Powdered Activated Carbon Dose Research Articles

Pilot scale removal of organic micropollutants by combining ozonation with powdered activated carbon

ABSTRACT Pilot experiments were conducted to assess the removal of organic micropollutants from biologically treated wastewater at a municipal wastewater treatment plant in Sweden. Powdered activated carbon (PAC) was combined with a low dose of ozone added directly before the PAC contact tank, enabling ozone to react simultaneously with the PAC and the wastewater contaminants. This combination of ozone and PAC was compared to PAC or ozone alone. The process, which included coagulation/flocculation and ballasted high-rate lamella sedimentation, proved to be both robust and efficient for the removal of micropollutants. The addition of 1.3 mg PAC/mg DOC resulted in a 73% average reduction of micropollutants. With the addition of 0.13 mg O3/mg DOC, the reduction increased to 83%, which was similar to the outcome with the addition of 26 mg PAC/mg DOC without ozone. The process configuration and operating conditions did not lead to any detectable bromate formation despite relatively high influent bromide levels. The estimated operating costs for combining PAC with a low dose of ozone were significantly lower than for applying a higher PAC dose. Thus, this way of combining PAC with ozone seems to have several advantages with respect to treatment efficiency and operation.

A thorough analysis of the occurrence, removal and environmental risks of organic micropollutants in a full-scale hybrid membrane bioreactor fed by hospital wastewater

The Urban Wastewater Treatment Directive recent draft issued last October 2022 pays attention to contaminants of emerging concern including organic micropollutants (OMPs) and requires the removal of some of them at large urban wastewater treatment plants (WWTPs) calling for their upgrading. Many investigations to date have reported the occurrence of a vast group of OMPs in the influent and many technologies have been tested for their removal at a lab- or pilot-scale. Moreover, it is well-known that hospital wastewater (HWW) contains specific OMPs at high concentration and therefore its management and treatment deserves attention. In this study, a 1-year investigation was carried out at a full-scale membrane bioreactor (MBR) treating mainly HWW. To promote the removal of OMPs, powdered activated carbon (PAC) was added to the bioreactor at 0.1 g/L and 0.2 g/L which resulted in the MBR operating as a hybrid MBR. Its performance was tested for 232 target and 90 non-target OMPs, analyzed by UHPLC-QTOF-MS using a direct injection method. A new methodology was defined to select the key compounds in order to evaluate the performance of the treatments. It was based on their frequency, occurrence, persistence to removal, bioaccumulation and toxicity. Finally, an environmental risk assessment of the OMP residues was conducted by means of the risk quotient approach. The results indicate that PAC addition increased the removal of most of the key OMPs (e.g., sulfamethoxazole, diclofenac, lidocaine) and OMP classes (e.g., antibiotics, psychiatric drugs and stimulants) with the highest loads in the WWTP influent. The hybrid MBR also reduced the risk in the receiving water as the PAC dosage increased mainly for spiramycin, lorazepam, oleandomycin. Finally, uncertainties and issues related to the investigation being carried out at full-scale under real conditions are discussed.

The adsorption of biogenetic odorants onto activated carbon: Adsorption characteristics and impacts of algal organic matter

Powdered activated carbon (PAC) adsorption is regarded as an efficient method for removing odorants from drinking water. However, in eutrophic aquatic environments, the presence of algal organic matter (AOM) produced by cyanobacteria considerably impedes the adsorption of odorous compounds by activated carbon. This study focused on investigating the adsorption characteristics of three representative odorants: 2-methylisoborneol (2-MIB), β-cyclocitral (β-cyclo), and butyl sulfide (BS) by PAC and the effects of AOM on the PAC adsorption of odorants. The removal of the three odorants reached 83.5–97.5% at a PAC dosage of 10 mg/L after 12 h of exposure in a competition-free scenario. The adsorption kinetics demonstrated higher conformity (R2 > 0.9) with the pseudo-second-order model, whereas the adsorption capacity exhibited stronger conformity (R2 > 0.9) with the Freundlich model. The presence of AOM resulted in varying levels of competition for PAC for the adsorption of the three odorants. As the concentration of AOM increased from 0 to 5 mg C/L, the removal of 2-MIB was the most affected (from 83.5% to 10.0%), followed by β-cyclo (from 86.6% to 55.0%), and BS (from 97.5% to 92.0%). The competitive adsorption of AOM at the molecular level was studied using density functional theory (DFT). The DFT results suggested that odorants with higher and more uniformly distributed electrostatic potentials exhibited a heightened affinity for PAC adsorption and a diminished susceptibility to disruption caused by AOM. This study provides valuable insights into the mitigation of odorous compounds during drinking water purification.

