Internal mass transfer effect on biodegradation of phenol by Ca-alginate immobilized Ralstonia eutropha

Identification of novel strain Acinetobacter baumannii H1 and its improvement capacity for nutrient removal after coimmobilized on activated carbon and CaCO3 in real aquaculture wastewater

A new strain H1, Acinetobacter baumannii, exhibited the 96 % nitrogen and 76 % phosphate removal efficiencies in suspension environment after 48 h, and the optimal conditions were obtained at pH of 7-8, temperature of 30 °C, carbon source of succinate, carbon-nitrogen ratio of 10 and phosphorus-nitrogen ratio of 0.2, respectively. The immobilization experiments with activated carbon and CaCO3 were carried out, the optimal formula was 30 g/L CaCO3, 15 g/L activated carbon-bacteria complex, 2 % CaCl2 and a 1:1 embedding agent ratio. The removal efficiency of NH4+-N, total nitrogen, total phosphorus and chemical oxygen demand in immobilized H1 was 288.89 %, 121.87 %, 135.69 % and 667.21 % higher than that by free strain in group With Indigenous Bacteria, respectively. Under the real water environment, the nitrogen concentrations in the immobilization groups were 3-4 times lower than those of the suspension groups, and the abundances of N and P metabolism-associated bacterial communities (Proteobacteria and Patescibacteria) were higher in the immobilization groups. These results provided an approach for the practical application in aquaculture tailwater treatment.

Characterization of a novel 1,2-dichloroethane degrader Ancylobacter sp. J3 and use of its immobilized cells in the treatment of polluted groundwater

A novel 1,2-dichloroethane (1,2-DCA) degrading bacteria strain J3 was isolated from 1,2-DCA contaminated groundwater and identified as Ancylobacter sp. The strain J3 was associated with self-flocculation during the growth process, and the degradation pathway study showed that the bacteria could completely mineralize 1,2-DCA. The microorganism was immobilized and the optimum preparation conditions were obtained by orthogonal experiment: 6 % polyvinyl alcohol, 2 % sodium alginate, 1 % biochar, and 2 % CaCl2, and the immobilized cells were named J3C. The degradation rates of J3C at low pH, temperature, and high concentration NaCl were higher than that of free J3. The fitting results of the pseudo-first-order degradation kinetics model showed that for above 200 mg/L 1,2-DCA, the degradation rate of J3C was higher than that of free J3. The adsorption process of the sterile J3C aligns with the pseudo-first-order kinetic model and the intraparticle diffusion model. The internal mass transfer kinetics analysis revealed that the beads with biochar and a small diameter (0.34 cm) were more conducive to mass transfer. Finally, remediation of real polluted groundwater by J3C shows that for groundwater with a pH value of about 7, 1,2-DCA concentrations of about 100, 200 mg/L, 1,2-DCA can be completely degraded by J3C, while for groundwater with a pH value of 12, 250 mg/L 1,2-DCA, the degradation rate was 83.15 % by J3C, 66.91 % higher than that of free J3. The changes in microbial communities in groundwater showed that J3C disturbed the groundwater microbial little for the immobilized cells in J3C originated from the groundwater.

Development of multifunctional immobilized bacterial agents for multi-pesticides degradation and environment remediation

The proliferation of weeds, pests, and plant diseases in crop cultivation has driven the increased application of herbicide lactofen, insecticide acetamiprid, and fungicide carbendazim, contributing to environmental pollution. Microorganisms are requently employed to remove pesticide residues from the environment. However, Liquid bacterial agents encounter difficulties in transportation and preservation during application and the current immobilized bacterial agents have a single degradation function. This study developed immobilized bacterial agents containing the lactofen-degrading strain Bacillus sp. Za, the acetamiprid-degrading strain Pigmentiphaga sp. D-2, and the carbendazim-degrading strain Rhodococcus sp. djl-6. Preparation conditions, including activated carbon concentration, sodium alginate (SA), CaCl2, and immobilization time, were optimized using the response surface method (RSM). The degradation performance of the immobilized bacteria was evaluated, with degradation rates exceeding 70% for all three pesticides under conditions of 30 °C, pH 7.0, and 6% inoculation over 48 h. The immobilized bacterial agents were stored at pH 7.0 and 4 °C for 180 days, maintaining a preservation rate of 51.26% with a viable cell count of 1.04 × 108 CFU/g. These agents effectively remediated soil and water contaminated with multi-pesticides, achieving degradation rates of 92.50% and 98.50% for lactofen, 91.05% and 99.89% for acetamiprid, 88.43% and 98.99% for carbendazim within 21 in soil and 7 days in water, respectively. This study provides essential technical support for developing microbial agents capable of degrading multi-pesticides residues, with significant potential applications in agriculture and environmental protection.

