Bioresource Technology 44 (1993) 105-107

UTILISATION OF SOLID PAPER-MILL SLUDGE A N D SPENT BREWERY YEAST AS A FEED FOR SOIL-DWELLING

EARTHWORMS

Kevin R. Butt

Biosystems Research Group, Centre for Technology Strategy, The Open University, Milton Keynes, UK MK7 6AA

(Received 28 August 1992; accepted 4 September 1992)

Abstract Solid paper-mill residues amounting to thousands of tonnes per annum are usually disposed of in landfill sites. However, by the addition of spent yeast from the brewing industry, the carbon to nitrogen ratio of these paper sludges can be adjusted to make them into a feed which can satisfy the requirements of earthworm growth. Using one such feed comprising a 66:1 mixture, by mass, of wet paper waste and dry yeast extract, the lob worm (Lumbricus terrestris) can be grown from the hatchling stage (50 mg) to maturity (3-4 g) within 90 days, with an acceptably low level of mortality. These large, soil-dwelling earthworms have potential value as agents in soil amelioration projects if they can be reared intensively, therefore their utilisation may be encouraged by using the type of superior feed described.

Key words: Earthworms ( Lumbricus terrestris; Octola- sion cyaneum), growth, solid paper mill sludge, brew- ery waste, yeast extract, soil amelioration.

INTRODUCTION

The annual production of solid paper-mill sludge in the UK is at least 110000 dried tonnes (Pryce, 1991); approximately 3-5% of the total paper produced depending on the quality of the raw materials (Walder- meyer, 1962; Millett et al., 1973). To prevent contami- nation of groundwater the sludge is usually treated in effluent plants and the solid fraction is frequently dis- posed of in landfill sites. This is a loss of a potentially useful resource which has a high cellulose content. Many uses have been sought, including land applica- tion, where the high carbon content tends to lock up soil nitrogen resulting in low crop yields (e.g. Dolar et al., 1972). Other potential uses may be as animal feeds, utilising microbial enzyme activity to break down the lignin and cellulose (e.g. Kannan et al., 1990), or even

Bioresource Technology 0960-8524/93/S06.00 © 1993 Elsevier Science Publishers Ltd, England. Printed in Great Britain

as the base for the production of potting compost (e.g. Edwards & Burrows, 1988).

Recent research (Butt, 1990) showed that solid paper sludge was a suitable feed for soil-dwelling earth- worms such as Lumbricus terrestris (the lob worm). Under laboratory conditions this substance had no deleterious effects on the earthworms, although growth rates tended to be poor. The low level of nitrogen in the sludge, at 0-5% (total Kjeldahl N), was thought to be a limiting factor, and preliminary trials with addi- tions of an organic nitrogen source (laboratory-grade yeast extract) resulted in enhanced growth rates. This paper examines the potential for using paper-mill sludge enhanced with spent yeast from the brewing industry as feedstocks for soil-dwelling earthworms.

METHODS

Earthworms The earthworms used were two British, deep-burrow- ing species, Lumbricus terrestris L., renowned for its ability to improve soil quality and Octolasion cyaneum (Savigny), known for its parthenogenetic mode of reproduction (Sims & Gerard, 1985). All were obtained through breeding experiments of adults col- lected from pasture land. The hatchling earthworms emerged from cocoons maintained in Petri dishes half filled with distilled water, in temperature-controlled incubators at 20°C. On hatching they were transferred to and maintained, unfed, within a 5°C incubator for a maximum of 8 days until the experiment was started, by which time the required number (40 of each species) was assembled.

Feed materials The solid paper sludge was obtained fresh from Grove- hurst Energy, the service group to UK Paper and St Regis Paper, Kemsley, Kent. These mills utilise virgin pulp and waste-derived pulp, respectively, and have a combined annual sludge production of approximately 17000 dry tonnes. Characteristics of the sludge are given in Table 1.

