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.

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.

Reclaimed water driven lettuce cultivation in a hydroponic system: the need of micropollutant removal by advanced wastewater treatment.

For a novel approach of resource-efficient water reuse, a municipal wastewater treatment plant was extended at pilot scale for advanced wastewater treatment, i.e., ozonation and biological activated carbon filtration, and a hydroponic system for reclaimed water driven lettuce cultivation. The treatment specific wastewater lines with the corresponding lettuce plants, differentiated into roots and shoots, were monitored for priority wastewater micropollutants, i.e., acesulfame (sweetener), caffeine (stimulant), carbamazepine, diclofenac, ibuprofen, sulfamethoxazole with acetyl-sulfamethoxazole (human pharmaceuticals), 1H-benzotriazole, and 4/5-methylbenzotriazole (industrial chemicals). As clearly demonstrated, conventional tertiary treatment could not efficiently clean up wastewater. Removal efficiencies ranged from 3% for carbamazepine to 100% for ibuprofen. The resulting pollution of the hydroponic water lines led to the accumulation of acesulfame, carbamazepine, and diclofenac in lettuce root systems at 32.0, 69.5, and 135 µg kg-1 and in the uptake of acesulfame and carbamazepine into lettuce shoots at 23.4 and 120 µg kg-1 dry weight, respectively. In contrast, both advanced treatment technologies when operating under optimized conditions achieved removal efficiencies of > 90% also for persistent micropollutants. Minimizing the pollution of reclaimed water thus met one relevant need for hydroponic lettuce cultivation.

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

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

Removal of Trace Organic Contaminants by Parallel Operation of Reverse Osmosis and Granular Activated Carbon for Drinking Water Treatment.

In response to increasingly stringent restrictions for drinking water quality, a parallel operation of two common technologies, low-pressure reverse osmosis (LPRO) and activated carbon filtration (ACF), was investigated in a comprehensive five-month pilot study for the removal of 32 typical trace organic contaminants (TrOCs) from Rhine bank filtrates employing a semi- technical plant. TrOCs have been divided into three groups: polyfluorinated aliphatic compounds; pharmaceuticals, pesticides and metabolites; in addition to volatiles, nitrosamines and aminopolycarboxylic acids, which were also examined. The net pressure behavior, normalized salt passage and rejection of TrOCs by LPRO were investigated and compared with ACF operation. In addition, autopsies from the leading and last membrane modules were performed using adenosine triphosphate (ATP), total organic carbon (TOC), ICP-OES and SEM-EDX techniques. Generally, rather stable LPRO membrane performance with limited membrane fouling was observed. TrOCs with a molecular weight of ≥ 150 Da were completely retained by LPRO, while the rejection of di- and trichloro compounds improved as the filtration progressed. ACF also showed significant removal for most of the TrOCs, but without desalination. Accordingly, the ACF and LPRO can be operated in parallel such that the LPRO permeate and the ACF-treated bypass can be mixed to produce drinking water with adjustable hardness and significantly reduced TrOCs.

Implications of biological activated carbon filters for micropollutant removal in wastewater treatment.

Granulated Activated Carbon (GAC) filtration is a common process for advanced wastewater treatment. In such filters, the removal of organic substances results from adsorptive as well as biological processes. This work investigated the potential of biological processes and their influence on GAC-filter performance. During 32 months, the removal of micropollutants,Dissolved Organic Carbon (DOC) and the spectral absorption coefficient was monitored in six GAC-filters. The effects of pre-treatment (cloth- and/or membrane-filtration), EBCT (from 6 - 35 min) and GAC-type were evaluated. Likewise, the impact of the influent´s fluctuations in temperature, flow and concentration (ammonia, nitrate, and soluble reactive phosphorus (sRP)) were analysed. Biological processes were tracked by the frequency of backwashing, oxygen consumption, removal of poorly absorbable micropollutants and production of transformation products. Pre-treatment influenced biofilm growth significantly. Membrane filtration delayed the first backwashing event by 122 d in comparison to cloth-filtration, where the first backwash was conducted after only 21 d. Removal of poorly absorbable substances was observed early on (40 - 50 d). Parallel operation contributed to a better utilisation of the GAC-capacity and the biological removal potential. Influent nitrogen species > 0.5 mg N/L promoted biofilm growth, whereas sRP seemed to have no effect. The developed biofilm and optimal operating conditions led to longer life spans of the GAC-filters, making carbon usage rates comparable to those from PAC applications. The results suggest that biological processes accounted for about 25 - 42% of the totally removed DOC at the end of the operation.

Removal of CX3R-type disinfection by-product precursors from rainwater with conventional drinking water treatment processes.

