Evaluation of Ferrate Preoxidation for Drinking Water Treatment

Ferrate (Fe(IV)) has been proposed as a viable alternative for pre-oxidation in drinking water treatment (Jiang & Lloyd, 2002; Sharma, Kazama, Jiangyong, & Ray, 2005). The primary advantages of ferrate include a strong oxidation potential without the formation of halogenated by-products. In addition, the by-product of ferrate oxidation, ferric iron (Fe(III)), may have beneficial impacts on downstream particle destabilization and removal processes. Also, ferrate has disinfectant properties and may also provide pathogen inactivation in drinking water (Sharma et al., 2005). However, despite these advantages, there is a dearth of research experience that examines the implications of using ferrate for treating actual drinking water sources for potable water production. Studies were conducted evaluating the nature of particles that result from ferrate reduction in a laboratory water matrix and in a natural surface water with a moderate amount of dissolved organic carbon. Particle characterization included size, surface charge, morphology, X-ray photoelectron spectroscopy and transmission Fourier transform infrared spectroscopy. Characteristics of ferrate resultant particles were compared to particles formed from dosing ferric chloride, a common water treatment coagulant. In natural water, ferrate addition produced significantly more nanoparticles than ferric addition. These particles had a negative surface charge, resulting in a stable colloidal suspension. In natural and laboratory matrix waters, the ferrate resultant particles had a similar charge versus pH relationship as particles resulting from ferric addition. Particles resulting from ferrate had morphology that differed from particles resulting from ferric iron, with ferrate resultant particles appearing smoother and more granular. X-ray photoelectron spectroscopy results show ferrate resultant particles contained Fe2O3, while ferric resultant particles did not. Results also indicate potential differences in the mechanisms leading to particle formation between ferrate reduction and ferric hydrolysis. An analysis of soluble manganese oxidation by ferrate (Fe(VI)) was executed at the bench-scale, in a laboratory water matrix, both with and without the presence of natural organic matter (NOM). In the laboratory water matrix without NOM, the oxidation of Mn(II) by Fe(VI) was found to follow a stoichiometry of 2 moles Fe(VI) to 3 moles Mn(II), resulting in reduced, particulate Fe(III) and oxidized, particulate Mn(IV). The size distribution of resulting particles included significant amounts of nanoparticles. The observed stoichiometric ratio held for multiple initial Mn(II) concentrations and pH values. The presence of NOM did not significantly affect the stoichiometry, indicating limited competitive oxidant demand. Fe(VI) dosages above the stoichiometric ratio produced Mn(VII). The rate of the Mn(II) oxidation reaction was fast relative to typical time scales in drinking water treatment, with an estimated second order rate constant of approximately 1.0×104 M-1 s-1 at pH 9.2. A laboratory assessment of ferrate for drinking water treatment was conducted, including batch and continuous flow experiments on several different natural water samples. In batch experiments, ferrate preoxidation enhanced the removal of ultraviolet light absorbing compounds (UV254) by subsequent coagulation in a minority of water samples, while the majority of samples showed no improvement. In continuous flow experiments, ferrate was incorporated into small-scale models of existing treatment plants. In general, ferrate preoxidation improved finished water turbidity, UV254 absorbance and disinfection by-product formation as compared to no preoxidation and preoxidation with Mn(VII). However, for one natural water, improvements were similar in magnitude to those achieved by adding the same mass of Fe(III) in place of Fe(VI) prior to a formal coagulation step. Particulate iron resulting from Fe(VI) reduction was effectively destabilized and removed via coagulation and filtration. Ferrate may be a viable technology for drinking water treatment systems; and present a better alternative to existing oxidants by providing disinfection and oxidation of inorganics without negative impacts to downstream stream processes. The benefits of adding ferrate are likely to vary based on raw water quality and treatment goal

My Private Lead Service Line Replacement

3 Key Takeaways: A homeowner’s decision to replace their lead service line can be confounded by factors including their understanding of the science, their perceptions of their lead exposure risks, and the cost of the work. First draw and 5-minute flush samples may not capture the peak lead concentration, further confounding a customer’s replacement decision. In my case, lead service line replacement significantly lowered lead concentrations after stagnation based on sequential sampling

Literature review on appropriate health-based standards for direct and indirect potable reuse as well as various non-potable reuse scenarios

