Hybrid Bioreactor Research Articles

Treatment of gaseous toluene in an anoxic hybrid bioreactor: Optimization using response surface methodology

This study focuses on treating gaseous toluene emissions from chemical and petrochemical industries using an anoxic hybrid bioreactor (AnHBR) and optimizing the process using response surface methodology (RSM). By varying the gas flow rate (0.05–0.25 LPM) of toluene, the gas residence time (GRT) within the AnHBR ranged from 0.53 to 2.67 h, resulting in an inlet loading rate (ILR) between 0.36 to 14.33 g/m3 h. Simultaneously, the hydraulic retention time (HRT) of the liquid feed was varied from 24 to 72 h in the AnHBR. The operating parameters were varied to determine the optimal combination to achieve the maximum toluene removal, which remained above 96% throughout the operation. At the optimized combinations (flow rate: 0.15 LPM, GRT: 0.89 h, and HRT: 48 h) in AnHBR, toluene removal reached ∼99%, with end products generated consisting of 1.8% CO2 and 92.9% N2 gas. Metagenomics analysis revealed a dominance of toluene degraders (∼38%), highlighting their potential to degrade toluene in the AnHBR. The RSM enhanced toluene treatment in the AnHBR, demonstrating robustness in handling high pollutant loads and its potential for industrial applications.

Linking the shifts in the metabolically active microbiota in a UASB and hybrid anaerobic-aerobic bioreactor for swine wastewater treatment

Due to the high concentration of pollutants, swine wastewater needs to be treated prior to disposal. The combination of anaerobic and aerobic technologies in one hybrid system allows to obtain higher removal efficiencies compared to those achieved via conventional biological treatment, and the performance of a hybrid system depends on the microbial community in the bioreactor. Here, we evaluated the community assembly of an anaerobic-aerobic hybrid reactor for swine wastewater treatment. Sequencing of partial 16S rRNA coding genes was performed using Illumina from DNA and retrotranscribed RNA templates (cDNA) extracted from samples from both sections of the hybrid system and from a UASB bioreactor fed with the same swine wastewater influent. Proteobacteria and Firmicutes were the dominant phyla and play a key role in anaerobic fermentation, followed by Methanosaeta and Methanobacterium. Several differences were found in the relative abundances of some genera between the DNA and cDNA samples, indicating an increase in the diversity of the metabolically active community, highlighting Chlorobaculum, Cladimonas, Turicibacter and Clostridium senso stricto. Nitrifying bacteria were more abundant in the hybrid bioreactor. Beta diversity analysis revealed that the microbial community structure significantly differed among the samples (p < 0.05) and between both anaerobic treatments. The main predicted metabolic pathways were the biosynthesis of amino acids and the formation of antibiotics. Also, the metabolism of C5-branched dibasic acid, Vit B5 and CoA, exhibited an important relationship with the main nitrogen-removing microorganisms. The anaerobic-aerobic hybrid bioreactor showed a higher ammonia removal rate compared to the conventional UASB system. However, further research and adjustments are needed to completely remove nitrogen from wastewater.

Production of Acetic Acid and Whey Protein from Cheese Whey in a Hybrid Reactor under Response Surface Optimized Conditions

Experimental investigations were carried out in a membrane-integrated hybrid bio-reactor system for direct and continuous production of acetic acid and whey protein from waste cheese whey under response surface optimized conditions. In this novel scheme of fermentative production, using Acetobactor aceti, the major operating parameters such as temperature, concentrations of yeast extract, and glucose were optimized. Under the set of optimum operating conditions (temperature of 300 °C, pH of 6.0, yeast extract concentration of 15 g/L and glucose concentration of 44 g/ L), more than 95% pure acetic acid was produced with a concentration of 84.1 g/L, yield of 97.4% and productivity of 7.2 g/(L· h). Simultaneous production of whey protein powder makes the process more economically viable. Findings indicate that acetic acid could be produced directly and continuously from waste cheese whey with high productivity, yield and purity under response surface optimized conditions, in a simple, flexible, energy-saving and environmentally benign membrane-integrated hybrid reactor system.

