Acetic Acid by Product From Various Fermentations of Fermented Biogas Excess Sludge and Acidic Sludge Substrate

The aim of this study was to investigate the optimum conditions for acetic acid production from various excess sludge as carbon sources for biological phosphorus removal processes. Two substrates used to produce acetic acid which were wastes from fermented biogas production system after 10-day fermentation (fermentation sludge, (FS)). The fermentation was carried in batch system with 3 substrate series. The substrates were combined with FS and acid fermentation (AF) in three different ratios; FS: AF (1:1), RS: AF (4: 1) and RS:AF (1: 4) in series 1, 2 and 3, respectively. Further investigation regarding the influence of temperature, pretreatment and the proportion of fermentation sludge (FS) and acid fermentation (AF) were also conducted. The results showed that the highest concentration of acetic acid was 1,406 mg COD/L in the reactor containing FS: AF 1: 1 (series 1) substrate after 96 hours with control conditions at 35 °C whereas similar combinations in reactor 2 and 3 produced lower concentration of acetic acid (1,018 and 792 mg/l, respectively). The Paired t-test of series 1-3 showed significant difference of acetic acid production (p < 0.05) for FS in series 1 and RS in series 2-3. The composition in experimental series 1 can be applied to produce acetic acid as carbon source for the biological phosphorus removal for reducing the cost of acetic acid production.