Agricultural Wastes 9 (1984) 239-247

Effects of Disinfectants and Antibiotics on the Anaerobic Digestion of Piggery Waste

J. Poels, P. Van Assche & W. Verst raete

Faculty of Agricultural Sciences, State University of Gent, Coupure 653, 9000 Gent, Belgium

ABSTRACT

The effects of disinfectants and antibiotics on the anaerobic digestion of piggery waste were investigated. The disinfectants Tego 51, Dettol, NaOCl and Creolin, and the antibiotics, chlortetracyclin, tylosin, erythromycin, chloramphenieol, bacitracin and virginiamycin were tested at different concentrations. At concentrations normally used in practice, no inhibitory effect on methanisation process was detected. However, higher concentrations of the antimicrobial agents, Dettol, Creolin, bacitracin and virginiamycin, markedly inhibited biogas production. In order to minimize possible digester failures, farmers are advised to respect the normal recommended dose and to use low-toxicity antimicrobial agents.

I N T R O D U C T I O N

The use of disinfectants and antibiotics can disturb anaerobic digesters treating piggery wastes (Hilpert et al., 1982). Cleaning and disinfection of the pig houses occurs normally twice a year and is, depending on the particular farm routine, completed with intermediate cleanings. Further- more, the addition of antibiotics in the drinking water during several days to combat bacterial infective diseases is commonly practised on pig farms. This paper examines the influence of some disinfectants and antibiotics on the methane fermentation of piggery waste in laboratory scale digesters. Four disinfectants and six antibiotics were selected from the most frequently applied antimicrobial agents.

239 Agricultural Wastes 0141-4607/84/$03-00 © Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain

240 J. Poels, P. van Assche, IV. Verstraete

M E T H O D S

The effect o f different an t imicrob ia l agents on m e t h a n e p r o d u c t i o n f r o m piggery waste was tested in comple te ly mixed glass l a b o r a t o r y f e rmen to r s with a work ing vo lume o f 1500 ml. The gas was col lected and measured by water d isplacement . The digesters had a hydraul ic re ten t ion t ime o f 20 days and a loading rate o f 2 - 4 g C O D per litre o f r eac to r per day (semi- con t inuous feedings: 150 ml o f influent every 2 days). Th e digest ion tern-

TABLE 1 Characteristics and Applied Concentrations of the Tested Antimicrobial Agents in

Laboratory Experiments

Antimicrobial Characteristics Concentration* agent

Disinfectants Tego 51

Dettol

NaOCI

Creolin

Antibiotics Chlortetracyclin

Tylosin

Chloramphenicol

Erythromycin

Bacitracin

Virginiamycin

Dodecyldi(amino-ethyl)glycin

A mixture of para-chlormetaxylenol terpinol and iso-propanol

Containing 25-32 g free available chlorine per litre

A mixture of creosote oil, phenols (minimum 20 ~) and resin soaps

Tetracyclin

Macrolide antibiotic

Synthetic antibiotic containing a p-nitrophenyl, a dichloroacetylamino and a propanediol group

Macrolide antibiotic

Mixture of different antibiotic fractions with polypeptide nature

Mixture of different antibiotic fractions with peptolide nature

(ml litre- ~) Dose 1 0.17 Dose 2 1.70 Dose 1 0.83 Dose 2 8.30 Dose 1 1.70 Dose 2 16.70 Dose 1 0.17 Dose 2 1-70

(mg litre- l) Dose 1 3.3 Dose 2 16-7 Dose 3 33.3 Dose 1 1-7 Dose 2 8-3 Dose 3 16-7 Dose 1 16.7 Dose 2 83.3 Dose 3 166-6 Dose 1 0-4 Dose 2 2.0 Dose 3 4.0 Dose 1 3.3 Dose 2 16.7 Dose 3 33.3 Dose 1 1.7 Dose 2 8.3 Dose 3 16.7

* In digester.

Disinfectants and antibiotics in methane digesters 241

perature was 30-33 °C. The methanisation was followed and compared in control fermentors and fermentors treated with a disinfectant or an antibiotic. Several concentrations were used. The first concentration of each agent corresponded with the one used in practice on the basis of washing down the piggery once with an appropriate concentration of disinfectant. To calculate this concentration, the pig house was assumed to contain 180 fattening pigs on fully slatted floors and to have a 120 m 3 manure storage pit half full. The second concentration of the disinfectants corresponded with a dose ten times higher than the usual one. This dose should reveal effects on the methanisation process under extreme conditions (for example, very intensive disinfection). For the experiments with antibiotics the concentrations were calculated on the basis of one veterinary prescribed dose in the drinking water on one day (dose 1) all passing through the pigs and collecting in the manure pit. The second and third concentrations of antibiotics corresponded to those quantities present in the piggery manure storage pit after a consecutive daily treatment during a period of 5 (dose 2) and 10 days (dose 3), respectively. The characteristics and applied concentrations of the antimicrobial agents in the experiments are summarised in Table 1.

The effects of the antimicrobial agents were measured by changes in biogas production, composition of the biogas, soluble COD (CODs) Volatile Fatty Acids (VFA) content and VFA patterns. Microscopic investigation with a Polyvar microscopic, equipped with a 420nm fluorescence module, was carried out during the whole test period. The COD (Chemical Oxygen Demand) was determined according to the S tandard M e t h o d s (1971). Volatile Fatty Acids (VFA) were analysed by gas-liquid chromatography as described by Van Assche (1978).

