Empty Bed Research Articles

Study of 3D-Printed Pressure Release Nozzle for Microbubble Formation in Full-Scale Dissolved Air Flotation (DAF)

Pressure-release equipment for the formation of microbubbles is an important part of any DAF system. In this study, 3D printing was employed to produce new nozzles, followed by testing to find the optimum pressure and flowrate. The flowrate through the nozzle affected both the empty bed residence time (EBRT) of the saturator and also the nucleation of bubbles. With the increase of flow rate, the total number of bubbles was seen to increase. This is a significant observation meaning that the enhanced precipitation of bubbles outweighs the reduced EBRT. This fact can improve equipment sizing and reduce CAPEX. Meanwhile, DAF is a technology that can help extend membrane life and reduce operational issues in seawater reverse osmosis (SWRO). So for further validation, a full-scale DAF was built and tested for SWRO pretreatment on the coast of the Persian Gulf. The system was tested with/without coagulation as well as with/without filtration media embedded inside the DAF tank. The results showed that the use of coagulation alongside DAF reduced the turbidity by more than 60% while using a DAF with embedded filtration could reduce the turbidity to less than 1 NTU. In comparison to common media filters, the proposed setup showed better performance.

Sorption Characteristics and Removal Efficiency of Organic Micropollutants in Drinking Water Using Granular Activated Carbon (GAC) in Pilot-Scale and Full-Scale Tests

Granulated active carbon (GAC) is commonly used as a chemical barrier for the removal of organic micropollutants (OMPs) in drinking water treatment plants (DWTPs). However, little is known about the impact of dissolved organic carbon (DOC) and its long-term performance with regard to OMP removal efficiency. This study examined the performance of two GAC types (Norit 830W and Filtrasorb 400) in the removal of OMPs and DOC from natural lake water, in pilot-scale and full-scale tests run for almost one year. Potential early warning indicators of the exhaustion of GAC sorption capacity were also evaluated. The seven OMPs investigated (carbamazepine, lamotrigine, cetirizine, fexofenadine, oxazepam, fluconazole and N,N-diethyl-meta-toluamide (DEET)) all showed decreasing removal efficiencies after ~20,000 bed volumes (BV) in the pilot-scale Norit 830W and Filtrasorb 400 columns. However, columns with an 18-min empty bed contact time (EBCT) showed better performances than columns with 6-min EBCT. DEET was the OMP adsorbed most weakly. We found that DOC concentrations, methylene blue sorption kinetics, UV and fluorescence did not sufficiently explain the OMP breakthrough in the GAC columns. We concluded that carbamazepine, lamotrigine and fexofenadine can be used as indicators of decreasing GAC adsorption performance, due to their later breakthrough. Based on the results, UV and fluorescence removal could be used for the early detection of declining DOC removal, and online solid-phase extraction (SPE)–liquid chromatography–tandem mass spectrometry (SPE-LC-MS/MS) could be used for the early detection of OMPs in drinking water.

Performance of an air membrane bioreactor for methanol removal under steady and transient state conditions

The main aim of this study was to evaluate the performance of an air membrane bioreactor (aMBR) for the treatment of gas-phase methanol. A laboratory-scale hollow fiber aMBR was operated for 150 days, at inlet methanol concentrations varying between 2 and 30 g m−3 and at empty bed residence times (EBRT) of 30, 10 and 5 s. Under steady-state conditions, a maximum methanol removal efficiency (RE) of 98% was obtained at an EBRT of 30 s and a decrease in RE of methanol was observed at lower EBRTs. On increasing the inlet loading rate, some portion of gas-phase MeOH was stripped into the liquid phase due to its solubility in water. Under transient conditions, the MeOH removal efficiency dropped from an average value of 95%–90% after 5 h of 10-fold shock load and dropped from an average value of 95%–88% under 5-fold increase in shock load. During transient-state tests, the aMBR performed well under different upset loading conditions and a drop in RE of ∼ 5–10% was observed. However, the aMBR performance was restored within 1–2 days when pre-shock conditions were restored. The results from microbial structure analysis revealed a big shift of the dominant methanol degrader, from Candida boidinii strain TBRC 217 to Xanthobacter sp. and Fusicolla sp., respectively.

