Comparative evaluation of sludge characteristics and methane potential from different municipal wastewater treatment processes

The energy potential of sludge from the anaerobic/anoxic/aerobic (A²O) process, HRAS + MBR process, and AGS process was comparatively evaluated in the study. The sludge from the A²O process (S1) consists of proteins, hemicellulose, and cellulose in 46 %, 30 % and 8 % in order. Organic compounds in sludge from the AGS process (S2) were mainly 41 % protein, 33 % hemicellulose, 9 % lignin, and 7 % lipids, while sludge from the HRAS + MBR process (S3) was mainly composed of a high amount of proteins (53 %), hemicellulose (14 %), and lipids (14 %). Results showed that the sludge from the HRAS + MBR process had the highest methane, which was 212 ± 18 mL CH₄/g VS. Methane yield of sludge from the AGS process (173 ± 11 mL CH₄/g VS) was slightly lower than that from the A²O process (180 ± 1 mL CH₄/g VS). Compared to the A²O process, the organic matter in wastewater transformed to methane gas was nearly 21.0 % and 23.3 % for the AGS process, and HRAS + MBR process, respectively.