windrow composting of source separated kitchen biowastes in finland

Windrow composting of source separated kitchenbiowastes in Finland

All households in the City of JyvaÈskylaÈ have been required to

source-separate their wastes since June 1996. The

accumulation of kitchen biowaste was about 60 kg per

resident in 1997, with an ef®ciency of more than 75%. The

residents of almost 50% of the detached houses in the city

opted for small-scale composting. Ensuing kitchen biowaste

was surprisingly pure: the estimated content of non-

compostable material was less than 0.1% by weight. The

biowastes were composted at the Mustankorkea waste station

in open windrows. Adequate aeration of the windrows was

guaranteed when the initial height of the windrow was less

than 1.5 m and the blending ratio for biowaste and bulking

agent was one tonne of biowaste to one cubic metre of wood

chips. The temperature rose to 858C in these windrows.

Carbon concentration increased slightly during 64 weeks

composting, whilst the hydrogen concentration decreased.

The pH and the ash content also increased during

composting. As measured by pathogenic microbes

(Salmonella), the biowaste composts were hygienic. In

summer, the concentration of airborne microbes was high

during turning of the windrows, both in the composting ®eld

and in the cabin of the wheel loader. The concentration of

endotoxin in the cabin exceeded all recommended limits.

N. KoivulaK. HaÈnninenO. TolvanenUniversity of JyvaÈskylaÈ, Department of Biological and

Environmental Sciences, JyvaÈskylaÈ, Finland

Keywords ± Composting; humic chemical analysis; kitchen

biowaste; maturation; occupational hygiene; odour;

temperature

Corresponding authors: N. Koivula and K. HaÈnninen,

University of JyvaÈskylaÈ, Department of Biological and

Environmental Sciences. PO Box 35, Fin-40351 JyvaÈskylaÈ,

Finland

Received 8 March 1999, accepted in revised form 28 October

1999

Introduction

The objective of the Finnish Waste Act of 1993 (Waste Act

1072/93) is to support sustainable development by encoura-

ging the rational use of natural recourses and to protect

health and the environment from the risks associated with

wastes. Refuse disposal should be designed, organized and

®nanced in a manner that encourages speci®c waste

management plants for different kinds of waste. In

accordance with the act, the residents of major Finnish

municipalities have begun to separate their household wastes

at source. Municipalities are responsible for arranging both

collection and treatment, and they have control over the

waste ordinance, which regulates waste sorting. In many

parts of Finland, municipalities have joined together to

empower a comprehensive waste management or treatment

company to carry out the practical measures required by law

(HaÈnninen & Suoja 1998).

In Finland kitchen biowaste is de®ned as easily degraded

wastes of plant or animal origin. Although generated mainly

in households, they are also generated in the retail and

wholesale trade and in the food industry. The de®nition of

kitchen biowaste does not include similar wastes formed in

agriculture or forestry (Anonymous 1998a).

Waste Manage Res 2000: 18: 160±173

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Copyright # ISWA 2000

Waste Management & ResearchISSN 0734±242X

160

Composting is the decomposition of organic matter by a

mixed population of exothermic microorganisms in a warm,

moist, aerobic environment. During composting, most of the

oxygen demand of the wastes is met, the organic materials

are converted to more stable products such as humic acids

and carbon dioxide, and water and heat evolve (Biddlestone

& Gray 1985).

The composting waste material generates both inorganic

and organic volatile compounds, some of which may be

malodorous. Odours emitted from composting plants are

usually on account of volatile organic compounds of low

molecular weight, such as methyl mercaptans, methyl

sulphides and amines, which are released during the ®rst

stage of composting when the aeration is not suf®cient. The

odour threshold is particularly low for sulphur compounds,

and odours are the most sensitive issue when composting

plants are located close to residential areas. The potential for

odour was one of the ®rst concerns raised by residents in

JyvaÈskylaÈ, although no direct harmful effects to human

health have been demonstrated. In general, odours have

been rated as the primary concern of the public in regard to

the implementation of composting facilities (Bidlingmaier

1996).

Other environmental impacts of the windrow composting

of kitchen biowaste are the proliferation of pathogenic

bacteria, such as Salmonella, and indicator bacteria, such as

faecal streptococcus and faecal coliform bacteria, which the

waste mass initially may contain. These bacteria may have

direct harmful effects on human health if the material is

touched, and personal hygiene is inadequate. Destruction of

pathogens during composting is mainly affected by tem-

perature/time pro®les, microbial competition, depletion of

nutrients and antibiotic factors (Pereira Neto et al. 1987).

The temperature/time pro®le is the most important factor in

the control of the hygienization process during composting.

The main groups of microorganisms involved in the

composting are bacteria, fungi and actinomycetes. When the

compost is turned, these microorganisms may escape into the

air, and hover there for long periods of time. At present

Finland has no regulations regarding maximum emissions of

microorganisms in the work environment. Relative to the

surrounding areas, high concentrations of microorganisms

have been found only in the composting area. The staff of

such compost plants need to be protected from such

emissions (Fischer 1996).

As described in De Bertoldi et al. (1983), the main bene®t

of organic fertilizers like compost is to contribute to the

complexity of the humus balance and to soil structure.

Organic fertilizers improve the structure by enhancing

clumping and thereby improving the texture and the

permeability to air and water. The organic fractions of the

composted matter must be suf®ciently humidi®ed and have

achieved biological stability before the fertilizer is applied to

crops.

This paper comprises a documented case history of

kitchen biowaste windrow composting at the Mustankorkea

land®ll in the City of JyvaÈskylaÈ. The project extended from

June 1996, when composting of source separated kitchen

biowaste began, to December 1998. The following compost-

ing variables were measured: temperature and oxygen

concentrations inside the windrow, moisture content, ash

content, pH, conductivity, and concentrations of humic

matter, nutrients and the elements carbon, nitrogen,

hydrogen and oxygen. From the onset, the primary goal in

the management of the composting process was to avoid

odours, since the closest residential area to Mustankorkea is

just 1 km away. This was successfully realized by improving

the composting parameters (height of windrow, bulking

agent and mixture ratio, turning frequency and ®eld area)

during the project.

Materials and methods

Collection and transportation of source separatedhousehold wastesEach household in JyvaÈskylaÈ is required by the waste

ordinance to source separate wastes into eight fractions: (i)

kitchen biowaste; (ii) dry waste; (iii) paper and board; (iv)

glass; (v) metal; (vi) textiles; (vii) hazardous wastes; and

(viii) used liquid packaging board containers (milk and

juice). The kitchen biowastes are composted and the dry

wastes will be prepared as fuel for a waste handling plant

soon to be constructed (HaÈnninen et al. 1997).

A private company (WM-Environmental Services) is

responsible for the transport of all wastes in JyvaÈskylaÈ

throughout 1999. By the terms of the contract, this

responsibility includes receiving recyclable wastes and the

intermediate handling and shipment for processing. Col-

lected recyclable wastes are treated and stored by the

contractor separate from each other. Wastes are packed

according to instruction before being delivered to processing

plants where they will be utilized as either material or

energy. Kitchen biowaste and dry waste are directed to the

waste station at Mustankorkea, whilst hazardous wastes go to

the hazardous waste treatment plant Ekokem Ltd at

RiihimaÈki, and glass to a glass sorting plant at Jokioinen.

