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

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.

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

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

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.

Characterization and Performance of Peanut Shells in Caffeine and Triclosan Removal in Batch and Fixed-Bed Column Tests

Peanut shells' adsorption performance in caffeine and triclosan removal was studied. Peanut shells were analyzed for their chemical composition, morphology, and surface functional groups. Batch adsorption and fixed-bed column experiments were carried out with solutions containing 30 mg/L of caffeine and triclosan. The parameters examined included peanut shell particle size (120-150, 300-600, and 800-2000 µm), adsorbent dose (0.02-60 g/L), contact time (up to 180 min), bed height (4-8 cm), and hydraulic loading rate (2.0 and 4.0 m3/m2-day). After determining the optimal adsorption conditions, kinetics, isotherm, and breakthrough curve models were applied to analyze the experimental data. Peanut shells showed an irregular surface and consisted mainly of polysaccharides (around 70% lignin, cellulose, and hemicellulose), with a specific surface area of 1.7 m2/g and a pore volume of 0.005 cm3/g. The highest removal efficiencies for caffeine (85.6 ± 1.4%) and triclosan (89.3 ± 1.5%) were achieved using the smallest particles and 10.0 and 0.1 g/L doses over 180 and 45 min, respectively. Triclosan showed easier removal compared to caffeine due to its higher lipophilic character. The pseudo-second-order kinetics model provided the best fit with the experimental data, suggesting a chemisorption process between caffeine/triclosan and the adsorbent. Equilibrium data were well-described by the Sips model, with maximum adsorption capacities of 3.3 mg/g and 289.3 mg/g for caffeine and triclosan, respectively. In fixed-bed column adsorption tests, particle size significantly influenced efficiency and hydraulic behavior, with 120-150 µm particles exhibiting the highest adsorption capacity for caffeine (0.72 mg/g) and triclosan (143.44 mg/g), albeit with clogging issues. The experimental data also showed good agreement with the Bohart-Adams, Thomas, and Yoon-Nelson models. Therefore, the findings of this study highlight not only the effective capability of peanut shells to remove caffeine and triclosan but also their versatility as a promising option for water treatment and sanitation applications in different contexts.

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.

Deciphering the synergistic effects of photolysis and biofiltration to actuate elimination of estrogens in natural water matrix

The presence of estrogens in water environments has raised concerns for human health and ecosystems balance. These substances possess potent estrogenic properties, causing severe disruptions in endocrine systems and leading to reproductive and developmental problems. Unfortunately, conventional treatment methods struggle to effectively remove estrogens and mitigate their effects, necessitating technological innovation. This study investigates the effectiveness of a novel sequential photolysis-granular activated carbon (GAC) sandwich biofiltration (GSBF) system in removing estrogens (E1, E2, E3, and EE2) and improving general water quality parameters. The results indicate that combining photolysis pre-treatment with GSBF consistently achieved satisfactory performance in terms of turbidity, dissolved organic carbon (DOC), UV254, and microbial reduction, with over 77.5 %, 80.2 %, 89.7 %, and 92 % reduction, respectively. Furthermore, this approach effectively controlled the growth of microbial biomass under UV irradiation, preventing excessive head loss. To assess estrogen removal, liquid chromatography-tandem mass spectrometry (LC-MS) measured their concentrations, while bioassays determined estrogenicity. The findings demonstrate that GSBF systems, with and without photolysis installation, achieved over 96.2 % removal for estrogens when the spike concentration of each targeted compound was 10 µg L-1, successfully reducing estrogenicity (EA/EA0) to levels below 0.05. Additionally, the study evaluated the impact of different thicknesses of GAC layer filling (8 cm, 16 cm, and 24 cm) and found no significant difference (p>0.05) in estrogen and estrogenicity removal among them.

Influence of effluent particles and particle-bound micropollutants on the removal of micropollutants and UVA254 in wastewater effluent ozonation

This study systematically investigated the influence of effluent particles and activated sludge (AS) particles on the removal of micropollutants via wastewater effluent ozonation within typical effluent total suspended solids (TSS) concentrations. A series of batch experiments revealed that particle concentrations up to 30 mg/L had a minor impact on the removal of organic micropollutants (OMPs) in the aqueous phase. Moreover, the reduction of UV absorbance at 254 nm (UVA254) was negatively correlated to the level of particle concentration at ozone doses higher than 0.5 gO3/gDOC. It indicates that UVA254 abatement was more sensitive to the presence of particles compared to OMP removal. Organic micropollutants (OMPs) sorbed on effluent particles and sludge particles were extracted before and after ozonation. OMP sorption in effluent particles was 2-5 times higher than that in sludge particles. During the ozonation of raw secondary effluent, particle-bound micropollutants were removed comparably to the micropollutants in the aqueous phase. This suggests that the boundary layer surrounding the particle didn't affect the removal of OMPs in the particle phase. Furthermore, the removal of existing OMPs (irbesartan, sulfamethoxazole, and metoprolol) in the effluent was used to assess the ozone and •OH exposure. In water samples with and without particles, the elimination of OMPs could be reliably predicted (R² > 0.95) by calculated ozone and •OH exposures.

