Nitrification in Premise Plumbing: Role of Phosphate, pH and Pipe Corrosion

Abstract

Nitrification in PVC premise plumbing is a weak function of pH over the range 6.5-8.5 and is insensitive to phosphate concentrations 5-1000 ppb. Lead pipe enhanced nitrification relative to PVC, consistent with expectations that nitrifiers could benefit from ammonia recycled from nitrate via lead corrosion. Relatively new copper pipe (<1.5 years old) did not allow nitrifiers to establish, but nitrifiers gradually colonized over a period of months in brass pipes when copper concentrations were reduced by pH adjustment or orthophosphate. Nitrifiers were inhibited by trace copper, but not by lead levels up to 8000 ppb. In some systems using chloramines, brass in plastic plumbing systems might be more susceptible to lead/copper leaching, and accelerated dezincification, due to lower pH values resulting from nitrification.

Microbial Community Profile of a Lead Service Line Removed from a Drinking Water Distribution System

“…In other studies, Rhodococcus, Stenotrophomonas, and Xanthomonas have been shown to decrease copper levels by sorbing soluble copper in their exopolysaccharide (EPS) (2,28,47). Nitrification may also promote corrosion, as this process results in a pH drop which increases the solubility of most lead minerals commonly found on the surfaces of lead materials in DWDSs (48,49).…”

“…Biofilms have been shown to influence the corrosion behavior of metals, including those used in drinking water pipes (6,7,9,11,48). For example, drinking water isolates of the genera Agrobacterium, Acidovorax, Sphingomonas, and Micrococcus have been reported to increase copper levels in drinking water pipes, with corrosion dependent on microbial activity (9,10,14,23,37).…”

“…PCR tests on nucleic acid recovered from fire hydrant flush samples collected in the same distribution system did test positive for AOB. AOB have been associated with lead release, and the mechanism has been attributed to the drop in pH during the nitrification process (48,49).…”

Microbial Survey of a Full-Scale, Biologically Active Filter for Treatment of Drinking Water

“…When excessive levels of free ammonia are present in the source water or ammonia is added to form chloramines, nitrification may occur with sufficient dissolved oxygen (DO) (34). Nitrification in the DS, and the pH drop associated with nitrification, can impact the corrosion rates of the DS and premise materials (41). In addition, the increased chlorine demand and growth of heterotrophic biofilms produce undesirable taste and odor issues (30).…”

Impact of Pipe Materials and Chlorination on Planktonic and Biofilm Cells of Listeria monocytogenes

“…So, the copper plumbing material is widely used. This may be due to the easy fittings with different pipe varieties [55,56]. Metal-based materials can form the corrosion products on pipe surfaces and release metals into water as a result of chemical or biological reactions [57,58].…”