Effective Bioconversion Research Articles

Evaluation energy efficiency of bioconversion knot rejects to ethanol in comparison to other thermochemically pretreated biomass

Rejects from sulfite pulp mill that otherwise would be disposed of by incineration were converted to ethanol by a combined physical–biological process that was comprised of physical refining and simultaneous saccharification and fermentation (SSF). The energy efficiency was evaluated with comparison to thermochemically pretreated biomass, such as those pretreated by dilute acid (DA) and sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL). It was observed that the structure deconstruction of rejects by physical refining was indispensable to effective bioconversion but more energy intensive than that of thermochemically pretreated biomass. Fortunately, the energy consumption was compensated by the reduced enzyme dosage and the elevated ethanol yield. Furthermore, adjustment of disk-plates gap led to reduction in energy consumption with negligible influence on ethanol yield. In this context, energy efficiency up to 717.7% was achieved for rejects, much higher than that of SPORL sample (283.7%) and DA sample (152.8%).

Editorial: A Medium for Rapid Dissemination of Information on Basic and Applied R&D in Bioconversion of Wastes to Bioproducts

Today, we are faced with a planet where waste generation has taken a dimension never before experienced in recorded history. These wastes, mainly generated from both renewable and nonrenewable resources, constitute a major problem to sustainability and myriad of negative environmental consequences. Fossil fuels are fast depleting, forest/forest resources are at their lowest in the history of planet earth. The negative consequences of human activities on the atmospheric greenhouse gases, global warming, inter alia are obvious. It is imperative that we find a way to reuse the limited natural resources at our disposal, find scientific and sustainable approaches to natural resource conservation (i.e. use and management), in order to ensure their perpetuity. Actions in line with this would call for effective bioconversion of wastes to bioproducts useful in medicines, food and agricultural products. Efficient and economic approaches to conversion at individual through large industrial operations are needed. Despite the advances we have made in chemical conversion, any time we search, we contin-

Immobilized formaldehyde-metabolizing enzymes from Hansenula polymorpha for removal and control of airborne formaldehyde

Formaldehyde (FA)-containing indoor air has a negative effect on human health and should be removed by intensive ventilation or by catalytic conversion to non-toxic products. FA can be oxidized by alcohol oxidase (AOX) taking part in methanol metabolism of methylotrophic yeasts. In the present work, AOX isolated from a Hansenula polymorpha C-105 mutant ( gcr1 catX) overproducing this enzyme in glucose medium, was tested for its ability to oxidize airborne FA. A continuous fluidized bed bioreactor (FBBR) was designed to enable an effective bioconversion of airborne FA by AOX or by permeabilized mutant H. polymorpha C-105 cells immobilized in calcium alginate beads. The immobilized AOX having a specific activity of 6–8 U mg −1 protein was shown to preserve 85–90% of the initial activity. The catalytic parameters of the immobilized enzyme were practically the same as for the free enzyme ( k cat/ K m was 2.35 × 10 3 M −1 s −1 vs 2.89 × 10 3 M −1 s −1, respectively). The results showed that upon bubbling of air containing from 0.3 up to 18.5 ppm FA through immobilized AOX in the range of 1.3–26.6 U g −1 of the gel resulted in essential decrease of FA concentration in the outlet gas phase (less than 0.02–0.03 ppm, i.e. 10-fold less than the threshold limit value). It was also demonstrated that a FBBR with immobilized permeabilized C-105 cells provided more than 90% elimination of airborne FA. The process was monitored by a specially constructed enzymatic amperometric biosensor based on FA oxidation by NAD + and glutathione-dependent formaldehyde dehydrogenase from the recombinant H. polymorpha Tf 11-6 strain.

