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

Impact of corrosion inhibitors on antibiotic resistance, metal resistance, and microbial communities in drinking water

Corrosion inhibitors, including zinc orthophosphate, sodium orthophosphate, and sodium silicate, are commonly used to prevent the corrosion of drinking water infrastructure. Metals such as zinc are known stressors for antibiotic resistance selection, and phosphates can increase microbial growth in drinking water distribution systems (DWDS). Yet, the influence of corrosion inhibitor type on antimicrobial resistance in DWDS is unknown. Here, we show that sodium silicates can decrease antibiotic resistant bacteria (ARB) and antibiotic-resistance genes (ARGs), while zinc orthophosphate increases ARB and ARGs in source water microbial communities. Based on controlled bench-scale studies, zinc orthophosphate addition significantly increased the abundance of ARB resistant to ciprofloxacin, sulfonamides, trimethoprim, and vancomycin, as well as the genes sul1, qacEΔ1, an indication of resistance to quaternary ammonium compounds, and the integron-integrase gene intI1. In contrast, sodium silicate dosage at 10 mg/L resulted in decreased bacterial growth and antibiotic resistance selection compared to the other corrosion inhibitor additions. Source water collected from the drinking water treatment plant intake pipe resulted in less significant changes in ARB and ARG abundance due to corrosion inhibitor addition compared to source water collected from the pier at the recreational beach. In tandem with the antibiotic resistance shifts, significant microbial community composition changes also occurred. Overall, the corrosion inhibitor sodium silicate resulted in the least selection for antibiotic resistance, which suggests it is the preferred corrosion inhibitor option for minimizing antibiotic resistance proliferation in DWDS. However, the selection of an appropriate corrosion inhibitor must also be appropriate for the water chemistry of the system (e.g., pH, alkalinity) to minimize metal leaching first and foremost and to adhere to the lead and copper rule. IMPORTANCE Antibiotic resistance is a growing public health concern across the globe and was recently labeled the silent pandemic. Scientists aim to identify the source of antibiotic resistance and control points to mitigate the spread of antibiotic resistance. Drinking water is a direct exposure route to humans and contains antibiotic-resistant bacteria and associated resistance genes. Corrosion inhibitors are added to prevent metallic pipes in distribution systems from corroding, and the type of corrosion inhibitor selected could also have implications on antibiotic resistance. Indeed, we found that sodium silicate can minimize selection of antibiotic resistance while phosphate-based corrosion inhibitors can promote antibiotic resistance. These findings indicate that sodium silicate is a preferred corrosion inhibitor choice for mitigation of antibiotic resistance.

Reduction in water consumption in premise plumbing systems: Impacts on lead concentration under different water qualities

Water conservation measures are increasing in response to regulatory requirements addressing the need for lower environmental footprint and in response to water shortages. In households with lead service lines (LSLs), lowering consumption can adversely impact lead release as it will increase stagnation. Using a lead dissolution model and data from extensive pilot studies on excavated LSLs, the impact of adaptation to different water conservation strategies on dissolved lead contamination at the kitchen tap is assessed under three water qualities and three LSL lengths (3, 14 and 30 m) using hydraulic and water quality modelling. Consumers' behavioural variability is also assessed based on integration of EPANET and results of the stochastic water demand model SIMDEUM. Demand reduction increased the dissolved lead concentrations (Pb_diss) at the end of the LSL with mean values ranging from 28.4 to 63.3 μg/L (without corrosion control) and from 4.6 to 9.9 μg/L with corrosion control (addition of orthophosphate and pH adjustment). Adding orthophosphate (1 mg P/L) to the water reduces the mean Pb_diss values at the kitchen tap from 7.1 μg/L to 1.2 μg/L for a high water demand scenario and from 31.2 to 4.9 μg/L for a low water demand scenario. Finally, the Integrated Exposure Uptake Biokinetic (IEUBK) model is used to predict the potential blood lead levels (BLLs) for children aged 0-84 months. Results showed that the orthophosphate addition of only 1 mg P/L can significantly decrease the proportion of children with a BLL >5 μg/dL, from 82 % to 17 %, under the most extreme water conservation scenario studied, using the 90th percentile of Pb_diss concentrations during usage at kitchen tap. Wide variations of Pb_diss concentrations at the kitchen tap were calculated at times of use over a week (up to 155 μg/L in lower demand scenarios, without corrosion control) showing evident limitations of single random daytime sampling.

