As the environment preservation gradually becomes a matter of major social concern and more strict legislation is being imposed on effluent discharge, more effective processes are required to deal with non-readily biodegradable and toxic pollutants. Synthetic organic dyes in industrial effluents cannot be destroyed in conventional wastewater treatment and consequently, an urgent challenge is the development of new environmentally benign technologies able to mineralize completely these non-biodegradable compounds. This review aims to increase the knowledge on the electrochemical methods used at lab and pilot plant scale to decontaminate synthetic and real effluents containing dyes, considering the period from 2009 to 2013, as an update of our previous review up to 2008. Fundamentals and main applications of electrochemical advanced oxidation processes and the other electrochemical approaches are described. Typical methods such as electrocoagulation, electrochemical reduction, electrochemical oxidation and indirect electro-oxidation with active chlorine species are discussed. Recent advances on electrocatalysis related to the nature of anode material to generate strong heterogeneous OH as mediated oxidant of dyes in electrochemical oxidation are extensively examined. The fast destruction of dyestuffs mediated with electrogenerated active chlorine is analyzed. Electro-Fenton and photo-assisted electrochemical methods like photoelectrocatalysis and photoelectro-Fenton, which destroy dyes by heterogeneous OH and/or homogeneous OH produced in the solution bulk, are described. Current advantages of the exposition of effluents to sunlight in the emerging photo-assisted procedures of solar photoelectrocatalysis and solar photoelectro-Fenton are detailed. The characteristics of novel combined methods involving photocatalysis, adsorption, nanofiltration, microwaves and ultrasounds among others and the use of microbial fuel cells are finally discussed.

Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods. An updated review

A review on emerging contaminants in wastewaters and the environment: current knowledge, understudied areas and recommendations for future monitoring.

Occurrence of pharmaceutical compounds in urban wastewater: Removal, mass load and environmental risk after a secondary treatment—A review

More than 2,100 chemically defined organic chemicals are listed in the Research Institute of Fragrance Materials/Flavor and Extract Manufacturers' Association (RIFM/FEMA) Database that are used as ingredients of fragrances for consumer products. An approach was developed for prioritizing these fragrance materials for aquatic risk assessment by first estimating the predicted environmental concentration (PEC) of these fragrance materials in the aquatic environment based upon their physicochemical properties and annual volume of use. Subsequently, an effect level was predicted with a general quantitative structure-activity relationship (QSAR) for aquatic toxicity, and a predicted no-effect concentration (PNEC) was calculated from this effect level by using an assessment factor (AF) that accounts for uncertainty in the toxicity QSAR prediction. A conservative AF of 10(6) was applied to the endpoint predicted by the QSAR to provide an adequate margin of safety in the calculation of the PNEC. The PEC was compared to the PNEC to characterize the risk to freshwater aquatic organisms (e.g., Daphnia magna and Pimephales promelas). If the ratio of PEC to PNEC was below one, the material was considered to have negligible environmental risk and to be acceptable for the aquatic environment at current use levels. If this ratio exceeded one, the PNEC was refined by using more specific QSAR models (Ecological Structure-Activity Relationships [ECOSAR]). If the ratio continued to exceed one, the material became a candidate for further aquatic risk assessment procedures, which involve iterative steps to refine the PEC, the PNEC, or both by using measured ecotoxicological endpoints. Prioritization for this latter process can be based upon the magnitudes of the estimated PEC:PNEC ratios. When using the first tier of this approach, only 568 of 2,141 fragrance materials (26.5%) in the RIFM/FEMA Database had PEC:PNEC ratios greater than one. This percentage decreased to only 164 materials (7.7%) when PNECs were derived with ECOSAR. Comparison of predicted PECs and PNECs with those based upon measured data confirmed the conservatism and low risk for type I errors associated with the framework. These combined exercises demonstrated the ability of this highly precautionary risk-based screening approach to quickly prioritize a large number of materials without benefit of experimental ecotoxicological or fate data.

A framework for prioritizing fragrance materials for aquatic risk assessment.

Occurrences and removal of pharmaceuticals and personal care products (PPCPs) in drinking water and water/sewage treatment plants: A review