Odor reduction using hydrogen sulfide-removing bacteria in sludge filtration systems: Ferrous-oxidizing bacteria and sulfur-oxidizing bacteria

The preconditioning of digested sludge in sludge filtration systems produces hydrogen sulfide (H2S), a major odor-causing source. This study evaluated the effects of adding H2S-removing bacteria to sludge-filtration systems. Ferrous-oxidizing bacteria (FOB) and sulfur-oxidizing bacteria (SOB) were mass-cultivated in a hybrid bioreactor equipped with an internal circulation system. In this bioreactor, FOB and SOB effectively removed >99% of H2S; however, the acidic conditions created by adding a coagulant during digested sludge preconditioning were more favorable for FOB than for SOB. In batch tests, SOB and FOB removed 94 ± 1.1% and 99 ± 0.1% of H2S, respectively; therefore, digested sludge preconditioning proved more suitable for FOB activity than SOB activity. The results revealed that the optimal FOB addition ratio was 0.2%, validated using a pilot filtration system. Moreover, the 57.5 ± 2.9ppm H2S generated in the sludge preconditioning step was reduced to 0.01 ± 0.01ppm after adding 0.2% FOB. Therefore, the results of this study will be useful because they provide a process for biologically removing odor-causing sources without affecting the dewatering efficiency of the filtration system.

Hybrid bioreactor built-in with fixed bio-carriers for denitrification with low C/N ratio: Hydrodynamic optimization and microbial divergence

Hydrodynamics played an important role in the design and operation of bioreactors for wastewater treatment. In this work, an up-flow anaerobic hybrid bioreactor built-in with fixed bio-carriers was designed and optimized using computational fluid dynamics (CFD) simulation. The results indicated that the flow regime involving with vortex and dead zone was greatly affected by the positions of water inlet and bio-carrier modules. The ideal hydraulic features were obtained when the water inlet and bio-carrier modules located 9 cm and 60 cm above the bottom of reactor. Using the optimum hybrid system for nitrogen removal from wastewater with low carbon-to-nitrogen ratio (C/N = 3), the denitrification efficiency could reach 80.9 ± 0.4%. Illumina sequencing of 16S rRNA gene amplicons revealed that the microbial community divergence occurred among the biofilm on bio-carrier, the suspended sludge phase and the inoculum. Especially, the relative abundance of denitrifying genera Denitratisoma in the biofilm of bio-carrier reaches 5.73%, 6.2 times higher than that in the suspended sludge, implying the imbedded bio-carrier was conductive to enrich the specific denitrifiers to polish the denitrification performance with low carbon source. This work provided an effective method for the design optimization of bioreactor based on CFD simulation, and developed a hybrid reactor with fixed bio-carrier for nitrogen removal from wastewater with low C/N ratio.

Removal of Persistent Acid Pharmaceuticals by a Biological-Photocatalytic Sequential Process: Clofibric Acid, Diclofenac, and Indomethacin

The removal of three acid pharmaceuticals—clofibric acid (CLA), diclofenac (DCL), and indomethacin (IND)—by a biological-photocatalytic sequential system was studied. These pharmaceutical active compounds (PhACs) are considered to persist in the environment and have been found in water and sewage, producing adverse effects on the aquatic environment. For the biological process, in batch experiments, a fixed bed bioreactor and activated sludge (hybrid bioreactor), under aerobic conditions, was used as pretreatment. The pretreated effluent was exposed to a photocatalytic process employing TiO2 nanotubular films (NTF-TiO2) with the following characteristics: an internal diameter of 112 nm, a wall thickness of 26 nm, nanotube length of 15 µm, a roughness factor of 1840 points, and an anatase-rutile crystalline structure. In the hybrid bioreactor, 39% IND and 50% ACL and DCL were removed. The biological-photocatalysis sequential system achieved the degradation of up to 90% of the initial concentrations of the three acid pharmaceuticals studied. This approach appears to be a viable alternative for the treatment of these non-biodegradable effluents.

