Granular Activated Carbon Filtration Research Articles

Biological degradation of organic micropollutants in GAC filters–temporal development and spatial variations

The capacity for organic micropollutant removal in granular activated carbon (GAC) filters for wastewater treatment changes over time. These changes are in general attributed to changes in adsorption, but may in some cases also be affected by biological degradation. Knowledge on the degradation of organic micropollutants, however, is scarce. In this work, the degradation of micropollutants in several full-scale GAC and sand filters was investigated through incubation experiments over a period of three years, using 14C-labeled organic micropollutants with different susceptibilities to biological degradation (ibuprofen, diclofenac, and carbamazepine), with parallel 16S rRNA gene sequencing. The results showed that the degradation of diclofenac and ibuprofen in GAC filters increased with increasing numbers of bed volumes when free oxygen was available in the filter, while variations over filter depth were limited. Despite relatively large differences in bacterial composition between filters, a degradation of diclofenac was consistently observed for the GAC filters that had been operated with high influent oxygen concentration (DO >8 mg/L). The results of this comprehensive experimental work provide an increased understanding of the interactions between microbial composition, filter material, and oxygen availability in the biological degradation of organic micropollutants in GAC filters.

Metabolites are overlooked in environmental risk assessments and monitoring of pharmaceuticals: The case study of pantoprazole

The proton-pump inhibitor pantoprazole (PPZ) is one of the most consumed pharmaceuticals worldwide. Despite its high usage, reported PPZ concentrations in environmental water samples are comparatively low, which can be explained by the extensive metabolism of PPZ in the human body. Since most previous studies did not consider human PPZ metabolites it can be assumed that the current environmental exposure associated with the application of PPZ is substantially underestimated. In our study, 4′-O-demethyl-PPZ sulfide (M1) was identified as the predominant PPZ metabolite by analyzing urine of a PPZ consumer as well as the influent and effluent of a wastewater treatment plant (WWTP) using liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS). M1 was found to be ubiquitously present in WWTP effluents (max. concentration: 3 000 ng/L) and surface waters in Germany. On average, the surface water concentrations of M1 were approximately 30 times higher than those of the parent compound PPZ. Laboratory scale experiments demonstrated that activated carbon can considerably adsorb M1 und thus improve its removal during wastewater and drinking water treatment. Laboratory ozonation experiments showed a fast oxidation of M1, accompanied by the formation of several ozonation products. Certain ozonation products (identities confirmed via synthesized reference standards) were also detected in water samples collected after ozonation in a full-scale WWTP. Overall lower signal intensities were observed in the effluents of a sand filter and biologically active granular activated carbon filter, suggesting that the compounds were significantly removed during these post-ozonation treatment stages.

Activated carbon impregnated with Ag(0) and Cu oxides for the removal of Escherichia coli, Giardia, and Cryptosporidium (oo)cysts from water

Granular activated carbon (GAC) impregnated with silver or copper was evaluated as a point-of-use water treatment to improve the microbiological quality of drinking water processed by low-cost, newly developed GAC filters. Experiments were carried out in a point-of-use water purifying system using packed-bed filters of GAC impregnated with various concentrations of Ag(0) or Cu oxides. The pore and surface properties were studied in terms of BET volumetric measurement with nitrogen adsorption (BET area of metal-impregnated GAC lies within the range of 602 ∼ 866 m²g−1, while the surface area of non-treated GAC is 870 m²g-1), X-ray diffraction (identifying the presence of metallic silver and copper oxide in the GAC structure) and Scanning Electron Microscopy (revealed the presence of metal compounds deposited on the GAC surface). The performance of filters with GAC (water treatment capacity of 4 L/g) was evaluated against microbiological contaminants in synthetic water so that the best loading concentration to remove microorganisms from test water could be determined. The removal efficiency against Escherichia coli was higher when the amount of metal impregnated on GAC increased. GAC impregnated with Ag(0) at 5.0 wt% had a strong antibacterial activity for the growth of Escherichia coli. Samples of GAC impregnated with Ag(0) at 1.0 wt% and Cu oxides at 0.5 wt% were more efficient in the removal of Giardia and Cryptosporidium (oo) cysts. The above evaluations showed that the proposed apparatus, based on a gravitational point-of-use filter with an adsorbent with metals has antibacterial properties and may be recommended to communities for household treatment of drinking water.

