Full Length Research Paper
Modeling herbivorous animal digestive system as 3continuous stirred tank reactor (CSTR) and 1-plug flow reactor (PFR) in series with specific reference to Hippopotamus amphibious
Awolu,Olugbenga Olufemi1,2* and Layokun, Stephen Kolawole1
Department of Food Science and Technology, Federal University of Technology, Akure, Ondo State, Nigeria. 2 Department of Chemical Engineering, Obafemi Awolowo University, Ile Ife, Osun State, Nigeria.
Accepted 7 December, 2010
Herbivores contain microflora in their guts which digest lignocellulosics in their stomachs and intestines bysecreting the essential enzymes that perform the function so efficiently that the guts of these animals have been described as the best fermentation tanks known. Hippopotamus amphibious, a herbivorous animal, has three stomach compartments together with small and large intestines which are of similar structure and function. This work models each stomach compartment as continuous stirred tank reactor(CSTR) and the small and large intestines as plug flow reactor (PFR) arrangements in series in order to determine the performance of the herbivorous digestive system. Autocatalytic microbial fermentation takes place in the stomach, modeled as CSTR and described by Monod kinetics, whereas enzymatic digestion takes place in the intestines, modeled as PFR and described by Michaelis Menten equation.Designed equations derived from the two equations are used for the reactor sizing of the modeled reactors. This shows the efficiency of each reactor at converting the purely lignocellulosics substrates to useful products like protein, vitamin, fatty acid and the bye-products. The results showed that 3CSTR-IPFR model is the best and most efficient for converting lignocellulosics. Key words:Lignocellulosics, microflora, herbivore, catalytic, reactor. INTRODUCTION An herbivore is often defined as any organism that eats only plants. By this definition, many fungi, some bacteria, many animals, about 1% of flowering plants and some protists can be considered as herbivores. In zoology, a herbivore is an animal that is adapted to eat primarily plant matter (rather than meat) (Wikipedia, 2006).Thefollowing animals are considered as typical herbivores: Bovids (such as cows, sheep, goats and buffalo), horses (including domestic horses, donkeys and zebras), deer, elephants, rhinoceros, hippopotamus and some rodents such as guinea pigs. It has been reported that roughly 59% of the organic carbon on earth is tied up in cellulose (Bowen, 1996b) and represents an enormous source of energy in whichvertebrate cells cannot produce the cellulases necessary to break down this abundant material. Cellulose fibers account for 40 to 50% of the total weight of stems, leaves and roots. These fibres are embedded in a matrix of hemicelluloses and phenolic polymers (lignin-carbohydrate complexes) that are covalently cross linked. Cellulose itself is a linear polymer of glucose molecules linked to oneanother by -1-4 glucosidic bonds and herein lies the problem for the vertebrate digestive system (Bowen, 1996a). Microbes do secrete cellulases which allow them to utilize dietary cellulose and other plant cell wall materials. Cellulolytic microbes inhabit the digestive tract of all animals. It has been found that almost all these microbes are anaerobes or facultative anaerobes fermentative*Corresponding author. E-mail: firstname.lastname@example.org. Tel: +2348062204766. Abbreviations: CSTR, Continuous stirred tank reactor; PFR, plug flow reactor.
Awolu and Layokun
Figure 1. A diagrammatic representation of Hippopotamus amphibious gut as 1-continuous stirred tank reactor (CSTR)1- plug flow reactor (PFR).
microbes (Bowen, 1998). Bowen...