Biotechnology Letters Vol 6 No 11 747-752 (1984)

HIGH RATE ANAEROBIC DIGESTION OF PIGGERY MANURE WITII POLYURETHANE SPONGES AS SUPPORT MATERIAL

J. POELS+, P. VAN ASSCHE and W. VERSTRAETE

Faculty of Agricultural Sciences State University Gent, Coupure links 6.53 9000 GENT BELGIUM

&.,I ,$@y : 'l'he use of polyurethane foam sponges to colonize methanoge- nit associations for the digestion of piggery manure has been invcs- tigated. Fermentors containing polyurethane pads as colonization ma- trix reacheLI a biOgaS p~OdLlctiOIl rate Of Ca. 2.0 litTeS per 1itI-e ?XF- actor per day (30-33"C, hydraulic retention time 7.5 days) and a bio- gas yield of 16 litres per litre piggery manure (7-930 TS). Corrcs- ponding control fermentors containing no pads reached a gas produc- tion rate of 1.3 litres per litre reactor per day and only a-bout 10 litres oiogas per litrc piggery manure.

INTRODUCTION

The applicability of biogas production from piggery manure depends on the first place upon the possibility of using the biogas directly on site. The second important factor IS the rate of production of biogas per unit reactor volume. However, the amount of biogas obtained per lmit of manure digested shol~id not be sacrificed because otherwise the energy balance of the total system decreases drastically (Poels et al., 19841. A higher level of microbial biomass in the methane reactor can be sup- ported on a wide variety of support materials such as glass beads, vol- canic rock, wood bark (Salkinoja-Salonen et al., 1982), red drain tile clay, grey potters clay (Van den Berg and Kennedy, 1981; Murray and Van de Berg, 196.11 or stainless steel wire mesh (Good et al., 1982). Lynn and Whitmore (1982) investigated the colonization of reticulate<1 polyurethane (PIJR) foam as a means of increasing the rate of methane production; Huysman et al. C1983a, 1983b) also reported reticulated polyurethane foam as an excellent colonization matrix. These experi- ments generally relate to liquids with low suspended solids concentra- tions. This report deals with the influence of reticulated polyuretha- ne foam in the production of methane from piggery manure (7-9% dry mat- ter, 60-75 g suspended solids per litre).

Reactors. Two conventional laboratory fermenters with a working diges- ter volume of 1.5 litres were set up. One fermentor served as a con- trol, while the other one was equipped with PUR support matrixes. Gas production was measured by water displacement. The digesters wcrc fed twice daily and manually mixed two times a day. The incubation tempe- rature was 30 5 2°C. Substrate. __--- Piggery manure from fattening pigs, containing 7-9% dry matter, was u ed. -7 The levels of particulate organic matter ranged from 60 to 75 g.l ; total COD was 110-140 g.1 of which ca. 25% was soluHe (CODS) .

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Support material. Reticulated polyurethane (PUR) foam was type T 40 (Recticel, Wetteren, Belgium) with 40 pores per inch, average pore dia- meter of 0.43 mm, porosity 97%, density 30 kg/m3, specific surface ca. 600 m2/m3 matrix. The PUR foam pads had a size of 2 x 2 x 2 cm. One fermentor recieved 20 of these pads, a total volume of 160 ml or 10% of the working digester volume. Analyses. Gas analyses were performed on an Intersmat IGC 120 MB gas chromatograph, with a catharometer detector and a dual column arrange- ment of Porapak Q (go-100 mesh) and a molecular sieve 5 A. Volatile fatty acids were analyzed according to Holdeman et al. (1977) on a capillary gas chromatograph, Carlo Erba Fractovap 4160 equipped with a FID detector, on a FFAP column of 25 m, with H2 as carrier gas. Total fatty acids was estimated by steam distillation according to Deutsche Einheitsverfahren zur Wasseruntersuchung (1972). The total chemical oxygen demand (CODt) was measured according to the Standard Methods (1971). COD soluble (COD > was determined aftercentrifugation at 20 000 g for 10 minutes. The ?otal solids (TS) and the suspended solids (SS) after centrifugation at 20 000 g for 10 minutes were ana- lyzed according to Merck (1973). Microscopy. Microscopic enumeration of the methanogenic bacteria was estimated using a Petroff Hausser counting chamber with epifluorescen- ce illumination on a Polyvar microscope.

RESULTS AND DISCUSSION

Three test periods of 3 months each, with different process parameters, have been analyzed. Steady state conditions were reached about 4 weeks after imposing the process conditions. During the last 6 weeks of each test period, analyses of the various process parameters were performed. Hydraulic retention times of 15, 10 and 7.5 days with corresponding loading rates of 7.8, 13.2 and 14.6 g CODt per litre reactor per day, were applied. Figure 1 shows biogas productions, expressed as 1 bio- gas per 1 influent, during steady state conditions for the 3 retention times considered. The methane content of the biogas, analyzed at regu- lar times, varied between 65-70%. At a hydraulic retention time of 15 days, the gas productions of the control reactor and the reactor con- taining PUR sponges did not differ significantly (Table 13, but on de- creasing the hydraulic retention time to 10 days, the biogas yield of the PUR reactor continued at 19 1 per 1 influent, while the gas pro- duction of the control reactor decreased to 15 1 per 1 piggery manure, This effect was even more pronounced at a hydraulic retention time of 7.5 days; the control fermentor produced only 10 1 biogas per 1 influ- ent compared to 16 1 for the PUR fermentor. The influence of the pads was, when analyzed by a t-test on paired observations, significant at both 10 and 7.5 days retention time. Table 1 also shows that the bio- gas production rate of the PUR reactor increased at shorter hydraulic retention times. For the control reactor a slight increase from 1.3 to 1.5 l/l.d was obtained when lowering the retention time from 15 to 10 days, but at a hydraulic retention time of 7.5 days the gas produc- tion rate dropped to 1.3 l/l-d. The VFA-reductions decreased from 85 to 76 and to 25% respectively for the control fermentor at hydraulic retention times of 15, 10 and 7.5 days. For the PUR fermentor, a re- duction from 89% to 70% was noticed when the hydraulic retention time was lowered from 15 to 7.5 days. The reduction of COD decreased in a similar way (Table 1). Clearly it was not possible 50 maintain an