Techniques and mechanisms of bacteria immobilization on biochar for further environmental and agricultural applications

Bacteria immobilization on biochar is a promising approach to achieve high concentration and stability of microbial cells for several applications. The present review addressed the techniques utilized for bacteria immobilization on biochar, discussing the mechanisms involved in this process, as well as the further utilization in bioremediation and agriculture. This article presents three immobilization techniques, which vary according to their procedures and conditions, including cell growth, adsorption, and adaptation. The mechanisms for cell immobilization are primarily adsorption and biofilm formation on biochar. The favorable characteristics of biochar immobilization depend on the pyrolysis methods, raw materials, and properties of biochar, such as surface area, pore size, pH, zeta potential, hydrophobicity, functional groups, and nutrients. Scanning electron microscope (SEM) and colony forming unit (CFU) are the analyses commonly carried out to verify the efficiency of bacteria immobilization. The benefits of applying biochar-immobilized bacteria include soil decontamination and quality improvement, which can improve plant growth and crop yield. Therefore, this emerging technology represents a promising solution for environmental and agricultural purposes. However, it is important to evaluate the potential adverse impacts on native microbiota by introducing exogenous microorganisms.

Improving mass transfer rates in microbial cell immobilization system for environmental applications: Synergistic interaction of cells on crude oil biodegradation

Among the various techniques used to clean up polluted environments, bioremediation is the most cost-effective and eco-friendly option. The diversity of microbial communities in a consortium can significantly affect the biodegradability of hazardous organic pollutants, particularly for in situ bioremediation processes. This is largely attributed to interactions between members of a consortium. In this study, the effect of internal diffusion limitations in substrate model biodegradation was firstly examined by immobilized bacterial cells at different particle sizes produced by the electrospray technique. According to the obtained results, for particles with large size, the effectiveness factors (η) were about 0.58-0.67, and the resistance to diffusive on the biodegradation rate was significant, while with decreasing the particle size, η increases and approaches about 1. After selection of suitable bead size, heavy crude oil biodegradation was investigated using a consortium consisting of three oil-degrading bacterial strains at different treatment systems. The removal rate in the suspended co-culture system stands at minimum value of 38% with all three strains which is an indicator of negative interactions among consortium members. Independent immobilization of microorganisms minimizes the competition and antagonistic interactions between strains and leads to more crude oil removal, so that, the biodegradation rate reached 60%.

Development of multifarious carrier materials and impact conditions of immobilised microbial technology for environmental remediation: A review

Microbial technology is the most sustainable and eco-friendly method of environmental remediation. Immobilised microorganisms were introduced to further advance microbial technology. In immobilisation technology, carrier materials distribute a large number of microorganisms evenly on their surface or inside and protect them from external interference to better treat the targets, thus effectively improving their bioavailability. Although many carrier materials have been developed, there have been relatively few comprehensive reviews. Therefore, this paper summarises the types of carrier materials explored in the last ten years from the perspective of structure, microbial activity, and cost. Among these, carbon materials and biofilms, as environmentally friendly functional materials, have been widely applied for immobilisation because of their abundant sources and favorable growth conditions for microorganisms. The novel covalent organic framework (COF) could also be a new immobilisation material, due to its easy preparation and high performance. Different immobilisation methods were used to determine the relationship between carriers and microorganisms. Co-immobilisation is particularly important because it can compensate for the deficiencies of a single immobilisation method. This paper emphasises that impact conditions also affect the immobilisation effect and function. In addition to temperature and pH, the media conditions during the preparation and reaction of materials also play a role. Additionally, this study mainly reviews the applications and mechanisms of immobilised microorganisms in environmental remediation. Future development of immobilisation technology should focus on the discovery of novel and environmentally friendly carrier materials, as well as the establishment of optimal immobilisation conditions for microorganisms. This review intends to provide references for the development of immobilisation technology in environmental applications and to further the improve understanding of immobilisation technology.

Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

Enzyme immobilization has been developing since the 1960s and although many industrial biocatalytic processes use the technology to improve enzyme performance, still today we are far from full exploitation of the field. One clear reason is that many evaluate immobilization based on only a few experiments that are not always well-designed. In contrast to many other reviews on the subject, here we highlight the pitfalls of using incorrectly designed immobilization protocols and explain why in many cases sub-optimal results are obtained. We also describe solutions to overcome these challenges and come to the conclusion that recent developments in material science, bioprocess engineering and protein science continue to open new opportunities for the future. In this way, enzyme immobilization, far from being a mature discipline, remains as a subject of high interest and where intense research is still necessary to take full advantage of the possibilities.

PAHs biodegradation in soil washing effluent by native mixed bacteria embedded in polyvinyl alcohol-sodium alginate-nano alumina gel beads

In this study, the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil washing solution containing Tween 80 was conducted using native mixed bacteria (Pseudomonas sp. Z1, Sphingobacterium sp. Z2, and Klebsiella sp. K) embedded in polyvinyl alcohol-sodium alginate-nano alumina (PVA-SA-ALNPs) gel beads. The optimal dosage of immobilized beads and embedded biomass for the biodegradation of phenanthrene (PHE), fluoranthene (FLU), and pyrene (PYR) were 10 % (v/v) and 20 % (v/v), respectively. SEM analysis showed that the porous structure of the immobilized beads was a cross-linked network with abundant pores that provided many potential adhesion sites for microorganisms. The beads with the immobilized mixed bacteria maintained a high activity during batch experiments and could even be reused for 3 cycles (90 d). Compared with the beads containing individual immobilized strain, the immobilized mixed bacteria showed a more efficient biodegradation of PHE (91.67 %), FLU (88.6 %), and PYR (88.5 %) in synthetic soil washing effluent within 30 d. The first-order kinetic model suitably described the degradation process of the three target PAHs. By adding Tween 80 to the synthetic eluent, the degradation of PHE, FLU, and PYR increased by 16.39 %, 22.25 %, and 21.29 %, respectively, indicating that Tween 80 promoted PAHs biodegradation, even though it was also rapidly degraded during the reaction cycle. These findings suggest that the developed mixed bacteria embedded in PVA-SA-ALNPs gel beads has great potential for PAHs remediation.

