Understanding the fate of organic micropollutants in sand and granular activated carbon biofiltration systems

Biodegradation kinetics of organic micropollutants in biofilters for advanced wastewater treatment - Impact of operational conditions and biomass origin on removal

Biofiltration processes are often part of advanced wastewater treatment (aWWT) technologies for the removal of organic micropollutants (OMP) from conventional wastewater treatment plant (WWTP) effluents. Although biological effects are not always the main focus of these technologies (e.g. filtration through granular activated carbon), they have been shown to contribute significantly to total OMP removal. While OMP biodegradation kinetics in conventional biological wastewater treatment are well researched, no systematic comparison to biomass from aWWT is available. This biomass faces different growth conditions and higher OMP concentrations relative to the background organic matter. Adaptation to these conditions could be possible and could lead to faster OMP biodegradation kinetics, which would show in a larger pseudo first-order biodegradation kinetic constant kbiol. In this work, kbiol values for biomass obtained from aWWT biofilters were determined by evaluating OMP removals measured in lab-scale biofilters using a mechanistic model of the experimental setup. A comparison to kbiol values from literature for conventional wastewater treatment (with nutrient removal) revealed similar OMP biodegradation kinetics without any advantages of biomass from aWWT. A conceptual evaluation of influencing factors on OMP removal in biofilters showed that operational parameters (such as the biomass concentration or the empty bed contact time) and the affinity of OMPs to adsorb on biomass have a significant additional effect on biological OMP removal. Therefore, kbiol values alone are not sufficient to estimate biological OMP removal in biofilters and further information about the system is required.

New Perspectives on the Interactions between Adsorption and Degradation of Organic Micropollutants in Granular Activated Carbon Filters

The removal of organic micropollutants in granular activated carbon (GAC) filters can be attributed to adsorption and biological degradation. These two processes can interact with each other or proceed independently. To illustrate the differences in their interaction, three 14C-labeled organic micropollutants with varying potentials for adsorption and biodegradation were selected to study their adsorption and biodegradation in columns with adsorbing (GAC) and non-adsorbing (sand) filter media. Using 14CO2 formation as a marker for biodegradation, we demonstrated that the biodegradation of poorly adsorbing N-nitrosodimethylamine (NDMA) was more sensitive to changes in the empty bed contact time (EBCT) compared with that of moderately adsorbing diclofenac. Further, diclofenac that had adsorbed under anoxic conditions could be degraded when molecular oxygen became available, and substantial biodegradation (≥60%) of diclofenac could be achieved with a 15 min EBCT in the GAC filter. These findings suggest that the retention of micropollutants in GAC filters, by prolonging the micropollutant residence time through adsorption, can enable longer time periods for degradations than what the hydraulic retention time would allow for. For the biologically recalcitrant compound carbamazepine, differences in breakthrough between the 14C-labeled and nonradiolabeled compounds revealed a substantial retention via successive adsorption-desorption, which could pose a potential challenge in the interpretation of GAC filter performance.

Removal of organic micropollutants in biologically active filters: A systematic quantitative review of key influencing factors

Biofiltration utilizes natural mechanisms including biodegradation and biotransformation along with other physical processes for the removal of organic micropollutants (OMPs) such as pharmaceuticals, personal care products, pesticides and industrial compounds found in (waste)water. In this systematic review, a total of 120 biofiltration studies from 25 countries were analyzed, considering various biofilter configurations, source water types, biofilter media and scales of operation. The study also provides a bibliometric analysis to identify the emerging research trends in the field. The results show that granular activated carbon (GAC) either alone or in combination with another biofiltration media can remove a broad range of OMPs efficiently. The impact of pre-oxidation on biofilter performance was investigated, revealing that pre-oxidation significantly improved OMP removal and reduced the empty bed contact time (EBCT) needed to achieve a consistently high OMP. Biofiltration with pre-oxidation had median removals ranging between 65% and >90% for various OMPs at 10-45 min EBCT with data variability drastically reducing beyond 20 min EBCT. Biofiltration without pre-oxidation had lower median removals with greater variability. The results demonstrate that pre-oxidation greatly enhances the removal of adsorptive and poorly biodegradable OMPs, while its impact on other OMPs varies. Only 19% of studies we reviewed included toxicity testing of treated effluent, and even fewer measured transformation products. Several studies have previously reported an increase in effluent toxicity because of oxidation, although it was successfully abated by subsequent biofiltration in most cases. Therefore, the efficacy of biofiltration treatment should be assessed by integrating toxicity testing into the assessment of overall removal.

Fate of emerging contaminants in a sequencing batch reactor and potential of biological activated carbon as tertiary treatment for the removal of persisting contaminants

The study aims to understand the occurrence and removal of 20 emerging contaminants (ECs) in each unit process of a sequencing batch reactor-based wastewater treatment plant (WWTP) and explore the potential of biological activated carbon (BAC) for the treatment of residual ECs and organic matter in the secondary effluent. Analgesic-acetaminophen, anti-inflammatory drug-ibuprofen, and stimulant-caffeine were detected at high concentrations in the influent. Most of the removal was observed in the biological treatment stage in the SBR basins. The mass load of the ECs was 2.93 g/d in the secondary effluent and 0.4 g/d in the final sludge, while the total removal of the mass load of ECs till the secondary treatment stage was 93.22%. 12 of the 20 ECs were removed by more than 50%, while carbamazepine (negative removal), sulfamethoxazole, and trimethoprim were removed by less than 20%. As a polishing step and to remove residual ECs, two BAC units were studied for 11,000 bed volumes (324 days). Packed column studies on granular activated carbon were conducted, and GAC development to BAC was monitored. SEM and FTIR were used to confirm and characterize the BAC. The BAC appeared to be more hydrophobic than the GAC. The BAC removed 78.4% and 40% of the dissolved ECs and organic carbon at an optimum EBCT of 25 min. Carbamazepine, sulfamethoxazole, and trimethoprim were removed by 61.5, 84, and 52.2%, respectively. Parallel column tests revealed adsorption as an important mechanism for the removal of positively charged compounds. The results indicate that the BAC is an effective tertiary/polishing technique for removing organic and micropollutants in the secondary wastewater effluent.

Effect of filtration rates on the performance and head loss development in granular filters during the post-treatment of anaerobic reactor effluent

This study investigated the performance of a granular filtration system (GFS) composed of a rock filter (RF), a rapid sand filter (RSF), and an activated carbon filter (ACF), applied to the post-treatment of an anaerobic reactor effluent. Four filtration rates (FR) were applied to the GFS (in m3·m-2·d-1): 100-60-60, 100-90-90, 200-120-120, and 200-160-160, for RF-RSF-ACF, respectively. A clarified final effluent with low turbidity (~ 10 NTU), solids (~ 6.5 mg TSS.L-1), and organic matter content (~ 40 mg COD.L-1) was obtained when the GFS worked with FR up to 100-90-90 m3·m-2·d-1. For higher FR, the effluent quality was a little poorer. Principal component analysis showed when the RSF operated at 120 or 160 m3·m-2·d-1, it presented an effluent with higher turbidity which did not affect negatively the ACF performance. The hydraulic load limits in the RSF were reached in periods of 45, 30, and 24.5 h for the FR of 60, 120, and 160 m3·m-2·d-1, respectively, and head loss analysis depicted a more distributed solid retention through the sand depth with the lower FR. Thus, the results revealed that the RF-RSF-ACS system is a promising alternative for effluent polishing of anaerobic reactor, especially when the FR is set at 90 m3·m-2·d-1 or even higher.

