Monitoring and toxicity of sulfonated derivatives of benzene and naphthalene in municipal sewage treatment plants

Natural sunlight-driven aquatic toxicity enhancement of 2,6-di-tert-butylphenol toward Photobacterium phosphoreum

The tert-butylphenols (TBPs) are one group of alkylated phenolic compounds with wide applications in UV absorbers and antioxidants. They are becoming contaminants of emerging concern with residues frequently detected in natural surface water or drinking water. The direct sunlight may photolyze TBPs in waters and affect their aquatic toxicities; however, such data are very limited. In the present study, we investigate the photodegradation of 2,6-DTBP by direct sunlight in water and compare the aquatic toxicities of 2,6-DTBP with that of its product toward Photobacterium phosphoreum. 2,6-DTBP is photodegraded by 71.31 ± 2.64% under simulated sunlight following a pseudo-first-order kinetics with rate constant (k) of 0.061 h^-1. Density functional theory simulations at M06-2X/def2-SVP level reveal that the photodegradation occurred sequentially through oxidation, photo-isomerization and hydrogenation. The degradation product 2,5-DTBP is toxic to P. phosphoreum (EC₅₀ 3.389 × 10^-5 mol/L) whereas 2,6-DTBP is not harmful (EC₅₀ 3.917 × 10^-3 mol/L) as designated by the European Union Standard, indicating the enhanced toxicities driven by the direct sunlight photodegradation. We demonstrate the enhanced toxicities of 2,6-DTBP by natural sunlight, suggesting that negligence of photodegradation of TBPs-related contaminants will underestimate the comprehensive risk of these emerging contaminant in natural waters.

Electrodegradation of naphthalenic amines: Influence of the relative position of the substituent groups, anode material and electrolyte on the degradation products and kinetics

The electrodegradation of the 4-aminonaphthalene-1-sulfonic acid (4AN1S), 5-aminonaphthalene-2-sulfonic acid (5AN2S) and 8-aminonaphthalene-2-sulfonic acid (8AN2S) was studied, using two electrode materials as anode, BDD and Ti/Pt/PbO₂, and two different electrolytes, sodium sulfate and sodium chloride. The highest COD removal rates were obtained at BDD: for 5AN2S and 8AN2S results were similar in both electrolytes; for 4AN1S, results were better in sodium chloride. The lowest COD removal rates were obtained at the system Ti/Pt/PbO₂-sodium sulfate, for all the studied amines. The dissolved organic carbon (DOC) removal was much higher at BDD for all the amines, in sulfate for 5AN2S and 8AN2S and in chloride for 4AN1S. Nitrogen removal was always almost irrelevant in sulfate medium but higher than 60%, after 6-h assays, in chloride. The highest combustion efficiencies were attained at the system BDD-sodium sulfate and were: 4AN1S-75%; 5AN2S-84%; 8AN2S-74%. HPLC results show that total degradation of the studied aminonaphthalene sulfonates is attained at both anode materials, utilizing any of the electrolytes, with a first order kinetics. However, kinetic constants obtained with the variation of the amines concentration in time are 10-40 times higher in chloride, being slightly higher at Ti/Pt/PbO₂ than at BDD. Regarding the presence of carboxylic acids during the degradation assays, it was observed that the electrolysis of the amines 5AN2S and 8AN2S always lead to higher amounts of oxalic acid and lower quantities of acetic acid than the electrolysis of the amine 4AN1S.

Influence of Fenton's reagent doses on the degradation and mineralization of H-acid

The recalcitrant H-acid (1-amino-8-naphthol-3,6-disulfonic acid) in aqueous solution was oxidized by Fenton process, focusing on the relation of Fenton's reagent doses and degradation products. The experimental results showed that COD and TOC removals and biodegradability (BOD/COD ratio) of the solution increased with increasing Fenton's reagent doses. Over 80% COD can be removed and the biodegradability was improved significantly. It was found that major SO3H and NH2 groups in H-acid molecules were mineralized to SO4(2-) and NH4(+) ions during Fenton oxidation processes. H-acid degradation intermediates with benzene structures substituted by hydroxyl and/or carboxyl groups were identified by GC-MS. It was also found that short-chain fatty acids primarily oxalic acid were degradation products of H-acid by Fenton oxidation. Oxalic acid accumulated could account for approximately 60% of the residual TOC. The degradation pathway of H-acid was proposed based on above analyses in this work.