Impact of algal organic matter on the performance, cyanotoxin removal, and biofilms of biologically-active filtration systems

The occurrence of harmful algal blooms dominated by toxic cyanobacteria has induced continuous loadings of algal organic matter (AOM) and toxins in drinking water treatment plants. However, the impact of AOM on the active biofilms and microbial community structures of biologically-active filtration (BAF), which directly affects the contaminant removal, is not well understood. In this study, we systematically examined the effects of AOM on BAF performance and bacterial biofilm formation over 240 days, tracing the removal of specific AOM components, a cyanotoxin [microcystin-LR (MC-LR)], and microbial community responses. The component analysis (excitation and emission matrix analysis) results for AOM revealed that terrestrial humic-like substances showed the highest removal among all the identified components and were strongly correlated to MC-LR removal. In addition, reduced empty bed contact time and deactivation of biofilms significantly decreased BAF performances for both AOM and MC-LR. The active biofilm, bacterial community structure, and mlrA gene (involved in microcystin degradation) abundance demonstrated that bacterial biofilm composition responded to AOM and MC-LR, in which Rhodocyclaceae, Saprospiraceae, and Comamonadaceae were dominant. In addition, MC-LR biodegradation appeared to be more active at the top than at the bottom layer in BAF. Overall, this study provides deeper insights into the role of biofilms and filter operation on the fate of AOM and MC-LR in BAF.

Effective enzyme activity: A proposed monitoring methodology for biofiltration systems with or without ozone

“Effective Enzyme Activity”, or simply “Effective Activity”, is proposed as a biofiltration monitoring tool which combines enzyme activity with empty bed contact time (EBCT) to quantify biodegradation potential. The primary objective of this study was to evaluate the applicability of the Effective Activity concept for predicting water quality in biofiltration systems. This pilot-scale study evaluated eight different biofilter configurations in order to quantify impacts associated with filter media (anthracite/sand or granular activated carbon), pre-treatment (settled water with or without ozonation) and operating conditions (15- and 30-min EBCT, and backwash with or without chlorine). Microbial characterization included biomass concentration, as measured by adenosine triphosphate (ATP), in addition to esterase and phosphatase activity. Water quality parameters included dissolved organic carbon (DOC), trihalomethane (THM) formation potential (FP), haloacetic acid (HAA) FP, haloacetonitrile (HAN) FP, iodinated DBP FP (THMs and HAAs) and inorganic nutrients (phosphorus and nitrogen). Results confirmed the benefits to treated water quality associated with the application of an ozone residual of 0.5 mg/L, utilization of GAC filter media, eliminating chlorinated backwash, and extending EBCT. This study demonstrated a good relationship between effective esterase activity and reductions in DOC and THM FP, including those systems which incorporate pre-ozonation. As such, this study showed that Effective Activity may be appropriate for relating biomass characterization to treated water quality and highlights the importance of quantifying biomass activity in addition to quantity.

Application of Enhanced BAC Process for Improving Drinking Water Treatment Efficiency

