Influence of granular activated carbon media properties on natural organic matter and disinfection by-product precursor removal from drinking water

Adsorption kinetics, isotherms, and selectivity of trihalomethanes and haloacetonitriles by granular activated carbon

The performance capability of granular activated carbon (GAC) adsorption in terms of disinfection by-product (DBPs) removal was investigated with synthetic water containing 1) trihalomethanes (THMs), 2) haloacetronitriles (HANs), and 3) Mix-THMs & HANs. The initial 20 min of adsorption resulted in the maximum adsorption rate, with the total THMs, total HANs, and total Mix-THMs & HANs being 4.972, 2.071, and 6.460 µg/gGAC-min, respectively. GAC dosage affects the adsorption selectivity of THMs and HANs. Under a low GAC dosage, the selectivity of GAC adsorbs more bromo-THMs than chloro-THMs. The adsorption selectivity of THMs on GAC following bromoform > dibromochloromethane > bromodichloromethane > chloroform was investigated. As the GAC concentration increased, the selectivity of THM adsorption by GAC became comparable. Chloro-HAN, in contrast to THMs, has a higher adsorption selectivity than bromo-HAN. Trichloroacetonitrile was removed by GAC more rapidly than the other HAN species when the GAC dose was increased. The toxin of bromoform was primarily eliminated through GAC adsorption, caused by a greater removal rate than that of the other THMs. As an implemented measure, GAC is introduced to reduce THMs and HANs and the toxic contents associated with THMs and HANs.

Comparative investigation of known and unknown disinfection by-product precursor removal and microbial community from biological biochar and activated carbon filters

Biological activated carbon filter (BAC) is one of the most effective technologies for removing disinfection by-product (DBP) precursors from water. Biochar is a lower-cost medium that has the potential to replace granular activated carbon in BAC applications, thus leading to the development of biological biochar filter (BCF). This study compared BCF with BAC for the removal of DBP precursors using column experiments. Both BCF and BAC achieved the removal of DBP precursors, resulting in concentrations of all DBP formation potential below the World Health Organization guideline values for drinking water. Bromodichloromethane and unknown DBP precursor removal by BCF was comparable to that by BAC. However, BAC removed more chloroform and dichloroacetontrile precursors than BCF. For microbial community analysis, cell numbers in a bottom layer (inlet) of BCF and BAC columns were higher than those in the top layer. The abundances of Nordella and a microbial genus from Burkholderiaceae at the bottom layer showed a strong correlation to the number of DBP precursors removed and were comparable in BCF and BAC. This finding likely contributes to the similarities between DBPs species removed and the removal performances of some known and unknown DBP precursors by BCF and BAC. Overall results from this study revealed that biochar can be served as a low-cost and sustainable replacement of activated carbon in water filter for DBP precursor removal.

A robust self-regenerating graphene-based adsorbent for pharmaceutical removal in various water environments

The presence of active pharmaceutical ingredients (APIs) in wastewater effluents and natural aquatic systems threatens ecological and human health. While activated carbon-based adsorbents, such as GAC and PAC, are widely used for API removal, they exhibit certain deficiencies, including reduced performance due to the presence of natural organic macromolecules (NOMs) and high regeneration costs. There is growing demand for a robust, stable, and self-regenerative adsorbent designed for API removal in various environments. In this study, we synthesized a self-generating metal oxide nano-composite (S-MGC) containing titanium dioxide (TiO2) and silicon dioxide (SiO2) combined with 3D graphene oxide (GO) to adsorb APIs and undergo regeneration via light illumination. We determined optimal TiO2:SiO2:GO compositions for the S-MGCs through experiments using a model contaminant, methylene blue. The physical and chemical properties of S-MGCs were characterized, and their adsorption and photodegradation capabilities were studied using five model APIs, including sulfamethoxazole, carbamazepine, ketoprofen, valsartan, and diclofenac, both in single-component and multi-component mixtures. In the absence of TiO2/SiO2, 3D graphene oxide (CGB) displayed better adsorption performance compared to GAC, and S-MGCs further improve CGB's adsorption capacity. This performance remained consistent in two complex water environments: aqueous solutions at varying NOM levels and artificial urine. TiO2 supported on the GO surface exhibits similar photocatalytic activity to suspended TiO2. In a continuous fixed-bed column test, S-MGCs demonstrated robust API adsorption performance that is maintained in the presence of NOM or urine, and can be regenerated through multiple cycles of adsorption and light illumination.

Control of chlorination disinfection by-products in drinking water by combined nanofiltration process: A case study with trihalomethanes and haloacetic acids

Disinfection by-products (DBPs) are prevalent contaminants in drinking water and are primarily linked to issues regarding water quality. These contaminants have been associated with various adverse health effects. Among different treatment processes, nanofiltration (NF) has demonstrated superior performance in effectively reducing the levels of DBPs compared to conventional processes and ozone-biological activated carbon (O3-BAC) processes. In this experiment, we systematically investigated the performance of three advanced membrane filtration treatment schemes, namely "sand filter + nanofiltration" (SF + NF), "sand filter + ozone-biological activated carbon + nanofiltration" (SF + O3-BAC + NF), and "ultrafiltration + nanofiltration" (UF + NF), in terms of their ability to control disinfection by-product (DBP) formation in treated water, analyzed the source and fate of DBP precursors during chlorination, and elucidated the role of precursor molecular weight distribution during membrane filtration in relation to DBP formation potential (DBPFP). The results indicated that each treatment process reduced DBPFP, as measured by trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP), with the SF + O3-BAC + NF process being the most effective (14.27 μg/L and 14.88 μg/L), followed by the SF + NF process (21.04 μg/L and 16.29 μg/L) and the UF + NF process (26.26 μg/L and 21.75 μg/L). Tyrosine, tryptophan, and soluble microbial products were identified as the major DBP precursors during chlorination, with their fluorescence intensity decreasing gradually as water treatment progressed. Additionally, while large molecular weight organics (60-100,000 KDa) played a minor role in DBPFP, small molecular weight organics (0.2-5 KDa) were highlighted as key contributors to DBPFP, and medium molecular weight organics (5-60 KDa) could adhere to the membrane surface and reduce DBPFP. Based on these findings, the combined NF process can be reasonably selected for controlling DBP formation, with potential long-term benefits for human health.

