Zeolite Beads Research Articles

Adsorption‐Based Thermal Energy Storage Using Zeolites for Mobile Heat Transfer

ABSTRACTThe utilization of the water–zeolite pair as an adsorbate–adsorbent system has garnered significant attention in the realm of thermochemical energy storage, offering great potential for various applications. Despite promising results in laboratory settings, widespread implementation of this technology has yet to be realized. Recent advancements in mobile thermal energy storage (m‐TES) employing thermochemical materials have opened new avenues for enhancing the practicality and cost‐effectiveness of solar thermal energy harnessing and waste heat recovery. This experimental study investigates the feasibility of storing thermal energy in zeolites, charged externally to the heat recovery reactor, and discusses the potential applications of externally charged zeolites for m‐TES over short distances, shedding light on their practicality and significance in advancing the field of mobile thermal energy storage. Our findings reveal that zeolites charged at 200°C and subsequently stored outside the discharging unit exhibit an impressive energy storage density (ESD) exceeding 110 kWhth/m3 under conditions of 0.45 m/s air velocity and 60% relative humidity during zeolite discharging. These ESD values are comparable to previously reported figures in the literature. Moreover, ESD values of 30.6 kWhth/m3 were achieved by charging zeolite beads contained within packed transportable tubes constructed from stainless‐steel mesh.

An experimental comparison of thermal energy storage in directly and indirectly radiated adsorbent beds integrated with solar thermal collectors

AbstractAdsorbents heated using solar energy can be used to achieve thermal energy storage and sorption refrigeration with low environmental impacts. This research compares two different methods of heating adsorbents with solar energy to store thermal energy: (1) by exposing the adsorbents to incident light transmitted through a solar collector window, and (2) by heating a highly absorbing solar collector cover, and then transferring the heat from this solar absorber to adsorbents located beneath it. To carry out this comparison experiments are conducted for three cases of adsorbent beds using zeolite 13X and water as the adsorbent‐adsorbate pair. In the first case, the top of the adsorbent bed is a polycarbonate sheet, and the zeolites are heated directly by solar‐simulated light transmitted through this sheet. In the second case, a blackened aluminum sheet is placed beneath the polycarbonate sheet to generate heat by absorbing incident light. For the third case, the blackened aluminum absorber is placed directly on top of the zeolite beads and the absorber is isolated from the walls of the reactor to avoid heat losses. The outcomes reveal an energy storage density (ESD) of 43.6 kWh/m3 (63.4 Wh/kg) when light is directly incident onto the zeolite 13X and an ESD of 33.3 kWh/m3 (48.4 Wh/kg) when light is incident onto a blackened absorber plate that transfers heat to Zeolite beads residing beneath it. However, ESD values were improved to 48.9 kWh/m3 (71.0 Wh/kg) when the blackened absorber plate was thermally insulated from the walls of the adsorbent bed. These results demonstrate the importance of an optimal absorber arrangement in enhancing the adsorption process for the purpose of elevating energy storage densities.

Actual NOX and SOX removal rates in the atmospheric environment of concrete permeable blocks containing TiO2 powders, coconut shell powders, and zeolite beads

This study examined actual nitrogen oxide (NOX) and sulfur oxide (SOX) removal rates of concrete permeable blocks in the atmospheric environment. To give the concrete permeable block a NOX and SOX removal function, TiO2 submicron particle or coconut shell powder was embedded in the surface layer, and zeolite bead was embedded in the base layer. Using an actual factory production line, concrete permeable block specimens were prepared by adding TiO2 submicron particles and coconut shell powder to the surface layer of the concrete permeable block. The prepared concrete permeable block specimens were placed in a parking lot, and then NOX and SOX removal rates were directly measured for 6 months on the concrete permeable block specimens placed in the parking lot. Test results showed that the clear day removal rates of NOX and SOX for the concrete permeable block specimens embedded with TiO2 submicron particles during the day was 84% and 70%, respectively. Compared to the concrete permeable blocks embedded with coconut shell powder, the NOx removal rate of the specimens embedded with TiO2 submicron particles was 1.45 times higher, while the SOx removal rate was similar. However, during cloudy days and nights, the NOX removal rate of the concrete permeable block specimens embedded with TiO2 submicron particles was zero. On the other hand, NOX and SOX removal rates of the concrete permeable block specimens embedded with coconut shell powder and zeolite bead were maintained at approximately 51% and 77% for 6 months, respectively, in the atmospheric environment regardless of weather and day light conditions. Consequently, the coconut shell powder added to the surface layer of the concrete permeable block is a practically promising material in reducing the NOX in the atmospheric environment regardless of weather and day light conditions.

