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Vermicomposting of Pre-composted MixedFish/Shellfish and GreenWaste

July 2004

SR566

J. FredericksonOpen University

S. Ross-SmithThe Worm Research Centre

PROJECT PART-FINANCED BYTHE EUROPEAN UNION

THROUGH THE FINANCIALINSTRUMENTS FOR FISHERIES

GUIDANCE


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ISBN 0 903941 67 8

Working with the seafood industry to satisfy consumers, raisestandards, improve efficiency and secure a sustainable future.

The Sea Fish Industry Authority (Seafish) was established by theGovernment in 1981 and is a Non Departmental Public Body (NDPB).

Seafish activities are directed at the entire UK seafood industry includingthe catching, processing, retailing and catering sectors.


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Vermicomposting of pre-composted

mixed fish/shellfish and greenwaste

Prepared by:

Jim Frederickson

Open University([email protected])

and

Steven Ross-Smith

The Worm Research Centre Ltd

Phoenix Farm

Asselby

Howden

([email protected])

Date submitted:

26/7/04


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Executive summary

Partially composted mixed fish/shellfish and green waste was further vermicomposted

on a large-scale for seven weeks. The composition of the pre-composted waste was

such that it had elevated levels of pH and electrical conductivity. In the large-scale

vermicomposting system, the earthworms appeared to be reluctant to enter the wastedirectly for the first three weeks but then actively processed the waste. However,

laboratory experiments confirmed that the earthworms would have been capable of

processing the waste during this period and increasing their biomass significantly as a

result. It is likely that the earthworms were ingesting and processing the waste during

the first three weeks while remaining in the bedding material. Greenhouse gas

emissions were found to be low, probably due to the pre-composting phase reducing

carbon and nitrogen contents. The vermicompost which was derived from the process

showed the high nitrate concentration which is characteristic of typical

vermicomposts. On the basis of this and other characteristics, it would appear that

the vermicompost would be capable of being used as a basis for the formulation of

high value composts.

Waste composition and in-vessel composting

The partially composted material used in the vermicomposting trial was derived from

in-vessel composting of shellfish and fish with green waste.

Four different types of shellfish were used (crab, whelks, mussels andNephrops) andtwo types of fish: oily fish (mackerel) and mixed whitefish (cod, haddock etc).

Shellfish waste comprised shell and flesh waste not just shell on its own. Mackerel

waste was derived from every part of the fish but the fillet. Whitefish waste was

largely fish frames, with possibly some fish heads as well.

1.106 tonnes of shellfish (comprising the four types in approximate equal parts) were

mixed with 1.404 tonnes of mackerel and 1.156 tonnes of whitefish (total of 3.666

tonnes of mixed fish and shellfish). This mix was then combined with about 10 tonnes

of green waste and loaded into three composting chambers. The material sent to the

Worm Research Centre was a combination of material from all three chambers.

The mixed fish and shellfish composting trial started on 12th December and was

completed on 21

st

January. The waste was composted in the in-vessel system for atotal of 40 days.

Details of waste preparation and vermicomposting process

Vermicomposting is the use of selected species of earthworms to help decompose and

transform organic wastes into stable and useful compost. In vermicomposting

systems, it is the earthworms that fragment, mix and help aerate the waste. This is

compared with traditional composting where the compost piles (known as compost

windrows) are mixed and aerated mechanically. See Appendix 1 for more details

about vermicomposting.


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The mixed fish/shellfish waste was stored at the Worm Research Centre for

approximately four weeks prior to commencement of the vermicomposting trial. On

arrival, the waste emitted a very strong odour which was characteristic of ammonia

gas. This odour was found to reduce gradually over 7 days until no detectable pungent

odour remained. During the vermicomposting process, monitoring of odour took place

every 3-4 days, however, this proved to be unnecessary as odour from the processingbeds was negligible.

The vermicomposting bed (area 10 metre2) was prepared for use on 13th February

2004. Bedding material was moist, composted wood shavings and coir with a large

mesh wire screen placed on top (area 6 metre2) to keep the waste separated from the

bedding. Temperature probes and data loggers were installed and the bed heating

thermostat controlling electrically heated cables was set at 15 oC.

The earthworm density in the bed was determined as 3kg per metre2 of bed.

Earthworm species wasDendrobaena veneta. The mixed fish/shellfish/greenwaste

was prepared for vermicomposting by saturating it with water until its maximummoisture holding capacity was reached and a small amount of leachate was produced.

The waste was weighed as shown in Figure 1 and then manually placed on the

vermicomposting bed. The weight of the saturated waste placed on the bed was

approximately 1 tonne and this was placed directly on the wire mesh to a depth of

approximately 0.3 m. Figure 2 is a sample of the earthworm inoculum used for the

trial. Figure 3 shows the location of the waste relative to the bed and the bed was then

covered by an impervious membrane to exclude rain (shown retracted). Samples of

the waste were sent to the Open University for chemical analysis. The

vermicomposting trial commenced on 16th February 2004.