Nano manganese dioxide coupling carbon source preloading granular activated carbon biofilter enhancing biofilm formation and pollutant removal

The formation of stable and mature biofilms affects the efficient and stable removal of ammonium by biological activated carbon (BAC). In this study, the new granular activated carbon (GAC) was preloaded with the carbon source (glucose and sucrose) and nano manganese dioxide (nMnO2) before using. Then tests were performed to determine whether substrate preloading promoted ammonium removal. The ammonium removal treated by nMnO2 coupled with sucrose-loaded BAC reached 49.1 ± 2.5%, which was 1.7 times higher than that by the nonloaded BAC 28.2 ± 1.9%). The biomass on the substrate-loaded BAC reached 5.83 × 106-1.22 × 107 cells/g DW GAC on Day 7, which was 4.6-9.5 times higher than the value of the nonloaded BAC (1.28 × 106 cells/g DW GAC). The amount of extracellular polymer (i.e., protein) on nMnO2 coupled to sucrose-loaded BAC was promoted significantly. Flavobacterium (0.7%-11%), Burkholderiaceae (13%-20%) and Aquabacterium (30%-67%) were the dominant functional bacteria on the substrate-loaded BAC, which were conducive to the nitrification or denitrification process. The results indicated that loading nMnO2 and/or a carbon source accelerated the formation of biofilms on BAC and ammonium removal. Additionally, the ammonium removal treated by nMnO2 coupled with sucrose-loaded BAC was contributed by microbial degradation (56.0 ± 2.5%), biofilm adsorption (38.7 ± 2.1%) and GAC adsorption (5.3 ± 0.3%), suggesting a major role of microbial degradation.

Effect of biofilm thickness on the activity and community composition of phosphorus accumulating bacteria in a moving bed biofilm reactor

Can biofilms enhance the rates of phosphorus removal in wastewater treatment? In order to narrow the scientific gap on the effect of biofilm thickness on the activity and microbial community of phosphorus-accumulating bacteria, this study investigated biofilms of 30 to 1000 µm thickness in a moving bed biofilm reactor. Measurements on 5 different biofilm carriers showed that biomass-specific phosphorus release and uptake rates increased as a function of biofilm thickness for biofilms thinner than about 110 µm but were lower for thicker biofilms of about 550-1000 µm. The reduced phosphorus uptake and release rates in the thickest biofilms can result from substrate mass transfer limitations whereas the low activity in the thinnest biofilms can be related to a too high turnover rate in the biofilm due to heterotrophic growth. Additionally, the microbial ecology of the different biofilms confirms the observed phosphorus uptake and release rates. The results from the full-length 16S rRNA gene sequencing of the bacterial community showed that the thicker biofilms were characterized by higher relative abundance (40-58%) of potential phosphorus accumulating genera Zoogloea, Acinetobacter, Dechloromonas and Ca. Accumulibacter. In contrast, the thinner biofilms were dominated by the genus Ferribacterium (34-60%), which might be competing with phosphorus-accumulating bacteria as indicated by the relatively high acetate uptake rates in the thinner biofilms. It is concluded that there is an optimal biofilm thickness of 100-500 µm, at which the phosphorus accumulating bacteria have the highest activity.

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.

The Synthesis and Evaluation of Porous Carbon Material from Corozo Fruit (Bactris guineensis) for Efficient Propranolol Hydrochloride Adsorption

This study explores the potential of the corozo fruit (Bactris guineensis) palm tree in the Colombian Caribbean as a source for porous carbon material. Its specific surface area, pore volume, and average pore size were obtained using N₂ adsorption/desorption isotherms. The images of the precursor and adsorbent surface were obtained using scanning electron microscopy (SEM). Fourier transform infrared (FTIR) spectra were obtained to detect the main functional groups present and an X-ray diffraction analysis (XRD) was performed in order to analyze the structural organization of the materials. By carbonizing the fruit stone with zinc chloride, a porous carbon material was achieved with a substantial specific surface area (1125 m² g⁻¹) and pore volume (3.241 × 10-¹ cm³ g⁻¹). The material was tested for its adsorption capabilities of the drug propranolol. The optimal adsorption occurred under basic conditions and at a dosage of 0.7 g L⁻¹. The Langmuir homogeneous surface model effectively described the equilibrium data and, as the temperature increased, the adsorption capacity improved, reaching a maximum of 134.7 mg g⁻¹ at 328.15 K. The model constant was favorable to the temperature increase, increasing from 1.556 × 10^-1 to 2.299 × 10^-1 L mg^-1. Thermodynamically, the adsorption of propranolol was found to be spontaneous and benefited from higher temperatures, indicating an endothermic nature (12.39 kJ mol⁻¹). The negative ΔG⁰ values decreased from -26.28 to -29.99 kJ mol^-1, with the more negative value occurring at 328 K. The adsorbent material exhibited rapid kinetics, with equilibrium times ranging from 30 to 120 min, depending on the initial concentration. The kinetics data were well-represented by the general order and linear driving force models. The rate constant of the general order model diminished from 1.124 × 10^-3 to 9.458 × 10^-14 with an increasing concentration. In summary, the leftover stone from the Bactris guineensis plant can be utilized to develop activated carbon, particularly when activated using zinc chloride. This material shows promise for efficiently adsorbing propranolol and potentially other emerging pollutants.

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.

Predicting and improving the microbial removal of organic micropollutants during wastewater treatment: A review

Organic micropollutants (OMPs) consist of widely used chemicals such as pharmaceuticals and pesticides that can persist in surface and groundwaters at low concentrations (ng/L to μg/L) for a long time. The presence of OMPs in water can disrupt aquatic ecosystems and threaten the quality of drinking water sources. Wastewater treatment plants (WWTPs) rely on microorganisms to remove major nutrients from water, but their effectiveness at removing OMPs varies. Low removal efficiency might be the result of low concentrations, inherent stable chemical structures of OMPs, or suboptimal conditions in WWTPs. In this review, we discuss these factors, with special emphasis on the ongoing adaptation of microorganisms to degrade OMPs. Finally, recommendations are drawn to improve the prediction of OMP removal in WWTPs and to optimize the design of new microbial treatment strategies. OMP removal seems to be concentration-, compound-, and process-dependent, which poses a great complexity to develop accurate prediction models and effective microbial processes targeting all OMPs.