105

106 Kevin R. Butt

Table 1. Important characteristics of solid paper sludge fed to earthworms (all figures given as % except C: N and pH)

Total solids Cellulose Lignin Ash Total Kjel. N Total C C:N pH

19.6 49.1 12.0 10-2 0"5 46.7 93:1 7.1

Adapted from Butt (1990).

Three yeast extract supplements were used:

Laboratory grade (Sigma Chemical Co., St Louis, USA; No Y-4000) (treatment Y), Whitbread's pilot brewery, Luton, Beds. (treatment W), Banks and Taylor's brewery, Shefford, Beds. (treat- ment B).

The two brewery wastes were obtained in a liquid state. An extract was obtained by evaporating the liquid frac- tion at 105°C, and grinding the residue in a food blen- der. The total nitrogen content of each yeast extract was determined by the Kjeldahl method (Anon., 1986) and all three were found to lie within the range 82-87 kg.

Experimental design Hatchling worms of the two species, L. terrestris and O. cyaneum were placed individually in 300 ml plastic pots containing 150 g of loamy soil. The soil had been steam-sterilised to remove predators and competitors and then moistened to 20-25% wet soil mass. Forty pots of each species were randomly allocated to the feed treatments; 50 g of paper solids alone (treatment P) and the three treatments supplemented with yeast extract (W, B and Y), giving ten replicates per treat- ment. Each supplemented treatment had 0"75 g of the particular yeast extract added to 50 g of paper solids. This figure was determined from preliminary experi- ments with L. terrestris (Butt, 1990) and provided a carbon to nitrogen ratio (C:N) of approximately 25:1. Each yeast extract was sprinkled onto and mixed thoroughly with the paper sludge before feeding, and all feeds were supplied on the soil. The 80 pots were then capped, provided with 8 mounted needle-size air holes, and incubated at 20°C. Sampling, every 30 days, entailed individually emptying the pot contents onto a tray, locating each earthworm, washing it to remove adhering soil/feed, blotting it dry and measuring its mass. The sexual development of each worm was also recorded, as was any mortality. The soil and feed within the pots was completely replaced with fresh materials at every other sampling, i.e. every 60 days. The experiment was maintained until at least one earthworm of each species had reached sexual matu- rity.

RESULTS AND DISCUSSION

Figure 1 illustrates the mean growth of L. terrestris with the four feed treatments. After 120 days none of the animals supplied with paper solids alone (treatment P)

5

A

4

.A 3 o

2

0 m m l m

30 60 90 120 Time (days)

Fig. 1. Growth of Lumbricus terrestris at 20°C with four feeds based on paper sludge plus yeast extracts from differ- ent sources (treatments: o, paper only (P); o, plus Whitbread

(W); n, plus Banks & Taylor (B); m, plus lab. grade (Y)).

3 -

E

w

0

0 30 60 90 120

Time (days)

Fig. 2. Growth of Octolasion cyaneum at 20°C with four feeds based on paper sludge plus yeast extracts from differ- ent sources (treatments: o, paper only (P); o, plus Whitbread

(W); tz, plus Banks & Taylor (B); m, plus lab. grade (Y)).

had begun to develop sexual characteristics and a mean mass of only 0.7 g was attained. With each treatment supplemented with yeast extract, growth to maturity, at a mean mass greater than 3 g, was reached within 90 days. No significant difference was found between the growth rates of L. terrestris with the three supple- mented feeds over 90 days (p<0"01), although the mortality of earthworms was different. All L. terrestris survived to 60 days, but by 120 days the mortalities for treatments W, B and Y were 60, 40 and 50%, respect- ively. This compared with only 20% for treatment P (paper solids only).