Activated carbon enhanced traditional activated sludge process for chemical explosion accident wastewater treatment

With the development of industries, explosion accidents occur frequently during production, transportation, usage and storage of hazard chemicals. It remained challenging to efficiently treat the resultant wastewater. As an enhancement of traditional process, the activated carbon-activated sludge (AC-AS) process has a promising potential in treating wastewater with high concentrations of toxic compounds, chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N), etc. In this paper, activated carbon (AC), activated sludge (AS) and AC-AS were used to treat the wastewater produced from an explosion accident in the Xiangshui Chemical Industrial Park. The removal efficiency was assessed by the removal performances of COD, dissolved organic carbon (DOC), NH₄⁺-N, aniline and nitrobenzene. Increased removal efficiency and shortened treatment time were achieved in the AC-AS system. To achieve the same COD, DOC and aniline removal (90%), the AC-AS system saved 30, 38 and 58 h compared with the AS system, respectively. The enhancement mechanism of AC on the AS was explored by metagenomic analysis and three-dimensional excitation-emission-matrix spectra (3DEEMs). More organics, especially aromatic substances were removed in the AC-AS system. These results showed that the addition of AC promoted the microbial activity in pollutant degradation. Bacteria, such as Pyrinomonas, Acidobacteria and Nitrospira and genes, such as hao, pmoA-amoA, pmoB-amoB and pmoC-amoC, were found in the AC-AS reactor, which might have played important roles in the degradation of pollutants. To sum up, AC might have enhanced the growth of aerobic bacteria which further improved the removal efficiency via the combined effects of adsorption and biodegradation. The successful treatment of Xiangshui accident wastewater using the AC-AS demonstrated the potential universal characteristics of the process for the treatment of wastewater with high concentration of organic matter and toxicity. This study is expected to provide reference and guidance for the treatment of similar accident wastewaters.

Waste reclamation from municipal solid waste for the cost-efficient treatment of landfill leachate with a novel biological trickle reactor system

Mature landfill leachate (MLL) would be a tough nut to crack, how to realize waste reclamation while deal with the intractable by-products deserves for more considerations. In this study, a novel system, equipped with two biological trickle reactors developed by inert wastes and a connected organic feeder using waste-recycling rotten banana powder, was established for treating MLL. Results indicated that superior pollutant removal performance and long-term stability were achieved by this system, with only COD and TN concentrations slightly higher than the relevant standard limits. But the shortage about poor resistance to shock pollution loads, was underlined by the fluctuation of water quality. Anaerobic condition and carbon source supplementation contributed to more microbial similarities but less community richness and diversity among inert fillings, and the selective enrichment of denitrification and organic-degrading strains simultaneously occurred. The comparisons with common processes demonstrated that this system was a cost-efficient choice for MLL treatment.

Precise portrayal of microscopic processes of wastewater biofilm formation: Taking SiO2 as the model carrier

Precise characterization of the microscopic processes of wastewater biofilm formation is essential for regulating biofilm behavior. Nevertheless, it remains a great challenge. This study investigated biofilm formation on SiO₂ carriers under gradually increasing shear force combining the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory in a Couette-Taylor reactor, and precisely revealed the micro-interface interaction and species colonization during biofilm formation. The results indicated that bacterial reversible adhesion distance on SiO₂ carrier surface was 3.06 ± 0.48 nm. Meanwhile, the secondary minimum of total XDLVO interaction energy could be used as a novel indicator to distinguish biofilm formation stages. The revealed biofilm formation stages were also confirmed by the electrochemical analysis. Additionally, the pioneer species that colonized at first were Comamonadaceae, Azospira, Flavobacterium and Azonexus, while keystone species such as Hydrogenophaga, AKYH767, Aquimonas and Ignavibacterium determined the stability of microbial community. In conclusion, this study provided a methodological example to study wastewater biofilm micro-interface behavior through the integration of an experimental platform as well as multiple monitoring and analysis methods, which opened up new perspectives for biofilm research and provided useful guidance for the regulation of biofilm-related treatment processes and new technology development.

Sand and sand-GAC filtration technologies in removing PPCPs: A review

Concerns have been raised about the risks that pharmaceuticals and personal care products (PPCPs) in aquatic environments posed to humans and the environment. In recent years, sand filtration has been used to potentially remove these emerging contaminants from water. However, there has been no review of the effectiveness of this technology to date. This paper presents a brief introduction of sand filtration types, reviews the current progress in PPCPs removal through sand filtration, and discusses the mechanisms behind this process and the combination of granular activated carbon (GAC) and sand as an enhanced sand-GAC filtration technology. Sand filtration achieves a reasonable but highly variable degree of PPCPs removal. Biodegradation and adsorption are the two main mechanisms of PPCPs removal, in particular the biodegradation since adsorption capacity of sand is relatively low. Other processes, such as bio-sorption and indirect adsorption, may also contribute to PPCPs removal. To compensate for the inadequate PPCPs removal through sand filtration, porous GAC has been combined with sand to develop sand-GAC filtration technologies. Serial, dual, and sandwich filters have been investigated, and significant removal enhancement has been observed, due to the strengthened adsorption capacity, suggesting the applicability of these variants. Future research focus, such as investigating the influence of different operational conditions on sand filter performance, obtaining a deeper understanding of the various removal mechanisms, and investigating of long-term performance of the filter used for PPCPs removal, are suggested.

Exploring organic micropollutant biodegradation under dynamic substrate loading in rapid sand filters

Microbial removal of trace organic micropollutants (OMPs) from drinking water sources remains challenging. Nitrifying and heterotrophic bacteria in rapid sand filters (RSFs) are capable of biodegrading OMPs while growing on ammonia and dissolved organic matter (DOM). The loading patterns of ammonia and DOM may therefore affect microbial activities as well as OMP biodegradation. So far, there is very limited information on the effect of substrate loading on OMP biodegradation at environmentally relevant concentrations (∼ 1 µg/L) in RSFs. We investigated the biodegradation rates of 16 OMPs at various substrate loading rates and/or empty bed contact times (EBCT). The presence of DOM improved the biodegradation of paracetamol (41.8%) by functioning as supplementary carbon source for the heterotrophic degrader, while hindering the biodegradation of 2,4-D, mecoprop and benzotriazole due to substrate competition. Lower loading ratios of DOM/benzotriazole benefited benzotriazole biodegradation by reducing substrate competition. Higher ammonia loading rates enhanced benzotriazole removal by stimulating nitrification-based co-metabolism. However, stimulating nitrification inhibited heterotrophic activity, which in turn inhibited the biodegradation of paracetamol, 2,4-D and mecoprop. A longer EBCT promoted metformin biodegradation as it is a slowly biodegradable compound, but suppressed the biodegradation of paracetamol and benzotriazole due to limited substrate supply. Therefore, the optimal substrate loading pattern is contingent on the type of OMP, which can be chosen based on the priority compounds in practice. The overall results contribute to understanding OMP biodegradation mechanisms at trace concentrations and offer a step towards enhancing microbial removal of OMPs from drinking water by optimally using RSFs.

Digging deep into a GAC filter - Temporal and spatial profiling of adsorbed organic micropollutants

A large pilot-scale granular activated carbon (GAC) filter was operated downstream in a full-scale wastewater treatment plant to remove organic micropollutants. To describe the spatial and temporal developments of micropollutant adsorption profiles in the GAC filter, micropollutants were extracted from GAC media taken at various filter depths and number of treated bed volumes. At a low number of treated bed volumes (2600 BVs), most micropollutants were adsorbed in the top layers of the filter. At increasing number of treated bed volumes (7300-15,500 BVs), the adsorption front for micropollutants progressed through the filter bed at varying rates, with sulfamethoxazole, fluconazole, and PFOS reaching the bottom layer before carbamazepine and other well-adsorbing micropollutants, such as propranolol and citalopram. Higher amounts of adsorbed micropollutants in the bottom layer of the filter bed resulted in decreased removal efficiencies in the treated wastewater. Mass estimations indicated biodegradation for certain micropollutants, such as naproxen, diclofenac, and sulfamethoxazole. A temporary increase in the concentration of the insecticide imidacloprid could be detected in the filter indicating that extraction of adsorbed micropollutants could provide an opportunity for backtracking of loading patterns.

