Comparison of Anaerobic Co-Digestion of Buffalo Manure and Excess Sludge with Different Mixing Ratios under Thermophilic and Mesophilic Conditions

Abstract

In this study, the main aim is to evaluate the mixing ratio of co-digestion of buffalo manure (BM) and excess sludge (ES) influenced for methane yield and digestate dewaterability. Five batch experiments with different BM and ES mixing ratios were carried out under thermophilic and mesophilic conditions. The methane yield of co-digestion of BM and ES increased by 10.1–73.5% under thermophilic conditions and 87.9–153.3% under mesophilic conditions, compared with the mono-anaerobic digestion of ES under the same conditions. Shannon and Chao1 indices showed that the bacterial species of the mesophilic digesters were more abundant than that of the thermophilic digesters. With the increase in the BM proportion in the substrate, the normalized capillary suction time (NCST) and total solids (TS) of sediment (centrifugal dewatering) increased. The NCST at thermophilic temperature (8.98–12.54 s∙g−1-TS) was greater than that at the mesophilic temperatures (5.45–12.32 s∙g−1-TS). However, the TS of sediment was not directly related to the digestion temperature. This study has shown that anaerobic co-digestion of BM and ES at the appropriate ratio (BM/ES = 1:1.5) has a significant meaning in a high methane yield.

Effects of One-Step Abrupt Temperature Change on Anaerobic Co-Digestion of Kitchen Waste with Dewatered Sludge

“…Thermophilic conditions promoted the release of ammonia nitrogen while accelerating the consumption of organic acids by microorganisms, both of which were responsible for the rapid increase in pH under thermophilic conditions [38]. After adjusting pH, the overall pH-changing trend in the experimental and control groups was similar to that in previous studies [14,39]. However, the minimum pH value (7.1) in this study was higher than that in this experiment (6.9) under thermophilic conditions, which might be due to the higher VS/TS of the substrate in this experiment, allowing the formation of organic acids leads to a lower pH [37].…”

“…This was mainly because the rise to a higher operating temperature could lead to an increase in ammonia nitrogen, which could inhibit the life activities of anaerobic microorganisms [46]. Moreover, ammonia nitrogen could inhibit the activity of propionic acid-degrading microorganisms, leading to the accumulation of propionic acid [14,39]. Propionic acid, as a difficult-todegrade VFA, had the most obvious inhibitory effect on methanogens, therefore inhibiting the progress of anaerobic digestion [46].…”

“…AD not only stabilizes DS but also generates methane-rich biogas (with a methane content of approximately 65%) [12,13]. However, the slow hydrolysis process and low C/N ratio associated with sludge AD will result in a much lower methane yield than the theoretical methane yield [14].…”