Coagulant selection for water treatment process in Plant “C”, Maracaibo, Venezuela

• Javier Castillo Universidad del Zulia-Venezuela
• Nibis Bracho Universidad del Zulia-Venezuela
• Luis Vargas Universidad del Zulia-Venezuela
• Nathalie Romero Universidad del Zulia-Venezuela
• Gerardo Aldana Universidad del Zulia-Venezuela

Abstract

For more than 30 years, solid aluminium sulphate has been used traditionally with iron (SATA) and iron free (SALH) as a coagulant in the clarification process. In the last decades, new products, such as Polialuminium Chloride (PAC), Aluminium Chlorhydroxide, and liquid Aluminium Sulphate (SATA-SM) have been introduced to the market. There is limited scientific information in Venezuela and South America about the advantages and disadvantages reported by these products in the drinking water process. Based on this facts, a research was carried out in the Plant Alonso de Ojeda (C Plant), located in Maracaibo city, in order to select the coagulant that offers the best benefits to the process. Natural water samples were collected interdaily. Jarr tests for low, medium and high turbidity (8, 14 and 30 NTU, respectively) were performed and the optimum dose, turbidity, color, pH, alkalinity, total suspended solids (SST), settleable solids, residual aluminium, floc resuspension capacity, appearance time and flock settlement were determined. The optimum dose for the SATA-SM was obtained to be 2.4 to 3.2 times more than that for the SATA and SALH; it is similar for the PAC, and it is approximately half the dose for the chlorhydroxide. The aluminium sulphate costs are four times less than those of the new products. The best flock formation, stability and settlement time was exhibited by the SATA-SM, and the less SST and settleable solids quantity was registered for the SALH, which guarantee the less washing frequency of filters and sediment. All products present the same treatment quality related to color and turbidity remotion, achieving values, for the optimum doses, of 3.5 NTU and 10 apparent color units for all the coagulants.