MBR and GAC filtration followed by UV disinfection – implications for wastewater reuse at full scale

Abstract Influences of upstream wastewater treatment on the process combination of granular activated carbon (GAC) and ultraviolet (UV) disinfection were studied and the implications of this for wastewater reuse were assessed. GAC is an efficient chemical barrier but contributes little to the removal of indicator bacteria, and generally increases total bacteria concentrations, necessitating disinfection with UV radiation, for example, to ensure the safe reuse of wastewater. The efficiency of UV disinfection is impacted by factors such as particle concentration and UV absorbance of the water and is thus affected by upstream treatment processes. A full-scale wastewater treatment plant with a membrane bioreactor (MBR) followed by GAC filtration was compared to a treatment plant with a conventional activated sludge process and sand filtration, followed by GAC filtration. The removal of indicator bacteria was higher by the GAC filter that was preceded by an MBR. A UV fluence of 400 J/m2 was sufficient to reach irrigation water quality for both process combinations and to meet the criteria for microbial drinking water quality in the MBR + GAC effluent. One sample was selected for chemical analysis, comprising approximately 100 parameters, demonstrating that the MBR + GAC + UV (400 J/m2) effluent met all drinking water criteria except for nitrate levels.

Adaptation of water treatment processes for controlling disinfection byproducts in supply waters to compensate the effects of climate change

The water treatment processes (WTPs) need adaptation to climate change. Safe water supply is being challenged by the deteriorating trend of water quality, which can increase disinfection byproducts and impose cancer/non-cancer risks to humans. In this study, implications of climate change and water quality deterioration on the formation of trihalomethanes' (THMs), and risks from 2020 to 2050 were predicted. In 2020, averages of temperature, dissolved organic carbon (DOC) and pH in source waters from Newfoundland (Canada) were 7.92 °C, 6.40 mg/L and 6.53 respectively, which were predicted to be 9.95 °C, 8.56 mg/L and 7.65, respectively in 2050. Three scenarios of free chlorine and bromide ions [(2.0 mg/L, 10 μg/L), (3.5 mg/L, 25 μg/L) and (5.0 mg/L, 50 μg/L)] were simulated. Two models (Model-1 and Model-2) were applied for predicting THMs, risks and allowable DOC for target risks. For Model-1, DOC in 2030, 2040 and 2050 were predicted to be in the ranges of 4.53–4.92, 3.32–3.84 and 2.49–3.06 mg/L respectively to impose similar risks as of 2020. For Model-2, DOC ranges were 5.02–5.95, 3.92–4.99 and 3.60–4.80 mg/L respectively. The lower ranges of DOC in future years were due to increased effects of pH and temperature. To maintain the risks of 2050 to the levels of 2020, WTPs need to reduce DOC by 64.3–70.9 % (Model-1) and 43.8–57.9 % (Model-2). The granular activated carbon filtration is widely used for reducing DOC, which can be further assessed for extensive applications in the WTPs.

Activated carbon impregnated with Ag(0) and Cu oxides for the removal of Escherichia coli, Giardia, and Cryptosporidium (oo)cysts from water

Granular activated carbon (GAC) impregnated with silver or copper was evaluated as a point-of-use water treatment to improve the microbiological quality of drinking water processed by low-cost, newly developed GAC filters. Experiments were carried out in a point-of-use water purifying system using packed-bed filters of GAC impregnated with various concentrations of Ag(0) or Cu oxides. The pore and surface properties were studied in terms of BET volumetric measurement with nitrogen adsorption (BET area of metal-impregnated GAC lies within the range of 602 ∼ 866 m²g−1, while the surface area of non-treated GAC is 870 m²g-1), X-ray diffraction (identifying the presence of metallic silver and copper oxide in the GAC structure) and Scanning Electron Microscopy (revealed the presence of metal compounds deposited on the GAC surface). The performance of filters with GAC (water treatment capacity of 4 L/g) was evaluated against microbiological contaminants in synthetic water so that the best loading concentration to remove microorganisms from test water could be determined. The removal efficiency against Escherichia coli was higher when the amount of metal impregnated on GAC increased. GAC impregnated with Ag(0) at 5.0 wt% had a strong antibacterial activity for the growth of Escherichia coli. Samples of GAC impregnated with Ag(0) at 1.0 wt% and Cu oxides at 0.5 wt% were more efficient in the removal of Giardia and Cryptosporidium (oo) cysts. The above evaluations showed that the proposed apparatus, based on a gravitational point-of-use filter with an adsorbent with metals has antibacterial properties and may be recommended to communities for household treatment of drinking water.