Figure 1

Weighing the waste prior to applicationto the vermicomposting bed


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Figure 2

Earthworms used for the trial

Figure 3Vermicomposting bed


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Progress of the trial:

16th February to 8th March 2004

The earthworms made no significant movement from the bedding material into the

waste during the first three weeks. However, there was clear evidence that they were

ingesting the bottom layer of waste while remaining in the bedding. Waste sampleswere removed for determination of pH.

9th March to 15th March 2004

The waste showed signs of drying and water was applied to the bed. The first

significant movement of earthworms into the waste was recorded (9th March). Waste

samples were removed for determination of pH.

16th March to 6th April 2004

During this period a high density of earthworms were detected throughout the waste.

Sampling the surface of the waste for the emission of greenhouse gases was

undertaken. Waste samples were removed for determination of pH. The trial wasterminated on 7th April and final samples taken for chemical analysis.

Characteristics of the mixed fish/shellfish and greenwaste feedstock as applied to

the vermicomposting bed

Table 1

Waste type Dry

Matter

Loss on

Ignition

Organic

Carbon

Carbon

to

Nitrogenratio

pH Electrical

Conductivity

% % DM % DM S/cm

Fish/shellfish/GW 52.1 57.6 32.0 17:1 8.1 2040

Table 2

Waste Nitrogen

content(Kjeldahl)

NO3-N

(nitratecontent)

NH4-N

(ammoniumcontent)

(mg/kg DM) (% DM)

(mg/kg

DM)

(mg/kg

DM)

Fish/shellfish/GW 19000 1.90 Negligible 144


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A respirometer (see Appendix 3) was used to determine the microbiological activity

of partially composted fish/shellfish/greenwaste material, which is an indicator of

compost stability. Stability is defined as the degree of decomposition or maturity of

the composting material. The system employed in this study had 3 chambers each

holding 4kg of material. The compost moisture was amended to the optimum 60%

prior to being analysed. The operating temperature was 35o

C, maximising carbondioxide (CO2) production by providing conditions favourable to most of the microbial

population.

The respiration rate for the waste which was applied to the vermicomposting bed was

found to be 336 mgCO2 /hour/kg waste. It can be seen from Figure 4 for a comparable

waste (taken from Hobson A.M., Frederickson J. and Dise N. B. 2004) that the waste

supplied for vermicomposting in this case had a respiration rate which was relatively

low suggesting that the waste had been stabilised during in-vessel composting.

However, while the waste was relatively stable prior to vermicomposting, it can also

be seen from Figure 4 that further maturing of the waste was clearly required to lower

the respiration rate to levels typical of mature composts.

Figure 4

Respiration rates for source segregated household waste;

in-vessel composted (7 days) followed by windrow composting or vermicomposting

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50 60 70 80 90 100

Time (days)

RespirationratemgCO2/hr/Kg

Vermicomposting

Windrow


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Environmental impact of vermicomposting process

Leachate:

The processing bed was covered during vermicomposting to exclude rain and no

leachate was detected.

Greenhouse gas emissions (methane and nitrous oxide):

Methane and nitrous oxide emissions were monitored once during vermicomposting

using the static chamber method. A full account of the method can be found in

Hobson A.M., Frederickson J. and Dise N. B., (2004). Table 3 shows the gas fluxes

that were detected from the vermicomposting of the fish/shellfish and green waste.

These were relatively low and are comparable to fluxes found for similar waste types

such as mixed green waste and source segregated household waste (see Appendix 2

for these data).

Table 3

Waste type Rate CH4(methane)

(mg m-2

hr-1

)

N2O

(nitrous oxide)

(mg m-2

hr-1

)

Fish/shellfish

and green waste mean rate 0.04 0.69

peak rate 0.08 1.46

Table 4

Date pH of

waste

16/2/04 8.1

24/2/04 8.1

10/3/04 8.0

17/3/04 7.7

26/3/04 7.6

07/4/04 7.4


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Characteristics of mixed fish/shellfish and greenwaste vermicompost

Table 5

Characteristics of the Fish/shellfish/GW vermicompost (screened to under 10mm)

compared with typical composts

Compost Dry

Matter

%

Loss on

Ignition

% DM

Organic

Carbon

% DM

Carbon

to

Nitrogen

ratio

pH Electrical

Conductvity

S/cm

Fish/shellfish/GW

Vermicompost 46.1 42.5 23.6 12:1 7.2 1442

Typical green

waste compost 76.1 17.7 10.3 15:1 8.0 600

Typical

vermicompost 24.7 72.7 40.4 31:1 4.9 741

Table 6

Characteristics of the Fish/shellfish/GW vermicompost (screened to under 10mm)

compared with typical composts

Compost Nitrogen

content

(Kjeldahl)

