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Lignocellulosic biomass wastes are abundant resources that are usually valorized for methane-rich biogas via anaerobic digestion. Conversion of lignocellulose into volatile fatty acids (VFA) rather than biogas is attracting attention due to the higher value-added products that come with VFA utilization. This review consolidated the latest studies associated with characteristics of lignocellulosic biomass, the effects of process parameters during acidogenic fermentation, and the intensification strategies to accumulate more VFA. The differences between anaerobic digestion technology and acidogenic fermentation technology were discussed. Performance-enhancing strategies surveyed included (1) alkaline fermentation; (2) co-digestion and high solid-state fermentation; (3) pretreatments; (4) use of high loading rate and short retention time; (5) integration with electrochemical technology, and (6) adoption of membrane bioreactors. The recommended operations include: mesophilic temperature (thermophilic for high loading rate fermentation), C/N ratio (20–40), OLR (< 12 g volatile solids (VS)/(L·d)), and the maximum HRT (8–12 days), alkaline fermentation, membrane technology or electrodialysis recovery. Lastly, perspectives were put into place based on critical analysis on status of acidogenic fermentation of lignocellulosic biomass wastes for VFA production. Highlights: Strategies to enhance acidogenic fermentation of lignocellulosic biomass presented. Optimal parameters for anaerobic digestion and acidogenic fermentation are compared. Challenges of electrochemical fermentation of lignocellulosic biomass are discussed. Membrane technology and its further optimization are effective for VFAs extraction. [ABSTRACT FROM AUTHOR]

Purpose: To help minimize the negative impact of chemical fertilizers on the environment, recycle nitrogen and phosphorus nutrients of anaerobic digestate and reduce loss of nutrients via leaching, an eco-friendly slow-release fertilizer was prepared through recovery of nitrogen and phosphorus nutrition from digestate using superabsorbent fibers extracted from soybean curd residue as an adsorbent. Methods: The preparation method was proposed, and the fiber composite-based adsorbent was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscope (SEM) techniques. Results: The successful incorporation of N and P into the fiber composite-based adsorbent via adsorption was confirmed by results of these analyses. The prepared fertilizer showed a relatively high N content (3.65 wt%) and a limited P content (0.14 wt%). Also, the swelling capacity as well as water retention capability of the obtained fiber composite-based adsorbent were evaluated. The release behavior of N and P from impregnated fiber composites was examined and was found to be partially in good accordance with the standard of the Committee of European Normalization, showing good slow-release and water-retention properties. Furthermore, in order to assess the fertilizer quality of the prepared materials, the effects of different fertilizers (commercially available fertilizer and prepared slow-release fertilizer) on tomato plant growth and soil microbial communities were investigated. Conclusions: The obtained results demonstrated the potential of fiber composite-based slow-release fertilizer system for recycling N and P nutrition from digestate, improving the effectiveness of fertilizer as well as protecting the environment. [ABSTRACT FROM AUTHOR]

Graesiella emersonii was cultivated in an osmotic membrane photobioreactor (OMPBR) for nutrients removal from synthetic wastewater in continuous mode. At 1.5 days of hydraulic retention time and under continuous illumination, the microalgae removed nitrogen (N) completely at influent NH4+-N concentrations of 4–16 mg/L, with removal rates of 3.03–12.1 mg/L-day. Phosphorus (P) removal in the OMPBR was through biological assimilation as well as membrane rejection, but PO43−-P assimilation by microalgae could be improved at higher NH4+-N concentrations. Microalgae biomass composition was affected by N/P ratio in wastewater, and a higher N/P ratio resulted in higher P accumulation in the biomass. The OMPBR accumulated about 0.35 g/L biomass after 12 days of operation under continuous illumination. However, OMPBR operation under 12 h light/12 h dark cycle lowered biomass productivity by 60%, which resulted in 20% decrease in NH4+-N removal and nearly threefold increase in PO43−-P accumulation in the OMPBR. Prolonged dark phase also affected carbohydrate accumulation in biomass, although its effects on lipid and protein accumulation were negligible. The microalgae also exhibited high tendency to aggregate and settle, which could be attributed to reduction in cell surface charge and enrichment of soluble algal products in the OMPBR. Due to a relatively shorter operating period, membrane biofouling and salt accumulation did not influence the permeate flux significantly. These results improve the understanding of the effects of N/P ratio and light/dark cycle on biomass accumulation and nutrients removal in the OMPBR. [ABSTRACT FROM AUTHOR]