Objectives:In this study, we compared the properties of the attached biofilm with the ability to remove biodegradable dissolved organic carbon (BDOC) in the conventional BAC (biologically activated carbon) process and the enhanced BAC process with phosphorus and hydrogen peroxide added. The enhanced BAC process was designed to increase the operational efficiency of the old O<sub>3</sub>/BAC process by evaluating the applicability of large-scale water treatment facilities located downstream of the Nakdong River.Methods:The granular activated carbon which was used for 2 years in the O<sub>3</sub>/BAC process in the water treatment plant located downstream of the Nakdong River was used in this experiment. During the experiment period, the ozone dosage was fixed at 1 mg･O<sub>3</sub>/mg･DOC. Four acrylic columns with an inner diameter of 20 cm and a height of 250 cm were prepared. Empty bed contact time (EBCT) was fixed at 20 minutes and backwash was performed once a week. The four BAC columns are conventional BAC (control-BAC), enhanced BAC with hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>+BAC), enhanced BAC with phosphorus (PO<sub>4</sub>-P+BAC), and enhanced BAC with phosphorus and hydrogen peroxide together (PO<sub>4</sub>-P+H<sub>2</sub>O<sub>2</sub>+BAC). In the case of enhanced BAC with PO<sub>4</sub>-P added, PO<sub>4</sub>-P was added with a concentration of 0.010 mg/L in the influent, and in BAC with H<sub>2</sub>O<sub>2</sub>, H<sub>2</sub>O<sub>2</sub> was added with a concentration of 1 mg/L to the influent.Results and Discussion:As a result of evaluating the recovery ability of the damaged biofilm, there was no difference in the biomass recovery rate in the H<sub>2</sub>O<sub>2</sub>+BAC compared to the control-BAC, but the biomass was rapidly recovered in the PO<sub>4</sub>-P+BAC. Considered the biomass and activity of the attached biofilm after the ability to remove organic substances reached a steady state, the biomass and activity in the entire filter layer of the PO<sub>4</sub>-P+BAC increased by 20 to 86% and 7 to 14%, respectively, compared to the control-BAC. In the H<sub>2</sub>O<sub>2</sub>+BAC, only the activity increased by 3~11% and In the PO<sub>4</sub>-P+H<sub>2</sub>O<sub>2</sub>+BAC, biomass and activity were high, about 27 to 87% and 8 to 20%, respectively. In the H<sub>2</sub>O<sub>2</sub>+BAC, the BDOC removal rate was higher than the control-BAC by 20%, and in the PO<sub>4</sub>-P+BAC, the BDOC removal rate increased by more than 100%. Detached total cell counts (TCC) in the control-BAC effluent was 41.7×10<sup>6</sup> cells/mL on average, and in the H<sub>2</sub>O<sub>2</sub>+BAC, TCC was reduced by 49% compared to control-BAC and decreased by 67% and 85% in the PO<sub>4</sub>-P+BAC and the PO<sub>4</sub>-P+H<sub>2</sub>O<sub>2</sub>+BAC effluent. It means the biofilm of the enhanced BAC process was evaluated more stably than control-BAC.Conclusions:The biomass and the activity of the attached biofilm in the BAC process, are one of the important factors that determine the ability to remove contaminants. The enhanced BAC process combined PO<sub>4</sub>-P with H<sub>2</sub>O<sub>2</sub> was very effective in enhancing the biomass and the activity of the attached biofilm. The PO<sub>4</sub>-P added enhanced BAC was more effective in terms of biomass, BDOC removal rate, and biofilm stability than the H<sub>2</sub>O<sub>2</sub> added enhanced BAC. The enhanced BAC combined PO<sub>4</sub>-P with H<sub>2</sub>O<sub>2</sub> showed a slight increase additional efficiency compared to the PO<sub>4</sub>-P added BAC.

Biogas valorization via continuous polyhydroxybutyrate production by Methylocystis hirsuta in a bubble column bioreactor

Creating additional value out of biogas during waste treatment has become a priority in past years. Biogas bioconversion into valuable bioproducts such as biopolymers has emerged as a promising strategy. This work assessed the operational feasibility of a bubble column bioreactor (BCB) implemented with gas recirculation and inoculated with a polyhydroxybutyrate (PHB)-producing strain using biogas as substrate. The BCB was initially operated at empty bed residence times (EBRTs) ranging from 30 to 120 min and gas recirculation ratios (R) from 0 to 30 to assess the gas-to-liquid mass transfer and bioconversion of CH4. Subsequently, the BCB was continuously operated at a R of 30 and an EBRT of 60 min under excess of nitrogen and nitrogen feast-famine cycles of 24 h:24 h to trigger PHB synthesis. Gas recirculation played a major role in CH4 gas–liquid transfer, providing almost fourfold higher CH4 elimination capacities (~41 g CH4 m−3 h−1) at the highest R and EBRT of 60 min. The long-term operation under N excess conditions entailed nitrite accumulation (induced by O2 limiting conditions) and concurrent methanotrophic activity inhibition above ~60 mg N-NO2− L−1. Adjusting the N-NO3− supply to match microbial N demand successfully prevented nitrite accumulation. Finally, the N feast-famine 24 h:24 h strategy supported a stable CH4 conversion with a removal efficiency of 70% along with a continuous PHB production, which yielded PHB accumulations of 14.5 ± 2.9% (mg PHB mg−1 total suspended solids × 100). These outcomes represent the first step towards the integration of biogas biorefineries into conventional anaerobic digestion plants.