Submerged membrane/adsorption hybrid process in water reclamation and concentrate management-a mini review

Clean water shortage is a major global problem due to escalating demand resulting from increasing human population growth and industrial activities, decreasing freshwater resources and persistent droughts. Recycling and reuse of wastewater by adopting efficient reclamation techniques can help solve this problem. However, wastewater contains a wide range of pollutants, which require removal before it may be reused. Adsorption and membrane processes are two successful treatments used to remove most of these pollutants. Their efficiency increases when these processes are integrated as observed, for example in a submerged membrane adsorption hybrid system (SMAHS). It uses coarse air bubbling/sparging to produce local shear which minimises reversible membrane fouling, improves performance and extends the life of the membrane. Additionally, the adsorbent acts as a buoyant media that produces an extra shearing effect on the membrane surface, reduces membrane resistance and increases flux. In addition, it adsorbs the organics that would otherwise deposit on and cause fouling of the membrane. The use of activated carbon (AC) adsorbent in SMAHS is very effective in removing most pollutants including natural organic matter (NOM) and organic micropollutants (OMPs) from wastewaters and membrane concentrate wastes, the latter being a serious problem in practical applications of the reverse osmosis process. However, certain NOM fractions and OMPs (i.e. hydrophilic and negatively charged ones) are not efficiently removed by AC. Other adsorbents need to be explored for their effective removal.

Enhanced biodegradation of fluoroquinolones and the changes of bacterial communities and antibiotic-resistant genes under intermittent electrical stimulation

In this study, an anaerobic-aerobic coupling system under intermittent electrical stimulation was used to improve the biodegradation of synthetic wastewater containing fluoroquinolones (FQs). The effect of electrical stimulation on FQ removal performance is more pronounced with appropriate voltage and hydraulic retention time. In addition, the combination of anaerobic-anodic and aerobic-cathodic chambers is more conducive to improving the removal efficiency of FQs. Under 0.9 V, the removal efficiencies of ofloxacin, norfloxacin, ciprofloxacin, and enrofloxacin were significantly improved in the anaerobic-anodic and aerobic-cathodic system. The contribution of the anaerobic/aerobic anodic chambers to FQ removal was greater than that of the anaerobic/aerobic cathodic chambers. Electrical stimulation selectively enriched electroactive bacteria related to biodegradation (Desulfovibrio and Terrimonas), antibiotic-resistant bacteria (Atopobium and Neochlamydia), and nitrifying bacteria (SM1A02 and Reyranella). This study indicated the potential effectiveness of intermittent electrical stimulation in treating fluoroquinolone-containing wastewater in a biofilm reactor. However, electrical stimulation led to an increase in mobile genetic elements , induced horizontal gene transfer and enriched resistant bacteria, which accelerated the spread of antibiotic-resistant genes (ARGs) in the system, indicating that the diffusion of ARGs remains a challenge.

Microbial communities and processes in biofilters for post-treatment of ozonated wastewater treatment plant effluent

Ozonation is an established solution for organic micropollutant (OMP) abatement in tertiary wastewater treatment. Biofiltration is the most common process for the biological post-treatment step, which is generally required to remove undesired oxidation products from the reaction of ozone with water matrix compounds. This study comparatively investigates the effect of filter media on the removal of organic contaminants and on biofilm properties for biologically activated carbon (BAC) and anthracite biofilters. Biofilms were analysed in two pilot-scale filters that have been operated for >50,000 bed volumes as post-treatment for ozonated wastewater treatment plant effluent. In parallel, the removal performance of bulk organics and OMP, including differentiation of adsorption and biotransformation through sodium azide inhibition, were carried out in bench-scale filter columns filled with material from the pilot filters. The use of BAC instead of anthracite resulted in an improved removal of organic bulk parameters, dissolved oxygen, and OMP. The OMP removal observed in the BAC filter but not in the anthracite filter was based on adsorption for most of the investigated compounds. For valsartan, however, biotransformation was found to be the dominant pathway, indicating that conditions for biotransformation of certain OMP are better on BAC than on anthracite. Adenosine triphosphate analyses in the media-attached biofilms of the pilot filters showed that biomass concentrations in the BAC filter were significantly higher than in the anthracite filter. The microbial communities (16S rRNA gene sequencing) appeared to be similar with respect to the types of organisms occurring on both filter materials. Alpha diversity also exhibited little variation between filter media. Beta diversity analysis, however, revealed that filter media and bed depth substantially influenced the biofilm composition. In practice, the impact of filter media on biofilm properties and biotransformation processes should be considered for the design of biofilters.

Production of Modified Composite Nanofiber Yarns with Functional Particles

The study focused on the production of modified composite nanofiber yarns with fine functional particles. A device that incorporates fine functional particles into a nanofiber yarn wrapper was specially developed, which ensures the continuous production of modified yarn. It was demonstrated during the study that the specially designed equipment could be used effectively for incorporating fine functional particles into the nanofiber packaging, thus creating a unique yarn with high application potential. The use of particles with dimensions of just tens of micrometers results in the uneven flow of particles inside the chamber and the uneven supply of particles to the composite yarn. The study also determined that the number of particles incorporated into the composite yarn is affected by the particle concentration and the variation of the vortex velocity ratios in the chamber. During testing, it was also found that the nanofiber sheet of the composite yarn improves the mechanical properties of the produced yarn. In addition, the study included the semi-industrial production of a composite filter candle, which can be used for the treatment of fluids, especially air and water.