Contaminants of emerging concern reduction and microbial community characterization across a three-barrier advanced water treatment system

This research investigated the removal of contaminants of emerging concern (CECs) and characterized the microbial community across an advanced water treatment (AWT) train consisting of Coagulation/Flocculation/Clarification/Granular Media Filtration (CFCGMF), Ozone-Biological Activated Carbon Filtration (O3/BAC), Granular Activated Carbon filtration, Ultraviolet Disinfection, and Cartridge Filtration (GAC/UV/CF). The AWT train successfully met the goals of CECs and bulk organics removal. The microbial community at each treatment step of the AWT train was characterized using 16S rRNA sequencing on the Illumina MiSeq platform generated from DNA extracted from liquid and solid (treatment media) samples taken along the treatment train. Differences in the microbial community structure were observed. The dominant operational taxonomic units (OTU) decreased along the treatment train, but the treatment steps did impact the microbial community composition downstream of each unit process. These results provide insights into microbial ecology in advanced water treatment systems, which are influenced and shaped by each treatment step, the microbial community interactions, and their potential metabolic contribution to CECs degradation.

Optimizing backwash control using data on seasonal changes in the invertebrate community of granular activated carbon filters

Problems associated with the colonization and leakage of invertebrates in the granular activated carbon (GAC) filters of waterworks have received increased attention in recent years. To study the effect of environmental factors and water quality on invertebrate abundances, and the backwash control for minimizing invertebrate abundance. A survey of the invertebrate community of GAC filters was carried out monthly from March 2021 to May 2022. A pilot-scale GAC system established in the laboratory alongside a lake, with a volume of 35.3 L. 45 invertebrate species were detected, and 40 of these were rotifers. Significant variation in abundance was observed among seasons before and after GAC filtration, the average invertebrate abundance in the inlet water was 11.1 times that in the filtrate. The GAC filter contained invertebrates that might be responsible for the large number of organisms in the filtrate. Invertebrate abundance in the GAC filter decreased gradually with the carbon layer depth, which the mean invertebrate abundances were 6,926, 5,232, and 3818 ind./kg in the top layer (TL), middle layer (ML), and bottom layer (BL), respectively. Invertebrate abundance was correlated with water temperature and varied seasonally. Among eight water quality parameters, chlorophyll a (Chla) and the total plate count (TPC) were most significantly correlated with invertebrate abundance. According to the statistical modeling and the optimization process of response surface methodology (RSM). The predicted optimal values were a flow rate of 6.36 L/h, a backwash cycle of 3.26 d, and a backwash intensity of 14.97 L/(m2·s) for a minimum invertebrate abundance of 3013 ind./kg in the GAC filter. To maintain invertebrate abundance within an acceptable range, some of these measures might need to be modified depending on the actual conditions.

Assessing the potential of a membrane bioreactor and granular activated carbon process for wastewater reuse – A full-scale WWTP operated over one year in Scania, Sweden