The effect of water temperature on the removal of 2-methylisoborneol and geosmin by preloaded granular activated carbon

Granular activated carbon (GAC) is widely used by drinking water treatment plants in the Great Lakes region to control 2-methylisoborneol (MIB) and geosmin associated with summertime algal blooms. Recently, however, taste and odour events are being detected in the winter, but there is limited information in the literature about the effect of temperature on GAC performance. In this study, batch isotherm experiments were conducted at 4 °C, 10 °C, and 20 °C to evaluate the temperature impact on adsorption thermodynamics. Pilot-scale column tests were then performed at the same temperatures to evaluate the temperature effect on overall removal, including both thermodynamics and kinetics. The pore and surface diffusion model (PSDM) was applied to fit the experimental data of the pilot-scale column tests, which allowed the kinetic parameters to be determined at each temperature. The isotherm results showed that water temperature did not have a significant effect on the equilibrium adsorption capacity (i.e., the thermodynamics) for MIB and geosmin under the conditions tested, but the pilot tests showed an increased removal of MIB and geosmin by 20–30% at 20 °C compared to the lower temperatures. This demonstrates that water temperature has more impact on kinetics than thermodynamics. Numerical simulations showed that the overall external mass transfer coefficient, Kf’, had the greatest impact on breakthrough. An exponential equation was proposed to correlate temperature and Kf’, and it could be incorporated into a site-specific PSDM to predict the removals of MIB and geosmin in GAC contactors at different temperatures. The model could then be used by a utility, for example, to predict the required increase in empty bed contact time needed to control taste and odour in the winter to the same extent as in the summer.

Removal of pharmaceuticals from nitrified urine by adsorption on granular activated carbon

Nitrification and distillation of urine allow for the recovery of all nutrients in a highly concentrated fertilizer solution. However, pharmaceuticals excreted with urine are only partially removed during these two process steps. For a sustainable and safe application, more extensive removal of pharmaceuticals is necessary. To enhance the pharmaceutical removal, which is already occurring during urine storage, nitrification and distillation, an adsorption column with granular activated carbon (GAC) can be included in the treatment train. We executed a pilot-scale study to investigate the adsorption of eleven indicator pharmaceuticals on GAC. During 74 days, we treated roughly 1000 L of pre-filtered and nitrified urine spiked with pharmaceuticals in two flow-through GAC columns filled with different grain sizes. We compared the performance of these columns by calculating the number of treated bed volumes until breakthrough and carbon usage rates. The eleven spiked pharmaceuticals were candesartan, carbamazepine, clarithromycin, diclofenac, emtricitabine, hydrochlorothiazide, irbesartan, metoprolol, N4-acetylsulfamethoxazole, sulfamethoxazole and trimethoprim. At the shortest empty bed contact time (EBCT) of 25 min, immediate breakthrough was observed in both columns shortly after the start of the experiments. Strong competition by natural organic material (NOM) could have caused the low pharmaceutical removal at the EBCT of 25 min. At EBCTs of 70, 92 and 115 min, more than 660 bed volumes could be treated until breakthrough in the column with fine GAC. The earliest breakthrough was observed for candesartan and clarithromycin. On coarse GAC, only half the number of bed volumes could be treated until breakthrough compared to fine GAC. The probable reason for the later breakthrough with fine GAC is the smaller intraparticle diffusive path length. DOC and UV absorbance measurements at 265 nm indicated that both parameters can be used as indicators for the breakthrough of pharmaceuticals. In contrast to pharmaceuticals and DOC, the nutrient compounds ammonium, nitrate, phosphate, potassium and sulfate were not removed significantly. A comparison with literature values suggests that the amount of GAC needed to remove pharmaceuticals from human excreta could be reduced by nearly two orders of magnitude, if urine were treated on site instead of being discharged and treated in a centralized wastewater treatment plant.