Co-occurrence of odor-causing dioxanes and dioxolanes with bis(2-chloro-1-methylethyl) ether in Huangpu River source water and fates in O3-BAC process

In recent years, dioxanes and dioxolanes have been intermittently detected in water environment and have caused several offensive drinking water odor incidents worldwide. In this study, the co-occurrence of eight dioxanes, twelve dioxolanes and bis(2-chloro-1-methylethyl) ether was investigated in Huangpu River watershed to explore potential sources and contributions to septic/chemical odor. Totally 8 dioxanes and dioxolanes were detected in river, with 1,4-dioxane (212 -8310 ng/L) and 2,5,5-trimethyl-1,3-dioxane (n.d.-133 ng/L) as the dominated dioxanes, 2-methyl-1,3-dioxolane (49.5 -2278 ng/L), 2-ethy-4-methyl-1,3-dioxolane (n.d.-167 ng/L) and 1,3-dioxolane (n.d.-225 ng/L) as the major dioxolanes. Bis(2-chloro-1-methylethyl) ether was detected (n.d.-1094 ng/L) with significant correlation with dioxanes and dioxolanes, illustrating their similar polyester resin-related industrial origins. 2-Ethy-4-methyl-1,3-dioxolane, 2,5,5-trimethyl-1,3-dioxane and bis(2-chloro-1-methylethyl) ether with individual maximum odor activity value above 1, should contribute to septic/chemical odor in Huangpu River water. The increased concentrations of these chemicals in the downstream of some industrial areas illustrated the association with industrial discharge. Fates in a waterworks using the river water as source water were further explored. The adopting ozone-biological activated carbon treatment could permit a relatively high removal for bis(2-chloro-1-methylethyl) ether and 2,5,5-trimethyl-1,3-dioxane (> 80%), while limited removal for other chemicals. This study provides valuable information for the management of drinking source water and water environment.

Elucidating the removal of organic micropollutants on biological ion exchange resins

Biological ion exchange (BIEX) refers to operating ion exchange (IX) filters with infrequent regeneration to favor the microbial growth on resin surface and thereby contribute to the removal of organic matter through biodegradation. However, the extent of biodegradation on BIEX resins is still debatable due to the difficulty in discriminating between biodegradation and IX. The objective of the present study was to evaluate the performance of BIEX resins for the removal of organic micropollutants and thereby validate the occurrence of biodegradation. The removals of biodegradable micropollutants (neutral: caffeine and estradiol; negative: ibuprofen and naproxen) and nonbiodegradable micropollutants with different charges (neutral: atrazine and thiamethoxam; negative: PFOA and PFOS) were respectively monitored during batch tests with biotic and abiotic BIEX resins. Results demonstrated that biodegradation contributed to the removal of caffeine, estradiol, and ibuprofen, confirming that biodegradation occurred on the BIEX resins. Furthermore, biodegradation contributed to a lower extent to the removal of naproxen probably due to the absence of an adapted bacterial community (Biotic: 49% vs Abiotic: 38% after 24 h batch test). The removal of naproxen, PFOS, and PFOA were attributable to ion exchange with previously retained natural organic matter on BIEX resins. Nonbiodegradable and neutral micropollutants (atrazine and thiamethoxam) were minimally (6%-10%) removed during the batch tests. Overall, the present study corroborates that biomass found on BIEX resins contribute to the removal of micropollutants through biodegradation and ion exchange resins can be used as biomass support for biofiltration.

Understanding adsorption and biodegradation in granular activated carbon for drinking water treatment: A critical review

Drinking water treatment plants use granular activated carbon (GAC) to adsorb and remove trace organics, but the GAC has a limited lifetime in terms of adsorptive capacity and needs to be replaced before it is exhausted. Biological degradation of target contaminants can also occur in GAC filters, which might allow the GAC to remain in service longer than expected. However, GAC biofiltration remains poorly understood and unpredictable. To increase the understanding of adsorption and biodegradation in GAC, previous studies have conducted parallel column tests that use one column of GAC (potentially biologically active) to assess overall removal via both adsorption and biodegradation, and one column with either sterilized GAC or biological non-adsorbing media to assess adsorption or biodegradation alone. Mathematical models have also been established to give insight into the adsorption and biodegradation processes in GAC. In this review, the experimental and modeling approaches and results used to distinguish between the role of adsorption and biodegradation were summarized and critically discussed. We identified several limitations: (1) using biological non-adsorbing media in column tests might lead to non-representative extents of biodegradation; (2) sterilization methods may not effectively inhibit biological activity and may affect adsorption; (3) using virgin GAC coated with biofilm could overestimate adsorption; (4) potential biofilm detachment during column experiments could lead to biased results; (5) the parallel column test approach itself is not universally applicable; (6) competitive adsorption was neglected by previous models; (7) model formulations were based on virgin GAC only. To overcome these limitations, we proposed four new approaches: the use of gamma irradiation for sterilization, a novel minicolumn test, compound-specific isotope analysis to decipher the role of adsorption and biodegradation in situ, and a new model to simulate trace organic adsorption and biodegradation in a GAC filter .

A state of the art overview of carbon-based composites applications for detecting and eliminating pharmaceuticals containing wastewater

The growing prevalence of new toxins in the environment continues to cause widespread concerns. Pharmaceuticals, organic pollutants, heavy metal ions, endocrine-disrupting substances, microorganisms, and others are examples of persistent organic chemicals whose effects are unknown because they have recently entered the environment and are displaying up in wastewater treatment facilities. Pharmaceutical pollutants in discharged wastewater have become a danger to animals, marine species, humans, and the environment. Although their presence in drinking water has generated significant concerns, little is known about their destiny and environmental effects. As a result, there is a rising need for selective, sensitive, quick, easy-to-handle, and low-cost early monitoring detection systems. This study aims to deliver an overview of a low-cost carbon-based composite to detect and remove pharmaceutical components from wastewater using the literature reviews and bibliometric analysis technique from 1970 to 2021 based on the web of science (WoS) database. Various pollutants in water and soil were reviewed, and different methods were introduced to detect pharmaceutical pollutants. The advantages and drawbacks of varying carbon-based materials for sensing and removing pharmaceutical wastes were also introduced. Finally, the available techniques for wastewater treatment, challenges and future perspectives on the recent progress were highlighted. The suggestions in this article will facilitate the development of novel on-site methods for removing emerging pollutants from pharmaceutical effluents and commercial enterprises.

Pilot-Scale Biological Activated Carbon Filtration–Ultrafiltration System for Removing Pharmaceutical and Personal Care Products from River Water

Biological activated carbon (BAC) biofilter coupling ultrafiltration (UF) is a promising process for the treatment of river water contaminated by pharmaceutical and personal care products (PPCPs). However, the pilot-scale study should be conducted to reveal the long-term removal performance and the respective contributions of BAC and UF. In this study, a BAC-UF system with treatment capacity of 0.16 m3 h−1 was operated for 130 days. The water quality was analyzed in terms of CODMn, UV254, NH4+-N, and PPCPs. The results showed that both BAC and UF were related to the removal of organic matter (CODMn and UV254), achieving the removals of 56.00% and 55.25%, respectively. Similarly, BAC and UF were both relevant to the removal effects of ammonia nitrogen, nitrite, and nitrate. Moreover, the BAC-UF process was featured with a high efficiency in the removal of PPCPs, and the average removal of total PPCPs reached 47.84%, especially anhydroerythromycin, sulfachloropyridazine, sulfadiazine, trimethoprim, and caffeine. Besides, it was found that the BAC unit played a key role in PPCPs removal and the UF unit also degraded them by the biomass on UF membranes. Therefore, this study proved the removal performance of BAC-UF for treating popular pollutants from river water, and the BAC-UF process in this work can be considered as a feasible method of producing clean drinking water.

