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Butanol produced from renewable feedstock is defined as an emerging biofuel and biochemical. Research efforts made during the last three decades on biochemical production of butanol via conventional ABE (acetone-ethanol-butanol) fermentation has tried to bring biobutanol close to competition with petrobutanol. However, each new effort of development has been often countered by new challenges, confining biobutanol production mostly to the laboratory scale. This review provides a systematic, comparative analysis of different steps in biochemical production of butanol and identifies the counteractive aspects and challenges to overcome. A special emphasis is given on process inhibitors, applied detoxification techniques, chemical supplements and research & development in industry in order to enhance and update ABE fermentation and make it cost effective. Biobutanol future lies in utilization of inexpensive cellulose enriched lignocellulosic hydrolysates and hyper-butanol producing bacteria, combined with specific detoxification techniques and followed by efficient continuous fermentation technologies together with in situ product recovery.

Pulp and paper solid waste (PPSW) originating from paper industry, was experimented for the production of fumaric acid (FA) through submerged and solid state fermentation by utilizing the filamentous fungus Rhizopus oryzae 1526 . Physicochemical characterization, pH and moisture content analysis of PPSW was carried out. Pre-treatment of PPSW by size reduction resulted in particles of different size ranges (1.7 mm x ≤ 3.35 mm, 850 μm x ≤ 1.7 mm, 300 μm x ≤ 850 μm, 75 μm x ≤ 300 μm and 33 μm x ≤ 75 μm). In submerged fermentation with all particle size ranges, a maximum of 23.47 ± 0.70 g/L of FA was obtained with 33 μm x ≤ 75 μm under the fermentation conditions of 30 °C, 200 rpm, 5% pre-cultured inoculum ( v/v ) and at 48 h. Viscosity measurement and analysis of by-product of the fermented broths were performed. Microwave-phosphoric acid mediated hydrolysis of 33 μm x ≤ 75 μm particle size produced hydrolysate with maximum glucose (11.2 ± 0.8 g/L) and xylose (20.22 ± 0.85 g/L) contents. Submerged fermentation with this hydrolysate confirmed the utilization of xylose for both FA production and fungal growth. Solid state fermentation with 75 μm x ≤ 300 μm particle size resulted in highest FA production (41.45 g/kg dry weight) after 21 days. Scanning electron microscopy revealed the morphological features of the fungus grown on the particles. The results of the present study confirmed the utilization of PPSW as a source of carbon and trace elements by the fungus R. oryzae 1526 and also the bioconversion into FA during fermentation. FA being a high value platform chemical, its bioproduction from the low cost PPSW, is a value addition approach.

The aim of the present study was to explore the possible application of calcium carbonate nanoparticles (CCNPs) and microwave irradiation (MWI) in fumaric acid (FA) production and recovery, respectively. The fungal strain Rhizopus oryzae 1526 was employed as the biocatalyst for FA production. A glucose-basic salt medium was used as the fermentation medium. Scanning electron microscopy (SEM) analysis of CCNPs displayed the spherical shapes, while zetasizer measurements showed the CCNPs to be around 190 ± 20 nm in size. FTIR analysis of CCNPs confirmed the chemical composition. BET analysis confirmed higher specific surface areas of CCNPs (11.95 ± 0.03 m2 g−1) compared to calcium carbonate microparticles (CCMPs) (3.51 ± 0.02 m2 g−1). FA neutralization timing for CCNPs was much lower than CCMPs (190 and 350 seconds, respectively). CCNPs enhanced the volumetric productivity of FA from 0.47 g L−1 h−1 to 0.74 g L−1 h−1. At 20, 40 and 60 g L−1 concentrations and at 25 °C, viscosities of the CCNPs were found to be lower than respective CCMPs. Moreover, the CCNPs did not exhibit any toxicity towards the fungus. FA production obtained with CC micro and CCNPs were 67.34 ± 2 g L−1 and 66.92 ± 2.7 g L−1, respectively. Under MWI heating, 10 ± 1 min was found to be sufficient for recovery of FA and this was much lower than conventional heating timing of 28 ± 1 min.