Evaluation of Dissolved Organic Matter Removal Characteristics in GAC Adsorption Process in Drinking Water Treatment Process using LC-OCD-OND

Objectives:In this study, we used liquid chromatograph-organic carbon detector-organic nitrogen detector (LC-OCD-OND) to evaluate adsorption and breakthrough characteristics of NOM fractions (biopolymers (BP), humic substances (HS), building blocks (BB) and low molecular weight organic substances (LMW-O)) according to the various characteristics of the different materials of granular activated carbons (GACs).Methods:Breakthrough characteristics, adsorption capacity and partition coefficients were evaluated by NOM fractions (BP, HS, BB, and LMW-O) using a lab-scale GAC adsorption column filled with coal-, coconut- and wood-based GAC. The GAC column test was operated with 10 minutes empty bed contact time (EBCT). The pore characteristics of each GAC were evaluated using an automated gas sorption analyzer (Autosorb iQ3, Quantachrome, USA) and the concentrations of NOM fractions in the influent and effluent were analyzed using chromatography LC-OCD-OND (Model 8, DOC-Labor, Germany).Results and Discussion:NOM adsorption capacity was evaluated for different materials of laboratory scale GAC adsorption column test. To study the adsorption behavior of individual NOM fractions according to the operation time, NOM was fractionated into BP, HS, BB and LMW-O by LC-OCD-OND, and the individual NOM fractions were quantified. Higher MW like BP was not adsorbed to GAC, in contrast, HS, BB, and LMW-O were well removed during the initial operation period, the concentrations in the effluent gradually increased as increase the operation period until reaching to the pseudo steady-state. Poor removal of BP in GAC adsorption may be a result of blocking the pores with large MW BP and hinder the access to the pores. However, in the case of HS, BB, and LMW-O, as the molecular size decreased, these organic matters easily access to the pores inside of GAC. It was confirmed through the partition coefficient that the adsorption capacity of these NOM fractions increased in proportion to the MW. In addition, in order to achieve a high NOM removal efficiency in the GAC adsorption process, not only the specific surface area, pore volume, and pore width of the GAC must be large, but also the pH<sub>zpc</sub> must be higher than the neutral pH level.Conclusions:In order to achieve a high NOM removal efficiency in the GAC adsorption process, not only the specific surface area, pore volume, and pore width of the GAC must be large, but also the pH<sub>zpc</sub> must be higher than the neutral pH level. In addition, in the NOM fractions, BP were not adsorbed to GAC, while the adsorption capacity of the remaining NOM fractions increased as the MW of the NOM fractions decreased. LMW-O was the most adsorbed, followed by BB, HS and BP. BP and HS play an important role in the membrane fouling that are introduced a lot into domestic and foreign water treatment plants. This study showed that the BP was not removed by the adsorption mechanism of the GAC process. In addition, HS was adsorbed and removed at the beginning of the operation, but the adsorption capacity of HS decreased rapidly as the operation period increased compared to other NOM fractions. Therefore, the GAC adsorption process is not expected to be an effective pre-treatment technology for reducing membrane foulants. Previous studies showed that the yields of DBPs (µmol･DBP/µmol･C) in the high MW humic and low MW non-humic fractions are similar. Therefore, it is suggested that the GAC adsorption process is more effective for DBP precursor control in water containing a larger percentage of LMW NOM.

Removal of gaseous tetrahydrofuran via a three-phase airlift bioreactor loaded with immobilized cells of GFP-tagged Pseudomonas oleovorans GDT4

Tetrahydrofuran (THF) is a common highly toxic cyclic aliphatic ether that frequently exists in waste gases. Removal of gaseous THF is a serious issue with important environmental ramifications. A novel three-phase airlift bioreactor (TPAB) loaded with immobilized cells was developed for efficient THF removal from gas streams. An effective THF-degrading transformant, Pseudomonas oleovorans GDT4, which contains the pTn-Mod-OTc-gfp plasmid and was tagged with a green fluorescent protein (GFP), was constructed. Continuous treatment of THF-containing waste gases was succeeded by the GFP-labelled cells immobilized with calcium alginate and activated carbon fiber in the TPAB for 60 days with >90% removal efficiency. The number of fluorescent cells in the beads reached 1.7 × 1011 cells·g−1 of bead on day 10, accounting for 83.3% of the total number of cells. The amount further increased to 3.0 × 1011 cells·g−1 of bead on day 40. However, it decreased to 2.5 × 1011 cells·g−1 of bead with a substantial increase in biomass in the liquid because of cell leakage and hydraulic shock. PCR-DGGE revealed that P. oleovorans was the dominant microorganism throughout the entire operation. The maximum elimination capacity was affected by empty bed residence time (EBRT). The capacity was only 25.9 g m−3·h−1 at EBRT of 80 s, whereas it reached 37.8 g m−3·h−1 at EBRT of 140 s. This work provides an alternative method for full-scale removal of gaseous THF and presents a useful tool for determining the biomass of a specific degrader in immobilized beads.