Impact of harmful algal bloom severity on bacterial communities in a full-scale biological filtration system for drinking water treatment

The occurrence of harmful algal blooms (HABs) in freshwater environments has been expanded worldwide with growing frequency and severity. HABs can pose a threat to public water supplies, raising concerns about safety of treated water. Many studies have provided valuable information about the impacts of HABs and management strategies on the early-stage treatment processes (e.g., pre-oxidation and coagulation/flocculation) in conventional drinking water treatment plants (DWTPs). However, the potential effect of HAB-impacted water in the granular media filtration has not been well studied. Biologically-active filters (BAFs), which are used in drinking water treatment and rely largely on bacterial community interactions, have not been examined during HABs in full-scale DWTPs. In this study, we assessed the bacterial community structure of BAFs, functional profiles, assembly processes, and bio-interactions in the community during both severe and mild HABs. Our findings indicate that bacterial diversity in BAFs significantly decreases during severe HABs due to the predominance of bloom-associated bacteria (e.g., Spingopyxis, Porphyrobacter, and Sphingomonas). The excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) confirmed that filter influent affected by the severe HAB contained a higher portion of protein-like substances than filter influent samples during a mild bloom. In addition, BAF community functions showed increases in metabolisms associated with intracellular algal organic matter (AOM), such as lipids and amino acids, during severe HABs. Further ecological process and network analyses revealed that severe HAB, accompanied by the abundance of bloom-associated taxa and increased nutrient availability, led to not only strong stochastic processes in the assembly process, but also a bacterial community with lower complexity in BAFs. Overall, this study provides deeper insights into BAF bacterial community structure, function, and assembly in response to HABs.

Bioinspired stormwater control measure for the enhanced removal of truly dissolved polycyclic aromatic hydrocarbons and heavy metals from urban runoff

Stormwater harvesting (SWH) addresses the UN's Sustainable Development Goals (SDGs). Conventional stormwater control measures (SCMs) effectively remove particulate and colloidal contaminants from urban runoff; however, they fail to retain dissolved contaminants, particularly substances of concern like polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs), thereby hindering the SWH applicability. Here, inspired by protein folding in nature, we reported a novel biomimetic SCM for the efficient removal of dissolved PAHs and HMs from urban runoff. Lab-scale tests were conducted together with a more mechanistic investigation on how the contaminants were removed. By integrating hydrophobic organic chains with low-cost hydrophilic flocculant matrixes, our biomimetic flocculants achieved a 1.4-9.5 times removal of all detected dissolved PAHs and HMs, while enhancing the removal of a wide-spectrum of particulate and colloidal contaminants, compared to existing SCMs. Ecotoxicity, as indicated by newborn Daphnia magna as experimental organisms, was reduced from "acute toxicity" of the original runoff sample (toxic unit of ∼2.6) to "non-toxicity" (toxic unit < 0.4) of the treated water. The improved performance is attributed to the protein-folding-like features of the bioinspired flocculants providing: (i) stronger binding to PAHs (via hydrophobic association) and HMs (via coordination), and (ii) the ability of spontaneous aggregation. The bio-inspired approach in this work holds strong promise as an alternative or supplementary component in SCM systems, and is expected to contribute to sustainable water management practices in relation to SDGs.

Characteristics in dissolved organic matter and disinfection by-product formation during advanced treatment processes of municipal secondary effluent with Orbitrap mass spectrometry

Dissolved organic matter (DOM) is reported to be a precursor to disinfection by-products (DBPs), which have adverse effects on human health. Therefore, it is crucial to effectively remove DOM before water disinfection. Characteristics of DOM and DBPs formation during advanced treatment processes including coagulation, adsorption, ultraviolet (UV) irradiation, and ozone (O3) oxidation in municipal secondary effluent were investigated in this research. DOM was characterized by Fourier transform infrared spectroscopy (FTIR), excitation-emission matrix fluorescence spectroscopy (EEM), and Orbitrap mass spectrometry (Orbitrap MS). Moreover, DBPs formation potential under different advanced treatment processes was also discussed. FTIR results indicated that various functional groups existing in DOM may react with the disinfectant to form toxic DBPs. EEM analysis indicated that DOM in all water samples was dominated by soluble microbial product-like (SMPs) and humic acid-like (HA) substances. The municipal secondary effluent was abundant with DOM and rich in carbon, hydrogen, oxygen, and nitrogen atoms, contained a certain dosage of phosphorus and sulfur atoms, and the highest proportion is lignin. Most of the precursors (CHO features) had positive double bond equivalent subtracted oxygen per carbon [(DBE-O)/C] and negative carbon oxidation state (Cos) in all four different advanced treatment processes. DBPs formation potential (DBPFP) of coagulation, adsorption, UV irradiation, and O3 oxidation advanced treatment processes were 487 μg L-1, 586 μg L-1, 597 μg L-1, and 308 μg L-1, respectively. And the DBPs precursors removal efficiency of coagulation, adsorption, UV irradiation, and O3 oxidation advanced treatment processes were 50.8%, 40.8%, 39.8%, and 69.0%, respectively. This study provides in-depth insights into the changes of DOM in municipal secondary effluent at the molecular level and the removal efficiency of DBPs precursors during coagulation, adsorption, UV irradiation, and O3 oxidation advanced treatment processes.