A combined treatment of aerobic activated sludge and powdered activated carbon: Pilot-scale study of per/polyfluoroalkyls (PFASs), organic matters, chromium, and color removal from tannery wastewaters

A pilot-scale system of three parallel plug flow reactors was utilized for the treatment of tannery wastewaters with powdered activated carbon (PAC) at different dosage in activated sludge process. The SRT and the carbon replacement (XCI) were set at 35 d and 0 mg PAC/L (R1), 25 d and 100 mg PAC/L (R2), 20 d and 300 mg PAC/L (R3), at fixed HRT (4 days) and temperature (20–22 °C). The removal of per- and polyfluoroalkyls substances (PFASs), organics, chromium and color were assessed. Due to competition phenomena for adsorption between the organics and the PFASs, the highest PAC dosage (R3) was the only one able to decrease the concentration of total PFASs below the limit of 500 ng/L. Soluble COD and chromium removal efficiency up to 92.8 % and 68 % was respectively achieved; in terms of color abatement, the treated wastewaters showed a reduced absorbance up to 56 % compared to condition R1. The mass balance assessment revealed a maximum cost's increase of 0.923 €/m3 of treated water associated to the use of the PAC (R3), highlighting the necessity to adopt sustainable strategies to valorize the generated tannery sludge instead of landfilling, which is still the only disposal practice of this waste.

Effective removal of microcystin by a hybrid process combining PAC-submerged hollow fiber membrane from raw water

Abstract Microcystis aeruginosa is one of the most commonly detected cyanobacteria in aquatic systems. Therefore, this study evaluated the removal efficiency of total (cell-bound and dissolved) microcystin (MC) by a hybrid process combining powdered activated carbon (PAC)-submerged hollow fiber membrane and compared the hybrid process performance with that of PAC adsorption and submerged hollow fiber membrane processes separately. The results indicated that up to 84% of the total MC was removed using the PAC adsorption stand-alone process, while 90% of it was removed by submerged hollow fiber membrane stand-alone process (with a 10 μg/L feed concentration). When the PAC dose of 20 mg/L and equilibrium time of 480 min were applied with a 51.9 μg/L feed concentration to the hybrid process, the removal efficiency of total MC increased to 99%. Moreover, the cell-bound and dissolved MC concentrations in the permeate were 0.34 and 0.65 mg/L, respectively. This permeate concentration level was ensured by the World Health Organization (WHO) as the guideline value for MC (1 mg/L). Overall, the hybrid process combining PAC-submerged hollow fiber membranes can be successfully used as an alternative advanced treatment technology to mitigate total (cell-bound and dissolved) MC.

Effects of powdered activated carbon dosage on the performance of membrane bioreactors treating biochemical tail water

As a promising treatment technology for wastewater, the promotion of membrane bioreactors (MBR) is restricted by biological fouling. Among the measures used to mitigate membrane fouling, the addition of powdered activated carbon (PAC) to MBRs has been recognized as an effective practice. However, the effects of PAC dosage on the performance of MBRs that treat highly biochemical influent from wastewater treatment plants remain unclear. In this study, by investigating the treatment of biochemical tailwater by PAC–MBRs, we thoroughly analyzed the effects of PAC dosage on the contamination removal efficiency, membrane operation cycles, sludge mixture properties, and microorganism distributions. The results indicated that the addition of PAC enhanced the removal efficiency of MBRs depending on the contaminant of interest. For example, the removal efficiency of total nitrogen can be boosted from 30 % to 60 % with PAC addition, while the removal efficiencies of total phosphorus were comparable with or without PAC addition. Furthermore, the application of PAC in MBRs can prolong the duration of membranes by suppressing biological fouling. This was supported by the decreased microbial products, reduced smaller solid particles, and stronger stability of sludge particles. PAC addition also boosts the proportion of Proteus and decreases the proportion of Bacteroides, which helps to improve the removal efficiencies of contaminants. Finally, among the PAC dosages tested in our study, 1.5 g/L PAC was proposed as the optimal candidate for treating highly biochemical influents. For example, the corresponding time for transmembrane pressure to reach 0.03 MPa was 19 d at 1.5 g/L PAC, while these periods were 7 and 14 d at dosages of 0 and 0.5 g/L, respectively. Overall, the findings of this study will aid in the selection of optimal dosages for other systems with different types of influents.