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HYDRAULIC RETENTION TIME 15 DAYS

HYDRAULIC RETENTION TIME 10 DAYS

HYDRAULIC RETENTION TIME 7,5 DAYS

II 1 n 2 3

cl CONTROL

II 4

WEEKS

1 i WEEKS

1 ; WEEKS

FIGURE 1 : Biogas production of complete mixed slurry fermentors

without and with PUR sponges.

Each experimental ,run was followed for a period of

6 tieeks under steady state conditions.

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TABLE 2. VFA analyses of influent and effluent of fermentors with a hydraulic retention time of 7.5 days

Acid (meq.l-l)

Influent Effluents

Control PUR

Acetic 136.52 68.91 51.34

Propionic 26.41 53.81 4.38

Iso-butyric 3.54 0.27 0.17

Butyric 6.95 2.70

Iso-valeric 3.19 8.76 0.28

Valerie 1.29 0.27

TOTAL 177.86 134.86 56.17

- Not detectable

a b

FIGURE 2 : Epifluorescence micrographs of Methanogenic cocci (x 1200).

a. Mixed liquor control fermentor, containing 1.1 x 106 fluorescent cocci per ml liquor.

b. The inside of a PUR sponge, containing 2.2 x 108 fluo- rescent cocci per ml liquor pressed out of the matrix.

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efficient digestion at 7.5 days hydraulic retention time without PUR support material. By comparing the VFA-spectrum of the effluents at a 7.5 days hydraulic retention time (Table Z), it is quite clear'that there is a strong accumulation of propionic acid in the control reactor; the difference between the acetic /propionic acid ratio of the control fenentor and the PUR fermentor clearly demonstrates the positive ef- fect of the PUR carrier. Figure 2a shows the distribution of the me- thanogenic bacteria present in the mixed liquor of the control fermen- tor . Figure 2b illustrates the methanogenic colonization inside a PUR particle and demonstrates the intense fluorescence of irregular met%- zgi; yi $q 'croscopic enumeration revealed numbers of 1.1 x 10

. respectively; the morphology is quite typical for the methanogenic pipulation of pig manure digesters. These observa- tions are in accordance to Huysman et al. (1983a) who reported a rapid and dense colonization of reticulated polyurethane foam in upflow re- actors treating dilute wastewater. The results show that it is pos- sible to colonize PUR-sponges in completely mixed reactors digesting concentrated piggery manure. Indeed, at hydraulic retention times of 7.5 days and a volumetric loading rate of 14.6 g CO

f per litre reactor

per day, the rate of the biogas production amounted o ca. 2.0 1 per litre reactor per day with a yield of 16 litres per litre pig manure. Further research to explore the use of PLJR-pads in full scale design and operation of manure digesters appears warranted.

ACKNOWLEDGEMENT

These investigations were supported by the IWONL (Instituut tot Aanmoe- diging van het Wetenschappelijk Underzoek in Nijverheid en Landbouw), Brussels, Belgium.

REFERENCES

Deutsche Einheitsverfahren zur Wasseruntersuchung (1972) 3th ed.Verlag Chemie, Weinheim.

Fynn, G.H. and Whitmore, T.M. (1982). Biotech. Letters, 4, 577-582. Good, P., Moudry, R. and Fluri, P. (1982). Biotech. Letters,4,595-600. Holdeman, L-V., Cato, E.P. and Moore, W.E.C. (1977). Anaerobic Labo-

ratory Manual, 4th ed. Virginia Polytechnic Institute and State University, Blacksburg, Virginia.

Huysman, P., Van Meenen, P., Van Assche, P. and Verstraete, W. (1983a). Biotech. Letters, 5, 643-648.

Huysman, P., Van Meenen, P., Van Assche, P. and Verstraete, W. (1983b). Proceedings Anaerobic Waste Water Treatment, 23-25 November 1983, Noordwijkerhout, Netherlands, p.187-200.

Merck, E. (1973). Die Untersuchung von Wasser. Darmstadt. Murray, W.D. and Van den Berg, L. (1981). J. Appl. Bact.,Sl, 257-265. Poels, J., Neukermans, G., Debruyckere, M. and Verstraete, W. (1984).

Revue de l'Agriculture, 37, 17-27. Salkinoja-Salonen, M., Hakulinen, R., Valo, R. and Apajahali, J.(1982).

International Association Water Pollution Research Specialized Semi- nar, June 16-18, Copenhagen, Denmark.

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

Van den Berg, i. and Kennedy, K.J. (1981). Biotech. Letters,3,165-170.

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