin-derived phenolic inhibitor. In this study, we genetically engineered Escherichia coli cells by expressions of diguanylate cyclases (DGCs) to promote proteinaceous and aliphatic biofloc formation. Compared with the planktonic E. coli cells, the biofloc-forming cells improved phenol removal rate by up to 2.2-folds, due to their substantially improved tolerance (up to 149%) to phenol and slightly enhanced cellular activity (20%) of phenol hydroxylase (PheH). The engineered bioflocs also improved E. coli tolerance to other toxic compounds such as furfural, 5-hydroxymethylfurfural, and guaiacol. Additionally, the strategy of the engineered biofloc formation was applicable to Pseudomonas putida and enhanced its tolerance to phenol. This study highlights a strategy to form engineered bioflocs for improved cell tolerance and removal of toxic compounds, enabling their universality of use in bioproduction and bioremediation.

Low pressure plasma functionalized cellulose fiber for the remediation of petroleum hydrocarbons polluted water

This work reports the first example of effective purification, at laboratory level, of water polluted by petroleum hydrocarbons, by means of low pressure plasma fluorine grafted cellulose fiber extracted from Spanish Broom. In order to improve the affinity of the cellulosic surface towards water dispersed hydrocarbons, its original hydrophilic character was turned to super-hydrophobic, by a fluorine functionalization. Batch experiments were performed with the aim of studying kinetic and thermodynamic aspects of the adsorption process, as a function of the initial total hydrocarbon load and of the adsorbent amount. The kinetics data showed that the fiber removal efficiency ranged between 80-90% after one minute of contact time, in dependence of the initial hydrocarbon/fiber weight ratio (20-240 mg/g). A maximum adsorption capacity larger than 270 mg/g was estimated by fitting the adsorption isotherm measurements with the Langmuir model. It turned out that the functionalized fiber is capable to perform a significant hydrocarbons removal action if compared to other cellulosic materials reported in the literature. Finally, the efficiency of the plasma modified cellulose fiber, after iterative re-uses, was studied.

Development of a Zeolite A/LDH Composite for Simultaneous Cation and Anion Removal

Wastewater from the oil industry is a major problem for aqueous environments due to its complexity and estimated volume of approximately 250 million barrels per day. The combination of these petroleum pollutants creates risks to human health, and their removal from the environment is considered a major problem in the world today. Thus, this work has the objective of studying the treatment of this type of effluent through the adsorption method using the following exchange materials: cationic, anionic, their combination by a sequential method, and a composite material. Zeolite A, a layered double hydroxide (LDH), and the new composite material formed by zeolite A and LDH structures were synthesized for this study. All were used for the simultaneous treatment of cations and anions in a complex sample such as water produced from petroleum production. The composite demonstrated an excellent ability to simultaneously remove cations and anions. The results obtained after the different treatment modes of the effluent using different materials varied from 85% to 100% for the removal of cations and from 56% to 99.7% for the removal of anions.

Process bioengineering applied to BTEX degradation in microaerobic treatment systems

The effect of different microaeration flow rates and dosing points, and of effluent recirculation, on microaerobic BTEX degradation in an anaerobic bioreactor was assessed. Additionally, a sensitivity and recovery analysis for this system was performed during microaeration failure simulations. Under anaerobic conditions, BTEX removal efficiencies between 55 and 82% were achieved depending on the compound, being benzene the most recalcitrant one. Microaeration (0.5-2.0 mL air min^-1) ensured high removal efficiencies (>83%) for all compounds, and the best results were obtained for the flow rate of 1.0 mL air min^-1, particularly for benzene, with a 30% increase in its removal efficiency. Effluent recirculation showed to be an important factor to improve mass transfer and, consequently, BTEX removal. Volatilization was negligible even under microaerobic conditions, suggesting that microbial activity was the main removal mechanism. Finally, after microaeration shutdown periods, the bioreactor could recover its prior performance within up to 2 days.

