This work has evaluated the efficiency of two coagulants, aluminum sulfate (AS) and polyaluminum chloride (PACl), combined with the adsorption process using powdered activated carbon (PAC) on the removal of diclofenac (DCF), sulfamethoxazole (SMX), ethinylestradiol (EE2), estradiol (E2), estrone (E1), estriol (E3), and bisphenol-A (BPA) from low- and high-turbidity waters. The results have shown that the concomitant application of PAC and either coagulant has worsened the removal efficiency for all pharmaceuticals and endocrine disruptors tested, which might have occurred due to the covering of adsorption sites by aluminum hydroxide particles. In this configuration (coagulation in the presence of PAC, 10 mg L⁻¹), the best removal efficiency (∼40 %) was obtained for E1 and EE2 when AS was used as coagulant in contact times that varied from 13.5 to 23.5 min. When the coagulant was the PACl, contact times were lower (8.5 to 13.5 min) and the highest removal efficiency was observed for EE2 (∼52 %). When PAC was added as a pre-treatment (before addition of coagulant), the removal efficiency was greatly increased for all microcontaminants and the application of 2.5 mg L⁻¹of PAC with 120 min of contact led to removal efficiencies varying from 30 to 99.9 %.

The aim of the present study is to investigate the effects of operating conditions and establish the mechanism of xanthene dye removal from aqueous solutions by electrocoagulation (EC) using a batch-stirred cell operated under galvanostatic regime. The influence of the operating parameters such as: initial pH and dye concentration, electrolysis time, current density, electrode configuration, and electrical current type on the EC performances was investigated. EC tests were performed at current density values ranging from 45 to 109 A/m, initial dye concentrations ranged between 0.1 and 1 g/L, and initial pH values adjusted in the range from 3 to 9. The effects of several electrode configurations (aluminum–aluminum, mild steel–mild steel, and aluminum–mild steel) and current regimes (direct current and alternating pulsed current) on the removal efficiency and energy and material consumption are also discussed. Total organic carbon (TOC) analysis, UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and cyclic voltammetry (CV) were employed in order to elucidate the decolorization mechanism of Rhodamine 6G (R6G) dye by EC in aqueous solutions. With this aim in view, chemical coagulation tests were also carried out. The best performance was obtained when the EC process was conducted with iron-based electrode configuration in alternative pulse current (APC) mode. It was found that the removal of R6G is due to the co-precipitation of polymeric iron flocs with the phenyl-xanthene radicals remained in the bulk solution after the demethylation and deamination processes. Furthermore, the flocs are separated by flotation with the support of the molecular hydrogen generated at the cathode (in particular at relatively high values of current density) or by sedimentation.

The treatment of a non-biodegradable agrochemical wastewater has been studied by coupling of preliminary coagulation—flocculation step and further Fenton oxidation. High percentages of chemical oxygen demand (COD) removal (up to 58 %) were achieved in a first step using polyferric chloride as coagulant. This reduced significantly the amount of H₂O₂ required in the further Fenton oxidation. Using the stoichiometric amount relative to COD around 80 % of the remaining organic load was mineralized. The combined treatment allowed achieving the regional discharge limits of ecotoxicity at a cost substantially lower than the solution used so far where these wastewaters are managed as hazardous wastes.

Modern society grapples with large amounts of household waste. The anaerobic digestion of this waste offers a promising source for energy-rich biogas production but generates high toxic effluents that require treatment before reuse or disposal into the environment. This study aimed to investigate three techniques, namely coagulation/flocculation, electro-coagulation, and activated sludge, in terms of efficiency in the treatment of these effluents. It also aimed to assess their toxicity effects on the germination and growth of durum wheat Triticum aestivum L. seeds before and after 6 days of treatment. Activated sludge was most efficient in reducing chemical oxygen demand, turbidity, and conductivity (95.7 %, 15.8 %, and 37.5 %, respectively). The effluent treated with this technique induced a marked delay in germination (low mean time of germination) and a significant reduction in the percentages of seed germination and root and leaf growths. It was also noted to strongly induce lipid peroxidation in roots and leaves, which presumably explained the germination/growth inhibition of the wheat seeds. The effluent also induced marked lipid peroxidation effects and strongly inhibited the activities of butyrylcholinesterase in mice bone marrows. The effluent shows a high ability to inhibit the growth of three microalgae; these endpoints are useful tools to biomonitor the physico-chemical quality of this wastewater. Overall, while no significant alterations were observed in terms of animal and vegetable toxicities when the effluent was treated by coagulation/flocculation, activated sludge treatment proved efficient in reducing the toxicities induced by the untreated effluents. The results indicate that the application of this technique is promising with regards to attaining efficient, eco-friendly, and cost-effective strategies for the management and treatment of household waste.

