2. Experimental section
2.1. Drinking water treatment sludge
The sludge used in the presented experiments was collected from the drinking water treatment plant (Annaba, Algeria) immediately
Table 1
Composition of the sludge after drying (non-exhaustive composition).
Species Weight concentration (g kg−1)
Sodium 2 Calcium 11 Aluminum 105 Chloride 0.01 Carbonate 16.5 Sulfate 245
after the stage of raw water clarification with sulfate aluminum as coagulant. Recovered sludge was dried in an oven at 105 °C for 24 h before EK treatment. Metal cations contained in the sludge were analyzed by atomic absorption (Perkin Elmer 3110) and anions were assayed by ion chromatography (ICS 3000) using an Ionpack AS 18 column. Concentrations of the main inorganic species contained in the dry sludge are reported in Table 1.
2.2. Electrokinetic experiments
Electrokinetic experiments were conducted in a glass cell (Fig. 2) being 14 cm long, 5 cm high and 4 cm broad, consisting of three compartments: the cathode and anode chambers at the extremities of the cell were 2 cm long, and the 10 cm long central chamber contained the sludge slurry. Glass filter papers were used as separators to prevent sludge particles from flowing into the electrode compartments. Two sets of graphite rod electrodes – 6 cm high and 1 cm in diameter – were installed in the electrode chambers, right behind the filters.
The anode chamber was filled in all cases with 40 cm3 pure water. The cathode chamber was filled with 40 cm3 of aqueous solution of acetic acid, citric acid or EDTA – in the acid form – at various concentrations. The sludge suspension was prepared by thorough mixing of 75 g of the dry sludge in 100 cm3 of the washing solution. For runs conducted with EDTA, the washing solution was also EDTA as the same concentration as in the catholyte solution. For runs conducted with acetic or citric acids, pure water was used as washing medium. Taking into account the Al content of the sludge, approx- imately 7.8 g Al (0.289 mol) was introduced into the cell.
Approximately 150 cm3 of concentrated suspension was obtained and poured into the central compartment, and the run was started. Experiments were carried out batchwise at constant cell voltage with a power supply and the current was continuously monitored. Preliminary tests led to a suitable potential range for which appreciable currents could be measured. The pH in the electrolyte compartments was continuously measured using a Grimson pH- meter. Due to the loss of liquid by evaporation from the open cell, and
Fig. 1. Schematic representation of the experimental device and elementary processes involved in the treatment.

Fig. 2. Schematic view of the cell used for electrokinetic experiments.
possible water transport by electroosmosis to the cathode chamber, aliquots of the cathode solutions were poured regularly in the cell and the global volume added was recorded along the runs, which were conducted from 6 or 10 days at ambient temperature. The operating conditions are summarized in Table 2.
After EK treatment, the electrodes were removed and the cell was submitted to drying for 24 h: the solid cake recovered could be extracted from the glass cell, making it possible to take apart the solid from the electrode chambers and the central compartment. The 10 cm long portion recovered was cut into five 2 cm sections, named S1 to S5 for further analysis. The solid deposit on the cathode for some runs was also recovered. Solid samples S1–S5 were diluted into 1/10 wt. sludge/water suspensions. The pH of the dilute suspensions was measured and was reported as the “final pH” of the sludge in the graphs presented in the following section. Aluminum concentration was determined after digestion of dry solids recovered with aqua regia 6 N at 10 cm3 per gram solid, by atomic absorption spectrometer Perkin Elmer 3110. The amount of Al recovered in the various sections and chambers were then deduced, taking into account the weight of the solid fractions.
2. Experimental section2.1. Drinking water treatment sludgeThe sludge used in the presented experiments was collected from the drinking water treatment plant (Annaba, Algeria) immediatelyTable 1Composition of the sludge after drying (non-exhaustive composition).Species Weight concentration (g kg−1)Sodium 2 Calcium 11 Aluminum 105 Chloride 0.01 Carbonate 16.5 Sulfate 245after the stage of raw water clarification with sulfate aluminum as coagulant. Recovered sludge was dried in an oven at 105 °C for 24 h before EK treatment. Metal cations contained in the sludge were analyzed by atomic absorption (Perkin Elmer 3110) and anions were assayed by ion chromatography (ICS 3000) using an Ionpack AS 18 column. Concentrations of the main inorganic species contained in the dry sludge are reported in Table 1.2.2. Electrokinetic experimentsElectrokinetic experiments were conducted in a glass cell (Fig. 2) being 14 cm long, 5 cm high and 4 cm broad, consisting of three compartments: the cathode and anode chambers at the extremities of the cell were 2 cm long, and the 10 cm long central chamber contained the sludge slurry. Glass filter papers were used as separators to prevent sludge particles from flowing into the electrode compartments. Two sets of graphite rod electrodes – 6 cm high and 1 cm in diameter – were installed in the electrode chambers, right behind the filters.The anode chamber was filled in all cases with 40 cm3 pure water. The cathode chamber was filled with 40 cm3 of aqueous solution of acetic acid, citric acid or EDTA – in the acid form – at various concentrations. The sludge suspension was prepared by thorough mixing of 75 g of the dry sludge in 100 cm3 of the washing solution. For runs conducted with EDTA, the washing solution was also EDTA as the same concentration as in the catholyte solution. For runs conducted with acetic or citric acids, pure water was used as washing medium. Taking into account the Al content of the sludge, approx- imately 7.8 g Al (0.289 mol) was introduced into the cell.Approximately 150 cm3 of concentrated suspension was obtained and poured into the central compartment, and the run was started. Experiments were carried out batchwise at constant cell voltage with a power supply and the current was continuously monitored. Preliminary tests led to a suitable potential range for which appreciable currents could be measured. The pH in the electrolyte compartments was continuously measured using a Grimson pH- meter. Due to the loss of liquid by evaporation from the open cell, andFig. 1. Schematic representation of the experimental device and elementary processes involved in the treatment.Fig. 2. Schematic view of the cell used for electrokinetic experiments.possible water transport by electroosmosis to the cathode chamber, aliquots of the cathode solutions were poured regularly in the cell and the global volume added was recorded along the runs, which were conducted from 6 or 10 days at ambient temperature. The operating conditions are summarized in Table 2.After EK treatment, the electrodes were removed and the cell was submitted to drying for 24 h: the solid cake recovered could be extracted from the glass cell, making it possible to take apart the solid from the electrode chambers and the central compartment. The 10 cm long portion recovered was cut into five 2 cm sections, named S1 to S5 for further analysis. The solid deposit on the cathode for some runs was also recovered. Solid samples S1–S5 were diluted into 1/10 wt. sludge/water suspensions. The pH of the dilute suspensions was measured and was reported as the “final pH” of the sludge in the graphs presented in the following section. Aluminum concentration was determined after digestion of dry solids recovered with aqua regia 6 N at 10 cm3 per gram solid, by atomic absorption spectrometer Perkin Elmer 3110. The amount of Al recovered in the various sections and chambers were then deduced, taking into account the weight of the solid fractions.
การแปล กรุณารอสักครู่..