Brewery liquid waste (BLW), brewery spent grain (BSG), apple pomace solid wastes (APS), apple pomace ultrafiltration sludge (APUS) and starch industry waste (SIW) were evaluated as alternative feedstocks for levulinic acid (LA) production via microwave-assisted acid-catalyzed thermal hydrolysis. LA production of 204, 160, 66, 49 and 12 g/kg was observed for BLW, BSG, APS, APUS, and SIW, respectively, at 140 °C, 40 g/L substrate concentration (SC), 60 min and 2 N HCl (acid concentration). Based on the screening studies, BLW and BSG were selected for optimization studies using response surface methodology. Maximum LA production of 409 and 341 g/kg for BLW and BSG, respectively were obtained at 160 °C, 4.5 M HCl, 85 g/L SC and 27.5 min. Results demonstrated the possibility of using brewery wastes as promising substrates for economical and higher yield production of LA, a renewable platform chemical and versatile precursor for fuels and chemicals.

Utilization of apple industry solid waste, apple pomace (AP) for the production of fumaric acid (FA) using a rotating drum type solid-state bench scale fermenter was studied under optimized conditions and different mechanisms underlying the conversion were investigated. The filamentous fungal strain, Rhizopus oryzae 1526 was used in the study. The solid-state fermentation was carried out in continuous rotation, intermittent rotation and static mode of the fermenter operations for a maximum of 21 days. Two different moisture contents (70% and 50%, w/w) of AP were applied for each batch. The highest FA concentration (138 ± 9.11 g per kg dry weight of AP) was achieved at 50% moisture content and under continuous rotation after 14 days. Viability checking of the fungus showed maintenance of a high cell count (2.74 × 108 spores per g dry apple pomace) during fermentation. Analysis of AP fibre composition confirmed the conversion of insoluble dietary fibers into soluble dietary fibers and utilization of the dietary fibres for FA production. Total phenolic content of AP was considerably increased (by around 86%) from 185 ± 10.5 to 345 ± 8.5 mg per g lyophilizate after 18 days. LC/MS/MS analysis confirmed the consumption of sugars (glucose fructose and sucrose) present in AP by the fungus during fermentation. The presence of different phenolic compounds and changes in their content after fermentation was also confirmed by LC/MS/MS analysis. Two other operating conditions produced 82 ± 6.8 and 58 ± 8.5 g of FA per kg dry weight of AP, respectively after 18 days of fermentation.

Brewery industry liquid waste (BLW), brewery spent grain (BSG), apple pomace solid wastes (APS), apple pomace ultrafiltration sludge (APUS) and starch industry wastewater (SIW) have been considered as substrates to produce biobutanol. Efficiency of hydrolysis techniques tested to produce fermentable sugars depended on nature of agro-industrial wastes and process conditions. Acid-catalysed hydrolysis of BLW and BSG gave a total reducing sugar yield of 0.433 g/g and 0.468 g/g respectively. Reducing sugar yield from microwave assisted hydrothermal method was 0.404 g/g from APS and 0.631 g/g from APUS, and, 0.359 g/g from microwave assisted acid-catalysed SIW dry mass. Parameter optimization (time, pH and substrate concentration) for acid-catalysed BLW hydrolysate utilization using central composite model technique produced 307.9 g/kg glucose with generation of inhibitors (5-hydroxymethyl furfural (20 g/kg), furfural (1.6 g/kg), levulinic acid (9.3 g/kg) and total phenolic compound (0.567 g/kg)). 10.62 g/L of acetone-butanol-ethanol was produced by subsequent clostridial fermentation of the substrate.