Molecular complexation properties of Cd2+ by algal organic matter from Scenedesmus obliquus

A detailed understanding the metals binding with algal organic matter (AOM) is essential to gain a deeper insight into the toxicity and migration of metals in algae cell. However, the molecular complexation mechanism of the metals binding with AOM remains unclear. In this study, cadmium ion (Cd2+) binding properties of AOMs from Scenedesmus obliquus, which included extracellular organic matter (EOM) and intracellular organic matter (IOM), were screened. When Cd2+ < 0.5 mg/L, the accumulation of Cd2+ could reach 40%, while Cd2+ > 0.5 mg/L, the accumulation of Cd2+ was only about 10%. EOM decreased gradually (from 8.51 to 3.98 mg/L), while IOM increased gradually (from 9.62 to 21.00 mg/L). The spectral characteristics revealed that IOM was richer in peptides/proteins and had more hydrophilic than EOM. Both EOM and IOM contained three protein-like components (containing tryptophan and tyrosine) and one humic-like component, and their contents in IOM were higher than that in EOM. The tryptophan protein-like substances changed greatly during Cd2+ binding, and that the tryptophan protein-like substances complexed to Cd2+ before tyrosine protein-like substances in IOM was identified. Moreover, the functional groups of N-H, O-H, and CO in AOM played an important role, and the N-H group was priority to interacts with Cd2+ in the complexing process. More functional groups (such as C-O and C-N) were involved in the metals complexing in EOM than in IOM. It could be concluded that Cd2+ stress promoted the secretion of AOM in Scenedesmus obliquus, and proteins in AOM could complex Cd2+ and alleviate its toxicity to algal cell. These findings provided deep insights into the interaction mechanism of AOM with Cd2+ in aquatic environments.

An advanced treatment process for 3-high wastewater discharged from crude oil storage tanks

The wastewater discharged from crude oil storage tanks (WCOST) contains high concentrations of salt and metal iron ions, and high chemical oxygen demand (COD). It belongs to "3-high" wastewater, which is difficult for purification. In this study, WCOST treatments were comparatively investigated via an advanced pretreatment and the traditional coagulation-microfiltration (CMF) processes. After WCOST was purified through the conventional CMF process, fouling occurred in the microfiltration (MF) membrane, which is rather harmful to the following reverse osmosis (RO) membrane unit, and the effluent featured high COD and UV254 values. The analysis confirmed that the MF fouling was due to the oxidation of ferrous ions, and the high COD and UV254 values were mainly attributable to the organic compounds with small molecular sizes, including aromatic-like and fulvic-like compounds. After the pretreatment of the advanced process consisting of aeration, manganese sand filtration, and activated carbon adsorption in combination with CMF process, the removal efficiencies of organic matter and total iron ions reached 97.3% and 99.8%, respectively. All the water indexes of the effluent, after treatment by the advanced multi-unit process, meet well the corresponding standard. The advanced pretreatment process reported herein displayed a great potential for alleviating the MF membrane fouling and enhanced the lifetime of the RO membrane system in the 3-high WCOST treatment.

Reduction of byproduct formation and cytotoxicity to mammalian cells during post-chlorination by the combined pretreatment of ferrate(VI) and biochar

Ferrate [Fe(VI)] can efficiently degrade various pollutants in wastewater. Biochar application can reduce resource use and waste emission. This study investigated the performance of Fe(VI)/biochar pretreatment to reduce disinfection byproducts (DBPs) and cytotoxicity to mammalian cells of wastewater during post-chlorination. Fe(VI)/biochar was more effective at inhibiting the cytotoxicity formation than Fe(VI) alone, reducing the cytotoxicity from 12.7 to 7.6 mg-phenol/L. The concentrations of total organic chlorine and total organic bromine decreased from 277 to 130 μg/L and from 51 to 39 μg/L, compared to the samples without pretreatment. Orbitrap ultra-high resolution mass spectrometry revealed that the number of molecules of DBPs decreased substantially from 517 to 229 by Fe(VI)/biochar, with the greatest reduction for phenols and highly unsaturated aliphatic compounds. In combination with the substantial reduction of 1Cl-DBPs and 2Cl-DBPs, 1Br-DBPs and 2Br-DBPs were also reduced. Fluorescence excitation-emission matrix coupled with parallel factor analysis suggested that fulvic acid-like substances and aromatic amino acid was obviously reduce likely due to the enhanced oxidation of Fe(IV)/Fe(V) produced by Fe(VI)/biochar and adsorption of biochar. Furthermore, the DBPs generated by electrophilic addition and electrophilic substitution of precursors were reduced. This study shows that Fe(VI)/biochar pretreatment can effectively reduce cytotoxicity formation during post-chlorination by transforming DBPs and their precursors.