Improving wheat flour hydrolysis by an enzyme mixture from solid state fungal fermentation

In traditional cereal-based industrial processes, component separation is often incomplete resulting in a residue of mixed macromolecules including largely starch, protein, phytic acid and many others. The development of a viable cereal-based biorefinery would involve effective bioconversion of cereal components for the production of a nutrient-complete fermentation feedstock. Simultaneous starch and protein hydrolysis represents an effective approach to the production of platform chemicals from wheat. Solid state fermentations of wheat pieces and waste bread by Aspergillus oryzae and Aspergillus awamori have been combined in this study to enhance starch and protein hydrolysis. Kinetic studies confirmed that the proteolytic enzymes from A. oryzae introduced no negative effect on the stability of the amylolytic enzymes from A. awamori under the optimal conditions for starch hydrolysis. When applied to hydrolyse wheat flour, the enzyme solution from A. awamori converted nearly all of the starch into glucose and 23% of the total nitrogen (TN) into free amino nitrogen (FAN). Under the same reaction conditions the enzyme solution from A. oryzae hydrolysed 38% of the protein but only 18.5% of the starch. A mixture of the two enzyme solutions hydrolysed 34.1% of the protein, a 1.5-fold increase from that achieved by the enzyme solution from A. awamori, while maintaining a near completion of starch hydrolysis.

Revalorisation of vine trimming wastes using Lactobacillus acidophilus and Debaryomyces hansenii

AbstractBACKGROUND: Mild acid treatments of vine‐shoot trimmings result in the hydrolysis of hemicellulosic sugars that can be utilised by Lactobacillus acidophilus CECT‐4179 (ATCC 832) and Debaryomyces hansenii NRRL Y‐7426 as carbon sources to obtain food additives. Since the high content of glucose in these hydrolysates reduces the effective bioconversion of xylose into xylitol by D. hansenii, the use of Lactobacillus acidophilus, one of the main probiotic species, allows this problem to be solved by the selective consumption of glucose. In order to use both sugars (glucose and xylose), hemicellulosic vine‐shoot trimming hydrolysates can be sequentially fermented by both micro‐organisms.RESULTS: It was found that, in the first step, L. acidophilus generated almost exclusively lactic acid (32.7 g of lactic acid L−1, QLA = 1.363 g L−1 h−1, YLA/S = 0.72 g g−1) by homofermentative degradation of sugars (mainly glucose), and in the second step, the remaining hemicellulosic sugars were transformed primarily into xylitol by Debaryomyces hansenii (31.3 g of xylitol L−1, QXylitol = 0.708 g L−1 h−1, YXylitol/S = 0.66 g g−1). Furthermore, L. acidophilus proved to be a strong cell‐bounded biosurfactant producer. Cell extracts were able to reduce the surface tension (ST) of PBS in 18 mN m−1 units. Lactobacillus acidophilus cells showed no difference in viability before or after PBS extraction of biosurfactants, achieving values of 0.9 × 109 colony‐forming units (CFU) mL−1 in both cases.CONCLUSIONS: These results have made a serious contribution to the re‐evaluation of a useless and pollutant residue, producing a wide range of natural food additives. Copyright © 2008 Society of Chemical Industry

Ethanol production from paper sludge by immobilized Zymomonas mobilis

During past decades, the considerable efforts have been made to utilize lignocellulose as biomass feedstock for the optimal production of bio-ethanol as an alternative source of fuel. In this work, the effective bioconversion of paper sludge to ethanol was investigated by using Zymomonas mobilis NBRC 13756. Major components of the raw paper sludge were carbohydrates and ash. Fermentation utilizing strains of Z. mobilis instead of traditional yeasts and the use of simultaneous saccharification and fermentation (SSF) process have been proposed due to their high ethanol yields with cost-effectiveness. Free cells of Z. mobilis resulted in no ethanol production even after 24 h of incubation because cells’ growth was inhibited by metal ions contained in the paper sludge. The application of SSF with Ca-alginate-immobilized cells of Z. mobilis was performed and 18 g/L of ethanol was obtained after 48 h of incubation at an initial paper sludge concentration of 200 g/L. In addition, the repeated batch fermentation of Ca-alginate-immobilized Z. mobilis cells was attempted for producing ethanol up to run 4. Our work suggests that Ca-alginate-immobilized cells of Z. mobilis could effectively produce ethanol from paper sludge not only under the batch fermentation but also under the repeated batch fermentation.

