UV/H2O2 chemical oxidation for high loaded effluents: a degradation kinetic study of LAS surfactant wastewaters

Surfactants in aquatic and terrestrial environment: occurrence, behavior, and treatment processes

Surfactants belong to a group of chemicals that are well known for their cleaning properties. Their excessive use as ingredients in care products (e.g., shampoos, body wash) and in household cleaning products (e.g., dishwashing detergents, laundry detergents, hard-surface cleaners) has led to the discharge of highly contaminated wastewaters in aquatic and terrestrial environment. Once reached in the different environmental compartments (rivers, lakes, soils, and sediments), surfactants can undergo aerobic or anaerobic degradation. The most studied surfactants so far are linear alkylbenzene sulfonate (LAS), quaternary ammonium compounds (QACs), alkylphenol ethoxylate (APEOs), and alcohol ethoxylate (AEOs). Concentrations of surfactants in wastewaters can range between few micrograms to hundreds of milligrams in some cases, while it reaches several grams in sludge used for soil amendments in agricultural areas. Above the legislation standards, surfactants can be toxic to aquatic and terrestrial organisms which make treatment processes necessary before their discharge into the environment. Given this fact, biological and chemical processes should be considered for better surfactants removal. In this review, we investigate several issues with regard to: (1) the toxicity of surfactants in the environment, (2) their behavior in different ecological systems, (3) and the different treatment processes used in wastewater treatment plants in order to reduce the effects of surfactants on living organisms.

The degradation of linear alkylbenzene sulfonate (LAS) in the presence of light and natural biofilms: the important role of photosynthesis

Photosynthesis of algae usually changes the chemical conditions of microenvironment in natural waters. However, few studies have been carried out to examine the effects of diurnal variation and photosynthesis on behavior of organic pollutants in aquatic environments. In this study, linear alkylbenzene sulfonate (LAS) was selected as a representative of non-persistent organic pollutants to investigate the degradation of this type of pollutants in the presence of light and natural biofilms by laboratory batch experiments, with special emphasis on the effect of photosynthesis of the biofilms. The maximum decrease of LAS was observed in the coexistence of both illumination and fully active biofilms, and about 75% of the LAS were removed after a 36-h degradation experiment. The removal of LAS was found to be dominated by photosynthesis of the biofilms, with lesser roles attributed to biodegradation and adsorption by the biofilms, and the role of direct photolysis was negligible. The production of some reactive oxygen species might account for the role of photosynthesis in decomposing the LAS. The study confirms the important roles of algae biofilms and their photosynthesis in determining the fate of organic pollutants in aquatic environments.

H2O2/UV-C treatment of textile preparation wastewater: kinetic investigation on alternative combinations of commercial textile preparation auxiliaries

Four different textile preparation effluents were simulated to examine the applicability of the hydrogen peroxide/ultraviolet-C (H2O2/UV-C) advanced oxidation process for the treatment of real textile preparation (desizing, scouring and bleaching) wastewater bearing the non-ionic surfactant nonyl phenol decaethoxylate (NP-10). In the absence of any textile preparation chemical, NP-10 degradation was complete in 15 min (rate coefficient: 0.22 min(-1)) accompanied by 78% chemical oxygen demand (COD) (rate coefficient: 0.026 min(-1)) and 57% total organic carbon (TOC) (rate coefficient: 0.014 min(-1)) removals achieved after 60 min photochemical treatment. H2O2 consumption rates were not significantly affected by the introduction of carbonate and chloride ions (average rate coefficient: 0.032 min(-1)) at pH values <11.5, above which H2O2 dissociation to its conjugate base HO2(-) became pronounced. The organic, phosphonate-based sequestering agents competed with NP-10 for UV-C light absorption and HO* radicals. H2O2/UV-C oxidation of the simulated textile preparation effluent containing 3.0 g L(-1) Cl(-), 1.5 g L(-1) NaOH and 1.0 g L(-1) diethylenetriamine pentamethylene phosphonic acid (DTPMP) resulted in the worst treatment performance due to its high pH and organic carbon content. For this textile preparation effluent, NP-10 abatement was complete in 100min (rate coefficient: 0.018 min(-1)), while COD and TOC removals dropped down to only 16% and 8%, respectively, achieved after 60 min treatment. The highest H2O2/UV-C oxidation efficiency resulting in 34% COD and 28% TOC removals was obtained for the simulated textile preparation effluent comprising of 3.0 g L(-1) Cl(-), 1.5 g L(-1) NaOH and 1.0 g L(-1) 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP). For this textile preparation effluent, NP-10 degradation was complete after 50 min (rate coefficient: 0.061 min(-1)) exposure to H2O2/UV-C treatment.

