Biochemical Conversion Processes Research Articles

Response of Thermochemical and Biochemical Conversion Processes to Lignin Concentration in Alfalfa Stems

The technologies currently in place to convert lignocellulosic biomass to energy are either biochemical or thermochemical, the efficiencies of which may vary depending on the composition of the feedstock. One variable that conversion technologists have wrestled with, particularly in the simultaneous saccharification and fermentation process, is biomass lignin content. While lignin is considered a recalcitrant to biochemical conversion, it can be a good source of combustion fuel, but the true effect of composition on thermochemical conversion has not been well quantified. In this study we examined the effect of lignin content of alfalfa stems on two biofuel conversion methodologies: (i) biochemical conversion using in-vitro ruminal fermentation as a surrogate for fermentability to ethanol and (ii) thermochemical conversion using pyrolysis. Lignin was found to account for little of the variation in pyrolysis product yield compared to biochemical conversion. Linear regression of lignin concentration on pyrolysis product yields resulted in few significant relationships whereas in-vitro gas production exhibited a strong negative response to lignin content. For alfalfa stems, lignin had a much larger effect on biological conversion potential than it did on thermochemical conversion potential. The results suggest that genetic modification or agronomic management of lignocellulosic biomass for bioenergy feedstock composition should be based on the intended energy conversion platform.

Study of rotating biological contactor performance in wastewater treatment using multi-culture biofilm model

The rotating biological contactor (RBC) process offers the specific advantages of a biofilm system in treatment of wastewater for removal of soluble organic substances and stabilisation of nitrogen compounds. Being a unique adaptation of the moving-medium biofilm system, it facilitates easy and effective oxygen transfer. However, process optimisation and adaptability under different conditions remain challenging tasks for the efficient use of this technology. Although modelling helps to study system performance under various external conditions, satisfactory mathematical representation is lacking due to the dynamic nature of the RBC system. In this work, it has been attempted to frame a mathematical model for a three-stage RBC process in simple and realistic ways. The model is based on the well-known principles of one-dimensional mass transfer and transport of substances. The biochemical conversion process is adopted from the Activated Sludge Model No. 3 which represents a mixed-culture biomass environment. Owing to the dynamic nature of oxygen transfer, which is the typical limiting substrate in municipal wastewaters, the boundary layer is assumed to be completely mixed and concentrations averaged over the entire volume. A part of the boundary layer is assumed to be exposed to air and the rest submerged in bulk liquid at all times. The model results are compared with laboratory-scale experimental data available at 25 'C. Sensitivity analysis is performed with the model to study the significance of variation of different system parameters or the surrounding environment. In essence, the model helps to explore the flexibilities within a RBC system and optimise the process design accordingly.

Bioreactor performance: a more scientific approach for practice

In practice, the performance of a biochemical conversion process, i.e. the bioreactor performance, is essentially determined by the benefit/cost ratio. The benefit is generally defined in terms of the amount of the desired product produced and its market price. Cost reduction is the major objective in biochemical engineering. There are two essential engineering approaches to minimizing the cost of creating a particular product in an existing plant. One is to find a control path or operational procedure that optimally uses the dynamics of the process and copes with the many constraints restricting production. The other is to remove or lower the constraints by constructive improvements of the equipment and/or the microorganisms. This paper focuses on the first approach, dealing with optimization of the operational procedure and the measures by which one can ensure that the process adheres to the predetermined path. In practice, feedforward control is the predominant control mode applied. However, as it is frequently inadequate for optimal performance, feedback control may also be employed. Relevant aspects of such performance optimization are discussed.

Physical and chemical characterisation of selected weed species for energy production

Selected weed species were assessed for assessing their suitability as energy production sources using chemical conversion routes. The physical and chemical properties of 26 weed species were characterised. Physical characterisation included determination of number of branches, plant height, plant weight, stem diameter, density and chemical characterisation included determination of moisture content, ash content, volatile matter content and fixed carbon content. Abutilon indicum G.Don, Achyranthes aspera L. and Dyschoriste nagchan, Nees. were identified for thermochemical gasification and five weed species were selected for biochemical gasification. The rate of gas production from Abutilon indicum, G.Don., Achyranthes aspera, L. and Dyschoriste nagachann, Nees. in thermochemical conversion process was 1.709, 2.212 and 2.246 m 3 kg −1, respectively and a maximum biogas production of 20.13 l kg −1 was observed for Achyranthes aspera, L. in a biochemical conversion process.