Bioconversion of waste, a source of energy

Resources and Conservation, Elsevier Scientific Publishing

BIOCONVERSION

321

7 (1981) 321-325 Company, Amsterdam

OF WASTE,

A SOURCE

- Printed

in The Netherlands

OF ENERGY

W. MOOLENAAR N.V., Department

Grontmij

of Environmental

Engineering,

De Bilt

(The Netherlands)

ABSTRACT Waste energy

is no longer

is feasible

established

in different

RDF (refuse-derived methane

obtained

Processing achieving subject

considered

to be a nuisance;

on an industrial ways.

fuel),

Research

by bioconversion

acceptable

Energy

recovery recovery

has focussed

but also other potential

of cellulosic

of organic

material

bioconversion

show promising

scale.

results,

before

on production fuels,

and

can be

of not only

such as ethanol

and

wastes. digestion

rates. Research

especially

of raw materials from waste

with

is a prerequisite

and development

regard

for

on this

to enzymatic

hydrolysis.

INTRODUCTION Waste

disposal

tipping,

in the Netherlands

the main disposal

method,

areas due to the high population

is becoming increasingly is obstructed

density

difficult.

by a shortage

and high groundwater

Controlled

of suitable levels

dumping

in most of

the country. Incineration, waste

attractive

and the concurrent

environmental

for compost

is not considered.

is limited,

Recently

is based on the concept

cations

of resource

are yet available

reduction

with growing

of the

concern

of treatment

recovery.

The salability

production

on its

capacity

paper.

which

of some of the end-

for the separated

due to contamination

methods

of present

plant has been put into operation

especially

(and often quality-selected)

development

volume

is regarded

so extension

a recycling

is, so far, disappointing,

separated

of its important

recovery,

impact and its high cost.

The market

products

because

energy

paper.

and the availability

No appli-

of source-

In this context there is room for

for municipal

solid waste

(MSW) based on energy

conservation. Rising

prices

unconventional renewable succeed

for fossil

sources.

energy

source.

fuels has stimulated

In this respect However,

if this fuel is adapted

ties. At present,

mainly

0166-3097/81/0000~000/$02.75

gaseous

the search

for energy

MSW can be considered

application

of a

to the established

as an unconventional,

MSW-derived market

Publishing

fuel can only

and distribution

and liquid fuels are consumed.

0 1981 Elsevier Scientific

from

Company

facili-

The consumption

322

of solid fuels derived

fuel

is limited,

feasible

impact of burning

R & D activities

gradable

with

The production

present

distribution

PROCESS

CHARACTERISTICS

and the gas production viable.

amount

Table

activity

production

systems

are envi-

seems more

of either

provided

under anaerobic

1 shows the time necessary

ethanol

or methane

compatibility

with the

in a landfill

into biogas

is to a certain

those

of the biode-

gas can be achieved.

conditions

material

the conversion

especially

treatment

for natural

of biodegradable

conditions

results,

anaerobic

is attractive

from the landfill

Under natural

long time. Table

allows

of biogas

that conversion

conservation

show promising

and subsequent

and application

By studying microbial been learned

reasons

fuel can be derived.

into this subject

the hydrolysis

other

of refuse-

of MSW, and the possible

such fuel. Thus energy

or liquid

part of MSW. This process

(biogas).

in the Netherlands;

rates, due to the composition

if a gaseous

concerned

is the main reason why production

(RDF) is not yet practised

the low production ronmental

which

extent

of the organic

for converting

it has

is possible,

economically matter

50% of the

reqUireS

a

available

(TD.5).

1

T0.5 (years)

readily

degradable

Conversion

Component

rate (%)

1-5

100

food waste,

5-25

90

garden waste,

20-100

50

wood

paw moderately

degradable

cardboard hardly

degradable

-

It is evident

that the economic

by the time and by the production is estimated complete

to be 100 m3/ton

conversion

Because

anaerobic

the limiting matter.

takes decades

rate. At the moment,

lignocellulose

content

process

1, conversion

increases.

it is assumed

microbes

Although

to consist

is limited

convert

both

the total gas production

Under natural

due to the unfavourable

and facultative

in Table

of gas production

of MSW in 10 years.

step in the conversion

As is shown

understood,

viability

conditions

process

only soluble

is the solubilization

the

conditions. compounds, of solid organic

takes more time as the cellulose the conversion

of three phases.

process

and

is not fully

In the first phase the

323 microbes

excrete

molecular convert

enzymes

sugars

the solubilized

theorganicacids dioxide.

is the conversion

compounds

industrial-scale

of solids

In Pompano

Beach

acid. Finally

to methane

and carbon

is the hydrolysis

low-molecular

of this process

compounds.

according

stage,

that

The anaerobic

to the results

for waste water

a 100 tonne/day

the mechanically

portion

purification

of the

(10 kg

optimum

pilot plant has been constructed,

separated

organic

of the MSW is shredded,

into a digester.

The anticipated

process

into low-

the bacteria

such as acetic

group of bacteria

takes 24 to 48 hours,

(Florida)

the organic

acids,

phase

load).

is able to handle

fed directly

compounds

In the second

to organic

by another

into soluble

application

volumetric

monomers.

step of the whole

of the hydrolysate

COD/mj.day

process

soluble

are degraded

The rate-limiting

digestion

which

able to break down high-molecular

and other

The total conversion

conditions

part of MSW. In this

concentrated, takes place

for the digester

process

and as a slurry

in the same reactor

are 5 days retention

at 57°C. Apart

from mechanical

temperatures appointing

matter

process

conditions

reached.

are not optimal

The most plausible

and pressure solubilized

times of 15-20 days, turned

of refuse.

step,

at mesophilic out dis-

As the solubilization

it may be concluded

of

that either

, or the necessary enzyme concentration

conclusion

or hydrolysis

processes.