In addition to surface water and groundwater, rainwater is used as an important drinking water source in many parts of the world, especially in areas with serious water pollution or insufficient water resources. Conventional drinking water treatment technologies can remove dissolved organic matter and therefore reduce the formation of disinfection by-products (DBPs) during subsequent disinfection using surface water or groundwater as drinking water sources. However, little information has been known about the effect of conventional water treatment processes on DBP formation when rainwater is used as drinking water source. This study evaluated CX3R-type DBP precursors removal from rainwater by conventional drinking water treatments and the corresponding decrease of CX3R-type DBP (trihalomethanes (THMs), haloaldehydes (HALs), haloacetonitriles (HANs) and haloacetamides (HAMs)) formation and toxicity during the subsequent chlor(am)ination. The result showed that both sand filtration (SF) and activated carbon filtration (GAC) were able to remove DBP precursors and GAC outperformed SF, but no DBP precursors removal was observed during coagulation-sedimentation treatment. Among all treatments, SF + GAC was the most effective for DBP precursors removal, with removal efficiencies of 64.2% DOC, 98% DON and 76.6% UV254. Correspondingly, both SF and GAC decreased the formation of THMs, HALs, HANs and HAMs, and GAC performed better than SF. The combination of SF and GAC, especially SF + GAC, greatly decreased DBP formation, with average reduction of 79.2% and 85% during chlorination and chloramination respectively. After different treatments, the comprehensive toxicity risk of CX3R-type DBPs was all reduced, among which GAC + SF exhibited superior performance. Generally, the main contribution of integrated toxicity was HANs during chlor(am)ination. The formation potential of THMs, HALs, HANs and HAMs and the corresponding integrated toxicity were greater during chlorination than that during chloramination. Therefore, the combination of GAC and chloramination was promising in mitigating the comprehensive toxicity risk of THMs, HALs, HANs and HAMs for rainwater.

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.

Quantifying and identifying microplastics in the effluent of advanced wastewater treatment systems using Raman microspectroscopy.

Microplastics in wastewater treatment plant (WWTP) effluent have been identified and quantified, but few studies have examined the microplastics in advanced treatment systems. A new method for isolating, quantifying, and determining the polymer type of microplastics was developed that included chemical digestion coupled with Raman microspectroscopy to investigate microplastics in the effluent of reverse osmosis nanofiltration and activated carbon filtration systems. This method allows for the removal of organics and the quantification and identification of all microplastics present in the sample. A large number of microplastics, the majority of which were smaller than 10 µm, were identified in the effluent of the advanced filtration systems with polyethylene the most common polymer identified. This study not only reports a new method for microplastic identification and quantification but also shows the importance of measuring the smallest fraction of microplastics, those smaller than 20 µm, which have previously been understudied.

Transport of Enterococcus faecalis in granular activated carbon column: Potential energy, migration, and release.

An increasing number of water purification plants use granular activated carbon filtration as an advanced treatment technology. One of the main constraints of carbon filtration is bacterial leakage, which can impact public drinking water safety. In this study, Enterococcus faecalis, commonly detected in natural water, was employed as the target bacteria for investigating the mechanism of deposition and migration of bacteria in granular activated carbon medium. The repulsive barrier, secondary potential well and potential energy change curve under various conditions were depicted by DLVO theory. Moreover, the influence, including ionic strength, ionic charge and flow rate, on bacterial transport was comprehensively discussed. The Enterococcus faecalis penetration curve was in accordance with the van der Waals force and electrostatic repulsion force under different conditions. Finally, 8%-11% of Enterococcus faecalis was released into the effluent when ionic strength declined.

Nontarget analysis: A new tool for the evaluation of wastewater processes.

Strategies to determine the removal efficiency of micropollutants in wastewater treatment plants (WWTPs) are widely discussed. Especially the evaluation of the potential benefit of further advanced treatment steps such as an additional tertiary treatment based on ozonation or activated carbon have come into focus. Such evaluation strategies are often based on the removal behavior of known micropollutants via target or suspected analysis. The utilization of nontarget analysis is considered to lead to a more comprehensive picture as also unknown or not expected micropollutants are analyzed. Here, the results of an evaluation via target and nontarget analysis were compared for biological treatment (BT) processes of eleven full-scale WWTPs and three different post-treatments (PTs): one sand filter (SF) and two granular activated carbon (GAC) filters. The similarity of the determined removals from target and nontarget analysis of the BTs increased significantly by excluding easily degradable "features" from the nontarget evaluation. A similar ranking of the removal trends for the BTs could also be achieved by comparing this new subset of nontarget features with a set of nine readily to moderately biodegradable micropollutants. This observation suggests that a performance ranking of BTs based either on target or nontarget analysis is plausible. In contrast to the BTs, the evaluation of the three PTs revealed that the difference of feature removal between SF and the two GACs was small, but large for the target analytes with substantially higher removal effciencies for the GACs compared to the SF. In addition to the removal behavior, the nontarget analysis provided further information about the number and quantity of transformation products (TPs) in the effluent from the BTs. For all BTs more than half (55-67%) of the features detected in the effluent were not found in the influent. A comparable proportion of TPs was also detected after GAC and sand filtration due to their microbial activities.