Biotransformation is a green and useful tool for sustainable and selective chemical synthesis. However, it often suffers from the toxicity and inhibition from organic substrates or products. Here, we established a hollow fiber membrane bioreactor (HFMB)-based aqueous/organic biphasic system, for the first time, to enhance the productivity of a cascade biotransformation with strong substrate toxicity and inhibition. The enantioselective trans-dihydroxylation of styrene to ( S)-1-phenyl-1,2-ethanediol, catalyzed by Escherichia coli (SSP1) coexpressing styrene monooxygenase and an epoxide hydrolase, was performed in HFMB with organic solvent in the shell side and aqueous cell suspension in the lumen side. Various organic solvents were investigated, and n-hexadecane was found as the best for the HFMB-based biphasic system. Comparing to other reported biphasic systems assisted by HFMB, our system not only shield much of the substrate toxicity but also deflate the product recovery burden in downstream processing as the majority of styrene stayed in organic phase while the diol product mostly remained in the aqueous phase. The established HFMB-based biphasic system enhanced the production titer to 143 mM, being 16-fold higher than the aqueous system and 1.6-fold higher than the traditional dispersive partitioning biphase system. Furthermore, the combination of biphasic system with HFMB prevents the foaming and emulsification, thus reducing the burden in downstream purification. HFMB-based biphasic system could serve as a suitable platform for enhancing the productivity of single-step or cascade biotransformation with toxic substrates to produce useful and valuable chemicals. [ABSTRACT FROM AUTHOR]

Chlorella vulgaris encapsulated in alginate beads were added into a bioreactor treating synthetic wastewater using Pseudomonas putida. A symbiotic CO/O gas exchange was established between the two microorganisms for photosynthetic aeration of wastewater. During batch operation, glucose removal efficiency in the bioreactor improved from 50 % in 12 h without aeration to 100 % in 6 h, when the bioreactor was aerated photosynthetically. During continuous operation, the bioreactor was operated at a low hydraulic retention time of 3.3 h at feed concentrations of 250 and 500 mg/L glucose. The removal efficiency at 500 mg/L increased from 73 % without aeration to 100 % in the presence of immobilized microalgae. The initial microalgae concentration was critical to achieve adequate aeration, and the removal rate increased with increasing microalgae concentration. The highest removal rate of 142 mg/L-h glucose was achieved at an initial microalgae concentration of 190 mg/L. Quantification of microalgae growth in the alginate beads indicated an exponential growth during symbiosis, indicating that the bioreactor performance was limited by oxygen production rates. Under symbiotic conditions, the chlorophyll content of the immobilized microalgae increased by more than 30 %. These results indicate that immobilized microalgae in symbiosis with heterotrophic bacteria are promising in wastewater aeration. [ABSTRACT FROM AUTHOR]

BTEX biodegradation by a mixed community of micro-organisms offers a promising approach in terms of cost-effectiveness and elimination of secondary pollution. Two bacterial strains, Pseudomonas putida F1 and Pseudomonas stutzeri OX1 were chosen to formulate synthetic consortia based on their ability to biodegrade the mono-aromatic compounds. Benzene and toluene supported the growth of both the strains; while ethyl benzene and o-xylene were only utilized as growth substrates by P. putida F1 and P. stutzeri OX1, respectively. In a mixed substrate system, P. putida F1 exhibited incomplete removal of o-xylene while P. stutzeri OX1 displayed cometabolic removal of ethyl benzene with dark coloration of the growth medium. The biodegradation potential of the two Pseudomonas species complemented each other and offered opportunities to explore their performance as a co-culture for enhanced BTEX biodegradation. Several microbial formulations were concocted and their BTEX biodegradation characteristics were evaluated. Mixed culture biodegradation ascertained the advantages of the co-culture over the individual Pseudomonas species. This study also emphasized the significance of inoculum density and species proportion while concocting preselected micro-organisms for enhanced BTEX biodegradation. [ABSTRACT FROM AUTHOR]