A full-scale membrane bioreactor (MBR) with ultrafiltration, followed by granular activated carbon (GAC), was examined to determine the potential of reusing treated water as a source of drinking water or for irrigation. The major part of the bacteria removal took place in the MBR, whereas the GAC removed substantial amounts of organic micropollutants. Annual variations in inflow and infiltration resulted in a concentrated influent during summer and a diluted influent in the winter. The removal of E. coli was high throughout the process (average log removal 5.8), with effluent concentrations meeting the threshold for class B water standards for irrigation (EU 2020/741) but exceeding those for drinking water in Sweden. The total bacterial concentration increased over the GAC, indicating the growth and release of bacteria; however, E. coli concentrations declined. The effluent concentrations of metals met the Swedish criteria for drinking water. The removal of organic micropollutants decreased during the initial operation of the treatment plant, but after 1 year and 3 months, corresponding to 15,000 bed volumes, the removal increased. Maturation of the biofilm in the GAC filters might have resulted in biodegradation of certain organic micropollutants, in combination with bioregeneration. Although there is no legislation in Scandinavia with regard to many organic micropollutants in drinking water and water for irrigation, the effluent concentrations were generally in the same order of magnitude as to those in Swedish source waters that are used for drinking water production.

Efficient Mn(II) removal by biological granular activated carbon filtration

Sufficient and sustainable manganese(II) removal is a challenging task to prevent Mn-related drinking water discoloration problems. This study investigated Mn(II) removal by granular activated carbon (GAC) filtration under various conditions. The results showed that biological GAC filter columns could reduce Mn(II) from 400 μg/L to 10 μg/L after a short ripening period, while sand filter columns did not show evident Mn(II) removal function. Water quality changes, pretreatment with NaClO and chemogenic MnOx coating on GAC media surface did not influence the Mn(II) removal capacity of GAC filter columns. 16S rRNA gene sequencing showed that the abundance of potential Mn(II)-oxidizing bacteria in the GAC media was similar to that in the sand media. However, qPCR results indicated that GAC media colonized dramatically more biomass than sand media, resulting in highly effective Mn(II) removal by GAC filter columns. Under chlorinated conditions, GAC filtration underperformed sand filtration in Mn(II) removal, although activated carbon has been reported to be capable of catalyzing Mn(II) oxidation by chlorine. Fast chlorine decay in GAC filter columns made it hard to sustain chemical Mn(II) oxidation and thus led to less Mn(II) removal. This study highlighted the advantage of biological GAC filtration over sand filtration in Mn(II) removal.

Efficacy of activated carbon filtration and ozonation to remove persistent and mobile substances – A case study in two wastewater treatment plants

Persistent and mobile (PM) substances are able to spread quickly in the water cycle and were thus identified as potentially problematic for the environment and water quality. If also toxic (PMT) or very persistent and very mobile (vPvM) their regulation under REACH as substances of very high concern is foreseen. Yet, knowledge on the effectiveness of advanced wastewater treatment in removing PM-substances from WWTP effluents is limited to few rather well-known chemicals. The occurrence and behavior of 111 suspected and known PM-substances was investigated in two wastewater treatment plants employing either powdered activated carbon (PAC, full-scale) or ozonation with subsequent sand/anthracite filtration (pilot-scale) and an additional granular activated carbon (GAC) filtration was investigated. 72 of the 111 PM-substances analyzed were detected at least once in the secondary effluent of either wastewater treatment plant, resulting in total concentrations of 104 μg/L and 40 μg/L, respectively. While PAC removed 32 % of PM-substances well, the total PM burden in the effluent was only reduced from 103 μg/L to 87 μg/L. Ozonation and the subsequent sand/anthracite filtration was able to reduce the PM burden in wastewater from 40 μg/L to 19 μg/L, showing a higher removal efficacy than PAC in this study. The additional GAC filtration further reduced the total PM-concentration to 13 μg/L. Among the investigated PM-chemicals detected were constituents of ionic liquids: The anion hexafluorophosphate was one of few chemicals that was detected in effluent concentrations >1 μg/L and could not be removed by the processes studied, showing that for some chemicals preventive actions may be required.