Biological treatment of sewage treatment plant sludge by pure bacterial culture with optimum process conditions in a stirred tank bioreactor

Biological treatment of sewage treatment plant (STP) sludge by potential pure bacterial culture (Bacillus sp.) with optimum process conditions for effective biodegradation and bioseparation was carried out in the laboratory. The effective and efficient bioconversion was evaluated with the treatment of pure bacterial culture and existing microbes (uninnoculated) in sludge. The optimum process conditions i.e., temperature, 40°C; pH, 6; inoculum, 5% (v/v); aeration, 1 vvm; agitation speed, 50 rpm obtained from the previous studies with chemical oxygen demand COD at 30 mgL− 1 were applied for the biological treatment of sludge. The results indicated that pure bacterial culture (Bacillus sp.) showed higher degradation and separation of treated sludge compared to treatment with the existing mixed microbes in a stirred tank bioreactor. The treated STP sludge by potential pure bacterial culture and existing microbes gave 30% and 11%; 91.2% and 59.1; 88.5% and 52.3%; 98.4% and 51.3%; 96.1% and 75.2%; 99.4% and 72.8% reduction of total suspended solids (TSS, biosolids), COD, soluble protein, turbidity, total dissolved solids (TDS) and specific resistance to filtration (SRF), respectively within 7 days of treatment. The pH was observed at 6.5 and 4 during the treatment of sludge by pure culture and existing microbes, respectively.

Development of biological process with pure bacterial cultures for effective bioconversion of sewage treatment plant sludge

Forty-six bacterial strains were isolated from nine different sources in four treatment plants namely Indah Water Konsortium (IWK) sewage treatment plant (STP), International Islamic University Malaysia (IIUM) wastewater treatment plant-1,-2 and -3 to evaluate the bioconversion process in terms of efficient biodegradation and bioseparation. The bacterial strains isolated were found to be 52.2% (24 isolates) and 47.8% (22 isolates) in the IWK and IIUM treatment plants, respectively. The results showed that higher microbial population (9–10 × 104 cfu/mL) was observed in the secondary clarifier of IWK treatment plant. Among the isolates, 23 isolates were gram-positive bacillus (GPB) and gram-positive cocci (GPC), 19 isolates were gram-negative bacillus (GNB) and gram-negative cocci (GNC), and the rest were undetermined. Gram-negative cocci (GNC) were not found in the isolates from IWK. A total of 15 bacterial strains were selected for effective and efficient sludge bioconversion. All the strains were tested against sludge (1% total suspended solids, TSS) to evaluate the biosolids production (TSS% content), chemical oxygen demand (COD) removal and filtration rate (filterability test). The strain S-1 (IWK1001) showed lower TSS content (0.8% TSS), maximum COD removal (84%) and increased filterability (1.1 min/10 mL of filtrate) of treated sludge followed by the strains S-11, S-14, S-2, S-15, S-13, S-7, S-8, S-4, S-3, S-6, S-12, S-16, S-17 and S-9. The pH values in the fermentation broth were affected by the bacterial cultures and recorded as well. Effective bioconversion was observed during the first three days of sludge treatment.

Isolation and Purification of Bacterial Strains from Treatment Plants for Effective and Efficient Bioconversion of Domestic Wastewater Sludge

Forty six bacterial strains were isolated from nine different sources in four treatment plants namely Indah Water Konsortium (IWK) sewage treatment plant, International Islamic University Malaysia (IIUM) treatment plant-1,-2 and -3 to evaluate the bioconversion process in terms of efficient biodegradation and bioseparation. The bacterial strains isolated were found to be 52.2% (24 isolates) and 47.8% (22 isolates) in the IWK and IIUM treatment plants respectively. The results showed that the higher microbial population (9-10x104 cfu mL-1) was observed in the secondary clarifier of IWK treatment plant. Only the gram-staining identification was done in the strains isolated from IWK treatment plant not to be determined from IIUM. Among the isolates from IWK, 10 isolates of gram-positive bacillus (GPB) and gram-positive cocci (GPC), 10 isolates of gram-negative bacillus (GNB) and rest were both or undetermined. Gram-negative cocci (GNC) were not found in the isolates from IWK.