Low-temperature persulfate activation by powdered activated carbon for simultaneous destruction of perfluorinated carboxylic acids and 1,4-dioxane.

Carbonaceous materials have emerged as a method of persulfate activation for remediation. In this study, persulfate activation using powdered activated carbon (PAC) was demonstrated at temperatures relevant to groundwater (5-25°C). At room temperature, increasing doses of PAC (1-20gL-1) led to increased persulfate activation (3.06×10-6s-1 to 2.10×10-4 with 1 and 20gL-1 PAC). Activation slowed at lower temperatures (5 and 11°C); however, substantial (>70 %) persulfate activation was achieved. PAC characterization showed that persulfate is activated at the surface of the PAC, as indicated by an increase in the PAC C:O ratio. Similarly, electron paramagnetic resonance (EPR) spectroscopy studies with a spin trapping agents (5,5-dimethyl-1-pyrroline N-oxide (DMPO)) and 2,2,6,6-tetramethylpiperidine (TEMP) revealed that singlet oxygen was not the main oxidizing species in the reaction. DMPO was oxidized to form 5,5-dimethylpyrrolidone-2(2)-oxyl-(1) (DMPOX), which forms in the presence of strong oxidizers, such as sulfate radicals. The persulfate/PAC system is demonstrated to simultaneously degrade both perfluorooctanoic acid (PFOA) and 1,4-dioxane at room temperature and 11°C. With a 20gL-1 PAC and 75mM persulfate, 80 % and 70 % of the PFOA and 1,4-dioxane, respectively, degraded within 6h at room temperature. At 11°C, the same PAC and persulfate doses led to 57% dioxane degradation and 54 % PFOA degradation within 6h. Coupling PAC with persulfate offers an effective, low-cost treatment for simultaneous destruction of 1,4-dioxane and PFOA.

Concept for the valorization of cereal processing waste: Recovery of phenolic acids by using waste-derived tetrahydrofurfuryl alcohol and biochar

Valorization of agro-food waste by converting it into a renewable resource plays a crucial role in a bio-based circular economy. Therefore, this study was designed to evaluate the suitability of distillery stillage (DS), which comes from alcohol production from cereals, for producing value-added products that can be used synergistically. The main objective was to investigate the usefulness of two substances for the recovery of phenolic acids, which have antioxidant activity, from the liquid fraction of DS: namely, tetrahydrofurfuryl alcohol (THFA) as a solvent and biochar as an adsorbent, both produced from the solid fraction of cereal processing waste. The effect of THFA concentration (80 and 100%) on phenolic acid yield in ultrasound-assisted extraction was studied. The solubilization predictions of phenolic compounds by the Hansen solubility parameters were in accordance with the experimental results: the yield of phenolic acids in the extracts was highest (3.76 μg g−1 dry mass) with 80% THFA. Among the extracted phenolic acids, hydroxycinnamic acids predominated over hydroxybenzoic acids, which may affect the bioactive properties of the extracts and their future applications for industrial purposes. Phenolic acids from the extracts were adsorbed on 17–170 g biochar L−1 and desorbed into water at 40–60 °C. The phenolic acid recovery was highest (∼92%) when the biochar dose was 85 g L−1 and when desorption was performed at 50 °C. After adsorption/desorption, ∼95% of the antioxidant activity of the phenolic acids in the extracts was maintained. As biochar has a smaller specific surface area than commercial powdered activated carbon (PAC), the biochar dose should be about 5 times higher than an equivalent PAC dose for adsorption efficiency above 90%.