The objective of this study was to investigate the fate and removal of triclosan (TCS; 5-chloro-2-[2,4-dichloro-phenoxy]-phenol), an antimicrobial agent used in a variety of household and personal-care products, in wastewater treatment systems. This objective was accomplished by monitoring the environmental concentrations of TCS, higher chlorinated derivatives of TCS (4,5-dichloro-2-[2,4-dichloro-phenoxy]-phenol [tetra II]; 5,6-dichloro-2-[2,4-dichloro-phenoxy]-phenol [tetra III]; and 4,5,6-trichloro-2-(2,4-dichloro-phenoxy)-phenol [penta]), and a potential biotransformation by-product of TCS (5-chloro-2-[2,4-dicholoro-phenoxy]-anisole [TCS-OMe]) during wastewater treatment. These analytes were isolated from wastewater by using a C18 solid-phase extraction column and from sludge with supercritical fluid CO2. Once the analytes were isolated, they were derivatized to form trimethylsilylethers before quantitation by gas chromatography-mass spectrometry. Recovery of TCS from laboratory-spiked wastewater samples ranged from 79 to 88% for influent, 36 to 87% for final effluent, and 70 to 109% for primary sludge. Field concentrations of TCS in influent wastewater ranged from 3.8 to 16.6 microg/L and concentrations for final effluent ranged from 0.2 to 2.7 microg/L. Removal of TCS by activated-sludge treatment was approximately 96%, whereas removal by trickling-filter treatment ranged from 58 to 86%. The higher chlorinated tetra-II, tetra-III, and penta closans were below quantitation in all of the final effluent samples, except for one sampling event. Digested sludge concentrations of TCS ranged from 0.5 to 15.6 microg/g (dry wt), where the lowest value was from an aerobic digestion process and the highest value was from an anaerobic digestion process. Analysis of these results suggests that TCS is readily biodegradable under aerobic conditions, but not under anaerobic conditions. The higher chlorinated closans were near or below the limit of quantitation in all of the digested sludge samples. Based on results from this study, the chlorinated analogues and biotransformation by-product of TCS are expected to be very low in receiving waters and sludge-amended soils.

Measurement of triclosan in wastewater treatment systems

Environmental fate of Triclosan in the River Aire Basin, UK.

The concentrations and removals of 16 fragrance materials (FMs) were measured in 17 U.S. and European wastewater treatment plants between 1997 and 2000 and were compared to predicted values. The average FM profile and concentrations in U.S. and European influent were similar. The average FM profile in primary effluent was similar to the average influent profile; however, the concentration of FMs was reduced by 14.6−50.6% in primary effluent. The average FM profile in final effluent was significantly different from the primary effluent profile and was a function of the design of the wastewater treatment plant. In general, the removal of sorptive, nonbiodegradable FMs was correlated with the removal of total suspended solids in the plant, while the removal of nonsorptive, biodegradable FMs was correlated with 5-day Biological Oxidation Demand removal in the plant. The overall plant removal (primary + secondary treatment) of FMs ranged from 87.8 to 99.9% for activated sludge plants, 58.6−99.8% for carousel p...

Removal of fragrance materials during U.S. and European wastewater treatment.

An analytical method was developed and used to measure trace levels of fragrance materials (FMs) in municipal wastewater and treated wastewater. Sixteen FMs were selected as analytes because of their wide range of physical chemical properties. The analytical method included the use of nine perdeuterated FMs as internal standards, a high-flow C18 speed disk for the extraction of FMs from aqueous matrices, and an accelerated solvent extraction system for the extraction of FMs from solid matrices. For aqueous matrices, average FM recoveries (relative to the perdeuterated FM internal standard) were 97−115%, with limits of quantitation ranging from 0.5 to 35 ng/L. For activated sludge solids and primary influent solids, the average FM recovery from the extraction procedure was 81%. Concentrations and removal of FMs at an activated sludge and a trickling filter wastewater treatment plant were determined in the U.S. FM influent concentrations ranged from 0.3 to 154 μg/L, while FM effluent concentrations ranged f...

Trace Analysis of Fragrance Materials in Wastewater and Treated Wastewater

An extensive monitoring study was conducted to determine the fate of linear alkylbenzene sulfonate (LAS) during wastewater treatment and in the environment. Results showed that LAS was highly removed during activated sludge (99.3 ± 0.6%), lagoon (98.5 ± 1.8%), oxidation ditch (98.0 ± 4.2%), and rotating biological contact (96.2 ± 6.1%) treatment, with poorer removals observed at trickling filter (77.4 ± 15.5%) facilities. Concentrations of LAS in anaerobically digested sludge (10,462 ± 5170 μg/g) were one to two orders of magnitude greater than those observed for aerobically digested sludge (152 ± 119 μg/g), illustrating that LAS is rapidly degraded during aerobic sludge treatment. Receiving water concentrations of LAS in rivers of low effluent dilution were generally < 50 μg/L. Elevated river sediment concentrations of LAS were observed only below the outfall of trickling filter treatment plants (59.7-182.1 μg/g). Alkyl chain lengths of LAS averaged 12.0 carbon units in most environmental compartments, with the exception of sludge solids and river sediments, in which an enrichment of longer chain lengths was observed. Measured concentrations of LAS in river waters under critical low flow conditions were in agreement with PG-GRiDS model predictions [5], thus supporting the validity of the modeling approach.

W.S. Eckhoff

Papers

Measurement of triclosan in wastewater treatment systems

Environmental fate of Triclosan in the River Aire Basin, UK.

Removal of fragrance materials during U.S. and European wastewater treatment.

Trace Analysis of Fragrance Materials in Wastewater and Treated Wastewater

Fate of linear alkylbenzene sulfonate in the environment