Characterization, treatment and releases of PBDEs and PAHs in a typical municipal sewage treatment plant situated beside an urban river, East China

Characterization, treatment and releases of eight polybrominated diphenyl ethers (PBDEs) congeners and sixteen polycyclic aromatic hydrocarbons (PAHs) in wastewater were evaluated along the treatment processes of a typical secondary treatment municipal sewage treatment plant (STP) (in Hefei City) situated the beside Nanfei River, East China. The findings showed that the average concentrations of the total PBDEs in raw wastewater and treated effluent were 188.578 and 36.884 ng/L respectively. Brominated diphenyl ether (BDE) 209 congener, the predominant PBDE in the STP and Nanfei River, could be related to the discharge of car-industry-derived wastes. For PAHs, the average concentrations in raw wastewater and treated effluent were 5758.8 and 2240.4 ng/L respectively, with naphthalene, benzo[a]pyrene and indeno[1,2,3-c,d]pyrene being detected at the highest concentrations. PAHs mainly originate from the combustion of biomass/coal and petroleum. The STP reduced about 80% of the PBDEs and 61% of the PAHs, which were eliminated mainly by sedimentation processes. The removal rates of PBDEs/PAHs increased with the increase of their solid-water partitioning coefficients. Accordingly, the STP's effluent, containing some PBDE congeners (e.g., BDE 47, 99 and 209, etc.) and low-molecular-weight PAHs, could be an important contributor of these contaminants' input to Nanfei River. It resulted in a significant increase of PBDE/PAH concentrations and PAH toxicological risk in the river water downstream. About 4.040 kg/yr of PBDEs and 245.324 kg/yr of PAHs could be released into the Nanfei River. The current conventional wastewater treatment processes should be improved to remove the relatively low-molecular-weight PBDEs/PAHs more effectively.

Photocatalytic degradation of benzenesulfonate on colloidal titanium dioxide

Titanium dioxide-mediated photocatalyzed degradation of benzenesulfonate (BS) was investigated by monitoring chemical oxygen demand (COD), total organic carbon (TOC) content, sulfate concentration, pH as well as the absorption and emission spectral changes in both argon-saturated and aerated systems. Liquid chromatography-mass spectrometry analysis was utilized for the detection of intermediates formed during the irradiation in the UVA range (λ(max) = 350 nm). The results obtained by these analytical techniques indicate that the initial step of degradation is hydroxylation of the starting surfactant, resulting in the production of hydroxy- and dihydroxybenzenesulfonates. These reactions were accompanied by desulfonation, which increases [H(+)] in both argon-saturated and aerated systems. In accordance with our previous theoretical calculations, the formation of ortho- and meta-hydroxylated derivatives is favored in the first step. The main product of the further oxygenation of these derivatives was 2,5-dihydroxy-benzesulfonate. No decay of the hydroxy species occurred during the 8-h irradiation in the absence of dissolved oxygen. In the aerated system much more efficient desulfonation and hydroxylation, moreover, a significant decrease of TOC took place at the initial stage. Further hydroxylation led to cleavage of the aromatic system, due to the formation of polyhydroxy derivatives, followed by ring fission, resulting in the production of aldehydes and carboxylic acids. Total mineralization was achieved by the end of the 8-h photocatalysis. It has been proved that in this photocatalytic procedure the presence of dissolved oxygen is necessary for the cleavage of the aromatic ring because hydroxyl radicals photochemically formed in the deaerated system too alone are not able to break the C-C bonds.

Evaluating environmental impact of STPs situated on streams in the Czech Republic: an integrated approach to biomonitoring the aquatic environment

Sewage water treatment plants (STPs) are frequently associated with the release of xenobiotics and, consequently, with biological responses of fish to these substances. The impact of three STPs situated on small streams was assessed in 2009. Brown trout (Salmo trutta fario L.), captured upstream and downstream of these STPs, were used as biomonitors. The concentrations of 39 organic pollutants (PCBs, OCPs, PBDEs, HBCDs, and MCs), and the biological responses related to oxidative stress (lipid peroxidation and carbonyl protein), and antioxidant responses (superoxide dismutase, glutathione peroxidase and glutathione reductase) were measured. Through chemometrics of these parameters, three groups with 97.62% of the total accumulated variance were distinguished. Integration of the assessed biomarkers using the IBR index, ranked environment impact on sites as: DS Pacov > DS Prachatice > DS Brloh > US Pacov > US Prachatice > US Brloh (most to least affected). STPs are a major source of xenobiotic pollution in streams of the Czech Republic. The combined use of chemical analysis and biological responses is necessary to validate the efficacy of a battery of biomarkers chosen to detect environmental stress due to pollution.