Performance evaluation of duplex constructed wetlands for the treatment of diesel contaminated wastewater

A duplex constructed wetland (duplex-CW) is a hybrid system that combines a vertical flow (VF) CW as a first stage with a horizontal flow filter (HFF) as a second stage for a more efficient wastewater treatment as compared to traditional constructed wetlands. This study evaluated the potential of the hybrid CW system to treat influent wastewater containing diesel range organic compounds varying from C₇ - C₄₀ using a series of 12-week practical and numerical experiments under controlled conditions in a greenhouse (pH was kept at 7.0 ± 0.2, temperature between 20 and 23° C and light intensity between 85 and 100-μmol photons m^-2 sec^-1 for 16 h d^-1). The VF CWs were planted with Phragmites australis and were spiked with different concentrations of NH₄⁺-N (10, 30 and 60 mg/L) and PO₄^3--P (3, 6 and 12 mg/L) to analyse their effects on the degradation of the supplied petroleum hydrocarbons. The removal rate of the diesel range organics considering the different NH₄⁺-N and PO₄^3--P concentrations were simulated using Monod degradation kinetics. The simulated results compared well with the observed database. The results showed that the model can effectively be used to predict biochemical transformation and degradation of diesel range organic compounds along with nutrient amendment in duplex constructed wetlands.

Selective and reversible adsorption of cationic dyes by mixed ligand Zn(ii) coordination polymers synthesized by reactant ratio modulation

2D/3D luminescent Zn(ii)-based coordination polymers CP1 and CP2 have been synthesized by reactant ratio modulation. Photoluminescence studies of both CPs; selective and reversible adsorption/separation of cationic dyes by CP1 in the aqueous medium has been investigated.

MALDI-TOF MS for the Identification of Cultivable Organic-Degrading Bacteria in Contaminated Groundwater near Unconventional Natural Gas Extraction Sites

Groundwater quality and quantity is of extreme importance as it is a source of drinking water in the United States. One major concern has emerged due to the possible contamination of groundwater from unconventional oil and natural gas extraction activities. Recent studies have been performed to understand if these activities are causing groundwater contamination, particularly with respect to exogenous hydrocarbons and volatile organic compounds. The impact of contaminants on microbial ecology is an area to be explored as alternatives for water treatment are necessary. In this work, we identified cultivable organic-degrading bacteria in groundwater in close proximity to unconventional natural gas extraction. Pseudomonas stutzeri and Acinetobacter haemolyticus were identified using matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF MS), which proved to be a simple, fast, and reliable method. Additionally, the potential use of the identified bacteria in water and/or wastewater bioremediation was studied by determining the ability of these microorganisms to degrade toluene and chloroform. In fact, these bacteria can be potentially applied for in situ bioremediation of contaminated water and wastewater treatment, as they were able to degrade both compounds.

Effects of hydraulic retention time, co-substrate and nitrogen source on laundry wastewater anionic surfactant degradation in fluidized bed reactors

The aim of this study was to evaluate the influence of hydraulic retention time (HRT) on linear alkylbenzene sulfonate (LAS) removal in fluidized bed reactors (FBRs). FBR1 (HRT of 8h) and FBR2 (HRT of 12h) were fed laundry wastewater with 18.6±4.1 to 27.1±5.6mg/L of LAS in the following conditions: ethanol and nitrate addition (Phases I, II and III), nitrate (Phase IV), ethanol (Phase V) and laundry wastewater (Phase VI). LAS removal was 93±12% (FBR1) and 99±2% (FBR2). In FBR1, nitrate influenced significantly on LAS removal (99±3% - Phase IV) compared to the phase without nitrate (90±15% - Phase V). In FBR1 the absence of ethanol was more favourable for LAS removal (99±3% - Phase IV) compared to ethanol addition (87±16% - Phase II). In FBR2, 99±2% LAS removal was found up to 436days. By microbial characterization were identified bacteria as Acinetobacter, Dechloromonas, Pseudomonas and Zoogloea.

Characterisation and treatment of VOCs in process water from upgrading facilities for compressed biogas (CBG)

Compression and upgrading of biogas to vehicle fuel generates process water, which to varying degrees contains volatile organic compounds (VOCs) originating from the biogas. The compostion of this process water has not yet been studied and scientifically published and there is currently an uncertainty regarding content of VOCs and how the process water should be managed to minimise the impact on health and the environment. The aim of the study was to give an overview about general levels of VOCs in the process water. Characterisation of process water from amine and water scrubbers at plants digesting waste, sewage sludge or agricultural residues showed that both the average concentration and composition of particular VOCs varied depending on the substrate used at the biogas plant, but the divergence was high and the differences for total concentrations from the different substrate groups were only significant for samples from plants using waste compared to residues from agriculture. The characterisation also showed that the content of VOCs varied greatly between different sampling points for same main substrate and between sampling occasions at the same sampling point, indicating that site-specific conditions are important for the results which also indicates that a number of analyses at different times are required in order to make an more exact characterisation with low uncertainty. Inhibition of VOCs in the anaerobic digestion (AD) process was studied in biomethane potential tests, but no inhibition was observed during addition of synthetic process water at concentrations of 11.6 mg and 238 mg VOC/L.

