Table 1.

Characteristics and alpha-diversity analyses of the bacterial and archaeal communities at different stages in the palm oil mill effluent (POME) treatment

POME treatment processes/Parameters	Mixed raw effluent	Mixing pond	Holding tank	Anaerobic		Facultative anaerobic pond	Aerobic (algae) pond	Final discharge
				Closed reactor	Open digester
Characteristics
pH	4.58±0.2	4.42±0.3	4.39±0.2	7.08±0.0	7.07±0.0	8.08±0.1	8.03±0.0	8.04±0.0
Temperature (°C)	65.57±0.8	43.63±0.7	41.62±1.0	40.59±2.8	37.89±1.3	32.92±1.4	32.95±1.7	31.91±0.7
Retention time (d)	0	1–2	1	20	20	20	14	0
Alpha-diversity analyses
No. of sequencesa	115880	140354	196849	187554	82687	95693	114515	200631
OTUb	93854	93681	148262	101477	38069	55923	63442	121368
Shannon-Weaver index (H′)	0.869	0.800	1.119	1.908	1.725	1.933	1.929	2.272
Evenness (E′)	0.050	0.077	0.073	0.120	0.115	0.111	0.109	0.145

Notes:

^aDetected sequence number;

^bDetected OTU number