Empty Bed Contact Time Research Articles

Optimization of operational parameters for the treatment of roof-harvested rainwater with biologically synthesised nanosilver coated on sand

Abstract Rainwater is a major source of drinking water in developing countries. Roof-harvested rainwater is generally microbiologically contaminated and thus needs to be treated effectively to meet drinking standards. Filtration of rainwater with sand coated by silver nanoparticles enhances the microbial removal efficiency. In this study, the filtration parameters of treating rainwater with biologically synthesized nanosilver coated sand are optimized. Of the various synthesis methods, the biological method was chosen due to benefits such as cost-effectiveness and its eco-friendly nature. Silver nanoparticles were synthesised using papaya fruit extract and then coated on sand. The synthesized nanosilver coated sand was subjected to characterization methods such as energy dispersive spectroscopy and X-ray diffraction (XRD) analysis. With silver coated sand as control, multiple long duration tests were performed to treat rainwater with nanosilver coated sand to find the optimal values for filtration parameters such as filter bed depth and empty bed contact time (EBCT). The crystallite size of the nanosilver coated sand was found to be 43.8 nm. The optimal values for filter bed depth and EBCT were found to be 12 cm and 15 minutes respectively. The rainwater treated with nanosilver coated sand met drinking water standard IS 10500: 2012 until the media got exhausted.

Performance promotion and its mechanism for n-hexane removal in a lab-scale biotrickling filter with reticular polyurethane sponge under intermittent spraying mode

Mass transfer limitations commonly challenge biofiltration for n-hexane emissions due to its high hydrophobicity. In this study, a bench-scale biotrickling filter (BTF) packed with reticulated polyurethane sponge was evaluated for n-hexane removal at various organic loading rates (OLRs) (ranging from 15 to 60 g m−3 h-1) and gas empty bed contact times (EBCTs) (ranging from 30 to 7.5 s). The obtained results show that the designed BTF can effectively remove n-hexane under intermittent spraying mode of the nutrient solution and the reticulated configuration of the packing media, which resulted in the spatial development of mycelium and enhanced mass transfer of n-hexane. The mean maximum removal efficiencies (REs) of n-hexane were 92.6 ± 0.9 %, 86.7 ± 4.8 %, and 63.8 ± 3.3 % under the OLRs of 15.67, 30.20, and 61.59 g m−3 h-1, respectively. When the BTF was operated under gas EBCTs of 30, 15, and 7.5 s, average REs of 85.9 ± 5.7 %, 44.8 ± 6.3 %, and 31.2 ± 2.5 % were achieved. The BTF also showed a superior fluctuation resistance capability and prevented excessive biofilm accumulation due to the reticular configuration of the polyurethane sponge. Results present in this study could provide an alternative consideration for the practical industrial application in treating hydrophobic VOC like n-hexane.

Pesticide bioremediation by Trametes versicolor: Application in a fixed-bed reactor, sorption contribution and bioregeneration

Although immobilization on lignocellulosic materials has recently become a promising strategy in the fungal-based technology for micropollutant bioremediation, research evidence in this area is still scarce and significant knowledge gaps need to be addressed. In this study, Trametes versicolor immobilized on Quercus ilex wood chips was initially proposed to remove two pesticides, diuron and bentazon, from real agricultural wastewater. Thus, a bioremediation treatment was performed in a fixed-bed bioreactor at two empty bed contact times (EBCT) of 1 and 3 days. Bentazon saturation was achieved after 5 EBCTs, while diuron sorption remained below 50% even after 40 days of treatment. The differences in diuron and bentazon removals were linked to their different hydrophobicity and thus, affinity for wood. However, in any case, the sorption contribution of wood was found to be predominant compared to fungal biodegradation. These results motivated a comprehensive study to evaluate the pollutant sorption capacity of wood. Afterwards, pesticide-contaminated wood was successfully bioregenerated by T. versicolor in a biopile-like system, reaching high fungal colonization (up to 0.2451 mg ergosterol·g−1 dry weight), degradation rate (up to 2.55 mg·g−1·d−1) and degradation yields (up to 92.50%). The combined treatment consisting of the fixed-bed bioreactor followed by the re-inoculated biopile showed the best performance in terms of fungal content and pesticide degradation. This is an important step toward the implementation of fungal-based technology for the removal of pesticides from agricultural water.