The performance of a Multi-Stage Hybrid Reactor to treat real wastewater: Benzophenone and Diethyl Phthalate removal

One of the consequences of the increasing diversity of new chemical compounds used in industrialized products is the release of these compounds as micropollutants (MPs) in the environment around the world, particularly in aqueous matrices. Benzophenone (BP) and Diethyl Phthalate (DEP), two MPs of environmental concern due to their potential toxicity are widely used and found with considerable concentrations mostly in wastewaters. Information about the efficiency of biological treatment in removing DEP from the wastewater is scarce and until recently, there was no information on the removal of BP. Due to the risks these substances pose to the human and environmental health there is a worldwide demand for the improvement of biological treatment plants with focus on the removal of these and other MPs, since conventional Wastewater Treatment Plants (WWTP) have very limited capacity to remove them and advanced treatment steps (e.g.: ozonation, photocatalysis, ultrafiltration.) increases substantially the treatment costs. A promising biological treatment approach for the removal of MPs combines fixed and suspended biomasses in the same reactor (hybrid reactors) and includes multiple compartments with different redox conditions. The objective of this study was to assess the performance of a new Multi-Stage Hybrid Reactor, focusing on the removal of Benzophenone (BP) and Diethylphthalate (DEP). The pilot system has seven units (anaerobic, anoxic 1, aerobic, anoxic 2, re-aeration and 2 sedimentation tanks) and it was installed at a large Municipal WWTP in Rio to treat real domestic wastewater. The total volume was 400 L and 50% of the aerobic tank (120 L) was filled with carriers (support media). The reactor’s efficiency was evaluated during two periods: (a) one with predominantly suspended biomass and (b) another one with predominantly fixed biomass in the aerobic tank. The highly variable composition of the affluent, affecting the organic load, caused fluctuations in the treatment performance. Even though, multi-stage hybrid bioreactor was able to remove up to 69.6% of BP and up to 74.5% of DEP, being the highest removal efficiencies achieved during the period when the aerobic tank had predominantly fixed biomass.

A mobile-organic biofilm process for wastewater treatment.

The mobile-organic biofilm (MOB) process includes mobile biofilms and their retention screens with a bioreactor and liquid and solid separation. The MOB process is inexpensive and easy to integrate with wastewater treatment (WWT) processes, and it provides for high-rate WWT in biofilm or hybrid bioreactors. This paper describes three modes of MOB process operation. The first mode of operation, Mode I, has a mobile-biofilm reactor and a mobile-biofilm retention screen that is downstream of and external to a bioreactor and upstream of liquid and solid separation. Modes II and III have a hybrid (i.e., mobile biofilms and accumulated suspended biomass) bioreactor and liquid and solid separation. Mode II includes a mobile-biofilm retention screen that is downstream of and external to a hybrid bioreactor and upstream of liquid and solid separation. Mode III includes mobile-biofilm retention screening that is external to a hybrid bioreactor and liquid and solid separation, receives waste solids, and relies on environmental conditions and wastewater characteristics that are favorable for aerobic-granular sludge formation. This paper presents a mechanistic approach to design and evaluate MOB processes and describes MOB process: (1) modes of operation, (2) design and analysis methodology, (3) process and mechanical design criteria, (4) mathematical modeling, (5) design equations, and (6) mobile-biofilm settling characteristics and return. A mathematical model was applied to describe a fixed bioreactor volume and secondary-clarifier area with Modes I, II, and III. The mathematical modeling identified key differences between MOB process modes of operation, which are described in this paper. PRACTITIONER POINTS: MOB is a municipal and industrial wastewater treatment (WWT) process that reduces bioreactor and liquid and solids separation process volumes. It may operate with a mobile-biofilm reactor or a hybrid (mobile biofilms and suspended biomass) bioreactor. This paper provides a mechanistic basis for the selection and design of a MOB process mode of operation, and it describes MOB process modes of operation, design criteria, design equations, mathematical modeling, and mobile-biofilm settling characteristics. MOB integrated WWT plants exist at full scale and reliably meet their treatment objectives. The MOB process is an emerging environmental biotechnology for cost-effective WWT.

A general deep hybrid model for bioreactor systems: Combining first principles with deep neural networks

Numerous studies have reported the use of hybrid semiparametric systems that combine shallow neural networks with First Principles for bioprocess modeling. Here we revisit the general bioreactor hybrid model and introduce some deep learning techniques. Multi-layer networks with varying depths were combined with First Principles equations in the form of deep hybrid models. Deep learning techniques, namely the adaptive moment estimation method (ADAM), stochastic regularization and depth-dependent weights initialization were evaluated in a hybrid modeling context. Modified sensitivity equations are proposed for the computation of gradients in order to reduce CPU time for the training of deep hybrid models. The methods are illustrated with applications to a synthetic dataset and a pilot 50 L MUT+ Pichia pastoris process expressing a single chain antibody fragment. All in all, the results point to a systematic generalization improvement of deep hybrid models over its shallow counterpart. Moreover, the CPU cost to train the deep hybrid models is shown to be lower than for the shallow counterpart. In the pilot 50L MUT+ Pichia pastoris data set, the prediction accuracy was increased by 18.4% and the CPU decreased by 43.4%.