Windrow composting of source separated kitchen biowastes

Waste Management & Research 161

In JyvaÈskylaÈ paper is separated from board by contractor.

Paper is transported to the Kaipola pulp and paper mill in

JaÈmsaÈ and board is delivered for processing to Corenso board

mill in Pori.

Source separation and composting of kitchen biowastes

began in JyvaÈskylaÈ in June 1996. Most of the kitchen

biowaste was collected into 120 or 240 l bins located at each

block of ¯ats. The bins were ®tted on the inside with a paper

sack. In some residential areas the biowastes were collected

into 1300 l Molok deep collection containers. Residents in

detached housing had the option of carrying out small-scale

composting of biowastes on-site (Hietanen & HaÈnninen

1996). The kitchen biowastes were transported to Mustan-

korkea waste station where they were composted in

windrows in the open air.

Composting on the ®eldThe initial composting area was a 3000-m2 asphalt ®eld, and

in November 1996 a further 7000 m2 of asphalt ®eld became

available. Curing was carried out in four separate ®elds with a

total area of 7000 m2.

The windrow composting was carried out in three different

ways according to the use of bulking agent and turning

frequency. For windrows piled up in summer 1996, the bulking

agent was a mixture of wood chips and composting peat. The

ratio of biowaste to bulking agent was 1 : 1 (w/v) and the

windrows were turned once a month. In windrows piled up in

autumn 1996; the ratio of biowaste to bulking agent (bark) was

1 : 2 (w/v) and theheight of thewindrows wasabout 2 m. Now

the windrows were turned three times: at the initial blending,

after 1 week of composting and after 3 to 10 weeks, depending

on how crowded the compost ®eld was. Beginning in June 1997

the bulking agent was waste-wood chips from building sites,

the ratio of biowaste to bulking agent was (1 : 1) (w/v) and the

height of the windrow was reduced to about 1 to 1.5 m. The

windrows were turned once a week during the ®rst month, after

which two windrows were combined into one larger pile.

All windrows are designated according to when they were

piled up (month, ®rst or second windrow of the month,

year, e.g. March II (97)) Curing piles are designated with

successive numbering (e.g. curing pile 2).

The staff at the Mustankorkea sanitary land®ll were highly

motivated to perform their work well. Careful planning was

carried out to rationalize the different work periods. In the

®rst year of the project the kitchen biowaste was not crushed

before building up the windrow. For turning of the compost

piles a special truck fork with ®ve 200-cm long rods was

constructed by the staff. After the summer of 1997 a

screener-crusher bucket from Idealchips Ltd was added for

turning of the piles as well as crushing of the incoming

biowaste.

Chemical and physical determinations of the kitchenbiowaste compostFrom 16 July 1996, temperatures were measured twice a week

at three points of the windrow. At each of these points

temperatures were measured on the upper part (surface) and

at the lower part (core) of the windrow. Oxygen measure-

ments began in September 1997, at the same points as the

temperature measurements.

Samples for chemical and microbiological determinations

were taken monthly or bimonthly. For sampling purposes,

the windrow was opened at four points with the bucket of a

wheel loader and a sample of 30 l was removed. The compost

material was mixed well and a subsample of 2 l was removed

for laboratory analysis.

The maturity of the compost was determined by measuring

the moisture content, pH, conductivity, density, nutrients,

and ash content. Replicate samples were measured. Moisture

content was determined by oven-drying a 175-g sample at

1058C for 24 h. In pH and conductivity measurements, a

40-g sample was diluted in 100 ml water, mixed, and left to

stand at room temperature for 24 h. The solution was then

stirred and pH and conductivity were measured (Anonymous

1993). Approximate density was measured by weighing

800 ml of compost sample.

For the determination of ash content and volatile

substances, the compost samples were dried at 358C for

2 weeks and then air-dry samples were ground through a

0.5-mm sieve. Ash content was determined by burning the

sample (1 g) in an oven at 5508C for 2 h (Greenberg et al.

1985). Volatile substances were determined by burning the

air-dry samples (1 g) in an oven at 9008C for 7 min (DIN

51720).

Heavy metal analyses (Cd, Cr, Cu, Hg, Pb and Zn) were

carried out for a 10-month-old curing pile in a commercial

laboratory. Humic chemical analysis of four compost samples

of different ages (1, 23, 36 and 77 weeks) and one bark

sample was made according to HaÈnninen et al. (1995).

Nitrogen, carbon, hydrogen and oxygen were determined for

ground samples with a Fison Instruments EA 1110 analyser

(Le Instruments, Milan, Italy). Since there was no possibility

to take samples of different ages from the same windrow,

conclusions about how the concentrations changed with the

age of the compost were based on samples from different

windrows. The heat of combustion (GHV, gross heat value)

N. Koivula, K. HaÈnninen, O. Tolvanen

162 Waste Management & Research

of the compost was calculated with equation 1 (Kirsten et al.

1988):

GHV 5 a 3 C% + b 3 (H% ± d 3 O%) + e 3 S% [1]

where a 5 82; b 5 344; d 5 0.125; e 5 25

Soil amendments are manufactured from the mature

compost by blending mineral soil to compost in different

ratios depending on the intended use of the amendment.

Nutrient analysis was carried out on mature compost, 10-

month-old compost, and a soil blend. The ratio of mature

compost (15-month-old) to mineral soil in the soil blend was

2 : 1. Water-soluble nutrient analysis was carried out on

seven compost samples of different age and on one soil blend

that was made in winter 1998 by blending mineral soil and

peat with mature compost. The nutrient concentrations

were determined in a commercial laboratory.

Hygienization, air-borne microbes, dust and endotoxinsThe hygienization of the compost process was followed by

measuring pathogenic microbes (Salmonella) and indicator

microbes of pathogenicity (faecal chain coccus and thermo-

philic faecal coliform bacteria) at regular intervals in the

City of JyvaÈskylaÈ Environmental Laboratory.

Occupational hygiene measurements were made at

AÈ mmaÈssuo in the summer of 1998 to determine the

concentrations of air-borne microbes (fungi, bacteria and

actinomycetes), dust and endotoxin. Measurements were

made in the composting ®eld, when the windrows were not

being handled, and in the composting ®eld and the cabin of a

wheel loader during turning of the windrows. All samples

were taken from the breathing zone of workers.

The concentration of air-borne microbes was measured in

samples taken by CAMNEA method (Palmgren et al. 1986).