Impact of ozonation and biologically enhanced activated carbon filtration on the composition of micropollutants in drinking water.

A pilot-scale drinking water treatment process for Songhua River, including conventional treatment (coagulation-settlement and rapid sand filtration), ozonation, biological enhanced activated carbon (BEAC) filtration, and chlorination disinfection, was carried out in this study. To investigate the impact of ozonation and BEAC filtration on removing the composition of micropollutants in drinking water, we detected the micropollutant composition from each stage of the treatment process by non-targeted analysis using a GC-MS technique and compared the results between effluents of single BEAC and O3-BEAC processes. Aromatic compounds and esters could be abated efficiently during single BEAC filtration via biodegradation and adsorption; however, possible metabolic products (i.e., alkenes) were formed by biodegradation. Comparatively, O3-BEAC process could reduce micropollutants much more significantly than single BEAC process especially for aromatic compounds including substituted benzenes and polycyclic aromatic hydrocarbons (PAHs) without the formation of metabolic products through the coupling effect of oxidation, biodegradation, and adsorption, suggesting that ozonation improved the removal potential of micropollutants in the BEAC process. In addition, conventional and novel chlorinated disinfection by-products were also measured during post-chlorination.

Physical-chemical treatment of rainwater runoff in recovery and recycling companies: lab-scale investigation.

Scrap material recovery and recycling companies are producing wastewater in which common pollutants (such as COD, nutrients and suspended solids), toxic metals, polyaromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB) frequently can exceed the discharge limits. Lab-scale optimisation of different possible physical-chemical treatment techniques was performed on the wastewater originating from three different companies in view of further testing at pilot-scale testing and implementation at full-scale. The lab-scale tests demonstrate that sedimentation or hydrocyclone treatment as stand-alone technique cannot be used for proper treatment of this type of wastewater. Dual bed filtration or coagulation/flocculation proved to be more promising with removal efficiencies of about 71-95% (dual bed filtration) and 61-97% (coagulation/flocculation) for the above-mentioned pollutants (metals, PAH and PCB).

Seasonal-related effects on ammonium removal in activated carbon filter biologically enhanced by heterotrophic nitrifying bacteria for drinking water treatment.

To determine the potential effects of seasonal changes on water temperature and water quality upon removal of ammonium and organic carbon pollutants and to characterize the variations in microbial characteristics, a pilot-scale activated carbon filter biologically enhanced with heterotrophic nitrifying bacteria was investigated for 528 days. The results show that 69.2 ± 28.6% of ammonium and 23.1 ± 11.6% of the dissolved organic carbon were removed by the biologically enhanced activated carbon (BEAC) reactor. It is shown that higher biodegradable dissolved organic carbon enhances ammonium removal, even at low temperatures. The C/N ratio consumed by the BEAC reactor reached a steady value (i.e., 3.3) after 2 months of operation. Despite seasonal fluctuations and competition of the indigenous community, the heterotrophic nitrifying bacteria (Acinetobacter sp. HRBLi 16 and Acinetobacter harbinensis strain HITLi 7) remained relatively stable. The amount of carbon source was the most significant environmental parameter and dramatically affected the microbial community compositions in the BEAC reactor. The present study provides new insights into the application of a BEAC reactor for ammonium removal from drinking water, resisting strong seasonal changes.

Elimination of micropollutants and transformation products from a wastewater treatment plant effluent through pilot scale ozonation followed by various activated carbon and biological filters.

Conventional wastewater treatment plants are ineffective in removing a broad range of micropollutants, resulting in the release of these compounds into the aquatic environment, including natural drinking water resources. Ozonation is a suitable treatment process for micropollutant removal, although, currently, little is known about the formation, behavior, and removal of transformation products (TP) formed during ozonation. We investigated the elimination of 30 selected micropollutants (pharmaceuticals, X-ray contrast media, industrial chemicals, and TP) by biological treatment coupled with ozonation and, subsequently, in parallel with two biological filters (BF) or granular activated carbon (GAC) filters. The selected micropollutants were removed to very different extents during the conventional biological wastewater treatment process. Ozonation (specific ozone consumption: 0.87 ± 0.29 gO3 gDOC(-1), hydraulic retention time: 17 ± 3 min) eliminated a large number of the investigated micropollutants. Although 11 micropollutants could still be detected after ozonation, most of these were eliminated in subsequent GAC filtration at bed volumes (BV) of approximately 25,000 m(3) m(-3). In contrast, no additional removal of micropollutants was achieved in the BF. Ozonation of the analgesic tramadol led to the formation of tramadol-N-oxide that is effectively eliminated by GAC filters, but not by BF. For the antiviral drug acyclovir, the formation of carboxy-acyclovir was observed during activated sludge treatment, with an average concentration of 3.4 ± 1.4 µg L(-1) detected in effluent samples. Subsequent ozonation resulted in the complete elimination of carboxy-acyclovir and led to the formation of N-(4-carbamoyl-2-imino-5-oxo imidazolidin)-formamido-N-methoxyacetetic acid (COFA; average concentration: 2.6 ± 1.0 µg L(-1)). Neither the BF nor the GAC filters were able to remove COFA. These results highlight the importance of considering TP in the evaluation of advanced wastewater treatment processes. The results further indicate that post-treatment of ozonated wastewater with GAC filtration seems to be more suitable than BF, due to the sorption of formed TP to the activated carbon.