Integrating electrocoagulation process with up-flow anaerobic sludge blanket for in-situ biomethanation and performance improvement

In this study, the integration of the electrocoagulation (EC) process with anaerobic digestion as a novel in-situ biomethanation approach was considered for the first time. As a result of this integration (iron electrodes, current density of 1.5 mA/cm2 and an exposure mode of 10-min-ON/ 30-min-OFF), the carbon dioxide content of biogas reached below 2%. Also, the methane production rate improved by 18.0 ± 0.4%, whereas the removal efficiencies of chemical oxygen demand, turbidity, phosphate, and sulfate increased by 12.0 ± 1.5%, 30.7 ± 1.7%, > 99%, and 75.7%, respectively. Anaerobic granular sludge characteristics were also improved. Moreover, the EC process stimulated growth and quantity of functional microorganisms, especially Acinetobacter in bacterial and Methanobacterium in archaeal community. Methane concentration, however decreased due to possible excess hydrogen production. The application of the biogas as bio-hythane, and the optimization of the hybrid bioreactor to decrease hydrogen production, are possible avenues for further research.

Preparation of Spheroids from Primary Pig Cells in a Mid-Scale Bioreactor Retaining Their Myogenic Potential.

Three-dimensional cell culture techniques mimic the in vivo cell environment more adequately than flat surfaces. Spheroids are multicellular aggregates and we aimed to produce scaffold-free spheroids of myogenic origin, called myospheres, using a mid-scale incubator and bioreactor hybrid. For the first time, we obtained spheroids from primary porcine muscle cells (PMCs) with this technology and compared their morphology and growth parameters, marker expression, and myogenic potential to C2C12-derived spheroids. Both cell types were able to form round-shaped spheroids in the bioreactor already after 24 h. The mean diameter of the C2C12 spheroids (44.6 µm) was larger than that of the PMCs (32.7 µm), and the maximum diameter exceeded 1 mm. C2C12 cells formed less aggregates than PMCs with a higher packing density (cell nuclei/mm2). After dissociation from the spheroids, C2C12 cells and PMCs started to proliferate again and were able to differentiate into the myogenic lineage, as shown by myotube formation and the expression of F-Actin, Desmin, MyoG, and Myosin. For C2C12, multinucleated syncytia and Myosin expression were observed in spheroids, pointing to accelerated myogenic differentiation. In conclusion, the mid-scale incubator and bioreactor system is suitable for spheroid formation and cultivation from primary muscle cells while preserving their myogenic potential.

Nitrogen removal of mine-influenced water in a hybrid bioreactor with floating hook-moss (Warnstorfia fluitans) in cold climate conditions

To remove nitrogen in cold conditions, we studied new nature-based treatment solutions using six pilot-scale reactors. The pilots were woodchip bioreactor (WBR), aquatic floating hook-moss (Warnstorfia fluitans) (MBR), and a combined woodchip and floating hook-moss hybrid unit (HBR) with an improved hydraulic design. The experiment was run in a climate room at temperatures of 10 °C and 5 °C and using mine water from two sites located in northern Finland. Unlike traditional horizontal flow woodchip bioreactors, in this study the hydraulic efficiency was improved from poor (λ = 0.06) in the woodchip bioreactor to satisfactory (λ = 0.51) in the hybrid unit by inserting two inner plates along the water flow and adding floating hook-moss. The hybrid bioreactor revealed the highest capability of nitrogen removal in all inorganic forms at T ≤ 10 °C with a mean HRT of 70.5 h. On average, 30–78 % of dissolved inorganic nitrogen was removed in the hybrid unit, which was 2 and 3 times more than in units consisting only of woodchip or floating hook-moss. The hybrid bioreactor revealed a maximum NO−3-N removal rate of 1.0–5.2 g m−3 d−1 and a 21.8–99.7 % removal efficiency for an average incoming NO−3-N load of 40 g d−1. The maximum NH+4-N removal efficiency of 75.6 and 53 % took place in HBR and MBR, respectively, when the incoming NH+4-N load was 23.6 ± 0.7 g d−1 at 10 °C. Over the 154 days of the experiment, the hybrid unit removed a total of 2.95 kg DIN-N, which was 0.8 kg higher than the sum of the DIN-N mass removed in the individual woodchip (1.7 kg) and moss units (0.55 kg). The nitrogen content of the aquatic moss was higher in the hybrid unit compared to the moss unit, showing a higher contribution of N plant uptake. Overall, our results suggest that combining woodchips and aquatic moss in a hybrid unit with improved hydraulic efficiency using inner walls may enhance nitrogen removal in cold climate conditions.