Sterilized polycarbonate ®lters (pore size 0.2 mm, diameter

37 mm), sterilized ®lter cases and a pump operating at a ¯ow

rate of 4 l min± 1 were used in the collection. The

measurement time was 30 min. For determination of

viable microbes, the samples were cultivated on four

different substrates. Table 1 details the substrates and

incubation conditions. After incubation, colonies were

calculated and fungi were identi®ed. For determination of

both viable and non-viable microbes the samples were

®ltered and the ®lters were coloured with 0.01% acridine

orange. Microbes on the ®lters were counted with the help of

a ¯uorescence microscope with enlargement 1000. At least

400 microbes were counted.

The concentrations of dust and endotoxins were measured

according to Finnish Standard No. 3860 (1988). The dust

samples were collected onto Millipore cellulose-acetate

®lters (pore sizes 0.8 mm, diameter 37 mm) and the

endotoxins onto a ®breglass ®lter with the aid of pumps.

The ¯ow rate for dust samples was 5 l min± 1 and the

measurement time 1 h. For endotoxins, the ¯ow rate was

2 l min± 1 and the measurement time 2 h. The dust samples

were analysed by weighing the ®lters before and after

sampling. The concentration of endotoxins was determined

by the kinetic Bio Whittaker-QCL method, which relies on

use of the Limulus amebosyte lysate enzyme.

The number of particles in the air during turning was

measured with an automatic particle sampler, the APS-1000

collector, which divides the particles into four classes:

i 0.3, 0.5, 1.0 and 5.0 mm. The measurement time was

2 min and 48 measurements were carried out in the ®eld.

Background measurements (23 3 5 min and 5 3 5 min)

were made in an of®ce at the University of JyvaÈskylaÈ during

the summer of 1998.

Results and discussion

Accumulation of kitchen biowasteIn the time period studied all 75 500 residents of JyvaÈskylaÈ

participated in the source separation of kitchen biowaste.

Table 1. Substrates, incubation temperatures and incubation times for determination of viable microbes

Fungi Bacteria and actinomycetes Actinomycetes

Substratum 1) Malt extract agar

(DIFCO 0112-17-6) 52.7 g l±1

+streptomycin sulphate 40 mg

Plate count agar (PCA)

(DIFCO 0479-17) 23.5 g/l+0.5 g

sycloheximide

K-strong nutrient agar: nutrient

agar (DIFCO 0001-17-0) 14 g l±1

+bacto-agar (DIFCO 0140-01) 10 g l±1

+sycloheximide 25 mg+novobiosin 25 mg

2) DRCB Agar (DIFCO 0587-17-0)

31.6 g l±1

Incubation

temperature

Mesophilic +258C Mesophilic +258C Mesophilic +258C

Thermophilic +408C Thermophilic +408C Thrmophilic +408C

Incubation

time

Mesophilic 7 days Bacteria 5 days, 11 days

Thermophilic 3±4 days Actinomycetes 14 days



Of these, about 11 500 residents living in 3000 terraced or

detached houses (50% of all detached houses) had elected

to compost their kitchen biowaste in small composters and

pay a reduced waste management fee. The rest were

participating in the centralized collection of biowaste. The

total accumulation of kitchen biowaste in 1997 was about

4600 t (60 kg per resident). The amount of bulking agents

(coniferous bark, peat and waste-wood from building sites)

added was 2700 t. The kitchen biowaste was surprisingly

pure, with the estimated content of non-compostable

material less than 0.1% by weight. The average

accumulation ef®ciency for the kitchen biowaste was

more than 75%.

The normal ef®ciency of the collection of kitchen

biowastes in other Finnish cities is currently about 50%.

Waste ordinances in these other cities only require source

separation of kitchen biowaste for blocks of eight to 10 ¯ats

or more. The potential accumulation of source separated

kitchen biowaste in Finland can be estimated at 0.25 million

tonnes with 50 to 55% ef®ciency (HaÈnninen 1996). In

Germany the present ef®ciency of kitchen biowaste

accumulation is also about 50%. The accumulation in

Germany in 1995 was 2.0 million tonnes, but this is

expected to rise to 4.0 million tonnes by the year 2000, to

5.7 million tonnes by 2005 and to 6.7 million tonnes by 2010

(Anonymous 1998b).

There are several ways in which the sorting ef®ciency of

kitchen and other biowastes in JyvaÈskylaÈ could be increased

further. Garden and green wastes could be accepted free at

the gate of the Mustankorkea waste station on speci®ed days.

Small-scale composting on site could be encouraged,

especially for terraced houses and single-family dwellings.

General features of the compostingThe paved area at Mustankorkea on which composting was

begun turned out to be too small. With the unexpectedly

high accumulation of kitchen biowaste, the windrows

became bigger and more compact. During summer and

autumn of 1996 there was some odour in the ®eld, especially

during turning, and some complaints were made by city

of®cials and the maintenance staff of Mustankorkea, though

not by residents. Large and compact windrows emitted odour

during turning and the temperature of the piles was below

508C, indicating anaerobic conditions inside the windrow.

To correct the situation the volume of bulking agent was

increased. This improved the aeration of the windrows, the

temperature rose and the odour decreased. The composting

process was active and there were no odour problems on the

®eld in winter or spring of 1997.

The biowaste composted in the summer of 1996 was still

malodorous in the autumn of 1997. Evidently persistent

odours cling to the compost mass so strongly that they are

apparent even after 18 months of composting and curing.

Additional curing was considered necessary and the com-

post, which was to be used for green area construction, was

mixed with sand.

Clinging of odours to the maturing mass was not observed

with adequate use of bulking agent. The costs as a result of

the bulking agent were considered too high, however, and

the ratio of bulking agent to biowaste was reduced to 1 : 1

and bark was replaced by waste-wood chips. Fortunately,

crushing and blending of incoming biowaste and bulking

agent on the ®eld with a screener-crusher bucket began at

the same time. The height of the windrows was also limited

to between 1 and 1.5 m. After 1 month of composting, two

Table 2. Surface temperatures and oxygen concentrations of representative windrows at Mustankorkea 20 April to 7 September 1998

Identi®cation number Construction date Age (days) Middle measuring point of the windrow

Temperature (8C) Oxygen (%)

26 7 April 13 82 5

28 42 19

42 37 19

34 20 May 13 71 18

26 70 15

39 55 15

35 25 May 8 80 10

21 61 15

34 51 11

47 4 August 3 41 14

13 69 15

34 28 20



low piles were combined into one larger one, and after an

additional 3 months of composting, another doubling of the

windrows was carried out. Thereafter the composts were

removed to large windrows on the curing ®eld.

When the composting was carried out with suf®ciently

low windrows (initial height of 1.0 to 1.5 m), the clinging of

odours to the maturing mass was not observed in spite of

reduced amount of bulking agent. Most of the time the odour

level at the composting ®eld was satisfactory and nearby

residents experienced no odour problems. The windrow

composting at Mustankorkea was ®nally functioning

smoothly; the odour nuisance was restricted to turnings in

a limited area of the land®ll. For political reasons, since

autumn 1998 the ®rst stage of composting has been carried

out in an in-door static bed composting plant.

