Table 2.

Selected studies that investigated long-term microbial dynamics during anaerobic digestion of municipal sewage sludge from a search on the Web of Science^™ database (Clarivate Web of Science Core Collection).

Feed types	Scale	Reactor size	Reactor qty	Temp °C	Days	SRT/HRT	OLR	Aim	Findings	Location	Year
Digested sludge	Full-scale	3,300 m3	2	33	315	19	1.75 a	Investigate microbial dynamics during start-up phase	Waste activated sludge was suitable inoculum, clear shifts observed, enrichment of acetoclastic methanogens	Venice, Italy	2021A
PS and (T)WAS	Pilot-scale	2 m3	4	35	160	51.5, 25.9	1.1, 1.5 a	Effect of phenylacetic acid on performance	Mixed sludge was less affected compared to PS	Santiago, Chile	2015B
PS/WAS mix	Lab-scale	2 l	various	37	93	20	3.7–9.4 b	Study effect of mixing	Increased mixing inhibited syntrophic oxidation of VFAs	Urbana, USA	2001C
PS	Lab-scale	4 l	6	36	42	-	3.4–5 b	Study effect of OLR	Increased loading promoted methane production; the community was unaffected	Wooster, USA	2011D
PS/WAS mix	Lab-scale	0.5 l	6	55	319	5–30	1–2 b	Study effect of biochar	Cornstove biochar increased methane content and flow rate	Lemont, USA	2017E
PS/WAS mix	Lab-scale	3w L	6	35	130	15	3 b	Study effect of antibiotics	Reduced methane production, increased risk of AMR	Changsha, China	2019F
(T)WAS	Lab-scale	1.5w L	4	37	155	15	2.7 c	Study effect of synthetic musk	Synthetic musk inhibited hydrolysis	Sydney, Australia	2020G
Food/WAS mix	Lab-scale	10 l	2	36	100	20	0.8–1.7 b	Understanding instability	Mixing WAS with Foodwaste increased stability, related to trace elements and microbes	Monterotondo, Italy	2020H
(T)WAS	Lab-scale	1.3 l	4	35	300	12	1.4 a	Study effect of nitrous acid pre-treatment	Free nitrous acid pre-treatment improved methane yields but also increased pathogens	St Lucia, Australia	2021I
(T)WAS	Lab-scale	0.5 l	2	35	60	5	-	Study effect of contaminants on stability	Cell lysis by plastic additive, but process was stable	Changsha, China	2021J

Refer to Supplementary materials for search criteria; Reactor size = total volume unless marked `w` for working volume.

^akgVS m³ day^-2.

^bgVS L^-1 day^-2.

^cgCOD L^-1 day^-2; SRT, sludge retention time; HRT, hydraulic retention time; OLR, organic loading rate; PS, primary sludge; WAS, waste activated sludge; TWAS, thickened waste activated sludge. References: A (Tonanzi et al., 2021); B (Cabrol et al., 2015); C (McMahon et al., 2001); D (Gómez et al., 2011); E (Shen et al., 2017); F (Xu et al., 2019); G (Wei et al., 2020); H (Tonanzi et al., 2020); I (Calderon et al., 2021); J (Tang et al., 2021).