Impact of zinc orthophosphate on simulated drinking water biofilms influenced by lead and copper

Phosphate, a key nutrient for bacterial growth, is also a key component of many corrosion-control programs to manage lead and copper corrosion in premise plumbing. Bench-scale stagnant water galvanic macrocells with lead and copper components were fed with drinking water containing three levels of zinc orthophosphate [0 (control), 1, and 3 mg l⁻¹-PO₄]. Suspended polycarbonate coupons, representing benign downstream fixtures, were placed in the macrocells, thus enabling biofilm formation on this material. Community profiling using denaturing gradient gel electrophoresis (16S rDNA PCR-DGGE) revealed that phosphate dose (primarily) and metal type (to a lesser extent) influenced biofilm community diversity. Generally, community diversity increased with increasing heterotrophic plate counts that in turn rose in response to elevated phosphate. Partial 16s rDNA sequences obtained from DGGE gel bands identified the dominant bacterial taxa as the phyla Verrumicrobia, Firmicutes, Bacteroidetes, and α-Proteobacteria. The increase in size and diversity of biofilm communities as a result of phosphate treatment further highlights the challenges of a phosphate corrosion-control program.