Temperature of the windrowsOn average, composting temperatures of 55 to 658C are

reached within 2 weeks. In winter the kitchen biowaste and

bulking agent were frozen upon arrival at the composting

®eld and the delay before composting could begin was 3 to

5 weeks. After this, the increase in the average composting

temperature was dramatic. For 3 to 6 months the tempera-

tures in the curing piles were high, about 60 to 708C, before

decreasing to 40 to 508C.

During the summer of 1997 very dry and warm weather

prevailed for 6 to 8 weeks and weekly turning of the small

piles during this period resulted in drying. In some of the

windrows the moisture content dropped below 30% and the

composting process stopped. The piles were watered in an

attempt to restart the composting, but the effort failed. In

contrast, the spring and summer of 1998 were rainy and

relatively cold. The temperature of composts in low

windrows spontaneously climbed above 858C within a few

days of start-up, but temperatures also decreased to below

508C within 30 to 40 days (see Table 2 and Fig. 1). The

oxygen readings were relatively high at the same time,

indicating suf®cient aeration. No open ®re evolved despite

the high temperatures. Composting seems to proceed fast at

such temperatures. Workers at Mustankorkea have com-

mented that the biowaste just seemed to disappear, with only

the bulking agent remaining visible.

Our results lead us to important conclusions about the

limits of microbial activity. It is almost universally believed

that the optimum temperature of composting is 558C or less.

This result has been arrived at respirometrically by

measuring the amount of atmospheric oxygen consumed

by the microbes. When the temperature rises to about 558C

the amount of oxygen taken from the air decreases, and this

has been taken as evidence that the rate of composting is

decreasing. For higher organisms with a cell nucleus the

explanation is acceptable. However, reports in the literature

(Jennings & Lysek 1996), as well as our own observations,

indicate that the temperature in compost may spontaneously

rise to over 808C. For microorganisms at a less advanced

stage of evolution, another explanation may be relevant.

Above 558C microbes may retrieve the oxygen they require

directly from the chemically bound atomic oxygen of the

waste and bulking agent, so that, as the temperature

increases, the total consumption of oxygen increases

whilst the consumption of atmospheric oxygen decreases.

Moisture, pH, conductivity and ash contentDuring the summer and autumn of 1996 the moisture

content of the relatively high windrows exceeded 70%. The

average moisture content between mid-September 1996 and

mid-December 1997 was 63.8% with a range from 27.3 to

76.8%. The large windrows became compacted, causing

anaerobic zones inside the windrows and some odour

problems. Proper moisture conditions were achieved in

compost piles when adequate amounts of bulking agent were

used and the windrow height was low enough. The ambient

weather conditions did not affect the composting as much as

Fig. 1 (a, b). (a) Surface temperatures and (b) oxygen concentrations inrepresentative windrows. Windrow No. 26 was constructed on 20 April 1998,No. 34 on 30 April 1998, No. 35 on 25 May 1998 and No. 47 on 4September 1998.



the windrow height and the ratio between bulking agent and

biowaste. The approximate density of the windrows ranged

from 200 to 570 kg m± 3 and the average density was

440 kg m± 3.

The pH of windrows rose during composting, but much

more slowly in the large windrows that were made in the

autumn of 1996 than in the small ones made in the summer of

1997 (Fig. 2). It took 3 to 4 months for the pH in large

windrows to increase from 4 to 6, whilst in small windrows it

took 1K months for an increase from 4 to 7. The pH values

were higher in the small than the large windrows (Table 3).

Also, the average conductivity was higher in the smaller

windrows, but no clear correlation was detected between

conductivity and the age of the windrow. High conductivity

(over 0.6 mScm±1) in compost fertilizer is undesirable

because it reduces the supply of water and nutrients to

plants and diminishes the rooting of plants. The conductance

could be decreased by blending the compost with mineral soil.

The average ash content of the compost samples was

23.1% with a range from 8.3 to 53.6%. On account of the

inhomogeneity of the compost material, there was consider-

able variation in the ash content, even in samples taken from

the same compost pile (Fig. 3a). Mineralization by compost-

ing is a relatively slow process. Doubling of the ash contents

took about 6 to 9 months (Fig. 3b). The concentration of

volatile substances did not vary as much as the ash content.

The average concentration of volatile substances was 57.3%

and the range from 32.5 to 68.0%. The concentration of

volatile substances decreased as the compost aged, which

makes it a suitable measure of the maturation of compost.

Fig. 2 (a±d). The pH and conductivity of representative windrows: (a) and (b) are large windrows and (c) and (d) small windrows. The date of construction isshown. The solid line represents pH and the dotted line conductivity (mS cm± 1).

Table 3. Average values of pH and conductivity (mS cm± 1) in large and small windrows

pH Conductivity

Large windrow Small windrow Large windrow Small windrow9 Sept. 1996 to 25 June 1997 to 9 Sept. 1996 to 25 June 1997 to

Time 22 July 1997 16 Dec. 1997 22 July 1997 16 Dec. 1997

Average 5.1 6.1 2.6 4.4

Min 3.5 4.2 0.6 2.6

Max 6.9 8.3 7 7



Humic chemical analysisHumic chemical analysis showed the amount of hot water

extract (HWE) to remain the same and bitumen to decrease

during composting. The material extracted with hot water

came mainly from the kitchen biowastes because HWE of the

bark was only 5.4 mg g± 1 organic matter. The amount of HA

increased only slowly during composting: it was almost the

same in bark and in 1-week and 23-week-old composts and was

noticeably increased only in the two oldest samples (Table 4).

Heavy metals, elemental C, H, N, O and heat valueCommercial soil amendments in Finland (such as kitchen

biowaste compost) are not allowed to contain more than

speci®ed concentrations of arsenic (As) and heavy metals

(Hg, Cd, As, Ni, Pb, Cu and Zn). The relative amounts of

heavy metals increase during composting because of the

mineralization of organic matter. Absolute concentrations of

heavy metals (Table 5) were considerably below the

concentration limits and with respect to heavy metals the

compost is suitable for soil amendments.

The optimal carbon to nitrogen ratio of the initial

compost mixture is 25 (de Bertoldi et al. 1983). The C/N

ratio of our 1-week-old compost was 38. In the oldest sample

of 77 weeks it decreased to 20, which indicates that the

compost was mature. Nitrogen represents 3% of the organic

matter in kitchen biowaste and from 0.2 to 0.5% of the

organic matter of bulking agent (Table 6). The results of

elemental C,H,N analysis of the compost samples were

plotted against the age of the samples from 1 week to

64 weeks (Fig. 4). The results of the analyses varied widely.

Nitrogen concentration and N/C ratio calculated on organic

matter basis remained more or less constant during the

64 weeks: the average nitrogen concentration was 2.5% and

the average C/N ratio 22.4. The carbon concentration

increased slightly from 52.1 to 54.5%, whilst the hydrogen

concentration decreased from 6.8 to 5.7%. During the same

time the gross heat value decreased slightly.