Figure 2 illustrates the growth of O. cyaneum with the four feed treatments. Treatment P led to the slowest growth rates. After 120 days a mean mass of only 0.4 g had been achieved with no development of sexual

A mended paper-making sludge as worm food 107

characteristics. Growth with the supplemented feeds led to increased mass attainment, but the responses differed between the three feeds. From day 30 to day 60 a growth rate of 297 rag/g/day was achieved by the earthworms in treatment W in reaching a mean mass of 1.4 g. However, these animals subsequently lost mass and after 120 days the mean figure was reduced to 1.0 g. A slower initial growth but no decline thereafter was exhibited by earthworms in the other two supplemented treatments. Worms in treatment B reached 1.7 g after 120 days and showed the first signs of developing sexual characteristics, whilst those in treatment Y reached 2-3 g and all survivors became fully sexually mature. The mortalities for three of the treat- ments of O. cyaneum after 120 days were all 40%, the fourth was treatment B where 80% died.

L. terrestris results showed that this species responded favourably to the provision of a composite feed formed from paper sludge and yeast extract, and that the origin of the latter had little effect on growth. Rapid growth was achieved and healthy, mature indi- viduals were produced. Mortality was greater than that predicted by the model for hatchling growth in the field (Lakhani & Satchell, 1970). However, this was not unexpected due to increased maturation rates under, for example, higher temperatures than would be expected in the field.

Results for O. cyaneum did not follow the clear trend shown by L. terrestris. Additions of yeast extracts enhanced growth in all instances, compared with paper solids only, but the responses were of varying effect and led in one case (treatment W) to a steady decrease in mass, after an initially rapid increase. From these results it is clear that this type of feed, in this particular form, is not ideally suited for this species of earthworm, as only in one treatment (Y) was full maturity reached within 120 days. The use of solid paper sludge supple- mented with spent yeast does therefore have potential as a feed for certain soil-dwelling earthworms, but the responses of the two experimental species used illu- strates that it is not suitable for all species. Previous results (Butt, 1990) have also shown that paper sludge from different origins may contain unidentified sub- stances which are harmful to earthworms in general. Small-scale trials would therefore be necessary if paper solids from any source were considered for this type of worm production. Similarly the economics of this

process would need to be examined closely before embarking on a larger-scale production system as, for example, a saving may be made by not landfilling the paper sludge but the spent yeast might need to be purchased. Some breweries do not regard this as waste and presently convert such materials into hydrolysates and autolysates for use as flavouring agents (Berry, 1982). However, the increasing need for earthworms, as part of land restoration schemes (e.g. Butt, 1992), may lead to research which will encourage manufactu- rers of paper and certain alcoholic beverages to recon- sider the fate of their waste products.

REFERENCES

Anon. (1986). The Analysis of Agricultural Materials. HMSO, London.

Berry, D. R. (1982). The Biology of Yeast. The Institute of Biology's Studies in Biology No. 140, Edward Arnold, London.

Butt, K. R. (1990). An investigation into the growth and reproduction of the earthworm Lumbricus terrestris L. under controlled environmental conditions. PhD thesis, The Open University, 141 pp.

Butt, K. R. (1992). Development of an earthworm cultivation and soil-inoculation technique for land restoration. Pro- ceedings of the 3rd British Grassland Society, Antrim.

Dolar, S. G., Boyle, J. R. & Keeney, D. R. (1972). Paper mill sludge disposal on soils: effects on the yield and mineral nutrition of oats. (Avena sativa L.). Journal of Environ- mental Quality, 1 (4), 405-9.

Edwards, C. A. & Burrows, I. (1988). The potential of earth- worm composts as plant growth media. In Earthworms in Waste and Environmental Management, ed. C. A. Edwards & E. E Neuhauser. SPB Academic Publishing, The Hague, pp. 211-19.

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Millett, M. A., Baker, A. J., Satter, L. D., McGovern, J. N. & Dinius, R. A. (1973). Pulp and papermaking residues as feedstuffs for ruminants. J. Animal Science, 37, 599-607.

Pryce, S. (1991). The Peat Alternatives Manual. Friends of the Earth, London.

Sims, R. M. & Gerard, B. M. (1985). Synopses of the British fauna (31) -- Earthworms. Linnean Society, London.

Waldermeyer, T. (1962). Disposal of solids in the paper industry. Journal of the Institute Sewage Purification, 61 439-51.