Deniz Cekmecelioglu

Cost-effective approach to ethanol production and optimization by response surface methodology

Food wastes disposed from residential and industrial kitchens have gained attention as a substrate in microbial fermentations to reduce product costs. In this study, the potential of simultaneously hydrolyzing and subsequently fermenting the mixed carbohydrate components of kitchen wastes were assessed and the effects of solid load, inoculum volume of bakers yeast, and fermentation time on ethanol production were evaluated by response surface methodology (RSM). The enzymatic hydrolysis process was complete within 6h. Fermentation experiments were conducted at pH 4.5, a temperature of 30°C, and agitated at 150 rpm without adding the traditional fermentation nutrients. The statistical analysis of the model developed by RSM suggested that linear effects of solid load, inoculum volume, and fermentation time and the quadratic effects of inoculum volume and fermentation time were significant (P<0.05). The verification experiments indicated that the developed model could be successfully used to predict ethanol concentration at >90% accuracy. An optimum ethanol concentration of 32.2g/l giving a yield of 0.40g/g, comparable to yields reported to date, was suggested by the model with 20% solid load, 8.9% inoculum volume, and 58.8h of fermentation. The results indicated that the production costs can be lowered to a large extent by using kitchen wastes having multiple carbohydrate components and eliminating the use of traditional fermentation nutrients from the recipe.

Kinetic modeling of enzymatic hydrolysis of pretreated kitchen wastes for enhancing bioethanol production.

It is well known that use of low cost and abundant waste materials in microbial fermentations can reduce product costs. Kitchen wastes disposed of in large amounts from cafeterias, restaurants, dining halls, food processing plants, and household kitchens contain high amounts of carbohydrate components such as glucose, starch, and cellulose. Efficient utilization of these sugars is another opportunity to reduce ethanol costs. In this study, the effect of pretreatment methods (hot water, acid solutions, and a control) on enzymatic hydrolysis of kitchen wastes was evaluated using a kinetic modeling approach. Fermentation experiments conducted with and without traditional fermentation nutrients were assessed at constant conditions of pH 4.5 and temperature of 30°C for 48h using commercial dry bakers yeast, Saccharomyces cerevisiae. The control, which involved no treatment, and hot water treated samples gave close glucose concentrations after 6h. The highest and lowest rates of glucose production were found as 0.644 and 0.128 (h(-1)) for the control (or no-pretreated (NPT)) and 1% acid solutions, respectively. The fermentation results indicated that final ethanol concentrations are not significantly improved by adding nutrients (17.2-23.3g/L). Thus, it was concluded that product cost can be lowered to a large extent if (1) kitchen wastes are used as a substrate, (2) no fermentation nutrient is used, and (3) hydrolysis time is applied for about 6h. Further optimization study is needed to increase the yield to higher levels.

OPTIMIZATION OF WINDROW FOOD WASTE COMPOSTING TO INACTIVATE PATHOGENIC MICROORGANISMS

Composting is a popular means of treating organic wastes, and properly controlled composting can destroy the pathogenic microorganisms present in wastes for a human- and environment-friendly end product. Therefore, optimization of windrow composting of food waste, manure, and bulking agents was evaluated for maximum pathogen inactivation (Salmonella and E. coli O157:H7). Seasonal effects on reductions of Salmonella and E. coli O157:H7 according to the compost temperatures were studied (90 to 150 days). Fecal coliforms and fecal streptococcus were also monitored during composting. The most probable number (MPN) method was used for enumerating both indicator and pathogenic microorganisms. The results of this study indicated that seasonal differences caused significant effects on the peak temperatures and the duration of high thermophilic temperatures (>55°C) of windrows. Winter conditions resulted in inconsistent inactivation of pathogenic microorganisms including regrowth to high values during several time intervals. The reduction levels of Salmonella spp. and E. coli O157:H7 ranged from initial ranges of 377-483 MPN/g to final ranges of 6-150 MPN/g in winter, and to <0.3 MPN/g in summer. It was also observed that summer composting resulted in a better correlation (r2 > 0.90) between the number of fecal coliforms and the pathogenic microorganisms (Salmonella spp. and E. coli O157:H7). Fecal streptococcus was only slightly reduced in the majority of the trials from 377-483 MPN/g to 221-514 MPN/g in winter and from 365-460 MPN/g to a range of 11-265 MPN/g in summer. Extreme Vertices Mixture Design (EVMD) analysis suggested an optimum mixture as: 43.3% food waste, 28.3% manure, and 28.3% bulking agents. The performance of the optimum mixture has been validated, achieving a high level of inactivation of pathogens similar to that with previous trials, with good correlations of fecal coliforms to the pathogens of interest, but with a high resistance of fecal streptococcus to inactivation. It was concluded that the EVMD design was successful in optimizing mixture components for windrow composting in order to achieve maximum pathogen reduction.