Project Summary Objectives: Water reuse is an increasingly important response to water stress; however, major advancements in water reuse have neglected small, rural communities that comprise most public water systems. The objective of this project is to accelerate water reuse adoption in rural communities by increasing technical and community readiness. The general hypothesis is that community readiness for water reuse in small systems can be accelerated by a convergence of technical, informational, social, and institutional innovation. Also, we hypothesize that severe water scarcity need not be a prerequisite for water reuse implementation, given careful attention to windows of opportunity that integrate multiple community concerns. Approach: Barriers to water reuse adoption are intertwined and complex. Therefore, our proposed work will be an integrated research and engagement program in which we: (1) address knowledge gaps and generate frameworks for overcoming these barriers, and (2) use research outputs to evaluate and accelerate community readiness for reuse in five case studies. Both general activities will be executed in parallel such that knowledge can be co-produced with decision-makers. Specific methods to address knowledge gaps include community surveys, the use of a prototype calculation engine, and desktop, bench-scale and pilot-scale evaluations of treatment technologies. Specific methods to accelerate community readiness include legal and policy analyses and case-study evaluations of five small water systems. Expected Results: This project is expected to produce outputs and outcomes that lead to acceleration of community readiness for reuse in small systems. Specifically, key results include modular, decision support tools such as water inventories, technology databases, and cost and demand curves for reuse. These outputs will be integrated into institutional and regulatory decision-making processes in small, rural, underserved communities with results made available to communities through workshops, outreach events, and publications. We will go through many iterative processes throughout the project in which feedback from small community members and stakeholders will inform the modifications of tools and outputs so that they are indeed meaningful and useful to small communities facing unique challenges

Pilot-scale evaluation of sulfite-activated ferrate for water reuse applications

Ferrate is a promising, “green” (i.e., iron-based) pre-oxidation technology in water treatment, but there has been limited research on its potential benefits in a water reuse (wastewater recycling) paradigm. Recent studies have shown ferrate treatment processes can be improved by activation, the addition of reductants (i.e., sulfite) to the reaction. Prior bench scale experimentation suggests sulfite-activated ferrate may be a feasible option for water reuse applications; however, extent questions need to be addressed. This study evaluated the viability of sulfite-activated ferrate in water reuse treatment through continuous-flow experiments using synthetic and field-collected secondary wastewater effluents. The effluents were processed through the piloting system which included various physicochemical processes such as ferrate pre-oxidation, coagulation, clarification, and dual-media filtration. In each trial, the system was run continuously for eight hours with data collected via grab samples and online instrumentation with real-time resolution. Results demonstrate that reuse systems using activated ferrate pre-oxidation can produce effluents with water quality meeting most regulatory requirements without major impacts on downstream physicochemical processes. When compared to traditional ferrate pre-oxidation, activation showed several improvements such as lower byproduct yields. Operationally, activated ferrate does increase the development of headloss across the dual-media filter. In general, sulfite-activated ferrate is viable in a water reuse setting, resulting in several improved water quality outcomes. Results from this work create a pathway for adaptation at scale

Versatility, Cost Analysis, and Scale-up in Fluoride and Arsenic Removal Using Metal-organic Framework-based Adsorbents

Fluoride and arsenic are hazardous inorganic contaminants due to associated health risks and relatively higher levels of occurrence in groundwater. Metal-organic frameworks, (MOFs) with their high surface area, versatile building blocks and numerous active sites, are a novel approach to fluoride and arsenic uptake. This review presents the different types of MOFs for fluoride and arsenic removal along with a study of dynamic breakthrough times and cost analysis. MOF performances are based on a variety of synthesis methods, notable among which solvothermal one is more described. However, all research works concluded that MOFs have poor yield compared to conventional adsorbents. But, their high adsorption capacity, tailored chemical structure and ionic uptake of fluoride and arsenic make them a more favorable option than many other adsorbents. The cost of different MOFs usually varies between 0.1 and 5 US$/g depending on the synthesis routes

Comparison of ferrate and ozone pre-oxidation on disinfection byproduct formation from chlorination and chloramination

This study investigated the effects of ferrate and ozone pre-oxidation on disinfection byproduct (DBP) formation from subsequent chlorination or chloramination. Two natural waters were treated at bench-scale under various scenarios (chlorine, chloramine, each with ferrate pre-oxidation, and each with pre-ozonation). The formation of brominated and iodinated DBPs in fortified natural waters was assessed. Results indicated ferrate and ozone pre-oxidation were comparable at molar equivalent doses for most DBPs. A net decrease in trihalomethanes (including iodinated forms), haloacetic acids (HAAs), dihaloacetonitrile, total organic chlorine, and total organic iodine was found with both pre-oxidants as compared to chlorination only. An increase in chloropicrin and minor changes in total organic bromine yield were caused by both pre-oxidants compared to chlorination only. However, ozone led to higher haloketone and chloropicrin formation potentials than ferrate. The relative performance of ferrate versus ozone for DBP precursor removal was affected by water quality (e.g., nature of organic matter and bromide concentration) and oxidant dose, and varied by DBP species. Ferrate and ozone pre-oxidation also decreased DBP formation from chloramination under most conditions. However, some increases in THM and dihaloacetonitrile formation potentials were observed at elevated bromide levels

