124 research outputs found
Degradation of perfluorooctane sulfonate via in situ electro-generated ferrate and permanganate oxidants in NOM-rich source waters
No full textA novel process involving the in situ electrochemical generation of ferrate and permanganate oxidants, in circumneutral conditions, from low concentration aqueous iron (Fe2+) and manganese (Mn2+), is investigated for the treatment of the ubiquitous and highly recalcitrant micro-pollutant, perfluorooctane sulfonate (PFOS). The present study investigated the efficacy of both electro-oxidation (EO), and the simultaneous EO and ferrate/permanganate generation and oxidation, of PFOS as a potential drinking water treatment technology. While permanganate was shown to have little effect on PFOS removal, significantly increased degradation was observed when EO was coupled with ferrate generation and oxidation, significantly exceeding that of solely EO. From an initial concentration of 0.80 μM, final PFOS concentrations of 0.53 (±0.004), 0.43 (±0.01) and 0.27 (±0.01) μM were yielded during 10, 40 and 80 mA cm−2 electrolysis and an initial Fe2+ = 179 μM. In general, PFOS degradation rates increased with both increasing current density and initial Fe2+ concentration. Degradation was observed to follow mixed zero- and pseudo-first-order reaction kinetics for both the EO and simultaneous EO and ferrate oxidation. Finally, PFOS oxidation was not inhibited by the presence of low and high molecular weight organic scavenger species, and high concentrations of natural organic matter (NOM) improved PFOS removal due to hydrophobic interaction. Reduced ferrate species were also observed to increase NOM removal after electrolysis, by iron coagulant formation and subsequent flocculation
Combining magnetic ion exchange media and microsand before coagulation as pretreatment for submerged ultrafiltration: biopolymers and small molecular weight organic matter
No full textIn order to reduce the fouling of ultrafiltration (UF) systems caused by influent organic matter and microbial activities in the membrane tank, a novel pretreatment process has been evaluated involving the combination of magnetic ion exchange media (MIEX), microsand, and alum coagulation. Using a continuous flow bench-scale UF membrane apparatus and synthetic water, the influence of MIEX and microsand with alum pretreatment on membrane fouling was studied in comparison to a conventional pretreatment by alum alone. It was found that the continuous addition of low doses of MIEX and microsand substantially reduced (∼50%) membrane fouling for nearly 60 days of operation, both in terms of reversible and irreversible fouling. MIEX adsorption increased the removal of dissolved organic matter, particularly hydrophobic and proteinaceous substances, and some fractions of humic-type substances, while the addition of microsand increased the density of flocs, and thus improved the removal of flocs and microorganisms (with flocs) in the membrane tank. As a consequence, the UF membrane with the MIEX/microsand pretreatment had a much reduced cake layer and accumulated material within membrane pores; in particular, the cake layer had much less protein-type and polysaccharide-type substances
In-situ electrochemical generation of permanganate for the treatment of atrazine
No full textA novel process involving the simultaneous electrochemical oxidation and electrosynthesis of permanganate oxidant has been explored for the treatment of the triazine organic herbicide, atrazine. The electrochemical synthesis of permanganate in neutral pH conditions using low concentration manganese (Mn2+), analogous to levels found in some raw groundwater sources, and their subsequent effect on atrazine degradation were studied in bench-scale experiments. Permanganate synthesis was found to be largely unaffected by the operating current density (10, 40 and 80 mA cm−2) during electrolysis, indicating as mass transport controlled process. Under the same operating conditions, hydroxyl radical mediated oxidation was observed to degrade atrazine from an initial concentration of 9.27 µM (2 mg L−1), to 6.22, 4.88 and 2.36 µM after 120 min of electrolysis for 10, 40 and 80 mA cm−2 conditions. When 55 µM (3.0 mg L−1) Mn2+ was added to the water matrix, atrazine degradation increased, yielding final concentrations of 5.80, 3.66 and 2.17 µM, respectively. Atrazine degradation was found to be accurately described by pseudo-first-order reaction kinetics, with and without the enhanced oxidation by permanganate generation, as the concentration of hydroxyl radicals remained constant and comparatively high throughout electrolysis. Finally, the yielded second-order reaction rate constants of electrochemically generated permanganate, and dosed potassium permanganate, with atrazine were 9.79 and 8.35 M−1 s−1, respectively, whereby the latter degradation mechanism was kinetically limited and the former was under mass transfer control due to an extremely low permanganate-atrazine ratio. Finally, four primary oxidation by-products were observed to form in the reactions, including deethylatrazine, deisopropylatrazine and deethyldeisopropylatrazine
Insights into chemical regeneration of activated carbon for water treatment
