PERGAMON Renewable Energy 16 (1999) 106&1069

Anaerobic Co-digestion of Urban and Rural Wastes

Mogens Hedegaard and Volker Jaensch

Department 660-Bioenergy, KRUGER A/S, International Division, Khunsagervej 2-4, DK-8230 Aabyhoej.

ABSTRACT

So far the technology of anaerobic digestion has not been able to meet the predicted expectation to its potential. Many factors have been influencing this but a generally trend has been that the biogas plants constructed have had problems of both technical and financial art even they as a rule have been subsidised with close to 50%. Recently KRUGER has succeeded in construction of a new generation of standard&l biogas plants for co-fermentation of both rural and urban wastes. The intention has been to put the technology back to its original enthusiasm by demonstrating viable solutions in both technical and financial terms. Furthermore, in 1997 a concept of energy neutral wastewater treatment has been demonstrated by means of co-digestion of sewage sludge and MSW which project was supported by the THERMIE programme of the EU. This concept has had an important impact to the chosen technical solutions at wastewater treatment plants and has contributed to a renewed interest in anaerobic digestion related to sewage plants. 0 1998 Published by Elsevier Science Ltd. All rights reserved.

KEYWORDS

Biogas, co-digestion, urban and rural wastes, standard&l engineering, heat exchanging.

CONTENT 1. Presentation of actual constructed biogas plants - Schweden and Denmark.

2. New concept, mechanical cell-wall disintegration related to a German biogas plant.

3. Process description of the Genthin biogas plant supplied with mechanical cell disintegration.

0960-1481/99/%-see front matter Q 1998 Published by Elsevier Science Ltd. All rights reserved. PII: SO960-1481(98)00372-3

WREC 1998

1 .a. Kristianstads bioeas slant - Schweden.

capecity:

Kristians@ds. biogas plant is Sweden’s largest plant for treatment of household, industrial and agricultural waste.

Digester vdume:

The recovered biogas set-&s as Gas quantity:

energy source for heat production Energy productIon: Client:

in the “AMverket”. Form of a&red:

The energy content in the gas scope of ellpgy:

corresponds to the heat PIUCMS: requirements for 600-800 households. It is the intention in future, if possible, also to use the gas in the vehicles transporting the biological waste.

Furthermore source separated household waste, organic waste and manure are transformed into an environmentar friendly fertiliser. The pasteufisatton step ensures 100% sanitation which means that the fertiliser can be spread on farmland without risk.

73,000 ton.9 /year

2QOhsMay 135 ton&Jay of manure 35 tcddey of wganic hlduew we!3te 30 tondday WQenic twwhold waste 4,500 ma S-Q,000 ms btoQae/day l.Q-2.oMw Krtetianstad~ Renhllttnlngs AS (Km) TUrllkeyWpptyKrOQerAfS Supply and inetellation of the

1065

1066

1 .b. Grin&ted bioeas dant - Denmark.

WREC 1998

THERMIE project BM 77/94 “Grindsted Municipality Waste Water Treatment Plant” CPH generation based upon co-digestion of #WSW and sewage sludge.

Kri@er A/S THERMIE Coordinator att. Mogens Hedegaard Aboulwarden 52 DK- 8700 Horwns

Tk otherporticiponts in the THERM/E project ore: CRINDSTEO Munidpality att Tage Christensen DK- 7200 Grindsted S.E.E. SA att. Ceorges Petmawodsky 8- 1050 8~s.sels

WREC 1998 1067

1 .c. Laholm bioas dant - Schweden.

FLOW DIAGRAM - LAHOLM BlOGAS PLANT

6

Process: BigadmP

I. Primary and mixing tank incorporated in the recep- 4. Digester: retention time 19 to 22 days at 3R’C.

tion building. 5. Combined heat and power unit; conversion of biogas

2. Counter-current heat exchangers; the process heat to combined heat and power.

requirement is reduced to max. 10% of the gas yield. 6. Storage tank for digested manure.

3. Pasreurisation unit; heot treatment at 70Tfor min. 1 hour.

TECHNICAL DATA I Capacity:

Reactor volume:

Gas yield:

Combined heat

and power:

Client:

Form of supply:

100 tons of livestock manure/d

20 tons of organic industtial waste/d

2250 m’

3-4BOO m’ of biogas/d

350 kW electricity

500 kW heat

Laholms Biogas AB

- formed by three interested partres

SHK Energi

Lahohn Municipality

Vallberga Lantmitnn

Turnkey, I. Kruger Engineering AS

Bigadan”

STANDARD SOLUTIONS

The Laholm plant is a Bigadaa standard plant for which the

mechanical, SCADA and electrical equipment is delivered

pre-assembled IO the site in 2 or 3 prefabricated container

modules.