Microalgae and bio-polymeric adsorbents: an integrative approach giving new directions to wastewater treatment

This review analyses the account of biological (microalgae) and synthetic (bio-polymeric adsorbents) elements to compass the treatment efficiencies of various water pollutants and mechanisms behind them. While considering pollutant removal, both techniques have their own merits and demerits. Microalgal-based methods have been dominantly used as a biological method for pollutant removal. The main limitations of microalgal methods are capacity, scale, dependence on variables of environment and duration of the process. Biopolymers on the other hand are naturally produced, abundant in nature, environmentally safe and biocompatible with cells and many times biodegradable. Algal immobilization in biopolymers has promoted the reuse of cells for further treatment and protected cells from toxic environment monitoring and controlling the external factors like pH, temperature and salinity can promote the removal process while working with the mentioned technologies. In this review, a mechanistic view of both these techniques along with integrated approaches emphasizing on their loopholes and possibilities of improvement in these techniques is represented. In addition to these, the review also discusses the post-treatment effect on algal cells which are specifically dependent on pollutant type and their concentration. All these insights will aid in developing integrated solutions to improve removal efficiencies in an environmentally safe and cost-effective manner.Novelty statement The main objective of this review is to thoroughly understand the role of micro-algal cells and synthetic adsorbents individually as well as their integrative effect in the removal of pollutants from wastewater. Many reviews have been published containing information related to either removal mechanism by algae or synthetic adsorbents. While in this review we have discussed the agents, algae and synthetic adsorbents along with their limitations and explained how these limitations can be overcome with the integration of both the moieties together in process of immobilization. We have covered both the analytical and mechanistic parts of these technologies. Along with this, the post-treatment effects on algae have been discussed which can give us a critical understanding of algal response to pollutants and by-products obtained after treatment. This review contains three different sections, their importance and also explained how these technologies can be improved in the future aspects.

Bacterial behaviour in the biodegradation of phenol by indigenous bacteria immobilized in Ca-alginate beads

The phenol biodegradation by Ca-alginate immobilized indigenous bacteria was performed in batch system. The effects of some operational parameters were evaluated, including % weight of alginate, calcium and CaCl₂, diameter of spheres; jellification time; solution concentration; adaptation concentration and alginate/cells ratio. The optimal biodegradation conditions were found for 2% and 3% of weight for respectively the sodium alginate and calcium chloride. The hardening time was 30  min and beads diameter of 4 cm. The degradation efficiency of the immobilized strains in these conditions exceeds 800 mg·L^-1. The results show that the mass transfer flow (nutritional intake) which depends on the concentration gradient (dC/dz), the physical-chemical properties of alginate beads through the diffusivity coefficient (D), govern the bacterial kinetics and the spatial and temporal behaviour of bacteria.

Bioremediation of Artificial Diesel-Contaminated Soil Using Bacterial Consortium Immobilized to Plasma-Pretreated Wood Waste

Bioaugmentation is a bioremediation option based on increasing the natural in-situ microbial population that possesses the ability to degrade the contaminating pollutant. In this study, a diesel-degrading consortium was obtained from an oil-contaminated soil. The diesel-degrading consortium was grown on wood waste that was plasma-pretreated. This plasma treatment led to an increase of bacterial attachment and diesel degradation rates. On the 7th day the biofilm viability on the plasma-treated wood waste reached 0.53 ± 0.02 OD 540 nm, compared to the non-treated wood waste which was only 0.34 ± 0.02. Biofilm attached to plasma-treated and untreated wood waste which was inoculated into artificially diesel-contaminated soil (0.15% g/g) achieved a degradation rate of 9.3 mg day-1 and 7.8 mg day-1, respectively. While, in the soil that was inoculated with planktonic bacteria, degradation was only 5.7 mg day-1. Exposing the soil sample to high temperature (50 °C) or to different soil acidity did not influence the degradation rate of the biofilm attached to the plasma-treated wood waste. The two most abundant bacterial distributions at the family level were Xanthomonadaceae and Sphingomonadaceae. To our knowledge, this is the first study that showed the advantages of biofilm attached to plasma-pretreated wood waste for diesel biodegradation in soil.

