Effect of phosphorus on microbially induced corrosion to copper metal and possible implications for drinking water quality

Abstract

Microbial corrosion is defined as the degradation of industrial material by microbiological activity. In home drinking water systems, corrosion of piping material can lead to hazardous levels of copper or lead in potable water. Current monitoring and remediation practices focus mainly on chemical factors while giving little attention to biological ones. A grade of copper pipe commonly referred to as DHP (C12200) is commonly used for home water distribution. This grade of copper pipe contains trace amounts of phosphorus left over from the smelting process. If microbial corrosion under phosphorus limited conditions is able to liberate copper-bound phosphorus it could be a new source of phosphorus that microbes could use for growth. This study examined the potential of microbially induced corrosion to release phosphorus for microbial utilization using two grades of copper coupons, DHP and Pure (C10100). The phosphorus amount in each environment was also manipulated and used as control groups. Biofilms were grown on copper coupons housed in "biofilm chambers", which were supplied with fresh nutrient bulk water weekly. Corrosion to coupons were assessed using scanning electron microscopy of used coupon surfaces and detection of total copper in spent bulk water by microwave plasma atomic emission spectroscopy. Utilization of phosphorus from corroded copper was assessed by secondary production and comparison of carbohydrate and protein amounts in biofilm scraped from copper coupons. Microbial corrosion occurred on coupons in phosphorus limited environments, regardless of coupon metal grade. Pitting was only observed on coupons from phosphorus limited environments. Bulk water total copper concentrations were significantly greater in phosphorus limited chambers and remained constant from week to week. Biofilm carbohydrate and protein assays produced unexpected results that did not agree with findings in other literature. Microbial utilization of phosphorus from corroded copper was inconclusive at the tested conditions. It is suspected that using a mixture of carbon source may affect phosphorus- based carbohydrate and protein trends.