Storability of Different Hermetic Bags on Seed Quality Attributes of Maize in Khumaltar, Lalitpur

To evaluate the comparative superiority of exotic hermetic seed storage bags versus locally available bags supplemented with or without desiccants for on-farm seed storage of smallholders, an experiment was conducted in the National Seed Science and Technology Research Centre (NSSTRC) of Nepal Agricultural Research Council (NARC) from May 2017 to June 2019. Maize seed variety Manakamana-3 was allocated in 8 treatments based on storage devices with three replications in a completely randomized design (CRD). The 98% initial germinating seed was stored in eight different storage containers viz., S1, Super grain bag; S2, PICS bag; S3, Safe Grain bag; S4, 400-gauge plastic bag; S5, 400-gauge plastic double liner; S6, 400 gauge + metal bin; S7, 400 gauge + Zeolite beads; S8, 400 gauge + roasted wheat. All seed attributing data were taken in tri-monthly intervals for two and half years. In the first year, all seven treatments were found statistically at par results for germination above 85% by meeting the Nepalese maize seed standard except 400-gauze plastic bag-single liner. However, significant differences were seen in each treatment in the second year. Results on germination of storage structures with desiccants viz., 400 gauge + Zeolite beads, and 400 gauge + roasted wheat were found superior to any other storage structures such as PICS bag, Super grain bag, Safe grain bag, 400 gauge + metal bin, & 400-gauge plastic double liner. Whereas, the single liner of a 400-gauge plastic bag was found non-suitable and found vulnerable to fungal infestation in long-run storage in ambient storage conditions. Hence, it was concluded that the locally fabricated seed storage bags provided equal results to exotic hermetic bags for one season seed storage in Mid-hill, humid and sub-temperate condition of Nepal and hence, found economical modified atmospheric storage (MAS) option for small holder farmers.

A Novel Process for the Preparation of Binder‐Free Zeolite Beads (Lta‐5a) via Photopolymerization Applied in Co2 Adsorption Field

AbstractThe increasing CO2 concentration in the atmosphere has a severe influence on both the environment and human health, resulting in global warming. According to the high adsorption capacity for CO2 removal, zeolites play an important role for CO2 capture and sequestration. However, its powdery form limits their use in adsorption applications. When binding agents are used, the zeolite porosity is partially occluded that compromises the CO2 adsorption capacity severely. How to prepare binder‐free zeolite beads with a certain structure strength and how to keep the high surface area and porosity are a great challenge. In this work, LTA‐5A beads composites (80 wt.%) are prepared via cationic photopolymerization and then calcination is performed to remove organic part to obtain LTA‐5A beads with different sizes (<1.0 mm, 1.0–2.0 mm, and 2.0–3.0 mm). These beads (0.1 g) are characterized by good mechanical strength without any binder (partial bead fragmentation under 200 g‐load) with a preserved zeolite porosity. This method allows to exploit the zeolite beads reaching a high specific surface area (586 688 m2 g−1) and good CO2 adsorption capacity (4.5‐4.9 mmol g−1). These values are higher than those of commercial LTA‐5A beads (515 m2 g−1 and 3.8 mmol g−1, respectively), which is in agreement with their binder‐free structure.

