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Over 100 tons of dyes are released per year into the wastewaters without prior treatment which adds to the contamination of freshwater resources globally. Thus, the development of economical, and sustainable control measures to avoid the pollution of natural resources remains imperative. In the present scenario, recent advancements in biological approaches have escalated bioremediation as a potential strategy for treatment of dyes and associated derivatives. These biological approaches utilize simple to complex microorganisms, plants, and wastes generated from different animal products as tools to remediate and remove dye molecules from wastewater. This particular chapter targets to address the recent advancements in the past three to four years in the sustainable treatment of dye molecules from wastewater using bioremediation approaches. The study also includes the prevailing hurdles, and research prospects in the bioremediation techniques utilized for the reduction of dyes from wastewater.

The inherent recalcitrance of lignocellulosic biomass is a significant barrier to efficient lignocellulosic biorefinery owing to its complex structure and the presence of inhibitory components, primarily lignin. Efficient biomass pretreatment strategies are crucial for fragmentation of lignocellulosic biocomponents, increasing the surface area and solubility of cellulose fibers, and removing or extracting lignin. Conventional pretreatment methods have several disadvantages, such as high operational costs, equipment corrosion, and the generation of toxic byproducts and effluents. In recent years, many emerging single-step, multi-step, and/or combined physicochemical pretreatment regimes have been developed, which are simpler in operation, more economical, and environmentally friendly. Furthermore, many of these combined physicochemical methods improve biomass bioaccessibility and effectively fractionate ∼96 % of lignocellulosic biocomponents into cellulose, hemicellulose, and lignin, thereby allowing for highly efficient lignocellulose bioconversion. This review critically discusses the emerging physicochemical pretreatment methods for efficient lignocellulose bioconversion for biofuel production to address the global energy crisis.

Microbial fuel cells (MFCs) are one of the sustainable technologies that can effectively treat wastewater with concomitant generation of electricity. The present study investigated the treatment of real dairy wastewater (RDW) using Shewanella algae (MTCC-10608) within a single chamber microbial fuel cell (SCMFC). The study was conducted in both batch and fed-batch modes with initial chemical oxygen demand (COD) of 4000 mg/L and 2000 mg/L, respectively, in 0.2 L working volume of RDW for 15 days. However, the fed-batch strategy involved subsequent feeding of dairy wastewater with 6000 mg/L and 8000 mg/L COD on the 5th and 10th day, respectively. This two-step feeding strategy resulted in a maximum open-circuit voltage of 666 mV at 286 h of incubation with a COD removal efficiency of 92.21% and a columbic efficiency of 27.45%. The kinetic studies predicted the saturation constant of 55.83 mg COD/L and current density of 143.3 mA/m2, which are similar to the findings from the experiments and polarization curve obtained. The maximum current density and power density from experiments were found to be 141 mA/m2 and 50 mW/m2 respectively. Thus, this study successfully indicates the utilization of dairy wastewater as a potential substrate for the sustainable power generation using Shewanella algae as a biocatalyst in the microbial fuel cell.

An inadequate lignocellulolytic capacity of a conventional anaerobic digester sludge (ADS) microbiota is the bottleneck for the maximal utilization of lignocellulose in anaerobic digestion. A well-constructed microbial consortium acclimatized to lignocellulose outperformed the ADS in terms of biogas productivity when fractionated biocomponents of rice straw were used to achieve a high methane bioconversion rate. A 33.3 % higher methane yield was obtained with the acclimatized consortium (AC) compared to that of ADS control. The dominant pair-wise link between Firmicutes (18.99-40.03 %), Bacteroidota (10.94-28.75 %), and archaeal Halobacteriota (3.59-20.57 %) phyla in the AC seed digesters indicated that the keystone members of these phyla were responsible for higher methane yield. A high abundance of syntrophic bacteria such as Proteiniphilum (1.22-5.19 %), Fermentimonas (0.71-5.31 %), Syntrophomonas (0.87-3.59 %), and their syntrophic partner Methanosarcina (4.26-18.80 %) maintained the digester stability and facilitated higher substrate-to-methane conversion in the AC seed digesters. The present combined strategy will help in boosting the 'biomass-to-methane" conversion.