Performance and fungal diversity of bio-trickling filters packed with composite media of polydimethylsiloxane and foam ceramics for hydrophobic VOC removal

Bio-trickling filters (BTFs) can be used for the treatment of hydrophobic VOC-contaminated air. To improve treatment performance, two novel polydimethylsiloxane (PDMS) packing media were produced and trialled in BTFs inoculated with Cladophialophora fungus. The BTF packed with PDMS/foam ceramic composite filler showed superior performance: rapid start-up within 3 days, rapid restart within 7 days after starvation for 1 month, a maximum toluene elimination capacity (EC) of 264.4 g m−3·h−1 at an empty bed residence time of 10 s, and a pressure drop that was controllable by adjusting the nutrient supply regime. High-throughput sequencing was used to analyse the effect of spatial position on the microbial communities in the top and bottom filler layers. Meanwhile, by investigating the EC in the vertical direction of the BTF, spatial heterogeneity in the fungal degradation of a hydrophobic VOC was preliminarily explored.

Interactions and microbial variations in a biotrickling filter treating low concentrations of hydrogen sulfide and ammonia

A lab-scale biotrickling filter (BTF) packed with porcelain Rasching ring and ceramsite was applied for co-treating of low concentrations of hydrogen sulfide (H2S) and ammonia (NH3), as major pollutants typically found in e.g., intensive livestock production facilities. In this study, the outlet gas concentrations of H2S and NH3 were used for indicators if the treated gas reached odor-free condition. Overall, excellent removal efficiencies were obtained for both H2S and NH3 in the BTF during Stage I (H2S alone) and Stage II (H2S and NH3). Specifically, the H2S outlet concentration was below the detection limit (∼3.6 ppbv) and the NH3 outlet concentration was less than 0.4 ppmv when the inlet concentrations of H2S and NH3 were around 1.8 ppmv and 35.3 ppmv, respectively. In this case, the running empty bed residence time was 10.2 s. During Stage II, the outlet H2S concentration was decreased significantly when the inlet NH3 concentration was increased, likely due to the influence by pH. Meanwhile, the outlet nitrous oxide (N2O) concentration was kept low (<2% NH3) during the experiment, suggesting a proper operation of the BTF. After the inlet gas shifted from H2S alone at Stage I to H2S and NH3 at Stage II, the main sulfur-oxidizing bacteria (SOB) species in the BTF switched from Acidithiobacillus to Thiobacillus.

Effect of hydrophobic fumed silica addition on a biofilter for pentane removal using SIFT-MS

Biofiltration is a typical air pollution control process for the treatment of volatile organic compounds (VOCs). Mass transfer of hydrophobic VOCs to the biofilm is limited which leads to low removal efficiency (RE). Aiming to enhance the transport of hydrophobic VOCs, the effect of hydrophobic fumed silica (HFS) addition to a biofilter (BF) for pentane removal was studied in this paper. The effect of HFS on pentane removal was evaluated by daily RE measurements and periodical headspace gas pentane pulse injections using SIFT-MS as analysis apparatus. The BF was operated during more than 100 days at an empty bed residence time (EBRT) of 120 s reaching an elimination capacity (EC) up to 93.8 g pentane m−3 h−1. At the last stage of the study, when a higher nutrient pulse and HFS to a concentration of 1.5% w/w wet were added, the BF showed better EC (46.3 ± 14.9 g pentane m−3 h−1; RE = 96.2%) compared to the previous stages (28.3 ± 4.4 g pentane m−3 h−1; RE = 68.3%). This overall performance improvement was in line with the short peak perturbation experiments carried out during the operational time which demonstrated, by net retention time (NRT) determination, to be a fast and reliable tool to gain insights into the behaviour of pollutants inside the BF and its state. Pentane demonstrated to have larger interactions with the packing material when HFS was added. NRT/EBRT ratio variated along the whole operational time, being larger at the last stage.