The results of the elemental analysis of humic chemical

fractions of one bark and three compost samples are set out

in Table 7. In the original samples the carbon and nitrogen

concentrations of the organic matter varied from 53.0 to

55.5% and 0.5 to 2.7%, respectively. The nitrogen content

of the bulking agent (bark) was low: in all fractions the

highest C/N ratio was for the bark extract. The nitrogen

concentrations were highest in the HWE and HA fractions.

The carbon concentrations of organic matter were highest in

the original samples and only a little lower in humic acids.

The carbon-to-hydrogen ratio was lowest in the HWE

fraction and highest in humic and fulvic acids.

Nutrients and the use of compostEvidently the water-soluble calcium and magnesium con-

centrations decreased during composting (Table 8). The

concentration of NO3-nitrogen was low in all samples, whilst

Fig. 3 (a, b). Concentrations of ash content (solid line) and volatile substances (dotted line) in two curing piles.

Table 4. The results of humic chemical analysis of bark and compost samples of different age ± hot water extract (HWE), bitumen, humic acid (HA) and humin.(mg g± 1 of organic matter (OM) and mg g± 1 of dry matter (DM))

Age Sample HWE Bitumen HA Humin(weeks) description mg g±1 OM mg g±1 OM mg g±1 OM mg g±1 DM

0 Bark 5.4 36.8 86.6 690

1 March II (97) 36.4 61.1 95.7 604

23 Curing pile 3 38.1 43.2 106.1 772

37 Curing pile 1 35.2 24.8 182.6 684

77 Curing pile 1 and 2 52.1 49.0 206.7 860



NH4-nitrogen varied from , 10 to 1510 mg g± 1 of dry

matter. Low nitrate levels in conjunction with high

ammonium concentrations in compost indicate instability

and potentially high microbial activity (Leege & Thompson

1997).

According to the decision of the Finnish Ministry of

Agriculture and Forestry (45/1994), organic fertilizer should

contain at least 4% (N + P + K) or 3% (N + P) (N + K) or

(P + K), whilst composted animal manure should contain at

least 2% (N + P + K). Biowaste composted for 10 months

contained in total 3.1% of N, P and soluble K, which is more,

than is required in composted animal manure. The soil

amendment, a mixture of mature compost and mineral soil,

contained only 0.5% of N, P and soluble K (Table 9) and did

not meet the requirement for organic fertilizer, but the ®nal

compost product is sold as soil amendment, not fertilizer.

Finland has not yet set exact regulations for the nutrient

content of soil amendment.

The mature biowaste compost can be used as a soil

amendment in green area constructions. Some of the

Table 5. Concentrations of heavy metal in a 10-month-old curing pile, and the legal heavy metal limits for commercial soil amendments in Finland, mg kg± 1

Hg Cd As Ni Pb Cu Zn

Curing pile (10 months) 0.03 0.17 Ð Ð 20 3.0 13.1

Legal limit 2.0 3.0 50 100 150 600 1500

Table 6. Elemental C, H, N, O analysis (% of organic matter) and gross heat value (kcal kg± 1) of compost raw materials

Fixed solids % N C H O C/N C/H GHV

Kitchen biowaste 7.90 3.05 52.10 7.88 38.38 17.05 6.61 4911

Bark 14.31 0.47 52.96 6.12 40.10 113.45 8.66

Waste-wood chips 9.60 0.15 53.94 6.89 45.96 361.54 7.82 4356

Fig. 4 (a±d). Percentage of organic matter and estimated gross heat value during 1 to 64 weeks composting. (a) Nitrogen (b) carbon (c) hydrogen and (d)estimated gross heat value. The solid line is the analysed value and the dotted line the linear ®t to the data.



material composted at Mustankorkea was used as surface

cover on the land®ll. At present, mineral soil and peat are

mixed with the mature compost with the mixing ratio

depending on the ®nal use of the product. The studied soil

blend was homogeneous and there were few impurities. The

compost mixture is marketed under the name `Biosoil'

(VAPO Ltd., Finland, JyvaÈskylaÈ) and sells very well for

private and municipal use.

Hygienic and occupational safety of the composting andcompostsThe content of pathogenic microbes must be low in all

mature compost applied in farming. The Finnish compost

working-group recommends a value below 5000 cfu g± 1 for

pathogenic (enterococci) microorganisms in mature com-

post (Harjula et al. 1992). To achieve this, the temperature

in the windrow should be 508C for 5 days and above 558Cduring a minimum of 4 hours during those days (Golueke

1991). These requirements were met in all windrows at

Mustankorkea.

As measured by pathogenic microbes (Salmonella), the

biowaste composts were at all times hygienic. Salmonella

was found in only two of 36 samples. These were 2-and 3-

week-old composts created in September and October

1997. This result was as expected because food in Finland

rarely contains Salmonella. The number of indicator

microbes of pathogenicity (faecal chain coccus and thermo-

philic faecal coliform bacteria) was high throughout the ®rst

year of composting even though the temperatures of the

windrows were over 608C for a very long time. Possibly the

hygienization was not complete because the biowaste was

not crushed before the windrow was set up, or perhaps

recontamination occurred when the windrows were turned

since the same bucket of the wheel loader was used

elsewhere in the land®ll. It was also noted that the

measurement of pathogenic indicator bacteria is not

particularly informative for compost samples (Ridell,

personal communication). In windrows made since the

summer of 1997 the number of these microbes decreased

during the process, and the windrows were sanitized fairly

quickly (Table 10). The number of indicator microbes

decreased as expected when the biowaste was crushed with

a screener-crusher bucket that was not used elsewhere in

the land®ll.

Table 7. Results of elemental analysis (C, H, N) of samples and their humic chemical fractions from composts of four different ages, percentage of dry matter of thefraction (DM) and percentage of organic matter of the fraction (OM)

AgeCarbon Hydrogen Nitrogen C/N C/H

Sample description (weeks) % DM % OM % DM % OM % DM % OM

Original samples:

Curing pile 1 38 to 36 33.0 55.5 3.9 6.5 1.6 2.7 20.3 8.5

Curing pile 3 25 to 21 42.1 55.5 5.0 6.6 1.6 2.1 26.0 8.4

March II (97) 1 43.8 53.6 5.3 6.5 1.1 1.3 39.8 8.3

Bark Ð 45.3 53.0 5.2 6.1 0.4 0.5 113.4 8.7

Hot water extract:

Curing pile 1 38 to 36 24.6 50.7 3.6 7.4 2.1 4.4 11.5 6.8

During pile 3 25 to 21 28.2 45.8 4.4 7.1 2.5 4.1 11.3 6.4

March II (97) 1 31.9 42.2 5.2 6.9 1.8 2.4 17.6 6.1

Humic acids:

Curing pile 1 38 to 36 49.2 52.3 4.9 5.2 3.7 4.0 13.2 10.0

Curing pile 3 25 to 21 47.7 52.4 5.0 5.5 3.3 3.6 14.6 9.5

March II (97) 1 49.6 51.7 5.2 5.4 2.6 2.7 19.1 9.6

Bark Ð 50.8 52.3 5.0 5.2 1.2 1.2 42.0 10.1

Fulvic acids:

Curing pile 1 38 to 36 40.7 49.8 4.2 5.2 2.2 2.6 18.9 9.5

Curing pile 3 25 to 21 41.2 49.3 4.3 5.1 1.4 1.7 28.8 9.6

March II (97) 1 43.2 49.7 4.6 5.3 1.1 1.3 37.4 9.4

Bark Ð 47.7 51.0 4.6 5.0 0.4 0.4 116.3 10.3

Humin:

Curing pile 1 38 to 36 21.1 40.8 2.6 5.1 0.9 1.8 23.0 8.0

Curing pile 3 25 to 21 34.5 50.7 4.2 6.2 0.9 1.3 36.9 8.2

March I (97) 1 37.3 48.1 4.7 6.1 0.8 1.0 46.8 7.9

Bark Ð 44.2 53.5 5.4 6.5 0.4 0.4 117.8 8.2



Occupational measurements

The concentrations of viable air-borne microbes are

presented in Fig. 5. The number of fungi in the composting

®eld was clearly higher during turning than when the

windrows were not handled. When there were no activities

in the ®eld, the concentrations of fungi were 1.2

3 103 cfu m3 (mesophilic) and 180 cfu m3 (thermophilic),

whereas during turning the corresponding concentrations

were about 7.3 3 104 cfu m3 and 3.3 3 106 cfu m3. The

numbers of fungi were lower in the cabin of the wheel loader,

about 9.4 3 103 cfu m3 (mesophilic) and 2.3 3 104 cfu m3

(thermophilic), but still higher than the number in the ®eld

when turning was not carried out. Depending on the

weather, the normal fungi concentration in outside air is

usually about 103 to 104 cfu m3 (Crook et al. 1988).

The most common fungus in the composting ®eld during

turning was Aspergillus fumigatus, which comprised 38% of all

air-borne fungi in the air (Fig. 6). Other Aspergillus species

were common (24%) as well. In samples taken from the ®eld

when there was no turning, yeast were common fungi (14%)

in the air, whilst Aspergillus species represented less than 5%

(Fig. 7). Common in the cabin of the wheel loader were A.

fumigatus and other Aspergillus (Fig. 8). There was also

considerable Penicillium in the air.

The probable reason for the plentiful appearance of A.

fumigatus was the use of wood chips as a bulking agent (De

Bertoldi 1981; Golueke 1991) and perhaps also the high

composting temperature in summer 1998. A. fumigatus is a

thermophilic, pathogenic fungus and has been identi®ed

elsewhere (Crook et al. 1988) as the most common fungus in

the working air of a composting area.

The number of mesophilic bacteria during turning

exceeded the determination limit (over 300 colonies on

the substratum). The number of thermophilic bacteria in the

working air was 2.5 3 104 to 3.7 3 104 cfu m3 during

turning and about 9 3 103 cfu m3 at other times. Numbers

exceeded the following threshold values for bacteria:

1000 cfu m3 (Rylander et al. 1983) and 5000 cfu m3

(Peterson & VikstroÈm 1984). When there were no activities

in the ®eld the concentration of thermophilic actinomycetes

was only about 180 cfu m3. Concentration was noticeably

higher during turning: about 1.2 3 104 cfu m3 in the cabin

and 2.4 3 104 cfu m3 in the ®eld.

During the turning, the total number of microbes (viable

+ nonviable) was 24.7 3 106 particles/m3 on the ®eld and

71 3 106 particles/m3 in the cabin of the wheel loader. Most

studies have focused on the concentrations of viable

Table 8. Water-soluble nutrients in composts established in 1996 and one soil blend made in winter 1998 (g kg± 1 dry matter)

Sample July I and II (96) Curing pile 1 Sept. III (96) Sept. III (96) Oct. III (96) Oct. III (96) Nov. IV (96) Soil blendAge of compost (weeks) 16 25 7 16 3 12 7

Ca 1010 220 450 280 1110 230 1940 Ð

Mg 280 40 180 71 340 60 460 Ð

K 3790 1580 2430 2330 2600 1870 3710 277

PO4-P 330 190 270 360 280 260 540 47

NO3-N 30 64 ,10 ,5 ,10 10 ,5 35

NH4-N 1510 ,10 510 220 470 40 1050 42

SO4-S 80 20 30 8 70 6 60 17

Fig. 5. Distribution of fungi in air when the compost windrows were nothandled.

10 000 000

1 000 000

100 000

10 000

1000

100

10

0

Field, turning Cabin, turning Field, no turning

Mesophilic fungiThermophilic fungiMesophilic bacteriaThermophilic bacteriaThermophilic actimomycetes

> de

scrib

ing

limit

> de

scrib

ing

limit

n=2

n=1

n=1n=2

n=4

n=4 n=2

n=4

n=4

n=4

n=2

n=2

n=4

cfu

m−3

Fig. 6. Viable air-borne microbes (cfu m3) at Mustankorkea during turningand when the windrows were not handled.



microbes, but dead microbes and parts of them may also be

harmful to human health (Gladding 1998). In the measure-

ments made at Mustankorkea the total number of microbes

was very much higher than the number of viable microbes.

The particle (size over 0.3 mm) concentration was about

8.9 3 106 particles/m3 in the ®eld during turning, measured

with the APS collector. The particle distribution is

presented in Table 11. About 97.4% of the particles in

the working air during turning were small enough (diameter

less than 5.0 mm) to penetrate the pulmonary alveolus

(Terho 1993). In background measurements, which were

made in a university of®ce, the total number of particles was

a little lower, about 7.6 3 106 m3, but about 99.9% of the

particles were smaller in size than 5.0 mm. Thus the

percentage of harmful particles was about the same in the

composting ®eld and the of®ce.

Unexpectedly, the dust concentration during turning was

below the determination limit (Table 12). However, dust

concentrations when there was no turning at the ®eld were

2.7 mg m± 3 and 5.0 mg m± 3. Rainy weather before the

measurement during turning may have suppressed the

concentration by making the windrows moist, with the

result that dust particles were not emitted to the air so easily.

In any event, the Finnish recommended occupational

threshold value of 5 mg m± 3 was not exceeded (National

Board of Labour Protection 1987).

The concentration of endotoxins (Table 12) was highest

in the cabin of the wheel loader during turning, 650 ng m± 3

(5200 EU m3). On the ®eld the concentration was 25 ng m±

3 (200 EU m3) during turning and 5.7 ng m± 3 (63 EU m3)

when the windrows were not handled. An occupational

recommended threshold value for endotoxin in the

pharmaceutical and biotechnology industries and genetic

engineering is 30 ng m± 3 (Palchak et al. 1988). For the

cotton industry, the value is 100 ng m± 3 (Rylander 1987).

Malmros et al. (1992) have recommended a threshold value

of 100 to 200 ng m± 3 and the Dutch Expert Committee a

value of just 4.5 ng m± 3 (Heederik & Douwes 1997).