Effective fractionation of lignocellulosic biocomponents of lignocellulosic biomass can increase its utilization in anaerobic digestion for high yield biomethane production. A hydrothermal process was optimized and integrated with a deep eutectic solvent (DES) pretreatment to preferentially fractionate hemicellulose, cellulose, and lignin in rice straw. The optimized hydrothermal process resulted in 96% hemicellulose solubilization at moderately low combined pretreatment severity (log S = 2.26), allowing increased hemicellulosic sugar recovery with minimal formation of inhibitory byproducts. Subsequent DES pretreatment resulted in highly bioaccessible cellulosic pulp, removing 81.3% of lignin that can be recovered and converted into value-added products. Anaerobic digestion of hemicellulosic fraction and cellulosic pulp using a microbial methanogenic consortium seed acclimatized to the lignocellulosic inhibitors resulted in a 33.4% higher yield of methane (467.84 mL g

The effective fractionation of structural components of abundantly available lignocellulosic biomass is essential to unlock its full biorefinery potential. In this study, the feasibility of humic acid on the pretreatment of Kentucky bluegrass biomass in alkaline condition was assessed to separate 70.1% lignin and hydrolyzable biocomponents. The humic acid-assisted delignification followed by enzymatic saccharification yielded 0.55 g/g of reducing sugars from 7.5% (w/v) pretreated biomass loading and 16 FPU/g of cellulase. Yeast fermentation of the biomass hydrolysate produced 76.6% (w/w) ethanol, which was subsequently separated and concentrated using direct contact membrane distillation. The hydrophobic microporous flat-sheet membrane housed in a rectangular-shaped crossflow module and counter-current mode of flow of the feed (hot) and distillate (cold) streams yielded a flux of 11.6 kg EtOH/m

Bioaugmenting lignocellulose digestion with potent lignocellulolytic microbiomes (LMs) facilitates efficient biomethanation. Assessing the metabolic roles of microbial communities of the LMs and their complex interactions with the indigenous anaerobic digester microbiome is pivotal in implementing bioaugmentation. Multiple meta-omics are the frontline approaches to investigating gene functions, metabolic roles, and the ecological niches of LMs.

Food waste is a promising renewable feedstock, which contains a significant amount of fermentable carbohydrate for biohydrogen production. The present research was conducted to investigate the effects of pH (5–7), chemical oxygen demand (COD) in food waste (8–10.8 g/L), and different substrate pretreatment methods on biohydrogen production from food waste. Inoculum enrichment was done by treating anaerobic digester sludge with 2-bromoethanesulfonate (BES) to inhibit methanogenic microorganisms. Dark fermentation was carried out at an initial pH of 7 for 48 h at 37 °C. Total protein before and after fermentation is estimated to be 646.5 µg/mL and 0.1 µg/mL, respectively while total carbohydrate is found to be 5.38 mg/mL and 3.885 mg/mL, respectively. Volatile fatty acids and ethanol production accompanied biohydrogen production which was detected through HPLC. Under optimized conditions of pH 7, temperature 37 °C for 48 h and without any substrate pretreatment around maximum 52% H2 was obtained in the produced biogas.