Tuning the crosslink structure of cationic hydrogel for enhanced chromium(VI) removal: The covalent and electrostatic co-crosslinked effects and adsorption mechanism

Elevated chromium(VI) (Cr(IV)) concentrations in drinking water or ground water can pose a public health concern. In this study, layered double hydroxides-isethionate (LDH-ise) assisted covalent and electrostatic co-crosslinked cationic hydrogel (CH-LDH-ise) was prepared as a potential adsorbent for Cr(VI) removal from aqueous solution. The scanning electron microscopy and X-ray diffraction results indicated that the LDH-ise sheets were exfoliated and crosslinked with the 3-(Acryloylamino) propyltrimethylaminium chloride (APTMACL) polymer chains. The adsorption of Cr(VI) onto the CH-LDH-ise was highly pH-dependent, and the removal efficiency by CH-LDH-ise composites was much higher than the CH (no crosslinker). The adsorption kinetic followed a pseudo-second-order, and reached equilibrium within 2 h. The corresponding maximum Cr(VI) adsorption capacity of CH-LDH-ise was 408.4 mg/g at the equilibrium concentration of 364.4 mg/L. The enhanced adsorption of Cr(VI) was also achieved in the presence of competing anions (including Cl−, NO3−, SO42−, HCO3−, SiO44−, and HA). Moreover, the in situ regeneration/recycle results implied the column adsorption capacity of CH-LDH-ise was 2250 bed volumes as the concentration of Cr(VI) decreased from 2.5 mg/L to 0.1 mg/L (The US drinking water standard for total chromium) at empty bed contact time = 6 min, and slightly decreased in the second recycle. The combination analysis of in situ Fourier transform infrared, in situ Raman, X-ray photoelectron spectra, and electron paramagnetic resonance revealed that the Cr(VI) capture mechanism was dominated by the electrostatic interactions and hydrogen bonding effect - the sources of the –N+(CH3)3 and –NH groups in CH-LDH-ise, respectively.

Dynamic performance of a fungal biofilter packed with perlite for the abatement of hexane polluted gas streams using SIFT-MS and packing characterization with advanced X-ray spectroscopy

The use of Fusarium solani fungi in an expanded perlite packed biofilter was investigated for the treatment of a hexane polluted waste gas stream using selected ion flow tube mass spectrometry (SIFT-MS). The latter analytical technique proved to be of utmost importance to evaluate the performance of the biofilter at high time resolution (seconds) under various transient conditions, analogous to industrial situations.The biofilter was operational for 277 days with inlet loads varying between 1 and 14 g m−3 h−1 and applying an empty bed residence time of 116 s. The results showed a positive behaviour of the biofilter against different types of disruptions such as: (i) changes in the relative humidity of the inlet gas, (ii) stopping the carbon supply for 1, 5 and 10 days, (iii) varying the inlet hexane concentration (step increases and intermittent pulses) and (iv) limiting the availability of nutrients.X-ray imaging (both conventional 2D μCT and X-ray fluorescence, XRF) was applied for the first time on biofilter media in order to get insight in the internal structure of expanded perlite and to visualise the biomass growth. The latter in combination with online porosity measurements using SIFT-MS provides fundamental information regarding the biofiltration process.

The locally resolved filtration process for removal of phosphorus and micropollutants with GAC

Flocculation filtration in deep bed is one of the techniques to achieve advanced phosphorus removal. In addition to particle retention and phosphorus removal, granular activated carbon may serve as a filtration medium but also as an adsorption bed for micropollutants. The aim of the study was to investigate the simultaneous elimination of total phosphorus (TP) and selected micropollutants. In the first part of the study the target phosphorus threshold of 0.2 mg/L TP in the filtrate was achieved in a dual-bed media filter with anthracite and sand up to filter velocities of 16 m/h. By using a detailed sampling protocol and headloss curves, the influence of different operation modes on retention could be identified. Afterwards, the filter media were replaced by three types of GAC. In all filter beds substantial differences were found in the mode and efficiency of particle retention. This led to different filter run times, which is one of the main parameters for efficient and economical filter operation. Specific curves were generated for the different bed materials showing the dependency of filter run time on the specific load of suspended solids. Elimination of micropollutants in a GAC 4 × 8 mesh filter bed was low due to coarse grains and low empty bed contact time (EBCT). The application of GAC 8 × 14 mesh filter bed resulted in high elimination of most micropollutants. These results can be applied when choosing filter bed material. This may involve a compromise between filter run time and adsorption of micropollutants.

