C-13 NMR studies on vinasses effluent treated with iron

Controlling the concentration and toxicity of propionic acid in upflow anae robic sludge blanket (UASB) reactors is a challenging problem in biological wastewater treatment. Addition of FeSO4. 7H(2)O and FeCl3. 6H(2)O to vinas ses effluent yields a precipitate and considerably reduction of propionic a cid in solution. This is due to the coordination of volatile fatty acids (V FAs) to metal ions, according to C-13 NMR techniques. C-13 NMR broadening o f signals was carried out in vinasses effluent as well as in pure propionic acid (5.0 g/l) with various concentrations of Fe ions. The results show th at Fe(II) is one of the micronutrients in anaerobic digestion, forms less s table complexes with propionic acid, and leads to a higher degree of bioass imilation of the dissolved organic compounds to produce biogas. This is one of the main reasons why FeSO4. 7H(2)O facilitates the anaerobic digestion. C-13 NMR signals of propionic acid and vinasses effluent with Fe(III) were considerably more broadened as compared to Fe(II), suggesting that chelati on of VFAs with Fe(III) is stronger than with Fe(II) and, however, Fe(III) reduced to Fe(II) at anaerobic conditions. Metal complexes were not readily degraded by bacteria as the biodegradability of the metal complexes depend s upon the stability and chemical nature of the complexes, and not on the t oxicity of the metal ions towards the bacteria. (C) 1998 Published by Elsev ier Science Ltd. All rights reserved.