Removal of organic micropollutants from municipal wastewater by powdered activated carbon - activated sludge treatment

In Powdered Activated Carbon (PAC)-Activated Sludge (AS) Treatment, PAC is directly dosed into the AS tank. In this study, batch and pilot plant experiments were carried out to investigate the efficacy of PAC-AS treatment concerning the removal of organic micropollutants (OMPs). Batch and pilot plant experiments showed comparable removal efficiency of nine OMPs: a mean removal of 80 % could be achieved at a specific PAC dose of 2.5 mg PAC/mg DOC; during a PAC cut-off experiment, the removal performance leveled off in the first 6 h without PAC dosage. A further investigation involving an intermittent dosage of PAC demonstrated that OMPs were removed stably when PAC was dosed every 6 h, which implies the possibility of reduced investment and maintenance costs of a dosing unit.DOC was removed by 18 ± 4 % when the PAC doses ranged from 1.9 to 2.3 mg PAC/mg DOC in this study. A more detailed characterization of the organic matter was performed by means of size exclusion chromatography coupled with organic carbon detection (SEC-OCD). The high molecular weight fraction (F1) and hydrophobic organic compounds (DOCh) were most adsorbed by PAC, revealed by batch and pilot plant experiments. It indicates a higher competition potential of these two fractions against OMP adsorption compared to other DOC fractions in the PAC-AS system.

Study on Treatment of Tiny Pollution Water with PAC-HUM System in Kuitun River

Kuitun city, Xinjiang is dry and short of water, so it is urgent to treat and utilize all kinds of unconventional water. In view of this problem, we conducted a study on the treatment of tiny pollution water in Kuitun River. We investigated the effect of dosage of powder activated carbon (PAC) on hollow-fiber ultrafiltration membrane (HUM) performance. The results show that the stable operation time of hollow fiber ultrafiltration membranes lengthened and the rate of reduction of the flux was reduced when the PAC dosage was increased. The addition of PAC had no obvious effect on the resistance of membrane filtration. We conducted experiments to evaluate the effect of ultrafiltration of tiny pollution water in combination with PAC. When the parameters of operation and PAC dosage were appropriately regulated, the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH3-N) and ferric ions (Fe) reached 62%, 32% and 90%, respectively. When the PAC dosage was 200 mg/L, 100 mg/L and 150 mg/L, the highest removal rates were achieved under normal temperature and pressure. The effluent COD was less than 5.0 mg/L, NH3-N was less than 1.5 mg/L and Fe was less than 0.5 mg/L, achieving better results than the quality standard of surface water (GB3838-2002). The treated water can be discharged into the river or recirculated to utilities. The fouled membrane was cleaned by water rinsing, water/acid rinsing and water/alkali rinsing, with recovery ratios of 44%, 81% and 88%, respectively. The results of this study can serve as a foundation for the efficient utilization of water resources and the development of new water treatment technologies in Xinjiang.

Removal of algae and algogenic odor compounds via combined pre-chlorination and powdered activated carbon adsorption for source water pretreatment

This study investigated the combination sequence and time interval of chlorination and powdered activated carbon (PAC) adsorption for the control of algae inactivation, algogenic odor removal, and disinfection by-product (DBP) formation. Results indicated that pre-chlorination/post-PAC exhibited the highest algae removal efficiency in all sequential combinations of PAC adsorption and chlorination, while it had displayed slight effect on the removal of DBPs. The evaluated sequential combinations all had significant effect on the removal of odor. Nevertheless, prolonged time interval between chlorination and PAC adsorption exhibited enhanced control of algae and odor compounds in all experiments; with increasing time interval from 0 to 15 min in pre-chlorination/post-PAC process, the removal efficiency of Chl-a, algal cell viability, GSM, and 2-MIB increased by 46%, 15%, 15% and 23%, respectively. In the combined processes, the odor removal efficiency was positively correlated with PAC dosage but negatively correlated with chlorine dosage. Furthermore, PAC addition could effectively reduce the total DBP yields, especially the N-DBPs. This study can provide a better understanding of improving in-situ operation of the pre-chlorination and PAC dosing systems for source water pretreatment.

