Production of Bioethanol from Wild Cassava Manihot glaziovii through Various Combinations of Hydrolysis and Fermentation in Stirred Tank Bioreactors.

Aim of the Study: The aim of this study was to evaluate three ethanol fermentation approaches namely (I) separate hydrolysis and common fermentation (II) separate hydrolysis and fermentation and (III) simultaneous saccharification and fermentation in stirred tank reactors using inedible wild cassava as feedstock. Study Design: Tubers of wild cassava (Manihot glaziovii) were obtained from two districts in Tanzania. Fermentation of hydrolysate and partially liquefied cassava flour was performed in stirred tank reactors. Methodology: Feedstock composition analysis for structural carbohydrate was performed using acid hydrolysis and high pressure liquid chromatography technique. Analysis of total nitrogen was done by Kjeldahl acid digestion technique, total cyanide was determined using linamarase loaded picrate paper whereas macro-and micronutrients were analysed by inductively coupled plasma atomic emission spectrometry. Thermostable α-amylase and glucoamylase were used to partially hydrolyze the cassava flour to fermentable sugars prior to yeast fermentation. The hydrolysis (liquefaction) was performed at 90°C, 1h followed by saccharification using glucoamylase at 60°C, 2h for approaches I and II. For approach III, liquefaction was performed at 90°C, 1h followed by direct saccharification and fermentation. Fermentation of hydrolysate and partially liquefied starch from wild cassava was done in stirred tank reactors at 30±2°C using baker’s yeast. Place and Duration of Study: Department of Biotechnology, Lund University from January to June 2014. Results: The wild cassava (M. glaziovii) tubers possessed comparable physical dimensions to the domesticated cassava, however they displayed higher average flesh proportion (76 to 79%) compared to the domesticated cassava (74%). Compositional analysis disclosed that the wild cassava possessed interesting properties for bioethanol production such as dry matter of up to 89% w/w, degradable carbohydrate up to 90% (dry weight basis), total kjeldahal nitrogen 0.8-1.6% w/w and satisfactory concentration of macro-and micronutrients. Amongst the three fermentation approaches, high ethanol titre of 10-11% (v/v) at high conversion efficiency of 97.6% was achieved for separate hydrolysis and fermentation and simultaneous saccharification and fermentation, whereas low ethanol titre (4.2% v/v) at efficiency of 39% was achieved for separate hydrolysis and common fermentation. Volumetric productivities for the three approaches; ‘separate hydrolysis and common fermentation’, ‘separate hydrolysis and fermentation’, and ‘simultaneous saccharification and fermentation’ were 2.0, 5.5 and 6.5 respectively. Conclusion: The results obtained in the present study demonstrated that wild cassava has a high starch content, contain balanced nutrients required for efficient bioethanol production and that simultaneous saccharification and fermentation is the best approach for bioconversion of the wild cassava to bioethanol using stirred tank reactors.

Isolation and Identification of Microorganisms from Crude oil Contaminated Soils of Dar es Salaam, Tanzania.

Aims: The aim of this study was to isolate and identify microorganisms in crude oil polluted soils in Eastern Tanzania. Study Design: Isolation and identification of microorganisms using conventional and molecular techniques. Place and Duration of Study: Department of Molecular Biology & Biotechnology, University of Dar es Salaam; October 2012 to June 2013. Methodology: Soils were collected from Mlalakua (ML), University of Dar es Salaam (UDSM) and Ubungo (Ub) local garages in Dar es Salaam, Tanzania. The selective isolation of microorganisms was done based on colony morphological appearance on agar plates and Gram reaction. Three isolates (one from each site) were subjected to molecular methods for the identification purposes. Phylogenetic analyses of bacterial 16S rRNA gene and fungal ITS region sequences were employed in this study to identify and determine the evolutionary relationships of the ML, Ub and UDSM isolates. Results: The 16S rRNA analysis revealed that the ML isolate belonged to the genus Klebsiella, while the ITS analysis on Ub and UDSM isolates assigned them to the genus Trichosporon and Candida, respectively. Conclusions: From these findings, further studies are recommended to assay for the biodegradative potentiality of the identified isolates for bioremediation of crude oil contaminated soils.

Performance of biofilm carriers in anaerobic digestion of sisal leaf waste leachate

Three methanogenic biofilm bioreactors were studied to evaluate the performance of three types of carriers. The carrier material were consisted of sisal fibre waste, pumice stone and porous glass beads, and the bioprocess evaluated was the methanogenesis anaerobic digestion of sisal leaf waste leachate. Process performance was investigated by increasing the organic loading rate (OLR) step-wise. The best results were obtained from the bioreactor packed with sisal fibre waste. It had the highest chemical oxygen demand (COD) removal efficiencies in the range of 80-93 percent at OLRs in the range of 2.4-25 g COD L-1d-1. The degradation pattern of volatile fatty acids (VFAs) showed that the degradation of propionate was limiting at higher OLRs. The stable pH and higher partial alkalinity (PA) of the outflow illustrated that packed-bed bioreactors have a good ability to withstand the variations in load and volatile fatty acid concentrations that can occur in a two-stage anaerobic process. In conclusion, sisal fibre waste was shown to be a novel promising biofilm carrier and would work very well in methanogenic biofilm bioreactors treating sisal leaf tissue waste leachate. Furthermore both sisal wastes are available in the neighbourhood of sisal industries, which makes anaerobic digestion scale up at sisal factory level feasible and cost-effective.