Chemical

after addition

is that both processes

of organic hydrolysis

tages of chemical

matter

the is not

have to be opti-

Sitton

hydrolysis.

part of MSW by alkaline

hydrolysis

can be executed

is executed

of acids or alkalies.

46% of corn stover by acidic

lized 56% of the organic

at elevated

temperature

et al (1) for instance,

Yc.Carty

hydrolysis.

are the high energy

by chemical

et al (2) solubiThe main disadvan-

input and the waste

water

dis-

problems.

R & D activities sis is possible. difficult

in the last few years

The lignocellulose

to hydrolyse

(3) investigated

particle

enzymatic

the conditions yields,

Bullock

, especially

hydrolysis.

from the optimum that enzyme

of enzymes

As expected

conditions

activity

waste

was not inhibited

was observed

during

between

types of cellulose-containing

paper could be converted

the optimum

process

70% into

conditions

for

turned out to be different

digestion.

by heavy-metal anaerobic

hydroly-

is the most

conditions.

the relationship

these conditions

for anaerobic

material

on its process

for different

et al (4) investigated

that enzymatic

of the organic

has focussed

It turned out that pot-milled

saccharides.

have indicated

component

and research

size and conversion

materials.

dation

the gas production

separately.

or biological

Spano

100 m3/tonne

is the rate-limiting

The solubilization

charge

(mixing),

(about 37°C) and at retention -- approximately

organic

mized

problems

Furthermore

they established

ions. Finally,

digestion.

no degra-

324 As the energy for chemical separate

requirement

hydrolysis,

enzymatic outlook.

reduction

and composition

PROSPECTS

FOR ENERGY

Table

are expected,

digestion

are adequate

process

particle

of MSW-derived

biogas,

has to be produced

inert materials,

either

only biodegradable

components

from this mixture

by mechanical

sorting

of biodegradable or by source

of MSW in 1979 (% by weight)

Institute

for Waste

Disposal,

Amersfoort,

the Netherlands

(5)

%

Component

*paper,

cardboard

glass

21.3

% moisture

35

13.8

metals

3.0

plastics

6.0

5

*wood

0.5

15

fabrics

2.1

17

0.7

10

leather,

rubber

ceramics

1.6

*food waste

30

*garden

15

waste

balance

*

size

of MSW in the Netherlands'is

2

SOURCE:

a

has a

complex.

In Table 2 the composition

The feedstock

Composition

lower than

PRODUCTION

For the production

biologically

problems

anaerobic

to be solved

of an enzyme

is considerably

discharge

and subsequent

The main problems

serve as feedstock.

hydrolysis

and no waste water

hydrolysis

promising

ported.

for enzymatic

Biodegradable.

** Overall moisture content 37%.

6.0

65 55 20

**

can reand

separation

325 The elemental

composition

can serve as a basis carbon

content

(approximately raw MSW

of the volatile

of dry organic

that fats, proteins

90%, and cellulose that processing

The contribution is very small;

can be coverted

of this process nevertheless

in Table

Assuming

into a gaseous

3,

that the

product

can be 230 m3/tonne

of

matter). can be enzymatically

can be 150 m3/tonne

tonnes of MSW may yield

gas equivalent,

as shown

output.

output

and carbohydrates

60%, the output

of 100,000

10 Mm3 of natural

Table

matter

components,

of the maximum

55% CH4, 45% CO*), the calculated

(470 m3/tonne

Assuming

of the biodegradable

for the calculation

which

represents

to the annual

local energy

15 Mm3 of biogas a heating

energy

converted

of raw MSW. This implies annually,

or

value of 300 TJ.

supply of the Netherlands

needs can be well

served.

3

Elemental

composition

of biodegradable

components

of MSW

(6)

Components

% dry

% vola-

weight

tile mat-

of MSW

ter

%C

%H

%O

%S

%N

-

paper,

cardboard

21.6

85

food waste

16.5

75

50

garden waste

10.7

75

41

0.6

85

50

6

wood -

43

6

44

0.2

0.05

7

26

0.22

2.5

6

41

0.15

1.6

42

0.1

0.15

REFERENCES 1 Sitton, O.C. et al., 1980. Ethanol from agricultural residues. In: D.L. Klass (Editor), Symposium Energy from Biomass and Wastes IV, Institute of Gas Technology (Chicago), pp. 685-700. 2 Mc.Carty P.L., et al. 1977. Heat treatment for increasing methane yields from organic materials. In: Schlegel, Barnea (Editors), Microbial Energy Conversion, Pergamon Press, pp. 179. 3 Spano, L.A., 1977. Enzymatic hydrolysis of cellulosic materials. In: Schlegel, Barnea (Editors) Microbial Energy Conversion, Pergamon Press 1977. 4 Bullock, L.D. et al., 1980. Enzymatic enchancement of solid waste bioconversion. In: D.L. Klass (Editor) Symposium Energy from Biomass and Wastes IV, Institute of Gas Technology (Chicago), pp. 319-332. 5 SVA/3550, Beperking en hergebruik van afval van particuliere huishoudingen (Limitation and reuse of municipal/waste). Institute for Waste Disposal, Amersfoort, the Netherlands. 6 Stegmann, R., 1978. Gase aus geordneten Deponien. In: Konferenz Sickerwasser und Gase am geordneten Deponien, Krattigen (Switzerland).