Structural and compositional variation of zeolite 13X in lithium sorption experiments using synthetic solutions and geothermal brine

This study provides insight into the potential application of zeolite 13X powder and beads for direct lithium extraction. The impact of variable stirring time, pH and temperature is investigated. The major ion-exchange process is found to be Li+ vs. Na+ or H+, reaching a maximum sorption capacity of 20.3 mg/g using 13X powder whereas only 8.6 mg/g Li is sorbed to 13X beads. Equilibrium between sorbent and fluid is reached within 1 min and 9 h contact time for powder and beads, respectively. The temperature effect on Li sorption is negligible, whereas pH adjustment to more acidic conditions decreases the Li sorption capacity by up to 68% compared to non-adjusted conditions. Chemical data fits well with changes in crystal parameters confirming the data's significance. Different sorption processes like physisorption, ion exchange of Na+ and H+ with Li+, and different Li sorption sites on zeolite 13X sorbent are indicated. Solutions of different concentrations have been tested for desorption. Lithium recovery from the previously loaded sorbent reaches 94–100%. Aiming at a direct Li extraction technique from geothermal brines in the future, this study shows that zeolite 13X is a promising sorbent although challenges regarding higher selectivity for Ca, K, Mn, Ba, and As need to be resolved for its application in a high saline environment.

Silver Loaded Zeolite Beads: Synthesis, Characterizations and its Antibacterial Study via Spot Diffusion Technique

Due to wide applications of antibiotics, the multidrug resistance in microorganisms are a serious concern. There is urgent need to develop suitable methods to produce antibacterial materials in large quantity and develop materials which have antibacterial properties. In this regard, we worked to prepare a composite of silver loaded zeolite and studied its applicability as antibacterial material. Zeolite beads loaded with different concentrations of silver was prepared and characterized using various techniques like SEM, FTIR, BET, AFM etc. For studying its antibacterial property, E. coli (gram negative) and S. aureus (Gram positive) microorganisms were used as model system. In antibacterial study, it was observed that silver loaded zeolite has antibacterial property against both E. coli (gram negative) and S. aureus (Gram positive) microorganisms.

Effect of Desiccant Beads on Groundnut Bruchid, Caryedon serratus (Olivier) Infestation in Stored Groundnut

The purpose of this study was to evaluate the effect of desiccant beads on the stored groundnut against groundnut bruchid, Caryedon serratus Olivier. The experiment was carried out in the storage laboratory of Department of Entomology, OUAT, Bhubaneswar during 2019-20 in Completely Randomised Design. Groundnut pods(100 grams) in each treatment were mixed with 2 types of beads viz., zeolite beads and sodium aluminium silicate in four different ratios (1:1, 1:0.9, 1:0.8, 1:0.7) along with an untreated control and the observations on the fecundity, adult emergence, weight loss(%), moisture content, germination(%) were recorded during 6 months of storage at an interval of 60 days. Among the different treatments, the pods mixed with zeolite beads in 1:1 ratio was found to be the most superior treatment after 2, 4 and 6 months with the lowest fecundity (14.67, 25.67 and 34.33 eggs, respectively) and adult emergence (10.00, 17.33 and 25.00 adults, respectively). However, all the treatment dosages were found significantly superior over control which recorded maximum weight loss due to bruchid infestation. It was also noted that there was reduction in moisture content of the groundnut kernels with the increase of storage period with desiccant beads as these beads absorbed the moisture from the groundnut and created unsuitable environment for insect development and infestation. These beads did not show any adverse effects on the germination of groundnut.

Binder‐free Zeolite Beta Beads with Hierarchical Porosity: Synthesis and Application as Heterogeneous Catalysts for Anisole Acylation

