Effluent solids recirculation to municipal sludge digesters enhances long-chain fatty acids degradation capacity

Table 1 Operating conditions of the laboratory stirred-tank anaerobic digesters (R1–R6)

	Days^a	R1	R2	R3	R4	R5	R6
PASS loading rate (gVS l⁻¹ day⁻¹)	0–200	1.3 ± 0.1	1.3 ± 0.1	1.3 ± 0.1	1.3 ± 0.1	1.3 ± 0.1	1.3 ± 0.1
PASS loading rate (gVS l⁻¹ day⁻¹)	201–255	0.0	0.0	0.0	0.0	0.0	0.0
Oleate loading rate (g l⁻¹ day⁻¹)	0–84	0.0	0.0	0.0	0.0	0.0	0.0
	85–91	0.0	0.08	0.08	0.0	0.08	0.08
	92–112	0.0	0.13	0.13	0.0	0.13	0.13
	113–130	0.0	0.25	0.25	0.0	0.25	0.25
	131–151	0.0	0.5	0.5	0.0	0.5	0.5
	152–171	0.0	1.0	1.0	0.0	1.0	1.0
Pulse feeding^b →	172–200	0.0	1.0	1.0	0.0	1.0	1.0
	201–255	0.0	0.0	0.0	0.0	0.0	0.0
Effluent solids recirculation rate (gTS l⁻¹ day⁻¹)	0–84	0.0	0.0	0.0	0.6 ± 0.0	0.5 ± 0.1	0.6 ± 0.1
	85–171	0.0	0.0	0.0	0.8 ± 0.2	0.8 ± 0.1	0.9 ± 0.2
	172–200	0.0	0.0	0.0	1.1 ± 0.1	1.2 ± 0.1	1.3 ± 0.1
	201–255	0.0	0.0	0.0	0.0	0.0	0.0
Sulfide addition (mmol l⁻¹ day⁻¹)	0–200	0.0	0.0	20	0.0	0.0	20
Sulfide addition (mmol l⁻¹ day⁻¹)	201–255	0.0	0.0	0.0	0.0	0.0	0.0

^aDay 0–84: start-up phase; day 85: start of oleate addition to R2, R3, R5, and R6; day 172: start of oleate pulse feeding; day 201: end of PASS and oleate feeding
^bAddition of 2.0 g l⁻¹ of oleate every second day is referred to as pulse feeding

ISSN: 2731-3654