Characterization of PCB-degrading bacteria immobilized in polyurethane foam

Enhanced bioremediation performance of diesel-contaminated soil by immobilized composite fungi on rice husk biochar

In response to the low removal capacity and poor tolerance of fungi to diesel-contaminated soil, a novel immobilization system using biochar to enhance composite fungi was proposed. Rice husk biochar (RHB) and sodium alginate (SA) were used as immobilization matrices for composite fungi, and the adsorption system (CFI-RHB) and the encapsulation system (CFI-RHB/SA) were obtained. CFI-RHB/SA exhibited the highest diesel removal efficiency (64.10%) in high diesel-contaminated soil over a 60-day remediation period compared to the free composite fungi (42.70%) and CFI-RHB (49.13%). SEM demonstrated that the composite fungi were confirmed to be well attached to the matrix in both CFI-RHB and CFI-RHB/SA. FTIR analysis revealed the appearance of new vibration peaks in diesel-contaminated soil remediated by immobilized microorganisms, demonstrating changes in the molecular structure of diesel before and after degradation. Furthermore, CFI-RHB/SA maintains a stable removal efficiency (>60%) in higher concentrations of diesel-contaminated soil. High-throughput sequencing results indicated that Fusarium and Penicillium played a key role in the removal of diesel contaminants. Meanwhile, both dominant genera were negatively correlated with diesel concentration. The addition of exogenous fungi stimulated the enrichment of functional fungi. The insights gained from experiment and theory help to provide a new understanding of immobilization techniques of composite fungi and the evolution of fungal community structure.

Development of biocatalytic microbial ecosystem (FPUS@RODMs@In-PAOREs) for rapid and sustainable degradation of various refractory organics

The removal of diverse refractory organics from complex industrial wastewater continues to be a challenge. Although biological treatments are commonly employed, only partial degradation and increasing emergence of nitrogenous compounds, i.e., nitrate (NO₃) and nitrite (NO₂) would pose severe toxicity to the intact microbes. Herein, an efficient biocatalytic microbial ecosystem (BCME) was designed over a porous bio-carrier made of a functional polyurethane sponge (FPUS). The BCME comprised a unique set of organisms (RODMs) with novel metabolism, efficiently degrading highly-concentrated aromatics. Strategic enzyme immobilization was utilized to introduce in-situ production and aggregation of the oxidation and reduction enzymes (In-PAOREs) onto the FPUS, thereby ensuing sustained functions of the RODMs community. The developed FPUS@RODMs@In-PAOREs system was found to enhance the refractory organics removal rate to 4 kg/m³/day, and it would be attributed to the enzymatic catalysis of refractory organics (2000 mg/L) accompanied by the removal of COD (1200 mg/L) and nitrogenous compounds (200 mg/L). Besides, the fluctuating concentration of extra polymeric substances (EPS) played a dual role through enhancing adhesion, promoting the development of a functional microbial ecosystem, and creating an EPS gradient within the FPUS bio-carrier. This differential distribution of enzymes was established to significantly boost biocatalysis activity reaching 400 U/g VSS.

Enhancement of the diesel oil degradation ability of a marine bacterial strain by immobilization on a novel compound carrier material

A novel floatable and biodegradable carrier material was made by coating puffed foxtail millet (PFM) with a calcium alginate (CA)-chitosan compound membrane. A diesel oil-degrading marine bacterial strain, Acinetobacter sp. F9, was immobilized on the carrier material. The number of viable F9 cells immobilized on the carrier material reached approximately 5×10(9) CFU/g. This formulation could be stored at -20°C and 4°C for 10 weeks without a significant decrease in the number of viable immobilized cells. SEM results showed that the coating membrane was porous and that F9 cells were immobilized on the walls of the pores. The immobilized F9 cells were able to remove more than 90% of the diesel oil by the second day, while free F9 cells did not remove 90% of the diesel oil until the seventh day. GC-MS analysis indicated that the immobilized F9 cells could remove diesel oil more completely than free cells. The immobilization of the F9 cells enhanced their ability to biodegrade diesel oil.

Xylitol production from corncob hydrolysate using polyurethane foam with immobilized Candida tropicalis

Polyurethane foam (PUF) was used as a carrier for Candida tropicalis (C. tropicalis) in the multi-batches fermentation of xylitol from xylose-containing corncob hemicellulose hydrolysate. After washing and sterilization, PUF (density of 320 kgm(-3), specific surface area of 1.5-2.0 × 10(5) m(2) m(-3), average porosity of 95%, pore diameter of 0.03 mm and cubic length of 5mm) was mixed with the culture medium at appropriate proportion followed by the inoculation. The fermentation parameters such as initial cell concentration, PUF dosage, pH value and temperature were controlled to study the effects on xylitol fermentation. In the 21-day durability tests, the optimal xylitol yield and volumetric productivity reached to 71.2% and 2.10 gL(-1)h(-1) respectively. Moreover, the average xylitol yield and volumetric productivity were 66.3% and 1.90 gL(-1)h(-1) for ten batchwise operations. The current research demonstrated that the PUF immobilization could serve as an efficient method for improving the cells vitality and enzyme reactivity in the continuous operation of fermentation.

Biodegradation of benzo[a]pyrene in soil by Mucor sp. SF06 and Bacillus sp. SB02 co-immobilized on vermiculite

Two indigenous microorganisms, Bacillus sp. SB02 and Mucor sp. SF06, capable of degrading polycyclic aromatic hydrocarbons (PAHs) were co-immobilized on vermiculite by physical adsorption and used to degrade benzo[a] pyrene (BaP). The characteristics of BaP degradation by both free and co-immobilized microorganism were then investigated and compared. The removal rate using the immobilized bacterial-fungal mixed consortium was higher than that of the freely mobile mixed consortium. 95.3% of BaP was degraded using the co-immobilized system within 42 d, which was remarkably higher than the removal rate of that by the free strains. The optimal amount of inoculated co-immobilized system for BaP degradation was 2%. The immobilized bacterial-fungal mixed consortium also showed better water stability than the free strains. Kinetics of BaP biodegradation by co-immobilized SF06 and SB02 were also studied. The results demonstrated that BaP degradation could be well described by a zero-order reaction rate equation when the initial BaP concentration was in the range of 10-200 mg/kg. The scanning electronic microscope (SEM) analysis showed that the co-immobilized microstructure was suitable for the growth of SF06 and SB02. The mass transmission process of co-immobilized system in soil is discussed. The results demonstrate the potential for employing the bacterial-fungal mixed consortium, co-immobilized on vermiculite, for in situ bioremediation of BaP.