Interactions between H2O2 and dissolved organic matter during granular activated carbon-based residual H2O2 quenching from the upstream UV/H2O2 process

Granular activated carbon (GAC) filtration can be employed to synchronously quench residual H₂O₂ from the upstream UV/H₂O₂ process and further degrade dissolved organic matter (DOM). In this study, rapid small-scale column tests (RSSCTs) were performed to clarify the mechanisms underlying the interactions between H₂O₂ and DOM during the GAC-based H₂O₂ quenching process. It was observed that GAC can catalytically decompose H₂O₂, with a long-lasting high efficiency (>80% for approximately 50,000 empty-bed volumes). DOM inhibited GAC-based H₂O₂ quenching via a pore-blocking effect, especially at high concentrations (10 mg/L), with the adsorbed DOM molecules being oxidized by the continuously generated ·OH; this further deteriorated the H₂O₂ quenching efficiency. In batch experiments, H₂O₂ could enhance DOM adsorption by GAC; however, in RSSCTs, it deteriorated DOM removal. This observation could be attributed to the different ·OH exposure in these two systems. It was also observed that aging with H₂O₂ and DOM altered the morphology, specific surface area, pore volume, and the surface functional groups of GAC, owing to the oxidation effect of H₂O₂ and ·OH on the GAC surface as well as the effect of DOM. Additionally, the changes in the content of persistent free radicals in the GAC samples were insignificant following different aging processes. This work contributes to enhancing understanding regarding the UV/H₂O₂-GAC filtration scheme, and promoting the application in drinking water treatment.

Effects of chlorination on microplastics pollution: Physicochemical transformation and chromium adsorption

The large number of microplastics (MPs) that appear in the environment has drawn much attention. Few studies, however, have examined the transformation of MPs in water treatment processes and their effects on environmental pollutants. In this study, the alteration of the physicochemical characteristics of polyethylene and thermoplastic polyurethane upon chlorination, as well as the influence of this alteration on contaminants, were investigated. The findings indicated that microplastics underwent significant morphology and O-functional groups changes during chlorination. It is noteworthy that the mechanisms controlling the chlorination treatment of the two MPs are clearly different. The results of aggregation and adsorption experiments showed that the chlorination treatment enhanced the aggregation ability of the MPs in brine and their interaction with Cr(VI). The present discoveries further suggested that water treatment could alter the migration capacity of microplastics and the distribution of contaminants in the aqueous environment by altering the adsorption of microplastics to the contaminants.

A review of long-term change in surface water natural organic matter concentration in the northern hemisphere and the implications for drinking water treatment

Reduced atmospheric acid deposition has given rise to recovery from acidification - defined as increasing pH, acid neutralization capacity (ANC), or alkalinity in surface waters. Strong evidence of recovery has been reported across North America and Europe, driving chemical responses. The primary chemical responses identified in this review were increasing concentration and changing character of natural organic matter (NOM) towards predominantly hydrophobic nature. The concentration of NOM also influenced trace metal cycling as many browning surface waters also reported increases in Fe and Al. Further, climate change and other factors (e.g., changing land use) act in concert with reductions in atmospheric deposition to contribute to widespread browning and will have a more pronounced effect as deposition stabilizes. The observed water quality trends have presented challenges for drinking water treatment (e.g., increased chemical dosing, poor filter operations, formation of disinfection by-products) and many facilities may be under designed as a result. This comprehensive review has identified key research areas to be addressed, including 1) a need for comprehensive monitoring programs (e.g., larger timescales; consistency in measurements) to assess climate change impacts on recovery responses and NOM dynamics, and 2) a better understanding of drinking water treatment vulnerabilities and the transition towards robust treatment technologies and solutions that can adapt to climate change and other drivers of changing water quality.

Cost-Effective H2 O2 -Regeneration of Powdered Activated Carbon by Isolated Fe Sites

The reuse of powdered activated carbon (PAC) vitally determines the economics and security of the PAC-based adsorption process, while state-of-the-art PAC regeneration technologies are usually unsatisfactory. Here, it is demonstrated that isolated Fe sites anchored on commercial PAC enable fast H2 O2 activation to produce Fe-based reactive oxygen species for highly efficient PAC regeneration at room temperature. Taking rhodamine B as a representative pollutant, PAC decorated with isolated Fe sites realize H2 O2 based regeneration with negligible adsorption capacity degradation for 10 cycles. Moreover, in terms of the PAC loss rate, this technology is greatly superior to traditional Fenton-based regeneration technology. Further operando experiments and theoretical calculations reveal that the high regeneration performance can be attributed to the isolated HOFeO motifs, which activate H2 O2 via a nonradical reaction pathway. These findings provide a very promising strategy toward reducing the cost of H2 O2 -based PAC regeneration technology.

Screening of new adsorbents to remove algal organic matter from aqueous solutions: kinetic analyses and reduction of disinfection by-products formation

