8 Product yield in anaerobic digestion Anaerobic digestion of volatile acids by methane bacteria is represented by the equation: CH3COOH + NH 3 –9…

4.8 Product yield in anaerobic digestionAnaerobic digestion of volatile acids by methane bacteria isrepresented by the equation:CH3COOH + NH 3 –9 biomass + CO 2 + H20 + CH 4.(acetic acid) (methane)The composition of methane bacteria is approximated by theempirical formula CH1.4Oo.40N0.20. For each kg acetic acidconsumed, 0.67 kg CO 2 is evolved. How does the yield ofmethane under these conditions compare with the maximumpossible yield?4.10 Ethanol production by yeast and bacteriaBoth Saccharomyces cerevisiae yeast and Zymomonas mobilisbacteria produce ethanol from glucose under anaerobic conditionswithout external electron acceptors. The biomass yieldfrom glucose is 0.11 g g-1 for yeast and 0.05 g g-I for Z.mobilis. In both cases the nitrogen source is NH 3. Both cellcompositions are represented by the formula CH 1.800.5N0.2.(a) What is the yield of ethanol from glucose in both cases?(b) How do the yields calculated in (a) compare with thethermodynamic maximum?4.11 Detecting unknown productsYeast growing in continuous culture produce 0.37 g biomassper g glucose consumed; about 0.88 g 0 2 is consumed per gcells formed. The nitrogen source is ammonia, and the biomasscomposition is CH1.7900.56N0.17. Are other productsalso synthesised?4.14 Effect of growth on oxygen demandThe chemical reaction equation for conversion of ethanol(C2H60) to acetic acid (C2H402) is:C2H60 + 02 –~ C2H402 + H20.Acetic acid is produced from ethanol during growth ofAcetobacter aceti, which has the composition CH 1.800.5N0.2.Biomass yield from substrate is 0.14 g g- 1; product yield fromsubstrate is 0.92 g g-1. Ammonia is used as nitrogen source.How does growth in this culture affect oxygen demand foracetic acid production?

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