In the present study, the treatability of a metal plating wastewater containing complexed metals originating from the nickel and zinc plating process by electrocoagulation using stainless steel ...electrodes was experimentally investigated. The study focused on the effect of important operation parameters on electrocoagulation process performance in terms of organic complex former, nickel and zinc removals as well as sludge production and specific energy consumption. The results indicated that increasing the applied current density from 2.25 to 9.0
mA/cm
2 appreciably enhanced TOC removal efficiency from 20% to 66%, but a further increase in the applied current density to 56.25
mA/cm
2 did not accelerate TOC removal rates. Electrolyte concentration did not affect the process performance significantly and the highest TOC reduction (66%) accompanied with complete heavy metal removals were achieved at the original chloride content (≈1500
mg Cl/L) of the wastewater sample. Nickel removal performance was adversely affected by the decrease of initial pH from its original value of 6. Optimum working conditions for electrocoagulation of metal plating effluent were established as follows: an applied current density of 9
mA/cm
2, the effluent's original electrolyte concentration and pH of the composite sample. TOC removal rates obtained for all electrocoagulation runs fitted pseudo-first-order kinetics very well (
R
2
>
92–99).
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► Phenol was oxidizedvia persulfate, hydrogen peroxide and peroxymonosulfate/UV-C processes. ► Complete phenol and TOC removals were achieved. ► Several oxidation products of phenol ...were identified via GC/MS and HPLC analyses. ► Dimerization products were evidenced for both studied oxidation processes. ► A hydroxycyclohexadienyl- and phenoxyl radical-initiated degradation pathway was postulated.
UV-C photo-assisted persulfate (PS), hydrogen peroxide (H2O2) and peroxymonosulfate (PMS) oxidation processes were evaluated and compared for aqueous phenol degradation. The effect of initial oxidant concentration on PS/UV-C, H2O2/UV-C and PMS/UV-C treatment efficiencies was examined on the basis of phenol and total organic carbon (TOC) removals. Complete phenol degradation could be achieved under all examined reaction conditions with apparent phenol degradation rate constants varying between 0.069±0.002–0.382±0.003min−1 accompanied with complete TOC removals (⩾97%) under optimized PS (20mM), H2O2 (30mM) and PMS (20mM) concentrations. Hydroquinone, catechol and benzoquinone were quantified during H2O2/UV-C and PMS/UV-C treatment of phenol verifying a HO-dominated oxidation pathway. During PS/UV-C oxidation, the identification of benzoquinone and 3-phenoxyphenol verified the hydroxycyclohexadienyl radical and phenoxyl radical pathways in SO4- mediated phenol oxidation.
Herein, the main aim is to study the influence of the materials’ structural properties on their ecotoxicological properties. The acute toxicity of the bulk (molybdenum disulfide) MoS2 and 2D ...nanosheet MoS2 was investigated using organisms of four different taxonomic groups. Ultrasound-assisted liquid-phase exfoliation method was used for preparing 2D nanosheets from bulk MoS2. Bulk and nanosheet MoS2 were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analyses. The acute toxicity of the bulk and nanosheet MoS2 catalysts was evaluated with four different bioassays using the test organisms Vibrio fischeri (a marine photobacterium), Pseudokirchnerialla subcapitata (a freshwater microalga), Daphnia magna (a freshwater crustacean) and the freshwater duckweed Spirodela polyrhiza. The toxic effect of the materials depended on their structural/size features and the type/sensitivity of the test organism. Generally speaking, bulk MoS2 was more toxic than its nanosheet form. The freshwater crustacean Daphnia magna appeared to be the most suitable, easy-to-handle, and at the same time sensitive test organism for bulk and nanosheet MoS2 among the tested organisms.
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•Nanosheet MoS2 prepared from bulk MoS2 by ultrasound-assisted exfoliation method.•Acute toxicity of bulk and nanosheet MoS2 was examined using four bioassays.•Bulk MoS2 was more toxic than the nanosheet form.•Toxicity depended on MoS2 structure and test organism.•Daphnia magna appeared to be the most suitable test organism.
The study evaluated the co-metabolism of nonylphenol polyethoxylate (NPEO) within a main substrate stream subjected to biodegradation in an activated sludge system. Peptone mixture simulating sewage ...was selected as the synthetic substrate. As a novel approach, the NPEO concentration was magnified to match the COD level of the peptone mixture, so that co-metabolism could be evaluated by respirometry and modeling. A sequencing batch reactor (SBR) set-up at high sludge age to also allow nitrification was operated for this purpose. A long acclimation phase was necessary to start NPEO biodegradation, which was completed with 15% residual by-products. Modeling of respirometric data could identify COD fractions of NPEO with corresponding process kinetics for the first time, where the biodegradation of by-products could be interpreted numerically as a hydrolysis mechanism. Nonylphenol diethoxylate (NP2EO) was observed as the major by-product affecting the biodegradation of NPEO, because NPEO and NP2EO accounted for 60 to 70% of the total soluble COD in the solution during the course of biological reactions. The co-metabolism characteristics basically defined NPEO as a substrate, with no appreciable inhibitory action on the microbial culture both in terms of heterotrophic and autotrophic activities.