Biological removal of benzalkonium chlorides from wastewater by immobilized cells of Pseudomonas sp. BIOMIG1 in an up-flow packed bed reactor

Quaternary ammonium compounds (QACs) are active ingredients of many disinfectants used against SARS-CoV-2 to control the transmission of the virus through human-contact surfaces. As a result, QAC consumption has increased more than twice during the pandemic. Consequently, the concentration of QACs in wastewater and receiving environments may increase. Due to their antimicrobial activity, high levels of QACs in wastewater may cause malfunctioning of biological treatment systems resulting in inadequate treatment of wastewater. In this study, a biocatalyst was produced by entrapping Pseudomonas sp. BIOMIG1 capable of degrading QACs in calcium alginate. Bioactive 3-mm alginate beads degraded benzalkonium chlorides (BACs), a group of QACs, with a rate of 0.47 µM-BACs/h in shake flasks. A bench-scale continuous up-flow reactor packed with BIOMIG1-beads was operated over one and a half months with either synthetic wastewater or secondary effluent containing 2–20 µM BACs at an empty bed contact time (EBCT) ranging between 0.6 and 4.7 h. Almost complete BAC removal was achieved from synthetic and real wastewater at and above 1.2 h EBCT without aeration and effluent recirculation. The microbial community in beads dominantly composed of BIOMIG1 with trace number of Achromobacter spp. after the operation of the reactor with the real wastewater, suggesting that BIOMIG1 over-competed native wastewater bacteria during the operation. This reactor system offers a low cost and robust treatment of QACs in wastewater. It can be integrated to conventional treatment systems for efficient removal of QACs from the wastewater, especially during the pandemic period.

Removal of arsenate using graphene oxide-iron modified clinoptilolite-based composites: adsorption kinetic and column study

In this study, graphene oxide (GO), iron modified clinoptilolite (FeZ), and composites of GO-FeZ (GOFeZA and GOFeZB) were synthesized and characterized using SEM, EDS, XRF, FTIR, and pHpzc. The arsenate uptake on composites of GOFeZA and GOFeZB was examined by both kinetic and column studies. The adsorption capacity increases with the increase of the initial arsenate concentration at equilibrium for both composites. At the initial arsenate concentration of 450 μg/L, the arsenate adsorption on GOFeZA and GOFeZB was 557.86 and 554.64 μg/g, respectively. Arsenate adsorption on both composites showed good compatibility with the pseudo second order kinetic model. The adsorption process was explained by the surface complexation or ion exchange and electrostatic attraction between GOFeZA or GOFeZB and arsenate ions in the aqueous solution due to the relatively low equilibrium time and fairly rapid adsorption of arsenate at the beginning of the process. The adsorption mechanism was confirmed by characterization studies performed after arsenate was loaded onto the composites. The fixed-bed column experiments showed that the increasing the flow rate of the arsenate solution through the column resulted in a decrease in empty bed contact time, breakthrough time, and volume of treated water. As a result of the continuous operation column study with regenerated GOFeZA, it was demonstrated that the regenerated GOFeZA has lower breakthrough time and volume of treated water compared to fresh GOFeZA.

Full-Scale Manipulation of the Empty Bed Contact Time to Optimize Dissolved Organic Matter Removal by Drinking Water Biofilters

A study was conducted at a water treatment plant to optimize parallel rapid gravity biofilters for dissolved organic matter (DOM) removal. The biofilters treat urban and agriculturally impacted river water using a commercial non-adsorptive, expanded-clay filter medium. The study aimed to locate the optimal operating conditions via experimental manipulation of the biofilter empty bed contact time (EBCT) during full-scale operation at the plant. During a two-month experiment, contact times in four parallel biofilters were switched to and maintained at 15, 30, 50, and 80 min by manipulating the hydraulic loading on each filter. The removal efficiency of organic matter fractions increased with EBCT for dissolved organic carbon (DOC) and microbial humic-like (F290/420) and protein-like (F280/340) fluorescent organic matter. Other DOM fractions were largely unaffected by biofiltration, or at slightly higher concentrations in the effluent. Protein-like fluorescence is associated with labile organic matter fractions, which are known to be removed poorly by drinking water treatment barriers apart from biological filters. The results suggest that long contact times (>30 min) have advantages for the operation of some biological filters, especially if placed ahead of barriers that are sensitive to biofouling, e.g., membranes.