Assessment of anaerobic membrane distillation bioreactor hybrid system at mesophilic and thermophilic temperatures treating textile wastewater

The performance of a lab-scale anaerobic membrane distillation bioreactor (An-MDBR) system was evaluated treating high-strength synthetic textile wastewater with a Chemical Oxygen Demand (COD) concentration of 3000 ± 130 mg/L. A novel hybrid process incorporating membrane distillation in a submerged anaerobic membrane bioreactor was developed at mesophilic and thermophilic temperatures and instigated. The An-MDBR process attained 99.99% inorganic salt rejection irrespective of the operating temperatures and high initial flux between 5.9 and 11.5 L/m2·h (LMH) at 35–50 °C. Removal efficiencies (%) of COD and color were in the range of 40–69% and 43–74%, respectively in an anaerobic bioreactor, whereas overall MD performance was in the range of 99 ± 0.9% for COD as well as color. Among the four temperatures, 40 °C exhibited the optimum performance for 47 days with the average COD and color removal efficiencies of 99 ± 0.9%, respectively with steady biogas production. Furthermore, the conductivity of An-MDBR was maintained at 4.0 ± 0.5 mS/cm using low-cost Woven Fiber Microfiltration (WF-MF) coupled with An-MDBR and the flux was optimized at 2 LMH. The removal efficiency of NH4+1-N was greater in the range of 89 to 93% at mesophilic temperatures while smaller in the range of 79 to 86% at thermophilic temperatures by maintaining pH between 6.8 and 7.2. The concentration of PO4−3-P in the permeate water was near zero, showing that PO4−3 can be rejected completely by the MD membrane. Due to membrane biofouling and scaling, wetting was observed for different durations at different temperatures.

Water reclamation and microbial community investigation: Treatment of tetramethylammonium hydroxide wastewater through an anaerobic osmotic membrane bioreactor hybrid system

Tetramethylammonium hydroxide (TMAH) is a toxic photoresist developer used in the photolithography process in thin-film transistor liquid crystal display (TFT-LCD) production, and it can be removed through anaerobic treatment. TMAH cannot be released into the environment because of its higher toxicity. A tight membrane, such as a forward osmosis (FO) membrane, together with an anaerobic biological process can ensure that no TMAH is released into the environment. Thus, for the first time, an anaerobic osmotic membrane bioreactor (AnOMBR) hybrid system was developed in this study to treat a low-strength TMAH wastewater and to simultaneously investigate its microbial community. Microfiltration extraction was used to mitigate the salinity accumulation, and a periodically physical water cleaning was utilized to mitigate the FO membrane fouling. The diluted draw solute (MgSO4) was reconcentrated and reused by a membrane distillation (MD) process in the AnOMBR to achieve 99.99% TMAH removal in this AnOMBR-MD hybrid system, thereby ensuring that no TMAH is released into the natural environment. Moreover, the membrane fouling in the feed and draw sides were analyzed through the fluorescence excitation-emission matrix (FEEM) spectrophotometry to confirm that the humic acid-like materials were the primary membrane fouling components in this AnOMBR. Additionally, 16S rRNA metagenomics analysis indicated that Methanosaeta was the predominant contributor to methanogenesis and proliferated during the long-term operation. The methane yield was increased from 0.2 to 0.26 L CH4/g COD when the methanogen species acclimatized to the saline system.