A lanthanide metal–organic framework (MOF-76) for adsorbing dyes and fluorescence detecting aromatic pollutants

A series of nano-sized luminescent lanthanide metal–organic frameworks (Ln-MOFs) are developed for application in dye adsorption and fluorescence sensing for monoaromatic hydrocarbons (BTEX).

Comparison of the efficiencies of attached- versus suspended-growth SBR systems in the treatment of recycled paper mill wastewater

The complexity of residual toxic organics from biologically treated effluents of pulp and paper mills is a serious concern. To date, it has been difficult to choose the best treatment technique because each of the available options has advantages and drawbacks. In this study, two different treatment techniques using laboratory-scale aerobic sequencing batch reactors (SBRs) were tested with the same real recycled paper mill effluent to evaluate their treatment efficiencies. Two attached-growth SBRs using granular activated carbon (GAC) with and without additional biomass and a suspended-growth SBR were used in the treatment of real recycled paper mill effluent at a chemical oxygen demand (COD) level in the range of 800-1300 mg/L, a fixed hydraulic retention time of 24 h and a COD:N:P ratio of approximately 100:5:1. The efficiency of this biological treatment process was studied over a 300-day period. The six most important wastewater quality parameters, namely, chemical oxygen demand (COD), turbidity, ammonia (expressed as NH3-N), phosphorus (expressed as PO4(3)-P), colour, and suspended solids (SS), were measured to compare the different treatment techniques. It was determined that these processes were able to almost completely and simultaneously eliminate COD (99%) and turbidity (99%); the removals of NH3-N (90-100%), PO4(3)-P (66-78%), colour (63-91%), and SS (97-99%) were also sufficient. The overall performance results confirmed that an attached-growth SBR system using additional biomass on GAC is a promising configuration for wastewater treatment in terms of performance efficiency and process stability under fluctuations of organic load. Hence, this hybrid system is recommended for the treatment of pulp and paper mill effluents.

Fate of volatile aromatic hydrocarbons in the wastewater from six textile dyeing wastewater treatment plants

The occurrence and removal of benzene, toluene, ethylbenzene, xylenes, styrene and isopropylbenzene (BTEXSI) from 6 textile dyeing wastewater treatment plants (TDWTPs) were investigated in this study. The practical capacities of the 6 representative plants, which used the activated sludge process, ranged from 1200 to 26000 m(3) d(-1). The results indicated that BTEXSI were ubiquitous in the raw textile dyeing wastewater, except for isopropylbenzene, and that toluene and xylenes were predominant in raw wastewaters (RWs). TDWTP-E was selected to study the residual BTEXSI at different stages. The total BTEXSI reduction on the aerobic process of TDWTP-E accounted for 82.2% of the entire process. The total BTEXSI concentrations from the final effluents (FEs) were observed to be below 1 μg L(-1), except for TDWTP-F (2.12 μg L(-1)). Volatilization and biodegradation rather than sludge sorption contributed significantly to BTEXSI removal in the treatment system. BTEXSI were not found to be the main contaminants in textile dyeing wastewater.

Determination of monoaromatic hydrocarbons (BTEX) in surface waters from a Brazilian subtropical hydrographic basin

This study examined surface water samples for the presence of the monoaromatic hydrocarbons benzene, toluene, ethylbenzene and xylene. Water samples were collected from the sub-basin of the Tegas River and the Marrecas Stream microbasin located in the metropolitan region of the municipality of Caxias do Sul (Rio Grande do Sul State, Brazil). For all sampling points evaluated, only toluene was detected, with concentrations values in the range of 1.70-18.44 μg L(-1). In general, the relatively high toluene concentration for the samples collected were above the limit of 2 μg L(-1) established by the Brazilian government for Class I rivers for the protection of aquatic life. However, they were well below the established limit of 170 μg L(-1) in water used for human consumption.