The aim of this study is the treatment of Basic Red 29 (BR29) dye solution using hybrid iron-aluminum electrodes by electrocoagulation and electro-Fenton methods. The effect of current density, initial pH, supporting electrolyte, H₂O₂, and initial dye concentration on dye removal efficiency was investigated, and the best experimental conditions were obtained. Time-coarse variation of UV-Vis spectra and toxicity and chemical oxygen demand (COD) removal were also examined at the best experimental conditions. Both systems were found very successful for the removal of BR29 dye. The removal efficiency of >95 % for BR29 dye solution was reached easily in a short time. At the best experimental conditions, for the initial BR29 concentration of 100 mg/L, >95 % BR29 dye and 71.43 % COD removal were obtained after 20 and 40 min of electrolysis, respectively. Additionally, toxicity results for electro-Fenton treatment of 100 mg/L BR29 were also very promising. According to the results obtained, although electro-Fenton is more effective, both systems can be used successfully to treat textile wastewater including dyes.

Metals concentrations and histolopathological lesions of gills and digestive gland were investigated in Carcinus maenas crabs sampled from Bizerta Lagoon and Kuriat Island (Tunisia) as control site. The concentrations of trace metals varied between tissues, sites and sampling time. The highest levels of the analysed metals in gills and digestive gland were noted in Menzel Bourguiba and Cimentery sites at both sampling times (February and July). The higher metals loads were associated with severe and various tissues alterations in contaminated crabs. We particularly noted in the gills a haemocytic infiltration, distension and enlargement of the lamellae, lifting of lamellar epithelium, necrotic lesions and fusion of lamellae in the most polluted sites (Menzel Bourguiba and Cimentery). Moreover, others pathological alterations were observed in digestive gland of crabs collected from polluted sites and with a severity site dependent. We observed necrotic tubules containing tissue debris in the lumen with more intensity in crabs collected from Cimentery site in both sampling times. The thickened basal laminae and the walling off of the tubules by haemocytes around the thickened basal laminae were more abundant at Menzel Bourguiba than at others sites. The coagulation in the thickened basal laminae was observed only at Cimentery in February. Tissues histopathological lesions were sensitive to discriminate crabs of different sites and demonstrated its usefulness in this biomonitoring study. We recommend the association of histopatholocial lesions to biochemical biomarkers in future biomonitoring studies.

A new inorganic-organic hybrid material zirconium-glycine complex (ZGC) was firstly used as a coagulant in a coagulation process to treat Pearl River raw water. Its coagulation performance was compared with commonly used aluminum (Al) coagulants such as aluminum sulfate (Al₂(SO₄)₃) and polyaluminum chloride (PAC), in terms of water quality parameters and floc properties. ZGC coagulation achieved higher removal of turbidity (93.8 %) than other traditional coagulants. Charge neutralization was proven to act as a dominant mechanism during ZGC coagulation. The aggregated flocs with ZGC showed the fastest growth rate and good recovery ability compared with the other coagulants and achieved the largest floc size within 5 min. The ZGC coagulant can decrease the hydraulic retention time and increase removal efficiency.