Pilot-scale removal of persistent and mobile organic substances in granular activated carbon filters and experimental predictability at lab-scale

Present knowledge about the fate of persistent and mobile (PM) substances in drinking water treatment is limited. Hence, this study assesses the potential of fixed-bed granular activated carbon (GAC) filters to fill the treatment gap for PM substances and the elimination predictability from lab-scale experiments. Two parallel pilot filters (GAC bed height 2 m, diameter 15 cm) with different GAC were operated for 1.5 years (ca. 47,000 BV throughput) alongside rapid small-scale column tests (RSSCT) designed based on the proportional diffusivity (PD) and the constant diffusivity (CD) approaches. Background dissolved organic matter (DOM) and a set of 17 target substances were investigated, among them 2-acrylamido-2-methylpropane sulfonate (AAMPS), adamantan-1-amine (ATA), melamine (MEL) and trifluoromethanesulfonic acid (TFMSA). Nine substances were predominantly present in the drinking water used as pilot filter influent (frequencies of detection above 80 %, median concentrations 0.003–1.868 μg/L) and their breakthrough behaviors could be observed: TFMSA was not retained at all, four substances including AAMPS and ATA reached complete breakthrough below 20,000 BV, three compounds were partially retained until the end of operation and oxypurinol was retained completely. The comparable PM candidate and DOM removal performances of both GAC aligns with their very similar surface characteristics and elemental compositions. The agreement of results between RSSCT with the pilot-scale filters were substance specific and no superior RSSCT design could be identified. However, CD-RSSCT provide a conservative removal prediction for most studied compounds. MEL adsorption was significantly underestimated by both RSSCT designs. Using the criterion of a carbon usage rate (with respect to 50 % breakthrough) below 25 mgGAC/Lwater for an economic retention by fixed-bed GAC filters, five (out of nine) substances met the requirement.

Removal of Haloacetic Acids via Adsorption and Biodegradation in a Bench-Scale Filtration System

Brominated disinfection byproducts (DBPs) are a concern to drinking water utilities due to their toxicity and increasing prevalence in water systems. Haloacetic acids (HAAs) are a class of DBPs that are partially regulated by the United States Environmental Protection Agency (USEPA), but regulations are likely to increase as evidenced by the brominated HAAs listed on the USEPA Fourth Unregulated Contaminant Monitoring Rule and Fifth Contaminant Candidate List. Utilities often use a pre-oxidant to assist in their treatment training, but this can lead to increased HAA formation during treatment. In this study, tap water was spiked with bromine (Br2) at varying concentrations to simulate bromine-to-chlorine ratios found in the natural environment and the DBPs that may be formed from those waters. The water was fed through a bench-scale biological filter (biofilter) with a small layer of fresh granular activated carbon (GAC) media followed by acclimated anthracite media. The HAA species studied were found to be removable by an average of 89.5% through combined GAC filtration and biofiltration. Biodegradation occurred predominantly in the first five minutes for the acclimated anthracite, with minimal additional removal observed at longer empty bed contact times (15 and 30 min EBCT). This study provides recommendations on biofilter parameters for utilities to reduce the formation of both regulated and unregulated HAAs during the drinking water treatment process.

The significance of granular activated carbon pore structure in modeling dissolved organic carbon removal in fixed-bed filters

A reliable model that describes DOC removal during biological-active granular activated carbon filtration for advanced wastewater treatment has to cover several aspects that influence biological and adsorptive removal processes. For this purpose, this work introduces a two-domain internal diffusion approach to a multicomponent adsorption model, which is combined with a traditional biofilm model for the first time. DOC was divided into fictive components according to biodegradability and adsorbability to calculate multicomponent adsorption equilibrium based on the ideal adsorbed solution theory. Adsorption kinetics included external mass transfer (diffusion through a boundary layer and a biofilm) and internal mass transfer (fast pore diffusion in the larger pores and slow surface diffusion in the micropores). Mass transfer in the micropore domain was implemented by adjusting the adsorptive driving force depending on the available internal surface area for DOC adsorption based on an empirical surface diffusion model. Simulated DOC breakthrough curves were sensitive to model parameters related to the pore structure of the granular activated carbon (GAC). The model was validated with two GAC types and empty bed contact times ranging between 6 and 33 min. The model results showed a good agreement with measured DOC breakthrough curves over the entire operation time, demonstrating the applicability and transferability of the model. In particular, the initial DOC breakthrough was well represented. However, some systematic deviations between measured and simulated DOC breakthrough curves were observed, which are probably due to the level of detail of the implemented biofilm model.

