Table 2 Comparison among different single stage HS-AD technologies

1

BEKON system/Germany

Batch

20.6–109.6

Agricultural waste/N/A

37–55

28–35

N/A

0.17–0.37

(i) It reduces the system complexity and machinery maintenance requirement

(ii) The problem of poor start up performance is reduced through the recirculation of leachate

The challenges of incomplete mixing and accumulation of VFAs due to high solids content of the feedstock still remains

The batch mode of the process, as well as, the recirculation of the percolate could allow the buildup of inhibitory compounds in the system

[89]

2

BIOCEL/Netherlands

Batch

95.9

OFMSW/30–40

35–40

15–21

N/A

N/A

The problem of mass transfer limitation due to high solids content of feedtock is improved through the recirculation of percolate

The problems of VFA build up which can affect the stability of the process still exists in the batch mode digester

[90,91,92,93]

3

BIOFerm/Germany

Batch

21.9

OFMSW/25

37

28

N/A

0.21–0.35

In addition to enhancing the startup performance, the technology improves the cost efficiency of the process through effective use of heat to maintain percolation temperature and energy input

The introduction of heat exchanger for effective heat usage could add to the cost of the procurement

[94, 95]

4

DRANCO/Belgium

Continuous

27.4 -191.8

OFMSW/10–32

50–55

20

10–15

0.21–0.30

The process does not require the introduction of mixers in the digester, thereby, eliminates the complexity of the system configuration. Mixing is done outside the digester through the addition of percolate to the fresh feedstock

The issue of incomplete mixing due to the inherent poor mass transfer limitation of the high solids feedstok still present. This makes the system structure to be complex and increases process and maintenance cost

[90,91,92, 96,97,98,99,100]

5

KOMPOGAS/Switzerlamd

Continuous

N/A

OFMSW/30

55

20

4.3

0.39–0.58

The poor mixing issue associated with the digestion process is addressed through the usage of impellers in the horizontal digester. Stratification problem is also reduced during the process

The introduction of impellers increases maintenance cost, thereby, reduces the overall cost effectiveness of the process

[92, 98, 101]

6

VALORGA/France

Continuous

54.8- 958.9

OFMSW/36–60

37–55

20–33

10–15

0.21–0.30

The system does not require percolate recirculation. Proper mixing of contents is done using injectors supplying biogas under high pressure every 15 min into the digester

Biogas injectors introduced into the system are often associated with clogging which require maintenance

[90, 92, 98, 102,103,104]