Hydrogen (H2) is considered as fuel for future and its biological production from renewable feedstocks is very promising. Dark fermentation of fruit-vegetable waste (FVW) and cottage cheese whey (CCW) for the production of H2 constitutes a promising way for combining energy generation and lignocellulosic waste management. In this work, process kinetics of biohydrogen production via dark fermentation of FVW and CCW by pretreated anaerobic sludge inocula were investigated. To inhibit H2 consuming methanogens, the effects of various inoculum pretreatment, viz., 2-bromoethanesulfonate, heat-shock, acid, alkali, UV, and ultrasonication on H2-production were investigated which revealed 2-bromoethanesulfonate, heat-shock and acid-treated inoculum resulted in maximum bioH2 production and yield of 118.12 ± 1.05, 93.37 ± 1.3, 96.32 mMol/L and 1.66, 1.22 ± 0.01, 1.39 ± 0.02 mMol/gCODinitial, respectively. The effects of system initial pH, substrate to inoculum (S0/X0) and carbon to nitrogen (C/N) ratio on H2-production were evaluated which revealed maximum H2 production and yield could be achieved at pH 7, S0/X0 of 10.6 gCOD/gVS, and C/N 26.8. Modified Gompertz model and Modified Logistic model were used to define various kinetic parameters pertaining to cumulative H2-production which showed high R2 values (≥0.98). The influence of pH on H2 and ethanol/volatile fatty acids production kinetics were evaluated using Andrew's and Ratkowsky's model showing relatively good R2 values (≥0.62). Remarkably high production of ethanol (2.43 ± 0.28 mg/L) was noticed alongside H2 production at pH 7 suggesting that bioethanol can be recovered at the end of fermentative H2 production. Terminal Restriction Fragment Length Polymorphism and 16s rDNA sequencing revealed dominance of 9 bacterial species such as Escherichia coli, Clostridium butyricum, Streptococcus henryi, and 6 others uncultured bacteroides. This research determined different kinetic parameters for an enhanced H2 production strategy by co-fermentation of FVW and CCW providing an understanding of process behavior which will in turn help in the upscaling of the H2-production processes.

The commercial feasibility of energy-efficient conversion of highly concentrated microalgal suspensions to produce high-titer biofuels is a major bottleneck due to high energy consumption. Herein, high-titer biofuels (bioethanol, higher-alcohols, and biodiesel) were generated from carbohydrate-rich Chlamydomonas mexicana and lipid-rich Chlamydomonas pitschmannii biomass through energy-saving microwave pretreatment, successive fermentation, and transesterification. Microwave pretreatment needed low specific energy (4.2 MJ/kg) for 100 g/L of microalgal suspension. Proposed sustainable integrated pretreatments method achieved unprecedented total conversion efficiency (67%) and highest biomass utilization (87%) of C. pitschmannii (100 g/L) with high yields of bioethanol (0.48 g-ethanol/g-carbohydrates), higher-alcohols (0.44 g-higher-alcohols/g-proteins), and biodiesel (0.90 g-biodiesel/g-lipids). Transmission electron microscopy showed the changes in the microalgal cellular integrity before and after sequential fermentations. Energy-efficient integrated pretreatments enhanced the extraction efficiency and whole utilization of high-concentration microalgae to generate high-titer biofuels with minimum waste production.

The commercial feasibility regarding conversion of the high-solid-loading microalgal suspensions for high-titer biofuels production is questionable owing to incomplete utilization and high processing costs. In this study, the production of multiple highly concentrated biofuels (bioethanol, higher alcohols, and biodiesel) was achieved through cost-effective integrated approach (pretreatment, serial fermentation of carbohydrate/protein, and transesterification of lipid) from highly concentrated (100 g/L) microalgal suspensions (Chlamydomonas mexicana and Chlamydomonas pitschmannii). This integrated approach attained unprecedented total conversion efficiency (48–63%) and maximum total biomass utilization (77–86%) for both the microalgal strains with high yields of bioethanol (0.48 g-ethanol/g-carbohydrate), higher alcohols (0.44 g-higher alcohols/g-protein), and biodiesel (0.82–0.89 g-biodiesel/g-lipid) at suspensions of 100 g/L. Transmission electron microscopy was employed to visualize the changes in the intercellular morphologies before and after serial fermentations. Thus, this study demonstrates a cost-effective and energy-saving integrated approach for the holistic conversion of high-solid-loading microalgal biomass to produce high-density biofuels with minimum waste generation.

This study determines the optimum food waste (FW) loading in an anaerobic digester for methane production. Interrelation between the degradation mechanism and microbial community composition was assessed through in-depth metabolic pathway analysis and gene quantification. Higher methane production and short lag phase were observed in the FW reactors with low substrate loadings (4% v/v) while extended lag phase and incomplete substrate utilization were observed in the reactors fed with higher substrates (6% v/v). The long-chain fatty acids (LCFAs) degradation was influenced by initial FW loading, and up to 99% LCFA degradation occurred at 4% FW reactor. The addition of 8 to 10% FW substrate inhibited methanogenesis due to the accumulation of volatile fatty acids (VFA) and low LCFA degradation. Under optimal conditions of substrate loading, Methanosaeta and Methanosarcina were abundant, indicating their role in methanogenesis and syntrophic acetogenesis, along with enhanced metabolic pathways specific for carbohydrate and lipid metabolism.