Biodegradation of high concentration phenol using sugarcane bagasse immobilized Candida tropicalis PHB5 in a packed-bed column reactor

Biodegradation of phenolic compounds in wastewater can be effectively carried out in packed bed reactors (PBRs) employing immobilized microorganisms. A low-cost, reusable immobilization matrix in PBR can provide economic advantages in large scale removal of high concentration phenol. In this study, we evaluated the efficiency and reusability of sugarcane bagasse (SCB) as a low-cost immobilization support for high strength phenol removal in recirculating upflow PBR. An isolated yeast Candida tropicalis PHB5 was immobilized onto the SCB support and packed into the reactor to assess phenol biodegradation at various influent flow rates. Scanning electron microscopy exhibited substantial cell attachment within the pith and onto the fibrous strand surface of the SCB support. The PBR showed 97% removal efficiency at the initial phenol concentration of 2400 mg L^-1 and 4 mL min^-1 flow rate within 54 h. Biodegradation kinetic studies revealed that the phenol biodegradation rate and biodegradation rate constant were dependent on the influent flow rate. A relatively higher rate of biodegradation (64.20 mg g^-1 h^-1) was found at a flow rate of 8 mL min^-1, indicating rapid phenol removal in the PBR. Up to six successive batches (phenol removal >94%) were successfully applied in the PBR using an initial phenol concentration of 400-2400 mg L^-1 at a flow rate of 4 mL min^-1 indicating the reusability of the PBR system. The SCB-immobilized C. tropicalis could be employed as a cost-effective packing material for removal of high strength phenolic compounds in real scale PBR.

Biodegradation potential of polycyclic aromatic hydrocarbons by immobilized Klebsiella sp. in soil washing effluent

A strain KL (Klebsiella sp.), with a high polycyclic aromatic hydrocarbons (PAHs) degradation efficiency, was isolated and purified. Immobilization of strain KL using a boric acid-CaCl₂ cross-linking method based on polyvinyl alcohol (PVA)-sodium alginate (SA)-nano alumina (ALNPs) composite was investigated for removal of phenanthrene (PHE), fluoranthene (FLA), and pyrene (PYR) in soil washing effluent. The concentration of PVA, SA, and ALNPs in immobilized beads had significant effects on the physicochemical properties and biodegradation performance. When beads had a PVA, SA, and ALNPs content of 10% (w/v), 0.8% (w/v), and 0.7% (w/v), and the initial biomass dosage was 10% (v/v), the biodegradation efficiency and mass transfer performance of the immobilized beads were optimal with the specific surface area of 13.3971 m²/g. Scanning electron microscopy (SEM) showed that the surface of immobilized beads was dense. The growth and adhesion of cells inside the beads were adequate, and pores of the beads were abundant and irregularly staggered. The immobilization method was successfully applied to the treatment of the three PAHs in soil washing effluent. Adsorption of beads contributed to PAHs removal in the initial stage of degradation. Higher residual concentrations of Tween 80 in the soil washing effluent have toxic effects on strain KL growth and reduce the PAHs degradation capacity. Tween 80 of 2500 mg/L was proper conditions for PAHs biodegradation efficiency. Compared to freely suspended KL cells, the removal rates of PHE, FLA, and PYR using the immobilization method on the 30th day were increased by 15.91%, 17.07%, and 19.08%, respectively.

Biotransformation of 4-nitrophenol by co-immobilized Geobacter sulfurreducens and anthraquinone-2-sulfonate in barium alginate beads

Geobacter sulfurreducens and anthraquinone-2-sulfonate (AQS) were used suspended and immobilized in barium alginate during the biotransformation of 4-nitrophenol (4-NP). The assays were conducted at different concentrations of 4-NP (50-400 mg/L) and AQS, either in suspended (0-400 μM) or immobilized form (0 or 760 μM), and under different pH values (5-9). G. sulfurreducens showed low capacity to reduce 4-NP in absence of AQS, especially at the highest concentrations of the contaminant. AQS improved the reduction rates from 0.0086 h^-1, without AQS, to 0.149 h^-1 at 400 μM AQS, which represent an increment of 17.3-fold. The co-immobilization of AQS and G. sulfurreducens in barium alginate beads (AQS_i-G_i) increased the reduction rates up to 4.8- and 7.2-fold, compared to incubations with G. sulfurreducens in suspended and immobilized form, but in absence of AQS. AQS_i-G_i provides to G. sulfurreducens a barrier against the possibly inhibiting effects of 4-NP.

Immobilization of Sphingomonas sp. GY2B in polyvinyl alcohol-alginate-kaolin beads for efficient degradation of phenol against unfavorable environmental factors

In this study, batch experiments were carried out to evaluate the biodegradation of phenol by Sphingomonas sp. GY2B, which were immobilized in polyvinyl alcohol (PVA)-sodium alginate-kaolin beads under different conditions. The optimal degradation performance was achieved by GY2B immobilized in beads containing 1.0% (w/v) of kaolin, 10% (w/v) of PVA, 0.3% (w/v) of sodium alginate, 10% (v/v) of biomass dosage, and exposed to an initial phenol concentration of 100 mg/L. The experimental results indicated that PVA-sodium alginate-kaolin beads can accelerate the degradation rate of phenol by reducing the degradation time and also improve degradation rate. The biodegradation rate of phenol by immobilized cells (16.79 ± 0.81 mg/(L·h)) was significantly higher than that of free cells (11.49 ± 1.29 mg/(L·h)) under the above optimal conditions. GY2B immobilized on beads was more competent than free GY2B in degradation under conditions with high phenol concentrations (up to 300 mg/L) and in strong acidic (pH = 1) and alkaline (pH = 12) environments. Higher phenol concentrations inhibit the biomass and reduce the biodegradation rate, while the lower biodegradation rate at low initial phenol concentrations is attributed to mass transfer limitations. The Haldane inhibitory model was in agreement with the experimental data well, revealing that phenol showed a considerable inhibitory effect on the biodegradation by Sphingomonas sp. GY2B, especially at concentrations higher than 90 mg/L. Intra-particle diffusion model analysis suggests that adsorption of phenol by immobilized beads was controlled by both rapid surface adsorption as well as pore diffusion mechanism. It's worth noting that the presence of 1 mg/L Cr(VI) enhanced the biodegradation of phenol by free cells, while Cr(VI) showed no obvious impact on the removal of phenol by immobilized cells. In addition, immobilized cells were reused 16 times and removed 99.5% phenol, and when stored at 4 °C for 90 days, more than 99% phenol was removed. These results showed that immobilized cells can significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. It is implied that PVA -sodium alginate-kaolin beads have great potential to be applied in a practical and economical phenolic wastewater treatment system.