AbstractThree zeolites (H‐Beta, H‐ZSM‐5 and H‐Y) were synthesized in the form of binder‐free macroscopic beads (d=215–840 μm) using a hydrothermal method employing anion‐exchange resin beads as hard template. The beads obtained after removal of the hard template by calcination consisted of crystalline zeolite domains connected with each other to form a hierarchical porous network in which the zeolitic micropores are accessible through meso‐ and macropores, as proven by characterization with XRD, N2 physisorption, SEM, and TEM. The composition, the nature and amount of acid sites and the degree of hydrophobicity of these beads were investigated by means of XRF, solid‐state NMR, pyridine‐FTIR and TGA. The zeolite beads were tested as heterogeneous catalysts in the Friedel‐Crafts acylation of anisole with acetic anhydride to produce para‐methoxyacetophenone. H‐Beta‐Beads displayed the best catalytic performance with 95 % conversion of acetic anhydride and 76 % yield of para‐methoxyacetophenone in a batch reactor test (90 °C, 6 h). Next, the catalytic performance of H‐Beta‐Beads was compared in both batch and continuous‐flow mode to extrudates prepared by mixing zeolite Beta powder with either kaolin or bentonite binders. H‐Beta‐Beads outperformed the extrudates in batch‐mode reactions and could be reused in multiple runs without discernible loss of activity. In the continuous‐flow test, H‐Beta‐Beads demonstrated higher average activity but deactivated more rapidly than the extrudates.

Construction of high performance binder-free zeolite monolith

Compared to conventional spheres, strips, and granules, structural adsorbents offer shaping of the adsorbent materials. In this work, we report a straightforward procedure to shape binder-free zeolite monolith (BF-ZM). During the synthesis, hydroxypropyl methylcellulose was applied as a binder, and the zeolite precursor material halloysite nanotubes and Y zeolites were mixed to produce the initial zeolite monolith. The binder was removed by high-temperature calcination to gain preliminary mechanical strength, followed by hydrothermal crystallization to convert the binder into Y zeolites to obtain a 100% pure Y zeolite structure. The as-synthesized BF-ZM exhibits excellent mechanical properties, showing negligible powdering after 1.34 × 105 cycles of accelerated pressurization/depressurization test; in comparison, ordinary packed columns using zeolite beads suffered from 3.51% loss due to powdering. This result indicates that BF-ZM is favorable for filling large pressure swing adsorption columns and can significantly alleviate the issue of adsorbent chalking and slabbing caused by the reciprocal pressure swing of the gas flow. The BF-ZM also achieved a high CO2 adsorption capacity of 6.4 mmol·g−1 at 1.2 bar and 273 K, superior to commercial Y zeolite pellets. The results of the breakthrough experiments showed a CO2 adsorption capacity of 4 mmol·g−1 at 333 K and 1.25 bar before the permeation started. The selectivities (CO2/N2:15/85) of BF-ZM have been calculated using the IAST method, showing 74 excellent selectivity at 333 K and 1 bar. This study provides a straightforward approach to the design and fabrication of high-strength binder-free adsorbents for large-scale industrial gas separations.

Experimental investigation of dehumidification and regeneration of zeolite coated energy exchanger

Zeolite desiccant particles are well known for their strong affinity to adsorb water vapor molecules; however, they require significant regeneration energy to be created. This paper presents an experimental study of the adsorption and regeneration processes of a monolayer zeolite for indoor dehumidification to the 13X zeolite beads with a 4 × 8 mesh bead size and a pore opening 10 A⁰ were used as this monolayer. An experimental investigation was conducted to determine the effects of the relative humidity, temperature, and air flow rate on the adsorption and regeneration processes. The results show the effectiveness of the monolayer coating method and the relative humidity significantly affects the adsorption process, and that the airflow rate surrounding and through the zeolite beads increases the adsorption and desorption of the water vapor molecules. In the absence of the meniscus radius formation due to the monolayer arrangement prevents external condensation. With an airflow rate of Re = 1773, the full adsorption process at a relative humidity of 99% was obtained within 37 min; meanwhile, the regeneration process proceeded at 100 °C within 66 min. The adsorption time was reduced by 27% and 43% as the Reynold number increases to 2586 and 3325, respectively. Likewise, the effectiveness of the regeneration time is decreased by 0.07% and 14% within the same Reynold number increases. Results obtained from this research can be used to guide the future development of polymer-coated energy exchangers.