Adsorption-desorption of organic micropollutants by powdered activated carbon and coagulant in drinking water treatment

The addition of powdered activated carbon (PAC) and a coagulant during the coagulation-flocculation process is an easy and common option for tackling pollution peaks from organic micropollutants (OMPs) in the production of drinking water. However, the adsorption-desorption mechanisms during this process have not been thoroughly explored. Thus, this research aims to study the mechanisms involved and the impact of the operating conditions when PAC and coagulant are simultaneous used. A commercial PAC with a BET-specific surface area of 961 m2/g, and ferric chloride (FeCl3) were added simultaneously to three different waters spiked with 15 OMPs (pesticides and pharmaceuticals). Different parameters such as PAC and coagulant dosage, pH, contact time and the nature/content of the natural organic matter (NOM) were examined. Results showed that using coagulant + PAC reduced OMP adsorption efficiency, whereas increasing PAC dosage and extending contact time enhanced OMP removal efficiency. Furthermore, a high concentration of NOM affected micropollutant adsorption by competing for adsorption sites. This study highlights for the first time an unexpected phenomenon that significantly affects overall efficiency: i.e. OMPs adsorbed during the slow mixing step that desorbed during the sedimentation step. Desorption sometimes reduced by >30 % the overall efficiency of OMP removal. The parameters that affected efficiency loss were pH, contact time, NOM concentration, and PAC and FeCl3 dosage. Some operational adaptations could be considered regarding these parameters to avoid or reduce desorption, making the process more cost-effective.

Characterization of ultra-micropore powder activated carbon for use in removing regulated disinfection by-product precursors

This work investigated the adsorption kinetics and adsorption isotherms of ultra-micropore powder activated carbon (PAC) for the application of disinfection by-products precursors removal from Hatyai, Songkhla, and Bangkhen, Bangkok raw water sources in Thailand. Poly aluminum chloride (PACl) was used as the pre-treatment prior to the PAC adsorption. The remaining dissolved organic carbon (DOC) after PACl coagulation at a low dose of 20 mg/L resulted in a high concentration of trihalomethanes in the pre-treated water. Three PACs with a micropore area in the range of 1189 to 1544 m2/g were employed to adsorb the remaining DOC. An equilibrium contact time of roughly 60 min was determined. The three PACs have comparable adsorption rates, ranging from 2.4 to 3.3 mg/g-h. The adsorption capacities from 17.9 to 28.4 mg DOC/g PAC were found. These values increased when the number of micropores increased. A good linear relationship between micropore area and the adsorption capacities of DOC was determined. The micropore area was the important parameter for selecting PAC to remove DOC. Doubling the PACl dosage for the pre-treatment of the water samples before PAC adsorption decreased the PAC dosage in a range from 30 % to 43 %. The isotherms could be applied to other water sources that have correlated characteristics. Using ultra-micropore PAC after PACl coagulation with controlled equilibrium concentration in terms of DOC to <1.8 mg/L could reduce trihalomethanes to lower than the World Health Organization, the Japan, and the European Union drinking water standards.

Removal of saxitoxin and anatoxin-a by PAC in the presence and absence of microcystin-LR and/or cyanobacterial cells

Cyanobacteria can produce cyanotoxins such as microcystin-LR (MC), saxitoxin (STX), and anatoxin-a (ANTX-a) which are harmful to humans and other animals. Individual removal efficiencies of STX and ANTX-a by powdered activated carbon (PAC) was investigated, as well as when MC-LR and cyanobacteria were present. Experiments were conducted with distilled water and then source water, using the PAC dosages, rapid mix/flocculation mixing intensities and contact times of two drinking water treatment plants in northeast Ohio. At pH 8 and 9, STX removal was 47%-81% in distilled water and 46%-79% in source water, whereas it was 0-28% for pH 6 in distilled water and 31%-52% in source water. When 1.6 µg/L or 20 µg/L MC-LR was present with STX, STX removal was increased with PAC simultaneously removing 45%-65% of the 1.6 µg/L MC-LR and 25%-95% of the 20 µg/L MC-LR depending on the pH. ANTX-a removal at pH 6 was 29%-37% for distilled water and 80% for source water, whereas it was 10%-26% for pH 8 in distilled water and 28% for pH 9 in source water. The presence of cyanobacteria cells decreased ANTX-a removal by at least 18%. When 20 µg/L MC-LR was present with ANTX-a in source water, 59%-73% ANTX-a and 48%-77% of MC-LR was removed at pH 9 depending on the PAC dose. In general, a higher PAC dose led to higher cyanotoxin removals. This study also documented that multiple cyanotoxins can be effectively removed by PAC for water at pH's between 6 and 9.