Conidiation and lytic enzyme production by Trichoderma viride at different solids concentration of pre-treated municipal wastewater sludge was examined in a 15-L fermenter. The maximum conidia concentration (5.94 × 107 CFU mL−1 at 96 h) was obtained at 30 g L−1 suspended solids. The maximum lytic enzyme activities were achieved around 12–30 h of fermentation. Bioassay against a fungal phytopathogen, Fusarium sp. showed maximum activity in the sample drawn around 96 h of fermentation at 30 g L−1 suspended solids concentration. Entomotoxicity against spruce budworm larvae showed maximum value ≈17290 SBU μL−1 at 30 g L−1 suspended solids concentration at the end of fermentation (96 h). Plant bioassay showed dual action of T. viride, i.e., disease prevention and growth promotion. The rheological analyses of fermentation sludges showed the pseudoplastic behaviour. In order to maintain required dissolved oxygen concentration ≥30%, the agitation and aeration requirements significantly increased at 35 g L−1 compared to 30 and 25 g L−1. The oxygen uptake rate and volumetric oxygen mass transfer coefficient, kLa at 35 g L−1 did not increase in comparison to 30 g L−1 due to rheological complexity of the broth during fermentation. Thus, the successful fermentation operation of the biocontrol fungus T. viride is a rational indication of its potential for mass-scale production for agriculture and forest sector as a biocontrol agent.

Rheology of Bacillus thuringiensis fermentation of hydrolyzed sludge was investigated in bench scale fermenter. Stable liquid formulations were developed and optimized for two-year based studies comprising various physical/chemical (viscosity, particle size, corrosion and suspendibility) and biological (microbial contamination, viable spores and entomotoxicity) parameters at different pHs and temperatures. The hydrolyzed sludge depicted non-Newtonian and pseudoplastic behaviour during fermentation with 90% to 96% confidence of fits into Casson, Power and IPC paste models. Higher values of consistency and flow index during exponential growth and stationary phase, respectively, affected downstream processing. The power law was also followed by stable formulations. Sorbitol, sodium monophosphate and sodium metabisulfite (2.2:1:1) as suspending agents produced suspendibility ranging from 69% to 94%. The stable formulation (FH-4) comprising sorbitol, sodium monophosphate and sodium metabisulfite deteriorated at pHs 6, 6.5 and temperatures, 40 and 50 degrees C, with no signs of corrosion and microbial contamination. The viscosity of FH-4 formulations decreased with shear rate which could improve handling and consequent spraying.

Apple pomace is a by-product from the apple processing industry and can be used for the production of many value-added compounds such as enzymes, proteins, and nutraceuticals, among others. An investigation was carried out to study the improvement in the protein content in apple pomace by solid-state fermentation using the fungus Phanerochaete chrysosporium by tray fermentation method. The effect of this protein in terms of how it enriched apple pomace as animal feed for pigs has also been studied. There was a 36% increase in protein content in the experimental diet with 5% w/w fermented apple pomace. The efficiency of conversion of ingested food was increased from 43.5 ± 2.5 to 83.1 ± 4.4 in the control group and the efficiency of conversion of feed increased from 55.4 ± 4.5 to 92.1 ± 3.6 in the experimental group during the animal feed experiment. Similarly, the effect of a protein enriched diet on odor emission and greenhouse gas emission has also been studied. The results demonstrated that the protein enrichment of apple pomace by solid state cultivation of the fungus P. chrysosporium makes it possible to use it as a dietary supplement for pigs.

Dissolved oxygen (DO) concentration was selected as a principal parameter for translating results of shake flask fermentation of Trichoderma viride (biocontrol fungi) to a fermenter scale. All fermentations were carried out in a 7.5 l automated fermenter with a working volume of 4 l. Fermentation performance parameters such as volumetric oxygen transfer coefficient (k (L) a), oxygen uptake rate (OUR), rheology, conidia concentration, glucose consumption, soluble chemical oxygen demand, entomotoxicity and inhibition index were measured. The conidia concentration, entomotoxicity and inhibition index were either stable or improved at lower DO concentration (30%). Variation of OUR aided in assessing the oxygen supply capacity of the fermenter and biomass growth. Meanwhile, rheological profiles demonstrated the variability of wastewater during fermentation due to mycelial growth and conidiation. In order to estimate power consumption, the agitation and the aeration requirements were quantified in terms of area under the curves, agitation vs. time (rpm h), and aeration vs. time (lpm h). This simple and novel strategy of fermenter operation proved to be highly successful which can be adopted to other biocontrol fungi.