Biological filtration for wastewater treatment in the 21st century: A data-driven analysis of hotspots, challenges and prospects

Biological filtration has been widely used in wastewater treatment around the world, yet achieving satisfactory removal of pollutants remains a challenge due to the complexity of water pollution. In order to reveal the hotspots and trends of biological filtration from the perspective of research innovation, 5454 SCI papers and 14,287 patents collected from the Web of Science Core Collection and Derwent Innovation Index database were analyzed by visualization techniques. The results showed that China ranked first in the number of both papers and patents, while the USA and Japan contributed significantly in papers and patents, respectively. Co-occurrence analysis obtained the mapping knowledge domains and demonstrated distinct associations between contaminants ("nitrogen", "pharmaceuticals", "personal care products"), chemicals ("carbon", "activated carbon", "media"), process ("biodegradation", "adsorption" or "ozonation") and characteristics ("kinetics", "performance", "diversity"). Moreover, this review summarized the recent advances of biological filtration media, microorganism and combined process being applied. It was concluded that environmentally friendly biological filtration ("phytoremedi", "microalga", "recirculating aquaculture system"), bio-enhanced biological filtration ("bioaugment", "fungi", "low augment") and emerging pollutants ("emerging contamin", "antibiotic resistance gen", "organic micropollut", "trace organic chem") were the hotspots through data-driven analyses. Technology evolution path of biological filtration generally indicated the transition from conventional biological filtration for nitrogen and phosphorus removal to Fenton-biofiltration combined technology and finally to ozone-biological filtration. Furthermore, the technical innovation direction of the collaborative control of multi-media pollution, the low-carbon biological filtration and short-process technology was prospected. This work can serve as a quick reference for early-career researchers and industries working in the area of biological filtration.

Is In-Service Granular Activated Carbon Biologically Active? An Evaluation of Alternative Experimental Methods to Distinguish Adsorption and Biodegradation in GAC

In-service granular activated carbon (GAC) may transform into biological activated carbon (BAC) and remove contaminants through both adsorption and biodegradation, but it is difficult to determine its biodegradative capacity. One approach to understand the GAC biodegradative capacity is to compare the performance between unsterilized and sterilized GAC, but the sterilization methods may not ensure effective microbial inhibition and may affect adsorption. This study identified the ¹⁴C-glucose respiration rate as the best metric to evaluate the effectiveness of three sterilization methods: sodium azide addition, autoclaving, and γ irradiation. The sterilization protocols were refined, including continuously feeding 300 mg/L of sodium azide, three cycles of autoclaving, and 10-12 kGy of γ irradiation. Parallel minicolumn tests were conducted to identify sodium azide addition as the most broadly effective sterilization method with an insignificant effect on adsorption in most cases, except for the adsorption of anionic compounds under certain conditions. Nevertheless, this problem was solved by decreasing the azide dosage as long as it is still sufficient to provide effective microbial inhibition. This study helps to develop an approach that differentiates adsorption and biodegradation in GAC, which could be used by future studies to advance our understanding of BAC filtration.

The effect of ultrafiltration process on the fate of antibiotic-related microcontaminants, pathogenic microbes, and toxicity in urban wastewater

Ultrafiltration (UF) was assessed at chemical, microbiological, genetical and toxicological level and in terms of removing specific antibiotic-related microcontaminants from urban wastewater. The UF capacity to remove various antibiotics (clarithromycin, erythromycin, ampicillin, ofloxacin, sulfamethoxazole, trimethoprim, and tetracycline; [A₀] = 100 μg L^-1) was optimised with respect to the feed recirculation rate (25-50%) and feed/transmembrane pressure (1.5-3/1.5-2.4 bar, respectively). Here, we tested the UF capacity to reduce the cultivable bacteria (faecal coliforms, total heterotrophs, Enterococci, Pseudomonas aeruginosa), enteric opportunistic pathogens, including antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs) load. Moreover, the toxicity towards Daphnia magna and three plant species was investigated. Upon optimisation of UF, the removal of antibiotics ranged from 19% for trimethoprim to 95% for clarithromycin. The concentration of cultivable faecal coliforms in the permeate was significantly reduced compared to the feed (P < 0.001), whereas all the bacterial species decreased by more than 3 logs. A similar pattern of reduction was observed for the ARGs (P < 0.001) and enteric opportunistic pathogens (~3-4 logs reduction). A nearly complete removal of the antibiotics was obtained by UF followed by granular activated carbon adsorption (contact time: 90 min), demonstrating the positive contribution of such combination to the abatement of chemical microcontaminants.

Highly Effective Removal of Ofloxacin from Water with Copper-Doped ZIF-8

Residual antibiotics in wastewater have gained widespread attention because of their toxicity to humans and the environment. In this work, Cu-doped ZIF-8s (Cu-ZIF-8s) were successfully synthesized by the impregnation of Cu²⁺ in ZIF-8 and applied in the removal of ofloxacin (OFX) from water. Remarkably, excellent adsorption performance was obtained in Cu-ZIF-8s, especially for Cu-ZIF-8-1, in which the adsorption capacity (599.96 mg·g⁻¹) was 4.2 times higher than that of ZIF-8 and superior to various adsorbents reported previously. The adsorption kinetics and adsorption isotherm follow the pseudo-second-order model and the Langmuir model, respectively. Furthermore, the removal efficiencies of OFX in Cu-ZIF-8-1 reached over 90% at low concentrations. It was revealed that electrostatic interaction and complexation play important roles in the adsorption process. In addition, the material can be regenerated by simple methods. Therefore, the obtained Cu-doped MOFs may have a promising application in the treatment of antibiotic-containing wastewater.

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.

Effect of antibiotic mixtures on the characteristics of soluble microbial products and microbial communities in upflow anaerobic sludge blanket

Two upflow anaerobic sludge blanket reactors (UASBs) were used to investigate the effects of three antibiotic mixtures (erythromycin, sulfamethoxazole, and tetracycline) on reactor performance, soluble microbial products (SMPs) composition and microbial community. One reactor (UASB_antibiotics) was fed with antibiotic mixtures, whereas another reactor (UASB_control) was used as a control without the addition of antibiotic mixtures. Compared with those in UASB_control, UASB_antibiotics show lower chemical oxygen demand removal efficiency and biogas content. A higher removal efficiency of antibiotic mixtures was obtained in first few stages in UASB_antibiotics. The SMPs composition of effluent from the two reactors did not differ significantly, and the main components were protein-like substances, which produced higher fluorescence intensity in UASB_antibiotics. Gas chromatography-mass spectrometry analysis revealed that the main compounds identified as SMPs (<580 Da) were alkanes, aromatics and esters, with only 20% similarity of SMPs between UASB_antibiotics and UASB_control. Antibiotics had a significant effect on the microbial community structure. Notably, in UASB_control, hydrogenotrophic methanogens, key microorganisms in anaerobic digestion, had an obvious advantage at all stages compared with UASB_antibiotics, whereas acetoclastic methanogen exhibited the opposite pattern. The above results demonstrated that antibiotic mixtures influenced the effluent quality during anaerobic treatment of synthetic wastewater, resulting in changes in the microbial community structure. This study clarified the effect of antibiotic mixtures on the operation of UASBs. It could contribute to identifying potential strategies for improving effluent quality in anaerobic treatment.