Methanation was improved during the dual-stage pulse-feed anaerobic co-digestion of extracted lipid (EL) from food waste leachate using acclimatized consortia by gradually increasing the organic loading rates (OLRs) in the subsequent phases. The utilization of major saturated and unsaturated long chain fatty acids (LCFAs) reached 78% and 98% in the acidogenic fermenters with consecutive organic loading, respectively. The acclimatized consortium induced the LCFA degradation and interconversion of short-medium chain fatty acids (SCFA–MCFAs) in the fermenters, even under highest OLR values. The highest methane yield (0.46 g g−1 VSinitial) was achieved in the third phase (61% EL loading of total injected volatile solid) with the complete utilization of LCFAs and SCFA–MCFAs in the digester. The assessment of the microbial community revealed that acidogenic Intestinimonas and Megasphaera, and acetogenic Levilinea were predominant in the fermenters due to their preeminent activities. The predominance of acetogenic Syntrophomonas (26%) indicated that it played a major role in β-oxidation, and its syntrophy with mixotrophic methanogens, such as Methanosarcina (93%), facilitated methanation through the complete degradation of EL in the digesters. The use of pulse-feed operation in dual-stage anaerobic co-digestion improved the methanation through complete utilization of EL under varied OLRs mediated by the acclimatized consortia.

Biological pretreatment of polysaccharidic wastes (PWs) is a cost-effective and environmentally friendly approach to improve the digestibility and utilization of these valuable substrates in dual-stage biohythane production. In order to reduce the prolonged incubation time and loss of carbohydrate during the pretreatment of PWs with Aspergillus fumigatus, a systematic optimization using Taguchi methodology resulted in an unprecedented recovery of soluble carbohydrates (362.84 mg g−1) within 5 days. The disruption and fragmentation of lignocellulosic structures in PWs, and possible saccharification of cellulose and hemicellulose components, increased its digestibility. A dual-stage biohythane production with pretreated PWs showed increased yield (214.13 mL g−1 VSadded), which was 56% higher than the corresponding value with the untreated PWs. This resulted in 47% higher energy recovery as biohythane in pretreated biomass compared to untreated biomass. Optimized fungal pretreatment is, therefore, an effective method to improve the digestibility of PWs and its subsequent conversion to biohythane.

Cost-effective biomass drying is a key challenge for energy recovery from biomass by direct combustion, gasification, and pyrolysis. The aim of the present study was to optimize the process of biomass drying using hot air convection (HA), infrared (IR), and combined drying systems (IR-HA). The specific energy consumption (SEC) decreased significantly by increasing the drying temperature using convective drying, but higher air velocities increased the SEC. Similarly, increasing air velocity in the infrared dryer resulted in a significant increase in SEC. The lowest SEC was recorded at 7.8 MJ/kg at an air velocity of 0.5 m/s and an IR intensity of 0.30 W/cm2, while a maximum SEC (20.7 MJ/kg) was observed at 1.0 m/s and 0.15 W/cm2. However, a significant reduction in the SEC was noticed in the combined drying system. A minimum SEC of 3.8 MJ/kg was recorded using the combined infrared-hot air convection (IR-HA) drying system, which was 91.7% and 51.7% lower than convective and IR dryers, respectively. The present study suggested a combination of IR and hot air convection at 60 °C, 0.3 W/cm2 and 0.5 m/s as optimum conditions for efficient drying of biomass with a high water content.

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.

