12th Nordic Wastewater Conference

12. Pohjoismainen jätevesikonferenssi

12:e Nordiska Avloppskonferensen

14-16.11.2011, Marina Congress Center, Helsinki

Anaerobic contact reactor with sludge recirculation to increase biogas production

Erik Levlin1,2 Lars Bengtsson1, Christian Baresel1

  1. IVL Swedish Environmental Research Institute,
    Box 210 60, SE-100 31 Stockholm, Sweden
  2. Dep. of Land and Water Resources Engineering, KTH Royal Institute of Technology,
    SE-100 44 Stockholm, Sweden

Keywords: pilot plant, biogas production, extended solid retention process

        

 

 






Project Increased biogas production at Hammarby Sjöstadsverk

The idea was to increase the biogas production by separation and reprocessing a fraction of the digested sludge. By making the sludge retention time longer than the hydraulic retention time more biogas can be produced with the same reactor volume. Since methane producers grow more slowly the long sludge retention time makes the process more stable and biogas production is increased. The process is defined as Extended Sludge Retention Time process (EXRT).


  Traditional digestion:

       HRT = SRT

  HRT Hydraulic Retention Time
  SRT Sludge Retention Time

 

Methane bacteria are slow grower, thus need a long SRT. At short SRT growth of fermentative bacteria will cause accumulation of VFA inhibiting methane bacteria.

¡          HRT determines reactor volume
Short HRT gives a small digester volume

¡          SRT determines biogas production
Long SRT gives a large biogas production

 

In to
digest.

Out of
digest.

Dewat.
sludge

Reject
water

Unit

Flow

0.816

0.803

0.074

0.852

m3/day

Total Solids TS

0.86

2.39

23.38

0.11

%

VS Volatily Solids

0.71

1.58

15.68

0.053

%

 

Results

 Parameter

EXERT-process

Henriksdal WWTP

Unit

Hydraulic retention time HRT

10.6

19.7

Days

Sludge retention time SRT

218

19.7

Days

Degree of digestion

78.7 1
21.6 2

49.5

%

Methane content

56.1

65.6

%

Specific gas production

0.78

0.47

Nm3/kg VS

Specific methane production

0.44

0.31

Nm3/kg VS

Gas production

0.51

0.66

Nm3/(m3∙day)

Methane production

0.29

0.43

Nm3/(m3∙day)

Organic loading rate OLR

0.69 3
2.08 4

1.5

kg VS/(m3∙day)

Total Solids TS in

0.86

4

%

Volatily Solids VS in

0.71

3.32

%
1 Calculated for entire system.
3 Calculated on incoming sludge
 2 Calculated for the digestion chamber.
4 Calculated on incoming and recirculated sludge

Hammarby Sjöstadsverk
was 2008 jointly taken over by KTH Royal Institute of Technology and IVL Swedish Environmental Research Institute with wastewater treatment lines in pilot plant scale (150 p.e. = 1,5 m3/hour):

·                Aerobic treatment with activated sludge
process and sedimentation.

·                Aerobic treatment with membrane bioreactor (MBR), an aerobic reactor with submerged micro filter, and drum filter for separation of primary sludge.

·                Anaerobic treatment with UASB-reactors
(Upstream Activated Sludge Blanket).

·                The produced sludge can be thickened, digested and dewatered.

 


UASB and sludge digesters


Aerobic with sedimentation


MBR

 

 

Decanter centrifuge
for dewatering

More information:

Homepage: www.sjostadsverket.se

Project despription