ANALYSIS OF THE PHYSICAL AND CHEMICAL PROPERTIES OF ARSENIC SLUDGE TO IMPROVE DEWATERING AND DISPOSAL
*Garrido Hoyos S.E.1, García Mendoza K.2 Miranda Zamora E.3
1Instituto Mexicano de Tecnología del Agua, Paseo Cuauhnáhuac, 8532, Col. Progreso. C.P. 62550, Jiutepec, Morelos, México.
2Universidad Nacional Autónoma de México, Programa de Maestría y Doctorado en Ingeniería Ambiental, campus Morelos. Paseo Cuauhnáhuac, 8532, Col. Progreso. C.P. 62550, Jiutepec, Morelos México.
3Universidad Politécnica de Morelos. Boulevard Cuauhnáhuac 566, Col. Lomas del Texcal, Jiutepec, Morelos. CP. 62550 México.
*Author’s e-mail: sgarrido@tlaloc.imta.mx
Keywords: Arsenic, sludge, conditioning, dewatering, disposal
The aim of this study was to optimize the thickening, conditioning, and dewatering of the sludge generated during the coagulation and flocculation carried out to remove arsenic (As) from water for human consumption. Arsenic is considered carcinogenic to humans when it is consumed lengthily as arsenical water. Therefore, nowadays there are a number of technologies that remove this metalloid from water for human consumption, which produce waste (such as sludge, water rejection, backwash water filters, and water regeneration exchangers) with high concentrations of arsenic. Water regeneration exchangers are discharges to bodies of water or drainage networks that change environmental conditions such as pH, redox potential, and mobilize arsenic into the water again. First, in order to achieve the removal of Arsenic (As) from water for human consumption and generate sludge through coagulation and flocculation processes, a central composite experimental design 2k was employed and the following optimal conditions were obtained: pH of 7.20; dosing of ferric chloride (FeCl3) of 34.4 mg/L, and polymer of 0.89 mg/L, with the following response variables: settleable solids (SETS) of 7.59 mg/L and a concentration of As(V) in the supernatant of 0.003 mg/L for a confidence interval of 95%. Secondly, the thickening was achieved through gravity (for 12 hours). Third, the chemical conditioning of the thickened sludge was conducted through five organic polymers, which after comparing them, the polymer P1 Bufloc 5240 anion was selected, since it performed better in physical properties: specific resistance filtration (SRF) of 6 10+19 cm/g, a filtration time (Ft) of 107 s, compressibility of 520 mmHg, density specific of 1.011 g /mL, and total solids of 6.03 g/L. As for the chemical properties of water, they were mainly found in the sludge conditioned as interstitial: 42% and 30% in surface water, according to the analysis of moisture distribution, which influenced sludge dewatering. Conditioning with polymer P1 significantly affected surface water fractions but it did not affect the water fraction that was chemically bounded. Nevertheless, the free water fraction could be reduced with higher doses of the polymer. Fourth, for the dewatering process, the total solids determined in the belt filter press from filter cake were 6.03 g/L and 22.48 g/L for centrifugation. Finally, the disposal of arsenic immobilized residues could go into landfill for specific toxic waste.