Acidification during anaerobic digestion (AD) due to organic overloading is one of the major reasons for process failures and decreased methane productivity in anaerobic digesters. Process failures can cause the anaerobic digesters to stall completely, prolong the digester recovery period, and inflict an increased operational cost on wastewater treatment plants and adverse impacts on the environment. This study investigated the efficacy of bioaugmentation by using acclimatized microbial consortium (AC) in recovering anaerobic digesters stalled due to acidosis. Overloading of digesters with food waste leachate (FWL) led to the accumulation of volatile fatty acids (11.30 g L−1) and a drop in pH (4.67), which resulted in process failure and a 22-fold decline in cumulative methane production compared to that in the initial phase. In the failure phase, the syntrophic and methanogenic activities of the anaerobic digester microbiota were disrupted by a significant decrease in the abundance of syntrophic populations such as Syntrophomonas, Syntrophorhabdus, Sedimentibacter, and Levilinea, and the phylum Euryarchaeota. Bioaugmentation of the failed digesters by adding AC along with the adjustment of pH resulted in the prompt recovery of methane productivity with a 15.7-fold higher yield than that in unaugmented control. The abundance of syntrophic bacteria Syntrophomonas and phylum Euryarchaeota significantly increased by 29- and 17-fold in the recovered digesters, respectively, which showed significant positive correlations with methane productivity. Methanosarcina and acetoclastic Methanosaeta played a major role in the recovery of the digesters; they were later replaced by hydrogenotrophic Methanoculleus. The increase in the abundance of genes associated with biomethanation contributed to digester recovery, according to the functional annotation of 16S rDNA amplicon data. Thus, bioaugmentation with AC could be a viable solution to recover digesters experiencing process failure due to organic overloading.

This review article presents a comprehensive literature survey over the last two decades on the evaluation of production processes of succinic acid (SA) to further direct the research towards the membrane-based sustainable and economical production. The traditional chemical and petrochemical-based industries desperately need to switch from the conventional polluting and energy-intensive processes by the clean and green processes due to growing environmental concern, strict discharge limit and emaciated profit margin in a competitive world market. In recent years, the prospect for process intensification by the integration of highly selective customized membranes in an appropriate module with conventional fermenter for downstream separation, purification and concentration of SA seems imminent with the expectation of a turnaround in biochemical industries. Through a comprehensive literature survey of critical aspects, the review article has suggested a novel approach on the application of a multi-staged membrane-based system for the manufacturing of SA leading to the prospect of sustainable business.

Lignocellulosic biomass (LCB) is expected to play a significant role in achieving the goal of biomass-to-bioenergy conversion due to its wide distribution and low price. Acidogenic dark fermentation of LCB is a promising approach to the sustainable production of biohydrogen (bioH2) from this valuable substrate. Because of its inherent recalcitrance, LCB requires pretreatment to increase its digestibility and enable its improved utilization. Intense thermochemical pretreatments solubilize the lignin and hemicellulose and lead to the formation of a variety of inhibitory byproducts, such as short-chain carboxylic acids, furfural, 5-hydroxymethylfurfural (5-HMF), vanillin, and syringaldehyde, which interfere with the physiological and metabolic functions of dark fermentative microbiota, thus inhibiting bioH2 production. To offset the negative impacts of these inhibitors on bioH2 production, approaches to detoxify lignocellulosic hydrolysates have been considered. This review comprehensively discusses the generation of lignocellulosic inhibitory byproducts in commonly used, contemporary pretreatment regimens and their inhibitory effects on dark fermentative H2 production. Furthermore, the mechanisms of inhibiting H2 producing bacteria and their effects on bacterial community dynamics in mixed cultures are reviewed. State-of-the-art strategies for detoxifying pretreated LCB are discussed. The selection of desirable alternative lignocellulose pretreatment strategies that produce less or no inhibitory byproducts are highlighted. Finally, this review discusses the economic aspects of bioH2 production from LCB, considering the pretreatment and detoxification process. Given the limitations of previous studies, future research for developing cost-effective strategies to overcome byproduct inhibition during dark fermentation of pretreated LCB are suggested.