Feedstock optimization of in-vessel food waste composting systems for inactivation of pathogenic microorganisms.

An optimum composting recipe was investigated to reduce pathogenic microorganisms in a forced-aerated in-vessel system (55 liters). The feedstocks used for in-vessel composting were food waste, cow manure, and bulking materials (wood shavings and mulch hay). A statistical extreme vertices mixture design method was used to design the composting experiments and analyze the collected data. Each mixture (nine total) was replicated randomly three times. Temperature was monitored as an indicator of the efficiency of the composting experiments. The maximum temperature values of the mixtures were used as a response for both extreme vertices mixture design and statistical analyses. Chemical changes (moisture content, carbon/nitrogen ratio, volatile solids, and pH) and reductions of indicator (fecal coliforms and fecal streptococci) and pathogenic microorganisms (Salmonella and Escherichia coli O157:H7) were measured by the most-probable-number method before and after a 12-day composting period. Maximum temperatures for the tested compost mixtures were in the range of 37.0 to 54.7 degrees C. Extreme vertices mixture design analysis of the surface plot suggested an optimum mixture containing 50% food waste, 40% manure, and 10% bulking agents. This optimum mixture achieved maximum temperatures of 54.7 to 56.6 degrees C for about 3.3 days. The total reduction of Salmonella and E. coli O157:H7 were 92.3%, whereas fecal coliforms and fecal streptococci reductions were lower (59.3 and 27.1%, respectively). Future study is neededto evaluate the extreme vertices mixture design method for optimization of large-scale composting.

Optimization of culture conditions for Aspergillus sojae expressing an Aspergillus fumigatus α-galactosidase

Using Response Surface Methodology, carbon and nitrogen sources and agitation speed for cultivation of Aspergillus sojae expressing the α-galactosidase gene, aglB of Aspergillus fumigatus IMI 385708 were optimized. Compared to cultivation in modified YpSs medium, cultivation in 250-mL Erlenmeyer flasks agitated at 276 rpm and containing 100 mL of optimized medium consisting of 10.5% molasses (w/v) and 1.3% NH(4)NO(3) (w/v), 0.1% K(2)HPO(4), and 0.005% MgSO(4)·7H(2)O achieved a 4-fold increase in α-galactosidase production (10.4 U/mL). These results suggest the feasibility of industrial large scale production of an α-galactosidase known to be valuable in galactomannan modification.

MODELING OF COMPOST TEMPERATURE AND INACTIVATION OF SALMONELLA AND E. COLI O157:H7 DURING WINDROW FOOD WASTE COMPOSTING

A simulation model was developed to predict temperature and inactivation of E. coli O157:H7 and Salmonella during windrow composting. In particular, the model included an energy balance to estimate the change in temperature based on heat generated by biological decomposition and heat losses by convection, conduction, evaporation, and radiation. The model was validated with the measured data for the effects of seasonal variation on compost temperature and pathogen reduction. Sensitivity analysis was performed on the model to evaluate the variations in both seasons (winter and summer) and moisture contents (40% to 80%). The model showed the highest variation between experimental and predicted data only in winter composts. The results suggested that moisture content of 40% to 60% was appropriate for summer and 40% to <60% for winter composting. Higher moisture levels did not demonstrate pathogen inactivation during winter conditions, whereas it took a month to eliminate the pathogens in summer according to the model predictions. Overall, the model was promising for evaluation of the composting process for different conditions. Further research is needed to improve the model predictions using measured process parameters under different environmental conditions.

Hydrolysis of Hazelnut Shells as a Carbon Source for Bioprocessing Applications and Fermentation

Abstract Hazelnut shells are generated in large amounts from hazelnut processing. Currently, it is used as fuel. However, reuse in bioprocessing can release remarkable content of sugars, which can be used for production of additives such as enzymes widely used in the food industry. Thus, the present study was undertaken to determine the effect of single and combined chemical and enzymatic hydrolysis on the production of fermentable sugars from hazelnut shells. Batch hydrolysis was carried out under various conditions to select optimal conditions. The results revealed that an optimal sugar concentration of about 19.2 g/l was achieved after 3.42% (w/w) dilute acid pretreatment conducted at 130°C for 31.7 min and enzymatic load of 200 U/g for 24 h. The overall sugar yield was calculated as 72.4% (g reducing sugar/g total carbohydrate). Therefore, hazelnut shells can be considered a suitable feedstock to compete with synthetic sugars used in fermentations.

