Manganese removal from domestic water supply via chemical treatment

• Main Authors: Caronongan, Nathan T., Hong, Katherine A.
• Format: text
• Language: English
• Published: Animo Repository 2009
• Subjects: Groundwater—Pollution; Drinking water—Manganese content; Soils—Manganese content; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/5425
• Institution: De La Salle University

The Sto. Angel Production Well in San Pedro, Laguna, contains an average manganese level of 0.90 ppm. This is way above the standard limit of 0.40ppm and 0.05 ppm set by the Philippine National Standards for Drinking Water (PNSDW) and the World Health Organization (WHO), respectively. Because of this, authorities at the San Pablo City Water District (SPWD) were forced to cease its operations in the said well last 2005.Manganese exists naturally in some soils and enters into ground water or is washed down to surface water reservoirs. Reduced Mn(II) is typically present in the reduced state as the aquated manganous ion, Mn2+. Upon oxidation, it is transformed to Mn4+ which forms MnO2. Typical treatment to remove manganese involves oxidation followed by filtration. However, if even after oxidation MnO2 has not settled in the reservoir and remains in suspension, there is a need for subsequent processes to aid its removal.This study focused on the reduction of manganese level by using coagulation and flocculation methods. The dosages of the coagulants (alum, calcium hydroxide and calcium oxide) were varied from 10 to 500 ppm while the dosages of the flocculants (alum, calcium carbonate and PAC) were varied from 0.5 to 1.5ppm. The pH range tested was from 6 to 9. Rapid agitation rates tested were from 160 to 240 rpm while slow agitation rates tested were from 10 to 30 rpm. With the use of jar tests, optimum conditions (pH, dosages of the coagulant and flocculant, agitation rate, agitation time, and settling time) were determined to attain maximum manganese removal."The optimum conditions were found to be at a coagulant dosage of 100 ppm, pH of 8, rapid agitation rate of 200 rpm, and settling time of 30 minutes, for both CaO and Ca(OH)2 coagulants. The addition of flocculants was not necessary as coagulant alone already decreases the manganese concentration to ppb levels and satisfies both the PNSDW and WHO standards. At 10 ppm coagulant dosage, manganese concentration already met the PNSDW standard of 0.40 ppm. The choice of calcium coagulants proved to be more effective as these were able to impact the stability and dynamic aggregation of MnO2 facilitating its removal.