Environmental Engineering Reference
In-Depth Information
PROBLEMS
14.1
The hydrolysis rate coefficient of the biodegradable fraction of a feedstock
is 0.05 h
−1
. What retention time is required to obtain 80% degradation of
the biodegradable fraction of the substrate in a continuous stirred tank reactor
(CSTR)? What happens to the retention time required if we place two CSTRs in
series or in parallel?
14.2
Howmuch MW electricity can an anaerobic digester treating 100,000 tonnes of
OFMSW per year produce? In the Netherlands, approximately 1400 kt of
OFMSW is collected per year. If all this OFMSW would be treated by anaer-
obic digestion, estimate the potential contribution to the natural gas consump-
tion in the Netherlands (50
10
9
m
3
.y
−1
). Discuss the results obtained.
PROJECT
A food processing company generates 60,000 tonnes waste per year and is consider-
ing anaerobic digestion as a potential method for waste valorization. Measurements on
the waste provide the following data: TDM = 300 g.kg
−1
, ODM = 280 g.kg
−1
,N=3g.
kg
−1
, and COD = 400 g.kg
−1
. From the feedstock characteristics, estimate:
1. The elemental composition of the organic fraction of the biomass
2. The fractions of lipids, proteins, and carbohydrates in the feedstock
To assess (i) the biodegradable fraction of the feedstock and (ii) the
first-order rate coefficient for hydrolysis of the biodegradable fraction of the
feedstock, a batch biodegradability survey is conducted. The biodegradability
survey is conducted by incubating 25 g waste in a one liter bottle with methan-
ogenic biomass. The net methane production is monitored as a function of time,
and the following data are obtained:
Time (d)
CH
4
(L)
0
0.00
5
0.78
10
1.32
15
1.71
20
1.98
30
2.30
40
2.47
50
2.55
Due to the supply of methanogenic biomass in the test, the methane production
directly reflects the amount of substrate degraded. Full conversion of biode-
gradable substrate into methane can be assumed, and therefore, side reactions
like partial conversion of substrate into biomass or intermediate accumulation
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