Species-specific enumeration of mixed community is invaluable as it facilitates a better understanding of the significance of the individual strains, their interactions, and the underlying mechanisms of community dynamics. Mixed microbial community has been characterized by microbiological, biochemical, or molecular biology-based methods. While microbiological and biochemical techniques do not provide adequate quantitative information of the members of the consortia and require additional techniques for a more comprehensive analysis, molecular biology-based methods analyze the microbial consortium based on specific DNA sequences and do not require isolation and culturing of bacteria for quantitative analysis. These methods outshine conventional culture-based techniques in terms of better sensitivity, reproducibility, and reliability. Quantitative molecular biology methods have been classified as PCR-based and probe hybridization methods. The PCR-based methods includes quantitative real-time PCR and terminal restriction fragment length polymorphism, while fluorescent in situ hybridization and DNA microarrays fall under probe hybridization methods. The workflow, the quantification methods, and their potential applications are discussed in this review by highlighting their advantages and possible limitations. [ABSTRACT FROM AUTHOR]

Molecular biological methods for mixed culture analysis outshine conventional culture-based techniques in terms of better sensitivity and reliability. The majority of these methods exploit the 16S rRNA sequences of the community DNA, which often fall short for the analysis of closely related microorganisms. This research details the development and validation of a comprehensive methodology to differentiate and quantitatively characterize two Pseudomonas species in a mixed culture. A bioinformatics tool based on whole-genome polymorphism comparison was used to identify marker sequences to differentiate the two bacteria using quantitative real-time PCR. The quantification of the two species was achieved through a correlation of the genomic DNA versus cell number (genomic DNA purification) and threshold cycle number versus genomic DNA (real-time PCR). Several factors including the limitation of genomic DNA purification, effects of substrate concentrations and growth phase on cellular DNA, and choice of simplex or duplex reaction for real-time PCR were considered and evaluated. The developed method was experimentally validated against synthetically constructed consortia. [ABSTRACT FROM AUTHOR]

Biodegradation can achieve complete and cost-effective elimination of aromatic pollutants through harnessing diverse microbial metabolic processes. Aromatics biodegradation plays an important role in environmental cleanup and has been extensively studied since the inception of biodegradation. These studies, however, are diverse and scattered; there is an imperative need to consolidate, summarize, and review the current status of aromatics biodegradation. The first part of this review briefly discusses the catabolic mechanisms and describes the current status of aromatics biodegradation. Emphasis is placed on monocyclic, polycyclic, and chlorinated aromatic hydrocarbons because they are the most prevalent aromatic contaminants in the environment. Among monocyclic aromatic hydrocarbons, benzene, toluene, ethylbenzene, and xylene; phenylacetic acid; and structurally related aromatic compounds are highlighted. In addition, biofilms and their applications in biodegradation of aromatic compounds are briefly discussed. In recent years, various biomolecular approaches have been applied to design and understand microorganisms for enhanced biodegradation. In the second part of this review, biomolecular approaches, their applications in aromatics biodegradation, and associated biosafety issues are discussed. Particular attention is given to the applications of metabolic engineering, protein engineering, and “omics” technologies in aromatics biodegradation. [ABSTRACT FROM AUTHOR]