NO3-N

(nitrate

content)

NH4-N

(ammonium

content)

(mg/kg DM)% DM(mg/kg DM)(mg/kg DM)

Fish/shellfish/GW

vermicompost 19900 1.99 4820 Negligible

Typical green

waste compost 6824 0.68 9 Negligible

Typical

vermicompost 13300 1.3 5300 Negligible

Laboratory studies

Laboratory studies were conducted on earthworms when fed partially composted

fish/shellfish/greenwaste material to determine:

1. earthworm mortality

2. earthworm growth rates over time


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Five pots (0.5l) each containing coir bedding and five adult earthworms (mean

individual biomass 1.1g) were fed approximately 50g of the fish/shellfish/greenwaste

material. No unfed control was used since earthworms are known to fail to gain

weight on coir alone and quickly die. After 22 days the total earthworm biomass had

increased by 30%. One earthworm died during the experiment. The earthworms

gained weight at the rate of 8mg per worm per day and this rate is typical forearthworms fed on partially composted material (Frederickson, J., Butt, K.R. Morris,

R. M. & Daniel, C. 1997).

Observations from the trial

The fish/shellfish/greenwaste material that was supplied for vermicomposting had

been previously composted in an in-vessel system for 40 days. Respirometry

evaluation showed the material to have been well stabilised by the composting

process but also confirmed that the material needed to be further matured before it

could be considered to be an acceptable compost for high specification use. In this

project the material was subjected to further maturation using vermicomposting. Interms of the wastes suitability for vermicomposting, a number of points are worth

noting. Firstly, Frederickson, J., Butt, K.R. Morris, R. M. & Daniel, C. 1997 reported

that earthworms grew and reproduced better in fresh waste compared with pre-

composted waste and that the degree of pre-composting affected the long term

sustainability of the system. Pre-composting waste normally has the effect of greatly

reducing the carbon content and nutrient value of the waste for subsequent worm

composting. From Tables 1 and 2 it can be seen that the waste carbon and nitrogen

contents were relatively low prior to vermicomposting and it is also likely that these

compounds would have been in stable and humified forms. Hence, it would be

expected that the waste would experience very little further mass losses as a result of

worm composting.

Also from Tables 1 and 2, it can be seen that both the pH and electrical conductivity

of the pre-composted waste are very high and these characteristics are known to have

a negative effect on earthworms. It is likely that the high levels of these parameters

would have deterred the earthworms from entering the waste during the early stages

of worm composting and observation of the bed confirmed this. However, in the

laboratory experiments the worms gained 30% in weight during the first three weeks

when placed in the same waste, suggesting that the worms were capable of ingesting

and processing the waste despite the apparently hostile environmental conditions to

which they were subjected. It is likely that the earthworms were ingesting andprocessing the waste during the first three weeks while remaining in the bedding

material. Table 4 shows how the waste pH dropped over time probably due to

conversion of ammonia to nitrate, making the waste less hostile to the earthworms.

Table 3 showed that greenhouse gas emissions were not significant during

vermicomposting due to the pre-composting stage reducing both carbon and nitrogen

contents of the waste.

The earthworms were observed to be actively processing the waste after 3 weeks and

after approximately seven weeks vermicomposting, the project was terminated and

the final material was screened to 10mm. Approximately 60% m/m of the screenedvermicomposted waste was found to be under 10mm. The main feature of the


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vermicompost was the high nitrate content as shown in Table 6. This is a key

indicator of maturity and on this basis the vermicompost would appear to be suitable

for high specification plant growth applications when blended with other materials.


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References

Hobson A.M., Frederickson J. and Dise N. B., (2004). Emission of CH4 and N2O from

composting: comparing mechanically turned windrow and vermicomposting systems.

In proceedings: Treatment of biodegradable and residual waste. Harrogate, UK.

ISBN 0-9544708-1-8.

Frederickson, J., Butt, K.R. Morris, R. M. & Daniel, C. (1997) Combining

vermiculture with traditional green waste composting systems. Soil Biology and

Biochemistry29, 725-730. 0038-0717.


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Appendix 1

Vermicomposting and traditional composting

Vermicomposting is the use of selected species of earthworms to help decompose and

transform organic wastes into stable and useful compost. In vermicompostingsystems, it is the earthworms that fragment, mix and help aerate the waste. This is

compared with traditional composting where the compost piles (known as compost

windrows) are mixed and aerated mechanically. There are many different methods of

vermicomposting, making it impossible to present a definitive guide to best practice

and systems will vary depending on whether the aim is to produce vermicompost or

earthworms, or both.