Treatment of domestic sewage and leachate using a moving bed hybrid bioreactor

The treatment of domestic sewage using a moving bed hybrid bioreactor (MBHBR) was investigated by varying the concentrations of chemical oxygen demand (COD) (156 ± 14-1141 ± 78 mg/L), ammonia (NH3-N) (2 ± 0.08-48.24 ± 0.93 mg/L), phosphorus (PO4-P) (97 ± 3.2-281 ± 2.65 mg/L), and hydraulic retention times (HRTs). Initially, the reactor was operated at start-up mode (COD: 156 ± 14 mg/L), and gradually the COD concentrations were increased from phase-I (257 ± 24 mg/L) to phase-V (1141 ± 78 mg/L) by reducing the HRTs from 48 to 3 h. A significant improvement in COD removal, maximum up to 96%, was observed at a concentration of 858 ± 51 mg/L (phase-IV), then a sudden drop up to 81% was observed at a higher concentration of 1141 ± 78 mg/L (phase-V). Due to the increase in COD concentrations, average NH3-N removal was dropped from 85 to 32% from phase-I to Phase-V, respectively. In addition, the stability of MBHBR was studied to understand its performance in shut-down and shock loading phases. The co-treatment of sewage and leachate was also performed in MBHBR (COD: 864-881 mg/L and HRT: 6 h), which showed a COD removal of 77%–80% and NH3-N removal of 60%–94%. Proteobacteria was identified as a predominant species in MBHBR, which played a significant role in the co-treatment of sewage and leachate. The maximum biodegradation rate (rmax) and half-saturation constant (Ks) were estimated as 13.3 mg/L h and 361.8 mg/L, respectively.

Ethanol fermentation using macroporous monolithic hydrogels as yeast cell scaffolds

Ethanol fermentation with a hybrid system containing free and immobilized yeast cells on a macroporous monolithic hydrogel scaffold was investigated. Cell immobilization was achieved using N-isopropylacrylamide (NIPA) and methoxy triethyleneglycol acrylate (MTGA) hydrogels having macroporous monolithic structures containing interconnected micrometer-sized macropores. The immobilized cells grow within the hydrogel and can exit through the macropores into the fermentation medium, and thus a hybrid bioreactor consisting of free and immobilized yeast cells is constructed. The transformation of d-glucose to ethanol using Saccharomyces cerevisiae in batch and continuous fermentation processes was examined. Ethanol was successfully fermented using the macroporous hydrogels, whereas the conventional nonporous NIPA hydrogel does not effectively act as a cell scaffold. In continuous fermentation, the hybrid system containing both free yeast cells and those immobilized in the macroporous MTGA hydrogel showed higher ethanol productivity than the control system containing only free cells. Crucially, the macroporous hydrogel allowed the stable growth of immobilized yeast cells, resulting in a high cell density in the reactor. The hybrid system under steady-state fermentation had free and immobilized cell densities of 1.72 kg-free-cell/m3 and 29 kg-immobilized-cell/m3-gel, respectively, and the ethanol productivities 0.421 kg-ethanol/(kg-free-cell·h) and 0.128 kg-ethanol/(kg-immobilized-cell·h), respectively.

Enhancement of nitrogen removal in hybrid wastewater treatment system using ferric citrate modified basalt fiber biocarrier.

Developing biofilm carriers is of great significance for efficient wastewater treatment. In this work, ferric citrate was used to modify inorganic basalt fiber (BF) biocarrier, thus improving its surface properties and the nitrogen removal in hybrid wastewater treatment system. The results showed that the iron element on modified basalt fiber (Fe-MBF) existed in the forms of ferric citrate, Fe(OH)3, Fe2O3, and FeO. The ferric deposition increased the surface roughness, hydrophilicity and reduced the electronegativity of BF. The water contact angle of BF and Fe-MBF was 117.46° and 64.85°, respectively. The surface zeta potential of BF was -17.64 mV, but shifted positively (-8.67 mV) after deposition modification. The microorganism adhesion tests showed that the attached biomass and extracellular polymeric substances (EPS) content on Fe-MBF biocarrier significantly increased and the attached bacteria had also high viability. The Fe-MBF biocarrier showed good nitrogen removal performance in the hybrid bioreactor, with total nitrogen removal efficiency up to 95.35±0.82%, increasing by about 16% compared to that with unmodified BF biocarrier. This work also provided a green modification strategy to enhance biofilm carrier in wastewater treatment.

