Masters Theses

James Burnham

Date of Award

12-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental Engineering

Major Professor

R. Bruce Robinson

Committee Members

Chris Cox, Mriganka Ghosh

Abstract

The effectiveness of polyphosphate sequestering agents as used in New Jersey water treatment facilities was studied. The study examined the effect on iron, manganese, hardness constituents, color, and turbidity by two polyphosphates products currently in use, and the possible use of alternative agents; sodium silicate and an acrylic polymer. The study also experimented with different doses of one polyphosphate product at two water temperatures, 61 and 77° Celsius and the effect of laundry bleaching. A survey was conducted of facilities in New Jersey listed as using sequestering agents. Out of 62 facilities, 28 responded to questions about dosage and reasons for use of polyphosphates, and general water quality. The majority of participants in the survey listed iron, manganese, and hardness as the reasons for using polyphosphates. However, the average reported concentrations of these constituents was below EPA secondary standards, and hardness averaged 87.1 mg/L as CaCO3. Eight polyphosphate products were in use, produced by 4 manufacturers. In the field study, seven facilities were visited. Samples were taken before treatment, after treatment, and at hot and cold taps in the distribution system. Samples were taken in pairs, with half of the samples filtered through a 0.45μm membrane filter and the other half not filtered. The seven facilities generally had raw water concentrations of iron and manganese that were lower than reported in the survey and lower than secondary standards for iron (0.3 mg/L) and for manganese (0.05 mg/L). At these levels, the field study revealed that only one of seven facilities showed improved filterability of iron. Only one facility had sufficient manganese to compute filterability, and this facility showed declines after the addition of polyphosphates. Both iron and manganese concentrations declined as water moved from the well to sites in the distribution system. There was no effect on calcium and manganese filterability, and concentrations of these constituent showed minimal declines in the distribution system. Comparisons of copper concentrations at sites in the distribution system to initial concentrations at the well head showed marked increases possibly due to the addition of polyphosphates. Only one site with a high water hardness showed a decrease in copper concentrations. None of the sites before and after treatment or in the distribution system showed lead concentrations above the instrument detection limit (0.05 mg/L). Turbidity was significantly improved by the addition of polyphosphates. Five of seven facilities showed such improvement after treatment; however, turbidity increased as water moved further from the well head. However, virtually all raw water turbidity values were less than 1.0 NTU. All of the water samples appeared free of color. Comparisons of hot and cold water samples from sites in the distribution system showed lower iron, manganese, calcium, phosphorous, and hardness concentrations in the hot water, indicating a breakdown in polyphosphates and depositions in the hot water system. Higher hot water temperatures correlated with greater drops in the concentrations. Results of experiments with sodium silicate and an acrylic polymer were similar to the results of polyphosphates; filterability and turbidity results were similar. One case in which the hardness was high, however, the polymer did not perform well. Laundry bleaching had a negative effect on filterability and turbidity at facilities using polyphophates. Water from one of the seven facilities was used to test the effect of water heater temperature with five doses of polyphosphates: 0.000, 0.084, 0.256,0.513, and 1.70 mg/L as PO4. Experiments showed approximately 100% filterability of calcium and magnesium at 61 and 77°C, and at all doses of polyphosphate; thus, the addition of polyphosphate had no effect on filterability. Concentrations of iron and manganese were insufficient for evaluation. One dose of phosphate (0.084 mg/L) showed statistically significantly higher concentrations of calcium (10.2%) and magnesium (8.6%) at ITC, indicating a possible optimum phosphate dose for this particular water. The reasons for using polyphosphates as sequestering agents in New Jersey water treatment facilities were questionable in that the listed reasons did not match the reported concentrations which were below U.S. Environmental Protection Agency guidelines. Individual facilities may obtain benefits by experimenting with lower doses and testing waters to find the optimum dose.

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