Removal of dichloromethane from ground and wastewater: a review

Dichloromethane (DCM) is a toxic volatile compound which is found in the ground waters and wastewaters of the pharmaceutical, chemical, textile, metal-working and petroleum industries. DCM inhibits the growth of aquatic organisms, induces cancer in animals and is potentially carcinogenic for humans. This article aims to review existing water treatments for DCM removal, focusing on recent technological advances. Air stripping, adsorption and pervaporation were found to be effective in separating DCM from water with a process efficiency of about 99%, 90% and 80% respectively. Electrocatalysis over Cu-impregnated carbon fiber electrode, photo irradiation over TiO₂ and photo-Fenton process led to the complete decomposition of DCM. Aerobic and anaerobic water treatment achieved 99% and 95% removal of DCM respectively. The maximum efficiencies observed for acoustic cavitation, radiolysis and catalytic degradation of CH₂Cl₂ were 90%, 92% and 99% respectively. Ozonation and persulfate oxidation showed lower DCM degradation efficiencies, not exceeding 20%. Further combination of different water treatment methods will further increase DCM degradation efficiency.

Low-temperature anaerobic treatment of low-strength pentachlorophenol-bearing wastewater

The anaerobic treatment of low-strength wastewater bearing pentachlorophenol (PCP) at psychro-mesophilic temperatures has been investigated in an expanded granular sludge bed reactor. Using an upward flow rate of 4 m h(-1), a complete removal of PCP, as well as COD removal and methanization efficiencies higher than 75% and 50%, respectively, were achieved. Methanogenesis and COD consumption were slightly affected by changes in loading rate, temperature (17-28°C) and inlet concentrations of urea and oils. Pentachlorophenol caused an irreversible inhibitory effect over both acetoclastic and hydrogenotrophic methanogens, being the later more resistant to the toxic effect of pentachlorophenol. An auto-inhibition phenomenon was observed at PCP concentrations higher than 10 mg L(-1), which was accurately predicted by a Haldane-like model. The inhibitory effect of PCP over the COD consumption and methane production was modelled by modified pseudo-Monod and Roediger models, respectively.

Evaluation of integrated anaerobic/aerobic fixed-bed sequencing batch biofilm reactor for decolorization and biodegradation of azo dye acid red 18: comparison of using two types of packing media

Two integrated anaerobic/aerobic fixed-bed sequencing batch biofilm reactor (FB-SBBR) were operated to evaluate decolorization and biodegradation of azo dye Acid Red 18 (AR18). Volcanic pumice stones and a type of plastic media made of polyethylene were used as packing media in FB-SBBR1 and FB-SBBR2, respectively. Decolorization of AR18 in both reactors followed first-order kinetic with respect to dye concentration. More than 63.7% and 71.3% of anaerobically formed 1-naphthylamine-4-sulfonate (1N-4S), as one of the main sulfonated aromatic constituents of AR18 was removed during the aerobic reaction phase in FB-SBBR1 and FB-SBBR2, respectively. Based on statistical analysis, performance of FB-SBBR2 in terms of COD removal as well as biodegradation of 1N-4S was significantly higher than that of FB-SBBR1. Spherical and rod shaped bacteria were the dominant species of bacteria in the biofilm grown on the pumice stones surfaces, while, the biofilm grown on surfaces of the polyethylene media had a fluffy structure.

Dynamic modeling of biodegradation and volatilization of hazardous aromatic substances in aerobic bioreactor

The aerobic biological process is one of the best technologies available for removing hazardous organic substances from industrial wastewaters. But in the case of volatile organic compounds (benzene, toluene, ethylbenzene, p-xylene, naphthalene), volatilization can contribute significantly to their removal from the liquid phase. One major issue is to predict the competition between volatilization and biodegradation in biological process depending on the target molecule. The aim of this study was to develop an integrated dynamic model to evaluate the influence of operating conditions, kinetic parameters and physical properties of the molecule on the main pathways (biodegradation and volatilization) for the removal of Volatile Organic Compounds (VOC). After a comparison with experimental data, sensitivity studies were carried out in order to optimize the aerated biological process. Acclimatized biomass growth is limited by volatilization, which reduces the bioavailability of the substrate. Moreover, the amount of biodegraded substrate is directly proportional to the amount of active biomass stabilized in the process. Model outputs predict that biodegradation is enhanced at high SRT for molecules with low H and with a high growth rate population. Air flow rate should be optimized to meet the oxygen demand and to minimize VOC stripping. Finally, the feeding strategy was found to be the most influential operating parameter that should be adjusted in order to enhance VOC biodegradation and to limit their volatilization in sequencing batch reactors (SBR).