The physiological properties, including biochemical composition and cell wall thickness, of microalgal species have a remarkable effect on the pretreatment of biomass and its further conversion to biofuels. In the present study, multiple biofuels (bioethanol, higher alcohols (C3–C5), and biodiesel) were produced using energy-efficient microwave pretreatment, successive carbohydrate/protein fermentation, and lipid transesterification from three microalgal strains (Pseudochlorella sp., Chlamydomonas mexicana, and Chlamydomonas pitschmannii). The microwave pretreatment method required the lowest specific energy (5 MJ/kg) compared to ultrasound pretreatment. The proposed integrated approach achieved high conversion efficiency (46%) and maximum biomass utilization (93%) of C. mexicana with improved yields of bioethanol (0.46 g-ethanol/g-carbohydrates), higher alcohols (0.44 g-higher alcohols/g-proteins), and biodiesel (0.74 g-biodiesel/g-lipids). This study suggests that the application of an appropriate pretreatment method for microalgal strains having different physiological properties is essential for improving the extraction efficiency and conversion of biomass to biofuels with less waste production.

Sugarcane bagasse (SCB) as cheap, abundant, alternative cell immobilization matrix for phenol biodegradation was investigated in the present study. Scanning electron microscopy revealed that yeast Candida tropicalis PHB5 attached to the cavum of stalk cells of SCB efficiently through adsorption and maximum value of immobilization efficiency and cell retention were 87.74% ± 2.42 and 368384 ± 10195.96 cfu g−1 SCB, respectively. In order to assess the degradation efficacy of SCB immobilized cells, kinetics of phenol degradation was compared for free as well as alginate and SCB immobilized cells. The maximum specific degradation rates were 9.599, 1.665, and 2.481 g g−1 h−1 for free cells, alginate and SCB immobilized cells, respectively. The effective diffusivity and diffusion effectiveness factor of phenol in immobilization matrices were calculated for different sizes of matrix particles. The results showed that intraparticle diffusion resistance was comparatively less for SCB particle. Studies revealed that 23.45% of SCB immobilized cells can be effectively retained during storage at 4 °C up to 30 days and can be reused for 4–5 repeated batch degradation, giving almost similar results found with alginate immobilized cells. The foregoing results justify the applicability of SCB as carrier matrix for immobilization of microorganisms in removal of phenolic compounds from industrial wastewaters.

Research work was carried out to describe the kinetics of cell growth, substrate consumption and product formation in batch fermentation of rapamycin using shake flask as well as laboratory-scale fermentor. Fructose was used as the sole carbon source in the fermentation media. Optimization of fermentation parameters and reliable mathematical models were used for the maximum production of rapamycin from Streptomyces hygroscopicus MTCC 4003. The experimental data for microbial production of rapamycin fitted well with the proposed mathematical models. Kinetic parameters were evaluated using best fit unstructured models, viz. Andrew’s model, Monod model, Yano model, Aiba model. Andrew’s model showed a comparatively better R2 value (0.9849) among all tested models. The values of maximum specific growth rate (μmax), saturation constant (KS), inhibition constant (Ki), and growth yield coefficient (YX/S) were found to be 0.008 (h−1), 2.835 (g/L), 0.0738 (g/L), and 0.1708 (g g−1), respectively. The optimum production of rapamycin was obtained at 300 rpm agitation and 1 vvm aeration rate in the fermentor. The final production of rapamycin in shake flask was 539 mg/L. Rapamycin titer found in bioreactor was 1,316 mg/L which is 52 % higher than the latest maximum value reported in the literature.

A highly tolerant phenol-degrading yeast strain PHB5 was isolated from wastewater effluent of a coke oven plant and identified as Candida tropicalis based on phylogenetic analysis. Biodegradation experiments with C. tropicalis PHB5 showed that the strain was able to utilize 99.4 % of 2,400 mg l−1 phenol as sole source of carbon and energy within 48 h. Strain PHB5 was also observed to grow on 18 various aromatic hydrocarbons. Haldane model was used to fit the exponential growth data and the following kinetic parameters were obtained: μ max = 0.3407 h−1, K S = 15.81 mg l−1, K i = 169.0 mg l−1 (R 2 = 0.9886). The true specific growth rate, calculated from μ max, was 0.2113. A volumetric phenol degradation rate (V max) was calculated by fitting the phenol consumption data with Gompertz model and specific degradation rate (q) was calculated from V max. The q values were fitted with Haldane model, yielding following parameters: q max = 0.2766 g g−1 h−1, K S ′ = 2.819 mg l−1, K i ′ = 2,093 (R 2 = 0.8176). The yield factor (Y X/S ) varied between 0.185 to 0.96 g g−1 for different initial phenol concentrations. Phenol degradation by the strain proceeded through a pathway involving production of intermediates such as catechol and cis,cis-muconic acid which were identified by enzymatic assays and HPLC analysis.