The algal organic matter (AOM) is a problem in water treatment. Although the adsorption process is extensively applied to drinking water treatment, little information is known about the potential of new adsorbents to remove AOM. Herein, this work evaluated the removal of AOM and its main compounds (dissolved organic carbon (DOC), carbohydrate, and protein) by new adsorbents-mesoporous silica (SBA-16), graphene oxide material from citric acid (CA), and sugar (SU), and a composite of CA immobilized on sand (GSC). In general, the removal efficiencies followed the order of SBA-16 > CA > SU or GSC for DOC, carbohydrate, and protein. At environmental condition (5 mg DOC·L^-1 and pH 8), high removals were reported for SBA-16 (88.8% DOC, 80.0% carbohydrate, and 99.6% protein) and CA (70.0% DOC, 66.7% carbohydrate, and 89.7% protein), while moderate removals were found for SU (60.5% DOC, 47.9% carbohydrate, and 66.5% protein) and GSC (67.4% DOC, 60.8% carbohydrate, and 57.4% protein). Based on these results, further analyses were done with SBA-16 and CA. Both adsorbents' efficiencies decayed with the pH increment of the test water. Disinfection by-products reductions found using SBA-16 - trihalomethanes (58.2 to 94.7%) and chloral hydrate (48.7 to 78.8%) - were higher than the ones using CA-trihalomethanes (45.2 to 82.4%) and chloral hydrate (40.1 to 70.8%). This study showed the potential of applying these adsorbents for AOM removal, and further investigations are suggested to increase the adsorption capacity of these adsorbents.

Molecular-level characterization of natural organic matter in the reactive electrochemical ceramic membrane system for drinking water treatment using FT-ICR MS

Applications of electrochemical advanced oxidation processes are rising in drinking water treatment for effective mitigation of refractory organic compounds. This study explored the fate of natural organic matter (NOM) (lake water and standard NOM (SRNOM solution)) at molecular-level in the reactive electrochemical membrane (REM) system utilizing Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Fluorescence spectroscopy showed above 90 % removal of the humic-like component in both lake water and SRNOM solution in 10 min of REM operation compared to 70-80 % removal of the fulvic-like component after 30 min. REM-based treatment effectively eliminated (>70 %) the disinfection byproduct precursors. The lake water, sharing ~70 % of similar compounds with SRNOM, displayed a different propensity toward electrochemical oxidation, and its finished water was characterized with relatively lower double-bond equivalent (DBE), nominal oxidation state of carbon (NOSC), and aromaticity compared to that of SRNOM. The chloride ions in the water matrix of lake water impacted the electrochemical oxidation and generated significantly different transformation products than SRNOM solution. The heteroatoms (N and S) containing compounds (CHON and CHOS) were preferentially degraded in lake water; however, CHOS compounds were removed fewer in SRNOM. The electrosorption and electrochemical oxidation on the REM surface were the significant contributors for NOM removal. The newly formed compounds were mostly retained on the REM surface and fewer were released in finished water. This study is believed to help understand the fate of NOM in real source drinking water during electrochemical treatment.

Adsorption of fulvic acid on mesopore-rich activated carbon with high surface area

The loss of dissolved organic matter (DOM), especially fulvic acid (FA), from soil by rainfall and runoff will reduce soil fertility and result in water pollution of DOM. Carbon materials including biochars (BCs) and activated carbons (ACs) are widely suggested for soil remediation and carbon immobilization. However, these suggested carbon materials are dominated by micropores, and largely limiting the adsorption capacity for FA. Therefore, a mesopore-rich activated carbon (KAC) with high surface area was prepared from bamboo chips to investigate the adsorption of FA. This KAC can adsorb FA more than ACs and BCs investigated in this study and reported in previous studies not only because of the high surface area (3108 m²/g), but also the higher mesopore volume proportion (57%). The negative pH effect on adsorption performance of KAC was weaker than that on AC and BC, because of the less polarity of KAC. Moreover, KAC was favorable to adsorb FA fractions with various molecular weights, higher aromaticity and higher polarity. This study indicated that KAC was a promising adsorbent for FA, and revealed the underlying adsorption mechanism of FA on KAC, which are helpful for the carbon immobilization and pollution control in soil.

Validating the use of lyophilized natural organic matter as background material in GAC rapid small-scale column tests

Utilities often test the effectiveness of different granular activated carbons (GACs) to determine which is most advantageous for their system. For surface water systems, in particular, the seasonal and annual variability of natural organic matter (NOM) in the source water makes it difficult to benchmark the effectiveness of GACs over multiple contract periods. This study produced stable, lyophilized NOM from the filtered water (FW), i.e., the influent to GAC contactors, which was then reconstituted (Recon) and tested against the FW itself in parallel rapid small-scale column tests (RSSCTs). The results demonstrated nearly identical NOM breakthrough profiles. RSSCTs conducted with both FW and Recon were shown to simulate the full-scale contactor performance well, while similar RSSCTs with regenerated GAC yielded a slightly earlier breakthrough, possibly due to the changes in GAC characteristics during regeneration and grinding. RSSCTs evaluating the removal of microcystin-LR (MC-LR) in the presence of background NOM contained in FW and Recon showed slightly different results, possibly due to the difference in chloride concentrations of these two waters. This work validates that reconstituted lyophilized NOM can be used as a source water surrogate for GAC evaluations when the constituent of interest is NOM, and potentially for other constituents depending upon the influence of additional inorganic constituents that were not evaluated as part of this study.