As extra equipmenl. a complete combined heat and power mm

can be supplied. also built into a container module.

The standard solution offers the following advantages:

Short construct!on period and less dependency on weather

conditrons

Rapid and unproblematic running-in

Flexible plant design facilitating removal/extension

Lower installation and construction costs

Kriiger

1068 WREC 1998

3. New concert. mechanical cell-wall disintegration related to a German bioaas olant.

Genthin WasteAiVastewater Tresbnent Plant

WREC 1998 1069

3. . .

j n the I1 disitt~n.

she supp~ementaty organic waste is received batch-wise in a 80 cbm tank where it is @sed by means of steam prod& by the CHP unit. Emission gas from the steam treatment ) is used as primary combustion air by the CHP unit meaning that any kind of air poRution is avoided. Aftet steam pasteurization the supplementary organic waste is loaded to the mixing tank (300 cbm ) and mixed in with the cell disintegrated biological sludge prior to regular loads from here to the 3,m cbm digester. The digester itself is also connected to the mechanical cell disintegration facility enabling further cell disintegration of the total substrate. The innovative principle is to maximii the biodegradability by intensive mechanical cell disintegration of all substrate under a minimised specific energy consumption.

The heat recovery system comprises substrateMMate heat-exchangers recovering heat Ram the digested substrate to preheat raw subs&ate, which aheady is preheated as a function of the steam pasteurisntion of the supplementary organic wastes. Final digestion temperature is reached by substrate/water heat-exchanging. An in&grated innovative step by the heat exchanging system is that biological sludge for recycling, within tbe wastewater treatment plant and not bemg sttbjact to cell disintegration, also is passing through the heat-exchangas and preheated. Bspecially in periods of cold weather this is expected to means a higher capacity and mare. offtcient operation of the SBR wastewater treatment plant.

The digester can be operated both in mesophilic and thermophilic temperatme level.

Leaving digester and heat ax&anging the digested material is loaded to a covered and gas-tight after- digestion tank of capacity 300 cbm substrate and 200 cbm bii. I~C~US~UI of an a&-@&ion tank also presents an innovative step where certain amounts ofbiogas is e to be caught compared to the usual system of immediate processing or uncovered gas-tight storage of digested material.

The after-digested sludge is fhtally dewatered in an existing belt-press and the sludge cake is rscycled to farmland by means of an existing container system. The liquid phase is returnhtg to a 3,000 cbm pm- storage tank to the SBR wasmwatm beatmutt plant for recycling to water purification. Much transpottation energy can be saved by being related to a wastewater tmatmsnt plant enabling dewatering prior to final disposal upon farmland.

The produced biogas originating from’both the main digester and f&n the after-digestion tank is loaded to a CHP unit with steam pmduction for fmteurisation out of the gas-engine con&u&n flus gas wf&h slso pmaents an innovative step. Heat from the gas-engine cooling water is exdmqed into a centralised heat transmission system and sold to the detergent factory Henkel for industrial purposes.

The excessive electricity produced is delivered to the public grid.

Key figures are : j!g&t Biological sludge from industrial wastewater . . . . . . . . . . . . . . . . . . Biological sludge from municipal wastewater . . . . . . . . . . . . . . . . .

18tons/daywith8%drymatter

Septic sludge 18tonsAlaywith8%drymatter

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Industrial waste, f& . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . ._. . . . . . . . . . . . . . .

14tosm’daywith8%drymatter

Household waste, kitchen waste . . . . . . . . . . . . . . . . . . . . . . . . . . . ., . .__ 28 tons/day with 5.5 % dry matef 28 ton411y with 9.5 % dry matter

Biogas production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .._.. . ._ ._. . . . . .

Total electricity production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ _ _ . . . . . Ndelectri4Q’pfodu&ondeliveredtopublicgrid . . . . . . . . . . . . TotaJheatprodurtieo . . . . 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N~~tpmductiontransmitted(sotd) . . . . . . ..a.................

5,300 cubicmeter/day (65 YO methane)

I2.090 kWh#ay 9,500 kWWday

I7.500 kwwday (44 gAMuute) 13,090 kWWay (33 ul/mmute)

Digester : 3.000 cbm CHP unit : 500 kwu