Evaluation of emerging contaminants in a drinking water treatment plant using electrodialysis reversal technology.

Emerging contaminants (EC) have gained much attention with globally increasing consumption and detection in aquatic ecosystems during the last two decades from ng/L to lower ug/L. The aim of this study was to evaluate the occurrence and removal of pharmaceutically active compounds (PhACs), endocrine disrupting chemicals (EDCs) and related compounds in a Drinking Water Treatment Plant (DWTP) treating raw water from the Mediterranean Llobregat River. The DWTP combined conventional treatment steps with the world's largest electrodialysis reversal (EDR) facility. 49 different PhACs, EDCs and related compounds were found above their limit of quantification in the influent of the DWTP, summing up to a total concentration of ECs between 1600-4200 ng/L. As expected, oxidation using chlorine dioxide and granular activated carbon filters were the most efficient technologies for EC removal. However, despite the low concentration detected in the influent of the EDR process, it was also possible to demonstrate that this process partially removed ionized compounds, thereby constituting an additional barrier against EC pollution in the product. In the product of the EDR system, only 18 out of 49 compounds were quantifiable in at least one of the four experimental campaigns, showing in all cases removals higher than 65% and often beyond 90% for the overall DWTP process.

Ammonium removal of drinking water at low temperature by activated carbon filter biologically enhanced with heterotrophic nitrifying bacteria.

We sought to confirm whether use of Acinetobacter strains Y7 and Y16, both strains of heterotrophic nitrifying bacteria, was practical for removing ammonium (NH4 (+)-N) from drinking water at low temperatures. To test this, ammonium-containing drinking water was treated with strains Y7 and Y16 at 8 and 2 °C. Continuous ammonium treatment was conducted in order to evaluate the performance of three biologically enhanced activated carbon (BEAC) filters in removing ammonium. The three BEAC filters were inoculated with strain Y7, strain Y16, and a mixture of strains Y7 and Y16, respectively. A granular activated carbon (GAC) filter, without inoculation by any strains, was tested in parallel with the BEAC filters as control. The results indicated that NH4 (+)-N removal was significant when a BEAC filter was inoculated with the mixture of strains Y7 and Y16 (BEAC-III filter). Amounts of 0.44 ± 0.05 and 0.25 ± 0.05 mg L(-1) NH4 (+)-N were removed using the BEAC-III filter at 8 and 2 °C, respectively. These values were 2.8-4.0-fold higher than the values of ammonium removal acquired using the GAC filter. The synergistic effect of using strains Y7 and Y16 in concert was the cause of the high-ammonium removal efficiency achieved by using the BEAC-III filter at low temperatures. In addition, a high C/N ratio may promote NH4 (+)-N removal efficiency by improving biomass and microbial activity. This study provides new insight into the use of biofilters to achieve biological removal of ammonium at low temperature.

Physical-chemical treatment of rainwater runoff in recovery and recycling companies: Pilot-scale optimization.

Pilot-scale optimisation of different possible physical-chemical water treatment techniques was performed on the wastewater originating from three different recovery and recycling companies in order to select a (combination of) technique(s) for further full-scale implementation. This implementation is necessary to reduce the concentration of both common pollutants (such as COD, nutrients and suspended solids) and potentially toxic metals, polyaromatic hydrocarbons and poly-chlorinated biphenyls frequently below the discharge limits. The pilot-scale tests (at 250 L h(-1) scale) demonstrate that sand anthracite filtration or coagulation/flocculation are interesting as first treatment techniques with removal efficiencies of about 19% to 66% (sand anthracite filtration), respectively 18% to 60% (coagulation/flocculation) for the above mentioned pollutants (metals, polyaromatic hydrocarbons and poly chlorinated biphenyls). If a second treatment step is required, the implementation of an activated carbon filter is recommended (about 46% to 86% additional removal is obtained).