Table 9. Nutrients of curing pile 5 and the soil blend, g kg± 1 of dry matter

AgeNitrogen (N) Phosphorus (P)

Potassium (K) Magnesium (Mg) Calcium (Ca)Months Total Soluble Total Soluble Soluble Soluble Soluble

Curing pile 5 10 21 0.2 3.5 1.4 6.4 1.4 14

Soil Blend 15 3.0 ,0.1 0.6 0.2 1.2 0.3 3.2

Table 10. Summary of determinations of indicator microbes for pathogenicity in Mustankorkea compost samples for 1997

AgeNumber of determinations Range unit g±1

(weeks) TFCB FCC TFCB FCC

Kitchen biowaste 0 1 2 1 500 3 100 to 220 000

Compost 1 to 4 12 15 120 000 to 15 000 000 1 000 to 4 400 000

Compost 5 to 7 7 8 ,10 to 82 000 000 1 100 to 2 750 000

Compost 12 to 13 3 3 ,10 to 53 000 ,100 to 720 000

Curing piles 17 to 58 8 8 ,10 to 150 000 300 to 110 000

Curing piles 52 2 2 ,100 ,100

TFCB5thermophilic faecal coliform bacteria; FCC5faecal chain coccus.

Fig. 7. Distribution of fungi in the composting ®eld during turning. Fig. 8. Distribution of fungi in the cabin of the wheel loader during turning.



Conclusions

The changeover to source separation and composting of

biowaste occurred quite rapidly and ef®ciently in JyvaÈskylaÈ.

Annual accumulation of kitchen biowaste per resident was

about 60 kg in 1997. Including the composting in small units

the ef®ciency of the biowaste collection surpassed 75% in

that year. The average ef®ciency in other parts of the country

was 50%. The reason for the high ef®ciency in JyvaÈskylaÈ was

that every household in the city was obliged by the waste

handling ordinance to separate their wastes. The demon-

strated willingness of people to participate in waste sorting

and management is praiseworthy and most encouraging.

The closeness of the downtown area made it essential for

the odour nuisance to be avoided in the composting area.

Adequate aeration of the windrows was ®rst ensured by

restricting the initial height of the windrow to less than

1.5 m and also through the use of an adequate amount of

bulking agent (1 m3 wood chips to 1 t of biowaste). The

windrows were turned once a week and after that combined

into larger piles. Exceptionally high composting tempera-

tures were achieved in these low windrows (up to 858C).

From the autumn of 1998 onwards biowaste was treated for

2 weeks in an in-door tunnel composting plant before

windrow composting.

Normal composting temperatures of 558C to 658C were

reached within 2 weeks, except in winter when they were

reached within 4 to 5 weeks. According to pH measure-

ments the composting starts more ef®ciently in low windrows

than in larger ones, but the conductivity was higher in low

windrows. The ash content increased during composting, but

this is a slow process. The amount of humic acids doubled

during 77 weeks composting and a notable increase in HA

concentrations occurred after 37 weeks. The concentrations

of carbon, nitrogen, hydrogen and oxygen remained fairly

stable during composting. However the C/N ratio of the

oldest compost decreased to 20, indicating that the compost

was mature.

The number of indicator microbes for pathogenity

decreased during composting, although the number was

still fairly large in some old windrows. This may have been

the result of recontamination whilst the windrow was turned.

The windrow composting was an intense reaction, but the

mineralization was a relatively slow process.

Air-borne microbes were at a harmful level during

turning, both in the composting ®eld and in the cabin of

the wheel loader. The most common fungus in the working

air was the pathogenic thermophilic fungus Aspergillus

fumigatus. The concentration of endotoxin was also high

during the turning and in the cabin exceeded all

recommended limits. The windows of the wheel loader

were open during the measurement so it is not surprising that

the concentrations of microbes and endotoxins were high.

Since both microbes and endotoxins can be harmful to

human health, it is important that doors and windows of the

wheel loader be closed when compost or biowaste is handled.

Turning of the windrows clearly increases the concentra-

tions of microbes in the working air, to a level that may be

harmful to human health. Similar results were obtained at

the AÈ mmaÈssuo land®ll in Helsinki in 1992 to 1997, where

kitchen biowaste was being composted in windrows

(HaÈnninen et al. 1993; HaÈnninen et al. 1994; Tolvanen

et al. 1994).

Acknowledgements

The ®nancial support of Vapo Ltd for the practical work in

1996 and 1997 and of the Academy of Finland for the

occupational measurements (grant number 42503) and the

editing of the manuscript (project 44281) is gratefully

acknowledged. Special thanks are due to Vesa Miikki for

temperature measurements of the windrows. We are also

grateful to Kari Mutka and Arto RyhaÈnen of Vapo Ltd Biotech,

to Timo NyroÈnen and Olli Reinikainen of Vapo Ltd, to Teuvo

Table 11. Distribution of air-borne particles (%) at Mustankorkea duringturning and in an of®ce

Particle size (mm)

Proportion of airborne particles (%)

Mustankorkea, turning Of®ce at University of JyvaÈskylaÈ

0.3 to 0.5 12.0 52.7

0.5 to 1.0 48.6 40.1

1.0 to 5.0 36.8 7.1

.5.0 2.6 0.1

Table 12. Dust and endotoxin concentrations in the working air at Mustankorkea

Dust concentration Endotoxins

mg m3 Particles m3 ng m3 EU m3

Field, turning 0 8.93106 25 200

Cabin of machine, turning Ð Ð 650 5200

Field, no turning 2.7 to 5.0 Ð 5.7 63



Kari and Simo Suoja of the Technical Service Centre of

JyvaÈskylaÈ and to Rauno Kauppinen, Hannu MaÈttoÈ and Martti

Silvennoinen of the Mustankorkea waste station. Kay

Ahonen is thanked for revising the English of the manuscript.

ReferencesAnonymous (1998a) The National Waste Plan Until 2005. The Finnish

Environment 260. (In Finnish). Helsinki. Finland: Ministry of the

Environment, Edita Ltd.

Anonymous (1998b) Zweifach besser (Twice as good). Umwelt Magazin. 6, 40.

Anonymous (1993) Compost Products Declaration and Control of

Environmental and Quality Parameters. Nordiske Seminar-og

Arbejdsraporter 1993: 608, Copenhagen 1993.

de Bertoldi, M., Vallini, G. & Pera, A. (1983) The biology of composting.

Waste Management and Research 1, 157±176.

de Bertoldi, M. (1981) Pathogenic Fungi Associated with Land Application of

Sludge. Copenhagen, Denmark: World Health Organization. Regional

Of®ce for Europe.

Biddlestone, A. J. & Gray, K. R. (1985) Composting. In: Moo-Young, M.

(ed.) Comprehensive Biotechnology, Vol. 4, Oxford, UK: Pergamon

Press, pp. 1059±1070.

Bidlingmaier, W. (1996) Odour emissions from composting plants. In:

Bertoldi, M. Sequi, P. Lemmes, B. & Papi, T. (eds) The Science of

Composting. Glasgow, UK: Blackie Academic & Professional

Publishers, pp. 71±79.