Surface oxygen functional groups can affect the morphological characteristics, aggregation kinetics, and adsorption capacity of multi-walled carbon nanotubes (MWCNTs). However, little is known about the quantitative relationship between oxygen content and the dispersion stability of MWCNTs. To investigate the effects of surface oxidization, MWCNTs were oxidized using concentrated H₂SO₄/HNO₃acids for 0, 1, 2, 4, and 8 h, respectively. Experimental results showed that the oxygen content of MWCNTs increased with surface oxidization time. Linear correlations were found to exist between the oxygen content, critical coagulation concentration (CCC) for NaCl, and critical coagulation pH values of MWCNTs detected by optical density at 800 nm. The CCC values for CaCl₂increased with oxygen contents for unmodified MWCNTs and lowly oxidized MWCNTs, while which decreased after further increasing the surface oxidization. CCC ratios in the presence of Ca²⁺to Na⁺were consistent with the empirical Schulze–Hardy rule for unmodified MWCNTs and lowly oxidized MWCNTs; however, which were much lower than the expected values for highly oxidized MWCNTs. Fulvic acid can clearly increase the stability of MWCNT suspension with unmodified MWCNTs and lowly oxidized MWCNTs, while it cannot affect the dispersion of highly oxidized MWCNTs. This study implied that the oxidation and presence of fulvic acid will possibly increase the mobility, exposure, bioavailability, and toxicity of MWCNTs.

A novel dual coagulant system of polyaluminum chloride sulfate (PACS) and polydiallyldimethylammonium chloride (PDADMAC) was used to treat natural algae-laden water from Meiliang Gulf, Lake Taihu. PACS (Alₙ(OH)ₘCl₃ₙ₋ₘ₋₂ₖ(SO₄)ₖ) has a mass ratio of 10 %, a SO₄²⁻/Al₃⁺mole ratio of 0.0664, and an OH/Al mole ratio of 2. The PDADMAC ([C₈H₁₆NCl]ₘ) has a MW which ranges from 5 × 10⁵to 20 × 10⁵ Da. The variations of contaminants in water samples during treatments were estimated in the form of principal component analysis (PCA) factor scores and conventional variables (turbidity, DOC, etc.). Parallel factor analysis determined four chromophoric dissolved organic matters (CDOM) components, and PCA identified four integrated principle factors. PCA factor 1 had significant correlations with chlorophyll-a (r = 0.718), protein-like CDOM C1 (0.689), and C2 (0.756). Factor 2 correlated with UV₂₅₄(0.672), humic-like CDOM component C3 (0.716), and C4 (0.758). Factors 3 and 4 had correlations with NH₃-N (0.748) and T-P (0.769), respectively. The variations of PCA factors scores revealed that PACS contributed less aluminum dissolution than PAC to obtain equivalent removal efficiency of contaminants. This might be due to the high cationic charge and pre-hydrolyzation of PACS. Compared with PACS coagulation (20 mg L⁻¹), the removal of PCA factors 1, 2, and 4 increased 45, 33, and 12 %, respectively, in combined PACS–PDADMAC treatment (0.8 mg L⁻¹ + 20 mg L⁻¹). Since PAC contained more Al (0.053 g/1 g) than PACS (0.028 g/1 g), the results indicated that PACS contributed less Al dissolution into the water to obtain equivalent removal efficiency.

Laboratory experiments were carried out to study the effects of slow mixing conditions on magnesium hydroxide floc size and strength and to determine the turbidity and total suspended solid (TSS) removal efficiencies during coagulation of highly turbid suspensions. A highly turbid kaolin clay suspension (1,213 ± 36 nephelometric turbidity units (NTU)) was alkalized to pH 10.5 using a 5 M NaOH solution; liquid bittern (LB) equivalent to 536 mg/L of Mg²⁺was added as a coagulant, and the suspension was then subjected to previously optimized fast mixing conditions of 100 rpm and 60 s. Slow mixing speed (20, 30, 40, and 50 rpm) and time (10, 20, and 30 min) were then varied, while the temperature was maintained at 20.7 ± 1 °C. The standard practice for coagulation-flocculation jar test ASTM D2035-13 (2013) was followed in all experiments. Relative floc size was monitored using an optical measuring device, photometric dispersion analyzer (PDA 2000). Larger and more shear resistant flocs were obtained at 20 rpm for both 20- and 30-min slow mixing times; however, given the shorter duration for the former, the 20-min slow mixing time was considered to be more energy efficient. For slow mixing camp number (Gt) values in the range of 8,400–90,000, it was found that the mixing speed affected floc size and strength more than the time. Higher-turbidity removal efficiencies were achieved at 20 and 30 rpm, while TSS removal efficiency was higher for the 50-rpm slow mixing speed. Extended slow mixing time of 30 min yielded better turbidity and TSS removal efficiencies at the slower speeds.