The degradation pathways of benzoate at high concentration in Pseudomonas putida P8 were directly elucidated through mass spectrometric identification of some key catabolic enzymes. Proteins from P. putida P8 grown on benzoate or succinate were separated using two-dimensional gel electrophoresis. For cells grown on benzoate, eight distinct proteins, which were absent in the reference gel patterns from succinate-grown cells, were found. All the eight proteins were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry as catabolic enzymes involved in benzoate degradation. Among them, CatB (EC5.5.1.1), PcaI (EC2.8.3.6), and PcaF (EC2.3.1.174) were the enzymes involved in the ortho-cleavage pathway; DmpC (EC1.2.1.32), DmpD (EC3.1.1.-), DmpE (EC4.2.1.80), DmpF (EC1.2.1.10), and DmpG (EC4.1.3.-) were the meta-cleavage pathway enzymes. In addition, enzyme activity assays showed that the activities of both catechol 1,2-dioxygenase (C12D; EC1.13.11.1) and catechol 2,3-dioxygenase (C23D; EC1.13.11.2) were detected in benzoate-grown P. putida cells, undoubtedly suggesting the simultaneous expression of both the ortho- and the meta-cleavage pathways in P. putida P8 during the biodegradation of benzoate at high concentration. [ABSTRACT FROM AUTHOR]

A kinetic model to describe the degradation of phenol and cometabolic transformation of 4-chlorophenol (4-cp) in the presence of sodium glutamate (SG) has been developed and validated experimentally. The integrated model accounts for cell growth, toxicity of 4-cp, cross-inhibitions among the three substrates, and the different roles of the specific growth substrate (phenol) and the conventional carbon source (SG) in the cometabolism of 4-cp. In this ternary substrate system, the overall phenol degradation and 4-cp transformation rates are greatly enhanced by the addition of SG since SG is able to attenuate the toxicity of 4-cp and therefore increase the cell growth rate. Model analysis indicates that the maximum specific degradation rate of phenol (0.819 mg (mg.h)-1) is lowered by SG by up to 46% whereas the specific transformation rate of 4-cp is not directly affected by the presence of SG. The competitive inhibition coefficient of 4-cp tophenol degradation (Ki,cp) and that of phenol to 4-cp transformation (Ki,ph) were determined to be 6.49 mg l-1 and 0.193 mg l-1, respectively, indicating that phenol imposes much larger competitive inhibition to 4-cp transformationthan the converse. The model developed can simultaneously predict phenol degradation and 4-cp transformation, and is useful for dealing with cometabolism involving multiple substrates. [ABSTRACT FROM AUTHOR]

This paper reports on the feasibility of using glucose as an added substrate for cometabolic transformation of 4-chlorophenol (4-cp). When glucose was fed as the added growth substrate, only 78% and 43% of the initial 4-cp concentrations of 100 and 200 mg l-1, respectively, were transformed before the pH dropped to below 4.5 and stopped all reactions. By maintaining the medium pH, complete removal of 4-cp was achieved even at the high initial concentration of 200 mg l-1. Phenol induction prior to inoculation was not a prerequisite to ensure transformation of 4-cp when glucose was the added growth substrate. Compared with phenol as the added growth substrate, cells grown on glucose displayed a longer acclimation phase and, in general, a lower specific transformation rate. The volumetric transformation rate of 4-cp, however, was greatly enhanced due to the increased cell density. The results of this work suggest that 4-cp itself induced the enzymes necessary for its cometabolism. With NADH regenerated effectively through metabolism of glucose, 4-cp was transformed inthe absence of added phenol. Consequently, the competitive inhibition involved in cometabolism was avoided and the risks associated with addition of toxic growth substrates such as phenol were eliminated. [ABSTRACT FROM AUTHOR]

The enhancement of biodegradation of phenol and 4-chlorophenol (4-cp) as a cometabolised compound by Pseudomonas putida ATCC 49451 was accomplished by augmenting the medium with conventional carbon sources such as sodium glutamate and glucose. Compared with phenol as the sole carbon source, the addition of 1 gl-1 sodium glutamate increased the toxicity tolerance of cells toward 4-cp and significantly improved the biodegradation rates of both phenol and 4-cp even whenthe initial concentration of 4-cp was as high as 200 mgl-1. On the other hand, supplementation of glucose caused a significantdrop in the medium pH from 7.2 to 4.3 resulting in a reduction of degradation rate, leaving a considerable amount of 4-cp undegraded whenthe initial concentration of 4-cp was higher than 100 mgl-1. By regulating the pH of the medium, however, enhancement of degradation rates of phenol and 4-cp in the presence of glucose was achieved with a concomitant complete degradation of phenol and 4-cp. [ABSTRACT FROM AUTHOR]