Oxidative degradation of 1,5-naphthalenedisulfonic acid in aqueous solutions by UV-photolysis in the absence and presence of H2O2

Sulfonated aromatic pollutants such as 1,5-naphthalenedisulfonic acid (NDS or Armstrong's acid) are persistent compounds and thus resist environmental breakdown and microbial treatment. This study investigated the photo-oxidative degradation of such a persistent polar pollutant in the absence and presence of H2O2. The degradation of aqueous NDS solutions by photolysis was found to be efficient only in the presence of H2O2. The combination of UV irradiation and H2O2 leads to progressive degradation of NDS, which is converted into new, more biodegradable and non-toxic species.

Environmental risk assessment of pharmaceuticals in rivers: relationships between hazard indexes and aquatic macroinvertebrate diversity indexes in the Llobregat River (NE Spain)

Continuous input of pharmaceuticals into rivers, through wastewater treatment systems, may cause adverse effects on the aquatic ecosystems of the receiving waterbodies, due to the intrinsic biological activity of these compounds. To investigate this issue, we have carried out an Environmental Risk Assessment in the lower part of the Llobregat River basin (NE Spain). The survey was carried out along three campaigns in 7 sampling points, located in the main river and in one of its tributaries (Anoia River). In each sample, 29 commonly used pharmaceuticals, belonging to different therapeutical classes (analgesics and non-steroidal anti-inflammatories (NSAIDs), lipid regulators, psychiatric drugs, anti-histamines, anti-ulcer agents, antibiotics and beta-blockers) have been determined. Simultaneously, the macroinvertebrate community status of the same points has been also studied. Hazard quotient indexes have been estimated for the most representative compounds as the ratio between concentrations and EC(50) reported values, for three bioassays commonly used in environmental toxicology, namely, fish, Daphnia and algae. Hazard indexes are obtained for each sample by summing up the hazard quotients of all the compounds present, and taking its average along the three sampling campaigns. In general, hazard quotients tend to increase when going downstream. Only those points located most upstream of the two rivers can be qualified under low risk for the three bioassays. The most sensitive bioassay seems to be algae, followed by Daphnia and fish. Log-transformed hazard indexes show fairly good inverse correlations (r=-0.58 to -0.93, p<0.05) with Shannon diversity indexes of macroinvertebrates, determined from both densities and biomasses. Best correlations are obtained for Daphnia based hazard indexes, as expected from its taxonomical proximity to macroinvertebrates. The abnormal correlation behaviour found in one point located in the Anoia River is explained by the presence of other previously reported pollutants of industrial origin, generated by the nearby existing industry.

Acclimated biomass that degrades Sulfonated Naphthalene Formaldehyde Condensate

A number of aerobic species were isolated from textile industry activated sludge wastewater. The bacterial consortium was acclimated during seven days before testing its capacity of Sulfonated Naphthalene-Formaldehyde Condensate (SNFC) recalcitrant compound degradation. SNFC's degradation was evaluated by using different techniques including: vapour pressure osmometry, spectroscopy UV-Visible and Chemical Oxygen Demand (COD). The degradation of SNFC by acclimated bacterial consortium was determined by monitoring the decrease of absorbance and of COD at wavelength 288 nm. We were able to deduce that biodegradation of SNFC involves two steps: cleavage of CH2 bridges and the degradation of the aromatic nuclei. The bacteria species community that was able to degrade SNFC consisted of aerobic Gram-negative rods belonging to the Pseudomonadaceae family. The strains were identified as Bukholderia cepacia, Brevundimonas vesicularis, Pseudomonas stutzeri, Ralostonia picketti, Shewanella putrefaciens, Sphingomonas paucimobilis and Agrobacterium radiobacter.

