Environmental Engineering Reference
In-Depth Information
Table 8.11
Average characteristics of influent and effluent and performance of digesters
Characteristics
Influent
Effluent from
mesophilic
digester
Effluent from
thermophilic
digester
pH
6.5
7.9
8.1
TS
mg/L
66,250
44,250
46,880
VTS
mg/L
54,880
32,880
34,250
COD
Cr
mg/L
72,500
34,250
35,250
VFA
mg/L
8520
50
353
T-N
mg/L
3050
3040
3160
NH
4
+
-N
mg/L
1330
1840
2090
Alkalinity
mg/L
6280
12,120
12,630
T-P
mg/L
515
490
510
Coliform
bacteria
CFU/ml
722,500
5300
248
Fecal coliform
CFU/ml
439,200
1332
28
Performance
Mesophilic
digester
Thermophilic
digester
COD
Cr
reduction %
52.8
51.4
Biogas
production
Nm
3
/d/
m
3
-digester
0.9
1.0
Methane content %
Average 55.4
1.1 times that of the mesophilic digester. The average methane concentration in the
biogas from both digesters is 55.4 %. Average characteristics of influent and efflu-
ent and the performance of the digesters are shown in Table
8.11
. Higher
E. coli
and
F. coli
reduction through digestion was observed in the thermophilic digester
than in the mesophilic digester. In YBEC, a balance is basically maintained be-
tween the electric power produced from the biogas and that consumed in the plant.
If any excess electricity is produced, it is sold off to the WWTP. After the digested
sludge is dewatered, the liquid is treated by a wastewater process and the solid is
composted.
8.4.7
Two-Stage Process with Combined Hydrogen and Methane
Production
A two-stage anaerobic digestion system can be envisaged to produce both hydrogen
and methane. As shown in Fig.
8.19
, compared with the single phase, a two-phase
configuration not only degrades more waste, but also gains more net energy from
the system. In a single stage anaerobic digestion, a variety of higher organic acids,
such as propionic, butyric, and lactic, as well as alcohols and ketones, are also
formed during the breakdown of the organic substrates by acidogens. However,