Mechanism of powdered activated carbon enhancing caproate production

Caproate, produced by microbial chain elongation process, is potential to replace the diversified fossil-based products, contributing to carbon neutrality. However, its production performance is far from industrial application, so the cost-effective enhancement measures are highly needed. This study confirmed powdered activated carbon (PAC) has a significant effect on enhancing caproate production performance. The production, yield, and selectivity of caproate were improved by more than 1-fold by the optimized PAC dosage of 15 g/L, comparing with control. Mechanism investigation from a new visual angle showed that PAC accelerated ethanol oxidation to generate acetyl-CoA, and simultaneously boosted the efficiency of reverse β oxidation (RBO) by promoting the timely reaction of butyrate and acetyl-CoA to synthesis caproate. The addition of PAC also shifted the microbial community by enriching more caproate-producing bacteria but eliminating irrelevant ones. Furthermore, metagenomic analysis revealed that PAC effectively up-regulated the functional genes encoding key enzymes responsible for ethanol oxidation and RBO pathway, which was the root cause for the improved caproate production. This study presented the intrinsic insights into the mechanism of PAC promoting caproate generation, laying a foundation to the scale production of caproate.

Effect of adsorption and coagulation pretreatment sequence on ultrafiltration membrane fouling: Process study and targeted prediction

A novel combined pretreatment strategy, where the hydrophobicity of feedwater is reduced and the morphology of flocs is optimized by varying the sequence of powdered activated carbon (PAC) adsorption and coagulation, is applied to alleviate membrane fouling. To explore the effects of pretreatment sequence and the role of PAC on the membrane fouling, the combined pretreatments of adsorption followed by coagulation (A-C) and coagulation followed by adsorption (C-A) are investigated with various PAC dosages (10, 20, and 50 mg/L). The results reveal that since PAC directly participates in the growth of flocs as the core during A-C pretreatment, the A-C pretreatment is more conducive than the C-A pretreatment to form flocs with a larger size, higher strength, and smaller fractal dimension. Thus, the flocs can accumulate into a porous cake layer to improve the membrane permeability and fouling reversibility. Moreover, the irreversible fouling is highly linearly correlated SUVA values in the early ultrafiltration cycles (R2SUVA = 0.9536) and with the floc strength in the late cycles (R2Strength = 0.9348–0.9763). This finding can be used to make a targeted diagnosis of irreversible fouling in different cycles, providing valuable guidance for prolonging the service life of ultrafiltration membranes.

Powdered activated carbon full-scale addition to the activated sludge reactor of a municipal wastewater treatment plant: Pharmaceutical compounds control and overall impact on the process

Powdered activated carbon (PAC) dosing to a conventional activated sludge (AS) reactor is a low-investment option for controlling pharmaceutical compounds (PhCs) in municipal wastewater treatment, but its advantages and limitations in real operating environments are not fully assessed. A 3-week PAC-AS full-scale test was conducted in an oxidation ditch plant to assess PAC impact on effluent quality (PhCs, dissolved organic carbon (DOC) and other parameters), energy consumption, sludge production and costs. DOC-normalized PAC doses of 0.7–2.6 mgPAC/mgDOC significantly reduced recalcitrant PhC discharge (e.g. by 63–83 % for carbamazepine and 67–69 % for diclofenac), the higher dose yielding a more reliable effluent quality. Effluent quality for total phosphorus, colour, organic matter and transmittance was also enhanced and no interference with nitrification, oxidation-reduction potential or dissolved oxygen in the oxidation ditch was observed, resulting in no energy consumption increase. PAC had no impact on effluent turbidity and mixed liquor suspended solids settleability, showing a positive effect on dewatered sludge dry weight and ultimately a 7–9 % increase on final sludge production. After stopping PAC dosing, PAC remaining in the return sludge presented adsorption capacity for some PhCs until it was completely out of the system. Estimated costs for PAC addition to AS-reactor compare favourably with literature data for PAC and GAC post-treatment and similarly with post-ozonation.

