Chemical characteristics of substrates

SS (feeds) were collected from the secondary sedimentation tank of the Taiping wastewater treatment plant of Harbin (China) and were stored at 4 °C. To enhance the dissolution of the organics within the EPS, the sludge sample was disintegrated by ultrasonication. Specifically, 100 mL of excess sludge was sonicated in a tube using an ultrasonic cell disintegrator using 20 kHz ultrasound, operated at 1.5 W/mL for 10 min. CM was obtained from a dairy farm in Xiangfang District, Harbin. MS was obtained from a suburban farm in Harbin (7–8% moisture content), chopped to a particle size of approximately 1–2 cm, and then pretreated with 6% NaOH solution for 7 days (stirred for 30 minutes every day). Specifically, the feeds of SS, CM and MS had total carbon (TC) contents of 34.5 ± 3.1%, 43.1 ± 1.7% and 30.5 ± 1.1%, with C/N ratios of 5.32, 21.3, and 53.3, respectively. Detailed chemical characteristics of the SS, MS and CM feeds are given in the supplementary materials section.