Bioremediation of 27 Micropollutants by Symbiotic Microorganisms of Wetland Macrophytes

Background: Micropollutants in bodies of water represent many challenges. We addressed these challenges by the application of constructed wetlands, which represent advanced treatment technology for the removal of micropollutants from water. However, which mechanisms specifically contribute to the removal efficiency often remains unclear. Methods: Here, we focus on the removal of 27 micropollutants by bioremediation. For this, macrophytes Phragmites australis, Iris pseudacorus and Lythrum salicaria were taken from established wetlands, and a special experimental set-up was designed. In order to better understand the impact of the rhizosphere microbiome, we determined the microbial composition using 16S rRNA gene sequencing and investigated the role of identified genera in the micropollutant removal of micropollutants. Moreover, we studied the colonization of macrophyte roots by arbuscular mycorrhizal fungi, which are known for their symbiotic relationship with plants. This symbiosis could result in increased removal of present micropollutants. Results: We found Iris pseudacorus to be the most successful bioremediative system, as it removed 22 compounds, including persistent ones, with more than 80% efficiency. The most abundant genera that contributed to the removal of micropollutants were Pseudomonas, Flavobacterium, Variovorax, Methylotenera, Reyranella, Amaricoccus and Hydrogenophaga. Iris pseudacorus exhibited the highest colonization rate (56%). Conclusions: Our experiments demonstrate the positive impact of rhizosphere microorganisms on the removal of micropollutants.

Pharmaceutical compounds used in the COVID-19 pandemic: A review of their presence in water and treatment techniques for their elimination

During the COVID-19 pandemic, high consumption of antivirals, antibiotics, antiparasitics, antiprotozoals, and glucocorticoids used in the treatment of this virus has been reported. Conventional treatment systems fail to efficiently remove these contaminants from water, becoming an emerging concern from the environmental field. Therefore, the objective of the present work is to address the current state of the literature on the presence and removal processes of these drugs from water bodies. It was found that the concentration of most of the drugs used in the treatment of COVID-19 increased during the pandemic in water bodies. Before the pandemic, Azithromycin concentrations in surface waters were reported to be in the order of 4.3 ng L-1, and during the pandemic, they increased up to 935 ng L-1. Laboratory scale studies conclude that adsorption and advanced oxidation processes (AOPs) can be effective in the removal of these drugs. Up to more than 80% removal of Azithromycin, Chloroquine, Ivermectin, and Dexamethasone in aqueous solutions have been reported using these processes. Pilot-scale tests achieved 100% removal of Azithromycin from hospital wastewater by adsorption with powdered activated carbon. At full scale, treatment plants supplemented with ozonation and artificial wetlands removed all Favipiravir and Azithromycin, respectively. It should be noted that hybrid technologies can improve removal rates, process kinetics, and treatment cost. Consequently, the development of new materials that can act synergistically in technically and economically sustainable treatments is required.

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 .

Comparative Life Cycle Assessment of two advanced treatment steps for wastewater micropollutants: How to determine whole-system environmental benefits?

Advanced wastewater treatment (AWT) technologies are now considered to target urban micropollutants (MPs) before discharge into receiving water bodies and to comply with specific criteria for reuse. Extra energy and/or resources are necessary to achieve the elimination of MPs. Using the Life Cycle Assessment framework, this study assesses net environmental efficiencies for two AWTs (i) ozone systems (air-fed and pure oxygen-fed) and (ii) granular activated carbon filter. Sixty-five MPs with proven removal efficiency values and toxicity and/or ecotoxicity potentials were included in this study building on results from recent research. Consolidated Life Cycle Inventories with data quality and uncertainty characterization were produced with an emphasis on operational inputs. Results show that the direct water quality benefits obtained from AWT are outweighed by greater increases in indirect impacts from energy and resource demands. Future research should include water quality aspects not currently captured in life cycle impact assessment, such as endocrine disruption and whole-effluent toxicity, in order to assess the complete policy implications of MP removal strategies.

Role of carrier characteristics affecting microbial density and population in enhanced nitrogen and phosphorus removal from wastewater

This research aims to improve simultaneous nitrification-denitrification and phosphorus removal (SNDPR) using novel carriers and to demonstrate the effect of carrier characteristics on nutrient removal in a biofilm reactor. For this purpose, biofilms enriched with both polyphosphate-accumulating organisms (PAOs) and nitrifiers were cultivated in two parallel sequencing batch reactors containing conventional moving bed bioreactor carriers (MBBR) and a novel type of carriers (carbon-based moving carriers (CBMC)). The new carriers were produced based on recycled waste materials via a chemical-thermal process and their specific surface area were 10.4 times higher than typical MBBR carriers of similar dimensions. The results showed that the use of CBMC carriers increased bacterial adhesion by about 18.5% and also affected the microbial population inside the biofilms, leading to an increase in PAOs abundancy and thus an increase in biological phosphorus removal up to 12.5%. Additionally, it was corroborated that the volume of the anoxic zones with dynamic behavior is strictly influenced by the carrier structure and biofilm thickness due to a limitation in oxygen penetration. Accordingly, the formation of broader anoxic zones and shrinkage of these zones to a lesser extent resulted in the continuation of anoxic reactions for longer periods using the novel carriers. Thereby, an increase in nitrogen removal by about 15% was obtained mainly by denitrifying PAOs. The results also exhibited that a higher simultaneous nitrification-denitrification (SND) efficiency can be achieved by selecting an appropriate aeration program influencing the dynamic changes of anoxic zones. Overall, a biofilm system using the new carriers, with phosphorus and nitrogen removal efficiencies of 97.5% and 92.3%, was presented as an efficient, compact, and simple operation SNDPR process.

