Model‐based identifiable parameter determination applied to a simultaneous saccharification and fermentation process model for bio‐ethanol production

In this work, a methodology for the model‐based identifiable parameter determination (MBIPD) is presented. This systematic approach is proposed to be used for structure and parameter identification of nonlinear models of biological reaction networks. Usually, this kind of problems are over‐parameterized with large correlations between parameters. Hence, the related inverse problems for parameter determination and analysis are mathematically ill‐posed and numerically difficult to solve. The proposed MBIPD methodology comprises several tasks: (i) model selection, (ii) tracking of an adequate initial guess, and (iii) an iterative parameter estimation step which includes an identifiable parameter subset selection (SsS) algorithm and accuracy analysis of the estimated parameters. The SsS algorithm is based on the analysis of the sensitivity matrix by rank revealing factorization methods. Using this, a reduction of the parameter search space to a reasonable subset, which can be reliably and efficiently estimated from available measurements, is achieved. The simultaneous saccharification and fermentation (SSF) process for bio‐ethanol production from cellulosic material is used as case study for testing the methodology. The successful application of MBIPD to the SSF process demonstrates a relatively large reduction in the identified parameter space. It is shown by a cross‐validation that using the identified parameters (even though the reduction of the search space), the model is still able to predict the experimental data properly. Moreover, it is shown that the model is easily and efficiently adapted to new process conditions by solving reduced and well conditioned problems. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1064–1082, 2013     

Removal of Ca(II) and Mg(II) from aqueous single metal solutions by mercerized cellulose and mercerized sugarcane bagasse grafted with EDTA dianhydride (EDTAD)

In a previous work, chemically modified cellulose (EMC) and sugarcane bagasse (EMMB) were prepared from mercerized cellulose (MC) and twice-mercerized sugarcane bagasse (MMB) using ethylenediaminetetraacetic dianhydride (EDTAD) as modifying agent. In this work we described in detail the modification of these materials in function of reaction time and EDTAD amount in the reaction media. The resistance of ester bond at pH 1, 2, 11, and 12 was also evaluated by FTIR. The results were used to model the hydrolysis process and a kinetic model was proposed. The modified materials (EMMB and EMC) were used to adsorb Ca²⁺ and Mg²⁺ ions from aqueous single solutions. The adsorption isotherms were developed at two pH values. These materials showed maximum adsorption capacities for Ca²⁺ and Mg²⁺ ions ranging from 15.6 to 54.1 mg/g and 13.5 to 42.6 mg/g, respectively. The modified material from sugarcane bagasse (EMMB) showed larger maximum adsorption capacities than modified material from cellulose (EMC) for both metals.     

Anaerobic mixed‐culture fermentation of aqueous ammonia‐treated sugarcane bagasse in consolidated bioprocessing

The MixAlco process is an example of consolidated bioprocessing (CBP) in which anaerobic mixed‐culture fermentation biochemically converts any biodegradable feedstock into carboxylate salts. Downstream processing thermochemically transforms the resulting salts into mixed alcohol fuels or gasoline. To enhance digestibility, sugarcane bagasse was treated under mild conditions (55°C, 24 h, and 30% aqueous ammonia solution with a loading of 10 mL/g dry biomass). Using NH₄HCO₃ buffer, the feedstock (80% ammonia‐treated sugarcane bagasse/20% chicken manure) was anaerobically fermented by a mixed culture of marine microorganisms at 55°C. Four‐stage countercurrent fermentations were performed at various volatile solids loading rates (VSLRs) and liquid residence times (LRTs). The highest acid productivity (1.14 g/(L day)) occurred at a total acid concentration of 29.8 g/L. The highest conversion (65%) occurred at a total acid concentration of 27.6 g/L. The continuum particle distribution model (CPDM) predicted the experimental total acid concentrations and conversions within 4.98% and 10.41%, respectively. When using NH₄HCO₃ buffer, ammonia pretreatment is an attractive option. The CPDM “map” shows that both high volatile solid conversions (78.8%) and high acid concentrations (32.6 g/L) are possible with 300 g/(L liquid) substrate concentration, 30 days LRT, 2 g/(L day) solid loading rate and NH₄HCO₃ buffer. Biotechnol. Bioeng. 2010;106: 216–227. © 2010 Wiley Periodicals, Inc.     

Distribution of clinically important thermophilic actinomycetes in vegetable substrates and soil in north-western India

Medically important thermophilic actinomycetes were isolated from 218 (64%) of 341 samples of vegetable substrates and soil examined from sites in north-western India. Thermoactinomyces vulgaris (T. candidus) was the commonest species, occurring in 56% of samples, followed by Saccharomonospora viridis in 29%, Thermoactinomyces thalpophilus in 27%, Faenia rectivirgula (Micropolyspora faeni) in 21% and Thermoactinomyces sacchari in 14%. T. vulgaris and T. thalpophilus were isolated from all types of substrate examined, with T. vulgaris always more common than T. thalpophilus. Of the other thermophilic actinomycetes, F. rectivirgula was isolated predominantly from hay (44%) and S. viridis (56%) and T. sacchari (44%) from sugarcane bagasse. The largest populations of T. vulgaris and T. thalpophilus were found in paddy straw, followed by T. sacchari, S. viridis and F. rectivirgula in sugar-cane bagasse.The widespread occurrence of these clinically important thermophilic actinomycetes suggests that exposure of humans and animals to them may be frequent in north-western India. Studies are required to determine the prevalence of extrinsic allergic alveolitis (hypersensitivity pneumonitis) caused by thermophilic actinomycetes in the local population.