A multi-component model for granular activated carbon filters combining biofilm and adsorption kinetics

Along with the rise of biological active granular activated carbon (bGAC) filtration as advanced treatment technology for wastewater treatment plant (WWTP) effluents, the mathematical representation of such systems is gaining increasing importance. This work introduces a model that describes the performance of bGAC-filters for Dissolved Organic Carbon (DOC) removal from a WWTP effluent. The DOC removal within bGAC-filters is accomplished by two mechanisms: adsorptive removal and biological transformation. An appropriate representation of the adsorptive removal requires the DOC to be divided into fictive fractions according to its adsorbability. Likewise, a further DOC classification according to its biodegradability is necessary. Modeling a bGAC-filter then becomes a multi-component adsorption problem, with the simultaneous occurrence of DOC degradation within a biofilm. For dealing with this modeling task, this work integrated the Ideal Adsorbed Solution (IAS) theory into a traditional biofilm model compatible with the Activated Sludge Model (ASM) Framework. For the description of the adsorption dynamics, a Freundlich isotherm for the equilibrium and a pseudo first order model for the kinetics were selected. The biofilm consisted of heterotrophic bacteria able to oxidize DOC using oxygen as electron acceptor. The correctness of the model was evaluated using experimental data from a pilot plant. The predicted DOC breakthrough curve satisfactorily fitted the experimental measurements for empty bed contact times (EBCT) of 6, 12, 24 and 33 min. Moreover, the model predicted the relationship between EBCT, DOC removal and bGAC-filter lifespan. The developed model is the first that combines multi-component adsorption and biofilm kinetics in a wastewater treatment context.

Hydrous cerium oxides coated glass fiber for efficient and long-lasting arsenic removal from drinking water

A novel arsenic adsorbent with hydrous cerium oxides coated on glass fiber cloth (HCO/GFC) was synthesized. The HCO/GFC adsorbents were rolled into a cartridge for arsenic removal test. Due to the large pores between the glass fibers, the arsenic polluted water can flow through easily. The arsenic removal performance was evaluated by testing the equilibrium adsorption isotherm, adsorption kinetics, and packed-bed operation. The pH effects on arsenic removal were conducted. The test results show that HCO/GFC filter has high As(V) and As(III) removal capacity even at low equilibrium concentration. The more toxic As(III) in water can be easily removed within a wide range of solution pH without pre-treatment. Arsenic contaminated ground-water from Yangzong Lake (China) was used in the column test. At typical breakthrough conditions (the empty bed contact time, EBCT = 2 min), arsenic researched breakthrough at over 24,000 bed volumes (World Health Organization (WHO) suggested that the maximum contaminant level (MCL) for arsenic in drinking water is 10 mg/L). The Ce content in the treated water was lower than 5 ppb during the column test, which showed that cerium did not leach from the HCO/GFC material into the treated water. The relationship between dosage of adsorbents and the adsorption kinetic model was also clarified, which suggested that the pseudo second order model could fit the kinetic experimental data better when the adsorbent loading was relatively low, and the pseudo first order model could fit the kinetic experimental data better when the adsorbent loading amount was relatively high.