A literature review of bench top and pilot lead corrosion assessment studies

Bench top and pilot lead corrosion studies are gaining more interest, considering revisions and upcoming improvements to the Lead and Copper Rule. This literature review identified studies ranging from simpler month(s)-long bench top dump-and-fill stagnant water tests (coupon tests/standing pipe tests) to more complicated year(s)-long intermittent flow pilot studies (recirculating pipe loops/once through pipe rigs). With increasing complexity in design and operation, studies more closely approximated real plumbing conditions (e.g., by incorporating harvested lead pipes and intermittent flow regimes) at increased cost, footprint, and duration. Comparison of bench top and pilot designs (in terms of lead test piece age/dimensions/configuration/replicates, study duration, sample collection, and other factors) can assist drinking water utilities, consultants, academics, and others to select a design that matches their needs and constraints. No matter the choice, surrogate systems cannot replace actual system water testing and are best complemented by other corrosion assessment tools.

Early phase effects of silicate and orthophosphate on lead (Pb) corrosion scale development and Pb release

Orthophosphate is widely used to control lead (Pb) release in drinking water distribution systems, but phosphorus addition is not sustainable. Alternative corrosion control treatments are needed, and sodium silicate is one possibility. Here, pre-corroded Pb coupons-with and without free chlorine-were used to examine early-phase corrosion scale development after silicate addition, with orthophosphate as a reference corrosion inhibitor. Scale development was evaluated in terms of total Pb release, phase transformation, electrochemical impedance, morphological changes, Pb dissolution kinetics, and short-term Pb-Cu galvanic corrosion. Elevated Pb release occurred for approximately one month after silicate addition, and total Pb release peaked at 1968.1 μg/L and 1176.9 μg/L from systems with and without free chlorine, respectively. In contrast, orthophosphate-treated coupons exhibited fewer, less pronounced spikes in Pb release. By day 354, the median total Pb release from orthophosphate-treated coupons with and without free chlorine had decreased to 3.7 and 5.0 μg/L, respectively, while the median total Pb release from corresponding silicate-treated coupons was much higher, at 44.9 μg/L and 34.3 μg/L. Calcium lead apatite (Ca_0.56Pb_3.77(PO₄)₃OH_0.67) was identified in orthophosphate-treated scales, with hydroxylpyromorphite (Pb₅(PO₄)₃OH) present in the absence of free chlorine. Plattnerite occurred on coupons in all chlorinated systems. Pb silicate compounds were not detected, but Ca₂SiO₄ and Na₂Ca₂(SiO₃)₃ were identified by X-ray powder diffraction. The charge transfer: film resistance ratio characterizing the orthophosphate-treated coupons decreased slowly while that of the silicate-treated coupons increased after silicate was added. These variations suggest orthophosphate provided better corrosion control than silicate did. Silicate treatment generally caused degradation of the top Pb scale layer, resulting in elevated Pb release, while orthophosphate encouraged the growth of more structured, generally thicker, corrosion scales that were effective in limiting Pb release.

Roasted modified lead-zinc tailings using alkali as activator and its mitigation of Cd contaminated: Characteristics and mechanisms

To comprehensively reuse lead-zinc tailings, leaching residue (LR) of solid by-products was produced after the recovery of valuable metals. This study provided a "waste-ecology" strategy by a simple, inexpensive method of roasting prepared highly active silicon modified tailing (HAST) to eliminate the environment risk of LR, and investigates performance and mechanism of HAST as sorbents and passivators. The results indicated that HAST possesses high pH, abundant mineral content, microporous structure and high stability. The adsorption kinetic experiment revealed that chemisorption is the main reaction and the Q_m of Cd via Langmuir model is 72.75 mg/g. As further demonstrated by X-ray diffraction (XRD), energy dispersive X-ray (EDX), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis, the Cd was adsorbed onto the HAST surface successfully, with the main interaction mechanisms involving ion exchange, complexation, precipitation and electrostatic interaction. Besides, the soil incubation experiment results showed that HAST had positive effects on exchange fractions (Cd) converting to stable fractions in soil, which modifies Cd migration and transformation, HAST added into soil decreased the DTPA-Cd by 4.7%-8.1%, 5.9-9.8% and 9.1%-13.4%, respectively, in different stages, as compared with the control. Therefore, this study provides a novel strategy to address LR recycling, and the relevant, wastewater and soil treatment, which has high practicability for industrial applications.

Seasonal Lead Release into Drinking Water and the Effect of Aluminum

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 (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 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).