Denim is a cotton fabric specifically used to manufacture jeans. Denim processing generates complex effluents with high levels of pumice stone, color and chemical oxygen demand (COD). There is ...therefore a need for advanced treatment methods to limit pollution of natural waters. Here, we hypothesized that Fenton oxidation, a method using Fe
2+
and H
2
O
2
, could replace the traditional step of activated sludge treatment. We studied a daily composite sample at laboratory scale for preliminary settling, chemical settling and Fenton oxidation. We found that pumice stone can be effectively controlled by preliminary settling with partial COD removal and limited color removal. Chemical treatment improved COD removal, but color reduction still remained partial. Fenton oxidation decreased color below visual detection after 5 min and COD decreased to 110 mg/L after 30 min. These findings surpassed the performances of activated sludge treatment.
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•Removal of organic matter and antibiotic resistance in tertiary urban wastewater.•Highest organic carbon removals with UV-C-driven oxidation processes.•Highest inactivation of ...resistant bacteria with UV-C treatment.•Genomic and plasmid DNA persisted UV-C treatment.•No genomic and plasmid DNA detected for UV-C-driven oxidation processes.
Antibiotic resistance is frequently being observed in treated urban effluents as an alarming wastewater treatment issue and health risk. The potential of UV-A-assisted iron-based and UV-C-driven advanced oxidation processes to inactivate the ABR E. coli J53 strain bacteria and its aphA (kanamycin resistance gene) and tetA (tetracycline resistance gene) located on the plasmid RP4 was investigated in real tertiary treated urban wastewater. Besides inactivation performance, dissolved organic carbon (DOC) removals were also followed to evaluate the mineralization degree that could be achieved by the proposed photochemical/photocatalytic treatment systems. For UV-A-assisted Fenton/Fenton-like processes, antibiotic resistance and DOC removals (≈20 %) were rather limited. UV-C activation of the oxidants hydrogen peroxide (HP), persulfate (PS) and peroxymonosulfate (PMS) were the key photochemical advanced oxidation processes for efficient inactivation of multi-resistant E. coli bacteria (>6.5-log reduction) and gene copies (>3.0-log reduction) as well. Besides, 31 %, 40 % and 59 % DOC removals were achieved at a UV dose of 0.45 W/m2 for 2.0 mM HP-, PMS- and PS/UV-C treatments, respectively.
Treatability of synthetic azo dye production wastewaters from Acid Blue 193 and Reactive Black 39 production and real Reactive Black 39 production effluent via Photo-Fenton-like process was ...investigated. Response surface methodology was employed to assess individual and interactive effects of critical process parameters (Fe
3+, H
2O
2 concentrations; initial chemical oxygen demand (COD) and reaction time) on treatment performance in terms of color, COD and total organic carbon (TOC) removal efficiencies. Optimized reaction conditions for synthetic AB 193 production wastewater were established as Fe
3+
=
1.5
mM; H
2O
2
=
35
mM for CODs
≤
200
mg/L and a reaction time of 45
min. Under these conditions, 98% color, 78% COD and 59% TOC removals were experimentally obtained and fitted the model predictions well. The same model also described the treatment of synthetic Reactive Black 39 production wastewater satisfactorily. Experimentally achieved removals were considerably lower than model predictions for real Reactive Black 39 production effluent due to its high chloride content.
The application of layered double hydroxide (LDH) nanomaterials as catalysts has attracted great interest due to their unique structural features. It also triggered the need to study their fate and ...behavior in the aquatic environment. In the present study, Zn-Fe nanolayered double hydroxides (Zn-Fe LDHs) were synthesized using a co-precipitation method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and nitrogen adsorption-desorption analyses. The toxicity of the home-made Zn-Fe LDHs catalyst was examined by employing a variety of aquatic organisms from different trophic levels, namely the marine photobacterium
, the freshwater microalga
, the freshwater crustacean
, and the duckweed
. From the experimental results, it was evident that the acute toxicity of the catalyst depended on the exposure time and type of selected test organism. Zn-Fe LDHs toxicity was also affected by its physical state in suspension, chemical composition, as well as interaction with the bioassay test medium.
UV-A (near-UV), UV-C (short-UV) and visible-light assisted Fenton-like treatment of Bisphenol A (BPA) was investigated in pure water and raw freshwater samples spiked with BPA. Treatment performances ...were evaluated in terms of BPA degradation, dissolved organic carbon (DOC) removal and H2O2 consumption rates. Complete BPA degradation accompanied with significant DOC removal was achieved for all studied processes. Increasing the initial solution pH only exhibited a negative effect on treatment efficiencies when bicarbonate alkalinity was used for pH adjustment, whereas the raw freshwater matrix and irradiation type also influenced oxidation rates appreciably. Acute toxicity analysis employing Vibrio fischeri revealed that the inhibitory effect of BPA decreased significantly during the course of Photo-Fenton-like treatment. Several transformation products could be identified via HPLC and GC–MS analyses including hydroxylated phenolic compounds (hydroquinone; 2-methoxy, 1-4-benzenediol; 4-isopropenylphenol; 4′-hydroxy-acetophenone; 1-(4-cyclohexylphenyl) ethanone; 4-isopropylenecatechol; 4-4′-dihydroxybenzophenone; 4-ethyl,1,3-benzenediol), as well as the ring opening products hexanoic acid methyl ester, fumaric, succinic and oxalic acids. A reaction pathway featuring hydroxylation, dimerization and ring opening steps is proposed.
•Photo-Fenton-like treatment of BPA was investigated.•Effect of irradiation type and water matrix was studied.•Complete BPA degradation accompanied with high DOC removals was achieved.•Acute toxicity was mainly attributable to the presence of the mother compound BPA.•Several coupling and ring opening products were identified via HPLC and GC–MS.
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