Data Analytics Determines Co-occurrence of Odorants in Raw Water and Evaluates Drinking Water Treatment Removal Strategies

A complex dataset with 140 sampling events was generated using triple quadrupole gas chromatography-mass spectrometer to track the occurrence of 95 odorants in raw and finished water from 98 drinking water treatment plants in 31 cities across China. Data analysis identified more than 70 odorants with concentrations ranging from not detected to thousands of ng/L. In raw water, Pearson correlation analysis determined that thioethers, non-oxygen benzene-containing compounds, and pyrazines were classes of chemicals that co-occurred, and geosmin and p(m)-cresol, as well as cyclohexanone and benzaldehyde, also co-occurred, indicating similar natural or industrial sources. Based on classification and regression tree analysis, total dissolved organic carbon and geographical location were identified as major factors affecting the occurrence of thioethers. Indoles, phenols, and thioethers were well-removed through conventional and advanced treatment processes, while some aldehydes could be generated. For other odorants, higher removal was achieved by ozonation-biological activated carbon (39.3%) compared to the conventional treatment process (14.5%). To our knowledge, this is the first study to systematically identify the major odorants in raw water and determine suitable treatment strategies to control their occurrence by applying data analytics and statistical methods to the complex dataset. These provide informative reference for odor control and water quality management in drinking water industry.

Tracking 14C-Labeled Organic Micropollutants to Differentiate between Adsorption and Degradation in GAC and Biofilm Processes

Granular activated carbon (GAC) filters can be used to reduce emissions of organic micropollutants via municipal wastewater, but it is still uncertain to which extent biological degradation contributes to their removal in GAC filters. 14C-labeled organic micropollutants were therefore used to distinguish degradation from adsorption in a GAC-filter media with associated biofilm. The rates and extents of biological degradation and adsorption were investigated and compared with other biofilm systems, including a moving bed biofilm reactor (MBBR) and a sand filter, by monitoring 14C activities in the liquid and gas phases. The microbial cleavage of ibuprofen, naproxen, diclofenac, and mecoprop was confirmed for all biofilms, based on the formation of 14CO2, whereas the degradation of 14C-labeled moieties of sulfamethoxazole and carbamazepine was undetected. Higher degradation rates for diclofenac were observed for the GAC-filter media than for the other biofilms. Degradation of previously adsorbed diclofenac onto GAC could be confirmed by the anaerobic adsorption and subsequent aerobic degradation by the GAC-bound biofilm. This study demonstrates the potential use of 14C-labeled micropollutants to study interactions and determine the relative contributions of adsorption and degradation in GAC-based treatment systems.

A review of the adsorption-biological hybrid processes for the abatement of emerging pollutants: Removal efficiencies, physicochemical analysis, and economic evaluation

The limited efficiency of conventional wastewater treatment plants (WWTPs) in emerging pollutants (EPs) removal encourages the development of alternative technologies for the adequate treatment of wastewater, due to its adverse effects on human health and ecosystems. The biological, physical or chemical hybrid technologies to treat EPs results interesting since they can enhance the performance of WWTPs. Among them, hybrid adsorption/biological technology could offer different possibilities that are explored in this work (PAC-MBR, PACT/GAC-CAS, BAC configurations). In this way, different variations in the adsorption process have been considered: the form of the adsorbent, the feed to the system, and the type of biological process, either conventional activated sludge (CAS), membrane bioreactor (MBR) or biofilm systems. For each combination, the removal efficiency of micropollutants, classified according to their use into pharmaceuticals, personal care products (PCPs) and other micropollutants (mainly benzotriazoles) was analysed. From reported data, it was observed a beneficial synergistic effect of dipole moment and octanol-water partition coefficient on the removal efficiency of micropollutants by adsorption/biological hybrid technology. Finally, a preliminary economic evaluation of the powdered activated carbon in a conventional activated sludge reactor (PACT), powdered activated carbon-membrane bioreactor (PAC-MBR) and biological activated carbon (BAC) hybrid systems was carried out by analysing the capital expenditure (CAPEX) of plants for capacities up to 75,000 m³d^-1. Likewise, estimations of adsorbent concentration for a hypothetical plant with a capacity of 10,000 m³d^-1 is presented. Among these hybrid configurations, PAC-MBR achieved the highest micropollutant elimination percentages; however, it presents the highest CAPEX and activated carbon requirements.

Removal of antibiotics in sand, GAC, GAC sandwich and anthracite/sand biofiltration systems

Drinking water biofiltration offers the possibility of the removal of trace level micropollutants from source water. Sand, granular activated carbon (GAC), GAC sandwich (a layer of GAC loaded in the middle of sand bed), and anthracite-sand dual biofilters were set-up in duplicate at bench-scale to mimic the filtration process in real drinking water treatment works. During the 3-month system operation, removal of five antibiotics (amoxicillin, clarithromycin, oxytetracycline, sulfamethoxazole, and trimethoprim) and overall biofilter performance were evaluated. Natural surface water spiked with a mixture of the target antibiotics was used as feedwater to the biofilters. Results showed that the target antibiotics were substantially removed (>90%) by GAC-associated biofilters and partially removed (≤20%) by sand alone and anthracite-sand biofilters. In particular, the GAC sandwich biofilter exhibited superior performance compared to sand/anthracite biofilter, and the comparisons among all biofilters indicated that both adsorption and biodegradation contributed to the removal of the target antibiotics in the GAC-associated biofilters. Adsorption kinetics showed that sulfamethoxazole fitted with pseudo-first-order adsorption model, while trimethoprim, amoxicillin, oxytetracycline and clarithromycin fitted the pseudo-second-order model. All antibiotics fitted the Langmuir model according to the isotherm experiment. To date, this is the first study evaluating the removal of antibiotics by GAC sandwich biofilters. Overall, this research will provide useful information which can be used for optimising or updating existing biofiltration processes in industry to reduce antibiotic residues from source water.

Renovated filter filled with poly-3-hydroxybutyrateco-hydroxyvalerate and granular activated carbon for simultaneous removal of nitrate and PPCPs from the secondary effluent

Reclaimed water is in huge demand in water-deficient cities. However, nitrogen, pharmaceuticals and personal care products (PPCPs) are frequent contaminants in reclaimed water that are probable to bring environmental risks. To develop a technology for safe reclaimed water production, in this study, a renovated filter that integrates solid-phase denitrification (SPD) with biodegradable polymer poly-3-hydroxybutyrate-co-hydroxyvalerate (PHBV) and granular activated carbon (GAC) adsorption (SPD-GAC filter) was proposed and applied to remove nitrogen and target PPCPs (metoprolol and diclofenac) simultaneously. The influences of different ratio of the filled PHBV and GAC, and the hydraulic retention time (HRT) on the removal performances were investigated. The results showed that the filter with PHBV/GAC = 1 (25 cm PHBV/25 cm GAC) simultaneously achieved an average NO₃^--N removal efficiency of about 95% with no accumulation of ammonia and nitrite, and an average removal efficiency of PPCPs of about 80%. Compared with PHBV-based SPD system, the integrated SPD-GAC filter significantly improved the control of carbon release and the PPCP removals. SPD-GAC filter also exhibited a strong tolerance for the variation of influent NO₃^--N loading rate, achieving a highest denitrification rate of 0.76-0.82 g N·(L·d)^-1. The integrated SPD-GAC filter proves to be a promising technology for the simultaneous removal of nitrogen and PPCPs from the secondary effluent.

Differentiating between adsorption and biodegradation mechanisms while removing trace organic chemicals (TOrCs) in biological activated carbon (BAC) filters

Efficient adsorption of certain trace organic chemicals (TOrCs) present in secondary treated municipal wastewater treatment plant (WWTP) effluents onto granular activated carbon (GAC) has already been demonstrated at lab- and full-scale. Due to high organic matter concentrations in WWTP effluents, GAC filters eventually develop a biofilm and turn into biological activated carbon filters (BAC), where removal of organic compounds is governed by biodegradation as well as by adsorption. However, determining TOrC breakthrough by conducting a long-term BAC column experiment to discern between the removal mechanisms is not possible due to competition for adsorption sites, fluctuating water quality, and other variables. Therefore, a rapid small scale column test (RSSCT) was conducted to determine the contribution of adsorption for select chemicals at 10,000 bed volumes treated (BVT). These results were then used in the pore surface diffusion model (PSDM) to model adsorption behavior at 40,000 BVTs. Pseudo-Freundlich K values obtained from the PSDM model were compared with K values obtained from an integral mass balance calculation. This comparison revealed that the modeling was most accurate for moderately to poorly adsorptive compounds. In comparing RSSCT results to long-term BAC columns, the modeling approach best predicted BAC removal of well adsorbing compounds, such as atenolol, trimethoprim, metoprolol, citalopram, and benzotriazole. However, differences in predicted vs observed BAC removal for the removals of venlafaxine, tramadol and carbamazepine revealed that BAC adsorption capacity was not yet exhausted for these compounds. Therefore, a comparison was not possible. The approach would be improved by operation at longer EBCT and improved calculation of compound fouling indices.