Determination of linear alkylbenzenesulfonates (LASs) in sewage sludge and carrots by capillary electrophoresis--UV detection

A method based on capillary zone electrophoresis has been proposed in order to separate and determine four groups of linear alkylbenzenesulfonates in sewage sludge and carrots. The separation was carried out in a silica capillary of 50 cm x 75 microm at 25 kV using a sodium borate buffer solution of 100 mM which includes 40% of acetonitrile. The detection was made by UV-Vis diode array detector. Precision, accuracy, linearity, detection and quantification limits of the method were determined. Finally, the method was applied to analyse samples of sewage sludge from a wastewater depuration station in Crispijana (Alava, Spain) and carrots sown in soils spiked with this sludge. In this case, it is necessary to carry out an extraction step for its determination. The extraction was carried out by solid phase extraction with a C18 cartridge. The solid phase extraction (SPE) parameters were also optimized and the recoveries were calculated. Samples of sewage sludge were analysed weekly during two years and, in all cases, results under legal limits for their use in agriculture were obtained.

Degradation of xenobiotics originating from the textile preparation, dyeing, and finishing industry using ozonation and advanced oxidation

Effluents from textile preparation, dyeing, and finishing processes contain high concentrations of biologically difficult-to-degrade or even inert auxiliaries. Under these circumstances, it most often becomes inevitable to apply energy-intense and hence "imperative" treatment technologies (so-called advanced oxidation processes, AOPs) to achieve an acceptable reduction in the organic content of the effluent, thereby improving the biocompatibility of the originally refractory wastewater. The present experimental study focused on three problematic dyehouse effluent streams in order to alleviate the problem of toxicity and recalcitrance arising from the use of certain textile chemicals at source. For that purpose, the textile preparation stage was simulated by a nonionic surfactant (NS), the polyamide dyeing stage by a synthetic tannin (syntan; ST), and an aqueous biocidal finishing (BF) solution was employed to mimic typical textile finishing effluent. Synthetic effluent streams bearing NS, ST, or BF were subjected to treatment with different, well-established AOPs (ozonation at varying pH; advanced oxidation with H(2)O(2)/UV-C at varying H(2)O(2) concentrations) in order to degrade the active ingredients of the auxiliary formulations, thereby eliminating their toxicity and recalcitrance. Baseline experiments were conducted in order to optimize AOP conditions that were consecutively applied to observe changes in the originally poor effluent biodegradability and high toxicity. Obtained experimental findings revealed that (i) the COD content of NS could be reduced by at least 50% after H(2)O(2)/UV-C treatment at pH 9.0 accompanied by a nearly twofold improvement in its already fair biodegradability; (ii) the inhibitory effect of the biochemically reluctant ST on heterotrophic biomass was completely eliminated upon ozonation (dose=900 mg h(-1)) at pH 3.5; and (iii) the microbial toxicity exerted by BF totally disappeared after ozonation (dose=600 mg h(-1)) at pH 7.2. However, the achievement of detoxification and/or biodegradability improvement was accompanied with high electrical energy requirements.

Solar-chemical treatment of groundwater contaminated with petroleum at gas station sites: ex situ remediation using solar/TiO(2) photocatalysis and Solar Photo-Fenton

Groundwater samples contaminated by BTEX (benzene, toluene, ethylbenzene, xylene isomers and TPHs (total petroleum hydrocarbons) were treated with advanced oxidation processes (AOPs), such as TiO(2) photocatalysis and Fe(2+)/H(2)O(2) exposed to solar light (37 degrees N and 128 degrees E) with an average intensity of 1.7 mW/cm(2) at 365 nm. These AOP processes showed feasibility in the treatment of groundwater contaminated with BTEX, TPH and TOC (Total Organic Carbon). Outdoor field tests showed that the degradation efficiency of each contaminant was higher in the Fe(2+)/H(2)O(2) system without solar light compared to the TiO(2)/solar light and H(2)O(2)/solar light systems. However, the TiO(2)/solar light and the Fe(2+)/H(2)O(2)/solar light systems showed significantly enhanced efficiencies in the degradation of BTEX, TPH and TOC with the additional use of H(2)O(2). Near complete degradation of BTEX and TPH was observed within 2 and 4 hrs, respectively, however, that of TOC was slower. Without pretreatment of the groundwater, fouling of the TiO(2), due to the ionic species present, was observed within 1 hr of operation, which resulted in the inhibition of further BTEX, TPH and TOC destruction. The degradation rate of n-alkanes with carbon numbers ranging from C10 to C15 was relatively greater than that of n-alknaes with carbon numbers ranging from C16 to C20. From this work, the AOP process (Fe(2+)/H(2)O(2)/solar light and TiO(2)/H(2)O(2)/solar light) illuminated with solar light was identified as an effective ex situ technique in the remediation of groundwater contaminated with petroleum.