Stable metal–organic framework fixing within zeolite beads for effectively static and continuous flow degradation of tetracycline by peroxymonosulfate activation

Heterogeneous peroxymonosulfate (PMS) based advanced oxidation process has been proven as a promising method for tetracycline removal from water. Among the heterogeneous catalysts, Co based metal–organic framework (ZIF-67) is a good candidate to activate PMS in the aforementioned advanced oxidation system. However, their high metal ion leaching and fine powder form limit their practical application. Herein, zeolite bead-supported ZIF-67 was prepared through the Co ion-exchange and organic ligand reaction, which is simple, cost-efficient and recyclable. The obtained zeolite@ZIF-67 composites were employed for PMS activation to degrade tetracycline in the water. The uniform ZIF-67 loading could provide abundant catalytic sites and the results demonstrated that 93.7% of tetracycline (50 mg/L) could be removed in 60 min with high recycling stability. Intriguingly, due to the strong metal-support interaction, the Co ion leaching from the composite beads during the degradation reaction was much lower compared to pure ZIF-67 particles. In addition, zeolite@ZIF-67 composites with the microsphere form could be easily packed into the bed column to effectively remove tetracycline in a continuous flow process. The degradable mechanism and degradation pathway were comprehensively investigated by quenching experiments, electron paramagnetic resonance spectra, X-ray photoelectron spectroscopy and liquid chromatography-mass spectroscopy. Overall, our work provides a novel PMS heterogeneous catalyst based on macroscopic supported MOF composites for efficient tetracycline removal.

Immobilization of microorganisms in activated zeolite beads and alkaline pretreated straws for ammonium-nitrogen removal from urban river water

AbstractThe non-treated wastewater from residential areas contains high concentrations of ammonium-nitrogen (NH4+-N). When discharged into the drainage water system, it deteriorates the water quality in urban rivers. This study used two types of materials to form eco-bags, using activated zeolite bead (AZB) and alkaline pretreated straw (APS), in geotextile bags for easy recovery and reuse. The AZB and APS provided the breeding habitat for the microorganisms that promoted biofilm formation on their surface. The immobilization of engineered denitrification microorganisms facilitated the removal of NH4+-N from the urban river water. The NH4+-N removal in the AZB and APS bags were in the range of 64–73%, and 56–61%, respectively, while the chemical oxygen demand (COD) removal in the AZB and APS bags ranged from 33–36%, and 30–31%, respectively. In addition, as evident from DNA and microbial community analysis, the microorganisms demonstrated a greater proclivity to grow and proliferate on the surface of AZB and APS and improved the water quality of urban rivers.

Bimetallic Zeolite Beta Beads with Hierarchical Porosity as Brønsted-Lewis Solid Acid Catalysts for the Synthesis of Methyl Lactate

Bimetallic zeolite Beta in bead format and containing Al sites with Brønsted acid behavior and Sn, Zr or Hf sites with Lewis acid character, were prepared using a two-step synthetic route. First, zeolite Beta in the format of macroscopic beads (400 to 840 μm) with hierarchical porosity (micropores accessed through meso- and macropores in the range of 30 to 150 nm) were synthesized by hydrothermal crystallization in the presence of anion-exchange resin beads as hard template and further converted into their H-form. Next, the zeolite beads were partially dealuminated using different concentrations of HNO3 (i.e., 1.8 or 7.2 M), followed by grafting with one of the above-mentioned metals (Sn, Zr or Hf) to introduce Lewis acid sites. These bimetallic zeolites were tested as heterogeneous catalysts in the conversion of dihydroxyacetone (DHA) to methyl lactate (ML). The Sn-containing zeolite Beta beads treated by 1.8 M HNO3 and grafted with 27 mmol of SnCl4 (Sn-deAl-1.8-Beta-B) demonstrated the best catalytic activity among the prepared bimetallic zeolite beads, with 99% selectivity and 90% yield of ML after 6 h at 90 °C. This catalyst was also tested in combination with Au-Pd nanoparticles supported on functionalized carbon nanotubes (CNTs) as multifunctional catalytic system for the conversion of glycerol to ML, achieving 29% conversion of glycerol and 67% selectivity towards ML after 4.5 h at 140 °C under 30 bar air. The catalytic results were rationalized by means of a thorough characterization of the zeolitic beads with a combination of techniques (XRD, N2-physisorption, SEM, XRF, TEM, UV-vis spectroscopy and pyridine-FT-IR).