Microbiome, resistome and mobilome of chlorine-free drinking water treatment systems

Drinking water treatment plants (DWTPs) are designed to remove physical, chemical, and biological contaminants. However, until recently, the role of DWTPs in minimizing the cycling of antibiotic resistance determinants has got limited attention. In particular, the risk of selecting antibiotic-resistant bacteria (ARB) is largely overlooked in chlorine-free DWTPs where biological processes are applied. Here, we combined high-throughput quantitative PCR and metagenomics to analyze the abundance and dynamics of microbial communities, antibiotic resistance genes (ARGs), and mobile genetic elements (MGEs) across the treatment trains of two chlorine-free DWTPs involving dune-based and reservoir-based systems. The microbial diversity of the water increased after all biological unit operations, namely rapid and slow sand filtration (SSF), and granular activated carbon filtration. Both DWTPs reduced the concentration of ARGs and MGEs in the water by circa 2.5 log gene copies mL−1, despite their relative increase in the disinfection sub-units (SSF in dune-based and UV treatment in reservoir-based DWTPs). The total microbial concentration was also reduced (2.5 log units), and none of the DWTPs enriched for bacteria containing genes linked to antibiotic resistance. Our findings highlight the effectiveness of chlorine-free DWTPs in supplying safe drinking water while reducing the concentration of antibiotic resistance determinants. To the best of our knowledge, this is the first study that monitors the presence and dynamics of antibiotic resistance determinants in chlorine-free DWTPs.

Challenges of point-of-use devices in purifying tap water: The growth of biofilm on filters and the formation of disinfection byproducts

Currently, polypropylene (PP) and granular activated carbon (GAC) are widely used as the filters in point-of-use devices (POUs). However, the effect of biofilms formation in aged filters and subsequent formation/removal of disinfection byproducts (DBPs) during the use of POUs on purifying tap water remains unclear. In this study, the influence of filter replace event and filter usage time on the removal of DBPs by pristine or aged filters, such as trihalomethanes (THMs) and haloacetic acids (HAAs), was investigated. Additionally, the effect of biofilms-attached PP filters and GAC filters on DBPs concentration in treated water was explored. The results showed that POUs effectively removed over 60% of THMs and HAAs from tap water, while the removal efficiency decreased with the operation time. The increase in usage time of PP filters led to elevated levels of DBPs. Moreover, the pristine pre-GAC filters removed 12.31% of THMs and 6.62% of HAAs, respectively, while aged GAC filters enhanced the removal of HAAs. SEM and high-throughput sequencing analysis confirmed the attached growth of biofilms on aged PP and GAC filters. The biofilms growth on PP filters led to the formation of THMs and HAAs, and the formed DBPs increased with increasing influent chlorine concentration, lengthened filters usage time and stagnation time. Nevertheless, the DBPs in effluent of biofilms-attached GAC filters increased with increasing influent chlorine concentration and filter usage time while decreased with stagnation time. These results indicated that growth of biofilms commonly observed in filters of POUs leads to the formation of DBPs and increases the risk of DBPs exposure to users of POU devices.

Performance of Micropollutant Removal during Wet-Weather Conditions in Advanced Treatment Stages on a Full-Scale WWTP

The reduction of organic micropollutants (OMP) in rivers, lakes and groundwater is an essential legal obligation of the European Water Framework Directive. Since OMP treatment in full-scale wastewater treatment plants (WWTPs) is not state of the art yet, there is little knowledge regarding removal performances, in particular during wet weather. We aimed to contribute to filling this knowledge gap by providing insights from a German case study. On-site measurements were conducted to investigate the impact of rain events on OMP removal with activated carbon processes using powdered activated carbon (PAC) and granular activated carbon (GAC). The study focused on 26 OMPs with different entry paths in the combined sewer system (CSS) and various physico-chemical properties. The monitored OMPs showed higher mass loads during wet weather at all sampling points: effluent of the secondary clarifier, effluent of the PAC treatment stage, and effluent of the GAC filter. As a result of shortened hydraulic retention time (HRT) due to rain events, the overall OMP removal was significantly lower (42% PAC and 46% GAC) than during dry weather (68% PAC and 62% GAC). In order to achieve constant removal rates during all weather conditions, the critical process control parameters are currently being investigated in ongoing studies.