The role of medium molecular weight organics on reducing disinfection by-products and fouling prevention in nanofiltration

Nanofiltration (NF) is utilized in water treatment for controlling disinfection by-products formation potential (DBPFP) and disinfection by-products (DBPs). Attention regarding NF-based technology has been paid on membrane fouling of NF and the rejection efficiency of contaminants by NF membranes. Natural organic matter (NOM) presenting in surface waters is one main removal target in drinking water treatment by NF-based technology, and is thereby a contributor to the membrane fouling of NF. In application, pretreatments of other membrane filtration (e.g., microfiltration (MF) and ultrafiltration (UF)) has been taken prior to NF, resulting in the separation of NOM of specific molecular weight. Meanwhile, it is well known that NOM is composed of organic compounds of different molecular weights. However, the effect of NOM of specific molecular weight has been seldom investigated from the aspects of membrane fouling and the resulting DBPFP after membrane filtration. By using combinations of MF and UF (molecular weight cut-off of 100K or 20K) as pretreatment prior to NF, the NOM of various molecular weight on DBPFP and DBPs in the NF-treated water were investigated. The experiments were conducted with two real-world surface water samples and one tap water sample. It was found that medium molecular weight NOM, defined as NOM that passed UF100K but did not pass UF20K in this study, reduced fouling of the NF membrane. This is supported by the excitation and emission matrix (EEM) fluorescence spectra, size exclusion chromatography (SEC) and flux analysis. In addition, the medium molecular weight NOM also reduced the DBPFP in the NF treated water and eventually the DBPs by participating in forming a protective layer on the NF surface, blocking the transfer of small molecular weight NOM into the NF filtrate, thereby reducing the DBPFP of the NF filtrate since small molecular weight NOM was the major contributor to DBPFP in this study.

Density Functional Theory Calculations of the Effect of Oxygenated Functionals on Activated Carbon towards Cresol Adsorption

The mechanism of adsorption of p-cresol over activated carbon adsorbent and the specific role of oxygen functional groups on cresol adsorption were studied using density functional theory (DFT) calculations. All the energy calculations and geometry optimization pertaining to DFT calculations were done using the B3LYP hybrid functional at basis set 6-31g level of theory in a dielectric medium of ε = 80 (corresponding to water). The interaction of cresol with different activated carbon models, namely pristine activated carbon, hydroxyl functionalized activated carbon, carbonyl functionalized activated carbon, and carboxyl functionalized activated carbon, were considered, and their adsorption energies corresponded to −416.47 kJ/mol, −54.73 kJ/mol, −49.99 kJ/mol, and −63.62 kJ/mol, respectively. The high adsorption energies suggested the chemisorptive nature of the cresol-activated carbon adsorption process. Among the oxygen functional groups, the carboxyl group tended to influence the adsorption process more than the hydroxyl and carbonyl groups, attributing to the formation of two types of hydrogen bonds between the carboxyl activated carbon and the cresol simultaneously. The outcomes of this study may provide valuable insights for future directions to design activated carbon with improved performance towards cresol adsorption.

Influence of DOM characteristics on the flocculation removal of trace pharmaceuticals in surface water by the successive dosing of alum and moderately hydrophobic chitosan

Hydrophobically-modified chitosan (HC) has emerged as a promising flocculant for trace pharmaceutical removal from surface water. However, the variation in the characteristics of dissolved organic matter (DOM) in different water sources influences the efficacy of HC in removing pharmaceutical compounds. In this work, the flocculation performance of sequentially dosing alum and HC (alum+HC) for the treatment of five water types (three synthetic waters, and samples of two real waters collected from the Yangtze River and the Thames River), having different DOM and five representative pharmaceuticals (initial concentration: 100 ng/L), was assessed by bench-scale jar tests. The DOM characteristics were correlated quantitatively with the removal efficiencies (REs) of the pharmaceuticals. Density functional theory computations were performed to illuminate the interfacial interactions in the flocculation. Alum+HC exhibited a remarkably higher RE of all five pharmaceuticals (maximum RE: 73%-95%) from all waters compared to a conventional coagulant or flocculant (alum or polyacrylamide, respectively). In contrast to using HC alone, alum+HC also achieved a higher RE of pharmaceuticals with nearly half the HC dosage, thereby enhancing the cost-effectiveness of the alum+HC dosing system. Among the different key DOM characteristics, the surface charge and molecular weight of DOM had no evident correlation with RE(pharmaceutical), but the hydrophobic/hydrophilic nature and functional group composition of organic carbon of DOM were strongly correlated: Strongly hydrophobic fractions, with C-C & C=C functional groups (binding pharmaceuticals via hydrophobic association), were beneficial, while hydrophilic fractions with C-OH groups were less effective, for pharmaceutical removal. This work showed the enhanced performance of the alum+HC dosing combination in the removal of different pharmaceutical compounds from different waters, and filled the knowledge gap regarding the performance of hydrophobically-modified flocculants in the treatment of different surface water sources.

Changes in molecular dissolved organic matter and disinfection by-product formation during granular activated carbon filtration by unknown screening analysis with Orbitrap mass spectrometry

The minimization of disinfection by-product (DBP) formation by the removal of its precursors before water disinfection is a highly effective approach. Granular activated carbon (GAC) filtration is widely used for water treatment, but our understanding of molecular dissolved organic matter (DOM) remains insufficient. This research investigates the removal of DOM and the minimization of DBP formation by pilot-scale coal- and coconut-based granular activated carbon filtrations (coAC and ccAC, respectively) using unknown screening analysis with Orbitrap mass spectrometry. DOM adsorption rates by both GACs were fitted with pseudo-second order models with initial adsorption rates of 0.005 mg g^-1 min^-1 and 0.022 mg g^-1 min^-1 for ccAC and coAC, respectively. Based on observations, ccAC was more effective in the removal of dissolved organic carbon and prolonged adsorption longer than coAC, as the breakthrough of coAC was found on Day 10. ccAC removed compounds with carbon, hydrogen, and oxygen (CHO features) with a wide range of oxidation states, as indicated by the carbon oxidation state (C_os), and a wide range of unsaturation, as indicated by oxygen subtracted double bond equivalent per carbon ([DBE-O]/C), while coAC selectively removed only those CHO features with less oxidized characters. Less oxidized compounds (low C_os) were preferentially removed with less contact time, while more oxidized compounds needed more contact time to adsorb on the GACs. A biofilm was developed on Day 60, and many CHO features were found to have increased after GAC treatment on Day 60, indicating the formation of microbial products. Chlorination resulted in a decrease in many CHO and CHO with Cl atom (CHOCl) features and the formation of CHOCl DBPs more than CHO DBP features. ccAC was effective in the minimization of trihalomethane (THM) and CHOCl DBP feature formations on Day 10 and Day 60, while coAC was found to be much less effective.