Response surface methodology for xylitol production from sugarcane bagasse hemicellulosic hydrolyzate using controlled vacuum evaporation process variables

An effective bioconversion of xylose into xylitol by Candida guilliermondii FTI 20037 requires sugarcane bagasse hydrolyzate with a high level of xylose and a low concentrations of toxic compounds. The composition of the hydrolyzate depends on the vacuum evaporation process variables (pH, temperature, xylose concentration degree and treatment with activated charcoal before or after the process). The influence of these variables on xylitol volumetric productivity was measured using a 2 5−1 fractional factorial central composite design followed by a response surface methodology. The model predicted a xylitol volumetric productivity of 0.350 g/l h in hydrolyzate treated with charcoal (pH 0.92) and subsequently evaporated under vacuum to reach a xylose concentration of 51.0 g/l. Under these conditions, the xylose, acetic acid and arabinose consumption levels were 93, 57 and 13.62%, respectively, and xylitol yield and production were 0.54 g/g and 24.33 g/l, respectively. The final cell concentration was fivefold, the initial value (0.278×10 8 cell/ml). The temperature levels (43–80 °C) tested during vacuum evaporation did not influence xylitol production significantly.

Intensive bioconversion of sewage sludge and food waste by Bacillus thermoamylovorans

The main aim of this work was to intensify conventional composting of a mixture of sewage sludge and solid food wastes by a one-stage thermophilic bioconversion of these wastes into an organic fertilizer. An intensive process was carried out in a closed system, with or without addition of a starter culture of Bacillus thermoamylovorans. The most effective thermophilic bioconversion of the mixture of food waste and sewage sludge, with addition of starter culture, was when the pH was buffered with calcium carbonate, or the pH drop in the material was prevented by preliminary removal of sulphides from sewage sludge by hydrogen peroxide.

Bioconversion of domestic wastewater sludge by immobilized mixed culture of penicillum Corylophilum WWZA1003 and Aspergillus niger SCahmA103.

The bioconversion of domestic wastewater sludge by immobilized mixed culture of filamentous fungi was investigated in a laboratory. The potential mixed culture of Penicillium corylophilum WWZA1003 and Aspergillus niger SCahmA103 was isolated from its local habitats (wastewater and sludge cake) and optimized on the basis of biodegradability and dewaterability of treated sludge. The observed results in this study showed that the sludge treatment was highly influenced by the effect of immobilized mixed fungi using liquid state bioconversion (LSB) process. The maximum production of dry filter cake (DFC) was enriched with fungal biomass to about 20.05 g/kg containing 23.47 g/kg of soluble protein after 4 days of fungal treatment. The reduction of COD, TSS, turbidity (optical density against distilled water, 660 nm), reducing sugar and protein in supernatant and filtration rate of treated sludge were influenced by the fungal mixed culture as compared to control (uninnoculated). After these processes, 99.4% of TSS, 98.05% of turbidity, 76.2% of soluble protein, 98% of reducing sugar and 92.4% of COD in supernatant of treated sludge were removed. Filtration time was decreased tremendously by the microbial treatment after 2 days of incubation. The effect of fungal strain on pH was also studied and presented. Effective bioconversion was observed after 4 days of fungal treatment.

Effective Bioconversion with Continuous Product Recovery Using AOT/Lecithin Mixed Reverse Micellar Systems and Centrifugal Partition Chromatography as a Novel Bioreactor

AbstractThe application of reverse micellar micro‐bioreactor systems for enzymatic conversion with continuous recovery of water‐soluble products was demonstrated, based on the production of galactose by micelles containing β‐galactosidase (β‐gal). The β‐gal was firmly encapsulated in AOT (bis(2‐ethylhexyl)sodium sulfosuccinate)/Lecithin mixed micelles. The addition of lecithin to the AOT reverse micelles stabilized the micellar interface, and the leakage of the encapsulated β‐gal to the bulk aqueous phase was therefore negligible, while substrate and product were free to transfer and partition owing to their low molecular weights. The stability of the solubilized β‐gal was also increased in the AOT/Lecithin mixed micelles as compared to the conventional AOT micelles. A considerably higher activity was observed in the present systems than in the bulk buffer solution. Enzymatic conversion and product recovery was carried out in a continuous operation mode by use of centrifugal partition chromatography (CPC), employing the reverse micellar solution with encapsulated β‐gal as the stationary phase and the substrate aqueous solution as the mobile phase. Use of the CPC contactor eliminated any mass transfer limitation on the substrate and the product, and galactose was continuously recovered in the effluent. The recovery of galactose continued for a period of 5 h with more than a 85% conversion at the optimum operating condition. This reverse micellar micro‐bioreactor system was thus found to be very effective for the continuous production and recovery of hydrophilic products.