The Taguchi orthogonal array (OA) design of experiments methodology, a quality optimization tool, was used to improve the phenol biodegradation potential of the yeast Candida tropicalis PHB5. At three levels, an OA was selected to analyze the effects of the different physicochemical process factors. Experiments were undertaken to confirm the effectiveness of this method and the main factors affecting the growth of C. tropicalis on phenol and its subsequent degradation were found, together with the optimal factor levels. Predicted results showed that biomass yield could be increased from 1,051.96 to 2,495.74 mg/l and the subsequent amount of phenol degraded could be increased from 879.42 to 2,386.43 mg/l. Based on Taguchi methodology, an overall enhancement of growth by 137.24% and phenol degradation by 171.49% could be attained. Validation experiments showed that the growth and phenol biodegradation was significantly improved by up to 132.4% and 165.64%, respectively.

Candida tropicalis PHB5 was able to grow on 4-chlorophenol and to metabolize this substrate. 4-Chlorophenol degradation proceeds through a pathway involving transient production of three key metabolites 4-chlorocatechol, 4-chloropyrogallol and 4-carboxymethelenebut-2-en-4-olide which were identified by HPLC analysis. The Taguchi orthogonal array design methodology was used to improve the 4-chlorophenol biodegradation ability of strain PHB5. At 3 levels, an orthogonal array was selected to analyze the effects of the different physicochemical process factors. Experiments were undertaken to study the effects of eleven factors affecting the growth of C. tropicalis on 4-chlorophenol and its degradation. Taguchi methodology predicted that biomass yield on 4-chlorophenol could be increased from 409.7 mg l −1 to 1046.9 mg l −1 and the amount of 4-chlorophenol degraded could be increased from 314.5 mg l −1 to 949.7 mg l −1 . Based on Taguchi methodology, an overall enhancement of growth by 155.5% and of 4-chlorophenol degradation by 201.9% were predicted. The predicted values were validated by experimental data which showed than under optimal cultural conditions, the biomass yield was increased by 141.62% and 4-CP degradation by 183%.

A novel extracellular serine protease (70 kDa by SDS-PAGE) was purified and characterized. This enzyme retained more than 93% of its initial activity after preincubation for 30 min at 37 °C in the presence of 25% (v/v) tested organic solvents and showed feather degradation activity. The purified enzyme was deactivated at various combinations of pH and temperature to examine the interactive effect of them on enzyme activity. The deactivation process was modeled as first-order kinetics and the deactivation rate constant (k(d)) was found to be minimum at pH 9 and 37 °C. The kinetic analysis of enzyme over a range of pH values indicated two pK values at 6.21 and at 10.92. The lower pK value was likely due to the catalytic histidine in the free enzyme and higher pK value likely reflected deprotonation of the proline moiety of the substrate but ionization of the active site serine is another possibility. Inhibition kinetic showed that enzyme is serine protease because enzyme was competitively inhibited by antipain and aprotinin as these compounds are known to be competitive inhibitors of serine protease. The organic solvent, thermal and pH tolerances of enzyme suggested that it may have potential for use as a biocatalyst in industry.

An in depth process engineering study on the effect of temperature and pH on kinetic parameters of alkaline protease production by Bacillus licheniformis NCIM-2042 using starch as substrate has been reported.

The present research was conducted to define the approaches for enhanced production of rapamycin (Rap) by Streptomyces hygroscopicus microbial type culture collection (MTCC) 4003. Both physical mutagenesis by ultraviolet ray (UV) and chemical mutagenesis by N-methyl-N-nitro-N-nitrosoguanidine (NTG) have been applied successfully for the improvement of Rap production. Enhancing Rap yield by novel sequential UV mutagenesis technique followed by fermentation gives a significant difference in getting economically scalable amount of this industrially important macrolide compound. Mutant obtained through NTG mutagenesis (NTG-30-27) was found to be superior to others as it initially produced 67% higher Rap than wild type. Statistical optimization of nutritional and physiochemical parameters was carried out to find out most influential factors responsible for enhanced Rap yield by NTG-30-27 which was performed using Taguchi orthogonal array approach. Around 72% enhanced production was achieved with nutritional factors at their assigned level at 23 °C, 120 rpm and pH 7.6. Results were analysed in triplicate basis where validation and purification was carried out using high performance liquid chromatography. Stability study and potency of extracted Rap was supported by turbidimetric assay taking Candida albicans MTCC 227 as test organism.