Performance of biological activated carbon (BAC) filtration for the treatment of secondary effluent: A pilot-scale study

In addition to the adsorption capability for organic compounds, granular activated carbon (GAC) can also serve as a good media for the growth of microbial communities in biofilters. Despite its potential, the application of BAC filtration for municipal wastewater treatment has been little addressed in the literature. In this context, this paper aimed to investigate BAC filtration as a post-treatment of anaerobic effluent in pilot scale and its performance in removing organic matter and turbidity. Removal efficiencies during the biofilters run times and along biofilters depth were also evaluated. Three BAC filters were evaluated under different operating conditions of filtration rates (from 13 to 32 m d^-1) and empty bed contact time (EBCT) (from 45 to 112 min) during 170 days. The lowest filtration rate (13 m d^-1) presented the best performance in terms of dissolved organic carbon (DOC) removal (68.2 ± 4.0%), leading to mean DOC effluent concentration of 6.8 ± 0,9 mg L^-1. The BAC reached the stability of biological activity from the 63rd day of operation, however, the adsorption process was still occurring contributing to DOC removal. These DOC removals were higher than those results reported in the literature for BAC filters treating drinking water and municipal wastewater. The DOC removal efficiencies were maintained during the filter run times, showing the robustness of the system even after the interference caused by the backwashing process. BAC filtration was also capable of removing turbidity, with removal efficiencies between 84.5 ± 3.6% and 70.63 ± 6.8% depending on the filtration rate. The results indicated the capability of BAC systems to remove efficiently organic carbon and turbidity from effluents with high organic content, mean of 23.97 (±3.96) mg.L^-1, and also valuable support to determine adequate operating parameters for BAC filters application in secondary effluent treatment, such as filtration rate (13 m d^-1), EBCT (112 min), and detailed backwashing procedures.

The occurrence of non-steroidal anti-inflammatory drugs (NSAIDs) in Malaysian urban domestic wastewater

The water stream has been reported to contain non-steroidal anti-inflammatory drugs (NSAIDs), released from households and premises through discharge from Sewage Treatment Plant (STP). This research identifies commonly consumed NSAIDs namely ibuprofen (IBU), diclofenac (DIC), ketoprofen (KET) and naproxen (NAP) in the influent wastewater from two urban catchments (i.e. 2 STPs). We expand our focus to assess the efficiency of monomer (C18) and dimer (HLB) types of sorbents in the solid phase extraction method followed by gas chromatography mass spectrometry (GCMS) analysis and optimize model prediction of NSAIDs in the influent wastewater using I-Optimal design. The ecological risk assessment of the NSAIDs was evaluated. The HLB produced reliable analysis for all NSAIDs under study (STP1: 6.7 × 10^-3 mg L^-1 to 2.21 × 10^-1 mg L^-1, STP2: 1.40 × 10^-4 mg L^-1 to 9.72 × 10^-2 mg L^-1). The C18 however, selective to NAP. Based on the Pearson proximity matrices, the DIC_HLB can be a good indicator for IBU_HLB (0.565), NAP_C18 (0.721), NAP_HLB (0.566), and KET_HLB (0.747). The optimized model prediction for KET and NAP based on DIC are successfully validated. The risk quotients (RQ) values of NSAIDs were classified as high (RQ > 1), medium (RQ, 0.1-1) and low (RQ, 0.01-0.1) risks. The optimized models are beneficial for major NSAIDs (KET and NAP) monitoring in the influent wastewater of urban domestic area. An upgrade on the existing wastewater treatment infrastructure is recommended to counteract current water security situation.

The Use of Surface-Modified Nanocrystalline Cellulose Integrated Membranes to Remove Drugs from Waste Water and as Polymers to Clean Oil Sands Tailings Ponds

There is an urgent environmental need to remediate waste water. In this study, the use of surface-modified nanocrystalline cellulose (CNC) to remove polluting drugs or chemicals from waste water and oil sands tailing ponds has been investigated. CNC was modified by either surface adsorbing cationic or hydrophobic species or by covalent methods and integrated into membrane water filters. The removal of either diclofenac or estradiol from water was studied. Similar non-covalently modified CNC materials were used to flocculate clays from water or to bind naphthenic acids which are contaminants in tailing ponds. Estradiol bound well to hydrophobically modified CNC membrane filter systems. Similarly, diclofenac (anionic drug) bound well to covalently cationically modified CNC membranes. Non-covalent modified CNC effectively flocculated clay particles in water and bound two naphthenic acid chemicals (negatively charged and hydrophobic). Modified CNC integrated into water filter membranes may remove drugs from waste or drinking water and contaminants from tailing ponds water. Furthermore, the ability of modified CNC to flocculate clays particles and bind naphthenic acids may allow for the addition of modified CNC directly to tailing ponds to remove both contaminants. CNC offers an environmentally friendly, easily transportable and disposable novel material for water remediation purposes.

Instructive analysis of engineered carbon materials for potential application in water and wastewater treatment

Water remediation is an essential component for sustainable development. Increasing population and rapid industrialization have contributed to the deterioration of water resources. In particular, effluents from chemical, pharmaceutical, petroleum industries, and anthropogenic activities have led to severe ecological degradation. Many of these detrimental pollutants are highly toxic even at low concentrations, acting as carcinogens and inflicting severe long-lasting effects on human health. This review underscores the potential applications of engineered carbon-based materials for effective wastewater treatment. It focuses on the performance as well as efficiency of activated carbon, graphene nanomaterial, and carbon nanotubes, both with and without chemical functionalization. Plausible mechanisms of action between the chemically functionalized adsorbent and pollutants are also discussed. Based on the keywords from the literature published in the recent five years, a statistical practicality-vs-applicability analysis of these three materials is also provided. The review will provide a deep understanding of the physical or chemical interactions of the wastewater pollutants with carbon materials.