No full textGranular activated carbon (GAC) adsorption has found wide application as a treatment process for the removal of natural organic matter, small organic compounds (e.g. pesticides), inorganic compounds (e.g. heavy metals), taste and odour compounds in water over many years. During GAC operation, contaminants are adsorbed and the carbon becomes progressively saturated over time, requiring periodic regeneration of the media to restore its capacity. Chemical regeneration has been identified as an effective alternative to off-site thermal regeneration, which is the most commonly practiced carbon regeneration technique for carbon exhausted by organic contaminants. Off-site thermal regeneration poses significant disadvantages as it is a time-consuming process and represents a significant operational cost (e.g. reduced productivity) and environmental (energy/CO2) burden to water utilities. Chemical regeneration can be performed on-site, either in situ or off-line, by exposing the spent (exhausted) GAC to a selected chemical, or a combination of chemicals, to remove the adsorbed contaminants. Prior research on chemical regeneration has been limited in extent, but has considered both organic and inorganic solutions. Despite a significant number of studies, a suitable regenerant solution for desorbing a wide range of aqueous contaminants in drinking water treatment has not been identified to-date. In this paper, we provide a critical review of the performance of alternative regenerant solutions for the chemical regeneration of GAC loaded with different organic contaminants
Simultaneous electrochemical oxidation and ferrate generation for the treatment of atrazine: A novel process for water treatment applications
No full textA novel process involving the simultaneous electrochemical-oxidation (EO) and electrosynthesis of ferrate has been investigated for the treatment of the commonly detected and recalcitrant pesticide, atrazine. The present study considered the electrosynthesis of ferrate, in neutral pH, using low concentration iron (Fe2+) representative of raw water levels and its subsequent effect on atrazine degradation. Ferrate synthesis was unaffected by current density (10–80 mA cm−2), indicating mass transport limitations. Synthesis was affected by the initial iron concentration, whereby 0.051, 0.108 and 0.332 mg L−1 was generated with an Fe2+ concentration of 0.5, 1.0 and 3.0 mg L−1, respectively. When operating under simultaneous EO and ferrate oxidation, atrazine degradation exceeded that of a solely EO process. From an initial concentration of 2.00 mg L−1, atrazine was degraded to 1.34, 1.05 and 0.51 mg L−1 during 10, 40 and 80 mA cm−2, characterised by pseudo-first-order kinetics. Degradation with electrochemically-generated ferrate could be described by second-order kinetics, and yielded a degradation rate constant of 23.5 M−1 s−1. The effect of natural organic matter (NOM) on atrazine degradation was also investigated. Ferrate was observed to be mostly scavenged by resorcinol, a representative NOM compound, having a second-order reaction rate constant of 9.71 × 102 M−1 s−1
Application of boron-doped diamond electrodes for the anodic oxidation of pesticide micropollutants in a water treatment process: a critical review
No full textBoron-doped diamond (BDD) electrodes have the greatest known oxygen overpotential range; a characteristic that has allowed the material to be well suited for electro-oxidation processes in aqueous media. When operating in a potential range of water decomposition, strongly oxidising hydroxyl radicals are formed while oxygen evolution is minimised. The majority of research studies undertaken to-date have focused on the application of BDDs for the remediation of wastewater contaminants, however there is an increasing need for a suitable technology to address recalcitrant micropollutants in a drinking water context. Pesticide micropollutants are widely detected in surface- and ground-waters and are of increasing concern. In this paper, the treatment of pesticides by BDD electro-oxidation is reviewed. Their degradation and mineralisation, as well as the effect of operating conditions, formation of intermediate by-products, reaction pathways and kinetics are summarized. In general, BDD electro-oxidation was found to be effective for the degradation of pesticides with the degradation performance proportional to the electrolytic current, due principally to the increased generation of ˙OH radicals. Most contaminants followed pseudo first-order reaction kinetics under mass transport limitations. Generally, the same aromatic and aliphatic by-products were formed through similar oxidation pathways. Finally, research gaps and potential future research topics are discussed
Chemical regeneration of granular activated carbon: preliminary evaluation of alternative regenerant solutions
No full textGranular activated carbon (GAC) is used in drinking water treatment plants worldwide to remove micro-pollutants such as pesticides. Early breakthrough of problematic micro-pollutants leads to frequent and costly thermal regeneration off-site. A potential alternative approach is to chemically regenerate GAC on-site (possibly in situ) with an appropriate solution capable of desorbing organic contaminants, having a range of physico-chemical properties. In this study, four types of regenerant solution were evaluated in batch tests for their ability to desorb five target contaminants. The solutions were: high purity water, sodium hydroxide, ethanol, and a mixture of sodium hydroxide and ethanol. The contaminants included: phenol and nitrobenzene, as representative aromatic compounds; clopyralid and metaldehyde, as poorly-adsorbed pesticides; and isoproturon, a well-adsorbed pesticide. Among the properties of the contaminants, their hydrophobicity and aqueous solubility had the most significant influence on the desorption efficiency. NaOH/CH3CH2OH was found to be more effective than individual solutions in desorbing the target contaminants, indicating an ability to desorb both hydrophobic and hydrophilic compounds. The NaOH/CH3CH2OH regenerant solution yielded desorption efficiencies in the range of approximately 40–90%, with the efficiency dependent on the contaminant. A thermodynamic study provided valuable fundamental information regarding the adsorption and desorption mechanisms, and the existence of two binding sites involving a weak physisorption and a stronger chemisorption-like interaction between the contaminants and the GAC
Towards microplastics contribution for membrane biofouling and disinfection by-products precursors: The effect on microbes.
