Sulfide level in municipal sludge digesters affects microbial community response to long-chain fatty acid loads

Table 1 Operating parameters monitored during continuous feeding of primary and activated sewage sludge to digesters F1–F6

	Days^a	F1	F2	F3	F4	F5	F6
Specific biogas production (ml g⁻¹VS_input)	0–75	620 ± 55	645 ± 65	650 ± 60	645 ± 65	655 ± 65	680 ± 60
	76–132	540 ± 20	580 ± 30	585 ± 40	525 ± 35	530 ± 35	550 ± 20
	133–218	525 ± 65	570 ± 100	500 ± 100	505 ± 60	450 ± 90	575 ± 60
Methane (% of biogas)	0–75	61 ± 0	61 ± 0	61 ± 0	61 ± 1	63 ± 1	63 ± 0
	76–132	63 ± 1	62 ± 2	62 ± 3	64 ± 1	62 ± 4	64 ± 1
	133–218	61 ± 1	62 ± 1	61 ± 1	63 ± 1	62 ± 1	63 ± 1
Gaseous H₂S (ppm)	0–75	< 20	< 20	< 20	< 20	< 20	< 20
	76–132	< 20	< 20	< 20	280 ± 100	310 ± 115	250 ± 105
	133–218	< 20	< 20	< 20	510 ± 100	440 ± 70	470 ± 60
Total solids (% of total weight)	0–75	2.1 ± 0.2	1.9 ± 0.2	2.1 ± 0.2	2.1 ± 0.2	2.1 ± 0.2	2.1 ± 0.2
	76–132	2.1 ± 0.1	2.2 ± 0.1	2.1 ± 0.1	2.3 ± 0.1	2.3 ± 0.2	2.3 ± 0.2
	133–218	2.0 ± 0.2	2.1 ± 0.2	2.2 ± 0.3	2.2 ± 0.3	2.4 ± 0.2	2.2 ± 0.0
Volatile solids (% of TS)	0–75	62 ± 1	62 ± 1	63 ± 1	63 ± 1	62 ± 2	63 ± 1
	76–132	61 ± 1	61 ± 1	62 ± 2	58 ± 2	57 ± 4	58 ± 2
	133–218	62 ± 0	63 ± 1	65 ± 3	57 ± 1	59 ± 3	56 ± 0

^aDays 0-75: start-up phase; Day 76: start of sulfide addition to F4, F5, and F6; Day 133: start of LCFA addition to F2, F3, F4, and F5