Bioaugmentation of Biological Activated Carbon Filters for Enhanced Micropollutant Removal

Granular activated carbon (GAC) filtration is an important technology for micropollutant removal from water. In GAC filters, micropollutants adsorb onto the activated carbon and can also be biodegraded, prolonging the filter lifetime. Biodegradation can be enhanced by introducing micropollutants degrading microorganisms to the filters, that is, through bioaugmentation. We assessed pyrazole adsorption to activated carbon and biodegradation in GAC filters inoculated with pyrazole degrading biomass originating from a drinking water plant. Pyrazole was chosen as a model micropollutant because it was detected at high levels in 2015 in Dutch surface water, and little is known about its removal mechanism in water treatment. GAC filters without inoculation and inoculated at different moments were operated, and breakthrough curves were fit to an adsorption and biodegradation model based on surface diffusion and Monod kinetics. Pyrazole biodegradation was successfully transferred from a sand filter to GAC filters and contributed to decreasing pyrazole concentrations below 10 μg/L in the GAC filter effluent. Pyrazole degradation was a stable process that could be maintained despite the lack of pyrazole in the filter influent for up to 30 days. Achieving a combination of adsorption and biodegradation in GAC filters is essential to sustain high micropollutant removals in the long term.

Evaluation of organics reduction performance of the GAC filtration with regenerated carbons using the long-term operational data of drinking water treatment facilities

Abstract Degradation of raw water quality promoted the introduction of GAC (granular activated carbon) filtration and ozonation into Korean drinking water treatment facilities in 1994 in order to cope with organic pollutants. This study focuses on the evaluation of organics reduction performance of the GAC filtration with regenerated carbons using long-term operational data. Three drinking water treatment facilities at Busan were selected for this purpose. It was found in this study that GAC filtration and ozonation helped these facilities to reduce the treated levels of DOC (dissolve organic carbon) as well as of 1,4-dioxane. Regeneration affected organics reduction performance of GAC filtration. The GAC filtration with regenerated carbons was found more effective for DOC reduction, while the filtration with virgin carbons was more effective for THM (trihalomethane) reduction. These results were related to the pore size change that occurred after the regeneration. The regeneration increased the meso pore volume but decreased the micro pore volume. The regeneration cycle was important for the decrease in the micro pore volume. The micro pore volume remained relatively unchanged after the first regeneration but was substantially decreased after the regeneration was repeated by more than second time.

Microplastic occurrence after conventional and nanofiltration processes at drinking water treatment plants: Preliminary results

Microplastics (MP) have been detected in almost all matrices, including drinking water, and assessing the contamination of drinking water with this type of pollution is of the utmost sanitary importance. This study aims to evaluate MP contamination of inlet river water and drinking water at three drinking water treatment plants (DWTPs) in the Paris region in France. Each plant performs water treatment processes that are efficient for particulate matter removal such as coagulation-flocculation, sand filtration, and granular activated carbon filtration. One of the plants also has a parallel water treatment file that uses microfiltration and nanofiltration processes. This file was investigated to assess its efficiency compared to the others. To our knowledge, this study is the first to investigate MP contamination in a DWTP using nanofiltration processes. The drinking water distribution network was also investigated, with samples taken at three network points. Microplastics contamination of sizes 25–5,000 μm was characterized using micro-Fourier transform infrared spectroscopy (μ-FTIR) in large volume samples (500 L) with complete mapping of each sample. Concentrations ranging from 7.4 to 45.0 MP/L were found in inlet water while concentrations ranging from blank level (0.003 MP/L) to 0.260 MP/L were found in outlet drinking water (overall removal rate above 99%). Polyethylene, polypropylene, and polyethylene terephthalate were the main polymers found both at the inlet and outlet, but ratios varied significantly at the outlet. No MP were detected in four out of the six samples from the nanofiltration file, and were not found to have significantly different concentrations compared to blank level. Concentrations in the distribution network were higher overall than at the corresponding DWTP outlet, although a high degree of variation between samples was observed. Our results suggest that membrane processes of microfiltration and nanofiltration are more efficient than typical treatment processes, and also that a MP re-contamination within the distribution network itself might occur.