Pyrogenic carbon-promoted haloacetic acid decarboxylation to trihalomethanes in drinking water

Drinking water disinfection by chlorination or chloramination can result in the formation of disinfection byproducts (DBPs) such as haloacetic acids (HAAs) and trihalomethanes (THMs). Pyrogenic carbonaceous matter (PCM), such as activated carbon (AC), is commonly used as an ostensibly inert adsorbent to remove HAAs from water. HAA degradation has been mainly attributed to biological factors. This study, for the first time, revealed that abiotic HAA degradation in the presence of PCM could be important under water treatment conditions. Specifically, we observed complete destruction of Br3AA, a model HAA, in the presence of powder AC at pH 7 within 30 min. To understand the role of PCM and the reaction mechanism, we performed a systematic study using a suite of HAAs and various PCM types. We found that PCM significantly accelerated the transformation of three HAAs (Br3AA, BrCl2AA, Br2ClAA) at pH 7. Product characterization indicated an approximately 1:1 HAA molar transformation into their respective THMs following a decarboxylation pathway with PCM. The Br3AA activation energy (Ea) was measured by kinetic experiments at 15-45 °C with and without a model PCM, wherein a significant decrease in Ea from 25.7 ± 3.2 to 13.6 ± 2.2 kcal•mol-1 was observed. We further demonstrated that oxygenated functional groups on PCM (e.g., -COOH) can accelerate HAA decarboxylation using synthesized polymers to resemble PCM. Density functional theory simulations were performed to determine the enthalpy of activation (ΔH‡) for Br3AA decarboxylation with H3O+ and formic acid (HCOOH). The presence of HCOOH significantly lowered the overall ΔH‡ value for Br3AA decarboxylation, supporting the hypothesis that -COOH catalyzes the C-C bond breaking in Br3AA. Overall, our study demonstrated the importance of a previously overlooked abiotic reaction pathway, where HAAs can be quickly converted to THMs with PCM under water treatment relevant conditions. These findings have substantial implications for DBP mitigation in water quality control, particularly for potable water reuse or pre-chlorinated water that allow direct contact between HAAs and AC during filtration as well as PAC fines traveling with finished water in water distribution systems. As such, the volatilization and relative low toxicity of volatile THMs may be considered as a detoxification process to mitigate adverse DBP effects in drinking water, thereby lowering potential health risks to consumers.

Development of a VUV-UVC/peroxymonosulfate, continuous-flow Advanced Oxidation Process for surface water disinfection and Natural Organic Matter elimination: Application and mechanistic aspects

Surface waters are often charged with high amounts of natural organic matter (NOM), organic contaminants and pathogens. In this work, a Vacuum UV/PMS process (VUV-UVC/PMS) was employed for treating river water, assessing the simultaneous NOM mineralization and bacterial disinfection. The VUV-UVC process (without PMS) decreased TOC concentration from 3.83 to 0.15 mg/L within 20 min, achieving complete disinfection. Adding 5 mg/L PMS increased the rate of TOC removal by 80%; complete removal of TOC was achieved in 15 min and disinfection was attained twice as fast. The mechanism of NOM mineralization was scrutinized; aeration played a considerable role due to oxygen supply, mixing, and inducing in-situ H₂O₂ production. HO^• and SO₄^•- were the main radical species involved, alongside an important contribution of the matrix; sulfate enhanced TOC removal, due to the formation of additional radicals, underlining its importance. Furthermore, over 99% TOC reduction and complete disinfection was achieved in the VUV-UVC/PMS process operated under continuous-flow mode with a 2-min hydraulic retention time. Finally, the use of Atrazine (ATZ) as a probe compound and a series of scavenging tests led to an integrated proposal for the mineralization of NOM. Accordingly, the VUV-UVC/PMS process is evaluated as an efficient and promising technology for surface water treatment.

Characterization of algal organic matter as precursors for carbonaceous and nitrogenous disinfection byproducts formation: Comparison with natural organic matter

Algal organic matter (AOM) and natural organic matter (NOM) from a typical eutrophic lake were comprehensively investigated in terms of their physico-chemical property, components and disinfection byproduct formation potentials (DBPFPs). The relationships between specific chemical properties of AOM and NOM with their corresponding DBPFPs were further evaluated during chlorination. Results indicated that AOM had lower specific UV absorbance (SUVA) but richer organic nitrogen contents than NOM. Fluorescence excitation emission matrix spectroscopy further demonstrated that AOM were chiefly composed of aromatic protein-like and soluble microbial byproduct-like matters, while NOM were mainly contributed from humic acid-like and soluble microbial byproduct-like substances. Although the molecular weight (MW) distribution of AOM and NOM showed no significant difference, size-exclusion chromatography with organic carbon as well as organic nitrogen detection (LC-OCD-OND) revealed that AOM were concentrated with the fraction of building blocks and NOM had higher concentrations of biopolymers and humics (HS). Moreover, AOM displayed higher DBPFPs than NOM, especially for nitrogenous DBPFP (N-DBPFP). MW < 1 kDa fractions both in AOM and NOM contributed the largest proportion to the formation of carbonaceous disinfection byproducts (C-DBPs). In addition, Pearson correlation analysis showed that bulk parameter SUVA was significantly relevant to the formation potentials of trihalomethane both in AOM and NOM, but was ineffective for carbonaceous DBPFP (C-DBPFP) prediction. Dissolved organic nitrogen contents in biopolymer and HS characterized by LC-OCD-OND had strong correlations with N-DBPFPs from AOM and NOM, indicating that LC-OCD-OND quantitative analysis could improve the prediction accuracy of the DBP formation than bulk parameters during NOM and AOM chlorination.