Strengthening calcium alginate microspheres using polysulfone and its performance evaluation: Preparation, characterization and application for enhanced biodegradation of chlorpyrifos

Bacterial cell immobilization offer considerable advantages over traditional biotreatment systems using free cells. Calcium alginate matrix usually used for bacterial immobilization is susceptible to biodegradation in harsh environment. Current study aimed to produce and characterize stable macrocapsules (MCs) of Chlorpyrifos (CP) degrading bacterial consortium using biocompatible calcium alginate matrix coupled with environmentally stable polysulfone. In current study bacterial consortium capable of CP biodegradation was immobilized using calcium alginate in a form of microcapsule (MC) reinforced by being coated with a synthetic polymer polysulfone (PSf) through phase inversion. Consortium comprised of five bacterial strains was immobilized using optimized concentration of sodium alginate (2.5gL^-1), calcium chloride (6gL^-1), biomass (600mgL^-1) and polysulfone (10gL^-1). It has been observed that MCs have high thermal, pH and chemical stability than CAMs. In synthetic media complete biodegradation of CP (100-600mgL^-1) was achieved using macrocapsules (MCs) within 18h. CAMs could be reused effectively only upto 5cycles, contrary to this MCs could be used 13 times to achieve more than >96% CP degradation. Shelf life and reusability studies conducted for MCs indicated unaltered biomass retention and CP biodegradation activity (95%) over 16weeks of storage. MCs achieved complete biodegradation of CP (536mgL^-1) in real industrial wastewater and reused several times effectively. Metabolites (3,5,6-trichloro-2-pyridinol (TCP), 3,5,6-trichloro-2-methoxypyridine (TMP) and diethyl-thiophosphate (DETP) were traced using GC-MS and possible metabolic pathway was constructed. Study indicated MCs could be used for cleanup of CP contaminated wastewater repeatedly, safely, efficiently for a longer period of time.

Bio-immobilization of dark fermentative bacteria for enhancing continuous hydrogen production from cornstalk hydrolysate

Mycelia pellets were employed as biological carrier in a continuous stirred tank reactor to reduce biomass washout and enhance hydrogen production from cornstalk hydrolysate. Hydraulic retention time (HRT) and influent substrate concentration played critical roles on hydrogen production of the bioreactor. The maximum hydrogen production rate of 14.2mmol H₂L^-1h^-1 was obtained at optimized HRT of 6h and influent concentration of 20g/L, 2.6 times higher than the counterpart without mycelia pellets. With excellent immobilization ability, biomass accumulated in the reactor and reached 1.6g/L under the optimum conditions. Upon further energy conversion analysis, continuous hydrogen production with mycelia pellets gave the maximum energy conversion efficiency of 17.8%. These results indicate mycelia pellet is an ideal biological carrier to improve biomass retention capacity of the reactor and enhance hydrogen recovery efficiency from lignocellulosic biomass, and meanwhile provides a new direction for economic and efficient hydrogen production process.

Encapsulated Pseudomonas putida for phenol biodegradation: Use of a structural membrane for construction of a well-organized confined particle

Phenols are toxic byproducts from a wide range of industry sectors. If not treated, they form effluents that are very hazardous to the environment. This study presents the use of a Pseudomonas putida F1 culture encapsulated within a confined environment particle as an efficient technique for phenol biodegradation. The innovative encapsulation technique method, named the "Small Bioreactor Platform" (SBP) technology, enables the use of a microfiltration membrane constructed as a physical barrier for creating a confined environment for the encapsulated culture. The phenol biodegradation rate of the encapsulated culture was compared to its suspended state in order to evaluate the effectiveness of the encapsulation technique for phenol biodegradation. A maximal phenol biodegradation rate (q) of 2.12/d was exhibited by encapsulated P. putida at an initial phenol concentration of 100 mg/L. The biodegradation rate decreased significantly at lower and higher initial phenol concentrations of 50 and up to 3000 mg/L, reaching a rate of 0.1018/d. The results also indicate similar and up to double the degradation rate between the two bacterial states (encapsulated vs. suspended). High resolution scanning electron microscopy images of the SBP capsule's membrane morphology demonstrated a highly porous microfiltration membrane. These results, together with the long-term activity of the SBP capsules and verification that the culture remains pure after 60 days using 16S rRNA gene phylogenetic affiliation tests, provide evidence for a successful application of this new encapsulation technique for bioaugmentation of selected microbial cultures in water treatment processes.