The different chemical pollutants discharged by the industries to the environment can upset the delicate balance of the ecosystem. Bioremediation, the use of microorganisms and plants to remediate polluted environments, is a promising and growing area of environmental biotechnology. Bioremediation options encompass diverse types of biotechnological mechanisms that may lead to a target pollutant's mineralization, partial transformation, humification, or altered redox state. The use of extra cellular and/or cell-free enzymes has been also proposed as an innovative remediation technique. Perspectives and limitations to evolve and use this technology are critically discussed in this chapter with respect to the complexity of mixtures of xenobiotics often found in practice. Whereas the potential of bioremediation is substantial, its application has important limitations that are apparent from many examples and the authors feel that these limitations can be overcome only when adequate attention is directed to fundamental microbiological, chemical and engineering issues.

The present review emphasizes on the use of Polyphenol oxidase (PPO) enzyme in the bioremediation of phenolic contaminants from industrial wastewater. PPO is a group of enzyme that mainly exists in two forms; tyrosinase (E.C. 1.14.18.1) and laccase (E.C. 1.10.3.1) which are widely distributed among microorganisms, plants and animals. These oxidoreductive enzymes remain effective in a wide range of pH and temperature, particularly if they are immobilized on some carrier or matrices, and they can degrade a wide variety of mono and/or diphenolic compounds. However, high production costs inhibit the widespread use of these enzymes for remediation in industrial scale. Nevertheless, bench studies and field studies have shown enzymatic wastewater treatment to be feasible options for biodegradation of phenols through biological route. Nanomaterials-PPO conjugates have been also applied for removal of phenols which has successfully lower down the drawbacks of enzymatic water treatment. Therefore in this article various approaches and current state of use of PPO in the bioremediation of wastewater, as well as the benefits and disadvantages associated with the use of such enzymes have been overviewed.

A novel white rot fungus Alternaria alternata CMERI F6 decolorized 99.99% of 600 mg/L congo red within 48 h in yeast extract-glucose medium at 25 °C, pH 5 and 150 rpm. Physicochemical parameters like carbon and nitrogen sources, temperature, pH and aeration were optimized to develop faster decolorization process. Dye decolorization rate was maximal (20.21 mg/L h) at 25 °C, pH 5, 150 rpm and 800 mg/L dye, giving 78% final decolorization efficiency. Scanning electron microscopy and X-ray Diffraction analysis revealed that the fungus become amorphous after dye adsorption. HPLC and FTIR analysis of the extracted metabolites suggested that the decolorization occurred through biosorption and biodegradation. Thermogravimetric analysis (TGA), differential thermal analysis (DTA) and acid-alkali and 70% ethanol treatment revealed the efficient dye retention capability of the fungus. The foregoing results justify the applicability of the strain in removal of congo red from textile wastewaters and their safe disposal.

An extensive investigation was carried out to describe the kinetics of cell growth, substrate consumption, and product formation in the batch fermentation using starch as substrate. Evaluation of intrinsic kinetic parameters was carried out using a best-fit unstructured model. A nonlinear regression technique was applied for computational purpose. The Andrew's model showed a comparatively better R2 value among all tested models. The values of specific growth rate (micronmax), saturation constant (KS), inhibition constant (KI), and YX/S were found to be 0.109 h-1, 11.1 g/l, 0.012 g/l, and 1.003, respectively. The Leudeking- Piret model was used to study the product formation kinetics and the process was found to be growth-associated. The growth-associated constant (alpha) for protease production was sensitive to substrate concentration. Its value was fairly constant up to a substrate concentration of 30.8 g/l, and then decreased.