Effects of Additives on Volatile Fatty Acids Production in Anaerobic Digestion
By Prasanna Rao
Laboratory-scale experiments were conducted to study the effect of additives on the
process of anaerobic digestion in general and on the production of volatile fatty
acids in particular. Twelve reactors with a working volume of 3-liters were operated
as anaerobic digesters and were loaded daily with 150 ml of the primary sludge with
an average volatile solids content of about 3%. Five commercial additives - Biocope,
Medina d-part, MPC, Alken Murrary and Biosep - were added in duplicates to the total
of ten reactors and two reactors were operated as control. The influent and effluent
from each reactor were analyzed for total volatile solids, volatile fatty acids,
and pH.
The volatile fatty acids were analyzed by using gas chromatography. The addition
of Biocope results in the greatest reduction of the volatile solids of 47.5%. This
was 8.1% greater (P< 0.05) than the reduction of volatile solids in control reactors,
which did not receive any additives. Acetic and propionic acids were the only major
acids present in the reactors receiving Biocope and Medina d-part. The reactors receiving
MPC, Alken Murray and Biosep produced considerable amounts of six major fatty acids.
The reactors receiving MPC developed unbalanced conditions and hence resulted in
the lowest destruction in volatile solids and highest concentrations of volatile
fatty acids. It was found that only Biocope affected the anaerobic digestion process
in a significant manner by causing the highest destruction in volatile solids. A
cost analysis was performed for a wastewater treatment plant using Biocope as an
additive, which gave a benefit to cost ratio of 2.27, indicating the potential economic
advantages associated with its use.