3-Chloro-1,2-propanediol biodegradation by Ca-alginate immobilized Pseudomonas putida DSM 437 cells applying different processes: mass transfer effects

3-Chloro-1,2-propanediol (3-CPD) biodegradation by Ca-alginate immobilized Pseudomonas putida cells was performed in batch system, continuous stirred tank reactor (CSTR), and packed-bed reactor (PBR). Batch system exhibited higher biodegradation rates and 3-CPD uptakes compared to CSTR and PBR. The two continuous systems (CSTR and PBR) when compared at 200 mg/L 3-CPD in the inlet exhibited the same removal of 3-CPD at steady state. External mass-transfer limitations are found negligible at all systems examined, since the observable modulus for external mass transfer Ω ≪ 1 and the Biot number Bi > 1. Intra-particle diffusion resistance had a significant effect on 3-CPD biodegradation in all systems studied, but to a different extent. Thiele modulus was in the range of 2.5 in batch system, but it was increased at 11 when increasing cell loading in the beads, thus lowering significantly the respective effectiveness factor. Comparing the systems at the same cell loading in the beads PBR was less affected by internal diffusional limitations compared to CSTR and batch system, and, as a result, exhibited the highest overall effectiveness factor.

Cometabolic degradation of ethyl mercaptan by phenol-utilizing Ralstonia eutropha in suspended growth and gas-recycling trickle-bed reactor

The degradability of ethyl mercaptan (EM), by phenol-utilizing cells of Ralstonia eutropha, in both suspended and immobilized culture systems, was investigated in the present study. Free-cells experiments conducted at EM concentrations ranging from 1.25 to 14.42 mg/l, showed almost complete removal of EM at concentrations below 10.08 mg/l, which is much higher than the maximum biodegradable EM concentration obtained in experiments that did not utilize phenol as the primary substrate, i.e. 2.5 mg/l. The first-order kinetic rate constant (kSKS) for EM biodegradation by the phenol-utilizing cells (1.7 l/g biomass/h) was about 10 times higher than by cells without phenol utilization. Immobilized-cells experiments performed in a gas recycling trickle-bed reactor packed with kissiris particles at EM concentrations ranging from 1.6 to 36.9 mg/l, showed complete removal at all tested concentrations in a much shorter time, compared with free cells. The first-order kinetic rate constant (rmaxKs) for EM utilization was 0.04 l/h for the immobilized system compared to 0.06 for the suspended-growth culture, due to external mass transfer diffusion. Diffusion limitation was decreased by increasing the recycling-liquid flow rate from 25 to 65 ml/min. The removed EM was almost completely mineralized according to TOC and sulfate measurements. Shut down and starvation experiments revealed that the reactor could effectively handle the starving conditions and was reliable for full-scale application.

Decolorization characteristics of a newly isolated salt-tolerant Bacillus sp. strain and its application for azo dye-containing wastewater in immobilized form

Strain CICC 23870 capable of decolorization of various azo dyes under high saline conditions was isolated from saline-alkali soil. The oxygen-insensitive azoreductase in crude extracts exhibited a wide substrate adaptively in the presence of NADH as a cofactor. The decolorization process by free cells followed first-order kinetics, with a high Methyl Orange (MO) tolerance concentration up to 100 mg l(-1) estimated by Haldane model. The average decolorization rate of free cell system was 26.30 mg g(-1) h(-1) at initial MO concentration of 32.7 mg l(-1). However, the values for the systems of immobilized cells (4 mm) in alginate, alginate and nano-TiO2, and alginate and powered activated carbon (PAC) were 6.83, 4.64, and 11.34 mg g(-1) h(-1), respectively. The effective diffusion factors in the tree different matrices were calculated by diffusion-based mathematic model. The diffusion step controls the overall decolorization rate, and the effective diffusion coefficients varied with internal structure of the bead matrices. The diffusion coefficients were increased from 4.98 × 10(-9) to 2.25 × 10(-8) cm(2) s(-1) when PAC was added, but decreased to 6.62 × 10(-10) cm(2) s(-1) when nano-TiO2 was added. The immobilized matrices could be reused for at least three cycles but with a decreased decolorization rate, possibly due to the breakage of beads at the end of each cycle, which led to the loss of immobilized bacteria.

Enhanced U(VI) bioreduction by alginate-immobilized uranium-reducing bacteria in the presence of carbon nanotubes and anthraquinone-2,6-disulfonate

Uranium-reducing bacteria were immobilized with sodium alginate, anthraquinone-2,6-disulfonate (AQDS), and carbon nanotubes (CNTs). The effects of different AQDS-CNTs contents, U(IV) concentrations, and metal ions on U(IV) reduction by immobilized beads were examined. Over 97.5% U(VI) (20 mg/L) was removed in 8 hr when the beads were added to 0.7% AQDS-CNTs, which was higher than that without AQDS-CNTs. This result may be attributed to the enhanced electron transfer by AQDS and CNTs. The reduction of U(VI) occurred at initial U(VI) concentrations of 10 to 100 mg/L and increased with increasing AQDS-CNT content from 0.1% to 1%. The presence of Fe(III), Cu(II) and Mn(II) slightly increased U(VI) reduction, whereas Cr(VI), Ni(II), Pb(II), and Zn(II) significantly inhibited U(VI) reduction. After eight successive incubation-washing cycles or 8 hr of retention time (HRT) for 48 hr of continuous operation, the removal efficiency of uranium was above 90% and 92%, respectively. The results indicate that the AQDS-CNT/AL/cell beads are suitable for the treatment of uranium-containing wastewaters.