Activated carbon coupled with advanced biological wastewater treatment: A review of the enhancement in micropollutant removal

This study consists of a review on the removal efficiencies of a wide spectrum of micropollutants (MPs) in biological treatment (mainly membrane bioreactor) coupled with activated carbon (AC) (AC added in the bioreactor or followed by an AC unit, acting as a post treatment). It focuses on how the presence of AC may promote the removal of MPs and the effects of dissolved organic matter (DOM) in wastewater. Removal data collected of MPs are analysed versus AC dose if powdered AC is added in the bioreactor, and as a function of the empty bed contact time in the case of a granular activated carbon (GAC) column acting as a post treatment. Moreover, the enhancement in macropollutant (organic matter, nitrogen and phosphorus compounds) removal is analysed as well as the AC mitigation effect towards membrane fouling and, finally, how sludge properties may change in the presence of AC. To sum up, it was found that AC improves the removal of most MPs, favouring their sorption on the AC surface, promoted by the presence of different functional groups and then enhancing their degradation processes. DOM is a strong competitor in sorption on the AC surface, but it may promote the transformation of GAC in a biologically activated carbon thus enhancing all the degradation processes. Finally, AC in the bioreactor increases sludge floc strength and improves its settling characteristics and sorption potential.

Shifting from Conventional to Organic Filter Media in Wastewater Biofiltration Treatment: A Review

Biofiltration is a promising wastewater treatment green technology employed to remove various types of pollutants. The efficiency of biofiltration relies on biofilm, and its performance is significantly influenced by various factors such as dissolved oxygen concentration, organic loading rate, hydraulic retention time, temperature, and filter media selection. The existing biofilters utilize conventional media such as gravel, sand, anthracite, and many other composite materials. The material cost of these conventional filter materials is usually higher compared to using organic waste materials as the filter media. However, the utilization of organic materials as biofilter media has not been fully explored and their potential in terms of physicochemical properties to promote biofilm growth is lacking in the literature. Therefore, this review critically discusses the potential of shifting conventional filter media to that of organic in biofiltration wastewater treatment, focusing on filtration efficiency-influenced factors, their comparative filtration performance, advantages, and disadvantages, as well as challenges and prospective areas of organic biofilter development.

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.

Adsorption of five emerging contaminants on activated carbon from aqueous medium: kinetic characteristics and computational modeling for plausible mechanism

Pharmaceuticals and personal care products (PPCPs) do not have standard regulations for discharge in the environment and are categorized as contaminants of emerging concern as they pose potential threats to ecology as well as humans even at low concentrations. Conventional treatment processes generally employed in the wastewater treatment plants are not adequately engineered for effective removal of PPCPs. Identifying cost-effective tertiary treatment is therefore, important for complete removal of PPCPs from wastewater prior to discharge or reuse. Present study demonstrates adsorption using granular-activated carbon (GAC) as a possible tertiary treatment for simultaneous removal of five PPCPs from aqueous media. Adsorbent was characterized in terms of morphology, surface area, surface charge distribution, and presence of functional groups. Performance of GAC was investigated for sorption of three hydrophilic (ciprofloxacin, acetaminophen, and caffeine) and two hydrophobic (benzophenone and irgasan) PPCPs from aqueous solution varying the process parameters (initial concentration, adsorbent dose, pH, agitation time). Langmuir isotherm model (correlation coefficients (R2): 0.993 to 0.998) appeared to fit the isotherm data better than Temkin isotherm model for these adsorbates. Adsorption efficiencies of these compounds (8.26 to 20.40 mg g-1) were in accordance with their log Kow values. While the adsorption kinetics was best explained in terms of a pseudo-second-order kinetic model, the data suggested that adsorption mechanism was mainly governed by the intraparticle diffusion. The role of physical factors like molecular volume, molecular size, and area of targeted PPCPs were investigated through computational studies which in turn can help predicting their uptake onto GAC.

Emerging organic contaminants and odorous compounds in secondary effluent wastewater: Identification and advanced treatment

This study aims to address organic micropollutants in secondary effluents from municipal wastewater treatment plants (WWTPs) by first identification of micropollutants in different treatment units, and second by evaluating an advanced treatment process for removals of micropollutants. In secondary effluents, 28 types of pharmaceutical and personal care products (PPCPs), 5 types of endocrine disrupting chemicals (EDCs) and 3 types of odorous compounds are detected with total concentrations of 513 ± 57.8 ng/L, 991 ± 36.5 ng/L, 553 ± 48.3 ng/L, respectively. An integrated process consisting of in-situ ozonation, ceramic membrane filtration (CMF) and biological active carbon (BAC) filtration is investigated in a pilot scale (1000 m³/d) for removal of micropollutants in secondary effluents. The total removal efficiencies of PPCPs, EDCs and odorous compounds are 98.5%, 95.4%, and 91.1%, respectively. Removal mechanisms of emerging organic contaminants (EOCs) and odorous compounds are discussed based on their physicochemical properties. The remarkable removal efficiencies of micropollutants by the pilot system is attributed to synergistic effects of combining ozonation, ceramic membrane filtration and BAC filtration. This study provides a cost-effective and robust technology with the capability of treating secondary effluents for reuse applications.