The reactor design and comparison of Fenton, electro-Fenton and photoelectro-Fenton processes for mineralization of benzene sulfonic acid (BSA)

A new approach for promoting ferric reduction efficiency using a different electrochemical cell and the photoelectro-Fenton process has been developed. The use of UVA light and electric current as electron donors can efficiently initiate the Fenton reaction. Benzene sulfonic acid (BSA) was the target compound in this study. The parameters investigated to evaluate the reactor design include the electrode working area, electrode distance, energy consumption. Furthermore, the study also contains the intermediates and the mineralization efficiency of electrolysis, Fenton, electro-Fenton and photoelectro-Fenton process. Oxalic acid, the major intermediate of aromatic compound degradation, can complex with ferric ions. Meanwhile, a double cathode reactor could increase the current efficiency by 7%, which would translate to greater ferrous production and a higher degradation rate. Although the current efficiency of an electrode distance 5.5 cm device is 19% higher than 3.0 cm, results show that after 2 h of electrolysis the electronic expense using an electrode gap of 5.5 cm is much higher than 3.0 cm. The final TOC removal efficiency was 46, 64 and 72% using the Fenton, electro-Fenton and photoelectron-Fenton processes, respectively.

Microtox toxicity test: detoxification of TNT and RDX contaminated solutions by poplar tissue cultures

Poplar (Populus deltoidesxnigra DN34) tissue cultures removed 2,4,6-trinitrotoluene (TNT) from an aqueous solution in five days, reducing the toxicity of the solution from highly toxic Microtox EC value to that of the control. 1,3,5-Trinitro-1,3,5-triazacyclohexane (RDX) was taken up by the plant tissue cultures more slowly, but toxicity reduction of the solution was evident. The measurement of toxicity reduction of aqueous solutions containing TNT and RDX was performed using a novel methodology developed for use with the Microtox testing system. Radiolabeled TNT and RDX were used to confirm removal of explosives from hydroponic solutions containing plant tissue cultures and to verify that toxicity did not change in solutions where no plant cultures were present (positive controls). High Performance Liquid Chromatography (HPLC) and Liquid Scintillation Counter (LSC) measurements confirmed removal of TNT and RDX from solutions containing poplar plant tissue cultures and constancy of the plant-free controls. In addition, metabolites were identified in remediated solutions by HPLC, confirming the mechanism by which plants can remediate groundwater, surface water, and soil solutions.

Oxidation of two organophosphorous insecticides by the photo-assisted Fenton reaction

The photocatalytic degradation of two selected insecticides (dimethoate and methyl parathion) has been studied using the photo-assisted Fenton reaction. The degradation kinetics were studied under different conditions such as iron's and oxidant's concentration, temperature and inorganic ions. The degradation rates proved to be strongly influenced by these parameters. The replacement of hydrogen peroxide with peroxydisulfate was also tested in a photo-Fenton-like reaction. This system achieved high degradation rates of the selected compounds. Intermediate products formed during photocatalytic treatment were identified by means of solid-phase extraction (SPE) coupled to gas chromatography-mass spectroscopy techniques (GC-MS). Eight possible by-products were identified for parathion methyl and three for dimethoate formed through mainly oxidation and dealkylation reactions. Mineralization studies showed also that the photo-Fenton and the photo-Fenton-like systems are able to achieve mineralization of the insecticides. However, complete detoxification is achieved only in the presence of the photo-Fenton reagent.

Comparison of sulfonated and other micropollutants removal in membrane bioreactor and conventional wastewater treatment

Membrane bioreactors (MBRs) were compared with conventional activated sludge systems (CAS) for micropollutant degradation, in laboratory-scale spiking experiments with synthetic and real domestic wastewater. The target micropollutants were polar in nature and represented a broad range in biodegradability. The experimental data indicated that MBR treatment could significantly enhance removal of the micropollutants 1,6- and 2,7-naphthalene disulfonate (NDSA) and benzothiazole-2-sulfonate. 1,5-NDSA, EDTA and diclofenac were not removed in either the MBR or the CAS. The other compounds were equally well degraded in both systems. For 1,3-naphthalene disulfonate, the existence of a minimum threshold level for degradation could be demonstrated. Although MBRs could not always make a difference in the overall removal efficiencies achieved, they showed reduced lag phases for degradation and a stronger memory effect, which implies that they may respond quicker to variable influent concentrations. Finally, micropollutant removal also turned out to be less sensitive to system operational variables.