Laboratory Assessment of Ferrate for Drinking Water Treatment

A laboratory assessment of ferrate (Fe(VI)) for drinking water treatment was conducted, including batch and continuous flow experiments on natural water samples. In batch experiments, ferrate preoxidation enhanced the removal of ultraviolet light-absorbing compounds (UV254; absorbance at 254 nm) by subsequent coagulation in some water samples, while some samples showed no improvement. Ferrate oxidation was not found to have negative impacts on subsequent coagulation. In continuous flow experiments, ferrate preoxidation improved finished water turbidity, UV254 absorbance, and disinfection by-product formation as compared with no preoxidation and to preoxidation with permanganate. However, improvements were similar in magnitude to those achieved by adding the same mass of ferric iron in place of ferrate prior to a formal coagulation step, in one water study. Particulate iron resulting from Fe(VI) reduction was effectively destabilized and removed via coagulation and filtration. Ferrate may be a viable technology for drinking water treatment depending on raw water quality and treatment goals

Emerging investigator series: moving beyond resilience by considering antifragility in potable water systems

It is inherently difficult to plan water systems for a future that is non-predictive. This paper introduces a novel perspective for the design and operation of potable water systems under increasing water quality volatility (e.g., a relatively rapid and unpredicted deviation from baseline water quality). Increased water quality volatility and deep uncertainty stress water systems, confound design decisions, and increase the risk of decreased water system performance. Recent emphasis on resilience in drinking water treatment has partly addressed this issue, but still establishes an adversarial relationship with change. An antifragile system benefits from volatile change. By incorporating antifragility, water systems may move beyond resilience and improve performance with extreme events and other changes, rather than survive, or fail and quickly recover. Using examples of algal blooms, wildfires, and the COVID-19 pandemic, this work illustrates fragility, resilience, and antifragility within physicochemical process design including clarification, adsorption and disinfection. Methods for increasing antifragility, both individual process options and new system design tools, are discussed. Novel physicochemical processes with antifragile characteristics include ferrate preoxidation and magnetic iron (nano)particles. New design tools that allow for systematic evaluation of antifragile opportunities include artificial neural networks and virtual jar or pilot “stress testing”. Incorporating antifragile characteristics represents a trade-off with capital and/or operating cost. We present a real options analysis approach to considering costs in the context of antifragile design decisions. Adopting this antifragile perspective will help ensure water system improved performance during extreme events and a general increase in volatility

Preliminary Assessment of Ferrate Treatment of Metals in Acid Mine Drainage

We report a preliminary assessment of ferrate [Fe(VI)] for the treatment of acid mine drainage (AMD), focused on precipitation of metals (i.e., iron [Fe] and manganese [Mn]) and subsequent removal. Two dosing approaches were studied to simulate the two commercially viable forms of Fe(VI) production: Fe(VI) only, and Fe(VI) with sodium hydroxide (NaOH). Subsequent metal speciation was assessed via filter fractionation. When only Fe(VI) was added, the pH remained99% when only NaOH was added, indicating that oxidation by Fe(VI) did not play a significant role when added. The Fe(III) and Al(III) particles were relatively large, suggesting probable success in subsequent removal through sedimentation. Resultant Mn-oxide particles were relatively small, indicating that additional particle destabilization may be required to meet Mn effluent goals. Ferrate seems viable for the treatment of AMD, especially when sourced through onsite generation due to the coexistence of NaOH in the product stream. More research on the use of Fe(VI) for AMD treatment is required to answer extant questions

Quantifying and contextualizing disinfection byproducts during the Flint Water Crisis: a case study, and framework for broader application

Total trihalomethanes (TTHMs) and other disinfection byproducts (DBPs) have been a concern in Flint, Michigan, in both delivered water and water from home water heaters. Historical TTHM data and DBP sampling results from Flint were combined with models for predicting hot water TTHMs to assess the probability of certain DBP concentrations. Results were compared with hot and cold water DBPs from a water system in Florida. Flint results were used to estimate cancer risk resulting from chronic exposure to hot water TTHMs, and compared to similar risk assessments in other water systems. Results indicate TTHM concentrations decreased in Flint following a return to water from the Detroit Water and Sewerage Department, and were very near the mean value for public drinking water systems in the United States. Measurement of other unregulated DBPs also indicated levels within the typical ranges. Monte Carlo simulations coupled with modeling of hot water TTHMs indicated a low probability of TTHMs exceeding 80 μg/L in Flint in 2016. The estimated cancer risk from exposure to TTHMs in Flint is similar to other areas. The methods used in this work can apply broadly to other water systems to de-escalate perceptions of risk following a water crisis