Semi-Continuous Adsorption Processes with Multi-Walled Carbon Nanotubes for the Treatment of Water Contaminated by an Organic Textile Dye

Adsorbent columns, containing different amounts of multi-walled carbon nanotubes (MWCNTs), in a semicontinuous process were studied. The optimal conditions for the discoloration of water contaminated by an azoic organic textile dye were investigated. In particular, as representative of contaminated water, a highly concentrated solution of Reactive Black 5 (RB5) equal to 37 mg/L was utilized. A predetermined volume of dye solution, equal to 100 mL, was subjected to repeated cycles of adsorption until the eluted solution became colorless. This adsorption operation was carried out for different types of columns. Adsorbent performances as a function of characteristics of each column were investigated. For each column, the optimum quantity of MWCNTs, maximum volume of treatable solution, carbon usage rate (CUR), empty bed contact time (EBCT), and adsorption capacity were determined. The permeate was characterized by UV-VIS analysis and TOC analysis, while adsorbent material (MWCNTs) was characterized by thermogravimetric TG-DTA analysis. The column containing 2.5 g of carbon nanotubes was revealed to be the best one for the total amount of Reactive Black 5 adsorbed, i.e., 55 mg/g(MWCNTs) The research has shown the high adsorption efficiency of carbon nanotubes toward RB5 dye, highlighting the degradation of the dye molecule and the stratification, inside the columns, of the adsorbed compound.

Effect of Phosphate and Hydrogen Peroxide on Bacterial Community and Removal Efficiency of Biological Activated Carbon (BAC) Process for Enhanced Biofiltration

Objectives:The correlation between the organic material removal ability of the enhanced BAC process injected by the phosphate (PO4-P) and/or hydrogen peroxide (H2O2) and attached bacterial community was evaluated.Methods:As pilot plant for the purification of raw water downstream of Nakdong river, 4 acrylic columns with an inner diameter of 20 cm and a height of 250 cm were operated at an empty bed contact time of 20 minutes. The four BAC columns are as followed; conventional BAC (control-BAC), enhanced BAC with phosphorus (PO4-P+BAC), enhanced BAC with hydrogen peroxide (H2O2+BAC), and enhanced BAC with phosphorus and hydrogen peroxide (PO4-P+H2O2+BAC). 0.01 mg/L of PO4-P and 1 mg/L of H2O2 were added in influent in the enhanced BAC, respectively. After 18 months of operation, activated carbon was collected from the top of each BAC column and 16S rRNA amplicon sequence analysis was performed.Results and Discussion:The long-term addition of PO4-P and H2O2 contributes the increase of biomass and activity of attached bacteria, respectively. In the attached bacterial community of conventional and enhanced process, Proteobacteria phylum is the most dominant specie and both α-Proteobacteria class and β-Proteobacteria class are also highly present. Each enhanced BAC exhibits very high bacterial community similarity based on the composition of various genera but it is completely different with conventional BAC. In particular, Bradyrhizobium, Sphingomonas, Methylobacterium, Sphingobium, Belnapia, Burkholderia, Polaromonas, and Desulfuromonas, which have excellent metabolism functions for a wide range of organic substrates, are highly dominated in the enhanced BAC process. The concentration of Biodegradable Dissolved Organic Carbon (BDOC) is obtained close to 0.15 mg/L for conventional BAC and less than 0.15 mg/L for enhanced BAC process, respectively. In general, the higher BDOC concentration can result in reducing biostability in water supply and distribution system when the residual chlorine concentration does not meet requirements. As result, less than 0.15 mg/L BDOC accomplished by PO4-P and H2O2 enhances the biostability.Conclusions:Compared to the conventional BAC process, the biomass and activity of attached bacteria and the ratio of the organization composition of the bacteria insides (genus) are considerably higher in the enhanced BAC process. These results achieve higher water quality and improve biostability.

Advanced removal of water NOM by Pre-ozonation, Enhanced coagulation and Bio-augmented Granular Activated Carbon

Natural organic matters as intrinsic microorganic pollutants are a major concern in drinking water in scopes of water supply systems operation, consumer health, aesthetic and so on. This study was done on the real water samples that was first experienced in using integrated processes (pre-ozonation, enhanced coagulation and bio-augmented carbon) for upgrading existing processes of water treatment plant. The parameters of TOC, DOC, UV254, SUV, appearance color, turbidity, pH, TDS, heterotrophic plate count (HPC) and residual bromate were tested after each process. It was revealed that, using 0.5 mg O3/mg TOC, 15 mg/l polyaluminium chloride (PACl), pH = 7.5 and empty bed contact time (EBCT) of 5 min in bio-filter, the removal of TOC is 87%. The concentration of TOC in finished water was 0.8 mg/l that less than standard limit for chlorination (2 mg/l) without formation of bromate as carcinogenic by-product. Upgrading of existing plant by suggested process, not only could remove natural organic matters (NOMs) significantly but also protect reservoir and distribution network against regrowth of biofilm.