Biodegradation of Methyl Orange by alginate-immobilized Aeromonas sp. in a packed bed reactor: external mass transfer modeling

Azo dyes are recalcitrant and xenobiotic nature makes these compounds a challenging task for continuous biodegradation up to satisfactorily levels in large-scale. In the present report, the biodegradation efficiency of alginate immobilized indigenous Aeromonas sp. MNK1 on Methyl Orange (MO) in a packed bed reactor was explored. The experimental results were used to determine the external mass transfer model. Complete MO degradation and COD removal were observed at 0.20 cm bead size and 120 ml/h flow rate at 300 mg/l of initial dye concentration. The degradation of MO decreased with increasing bead sizes and flow rates, which may be attributed to the decrease in surface of the beads and higher flux of MO, respectively. The experimental rate constants (k ps) for various beads sizes and flow rates were calculated and compared with theoretically obtained rate constants using external film diffusion models. From the experimental data, the external mass transfer effect was correlated with a model J D = K Re (-(1 - n)). The model was tested with K value (5.7) and the Colburn factor correlation model for 0.20, 0.40 and 0.60 bead sizes were J D = 5.7 Re (-0.15), J D = 5.7 Re (-0.36) and J D = 5.7 Re (-0.48), respectively. Based on the results, the Colburn factor correlation models were found to predict the experimental data accurately. The proposed model was constructive to design and direct industrial applications in packed bed reactors within acceptable limits.

Biodegradation of tetrahydrofuran by Pseudomonas oleovorans DT4 immobilized in calcium alginate beads impregnated with activated carbon fiber: mass transfer effect and continuous treatment

A novel entrapment matrix, calcium alginate (CA) coupled with activated carbon fiber (ACF), was prepared to immobilize Pseudomonas oleovorans DT4 for degrading tetrahydrofuran (THF). The addition of 1.5% ACF increased the adsorption capacity of the immobilized bead, thus resulting in an enhanced average removal rate of 30.3mg/(Lh). The synergism between adsorption and biodegradation was observed in the hybrid CA-ACF beads instead of in the system comprising CA beads and freely suspended ACF. The effective diffusion coefficient of the CA-ACF bead was not significantly affected by bead size, but the bead's value of 1.14×10(-6)cm(2)/s (for the bead diameter of 0.4 cm) was larger than that of the CA bead by almost one order of magnitude based on the intraparticle diffusion-reaction kinetics analysis. Continuous treatment of the THF-containing wastewater was succeeded by CA-ACF immobilized cells in a packed-bed reactor for 54 d with a >90% removal efficiency.

Bioconversion characteristics of Rhodopseudomonas palustris CQK 01 entrapped in a photobioreactor for hydrogen production

The performance of the entrapped-cell photobioreactor during H2 production was assessed by using glucose as substrate in a continuous operation mode. The maximal hydrogen production rate and light conversion efficiency, 2.61 mmol/L/h and 82.3%, were obtained at a HRT of 11.4 h, an substrate loading rate of 4.2 mmol/h and an illumination of 590 nm and 6000 lux, the corresponding hydrogen yield and total energy efficiency were 0.62 mmol H2/(mmol glucose) and 4.8%, respectively. The results indicate the H2 production system illuminated at 590 nm wavelength engaged in energy storage for H2 production due to more ATP synthesized in primary reaction center, and was of higher energy recovery capacity. Furthermore, the total energy efficiency was far lower than the corresponding light conversion efficiency due to intermediates production.

Comparison of 4-chloro-2-nitrophenol adsorption on single-walled and multi-walled carbon nanotubes

The adsorption characteristics of 4-chloro-2-nitrophenol (4C2NP) onto single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs) from aqueous solution were investigated with respect to the changes in the contact time, pH of solution, carbon nanotubes dosage and initial 4C2NP concentration. Experimental results showed that the adsorption efficiency of 4C2NP by carbon nanotubes (both of SWCNTs and MWCNTs) increased with increasing the initial 4C2NP concentration. The maximum adsorption took place in the pH range of 2-6. The linear correlation coefficients of different isotherm models were obtained. Results revealed that the Langmuir isotherm fitted the experimental data better than the others and based on the Langmuir model equation, maximum adsorption capacity of 4C2NP onto SWCNTs and MWCNTs were 1.44 and 4.42 mg/g, respectively. The observed changes in the standard Gibbs free energy, standard enthalpy and standard entropy showed that the adsorption of 4C2NP onto SWCNTs and MWCNTs is spontaneous and exothermic in the temperature range of 298-328 K.

