Table 1.

Performance indicators and properties of the chain elongation process at long and at short HRT.

Performance indicator	Unit	Long HRT [4 d]	Short HRT [1 d]
STEADY STATE CHARACTERISTICS
Steady state interval	d	28–58	79–103
Number of HRTs	–	7.5	24.3
PRODUCTS
n-Caproate concentration	g/L	23.4 ± 1.0	7.1 ± 0.9
n-Caproate rate	g/L/d	5.5 ± 0.4	5.6 ± 0.9
n-Caproate selectivity	mol e %	76.5 ± 5.0	44.6 ± 7.8
MCFA selectivity	mol e %	81.6 ± 5.0	46.3 ± 8.0
Methane rate	mmol/L/d	12.8 ± 2.6	43.8 ± 2.5
SUBSTRATES
Ethanol loading rate	g/L/d	6.1 ± 0.2	30.6 ± 1.3
Ethanol concentration	g/L	2.8 ± 1.1	20.1 ± 1.6
Ethanol rate	g/L/d	−6.0 ± 0.3	−12.3 ± 1.1
EEO	g/L/d	0.9 ± 0.4	5.6 ± 1.4
EEO	% of total ethanol use	14.7 ± 5.5	45.0 ± 9.7
Acetate rate	g/L/d	−1.0 ± 0.2	−0.8 ± 0.5
Propionate rate	g/L/d	−0.3 ± 0.0	−0.7 ± 0.1
n-Butyrate rate	g/L/d	−0.9 ± 0.1	1.6 ± 1.1
SUBSTRATE TO PRODUCT CONVERSIONS
Consumed VFA per produced MCFA	mol C/mol C	0.29 ± 0.04	0.20 ± 0.07
Consumed Ethanol per produced MCFA	mol C/mol C	0.87 ± 0.07	1.83 ± 0.31
CONSUMPTION/PRODUCTION EFFICIENCY
Ethanol consumption efficiency	mol e %	98.6 ± 5.4	40.3 ± 3.5
VFA consumption efficiency	mol e %	45.8 ± 6.9	7.2 ± 2.3
n-Caproate production efficiency	mol e %	58.7 ± 2.9	12.8 ± 2.1
MCFA production efficiency	mol e %	62.6 ± 2.9	13.3 ± 2.2
NaOH USE
Sodium concentration in influent [AFW]	g/L	4.9 ± 0.1	4.8 ± 0.1
Sodium concentration in reactor	g/L	9.1 ± 0.5	7.0 ± 0.0
Consumed NaOH per produced MCFA	mol/mol	0.92 ± 0.04	1.93 ± 0.31
VSS
VSS concentration	g/L	0.34 ± 0.23	0.33 ± 0.03
VSS rate	g/L/d	0.02 ± 0.05	0.18 ± 0.33
Growth rate	g/g/d	0.07 ± 0.16	0.54 ± 1.00