Synthesis of composites from activated carbon based on olive stones and sodium alginate for the removal of methylene blue.

The present investigation involves the preparation of activated carbon (AC) from olive stones using a single-step activation process with potassium hydroxide (KOH) as an activating agent. The resulting activated carbon (AC) was used in conjunction with sodium alginate (Alg) to prepare the AC/Alg beads at different ratios (50/50, 60/40, and 80/20) for batch adsorption of methylene blue (MB). Characterization of the materials was conducted using FTIR, SEM, CHNS-O, and TGA-dTG thermal analysis. In batch adsorption studies, the AC/Alg beads were employed to remove MB from aqueous solutions, and various parameters, including contact time, initial pH of the MB solution, and initial MB concentration, were optimized to obtain maximum adsorption efficiency. The experimental results reveal that AC/Alg beads with a ratio of 60/40 exhibit the best adsorption performance. The pseudo-first-order kinetic model and the Langmuir adsorption isotherm, with a maximum adsorption capacity of 586 mg/g, best fit the experimental data.

The ability of drinking water treatment sludge to degrade methylene blue in water through combined adsorption/photo Fenton-like process.

In the present study, drinking water treatment sludge (DWTS) was reused as a catalyst in advanced oxidation processes for the removal of methylene blue (MB) from aqueous solutions. After determining their chemical and mineralogical compositions by X-ray Powder Diffraction (XRD), BET surface area, scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), Inductively Coupled Plasma (ICP), and FT-IR spectra. DWTS has been used as a heterogeneous photo Fenton-Like catalyst for the oxidation of MB under different parameters, including pH (3-6), H2O2 concentration (9.79-29.37 mM), and dose (1-2.5 g/L). The results showed that within 180 min and under UV light irradiation, more than 86% of MB having a concentration of 50 mg/L were removed using a catalyst loading of 1.5 g/L, a H2O2 dosage of 23.17 mM and a solution pH of 5. The DWTS has a satisfactory stability as the catalyst is stable and have very less iron leaching property.

Hydrothermal carbonization of vegetable-tanned leather shavings (HTC-VTS) for environmental remediation: optimization of process conditions.

Herein, the response surface methodology (RSM) has been used to study simultaneously the effects of carbonization temperature, residence time and moisture content on the activated hydrochar preparation-based vegetable-tanned leather shavings (VTS) using hydrothermal carbonization method (HTC). Owing to the desirability chosen, three responses were analysed, namely: the hydrochar yield, iodine and methylene blue numbers. The analysis of experimental results revealed that the hydrochar yield was decreased with increase in carbonization temperature which led to micropores formation inside the hydrochar network. The optimal preparation conditions retained were: 83.10%, 390.44 mg g-1 and 259.63 mg g-1 for the hydrochar yield, iodine and methylene blue number respectively. The hydrochar micrograph showed the presence of external pores, whereas the FTIR analysis recorded the presence of acidic functional groups found on hydrochar surface. The findings revealed that the VTS is a good precursor for the hydrochar preparation useful in the removal of organic and inorganic pollutants in aqueous media.

Dye removal by activated carbon produced from Agave americana fibers: stochastic isotherm and fractal kinetic studies.

The present work investigates the use of Agave americana fibers (AGF) as a precursor for activated carbon (AC) preparation via chemical activation using phosphoric acid (H3PO4), and the study of the influence of the preparation conditions on the adsorption capacity of the prepared AC toward Alpacide Yellow (AY). The preparation experiments have been conducted at different impregnation ratios: acid/AGF (20 g/1 g, 30 g/1 g, and 40 g/1 g) with varied impregnation times (2 h, 4 h, and 6 h) and at different carbonization temperatures (200 °C, 400 °C, and 600 °C). The impregnation ratio of 40 g/1 g, the impregnation time of 6 h, and the carbonization temperature of 400 °C were selected as the optimal conditions for the preparation of AC with enhanced properties. Despite its low specific surface area (25 m2/g), the prepared AC showed a higher adsorption capacity toward AY (5.71 mg/g) as compared with that of the commercial activated carbon (CC) (5.27 mg/g) which showed a higher specific surface area (825 m2/g). This could be due to the existence of pores and functional groups on the surface of AC, as evidenced by the analysis results of FTIR, DSC, and SEM. The adsorption process was found fast and fractal since it followed the kinetic model of the Brouers-Sotolongo fractal (BSf) (R2 = 0.999), while the mathematical modeling of the adsorption isotherm of AY on the synthesized AC was stochastic since it followed the General Brouers-Sotolongo (GBS) (R2 = 0.999).