New approach for the assessment of the contribution of adsorption, biodegradation and self-bioregeneration in the dynamic process of biologically active carbon functioning

This work developed an effective model of the cooperative removal process of organic compounds on biologically active carbon. This model involves the determination of the dynamics of adsorption efficiency and degradation of specific classes of target organic substances but also the dynamics of non-target filling of pores with products of vital microbial activity. It is possible to quantitatively assess the contributions of adsorption, biodegradation and self-bioregeneration in the process of biologically active carbon functioning and the changes in the activated carbon porous properties during the process. The model developed was applied to assess the efficiency of filtration of 2-nitrophenol through a biologically active carbon bed for 38 months. The activated carbon adsorption capacity for removing 2-nitrophenol was preserved after three years of the bed service due to the effective biodegradation that resulted in self-bioregeneration of the sorbent. Nontarget losses of porosity (filling with bioproducts) increased with increasing duration of system operation, and by the end of the experiment, these losses amounted to 61% of the pore volume of the fresh sorbent.

Can the removal of pharmaceuticals in biofilters be influenced by short pulses of carbon?

Biofilters, similar to those already used for, e.g., removing particles from stormwater and combined sewer overflow can remove organic micropollutants from polluted waters. This study investigated the effects on removal of pharmaceuticals with pulse loadings of increased amounts of pre-settled raw wastewater to four individual biofilters containing different materials (sand, filtralite, stonewool, and sand amended with 1% peat). The effect of increasing BOD concentration to the removal rate constants could be divided into two groups; 1) compounds influenced by increasing loading of BOD: atenolol, propranolol, venlafaxine, citalopram, metoprolol, iohexol, and diclofenac 2) compounds only little or not influenced by increasing concentration of BOD: sulfamethoxazole, sulfamethizole, trimethoprim, iomeprol, and carbamazepine. Though BOD clearly had effects on the degradation, no indications towards a complete stop of the degradation were observed under any circumstances. The different biofilter materials influenced (indirectly) the removal of micropollutants: While the overall best performance was seen in the filtralite biofilter, the stonewool biofilter generally had the lowest removal rate constants. Furthermore, we observed different metabolic pathways of metoprolol in the four different biofilters under formation (and removal) of metoprolol acid, α-hydroxymetoprolol, and O-desmethylmetoprolol.

Influence of the properties of 7 micro-grain activated carbons on organic micropollutants removal from wastewater effluent

Most studies dedicated to organic micropollutants (OMPs) removal from wastewater effluents by adsorption onto activated carbon (AC) only consider a few conventional AC properties. The link between OMPs removal and these properties is often missing, which limits the understanding of the adsorption process and the interpretation of the results. The chemical, physical and textural properties of seven newly commercialized micro-grain activated carbons (μGACs) were determined to assess their influence on the removal of 28 OMPs. Conventional batch tests with wastewater effluent showed that a high percentage of microporous volume (>65%) was detrimental for the removal of 10 OMPs, probably due to a higher blockage of micropores by dissolved organic matter (DOM). The removal of 5 OMPs was correlated with μGACs surface chemistry properties (i.e. charge) which were potentially modified by DOM adsorption or inorganic species, thus favoring the adsorption of positively-charged compounds. A combination of OMPs properties including their charge, hydrophobicity and minimal projection area could explain their removal. Correlations were found between the removal of several OMPs and UV₂₅₄, suggesting that DOM and OMPs interacted with each other or followed similar adsorption mechanisms. A decrease in μGACs particle size had a positive impact on UV₂₅₄ removal under continuous-flow conditions in columns representative of a large-scale pilot due to better expansion.

An innovative compact system for advanced treatment of combined sewer overflows (CSOs) discharged into large lakes: Pilot-scale validation

Combined sewer overflows discharging into natural water bodies could potentially contaminate them in terms of conventional wastewater parameters and coliform bacteria. When green water infrastructures are not technically feasible or practically sustainable for stormwater management, innovative compact and effective end-of-pipe systems can be of interest. This study presents long-term and real-environment validated data of a compact and rapid treatment system specifically applicable to CSOs that consists of a dynamic rotating belt filter, adsorption on granular activated carbon and UV disinfection steps. The results of treatment for Lake Garda in Italy, showed great potential for TSS, COD and E. coli removal efficiencies with more than 90%, 69% and 99% respectively. Due to the short contact time of GAC adsorption, nutrients removals were not very high. TN and TP removal of around 41% and 19% were observed respectively that suggests further specific nutrients removal processes are required for achieving higher efficiencies. The treatment system, due to its compactness and rapidness could be a great asset for water utilities in different EU catchments that are dealing with the frequent CSO events. In addition, the possibility of using different combinations of treatment steps allows the choice of different treatment scenarios depending on the treatment goals for any specific catchment.

A new decentralized biological treatment process based on activated carbon targeting organic micropollutant removal from hospital wastewaters

Although hospital wastewaters (HWWs) are usually discharged in urban sewage systems, their separate treatment has several benefits, such as the specific treatment of potential toxics as well as avoidance of further dilutions. In this work, an integrated industrial pilot plant (2200 L) corresponding to the technology SeMPAC^® is proposed and validated for such purpose. The process consists of a sequential batch reactor (SBR) connected to an external submerged microfiltration membrane, in which powdered activated carbon (PAC) is directly added into the biological reactor to enhance the removal of the organic micropollutants (OMPs). The combination of different redox conditions in the SBR, as well as the operation at long sludge retention times (SRTs) and high biomass concentrations favored OMP biotransformation in the SBR, being their final removal efficiencies enhanced clearly after PAC addition, especially for the recalcitrant compounds. A periodical renewal of the adsorbent is necessary to overcome its gradual saturation. The main operational conditions were influenced by (i) the recalcitrant OMP carbamazepine, which defines the PAC dosage; (ii) the easily degradable OMP ibuprofen, which can be used to optimize the duration of the aerobic cycle; and (iii) the denitrification efficiency, which defines the correct time length of the anoxic period.

Enhanced removal of pharmaceuticals in a biofilter: Effects of manipulating co-degradation by carbon feeding

Biofilm reactors are a promising biotechnology to eliminate pharmaceuticals from wastewater during tertiary treatment or in water works for drinking water production. This study aimed at investigating the effects of pulsed carbon feeding for promoting the co-degradation of indigenous pharmaceuticals from pre-treated wastewater in a fixed-bed porous biofilm reactor (slow sand filter). The addition of acetate (carbon source) resulted in three different enhancement/limitation effects, which were compound dependent: 1) atenolol and iohexol experienced enhanced co-degradation followed by constant (acetate independent) degradation; 2) metoprolol, iomeprol, diclofenac, propranolol and sulfamethizole co-degradation dependent on aerobic turnover, but inhibited at higher acetate concentrations (60-300 mg C/L); 3) sulfadiazine, sulfamethoxazole and trimethoprim were removed independently of oxygen and acetate concentration. Carbamazepine, ditriazoic acid, iopromide; tramadol and venlavaxine were not removed at any acetate dosage. Biofilm reactors can be employed for polishing treated wastewater, and the addition of a primary carbon source can enhance the performance of the bioreactor.