Effect of Hydrogen Peroxide and Phosphate Addition on Biopolymers Formation and Changes in Head Loss in Biological Activated Carbon Process

Objectives:The purpose of this study was to suggest a more efficient operation condition for the BAC(biological activated carbon) process by evaluating the change in the concentration of biopolymers in the effluent of the BAC process and the head loss of the BAC filter layer according to phosphate (PO4-P) and hydrogen peroxide (H2O2) input.Methods:During the experiment period (Feb. to Aug. 2020), the O3 dosage was fixed at 1 mg･O3/mg･DOC. Four columns with an inner diameter of 20 cm and a height of 250 cm were prepared. Empty bed contact time (EBCT) was fixed at 20 minutes and backwash was performed once a week. The four BAC columns are conventional BAC(control-BAC), enhanced BAC with hydrogen peroxide (H2O2+BAC), enhanced BAC with phosphate (PO4-P+BAC), and enhanced BAC with phosphate and hydrogen peroxide together (PO4-P+H2O2+BAC). In the case of enhanced BAC with PO4-P added, PO4-P was added with a concentration of 0.010 mg/L in the influent, and in BAC with H2O2, H2O2 was added with a concentration of 1 mg/L to the influent.Results and Discussion:According to the change of water temperature, the average head loss in control-BAC was 4.4 (25~28℃)~7.7 cm(8~12℃). In addition, PO4-P+BAC, H2O2+BAC and PO4-P+H2O2+BAC were 3.9~5.8 cm, 2.5~3.5 cm, and 2.6~3.5 cm, respectively. The head loss was reduced by the input of PO4-P and H2O2. During the low water temperature period, in control-BAC, the effluent biopolymers (BP) concentration was higher than the influent concentration, indicating that a large amount of EPS (extracellular polymeric substances) was produced and released from the attached biofilm. In PO4-P+BAC, H2O2+BAC and PO4-P+H2O2+BAC processes, the BP concentration ratio (Cout/Cin) was about 36~57% lower than that of the control-BAC during the low water temperature period. The BP concentration ratio was high when the water temperature (8~12℃) was low, and the BP concentration ratio gradually decreased as the water temperature increased. These results were very similar to those of the head loss change in the control-BAC process and the enhanced BAC process, and the BP concentration ratio and the head loss showed a very high correlation (r2=0.82~0.87). To evaluate the stability of the biofilm during the operation period, the total cell counts (TCC) in BAC treated waters were investigated. In control-BAC, PO4-P+BAC, H2O2+BAC and PO4-P+H2O2+BAC process, the average TCC was 46.8×106 cells, 30.3×106 cells, 21.8×106 cells, and 18.8×106 cells, respectively. Compared to the control-BAC, it was found to be 35~60% lower in the enhanced BAC processes. In addition, live cell count (LCC) ratio (LCC/TCC) was 0.84~0.89 in the enhanced BAC processes compared to 0.53 in the control-BAC. These results indicate that the biofilm stability of the enhanced BAC processes is higher than that of control-BAC.Conclusions:During the experiment, compared to the conventional BAC process, the enhanced BAC processes in which PO4-P and H2O2 were added showed a clear effect of reducing the head loss. In particular, the effect of reducing the head loss was higher when H2O2 was added than when PO4-P was added. A rapid head loss increase occurred in the conventional BAC process compared to the enhanced BAC processes in the low water temperature season is the result of the production of large amounts of EPS in the attached biofilm. The input of PO4-P or H2O2 reduces the head loss by improving the stability of the attached biofilm and reducing EPS production.