Treatability of 18 taste and odor compounds using powdered activated carbon in drinking water utilities

AbstractTaste and odor (T&amp;O) compounds in source waters can enter drinking water utilities causing customer concerns about the water quality if not removed during treatment. While there has been extensive research on two common T&amp;O compounds, 2‐methylisoborneol (2‐MIB) and geosmin, research on non‐MIB/geosmin compounds has been limited. This study evaluated the treatability of 16 non‐MIB/geosmin compounds, 2‐MIB, and geosmin using powdered activated carbon (PAC). Four types of PAC were tested: two bituminous‐based, one lignite‐based, and one wood‐based PAC. Among the 18 compounds, PAC was effective for 15 compounds with at least 90% removal with typical PAC dosing, but was not suitable for dimethyl disulfide, ethyl methyl dioxolane, and cis‐3‐hexenol. The bituminous‐based PACs showed greater removal with higher adsorption rates compared to the lignite‐ and wood‐based PACs. The adsorption behavior of T&amp;O compounds varied based on their physical and chemical characteristics, for example, hydrophobicity, and nature of functional groups.

Removal of micropollutants using a membrane bioreactor coupled with powdered activated carbon — A statistical analysis approach

The occurrence of micropollutants in wastewater is largely documented as well as the environmental risk posed by their residues in the aquatic environment. Many investigations have been carried out and plan to study and improve their removal efficiency in existing wastewater treatment plants. At the same time, efforts are being made to develop new technologies or upgrade existing ones to increase the removal of a selection of micropollutants. Due to the great variability in their chemical and physical properties, it would be advisable to find representative compounds or identify the factors which most influence the removal mechanisms under specific conditions. This study analyses the removal efficiencies of a great number of micropollutants in wastewater treated in a membrane bioreactor coupled with powdered activated carbon (PAC), which was the subject of a review article we have recently published. The main operational parameters (i.e. PAC dosage, PAC retention time and sludge retention time) and compound physico-chemical properties (i.e. octanol-water distribution coefficient, charge and molecular weight) were first selected on the basis of a dedicated screening step and then an attempt was carried out to clarify their influence on the removal of micropollutants from wastewater during its treatment. To this end, a statistical analysis, mainly based on exploratory methods (cluster analysis and principal component analysis) and regression analysis, was carried out to compare and discuss the different results published in the scientific literature included in the cited review article. It emerged, that, based on the collected dataset, micropollutant charge and LogDow seem to play the most important role in the removal mechanisms occurring in MBR coupled with PAC.

Development and application of a predictive model for advanced wastewater treatment by adsorption onto powdered activated carbon

This work presents a mathematical method to describe adsorptive removal of organic micropollutants (OMPs) and dissolved organic carbon (DOC) from wastewater treatment plant effluent using powdered activated carbon (PAC). The developed model is based on the tracer model (TRM) as a modification of the ideal adsorbed solution theory (IAST) and uses the fictive component approach for organic matter fractionation. It enables the simulation of multisolute adsorption of OMPs considering competitive adsorption behavior of organic background compounds (OBC). Adsorption equilibrium data for DOC and seven different OMPs as well as kinetic data for DOC were derived from batch experiments performed with secondary clarifier effluent of two municipal wastewater treatment plants (WWTP 1 and WWTP 2). Two conventional PAC products were investigated as well as one biogenic PAC (BioPAC). Verification and validation of the fitting results based on operational data of WWTP 1 showed promising prediction of DOC and OMP removal efficiency. However, when applied to a static simulation of a full-scale PAC adsorption stage, the model overpredicts the removal efficiency of sulfamethoxazole and candesartan. For benzotriazole, carbamazepine or hydrochlorothiazide, predicted removal falls below operational removal. The model can be used to predict removals of good adsorbable OMPs but fails to accurately predict the removals of OMPs with variable or low PAC affinity. The model was further used for a dynamic simulation of DOC and diclofenac effluent concentrations of a full-scale PAC adsorption stage with varying operating conditions and influent concentrations. Results show that the hydraulic retention time (HRT) in the contact reactor is a decisive operational parameter for OMP removal efficiency besides the PAC dose.