Phytotoxicity assessment of olive mill wastewater treated by different technologies: effect on seed germination of maize and tomato.

The phytotoxicity effect of olive mill wastewater (OMWW) treated in a combined system regrouping pretreatment by filtration on olive stones and coagulation-flocculation, and anaerobic digestion (AD) on seed germination of maize and tomato was evaluated through germination tests in petri dishes and growth tests in pots. Three samples, referenced as AD-40, AD-60, and AD-80, were collected from the anaerobic reactor operating with an influent at 40, 60, and 80% OMWW/water (% v/v). Concentrations between 25 and 100% were used for maize and between 5 and 25% were used for tomato using raw and pretreated samples, while anaerobic samples were used without dilution. For maize, 100% and 75% OMWW were very phytotoxic and completely prohibited seed germination, while phytotoxicity was decreased following dilution at 25% and 50% OMWW. Maize germinability was found highly enhanced when watered with anaerobic samples. For tomato, high dilution was required to reduce the phytotoxicity of raw and pretreated OMWW and a high relative germination percentage was registered at 5, 10, and 15% OMWW, while for samples anaerobically treated, a high phytotoxicity is still observed. Growth tests, showed more favorable results for maize watered with raw and pretreated samples at 25% OMWW and with biological samples. For tomato and with the exception of 25% OMWW and AD-80, seeds respond positively to all samples. It was concluded that if the OMWW will be used for irrigating maize, it could be directly used after anaerobic digestion, while for tomato further dilution is required. The phenolic profile analysis of the tested samples coupled with the results of the germination tests showed that the OMWW phytotoxicity appears to be determined by not only the monomeric phenols but also by other toxic components unaffected by the applied treatments.

Packed-bed biofilm reactor for semi-continuous anaerobic digestion of olive mill wastewater: performances and COD mass balance analysis.

In the present study, the treatability of olive mill wastewater (OMWW) using an anaerobic fixed bed biofilm reactor packed with granular activated carbon (GAC) and inoculated with non-acclimated biomass was performed in a semi-continuous mode under mesophilic conditions. Three organic loading rates (OLR) varied from 0.94 to 2.81 g COD/(L d) were applied. The results of batch adsorption tests on GAC and the experimental data from PBBR-GAC operation were used to set up a COD mass balance in order to investigate the effect of adsorption on the COD removal during the three anaerobic treatment steps. Despite the slight accumulation of volatile fatty acids (VFAs) during the second and the third steps, between 735 and 1135 mg COD/L (as acetic acid), a stable environment for methanogens was maintained for a period of 104 days. During the three steps, degradation levels were up to 80% of COD and 85% of phenolic compounds. An averaged specific biogas production of 1.77 LN/d and a methane (CH4) concentration of about 60%, corresponding to a CH4 yield of 0.31 L CH4produced/g CODdepleted, were reached at an OLR of 2.81 g COD/(L d). The results show that the COD mass balance was not closed during the first two steps, while in the third step, it could be around 96%. This finding suggests that the adsorption of organic substances on activated carbon occur just during the two first steps, while at 2.81 g COD/(L d) OLR no adsorption is occurring and the introduced COD becomes completely available for CH4 production.

Olive mill wastewater pretreatment by combination of filtration on olive stone filters and coagulation-flocculation.