Impact of Xylose on Dynamics of Water Diffusion in Mesoporous Zeolites Measured by NMR.

Zeolites are known to be effective catalysts in biomass converting processes. Understanding the mesoporous structure and dynamics within it during such reactions is important in effectively utilizing them. Nuclear magnetic resonance (NMR) T2 relaxation and diffusion measurements, using a high-power radio frequency probe, are shown to characterize the dynamics of water in mesoporous commercially made 5A zeolite beads before and after the introduction of xylose. Xylose is the starting point in the dehydration into furfural. The results indicate xylose slightly enhances rotational mobility while it decreases translational motion through altering the permeability, K, throughout the porous structure. The measurements show xylose inhibits pure water from relocating into larger pores within the zeolite beads where it eventually is expelled from the bead itself.

Synthesis of LTA zeolite beads using alum sludge and silica rich wastes

This study successfully recycled alum sludge with either lithium slag or bottle glass to make high purity zeolite LTA beads. The basic synthesis approach was to fuse the waste material with sodium hydroxide then complete hydrothermal crystallization. Separate fusion of individual wastes promoted zeolite LTA formation compared to combined fusion. Preferred synthesis conditions were: 10 Na2O:Al2O3:2.5 SiO2:300 H2O; hydrothermal temperature = 80 °C; time = 5 h. Zeolite LTA purity was between 80 and 85 wt% from the two waste combinations. Use of pseudoboehmite and carboxymethyl cellulose favoured granulation/extrusion/spheronization of zeolite LTA powder. However, the beading process decreased calcium exchange capacity (CEC) from 99.5 to 37 mg Ca2+/g for alum sludge + lithium slag and from 64.5 to 37 mg Ca2+/g for alum sludge + waste glass. Additionally, when using 20 wt% pseudo-boehmite as a binder the ion-exchange equilibrium time increased from 60 to 300 min. The importance of not only making zeolite powder from waste materials but also to extend studies to shaped forms was evident. It is recommended that future studies should also focus on making extrudates or beads as these are the forms used commercially.

Influence of desiccants on seed quality attributes of wheat crop under hermetic storage

An investigation was undertaken with main objectives to know the effect of desiccants on seed quality parameters of crop seeds during storage and to assess the benefit cost ratio of storage method (economics) in wheat with initial seed moisture content of 12.3 %, was carried out at Department of Seed Science and Technology, College of Agriculture, UAS, Dharwad. Quantity of desiccants stored per kilogram of seed in wheat seeds is 0.37 kg for zeolite beads, one kg for silica gel, calcium carbonate and control without desiccant in airtight container. The experiment was laid out in Completely Randomized Design with four treatments and five replications. Seed stored with zeolite beads recorded the highest germination (88.8 %) which was on par with silica gel (87.2 %) at the end of storage period. Lower seed moisture and hundred seed weight was observed in the seeds stored with silica gel at the end of storage period. Higher shoot length, root length, seedling vigour-I and seedling dry weight was observed in seeds stored with zeolite beads which was on par with Silica gel at the end of storage period. compared to control. Therefore, it can be concluded that the zeolite beads can safely be used for seed drying without impairment in seed quality.

Designing a simple volumetric apparatus for measuring gas adsorption equilibria and kinetics of sorption. Application and validation for CO2, CH4 and N2 adsorption in binder-free beads of 4A zeolite

The screening of adsorbents (zeolites, MOFs, ACs, etc) requires the measurement of adsorption equilibria and kinetics at the milligram scale. In this regard, a volumetric apparatus (constant volume variable pressure – batch adsorber) has been developed for studying adsorption equilibria and kinetics of sorption. Its validation was accomplished by studying the adsorption equilibria of carbon dioxide (CO2), methane (CH4) and nitrogen (N2) and the kinetics of sorption of CO2 on commercial binder-free 4A zeolite. The data collected has an acceptable agreement with already published values by a gravimetric and breakthrough flow technique. The isotherms were modeled using Sips model from low pressure till 8 bar at 303, 343 and 373 K. The sorption kinetics of CO2 was measured from the uptake rate experiments and fitted with a solid-film linear-driving-force model (LDF). It was observed that the LDF mass transfer coefficients increase with pressure and temperature. Finally, the statistical analysis of the data was performed by Response Surface Methodology (RSM) to determine the interactions among process variables such as temperature and pressure in the respective gas adsorption equilibria data.