Crook, B., Bardos, P. & Lacey, J. (1988) Domestic waste composting plants

as source of airborne micro-organisms. In: Griffths, W. D. (ed.)

Aerosols: Their Generation, Behaviour and Application. Aerosol Society

Second Conference. London, UK: Aerosol Society, pp. 63±68.

Decision of Ministry of Agriculture and Forestry Finland (1994) Decision

Regarding Fertilisers. Helsinki, Finland: Edita.

Fischer, K. (1996) Environmental impact of composting plants. In: de

Bertoldi, M. Sequi, P. Lemmes, B. & Papi, T. (eds) The Science of

Composting. Town?, UK: Chapman & Hall, pp. 81±86.

Gladding, T. (1998) Investigating health and safety hazards at MRFs.

Resource Recycling xx, 32±37.

Golueke, C. G. (1991) When is compost `Safe' ? In: Golueke, C. G. (ed.) The

Staff of Biocycle: the Biocycle Guide to the Art and Science of Composting.

Pennsylvania, USA: The JG Press, Inc., Emmaus, pp. 220±228.

Greenberg, A. E., Trussell, R. R. & Clesceri, L. S. (eds) (1985) Standard

Methods for the Examination of Water and Wastewater. Baltimore. USA:

American Public Health Association, p. 97.

Harjula, H., Levinen, R. & Lilja, R. (1992) Report of Compost Working

Group. Report of working group 67/1992. Helsinki, Finland: Ministry

of Environment.

Heederik, D. & Douwes, J. (1997) Towards an occupational exposure limit

for endotoxins? Annals of Agricultural and Environmental Medicine 4 (1),

17±19.

Hietanen, L. & HaÈnninen, K. (1996) Recovery and recycling of domestic

wastes with a deep-collection system. Seventh ISWA Yokohama, Japan

27.10. to 1.11. 1996. Proceedings I. Yokohama, Japan: ISWA,

pp. 133±140.

HaÈnninen, K. I. & Suoja, S. I. (1998) Solid waste management in Finland

with special reference to the JyvaÈskylaÈ region. Wastecon/ISWA World

Congress 1998. Swana's 36th Annual International Solid Waste

Exposition. Charlotte, North Carolina, USA: ISWA, 545±564.

HaÈnninen, K., Suoja, S., Koivula, N. & Miikki, V. (1997) Biowaste

recycling in JyvaÈskylaÈ. In: HoÈgmander, H. & Oikari, A. (eds) Third

Finnish Conference of Environmental Sciences. JyvaÈskylaÈ, Finland:

Finnish Society for Environmental Sciences, pp. 68±69.

HaÈnninen, K. (1996) Composting in Finland. In: de Bertoldi, M. Sequi, P.

Lemmes, B. & Papi, T. (eds) The Science of Composting. Part 2. Glasgow,

UK: Blackie Academic & Professional Publishers, pp. 673±683.

HaÈnninen, K. I., Kovalainen, J. T. & Korvola, J. (1995) Carbohydrates as

chemical constituents of biowaste composts and their humic and fulvic

acids. Compost Science and Utilization 3 (4), 51±68.

HaÈnninen, K. I., Tolvanen, O. K., Veijanen, A. K. & Villberg, K. T. (1994)

Bioaerosols in windrow composting of source separated biowastes. In:

Chartier, P. Beenackers, A. A. C. M. & Grassi, G. (eds) Biomass for

Energy, Environment, Agriculture and Industry. Proceedings of the 8th

European Biomass Conference, Vol. 2. Vienna, Austria: Pergamon Press,

pp. 1212±1221.

HaÈnninen, K., Huvio, T., Veijanen, A., Wihersaari, M. & LundstroÈm, Y.

(1993). Occupational Hygiene of Windrow Composting (in Finnish).

JyvaÈskylaÈ, Finland: VTT publications, p. 776.

Jennings, D. H. & Lysek, G. (1996). Fungal Biology: Understanding the Fungal

Lifestyle. Gulidford, UK: BIOS Scienti®c Publishers Ltd, p. 90.

Kirsten, B., Baccanti, M. & Dutko, B. (1988) Calculation of heat value of

solid and liquid fuels. International Laboratory xx, 51±53.

Leege, P. B. & Thompson, W. H. (1997) Test Methods for the Examination of

Composting and Compost. Maryland, USA: The US Composting

Council, p. 269.

Malmros, P., Sigsgaard, T. & Bach, B. (1992) Occupational health

problems due to garbage sorting. Waste Management and Research 10,

227±234.

National Board of Labour Protection (1987) Values known to be harmful (in

Finnish). Helsinki, Finland: National Board of Labour Protection.

Palchak, R. B., Cohen, R., Ainslie, M. & Lax Hoener, C. (1988) Airborne

endotoxin associated with industrial-scale production of protein

products in Gram-negative bacteria. American Industrial Hygiene

Association Journal 49, 420±421.

Palmgren, U., StroÈm, G., Blomquist, G. & Malmberg, P. (1986) Collection

of air-borne micro-organisms of nuclepore ®lters, estimation and

analysis: CAMNEA method. Journal of Applied Bacteriology 61, 401±

406.

Pereira Neto, J. T., Stentiford, E. I. & Mara, D. D. (1987) Comparative

survival of pathogenic indicators in windrow and static pile. In: De

Bertoldi, M. Ferranti, M. P. L'Hermite, P. & Zucconi, F. (eds)

Compost: Production, Quality and Use. London, UK: Elsevier Applied

Science, pp. 276±308.

Peterson, N. F. & VikstroÈm, P. (1984) Working environment in waste

management. Assembly of investigations (in Swedish). DRAV

Drifstudie Avfallsbehandling Nr 23, Svenska

RenhaÊllningsverksfoÈrening, Publikation 84: 19 November,

NaturvaÊrdsverket Rapport SNV PM 1901.

Rylander, R. (1987) The role of endotoxin for reactions after exposure to

cotton dust. American Journal of Industrial Medicine 12, 687±697.

Rylander, R., Lundholm, M. & Clark, C. S. (1983) Exposure to aerosols of

micro-organisms and toxins during handling of sewage sludge. In:

Wallis, P. M. & Lohman, D. L. (eds) Biological Health Risks of Sludge

Disposal to Land in Cold Climates. Calgary, Alberta, Canada: University

of Calgary Press, pp. 69±78.

Terho, E. O. (1993) Allergic bronchopulmonary aspergillosis. In: Haahtela,

T. Hannuksela, M. & Terho, E. O. (eds) Allergologia Duodecim (in

Finnish). Vammala, Finland: Publisher?

Tolvanen, O., HaÈnninen, K., Veijanen, A. & Villberg, K. (1994)

Occupational hygiene of source separated biowaste in windrow

composting PaÈaÈkaupunkiseudun julkaisusarja C, No. 15. Helsinki,

Finland. Finnish Waste Act of Finland 1072/93.



windrow composting of source separated kitchen biowastes in finland

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