TITLE:
Influence of Polyphosphate Hydrolysis on the Degradation of Volatile Fatty Acids (VFAs) in Anaerobic Digestion
AUTHORS:
Ikechukwu Maxwell Onoh, Gordian Onyebuchukwu Mbah, Albert Chibuzo Agulanna
KEYWORDS:
Volatile Fatty Acids (VFAs), Polyphosphate Salts, Anaerobic Digestion, Bioenergetics, Syntrophic Degradation
JOURNAL NAME:
Advances in Chemical Engineering and Science,
Vol.7 No.4,
October
23,
2017
ABSTRACT: The degradation rate of Volatile Fatty Acids (VFAs) produced predominantly
in the acidogenesis stage is a key process parameter to be optimised to ensure
a successful Anaerobic digestion (AD). Thermodynamically, the oxidation of
the VFAs are energetically unfavourable, and as such external energy source
apart from the energy derived from the hydrolysis of Adenosine Triphosphate
(ATP) is needed for the initial activation of the VFAs, initial growth of the
methanogens in AD process and improved degradation rate of the VFAs.
Thus, this research investigated the influence of polyphosphate hydrolysis on
the degradation rate of the VFAs at high concentration. Sodium-propionate,
Sodium-butyrate and Sodium-acetate salts were added at the start of experiments
in order to increase the concentration of the VFAs. The polyphosphate
salts used were; Na-hexametaphosphate, Na-tripolyphosphate and potassium
pyrophosphate. The control experiment was polyphosphate free and three
process parameters (degradation rate, cumulative biogas production and specific
methane content) of anaerobic digestion were investigated. The experiments
were carried out at a mesophilic temperature of 37.5°C for 41 days. The
results of the investigation showed that the treated reactors with the polyphosphate
salt solution in low concentration performed better than the reactors
with high concentration of the polyphosphate salts solution. All the
treated reactors with poly-P salts performed better than reactor Nr-9 (control
experiment), but reactor Nr-1 was outstanding with an improved degradation
rate of 47%, cumulative biogas production of 21% and specific methane content
of 23%.