Integration of processes induced air flotation and photo-Fenton for treatment of residual waters contaminated with xylene

Produced water in oil fields is one of the main sources of wastewater generated in the industry. It contains several organic compounds, such as benzene, toluene, ethyl benzene and xylene (BTEX), whose disposal is regulated by law. The aim of this study is to investigate a treatment of produced water integrating two processes, i.e., induced air flotation (IAF) and photo-Fenton. The experiments were conducted in a column flotation and annular lamp reactor for flotation and photodegradation steps, respectively. The first order kinetic constant of IAF for the wastewater studied was determined to be 0.1765 min(-1) for the surfactant EO 7. Degradation efficiencies of organic loading were assessed using factorial planning. Statistical data analysis shows that H(2)O(2) concentration is a determining factor in process efficiency. Degradations above 90% were reached in all cases after 90 min of reaction, attaining 100% mineralization in the optimized concentrations of Fenton reagents. Process integration was adequate with 100% organic load removal in 20 min. The results of the integration of the IAF with the photo-Fenton allowed to meet the effluent limits established by Brazilian legislation for disposal.

Post-treatment of anaerobically degraded azo dye Acid Red 18 using aerobic moving bed biofilm process: enhanced removal of aromatic amines

The application of aerobic moving bed biofilm process as post-treatment of anaerobically degraded azo dye Acid Red 18 was investigated in this study. The main objective of this work was to enhance removal of anaerobically formed the dye aromatic metabolites. Three separate sequential treatment systems were operated with different initial dye concentrations of 100, 500 and 1000 mg/L. Each treatment system consisted of an anaerobic sequencing batch reactor (An-SBR) followed by an aerobic moving bed sequencing batch biofilm reactor (MB-SBBR). Up to 98% of the dye decolorization and more than 80% of the COD removal occurred anaerobically. The obtained results suggested no significant difference in COD removal as well as the dye decolorization efficiency using three An-SBRs receiving different initial dye concentrations. Monitoring the dye metabolites through HPLC suggested that more than 80% of anaerobically formed 1-naphthylamine-4-sulfonate was completely removed in the aerobic biofilm reactors. Based on COD analysis results, at least 65-72% of the dye total metabolites were mineralized during the applied treatment systems. According to the measured biofilm mass and also based on respiration-inhibition test results, increasing the initial dye concentration inhibited the growth and final mass of the attached-growth biofilm in MB-SBBRs.

Fate of hazardous aromatic substances in membrane bioreactors

In this work, the removal of hazardous aromatic compounds was investigated in two types of membrane bioreactors (MBRs), based on cross-flow and semi dead-end filtration systems. BTEX and PAH were efficiently eliminated from wastewater during treatment via a membrane bioreactor (90-99.9%) but non-biotic processes, i.e. volatilisation and sorption, contributed significantly. The semi dead-end MBR showed slightly better removal efficiencies than the cross-flow MBR. However, non-biotic processes were more significant in the first process and, finally, degradation rates were higher in the cross-flow MBR. Higher degradation rates were explained by a higher bio-availability of pollutants. Differences in shear stress imposed in cross-flow and semi dead-end filtration systems radically modify the sludge morphology. High shear stress (cross-flow filtration) generates dispersed bacteria and larger quantities of dissolved and colloidal matter. Sorption of hydrophobic compounds (PAHs) on suspended solid was less marked in disaggregated sludge. The results suggest new strategies for improving micro-pollutant degradation in MBRs.

Biological treatment of refinery spent caustics under halo-alkaline conditions

The present research demonstrates the biological treatment of refinery sulfidic spent caustics in a continuously fed system under halo-alkaline conditions (i.e. pH 9.5; Na(+)= 0.8M). Experiments were performed in identical gas-lift bioreactors operated under aerobic conditions (80-90% saturation) at 35°C. Sulfide loading rates up to 27 mmol L(-1)day(-1) were successfully applied at a HRT of 3.5 days. Sulfide was completely converted into sulfate by the haloalkaliphilic sulfide-oxidizing bacteria belonging to the genus Thioalkalivibrio. Influent benzene concentrations ranged from 100 to 600 μM. At steady state, benzene was removed by 93% due to high stripping efficiencies and biodegradation. Microbial community analysis revealed the presence of haloalkaliphilic heterotrophic bacteria belonging to the genera Marinobacter, Halomonas and Idiomarina which might have been involved in the observed benzene removal. The work shows the potential of halo-alkaliphilic bacteria in mitigating environmental problems caused by alkaline waste.