Empty bed contact time: The key for micropollutant removal in activated carbon filters

The removal of micropollutants from wastewater is an emerging issue that currently concerns the wastewater sector the most. Granular Activated Carbon (GAC) has gained recognition as a suitable technology for dealing with this problem. This study assesses the performance of six GAC-filters for the removal of micropollutants installed as final treatment step at a municipal wastewater treatment plant. The influence of the GAC-type and the Empty Bed Contact Time (EBCT) on the filter performance was evaluated. The breakthrough behaviour of 13 selected micropollutants as well as the removal of the Dissolved Organic Carbon (DOC) and UV absorption at 254 nm were investigated. Besides, the adsorbed DOC (qDOC) was introduced as assessment parameter (adsorbed and biodegraded DOC), instead of the commonly used treated bed volume. Finally, Size Exclusion Chromatography (SEC) with online DOC and UV254nm detection was applied for a better understanding of the influent and effluent characteristics. The results showed that the pore size distribution is a crucial feature of the activated carbon. A balanced proportion of macro-, meso‑ and micropores may play a role in the better removal of micropollutants in presence of DOC. Regardless of the GAC-type, a minimum EBCT between 20 – 30 min was necessary. We proved that a short EBCT would not fully use the sorption capacity, whereas a long EBCT would increase the carbon demand without improving of the removal. Lastly, according to the SEC results, after a short operation time no difference between the influent and effluent chromatographable fractions (DOC and UV254nm) was observed.

Batch and Continuous Design of a Full‐Scale Treatment Facility for Removing Dissolved Natural Organic Matter

AbstractBatch and continuous flow adsorption experiments are carried out and the design of a full‐scale facility for removing dissolved natural organic matter (DNOM) from Catalan Lakewater is demonstrated. The adsorption efficiency is proportional to the temperature and the amount of adsorbent unlike pH increase. The highest DNOM removal rate is obtained at 35 °C, pH 4, and an adsorbent amount of 0.8 g L−1. Optimum contact time for batch studies is 60 min at equilibrium. Correlation constants (r) of Langmuir and Freundlich isotherms are 0.8905 and 0.9739, respectively. Based on the Freundlich isotherm, the highest adsorption capacity (qmax) obtained is 2.44 and 6.01 mg DNOM/g granulated activated carbon (GAC) for raw and enriched water, respectively. Consequently, the effects of adsorbent amount, bed depth, empty bed contact time, and organic loading on removal performance are investigated in the rapid small‐scale column test (RSSCT) columns. The targeted effluent concentration of 1 mg DNOM/L can easily be achieved in the columns. At the design capacity of the facility, 15 adsorption columns with dimensions of 7 m height, 4.33 m diameter, and 22 days of operation cycle are required to remove DNOM from raw water.

Performance of a granular activated carbon biologically active filter (GAC-BAF) for removing microcystin-LR (MC-LR) from eutrophic water

Abstract Microcystin-LR (MC-LR) removals linked with empty bed contact time (EBCT), temperature and backwash strategies are important for biologically active filter (BAF) application but remain not entirely clear. In addition, there is still a lack of understanding about the bio-regeneration of MC-LR adsorption capacity in a BAF. This study examined MC-LR removals by a granular activated carbon-biologically active filter (GAC-BAF) as a function of EBCT, temperature, and backwash strategies. Results demonstrated that the optimum EBCT (1.2 h for this study) likely depended upon an optimum superficial velocity as well as the GAC column height. A superficial velocity not greater than 0.5 m/h was deemed appropriate according to this research. The MC-LR removals achieved at the optimum EBCT reached 54.8%–72.0%. A higher temperature resulted in a greater MC-LR removal; adsorption might contribute to effective MC-LR removal by the GAC-BAF at a lower temperature. A strategy (Air + air-water + water) was suggested as an optimal backwash strategy for GAC-BAFs in terms of MC-LR removal. A comparison of the effectiveness of the experimental GAC-BAF in continuous and discontinuous operations on MC-LR removals was conducted, from which indirect evidence for bio-regeneration of MC-LR adsorption capacity of the GAC was obtained.