While vermicomposting and composting both involve the aerobic decomposition of

organic matter by microorganisms, there are important differences in the way the two

processes are carried out. The most notable being that vermicomposting is carried out

at relatively low temperatures (under 25C), compared with composting, where pile

temperatures can exceed 70C. The intention with traditional composting is to stack

waste material in sufficiently large piles so that the heat produced in the intense

breakdown of organic matter is retained in the compost pile. This temperature

increase stimulates the proliferation of heat loving (thermophilic) microorganisms and

it is mainly these that are responsible for the decomposition. With vermicomposting it

is vitally important to keep the temperature below 35C, otherwise the earthworms

will be killed. It is the joint action between earthworms and the aerobic

microorganisms that thrive in these lower temperatures (mesophilic) that breaks down

the waste. Hence it is common with vermicomposting systems to apply waste

frequently in thin layers, a few centimetres thick, to beds or boxes containingearthworms in order to prevent overheating and to help keep the waste aerobic.

It is difficult to directly compare composting with vermicomposting in terms of the

time taken to produce stable and mature compost products. With vermicomposting,

particles of waste spend only a few hours inside the earthworms gut and most of the

decomposition is actually carried out by microorganisms either before or after passing

through the earthworm. Hence, earthworms accelerate waste decomposition rather

than being the direct agent. With windrow composting it usually takes at least six to

twelve weeks to produce a stable compost and research suggests that

vermicomposting takes around the same time. However, processing rates will

crucially depend on many factors such as the system being used, the processingtemperature and other factors, the nature of the wastes and the ratio of earthworms to

waste.

One advantage that vermicomposting has over composting is that a net excess of

earthworms can be produced and these may be harvested for a variety of purposes. It

should be noted that it can take many months to build up a large working population

of earthworms capable of vermicomposting significant quantities of waste.

Vermicomposting does have one significant disadvantage and this is to do with the

destruction of human and plant pathogens that can be present in some wastes.

Destruction of most pathogens is more easily achieved in windrow composting due to

the high operating temperatures and the intense microbial reactions taking place.Although the destruction of human pathogens has also been shown to be possible with


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vermicomposting, elimination of pathogens requires very effective management of the

vermicomposting process. It is often recommended that wastes, such as sewage

sludge, which are known to contain human pathogens, are either pre-composted

before vermicomposting or else the resulting casts should be sterilized before use.

Vermicompost is the matured, processed material that is egested from earthworms ascasts. As earthworms feed on the rich diet of organic matter and micro-organisms in

waste, this ingested material is finely ground by the earthworms gut. This helps

micro-organisms decompose the organic matter and stimulates mineralisation of

complex compounds into simple nutrients, easily utilised by plants. At the same time

the organic matter and microbial cells are glued together by the secretions from the

earthworms gut forming casts. The amount of time that the waste spends in the

earthworm gut is only a few hours and therefore the egested cast material is very

microbially active and continues to decompose for some time. Once matured, the

casts are known as vermicompost and this can have excellent physical and chemical

characteristics. Compared with windrow composts, vermicomposts are likely to

contain higher levels of nitrogen because vermicomposting temperatures and nitrogenlosses are typically much lower.


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Appendix 2

Greenhouse gas emissions

The data below for mixed green waste and source segregated household waste has

been taken from Hobson A.M., Frederickson J. and Dise N. B., (2004). The waste hadbeen subjected to in-vessel composting for the first seven days before being

composted and vermicomposted.

Measured static chamber CH4 (methane) flux from windrow, vermicomposting and

control.

Day Windrow CH4flux mgm

-2hr

-1Windrow

temperatureVermicomposting CH4

flux mgm-2

hr-1

Control CH4 fluxmgm

-2hr

-1

7 6.604 36.075 0.016 0.003

14 4.142 40.800 0.057 -0.01021 1.055 60.862 0.019 -0.00635 6.120 50.112 0.040 0.001

50 5.020 46.683 0.076 -0.00764 0.862 18.758 0.027 -0.00278 0.050 14.150 0.027 -0.01492 0.215 8.562 0.378 0.016

Measured static chamber N2O (nitrous oxide) flux from windrow, vermicomposting

and control.

Day Windrow N2Oflux mgm-2hr-1

Vermicomposting N2Oflux mgm-2hr-1

Control N2O fluxmgm-2hr-1

7 0.370 0.425 0.025

14 0.271 0.807 0.12021 0.006 0.117 -0.06835 0.029 0.627 0.03050 0.627 0.526 0.08064 0.030 0.541 0.03178 0.005 1.013 -0.012

92 0.025 1.457 0.071


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Appendix 3

Respirometer for measuring waste stability

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