Wastewater treatment by slow sand filters using uncoated and iron-coated fine sand: impact of hydraulic loading rate and media depth

Two lab-scale slow sand filters (SSFs), packed with uncoated fine sand (SSF_u) and iron-coated fine sand (SSF_co), were operated to study their efficiency in treating municipal wastewater. The effects of sand coating; hydraulic loading rates (HLRs) (0.56, 0.85, and 1.12 cm/h); and filter depths (22, 32, and 42 cm) were evaluated. Sand coating did not have any significant effect on wastewater treatment by the SSF at all depths (p > 0.05). The removals of total suspended solids (TSS), chemical oxygen demand (COD), and phosphate decreased with increase in HLR. On the other hand, media depth had positive effects on the removal of turbidity, TSS, COD, and total coliforms (TC). At HLR of 0.56 cm/h, the average removals of each studied parameter, i.e., turbidity, TSS, and COD, at filter depth d₄₂ in SSF_u and SSF_co were 94.3, 90.1, and 56% and 92.7, 93, and 30.95%, respectively. Both filters efficiently removed the total coliforms (> 90%) and fecal coliform (up to 99%) but inefficient in nitrate removal. Frequent clogging was observed in SSF_u due to the colonization of microorganisms on the sand surface, which was confirmed by SEM images. Biofilm formation or microbial colonization was absent in SSF_co, which might be responsible for uninterrupted operation of SSF_co. Overall, the sand coating is beneficial for long-term operation of SSF.

Comparative adsorption of emerging contaminants in water by functional designed magnetic poly(N-isopropylacrylamide)/chitosan hydrogels

The magnetic poly(N-isopropylacrylamide)/chitosan hydrogel with interpenetrating network (IPN) structure was designed based on the functional groups of targeted emerging contaminants, represented by hydrophilic sulfamethoxazole (SMZ) and hydrophobic bisphenol A (BPA). The average particle size, specific surface area, and total pore volume of the hydrogel were turned out to be 103.7 μm, 60.70 m²/g and 0.0672 cm³/g, respectively. Adsorption results indicated that the maximum adsorption capacity occurred at the pH where SMZ was anionic and BPA was uncharged. When the adsorption temperature increased from 25 °C to 35 °C, the amount of adsorbed SMZ hardly changed, but that of BPA increased by two times. The adsorption capacity of the binary system (i.e., with both SMZ and BPA) was almost the same as that of the single system, indicating that simultaneous adsorption of SMZ and BPA was achieved. The adsorption equilibrium was reached quickly (within 5 min) for both SMZ and BPA. For adsorption isotherm, the Freundlich model fitted well for SMZ at 25, 35 and 45 °C. However, the adsorption of BPA exhibited the sigmoidally shaped isotherm at 25 °C with the Slips model fitting well, and both the Freundlich isotherm and the Slips isotherm fitted the data well at 35 °C and 45 °C, suggesting that the adsorption force was initially weak but greatly enhanced with an increase in adsorbate concentration or ambient temperature. The main adsorption mechanism was inferred to be electrostatic interactions for SMZ, and hydrophobic interactions as well as hydrogen bonding for BPA. The hydrogel adsorbent maintained favorable adsorption capacity for BPA after five adsorption-desorption cycles. These findings may provide a strategy for designing high performance adsorbents that can remove both hydrophilic and hydrophobic organic contaminants in the aquatic environment.

Application of a novel, continuous-feeding ultraviolet light emitting diode (UV-LED) system to disinfect domestic wastewater for discharge or agricultural reuse

In many low-income countries, the poor conditions of sanitation systems have been a significant cause of mortality since they accelerate waterborne disease transmission. Developing sanitation systems in these countries is a pressing concern in both the public and private sectors. This research investigated a decentralized domestic wastewater treatment system using ultraviolet light-emitting diodes (UV-LEDs). Although UV-LED disinfection has become more widespread in recent years, it is a novel approach for domestic wastewater treatment. Domestic wastewater was pretreated by a low-cost pretreatment system with an inclined settler and a sand filter prior to feeding a novel flow-through UV LED reactor. At an inlet flow rate of 30 L/h, the COD, TSS, and turbidity of the effluent were 17.7 mg/L, 3.0 mg/L, and 3.9 NTU, respectively. UV transmittance at 285 nm was enhanced from 29.1% to 70.4%, improving the influent quality for UV LED disinfection. The flow-through UV LED reactor was operated at various flow rates from 10 to 50 mL/min, resulting in applied UV doses of 69.4 to 47.8 mJ/cm² respectively. These doses are sufficient for inactivating total coliforms in the wastewater to meet the water reuse guidelines for agriculture for both processed food crops and non-food crops. Fouling, which was observed starting at 2 d of operation, decreased the disinfection efficacy to 27% after 25 days of continuous operation. Of the fouling layer, 67% was attributed to organic matter, in contrast to previous fouling studies with mercury UV lamps in which the fouling layer consisted primarily of inorganic compounds. The fouling was reversed by off-line citric acid cleaning for 4 h after every 400 h of continuous operation.

Comprehensive assessment of organic contaminant removal from on-site sewage treatment facility effluent by char-fortified filter beds

To remove organic contaminants from wastewater using cost-efficient and currently existing methods, our study investigated char-fortified filter beds for on-site sewage treatment facilities (OSSFs) in a long-term field setting. OSSFs are commonly used in rural and semi-urban areas worldwide to treat wastewater when municipal wastewater treatment is not economically feasible. First, we screened for organic contaminants with gas chromatography and liquid chromatography mass spectrometry-based targeted and untargeted analysis and then we developed quantitative structure-property relationship models to search for key molecular features responsible for the removal of organic contaminants. We identified 74 compounds (24 confirmed by reference standards) including plasticizers, UV stabilizers, fragrances, pesticides, surfactant and polymer impurities, pharmaceuticals and their metabolites, and many biogenic compounds. Sand filters that are used as a secondary step after the septic tank in OSSFs could remove hydrophobic contaminants. The addition of biochar significantly increased the removal of these and a few hydrophilic compounds (Wilcoxon signed-rank test, α = 0.05). Besides hydrophobicity-driven sorption, biodegradation was suggested to be the most important removal pathway in this long-term field application. However, further improvements are necessary to remove very hydrophilic contaminants as they were not removed with sand and biochar-fortified sand.

Contaminants of emerging concern in urban stormwater: Spatiotemporal patterns and removal by iron-enhanced sand filters (IESFs)

Numerous contaminants of emerging concern (CECs) typically occur in urban rivers. Wastewater effluents are a major source of many CECs. Urban runoff (stormwater) is a major urban water budget component and may constitute another major CEC pathway. Yet, stormwater-based CEC field studies are rare. This research investigated 384 CECs in 36 stormwater samples in Minneapolis-St. Paul, Minnesota, USA. Nine sampling sites included three large stormwater conveyances (pipes) and three paired iron-enhanced sand filters (IESFs; untreated inlets and treated outlets). The 123 detected compounds included commercial-consumer compounds, veterinary and human pharmaceuticals, lifestyle and personal care compounds, pesticides, and others. Thirty-one CECs were detected in ≥50% of samples. Individual samples contained a median of 35 targeted CECs (range: 18-54). Overall, median concentrations were ≥10 ng/L for 25 CECs and ≥100 ng/L for 9 CECs. Ranked, hierarchical linear modeling indicated significant seasonal- and site type-based concentration variability for 53 and 30 CECs, respectively, with observed patterns corresponding to CEC type, source, usage, and seasonal hydrology. A primarily warm-weather, diffuse, runoff-based profile included many herbicides. A second profile encompassed winter and/or late summer samples enriched with some recalcitrant, hydrophobic compounds (e.g., PAHs), especially at pipes, suggesting conservative, less runoff-dependent sources (e.g., sediments). A third profile, indicative of mixed conservative/non-runoff, runoff, and/or atmospheric sources and transport that collectively affect a variety of conditions, included various fungicides, lifestyle, non-prescription, and commercial-consumer CECs. Generally, pipe sites had large, diverse land-use catchments, and showed more frequent detections of diverse CECs, but often at lower concentrations; while untreated sites (with smaller, more residential-catchments) demonstrated greater detections of "pseudo-persistent" and other ubiquitous or residentially-associated CECs. Although untreated stormwater transports an array of CECs to receiving waters, IESF treatment significantly removed concentrations of 14 (29%) of the 48 most detected CECs; for these, median removal efficiencies were 26%-100%. Efficient removal of some hydrophobic (e.g., PAHs, bisphenol A) and polar-hydrophilic (e.g., caffeine, nicotine) compounds indicated particulate-bound contaminant filtration and for certain dissolved contaminants, sorption.

