Biomass streams

Liquefaction of wet biomass streams is done by hydrothermal processes at elevated pressures. The feed stocks for these high pressure liquefaction processes are slurries of biomass particles and water. Feeding these slurries into the high pressure equipment, at reasonable costs, is an important hurdle in the process development. For example, the reported operating conditions for high pressure liquefaction are in the range 280-360 °C and 90-250 bar [25, 26]. Under these conditions, biomass is converted, in a complex sequence of chemical reactions, into various compounds. Upon cooling, the reactor effluent consists of three... 

Co-gasification Entrained flow gasification of coal and biomass streams... 

Sugar can be converted to ethanol based on micro-organisms. Because starch and even celluloses can be converted more or less easily into sugar, such biomass streams are also a potential resource for the production of bioethanol in addition to naturally sugar-containing crops like sugar cane and sugar beet (see Chapters 8 and 9.3). 

Figure 2.5 Possible technological solutions to bioprocess problems a) Fed-batch culture b) Continuous product removal (eg dialysis, vacuum fermentation, solvent extraction, ion exchange etc) c) Two-phase system combined with extractive fermentation (liquid-impelled loop reactor) d) Continuous culture, internal multi-stage reactor e) Continuous culture, dual-stream multi-stage reactor f) Continuous culture with biomass feedback (cell recycling). (See text for further details).

The average biomass concentration is defined as the product of yield of biomass and change of substrate concentrations in inlet and outlet streams. The biomass balance is ... 

In designing a bioreactor, material balance is used for all the streams associated with the fermentation vessel. The biomass at inlet, outlet and the generated biomass must be balanced while the fermentation proceeds. The cell balance without any cell accumulation is shown in the following equation ... 

Cellulose in the wastewater stream is not generated but it is consumed and biomass produced by the microbial population as a substrate for energy. 

The performance data for plug versus mix reactor were obtained. The data were collected as the inverse of qx vs inverse of substrate concentration. Table E.1.1 shows the data based on obtained kinetic data. From the data plotted in Figure E.1.1, we can minimise the volume of the chemostat. A CSTR works better than a plug flow reactor for the production of biomass. Maximum qx is obtained with a substrate concentration in the leaving stream of 12g m 3. 

Aggradation or degradation of biomass or soil reservoirs may also produce effects that appear to be fractionation. This is because the elemental ratios in vegetation or soil reservoirs can be very different from those of bedrock. Sufficiently large and rapid changes in these reservoirs are sometimes evident in river chemistry. For example, the uptake and release of potassium in association with the seasonal growth and loss of leaves can affect the composition of streams that drain temperate deciduous forests (Likens et al, 1977 Vitousek, 1977). 

The development of bioreactor systems for the production of large-volume chemicals (see Chapter 3) could be the basis for reconsidering the production of biomass in limited quantities for fuel uses. This would require efficient microbial organisms to catalyze fermentation, digestion, and other bioconversion processes, as well as efficient separation methods to recover fuel products from process streams. 

Alternatively, an entirely new downstream process and product chain, using renewable raw materials, can be conceived (the biorefinery ). The chemistry will be more focused on that of oxohydrocarbons (particularly carbohydrates) rather than hydrocarbons. Understanding the materials chemistry of biomass and related products would need to be enhanced. However, work has already been undertaken to identify the top sugar-derived intermediates (Figure 1.9) on which down-stream chemical processing might be derived. 

K. Suberkropp, M. O. Gessner, and E. Chauvet, Comparison of ATP and ergosterol and indicators of fungal biomass associated with decomposing leaves in streams, Appl. Environ. Microbiol. 59 3361 (1993). 

In the above ODEs, X] and x2 represent the biomass and substrate concentration in the chemostat, cF is the substrate concentration in the feed stream (g/L) and D is the dilution factor (h 1) defined as the feed flowrate over the volume of the liquid phase in the chemostat. It is assumed that both state variables, xt and x2 are observed. 

In a separate study, Igwe and Abia46 determined the equilibrium adsorption isotherms of Cd(II), Pb(II), and Zn(II) ions and detoxification of wastewater using unmodified and ethylenediamine tetraacetic acid (EDTA)-modified maize husks as a biosorbent. This study established that maize husks are excellent adsorbents for the removal of these metal ions, with the amount of metal ions adsorbed increasing as the initial concentrations increased. The study further established that EDTA modification of maize husks enhances the adsorption capacity of maize husks, which is attributed to the chelating ability of EDTA. Therefore, this study demonstrates that maize husks, which are generally considered as biomass waste, may be used as adsorbents for heavy metal removal from wastewater streams from various industries and would therefore find application in various parts of the world where development is closely tied to affordable cost as well as environmental cleanliness.46... 

Currently, there is renewed interest in this process. At Twente University (The Netherlands), research is performed toward the use of bio-oil from (flash) pyrolysis as the reducing agent for the oxidized iron.149 Therefore, a CO-containing gas stream and a relatively pure H2 stream is generated separately from the biomass-derived bio-oil. 

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