Case study: reducing manganese (Mn⁺⁺) level in surface water with natural manganese-coated sand in Sinopec Shanghai Ltd

Sinopec Shanghai Ltd has been experiencing an increased manganese (Mn⁺⁺) level in its water source since 2000. The purpose of this research is to reduce Mn⁺⁺ in conventional gravitational filtration effluent to below the national standard and provide suggestions for Sinopec waterworks to carry out full-scale industrial tests. A pilot experiment, using natural manganese sand, quartz sand and their mixtures as the filtration medium, was conducted from 20 September 2003 to 26 December 2003 in Sinopec waterworks. The results indicated that the tested natural manganese sand has a stronger adsorption for Mn⁺⁺ than the quartz sand within the hydraulic retention time of the filtration bed (<30 min.). Water redox status was found to be vital in Mn⁺⁺ adsorption by the tested natural manganese sand. A dual-medium with a volumetric mix ratio between 1:1 and 1:2 (natural manganese sand: quartz sand) was suggested for engineering application in Sinopec waterworks. Meanwhile, the filtration loading rates should be kept within 6–8 m³ h⁻¹ m² and the suggested backwashing loading rate should be 15–16 l s⁻¹m⁻² for 5–6 min.