Enhanced arsenic removal from water by mass re-equilibrium: kinetics and performance evaluation in a binary-adsorbent system

Because arsenic (As) is highly toxic and carcinogenic, its efficient removal from drinking water is essential. Considering some adsorption media may adsorb As fast but are too expensive to be applied in a household, while others could be abundantly available at low cost but with slow uptake kinetics, we explored a novel mass re-equilibrium (MRE) process between two media with different adsorption characteristics to enhance the overall As removal. We employed an adsorbent with fast adsorption kinetics to grab As from water, and then allow it to transfer to a second adsorbent with large capacity for As retention. In the system containing two adsorbents separated by a dialysis membrane, the results showed that As associated with a fast-adsorbing iron-based ordered mesoporous carbon could diffuse to a slow-adsorbing but high-capacity iron-based activated carbon. Column tests were further conducted, showing that the mixed medium, composed of the two adsorbents, could be used to adsorb As at a very short empty bed contact time (≤ 1 min) and the removal was improved by the MRE that potentially redistributed solid-phase As during pump-off periods. This study points to a new direction that by the MRE process, novel binary-adsorbent approaches may be developed for contaminant removal, if suitable media and process configuration could be identified.

Removal of Molybdenum(VI) from Raw Water Using Nano Zero-Valent Iron Supported on Activated Carbon

Traces of Molybdenum (Mo) in drinking water pose potent dangers owing to its harmful effects on the health of humans. This study used nanoscale zero-valent iron (Fe0) supported by activated carbon (NZVI/AC) for removing Mo(VI) from raw water. In an attempt to gain an understanding of the various factors that affect the process, we designed the study to look into the impact of various experimental parameters including pH, adsorption kinetics, and coexisting ions on the Mo(VI) removal using fixed-bed column runs and a batch-adsorption method and for Mo(VI) removal using NZVI/AC. The optimum conditions were found to be pH 4.5 and an equilibrium time of 9 h and 72 h for simulation water (SW) and raw water (RW), respectively. The removal of Mo(VI) was remarkably inhibited by the presence of silicate (SiO42−) and phosphate (PO43−), while the impact of humic acid and some other anions was insignificant. Metal cations such as Fe3+, Al3+, Zn2+, and Ni2+ enhanced the adsorption of Mo(VI). The influent contaminant concentration Mo(VI) in raw water was found to be 0.1603 mg/L, the empty-bed contact time (EBCT) was 3 and 6 min, whereas the breakthrough empty-bed volumes were 800 and 1100 and at the value of 70 μg/L provided by WHO provisional guidelines, respectively.

Factors affecting removal of NDMA in an ozone-biofiltration process for water reuse

N-nitrosodimethylamine (NDMA) is a carcinogen and a disinfection byproduct that is formed by ozone and combined chlorine. Various factors affecting NDMA formation and removal were examined at pilot-scale for a treatment train consisting of ozone, biologically-active carbon (BAC) filtration, and granular activated carbon (GAC) adsorption applied to two distinct feed waters. High concentrations of ozone and monochloramine were added to the influent, demonstrating that ozone removed monochloramine precursors of NDMA. Further, longer empty bed contact times (EBCTs) of 10 min for BAC and 10 and 20 min for GAC removed NDMA to <10 ng/L for both feed waters. NDMA removal by the BAC process was most favorable >22 °C, presumably due to elevated microbial activity. A monochloramine residual of 3 mg/L-Cl2 in the BAC influent reduced NDMA removal in the 5 min EBCT BAC from 79% to 36% and in the 10 min EBCT BAC from 88.5% to 73.7%. The absence of ozone in the treatment process significantly reduced NDMA formed post ozone, but decreased NDMA removal in BAC, probably due to lower NDMA concentration in the BAC influent. Finally, adding 5 mg/L of allylthiourea, an inhibitor of ammonia-oxidizing bacteria, indicated that removal mechanisms for ammonia and NDMA are distinct. However, nitrification is still a good indicator for NDMA biodegradation potential, because nitrifying bacteria appear to flourish under similar EBCT, temperature. and monochloramine residual conditions during BAC filtration.