Drying Behavior of Meat Samples at Various Fiber Directions and Air Conditions

The aim of this study was to investigate the effects of meat fiber directions and air conditions on moisture and temperature developments, shrinkage, and effective diffusivity constants compared to homogenous minced meat samples. The lean meat with three fiber directions and minced meat samples were dried at temperatures of 48 and 70°C and air flow rates of 0.5, 1.0, and 1.7 m/s. The minced meat samples showed 1.0 ± 0.19 to 4.4 ± 0.03°C higher temperature values and 2.3 ± 0.004 to 6.2 ± 0.003% lower moisture losses than the lean meat samples in all fiber directions. The lowest temperatures were observed in lean meat with h 1 (normal flow, normal drying) fiber direction. The highest moisture loss and diffusion coefficient were observed in lean meat with h 2 (parallel flow, normal drying) and v (normal flow, parallel drying) fiber directions, which also possessed the shortest drying times (10.4 and 13.4 h, respectively). The estimated diffusion coefficient values ranged between 1.11 × 10−9 and 5.54 × 10−9. The results indicated that lean and minced meat samples differed in their drying behaviors in a tray dryer under the tested conditions with >90% reproducibility (or ≤10% coefficient of variation).

Optimization of Windrow Food Waste Composting to Inactivate Pathogenic Microorganisms

Composting is a popular means of treating organic wastes. Properly controlled composting can destroy the pathogenic microorganisms present in wastes for environmentally friendly end product. Optimization of windrow composting of food waste, manure, and bulking agents was evaluated for maximum pathogen inactivation (Salmonella and E. coli O157:H7). Seasonal effects on reductions of Salmonella and E. coli O157:H7 related to the compost temperatures were studied (90-150 days). Fecal coliforms and fecal streptococcus were also monitored during composting. The results of this study indicated that seasonal differences caused significant effects on the peak temperatures and the duration of high thermophilic temperatures ( =55oC) of windrows. Winter conditions resulted in inconsistent inactivation of pathogenic microorganisms including regrowth to high values during several time intervals. The reduction levels of Salmonella spp. and E. coli O157:H7 ranged from initial ranges of 377-483 MPN/g to final ranges of 6-150 MPN/g in winter, and to = 0.3 MPN/g in summer. It was also observed that summer composting resulted in a better correlation (r2>0.90) between number of fecal coliforms and the pathogenic microorganisms (Salmonella spp and E. coli O157:H7). Fecal streptococcus was slightly reduced in most trials from 377-483 to 221-514 MPN/g in winter and from 365-460 MPN/g to a range of 11-265 MPN/g in summer. Extreme Vertices Mixture Design (EVMD) analysis suggested an optimum mixture as: 43.3% food waste, 28.3% manure, and 28.3% bulking agents. The performance of the optimum mixture has been validated, achieving a high level of inactivation of pathogens similar to previous trials, good correlations of fecal coliforms to the pathogens of interest, and high resistance of fecal streptococcus. Therefore, it was concluded that the EVMD design was successful in optimizing windrow composting for maximum pathogen reduction.

Applicability of the Optimized In-vessel Food Waste Composting for Windrow Systems

Statistical Extreme Vertices Mixture Design Method was used to design, evaluate, and determine optimum mixture composition of in-vessel composting system (55 L) utilizing food waste (40-60%), cow manure (10-30%), and bulking agents (10-30%). The mixture design method yielded nine compost mixtures, and all was replicated 3 times. Temperature was monitored during 12-day composting period to indicate the efficiency of composting. Initial and final chemical characteristics (moisture content, C/N ratio, pH, and volatile solids) and microbial survival (fecal coliforms, fecal streptococcus, Salmonella spp. and E. coli O157:H7) of mixtures were also determined. Mixtures 4 and 6 reached thermophilic range (=45-50oC) in 3 days, and remained 2.5 days in this range. Also, mixture 6 demonstrated reduction of fecal coliforms from initial number of 459.5 MPN/g dry compost to 71.4 MPN/g dry compost. Similarly, Salmonella spp. and E. coli O157:H7 were reduced from initial values of 321.1 and 459.5 MPN/g dry compost to final values of <0.79 and 24.2 MPN/g dry compost, respectively. As a result of data obtained from nine compost mixtures, mixture surface analysis showed that the optimum level of food waste, manure, and bulking agents was 50, 40, and 10%, respectively. The optimum mixture was also attempted to validate by windrow composting. Conventional layering and mixing methods were used for windrow construction. Layering method resulted in higher and more stable temperature profiles remaining at 57-61oC for 20 days, while mixing method yielded 55-59oC for 4-5 days. Fecal coliforms and fecal streptococcus were reduced from 448.8 MPN/g dry compost to 0.4, and 65.9 MPN/g dry compost, respectively within 2 monthcomposting by layering method. Salmonella and E. coli O157:H7 were similarly reduced from 448.8 MPN/g dry compost to <0.4 MPN/g dry compost. However, all piles presented leaching problems for the first 15-20 days. Future work will be focused on minor revision of statistical approach for windrow composting to eliminate these environmental problems.