Biotrickling Filtration of Volatile Organic Compounds in Vented Gases from Surface-Coating Operations

The study used a bench-scale biotrickling filter packed with mixed plastic chips with specific surface area of 610±50 m2/m3 to test its performance for the removal of volatile organic compounds (VOCs) vented from paint-spraying operations. A paint containing ethyl acetate, butyl acetate, toluene, and xylenes as main solvents was used. The influent total hydrocarbon (THC) concentrations were in the range of 27–234 parts per million (ppm) (expressed as methane equivalent), and empty bed retention time (EBRTs) for the gas flowing through the empty bed space were 4.8–11.4 s in the experimental period of 125 days. Results show that a maximum THC removal capacity of 86 g as methane/m3 h with an EBRT of 4.8–8.2 s was obtained and the value implies that it is possible to effectively eliminate VOCs with the short EBRT compared with other related studies. Ethyl acetate and butyl acetate were more easily absorbed and removed by microbial films than toluene and xylenes because of the much lower volatility and higher water affinity of the former two compounds.

Effect of presence of hydrophilic volatile organic compounds on removal of hydrophobic n-hexane in biotrickling filters

Hydrophilic VOCs (volatile organic compounds) were applied to explore their positive influence on the elimination of the single hydrophobic VOC in biotrickling filters (BTFs). Comparison experiments were carried to evaluate the effect of 4-methyl-2-pentanone and toluene on the performance of BTFs for n-hexane removal. The results showed that the existence of 4-methyl-2-pentanone improved the removal performance of BTFs at short gas empty bed contact time (EBRT) of 15 s and low temperature of 10 °C. The degradation of n-hexane in the presence of 4-methyl-2-pentanone was slightly enhanced with a loading ratio of 6:1. When the mixing ratio was greater than 4, toluene significantly promoted the biodegradation of n-hexane with toluene loading rate less than 10 g m−3 h−1. Additionally, The promotion effect was not only reflected in the contents of proteins and polysaccharides, but also in the growth rates of microorganisms in biofilms. This work discussed the detailed effect between n-hexane and hydrophilic VOCs in BTFs, which would contribute to develop a more economical method to improve the removal performance of hydrophobic VOCs in BTFs.

Preliminary Investigation of CO2 Sequestration by Chlorella sorokiniana TH01 in Single and Sequential Photobioreactors

Increasing accumulation of CO2 in the atmosphere mainly caused by fossil fuels combustion of human activities have resulted in adverse global warming. Therefore, searching for treatment methods for effective utilization of CO2 have received a great attention worldwide. Among various methods (e.g., adsorption, absorption, storage, membrane technologies, etc.) have been developed and applied, the sequestration of CO2 using microalgae has recently emerged as an alternatively sustainable approach. In this work, a green microalgal strain Chlorella sorokiniana TH01 was used to investigate its capability in sequestration of CO2 in laboratory scale. Results indicated that the C. sorokiniana TH01 grew well under a wide range of CO2 concentration from 0.04% to 20% with maximum growth was achieved under CO2 aeration of 15%. In a single photobioreactor (PBR) with 10 min empty bed residence time (EBRT), the C. sorokiniana TH01 only achieved CO2 fixation efficiency of 6.33% under continuous aeration of 15% CO2. Increasing number of PBRs to 15 and connected in a sequence enhanced mean CO2 fixation efficiency up to 82.64%. Moreover, the CO2 fixation efficiency was stable in the range of 78.67 to 91.34% in 10 following days of the cultivation. Removal efficiency of NO3--N and PO43--P reached 82.54 – 90.25% and 95.33 – 98.02%, respectively. Our trial data demonstrated that the C. sorokiniana TH01 strain is a promising microalgal for further research in simultaneous CO2 mitigation via CO2 sequestration from flue gas as well as nutrients recycling from wastewaters.&#x0D; Keywords: Carbon dioxide, C. sorokiniana TH01, Photobioreactors, Sequestration, Nutrients removal.