Comparison of O3-BAC, UV/H2O2-BAC, and O3/H2O2-BAC treatments for limiting the formation of disinfection byproducts during drinking water treatment in India

Natural organic matter (NOM) acts as a precursor to toxic disinfection byproducts (DBPs). Recently it has been established that a mixture of natural and effluent derived organic matter (NefOM) leads to very high concentration of DBPs. Both conventional and non-conventional/advanced ways of drinking water treatment do not remove NefOM sufficiently. Advanced oxidation processes (AOPs) have been shown to oxidize dissolved organic carbon (DOC) effectively but entail high energy inputs. Therefore, combining AOP as a pre-oxidation step with an economical system like biological activated carbon (BAC) filtration is a more economical solution. In this study, BAC was developed from virgin granular activated carbon (GAC) with river Yamuna water, which has the highest levels of DOC in the world, as influent water. Two columns were used, with one of them as a control. For the development of BAC from GAC, Empty bed contact time (EBCT) of 12 min was found to be effective. Steady-state was achieved after 90 days of continuous operation of the columns. After the steady-state was achieved, EBCT of 16 min was found to be optimum for the diffusion of organic molecules inside the biofilm and mineralization by the attached biomass on the surface of BAC.The percentage DO consumption and, DOC/UV254 reduction was found to be constant from t = 90 to t = 120 days, after which the column was assumed to be acting as a BAC column. To optimize the AOP dose for AOP-BAC experiments, biodegradable DOC (BDOC) was measured after various doses of individual AOP treatments. The maximum increase in biodegradability was observed in case of O3/H2O2 with BDOC of 3.43 mg/L at an ozone dose of 5.44 mg/L and 0.5 mM H2O2. All three AOP treated water were passed through BAC columns and change in BDOC, DOC, hydrophobic fraction of DOC and UV254 were observed. The maximum DOC, hydrophobic fraction of DOC and UV254 reduction was observed with O3/H2O2-BAC, as expected from BDOC results. The primary reason is enhanced biodegradability after optimum O3/H2O2 treatment and thus better utilization of simpler organic molecules by microbes in the BAC column. Maximum trihalomethane formation potential (THMFP) reduction was also observed in the case of O3/H2O2-BAC treatment.

Implementing Ozone‐BAC‐GAC in potable reuse for removal of emerging contaminants

AbstractRemoval of contaminants of emerging concern (CECs) is an important consideration in potable reuse. The effectiveness of ozonation, biologically activated carbon (BAC) filtration, and granular activated carbon (GAC) adsorption was assessed in the removal of 96 CECs. During phase 1, O3/total organice carbon (TOC) was varied between 0 and 1.5. Ozone was successful in removing CECs, achieving a total CEC concentration of 20.5 μg/L at an O3/TOC of 1.5 compared with 70 μg/L in absence of ozone. CECs such as iohexol, meprobamate, sucralose and flame retardants, tris(2‐carboxyethyl)phosphine (TCEP), tris(1‐chloro‐2‐propyl) phosphate (TCPP), and tris(1,3‐dichloro‐2‐propyl)phosphate (TDCPP) were detected in the ozone effluent even at the highest ozone dose. BAC filters did not contribute measurably to CEC removal, while the 20‐min empty bed contact time (EBCT) GAC removed 57.6% of the influent CEC concentration, even though the adsorption capacity had been exerted through previous operation. During phase 2, the average O3/TOC ratio was 0.64, and the impact of new GAC media on CEC removal was studied. EBCT was maintained at 15 min for both GAC contactors, while the used GAC (133,600 bed volume [BV]) was replaced with new media in one GAC contactor. The GAC with new media removed CECs below the limit of quantitation, up to 10,000 BV, while removal decreased to 70% after 20,000 BV, with seven CECs—sucralose, iohexol, acesulfame‐k, meprobamate, cotinine, primidone, and acetaminophen—being detected. Ozone doses for CEC removal and BV needed for adsorption of CECs on activated carbon can be determined from this study. Thus, the results from this study can help design and optimize ozone, BAC, and GAC systems used for potable reuse to target the removal of specific CECs.