Pilot-scale comparison of sodium silicates, orthophosphate and pH adjustment to reduce lead release from lead service lines

Aghasadeghi, Kimia; Peldszus, Sigrid; Trueman, Benjamin F.; Mishrra, Anushka; Cooke, Mitchell G.; Slawson, Robin M.; Giammar, Daniel E.; Gagnon, Graham A.; Huck, Peter M.

doi:10.1016/j.watres.2021.116955

Cited by 22 publications

(31 citation statements)

References 30 publications

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“…While Rompré et al 2 and Kogo et al 19 indicated that biofilm accumulation was not influenced by corrosion inhibitor type (sodium silicate or orthophosphate), the results from this study suggest the opposite: tATP concentrations were significantly lower in the silicate-treated AR compared to the orthophosphate-treated AR. A similar finding was documented by Aghasadeghi et al 48 , who used a pilot-scale system with excavated lead service lines. In that study, heterotrophic plate counts were lower in pipe wall biofilm in the silicate-treated system compared with the orthophosphate-treated system.…”

Section: Cellular Atp (Catp) and Biofilm Atp (Tatp)supporting

confidence: 86%

Effect of sodium silicate on drinking water biofilm development

Munoz

Trueman

et al. 2021

Preprint

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Sodium silicates have been studied for sequestration of iron, coagulation, and corrosion control, but their impact on biofilm formation has not been documented in detail. This study investigated the impact of sodium silicate corrosion control on biomass accumulation in drinking water systems in comparison to orthophosphate, a common corrosion inhibitor. Biofilm growth was measured by determining ATP concentrations, and the bacterial community was characterized using 16S ribosomal RNA (rRNA) sequencing. A pilot-scale study with cast-iron pipe loops, annular reactors (ARs), and polycarbonate coupons demonstrated significantly lower biofilm ATP concentrations in the sodium silicate-treated AR than the orthophosphate-treated AR when the water temperature exceeded 20°C. However, an elevated sodium silicate dose (48 mg L-1 of SiO2) disturbed and dispersed the biofilm formed inside the AR, resulting in elevated effluent ATP concentrations. Two separate experiments confirmed that biomass accumulation was higher in the presence of orthophosphate at high water temperatures (20°C) only. No significant differences were identified in biofilm ATP concentrations at lower water temperatures (below 20°C). Differences in bacterial communities between the orthophosphate- and sodium silicate-treated systems were not statistically significant, even though orthophosphate promoted higher biofilm growth. However, the genera Halomonas and Mycobacterium—which include opportunistic pathogens—were present at greater relative abundances in the orthophosphate-treated system compared to the sodium silicate system.

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Section: Cellular Atp (Catp) and Biofilm Atp (Tatp)supporting

confidence: 86%

Effect of sodium silicate on drinking water biofilm development

Munoz

Trueman

et al. 2021

Preprint

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“…This is consistent with previous work documenting adsorption of lead to aluminum hydroxides 56 − 58 or mixed iron/aluminum (oxyhydr)oxides 59 and with lead and aluminum occurring in a common colloid size fraction. 20 , 54 , 55 The presence of aluminum, iron, and lead in distinct but overlapping colloid populations, however, cannot be ruled out completely. Moreover, these data do not provide a complete picture of colloid composition; the role of phosphorus, for example, is not clear.…”

Section: Resultsmentioning

confidence: 99%

Seasonal Lead Release into Drinking Water and the Effect of Aluminum

et al. 2022

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Monitoring lead in drinking water is important for public health, but seasonality in lead concentrations can bias monitoring programs if it is not understood and accounted for. Here, we describe an apparent seasonal pattern in lead release into orthophosphate-treated drinking water, identified through point-of-use sampling at sites in Halifax, Canada, with various sources of lead. Using a generalized additive model, we extracted the seasonally varying components of time series representing a suite of water quality parameters and we identified aluminum as a correlate of lead. To investigate aluminum’s role in lead release, we modeled the effect of variscite (AlPO 4 ·2H 2 O) precipitation on lead solubility, and we evaluated the effects of aluminum, temperature, and orthophosphate concentration on lead release from new lead coupons. At environmentally relevant aluminum and orthophosphate concentrations, variscite precipitation increased predicted lead solubility by decreasing available orthophosphate. Increasing the aluminum concentration from 20 to 500 μg L –1 increased lead release from coupons by 41% and modified the effect of orthophosphate, rendering it less effective. We attributed this to a decrease in the concentration of soluble (<0.45 μm) phosphorus with increasing aluminum and an accompanying increase in particulate lead and phosphorus (>0.45 μm).

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“…While variation in equilibrium lead solubility probably explains at least some of the difference between October and February point-of-use lead levels, particle-generating mechanisms are also likely to be important, including partitioning of lead to particulate (>0.45 µm) or colloidal (<0.45 µm) aluminum. 20,54,55 Particulate aluminum was seasonal in the distribution system we studied, with the median concentration in October less than half that in February (20 and 48 µg L -1 , respectively, Figure 4b). The particulate fraction of total aluminum ranged from 16% in August to 35% in February, as estimated from the cyclic cubic regression splines shown in Figure 4b.…”

Section: Colloidal Aluminum and Lead In The Distribution Systemmentioning

confidence: 92%

“…This is consistent with previous work documenting adsorption of lead to aluminum hydroxides [56][57][58] or mixed iron/aluminum (oxyhydr)oxides, 59 and with previous studies reporting occurrence of lead and aluminum in a common colloid size fraction. 20,54,55 The presence of aluminum, iron, and lead in distinct but overlapping colloid populations, however, cannot be ruled out completely. Moreover, these data do not provide a complete picture of colloid composition; the role of phosphorus, for example, is not clear.…”

Section: Colloidal Aluminum and Lead In The Distribution Systemmentioning

confidence: 99%

Seasonal lead release to drinking water and the effect of aluminum

Trueman

Bleasdale-Pollowy

Locsin

et al. 2021

Preprint

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Monitoring lead in drinking water is important for public health, but seasonality in lead concentrations can bias monitoring programs if it is not understood and accounted for. Here, we describe an apparent seasonal pattern in lead release to orthophosphate-treated drinking water, identified through point-of-use sampling at sites in Halifax, Canada, with various sources of lead. Using a generalized additive model, we extracted the seasonally-varying components of time series representing a suite of water quality parameters and we identified aluminum as a correlate of lead. To investigate aluminum’s role in lead release, we modeled the effect of variscite (AlPO4 · 2H2O) precipitation on lead solubility, and we evaluated the effects of aluminum, temperature, and orthophosphate concentration on lead release from new lead coupons. At environmentally relevant aluminum and orthophosphate concentrations, variscite precipitation increased predicted lead solubility by decreasing available orthophosphate. Increasing the aluminum concentration from 20–500 µg L-1 increased lead release from coupons by 41% and modified the effect of orthophosphate, rendering it less effective. We attributed this to a decrease in the concentration of soluble (<0.45 µm) phosphorus with increasing aluminum and an accompanying increase in particulate lead and phosphorus (>0.45 µm).

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Pilot-scale comparison of sodium silicates, orthophosphate and pH adjustment to reduce lead release from lead service lines

Cited by 22 publications

References 30 publications

Effect of sodium silicate on drinking water biofilm development

Effect of sodium silicate on drinking water biofilm development

Seasonal Lead Release into Drinking Water and the Effect of Aluminum

Seasonal lead release to drinking water and the effect of aluminum

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