Advanced biological activated carbon filter for removing pharmaceutically active compounds from treated wastewater

Through their release of effluents, conventional wastewater treatment plants (WWTPs) represent a major pollution point sources for pharmaceutically active compounds (PhACs) in water bodies. The combination of a biological activated carbon (BAC) filter coupled with an ultrafiltration (UF) unit was evaluated as an advanced treatment for PhACs removal at pilot scale. The BAC-UF pilot plant was monitored for one year. The biological activity of the biofilm that developed on the granular activated carbon (GAC) particles and the contribution of this biofilm to the overall removal of PhACs were evaluated. Two different phases were observed during the long-term monitoring of PhACs removal. During the first 9200 bed volumes (BV; i.e., before GAC saturation), 89, 78, 83 and 79% of beta-blockers, psychiatric drugs, antibiotics and a mix of other therapeutic groups were removed, respectively. The second phase was characterized by deterioration of the overall performances during the period between 9200 and 13,800 BV. To quantify the respective contribution of adsorption and biodegradation, a lab-scale setup was operated for four months and highlighted the essential role played by GAC in biofiltration units. Physical adsorption was indeed the main removal mechanism. Nevertheless, a significant contribution due to biological activity was detected for some PhACs. The biofilm contributed to the removal of 22, 25, 30, 32 and 35% of ciprofloxacin, bezafibrate, ofloxacin, azithromycin and sulfamethoxazole, respectively.

The application of GAC sandwich slow sand filtration to remove pharmaceutical and personal care products

Lab-scale GAC sandwich slow sand filters with different GAC layer depths were evaluated for the first time to remove selected pharmaceutical and personal care products (PPCPs) (namely DEET, paracetamol, caffeine and triclosan, 25 μg/L). Coarse sand (effective grain size of 0.6 mm) was used instead of conventional fine sand. In addition to single sand and GAC filters, GAC sandwich filters were assessed at three filtration rates (i.e. 5 cm/h, 10 cm/h and 20 cm/h) to compare removals. Sandwich filter with 20 cm GAC achieved the best average PPCP removal (98.2%) at 10 cm/h rate. No significant difference of average PPCP removal was found between 10 and 20 cm/h filtration rates for the three GAC sandwich filters (p > 0.05). Among the selected PPCPs, DEET, the recalcitrant compound, was most effectively removed by the GAC sandwich filters. Combining the GAC layers with the slow sand filters significantly enhanced the removal of the target PPCP compounds (p < 0.05), demonstrating that both adsorption and biodegradation contributed to the removals. Furthermore, pseudo-second-order equation (Type 1) could best represent the adsorption kinetics of the four target PPCP compounds onto GAC. In relation to other quality parameters, sandwich filter with 20 cm of GAC also showed good average removals of chemical oxygen demand (COD) of 65.8% and total organic carbon (TOC) of 90.3%, but occurrence of ammonium up to 0.76 mg/L concentration indicated inapplicability of filtration rate of 5 cm/h. No significant difference was found between 10 cm/h and 20 cm/h filtration rates for nitrogen and phosphate removals (p > 0.05). Results of this lab-scale investigation show that GAC sandwich slow sand filter is potentially an effective process for removing PPCPs from tertiary wastewater.

Removal of pharmaceuticals, perfluoroalkyl substances and other micropollutants from wastewater using lignite, Xylit, sand, granular activated carbon (GAC) and GAC+Polonite® in column tests - Role of physicochemical properties

This study evaluated the performance of five different sorbents (granular activated carbon (GAC), GAC + Polonite^® (GAC + P), Xylit, lignite and sand) for a set of 83 micropollutants (MPs) (pharmaceuticals, perfluoroalkyl substances (PFASs), personal care products, artificial sweeteners, parabens, pesticide, stimulants), together representing a wide range of physicochemical properties. Treatment with GAC and GAC + P provided the highest removal efficiencies, with average values above 97%. Removal rates were generally lower for Xylit (on average 74%) and lignite (on average 68%), although they proved to be highly efficient for a few individual MPs. The average removal efficiency for sand was only 47%. It was observed that the MPs behaved differently depending on their physicochemical properties. The physicochemical properties of PFASs (i.e. molecular weight, topological molecular surface area, log octanol water partition coefficient (K_ow) and distribution coefficient between octanol and water (log D)) were positively correlated to observed removal efficiency for the sorbents Xylit, lignite and sand (p < 0.05), indicating a strong influence of perfluorocarbon chain length and associated hydrophobic characteristics. In contrast, for the other MPs the ratio between apolar and polar surface area (SA/SP) was positively correlated with the removal efficiency, indicating that hydrophobic adsorption may be a key feature of their sorption mechanisms. GAC showed to be the most promising filter medium to improve the removal of MPs in on-site sewage treatment facilities. However, more studies are needed to evaluate the removal of MPs in field trials.

A non-targeted high-resolution mass spectrometry data analysis of dissolved organic matter in wastewater treatment

The dissolved organic matter (DOM) in wastewater is typically described by a limited number of concentration measurements of select DOM fractions or micro-contaminants, which determine the removal efficiency in a wastewater treatment. Current methods do not necessarily reflect the true performance of the treatment with regard to environmental and public health risk. Herein we describe the development and application of a non-targeted liquid chromatography-high resolution mass spectrometry (LC-HRMS) data analysis for the evaluation of wastewater treatment processes. Our data analysis approach was applied to a real wastewater system with secondary biological treatment and tertiary treatment consisting of sand filtration, UV-treatment, and chlorination. We identified significant changes in DOM during wastewater treatment. The secondary treatment removed 1617 of 2409 (67%) detected molecular features (grouped isotopologues belonging to the same molecule) from the influent while 255 of 1047 (24%) new molecular features appeared in the secondary effluent. A reduction in the number of large molecules (>450 Da) and an increase in unsaturated molecular features of the effluent organic matter was observed. Van Krevelen plots revealed the distribution of unsaturation and heteroatoms and Kendrick mass defect plots uncovered CH₂ homologous series implying a removal of heavy constituents in that fraction. The demonstrated approach is a step towards a more comprehensive monitoring of DOM in wastewater and contributes to the understanding of current treatment technologies.

Understanding the sorption and biotransformation of organic micropollutants in innovative biological wastewater treatment technologies

New technologies for wastewater treatment have been developed in the last years based on the combination of biological reactors operating under different redox conditions. Their efficiency in the removal of organic micropollutants (OMPs) has not been clearly assessed yet. This review paper is focussed on understanding the sorption and biotransformation of a selected group of 17 OMPs, including pharmaceuticals, hormones and personal care products, during biological wastewater treatment processes. Apart from considering the role of "classical" operational parameters, new factors such as biomass conformation and particle size, upward velocity applied or the addition of adsorbents have been considered. It has been found that the OMP removal by sorption not only depends on their physico-chemical characteristics and other parameters, such as the biomass conformation and particle size, or some operational conditions also relevant. Membrane biological reactors (MBR), have shown to enhance sorption and biotransformation of some OMPs. The same applies to technologies bases on direct addition of activated carbon in bioreactors. The OMP biotransformation degree and pathway is mainly driven by the redox potential and the primary substrate activity. The combination of different redox potentials in hybrid reactor systems can significantly enhance the overall OMP removal efficiency. Sorption and biotransformation can be synergistically promoted in biological reactors by the addition of activated carbon. The deeper knowledge of the main parameters influencing OMP removal provided by this review will allow optimizing the biological processes in the future.