Acetotrophic sulfate-reducing consortia develop active biofilms on zeolite and glass beads in batch cultures at initial pH 3.

Sulfate-reducing microbial communities remain a suitable option for the remediation of acid mine drainage using several types of carrier materials and appropriate reactor configurations. However, acetate prevails as a product derived from the incomplete oxidation of most organic substrates by sulfate reducers, limiting the efficiency of the whole process. An established sulfate-reducing consortium, able to degrade acetate at initial acidic pH (3.0), was used to develop biofilms over granular activated carbon (GAC), glass beads, and zeolite as carrier materials. In batch assays using glycerol, biofilms successfully formed on zeolite, glass beads, and GAC with sulfide production rates of 0.32, 0.26, and 0.14 mmol H2S/L·d, respectively, but only with glass beads and zeolite, acetate was degraded completely. The planktonic and biofilm communities were determined by the 16S rRNA gene analysis to evaluate the microbial selectivity of the carrier materials. In total, 46 OTUs (family level) composed the microbial communities. Ruminococcaceae and Clostridiaceae families were present in zeolite and glass beads, whereas Peptococcaceae was mostly enriched on zeolite and Desulfovibrionaceae on glass beads. The most abundant sulfate reducer in the biofilm of zeolite was Desulfotomaculum sp., while Desulfatirhabdium sp. abounded in the planktonic community. With glass beads, Desulfovibrio sp. dominated the biofilm and the planktonic communities. Our results indicate that both materials (glass beads and zeolite) selected different key sulfate-reducing microorganisms able to oxidize glycerol completely at initial acidic pH, which is relevant for a future application of the consortium in continuous bioreactors to treat acidic streams. KEY POINTS: • Complete consumption of glycerol and acetate at acidic pH by sulfate reduction. • Glass beads and zeolite are suitable materials to form sulfate-reducing biofilms. • Acetotrophic sulfate-reducing bacteria attached to zeolite preferably.

Performance evaluation of anoxic–oxic–anoxic processes in illuminated biofilm reactor (AOA-IBR) treating septic tank effluent

Abstract This study was conducted to evaluate the treatment performance of the anoxic–oxic–anoxic processes in illuminated biofilm reactor (AOA-IBR) in removing organics and nitrogen contained in septic tank effluent. The 27 L of the AOA-IBR was illuminated with red light-emitting diode (LED) lamps (peak wavelength of 635 nm, intensity of 100 μmol/(m2s)). Three types of biofilm media, namely ball ring®, plastic sheets and zeolite beads, were placed in the anoxic, oxic and anoxic zones, respectively, of the reactor to support the growth of microalgal–bacterial biofilm. The AOA-IBR was continuously fed with septic tank effluent and operated at hydraulic retention times (HRTs) of 24, 48 and 72 h. The experimental results found the increases in chemical oxygen demand (COD), total nitrogen (TN) and ammonia nitrogen (NH4-N) removal efficiencies with increasing HRTs in which the HRT of 72 h resulted in 78.6, 72.8 and 90.6% removals of COD, TN and NH4-N, respectively. The effluent quality of the AOA-IBR could meet the ISO 30500 effluent standards for Non-Sewered Sanitation Systems. The predominant microalgal biofilm species was observed to be Oscillatoria sp., while Proteobacteria was the predominant bacterial phylum found in the biofilm growing in the reactor. The above results suggested the applicability of the AOA-IBR in improving septic tank treatment performance which should result in better water pollution control.