A developed hybrid fixed-bed bioreactor with Fe-modified zeolite to enhance and sustain biohydrogen production

In this study, we describe the development of a hybrid bioreactor with integrated chlorinated polyethylene (CPE) fixed-bed and zeolite as a microorganism nutrition carrier (MNC), aiming at enhancing and sustaining biohydrogen production during the anaerobic digestion (AD) process. In the batch test, the hybrid bioreactor achieved a maximum biohydrogen production of 646.3 mL/L. Accordingly, the hybrid bioreactor significantly enhanced biohydrogen production and maintained a stable performance for 50 days of semi-continuous operation. This result should be attributed to the CPE providing roughness surface and high porosity for microorganism immobilization, resulting in the enhancement of microbial quantity, confirmed by our scanning electron microscope and immobilized biomass analyses. Moreover, the element ratio significantly decreased, indicating that zeolite could provide metal cations for stimulating microbial bioactivity and growth, as well as contributing to superior biohydrogen productivity during the 50-day operation. In order to further enhance and sustain long-term biohydrogen production, raw zeolite was modified with iron. The hybrid-Fe bioreactor (CPE with Fe-modified zeolite) operated mainly following the acetate pathway and exhibited higher sustainability in improving biohydrogen production with a peak value of 1893.0 mL/L during a 72-day-lasting operation. The synergistic mechanism of the Fe-modified zeolite and CPE fixed-bed revealed that it could effectively induce favorable pathways and contribute to the synthesis of essential enzymes, micronutrient supplementation, electoral conductivity, and microbial immobilization for biohydrogen production. Therefore, a hybrid-Fe bioreactor could provide a unique alternative for the enhancement of hydrogen production for practical applications.

Evaluation of nitrification kinetics for treating ammonium nitrogen enriched wastewater in moving bed hybrid bioreactor

Nitrification kinetics of wastewater characterized by high nitrogen and very low organic carbon was evaluated using a moving bed hybrid bioreactor (MBHBR) in batch mode by varying initial ammonium nitrogen (NH4+-N) concentration in the range of (500–1000) mg L−1 at a pH of 7.8 ± 0.15 and temperature around 28 ± 2°C. A maximum removal efficiency of 89 % in terms of ammonium nitrogen was achieved with initial NH4+-N concentration of 900 mg L−1 having a total biomass concentration around 2000 mg L−1 and at a batch period of 5 days. The experimental results were analyzed in the light of Monod’s kinetic theory and coefficients for nitrification were obtained as maximum substrate removal rate coefficient (μmax) = 0.52 day−1, yield coefficient (Y) = 0.63 mg VSS/mg NH4+-N, half saturation constant (Ks) =603.11 mg NH4+-NL−1 and endogenous decay constant (kd) = 0.008 day−1. The study confirms better nitrification efficiency in presence of attached biomass as compared to suspended growth condition. An interesting observation from the nitrate nitrogen profile establishes the possibility of denitrification, occurring simultaneously even in absence of organic carbon in the wastewater in aerobic MBHBR. This can be supported by the fact that the suspended flocs and/or attached biofilms in hybrid reactor was deep enough for creating necessary conditions for denitrification and the required organic carbon was partially obtained from endogenous degradation of the microorganisms.

Fast recovery of a single-stage partial nitrification/anammox-based hybrid bioreactor impacted by a sudden lactose shock load

This study reports the recovery of single-stage partial nitrification (PN)/anammox bioreactor treating nitrite-free and ammonium-rich synthetic wastewater affected by a high concentration of lactose (2000 mg/l). The lactose shock led to the collapse of the PN/anammox process in <24 h. Major negative effects included significant washout of the suspended biomass and detachment of biofilm, changes in the colour of the biomass from reddish to blackish, and a significant drop in ammonium removal efficiency from 95% to <5%. Batch tests with biomass exposed to the lactose-free and lactose-containing ammonium-rich medium suggested that the lack of sufficient nitrite production during the PN process was the limiting factor for the low activity of anammox due to the limited oxygen available to the aerobic nitrifiers. The reduction of lactose from 2000 to 200 mg/l and temperature increase from 25 °C to 30 °C, led to the full recovery of the PN/anammox process in <40 days.