Occurrences and removal of pharmaceuticals and personal care products (PPCPs) in drinking water and water/sewage treatment plants: A review

In recent years, many of micropollutants have been widely detected because of continuous input of pharmaceuticals and personal care products (PPCPs) into the environment and newly developed state-of-the-art analytical methods. PPCP residues are frequently detected in drinking water sources, sewage treatment plants (STPs), and water treatment plants (WTPs) due to their universal consumption, low human metabolic capability, and improper disposal. When partially metabolized PPCPs are transferred into STPs, they elicit negative effects on biological treatment processes; therefore, conventional STPs are insufficient when it comes to PPCP removal. Furthermore, the excreted metabolites may become secondary pollutants and can be further modified in receiving water bodies. Several advanced treatment systems, including membrane filtration, granular activated carbon, and advanced oxidation processes, have been used for the effective removal of individual PPCPs. This review covers the occurrence patterns of PPCPs in water environments and the techniques adopted for their treatment in STP/WTP unit processes operating in various countries. The aim of this review is to provide a comprehensive summary of the removal and fate of PPCPs in different treatment facilities as well as the optimum methods for their elimination in STP and WTP systems.

Effect of residual H2O2 from advanced oxidation processes on subsequent biological water treatment: A laboratory batch study

H₂O₂ residuals from advanced oxidation processes (AOPs) may have critical impacts on the microbial ecology and performance of subsequent biological treatment processes, but little is known. The objective of this study was to evaluate how H₂O₂ residuals influence sand systems with an emphasis on dissolved organic carbon (DOC) removal, microbial activity change and bacterial community evolution. The results from laboratory batch studies showed that 0.25 mg/L H₂O₂ lowered DOC removal by 10% while higher H₂O₂ concentrations at 3 and 5 mg/L promoted DOC removal by 8% and 28%. A H₂O₂ dosage of 0.25 mg/L did not impact microbial activity (as measured by ATP) while high H₂O₂ dosages, 1, 3 and 5 mg/L, resulted in reduced microbial activity of 23%, 37% and 37% respectively. Therefore, DOC removal was promoted by the increase of H₂O₂ dosage while microbial activity was reduced. The pyrosequencing results illustrated that bacterial communities were dominated by Proteobacteria. The presence of H₂O₂ showed clear influence on the diversity and composition of bacterial communities, which became more diverse under 0.25 mg/L H₂O₂ but conversely less diverse when the dosage increased to 5 mg/L H₂O₂. Anaerobic bacteria were found to be most sensitive to H₂O₂ as their growth in batch reactors was limited by both 0.25 and 5 mg/L H₂O₂ (17-88% reduction). In conclusion, special attention should be given to effects of AOPs residuals on microbial ecology before introducing AOPs as a pre-treatment to biological (sand) processes. Additionally, the guideline on the maximum allowable H₂O₂ concentration should be properly evaluated.

Biodegradation of naproxen by freshwater algae Cymbella sp. and Scenedesmus quadricauda and the comparative toxicity

Naproxen is one of the most prevalent pharmaceuticals and of great environment concern. Information about bioremediation of naproxen by algae remains limited and no study has been reported on the degradation mechanism and the toxicity of NPX on algae. In this study, both Cymbella sp. and Scenedesmus quadricauda showed complete growth inhibition (100%) at 100mgL^-1 within 24h. Biochemical characteristics including chlorophyll a, carotenoid contents and enzyme activities for these two microalgae were affected by NPX at relatively high concentrations after 4d of exposure. Degradation of naproxen was accelerated by both algae species. Cymbella sp. showed a more satisfactive effect in the bioremediation of NPX with higher removal efficiency. A total of 12 metabolites were identified by LC-MS/MS and the degradation pathways of naproxen in two algae were proposed. Hydroxylation, decarboxylation, demethylation, tyrosine conjunction and glucuronidation contributed to naproxen transformation in algal cells.

Pilot-scale UV/H2O2 advanced oxidation process for municipal reuse water: Assessing micropollutant degradation and estrogenic impacts on goldfish (Carassius auratus L.)

Low concentrations (ng/L-μg/L) of emerging micropollutant contaminants in municipal wastewater treatment plant effluents affect the possibility to reuse these waters. Many of those micropollutants elicit endocrine disrupting effects in aquatic organisms resulting in an alteration of the endocrine system. A potential candidate for tertiary municipal wastewater treatment of these micropollutants is ultraviolet (UV)/hydrogen peroxide (H2O2) as an advanced oxidation process (AOP) which was currently applied to treat the secondary effluent of the Gold Bar Wastewater Treatment Plant (GBWWTP) in Edmonton, AB, Canada. A new approach is presented to predict the fluence-based degradation rate constants (kf') of environmentally occurring micropollutants including carbamazepine [(0.87-1.39) × 10(-3) cm(2)/mJ] and 2,4-Dichlorophenoxyacetic acid (2,4-D) [(0.60-0.91) × 10(-3) cm(2)/mJ for 2,4-D] in a medium pressure (MP) UV/H2O2 system based on a previous bench-scale investigation. Rather than using removal rates, this approach can be used to estimate the performance of the MP UV/H2O2 process for degrading trace contaminants of concern found in municipal wastewater. In addition to the ability to track contaminant removal/degradation, evaluation of the MP UV/H2O2 process was also accomplished by identifying critical ecotoxicological endpoints (i.e., estrogenicity) of the treated wastewater. Using quantitative PCR, mRNA levels of estrogen-responsive (ER) genes ERα1, ERα2, ERβ1, ERβ2 and NPR as well as two aromatase encoding genes (CYP19a and CYP19b) in goldfish (Carassius auratus L.) were measured during exposure to the GBWWTP effluent before and after MP UV/H2O2 treatment (a fluence of 1000 mJ/cm(2) and 20 mg/L of H2O2) in spring, summer and fall. Elevated expression of estrogen-responsive genes in goldfish exposed to UV/H2O2 treated effluent (a 7-day exposure) suggested that the UV/H2O2 process may induce acute estrogenic disruption to goldfish principally because of the possible formation of various oxidation by-products. However, prolonged exposure of goldfish (60 days) in UV/H2O2 treated effluent showed a restoration trend of ER gene expressions, especially in the summer. Collectively, our findings provide valuable indications regarding the long-term in vivo assessment of the MP UV/H2O2 process for removing/degrading endocrine disrupting compounds detected in the municipal wastewater effluents.

Exogenous cofactors for the improvement of bioremoval and biotransformation of sulfamethoxazole by Alcaligenes faecalis

Sulfamethoxazole (SMX), an extensively prescribed or administered antibiotic pharmaceutical product, is usually detected in aquatic environments, because of its incomplete metabolism and elimination. This study investigated the effects of exogenous cofactors on the bioremoval and biotransformation of SMX by Alcaligenes faecalis. High concentration (100mg·L(-1)) of exogenous vitamin C (VC), vitamin B6 (VB6) and oxidized glutathione (GSSG) enhanced SMX bioremoval, while the additions of vitamin B2 (VB2) and vitamin B12 (VB12) did not significantly alter the SMX removal efficiency. Globally, cellular growth of A. faecalis and SMX removal both initially increased and then gradually decreased, indicating that SMX bioremoval is likely dependent on the primary biomass activity of A. faecalis. The decreases in the SMX removal efficiency indicated that some metabolites of SMX might be transformed into parent compound at the last stage of incubation. Two transformation products of SMX, N-hydroxy sulfamethoxazole (HO-SMX) and N4-acetyl sulfamethoxazole (Ac-SMX), were identified by a high-performance liquid chromatograph coupled with mass spectrometer. High concentrations of VC, nicotinamide adenine dinucleotide hydrogen (NADH, 7.1mg·L(-1)), and nicotinamide adenine dinucleotide (NAD(+), 6.6mg·L(-1)), and low concentrations of reduced glutathione (GSH, 0.1 and 10mg·L(-1)) and VB2 (1mg·L(-1)) remarkably increased the formation of HO-SMX, while VB12 showed opposite effects on HO-SMX formation. In addition, low concentrations of GSH and NADH enhanced Ac-SMX formation by the addition of A. faecalis, whereas cofactors (VC, VB2, VB12, NAD(+), and GSSG) had no obvious impact on the formation of Ac-SMX compared with the controls. The levels of Ac-SMX were stable when biomass of A. faecalis gradually decreased, indicating the direct effect of biomass on the formation of Ac-SMX by A. faecalis. In sum, these results help us understand the roles played by exogenous cofactors in eliminating SMX by A. faecalis and provide potential strategies for improving SMX biodegradation.