In the present study a new combined process, comprising filtration of raw olive mill wastewater (OMWW) on two successive olive stone (OS) filters followed by a coagulation-flocculation, was developed in order to perform an efficient pretreatment of OMWW. The results show that the use of OS filter leads to a higher removal of total suspended solids (TSS) and fatty matter (FM) from the raw OMWW (about 82.5% and 73.8%, respectively) and a depletion of total phenolic compounds (TP) and chemical oxygen demand (COD) (11.3% and 23.2%, respectively). The coagulation-flocculation was then applied to improve the removal of TP and COD from the filtered OMWW. For this purpose, a full-factorial design was used to study the effect of different factors involved in coagulation-flocculation. The studied variables were: pH (5-8), coagulant type (ferric chloride; FC and aluminum sulfate; AS), coagulant concentration (250-1000 mg/L) and flocculant (Anionique polyelectrolyte Superfloc A120 PWG) concentration (1-5 mg/L). The results reveal that the use of 250 mg/L FC and 5 mg/L flocculant at an acid pH (around 5) allows for, respectively, a removal of TP and COD of about 10.8% and 31.3%.

Capillary electrophoretic analysis of sulfur and cyanicides speciation during cyanidation of gold complex sulfidic ores.

A capillary electrophoretic protocol for the separation and quantification of the most important species potentially liberated during the cyanidation of gold sulfide-rich ores was accomplished in this study. The separation of 11 ions: S2O3(2-), Cu(CN)3(2-), Fe(CN)6(4-), Fe(CN)6(3-), SCN(-), Au(CN)2(-), Ag(CN)2(-), SO4(2-), OCN(-), SO3(2-), and HS(-) was achieved using an indirect UV detection method. The robustness of the analytical protocol was tested by analyzing ions speciation during the cyanidation of two gold sulfide-rich ores. The 1-h cyanidation of the two ores released up to six complexes into solution: S2O3(2-), Cu(CN)3(2-), SCN(-), Fe(CN)6(4-), OCN(-), and SO4(2-). The mineralogy of the ore was found to influence directly the nature and the amount of the dissolved species. Conserving the cyanidation solution for 72 h after sampling resulted in 96% total sulfur recovery. These results allow us to conclude that the analytical protocol developed in this study can become very useful for the optimization of precious-metals cyanidation plants.

Experimental design to optimize preparation of activated carbons for use in water treatment.

A series of seven activated carbons was obtained for use in drinking water treatments by steam-activation of olive-waste cakes. This raw material is an abundant and cheap waste byproduct of oil production, making these activated carbons economically feasible. The activated carbons, prepared by the one step method, were characterized, and the evolution of their characteristics (yield, adsorption capacities, and porosity) was analyzed as a function of the experimental parameters (activation temperature and activation time), using the Doehlert matrix. The Doehlert matrix allows the response surface to be studied with a good quality parameter estimation of the quadratic model. Each response has been described by a second order model that was adequate to predict responses in all experimental regions. The coefficients of the postulated model were calculated from the experimental responses by means of least squares regression, using the NEMROD software. We determined the region in which the optimum values of both activation temperature and activation time were achieved for the preparation of activated carbons suitable for use in water treatments. The "optimal activated carbon" was experimentally obtained, and its characteristic parameters showed a good agreement with those calculated from the model. The results obtained for activated carbons prepared by the one-step method were compared with those for activated carbons prepared by the two-step method. The characteristics of activated carbons obtained by the one-step and two-step methods showed that "one-step" activated carbons have a highly developed porous texture formed mainly of large macropores and micropores, whereas "two-step" activated carbons have a predominance of mesopores and narrow micropores. These activated carbons from olive-waste cakes showed a high capacity to adsorb herbicides (2,4-dichlorophenoxyacetic acid, 2,4-D; and 2-methyl, 4-chlorophenoxyacetic acid, MCPA) from water, with adsorption capacity values higher than those corresponding to a commercial activated carbon used from drinking water treatments.