No full textPublic awareness of plastic pollution and its impact on the ecosystem has increased rapidly. The microplastics in raw waters and their removal during drinking water treatment is receiving growing attention, but the impact on the efficiency of ultrafiltration has not been examined previously, especially in regard to the formation potential of disinfection by-products (DBPs-FP) in effluent water. In this study, two bench-scale continuous-flow ultrafiltration systems, with and without microplastics, were operated to examine the effect of microplastics on ultrafiltration. Results showed that the microplastics not only increased microbial growth, but also affected the microbial community (e.g. families Xanthobacteraceae, Sphingomonadaceae, Leptolyngbyaceae), which can promote the production of extracellular polymeric substances and nitrogen fixation, causing rapid membrane fouling. The formation potential of THM (TCM and BDCM) and N-DBP (TCNM) species in UF permeate increased with the presence of microplastics, due to changes in water quality. Statistical analysis indicated that tyrosine-like components (C3), ammonium (NH4+-N) and tryptophan-like component (C1) can be used as indicators of the DBPs-FP. This study provides new insights into the relationship between microplastics, membrane biofouling and DBPs-FP, and the potential adverse impact of microplastics on drinking water treatment
Direct generation of DBPs from city dust during chlorine-based disinfection
No full textChlorine-based disinfectants, such as sodium hypochlorite, are extensively used in our daily lives. In particular, during the recent Covid-19 pandemic and post-pandemic period, excessive amounts of chlorine-based disinfectants were used both indoors and outdoors to interrupt virus transmission. However, the interaction between disinfectants and city dust during the disinfection process has not been sufficiently evaluated. In this study, we conducted a comprehensive investigation into the intrinsic characteristics (e.g. morphology, size, elemental composition, and organic content, etc.) of dust collected from various indoor and outdoor areas. The results showed that the organic carbon content of indoor dust reached 6.14 %, with a corresponding measured dissolved organic carbon value of 4.17 ± 0.23 mg/g (normalized to the dust weight). Concentrations of regulated DBPs, resulting from the interaction between dust and NaClO, ranged from 57.78 ± 2.72 to 102.80 ± 22.63 µg/g for THMs and from 119.18 ± 6.50 to 285.14 ± 36.95 µg/g for HAAs (normalized to the dust weight). More significantly, using non-target analysis through gas chromatography quadrupole time-of-flight mass spectrometry (GC-qTOF-MS), we identified a total of 68, 89, and 87 types of halogenated DBPs from three typical indoor and outdoor sites (R-QH, C-JS, and W-BR, respectively). These unknown DBPs included compounds with higher toxicity compared to regulated DBPs. These findings highlight that city dust is a significant source of DBP generation during chlorine-based disinfection, posing potential harm to both the ecological environment and human health
Evaluation of a novel polyamide-polyethylenimine nanofiltration membrane for wastewater treatment: Removal of Cu2+ ions
No full textThis paper describes a novel approach for enhancing membrane technology for the removal of heavy metal cations in contaminated waters. A simple method of forming a positively charged polyamide (PA) nanofiltration (NF) membrane has been developed by attaching a layer of hyperbranched polyethylenimine (PEI) to the PA surface, involving the linking of PEI amino groups to the PA surface carboxyl groups. The nature of the PEI modified PA membrane, in terms of surface morphology, zeta potential and hydrophobicity was found to depend on the PEI molecular weight (MW), and the PEI concentration and membrane exposure time during preparation. In turn, the nature of the modified membrane determined its performance in terms of hydraulic flux and metal ion rejection. In tests using a model solution of 5 mg/L Cu2+ and a 70,000 MW PEI membrane the Cu rejection was >90%, with only a modest reduction in flux compared to blank water. The Cu2+ rejection was found to be a combination of electrostatic repulsion and adsorption, with the relative proportions depending on the nature of the PEI modified PA membrane. In addition, the Cu2+ rejection and membrane flux were found to be sustainable over repeated filtration cycles, and the rejection was not adversely affected by the presence of humic acid in solution (5 mg/L)
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