RESULTS AND DISCUSSION

The experiments were started on fermentors in a steady state, having had a VFA reduction of ca. 95 ~o over at least 3 weeks (Table 2). All the disinfectants tested had no inhibitory effect on the methane digestion when applied at the normal dose (Fig. 1). For the disinfectants Tego 51 and NaOCI, dose 2 had no negative consequences. The biogas production was inhibited, respectively by 50 ~ and 100 ~ for Creolin and Dettol. The decrease was immediate for Dettol while the maximum decrease in gas production for Creolin occurred only after 6 days. The methane content of the biogas dropped from 72 ~ to 62 ~ . Coupled with the decrease in gas

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Disinfectants and antibiotics in methane digesters 243

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Disinfectants and antibiotics in methane digesters 245

production, Creolin caused an increase of VFA ranging from 310mg litre- 1 to 4250 mg litre - 1 and an increase in CODs from 6150 mg litre - ~ to 9800 mg litre-1 (Table 2). In a subsequent experiment, Dettol was tested at half of dose 2. Immediately, a decrease of the biogas production of 50~o was noted. Furthermore, this decrease continued until a completely acidified fermentor was produced. Microscopic examination showed that the fluorescent bacteria decreased proportionally to the biogas production.

In the experiments with antibiotics, three doses were tested successively (Table 1). The digestion was not disturbed by the following antibiotics: chlortetracyclin, tylosin, erythromycin and chloramphenicol. On the other hand, the application of dose 3 for bacitracin and virginiamycin gave a large decrease in biogas production (Fig. 2). After only 2 days a decrease of 49 ~ for virginiamycin and 19 ~ for bacitracin was registered. With reference to the control, the maximum inhibition amounted to 87 for virginiamycin after 4 days and 86 ~ for bacitracin after 6 days. In these experiments, the decrease of gas production was coupled with an increase in VFA and CODs. The VFA content rose from 1130 mg litre- 1 to 4750 mg litre- ~ for virginiamycin and from 670 mg litre - ~ to 7400 mg litre- ~ for bacitracin. Propionic and butyric acid accumulated. The COD values increased from 6100 mg litre- 1 and 8600 mg litre - ~ to 16 400 mg litre -I and 17100mglitre -~ for bacitracin and virginiamycin, re- spectively (Table 3). Microscopic examination again showed the concomitant reduction of the fluorescent microbial species.

These experiments confirm that the application of antimicrobial agents, such as disinfectants and antibiotics, can indeed inhibit the digestion of piggery waste. For the disinfectants, the doses normally used in practice do not influence biogas production. However, higher doses of disinfectants containing phenols have inhibitory effects on the methane fermentation.

This is in accordance with the results of Pearson et al. (1980) who found that a shock-loading of 500mg per litre of phenol could decrease methanogenic activity by 50 ~o.

Purser et al. (1965), O'Connor et al. (1970), Fuller & Johnson (1981), Varel & Hashimoto (1981) and Hilpert et al. (1982) have reported accumulation ofpropionic acid and a decrease in gas production upon the application of antibiotics to methane digestions. The results of this study yield more specific information on the critical concentrations of these compounds for digesters treating piggery manure.

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Disinfectants and antibiotics in methane digesters 247

It can be concluded that, when antibiotics and disinfectants are used on piggery farms at normal doses, no detrimental influence on the gas production has to be feared. However, it is advisable to use those antimicrobial agents that have the lowest potential risk, particularly if repeated applications should be necessary. In this respect, the disinfectants Tego 51 and NaOC1, and the antibiotics, chlortetracyclin, tylosin, erythromycin and chloroamphenicol, appear to pose the lowest risks.

A C K N O W L E D G E M ENTS

Thanks are expressed to the Board of Administrators and the Direction of the Belgian Institute for the Encouragement of Scientific Research in Industry and Agriculture ( IWONL, Brussels) which subsidised this research.

R E F E R E N C E S

Fuller, J. R. & Johnson, D. E. (1981). Monensin and lasalocid effects on fermentation in vitro. Journal of Animal Science, 53, 1574-80.

Hilpert, R., Winter, J. Kandler, O. (1982). Feed additives and disinfectants as inhibitory factors in anaerobic digestion of agricultural wastes. In: Energy from biomass (2nd edn). E.C. Conference, London and New York, Applied Science Publishers, 552-8.

O'Connor, J. J., Meyers, G. S., Maplesden, D. C. & Vandernoot, G. W. (1970). Chemical additives in rumen fermentations: In vitro effects of various drugs on rumen volatile fatty acids and protozoa. Journal of Animal Science, 30, 812-18.

Pearson, F., Shiun-Chung, C. & Gautier, M. (1980). Toxic inhibition of anaerobic biodegradation. Journal of Water Pollution Control Federation, 52, 472-82.

Purser, D. B., Kloppenstein, T. J. & Cline, J. H. (1965). Influence of tylosin and aureomycin upon rumen metabolism and the microbial population. Journal of Animal Science, 24, 1039-44.

Standard Methods for the Examination of Water and Wastewater (1971) (13th edn). American Public Health Association, New York, Method 220.

Van Assche, P. (1978). Taxonomische studie van de Bacteroidaceae en van de dominante species bij de big. PhD Thesis, State University Gent, Belgium, 237 pp.

Varel, V. H. & Hashimoto, A. G. (1981). Effect of dietary monensin or chlortetracycline on methane production from cattle waste. Applied and Environmental Microbiology, 41, 29-34.