Fate and effects of microplastics in wastewater treatment processes

Microplastics (MPs) have garnered growing attention of researchers, as they are proved to be hazardous to the environment and humans. Wastewater treatment plants (WWTPs) are deemed as an important releasing source of MPs to the environment, and thus it is of significance to study the behavior of MPs in WWTPs. In this review, the fate of MPs in WWTPs and their effects on different wastewater treatment processes have been comprehensively discussed. Studies have shown that the secondary treatment is the most efficient process to remove MPs from wastewaters with a removal rate around 98%. The presence of MPs can increase reagent addition dosage, inhibit nitrogen conversion rate, and cause membrane fouling in wastewater treatment processes. Besides, the influences of MPs on activated sludge mainly exert on nitrification and denitrification processes, sludge digestion, and microbial communities. However, it is worth noting that different methods have been employed to determine the concentrations of MPs in WWTPs. As a result, the removal performance on MPs in WWTPs is difficult to be accurately assessed. Moreover, complicated interaction among MPs and other environmental pollutants may expand the impacts of MPs on wastewater treatment processes, which still remains insufficiently investigated. Therefore, this review has also proposed some knowledge gaps existing in present MP studies in WWTPs, and would provide reference to alleviate the adverse effects of MPs for future research.

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.

Decolourisation of Beet Sugar Syrup Using Activated Carbon and Glucose Oxidase Enzyme

This paper presents the development and optimization of a new approach which combines the utilization of activated carbon and glucose oxidase enzyme for decolourisation of beet sugar syrup. The combining of the physical adsorption with the enzymatic reaction was managed to improve the decolourisation of beet sugar syrup from 35.29 to 83.68% compared to the basic adsorption by activated carbon after 120 min of operation under the optimum conditions. The maximum decolourisation efficiency by the coupled process was achieved at glucose oxidase dosage of 0.07 g, glucose concentration of 20 mM, and solution pH 7 at the temperature of 30ºC using 0.01 g of activated carbon particles. Given the high effectiveness, reusability, and the eco-friendly nature of the process, the proposed method can serve as an alternative to ordinary decoloursation techniques.

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.

Efficient removal of 17α-ethinylestradiol from secondary wastewater treatment effluent by a biofilm process incorporating biogenic manganese oxide and Pseudomonas putida strain MnB1

This study proposes a biofilm process to immobilize biogenic manganese oxide (BMO) and Pseudomonas putida MnB1 (BMO-MnB1), which shows excellent synergistic effects for 17α-ethinylestradiol (EE2) from secondary wastewater treatment effluent (WWTE). Modified granular activated carbon (M-GAC) was used as the packing carrier, inoculated with Pseudomonas putida MnB1 and Mn(II) to form the BMO-MnB1 biofilm. Feasibility tests were performed to compare the EE2 removal efficiency with that of the conventional biofilm process (BAC) for heterogeneous microbial communities. Results show that in the BAC, EE2 was removed mainly by adsorption, with biodegradation contributing only slightly to the overall performance. In contrast, the BMO-MnB1 biofilter outperformed the BAC. Furthermore, less than 4% of the total EE2 removed was extracted from the biofilter medium over 150 days of operation, confirming that EE2 was biodegraded by P. putida MnB1 or chemically oxidized by BMO. Our results suggest that BMO-MnB1 biofilm processes have high potential for practical applications in removal of endocrine disrupting compounds from wastewater effluent.

Desorption of Organic Micropollutants from Loaded Granular Activated Carbon

The loading of granular activated carbon (GAC) is influenced by the amount of water treated and the concentrations of adsorbates present in the water matrix. Through extraction experiments, we aimed to investigate the total adsorbed mass of eight organic micropollutants by using ethanol as solvent and the maximum possible concentrations, due to the desorption of organic micropollutants, in water. Three different drying methods and the impact of the contact time, GAC particle size, and GAC/solvent ratio were investigated. Although no significant differences between the drying methods could be observed, the chosen contact time and particle size had a significant impact on the amount of organic micropollutants extracted. Lower GAC/solvent ratios positively affected the extraction yield. The masses extracted in ethanol were compared with the cumulated masses calculated from 72 feed and effluent samples, collected during filter operation, resulting in extraction yields between 0.5% and 30%. The composition of extracted micropollutants in ethanol reflected the concentrations in feed water of the pilot-scale filter. Desorption in water was mostly influenced by the solubility of the investigated micropollutants. The same substances found in the supernatants inf the experiments could also be identified in the backwash water of the filter.

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.

Composites for wastewater purification: A review

The review deals with different kinds of composites which have been used for wastewater treatment. The use of different types of composites ranging from nanocomposites, activated charcoal composites, polymer composites, oxide-based composites, hybrid composites, and biosorbent composites, etc. has been dealt with in detail, and presented as a central source of knowledge. The paper incorporates water purification explicitly via adsorption process, which has proven to be economical and efficient. These composites have been explored for treating or elimination of various hazardous substances like heavy metal species, different classes of colored contaminants (dyes), several organic and inorganic pollutants from wastewater. The composites discussed have successfully eliminated Zn²⁺, Ni²⁺, Cu²⁺, Pb²⁺, Hg, etc. In some instances the removal percentage of the contaminants was almost 100%. The presented data reveals the efficiency of composite materials in wastewater treatment over the conventional singular materials.

Effects of phosphate and hydrogen peroxide on the performance of a biological activated carbon filter for enhanced biofiltration

Biofilm formation on biofilters can influence their hydraulic performance, thereby leading to head loss and an increase in energy use and costs for water utilities. The effects of a range of factors, including hydrogen peroxide and phosphate, on the performance of biological activated carbon (BAC) and biofilm formation were investigated using laboratory-scale columns. Head loss, total carbohydrates, and proteins were reduced in the nutrient-enhanced, oxidant-enhanced, and nutrient + oxidant-enhanced BAC filters. However, there were no changes in the removal of dissolved organic matter, trihalomethane formation potential, or selected trace organic contaminants. The biofilm formation on polyvinyl chloride and stainless steel coupons using the laboratory biofilm reactor system was lower when the effluent from a nutrient-enhanced column was used, which indicated that there was less biofilm formation in the distribution systems. This may have been because the effluent from the nutrient-enhanced column was more biologically stable. Therefore, enhanced biofiltration could be used not only to reduce head loss in biofilters, but also to delay biofilm formation in distribution systems.