Formation factors and hazard evaluation of halogenated methyl sulfonic acid in drinking water

Halogenated methyl sulfonic acid (HMSAs) is a new type of disinfection by-product recently reported, and there are few relevant studies, so its source and harm are still unclear. This study mainly discusses the source of halogenated methyl sulfonic acid from the macroscopic level and evaluates the harm to human health. This study clarified that chlorine disinfection is one of the main ways of generating halogenated methyl sulfonic acids (HMSAs) in drinking water. The macroscopic properties of HMSA precursors were analyzed through liquid chromatograph-mass spectrometry (LC-MS/MS), 3D fluorescence, and Fourier transform infrared spectrometry. The results showed that polar and positively charged organic compounds with molecular weights of >3 KDa or <0.5 KDa can readily generate HMSAs. By analyzing the main components of natural organic compounds in water and comparing them with the characteristics of organic compounds such as dimethyl sulfoxide and ethyl mercaptan, it meant that natural organic compounds are easily degraded. Humic and fulvic acids contribute the most to HMSA generation. This study lasted for three years and collected water samples from 102 waterworks in 24 cities in China, and the existence of HMSAs in drinking water in different cities was analyzed. The potential health risks associated with HMSAs were used by the United States Environmental Protection Agency (U.S. EPA) health risk assessment model. The average and maximum concentrations of HMSAs in tap water from key cities in China were taken as evaluation objects. The results showed that the carcinogenic risk coefficient (R) value of both concentrations was far lower than the lowest acceptable carcinogenic risk (1.0 × 10^-6) provided by U.S. EPA. Therefore, HMSAs in drinking water in China currently pose no human health risks.

Sorptive removal of disinfection by-product precursors from UK lowland surface waters: Impact of molecular weight and bromide

The current study compared the impact of three different unit processes, coagulation, granular activated carbon (GAC), and a novel suspended ion exchange (SIX) technology, on disinfection by-product formation potential (DBPFP) from two UK lowland water sources with medium to high bromide content. Specific attention was given to the influence of the organic molecular weight (MW) fraction on DBPFP as well as the impact of bromide concentration. Whilst few studies have investigated the impact of MW fractions from Liquid Chromatography with Organic Carbon Detection (LC-OCD) analysis on dissolved organic carbon (DOC) removal by different processes, none have studied the influence of DOC MW fractions from this analysis on DBP formation. The impact of higher bromide concentration was to decrease the total trihalomethane (THM) and haloacetic acid (HAA) mass concentration, in contrast to previously reported studies. Results indicated that for a moderate bromide concentration source (135 μg/L), the THM formation potential was reduced by 22% or 64% after coagulation or SIX treatment, respectively. For a high bromide content source (210 μg/L), the THM formation potential removal was 47% or 69% following GAC or SIX treatment, respectively. The trend was the same for HAAs, albeit with greater differences between the two processes/feedwaters with reference to overall removal. A statistical analysis indicated that organic matter of MW > 350 g/mol had a significant impact on DBPFP. A multiple linear regression of the MW fractions against DBPFP showed a strong correlation (R² between 0.90 and 0.93), indicating that LC-OCD analysis alone could be used to predict DBP formation with reasonable accuracy, and offering the potential for rapid risk assessment of water sources.

Covalent organic frameworks as an efficient adsorbent for controlling the formation of disinfection by-products (DBPs) in chlorinated drinking water

2,5-Dimethyl-p-phenylenediamine-1,3,5-triformylphloroglucinol covalent organic frameworks (PATP COF) were prepared and used as novel adsorbent for controlling the formation potential (FP) and reducing the toxic potential of both carbonaceous disinfection by-products (C-DBPs) and nitrogenous DBPs (N-DBPs) during their subsequent chlorination. During the PATP COF adsorption pretreatment process, the FP of C-DBPs, N-DBPs and total organic halogen (TOX) were reduced by 86.5, 75.4 and 81.1%, respectively. These removal efficiencies were significantly higher when compared with those obtained using a traditional activated carbon (AC) adsorption pretreatment process (42.7, 19.4 and 28.7%, respectively). By comprehensive toxicity calculations, a significant reduction in both the acute and chronic toxic potential of C-DBPs and N-DBPs were observed during the PATP COF adsorption process (with reduction rates of ~85 and ~ 75% observed for the C-DBPs and N-DBPs, respectively), which were comparable to the removal efficiencies observed for C-DBPs FP and N-DBPs FP by weight, suggesting the simultaneous and effective control of DBPs FP and their toxic potential. Cycling tests and stability trial also showed the excellent reusability, wide pH adaptability, and high stability of PATP COF, demonstrating its great potential application to the treatment of drinking water.