Aerobic pretreatment of olive oil mill wastewater using Ralstonia eutropha

Olive oil mill wastewater (OMW) has a high polluting power, with total phenolics (TP) around 2.5 g l(-1) and chemical oxygen demand (COD) 85 g l(-1). Biological systems offer advantages in treating this type of agro-industrial wastewater. The performance of phenol-adapted Ralstonia eutropha for aerobic biotreatment of OMW has been studied, and a TP concentration of 250 mg l(-1) found to be fully degraded within 24 h. This simple procedure may be adopted as a pretreatment prior to the normal aerobic or anaerobic techniques used for treating OMW. The biodegradative capability of this non-pathogenic gram-negative bacterium towards the TP and COD content of OMW has been evaluated. The adapted free cells were found able to decrease TP and COD in the undiluted OMW by 56% and 42%, respectively. The Monod equation was found suitable to describe the capacity of the cells for growing on undiluted OMW, giving micromax 0.083 per day and Ks = 1846 mg l(-1). Using a packed-bed reactor the performance of loofa-immobilized R. eutropha was assessed and the reduction in TP and COD shown to be 73% and 64%, respectively.

The biodegradation pathway of triethylamine and its biodegradation by immobilized Arthrobacter protophormiae cells

A bacterial strain named R4 was isolated from a wastewater treatment pool containing triethylamine (TEA) as the sole source of carbon and nitrogen. Strain R4 was identified as Arthrobacter protophormiae based on 16S rRNA gene sequence analysis and morphological and physiological properties. The optimal pH, temperature and concentration of NaCl for TEA degradation by strain R4 were 7.0, 30°C and 0.5%, respectively. Strain R4 could completely degrade 100 mg l(-1) TEA to ammonia in 32 h, and could also effectively degrade diethylamine (DEA) and ethylamine (EA) to ammonia. The degradation of TEA was strongly inhibited by some metal ions (Cu(2+), Mn(2+), Zn(2+), Co(2+), Ni(2+) and Ag(+)) (1.0mM). Addition of either SO(4)(2-) or NH(4)(+) reduced the degradation efficiency of TEA by strain R4 to a certain extent. The inhibition became significant when the concentration of SO(4)(2-) and NH(4)(+) reached to 11 mM and 30 mM, respectively. Cell-free extracts prepared from cells grown in TEA exhibited TEA monooxygenase, DEA monooxygenase and EA monooxygenase activity. Here, we propose the metabolic pathway of TEA degradation in strain R4. The efficiency of TEA removal by immobilized cells of strain R4 was found to be equivalent to that of free cells. In addition, the immobilized cells could be reused without reduction in their ability to degrade TEA.

Enhanced degradation of phenol by Pseudomonas sp. CP4 entrapped in agar and calcium alginate beads in batch and continuous processes

Phenol is one of the major toxic pollutants in the wastes generated by a number of industries and needs to be eliminated before their discharge. Although microbial degradation is a preferred method of waste treatment for phenol removal, the general inability of the degrading strains to tolerate higher substrate concentrations has been a bottleneck. Immobilization of the microorganism in suitable matrices has been shown to circumvent this problem to some extent. In this study, cells of Pseudomonas sp. CP4, a laboratory isolate that degrades phenol, cresols, and other aromatics, were immobilized by entrapment in Ca-alginate and agar gel beads, separately and their performance in a fluidized bed bioreactor was compared. In batch runs, with an aeration rate of 1 vol(-1) vol(-1) min(-1), at 30°C and pH 7.0 ± 0.2, agar-encapsulated cells degraded up to 3000 mg l(-1) of phenol as compared to 1500 mg l(-1) by Ca-alginate-entrapped cells whereas free cells could tolerate only 1000 mg l(-1). In a continuous process with Ca-alginate entrapped cells a degradation rate of 200 mg phenol l(-1) h(-1) was obtained while agar-entrapped cells were far superior and could withstand and degrade up to 4000 mg phenol l(-1) in the feed with a maximum degradation rate of 400 mg phenol l(-1) h(-1). The results indicate a clear possibility of development of an efficient treatment technology for phenol containing waste waters with the agar-entrapped bacterial strain, Pseudomonas sp. CP4.

Modelling and simulation of steady-state phenol degradation in a pulsed plate bioreactor with immobilised cells of Nocardia hydrocarbonoxydans

A novel bioreactor called pulsed plate bioreactor (PPBR) with cell immobilised glass particles in the interplate spaces was used for continuous aerobic biodegradation of phenol present in wastewater. A mathematical model consisting of mass balance equations and accounting for simultaneous external film mass transfer, internal diffusion and reaction is presented to describe the steady-state degradation of phenol by Nocardia hydrocarbonoxydans (Nch.) in this bioreactor. The growth of Nch. on phenol was found to follow Haldane substrate inhibition model. The biokinetic parameters at a temperature of 30 ± 1 °C and pH at 7.0 ± 0.1 are μ (m) = 0.5397 h(-1), K (S) = 6.445 mg/L and K (I) = 855.7 mg/L. The mathematical model was able to predict the reactor performance, with a maximum error of 2% between the predicted and experimental percentage degradations of phenol. The biofilm internal diffusion rate was found to be the slowest step in biodegradation of phenol in a PPBR.