JOURNAL OF FERMENTATION AND BIOENGINEERING Vol. 79, No. 4, 398-399. 1995

Biomethanation of Cheese Whey Using Anaerobic Upflow Fixed Film Reactor

PRITI PATEL, MANIK DESAI, AND DATTA MADAMWAR*

Post-Graduate Department of Biosciences, Sardar Pate1 University, Vallabh Vidyanagar-388120, Gujarat, India

Received 4 July 1994IAccepted 13 December 1994

Performance of anaerobic upflow fixed 6lm reactors for biometbanation of high-strength cheese whey using different support material such as charcoal, gravel, brick pieces, PVC pieces and pumice stones at 37’C has been studied. Among them the charcoal fixed film reactor showed the best performance when operated at 2 d hydraulic retention times (HRT), achieving maximum COD removal of 81% (COD intluent =70 g/Z) and improved total gas production (6.7 I/d/l digester) with high methane content (72%).

[Key words: cheese whey, biomethanation, fixed film reactor, anaerobic digestion, energy]

In India, a large number of dairies dispose of their wastes, especially cheese whey, into the environment in enormous quantities. Since cheese whey has a very high BOD of above 30,0OOmg/l, its disposal remains major problem. Anaerobic digestion of cheese whey offers an excellent solution in terms of. both energy conservation and pollution control consideration (1). In the past, there has been a much interest in the anaerobic digestion of cheese whey (1, 2). The major advantages of this process are low cost, high energy efficiency and process simplicity as compared to other waste treatment methods. However, despite these advantages, anaerobic digestion is not widespread in the dairy industry, largely due to the problems of slow reaction which requires longer hydraulic retention times (HRT) and poor process stability using a conventional reactor. In order to solve these problems and to develop a better methanogenic process, several configuration of high-rate anaerobic reactors have been developed for treating soluble waste- water at relatively short HRT (3, 4). Retention of the active biomass independent of waste flow is achieved in advanced reactors (4, 5) such as a fixed film reactor (4, 6) which allows efficient digestion of high- and low- strength (in terms of suspended solids and organic materials) soluble wastes at much shorter HRT.

The tied film reactor is capable of retaining active biomass in the reactor without the need for biomass recirculation. This capability becomes crucial under high organic loading conditions, because it allows the fixed film reactor to function efficiently without cell wash-out problem even at very high loading rates (6).

As a support for the growth of microorganisms, materials such as activated carbon and pumice stone have been reported (7, 8). However, the employment of anaerobic upflow fixed film reactor technology needs in- depth analysis of biofilm formation and its performance during the steady-state conditions. The present study was carried out to identify an appropriate support material for the anaerobic fixed film reactor.

Here we report the performance of an anaerobic fixed film reactor in terms of energy recovery from cheese whey and its stabilization using different support materi- als at various HRT.

Cheese whey was obtained from AMUL Dairy (cheese

* Corresponding author.

manufacturing unit), Anand, India, had the following properties (w/v): lactose, 4.8-5%; protein, 0.9-l. 1%; salts, 0.9-1.0%; lactic acid, 0.7-0.9%; COD, 6-8%; total solids, 5.0-5.5%; volatile solids, 4.5-4.9; most of the water soluble vitamins present, and pH4.5-5.0. pH of the influent was adjusted to 7.0 by addition of lime.

Twenty anaerobic upflow fixed film reactors were used in this study. Each reactor consisted of a glass column with a void volume of 1 I, packing height of 9OOmm and packing volume of 1.5 1. They were packed with one of the 5 bedding materials: charcoal, brick pieces, pumice stones, gravel and PVC pieces with an average size of 5 x5 x 5 mm (each in quadruplicate) and biofilms were allowed to develop on bedding materials using effluent from another operating whey reactor as initial inoculum. This initial inoculum was slowly replaced by fresh cheese whey which was filtered through muslin cloth to remove floe which was formed after adjusting pH 7.0 using lime. Steady-state condition was attained in 26 d in the case of charcoal, 30 d for gravel and brick pieces and 35 d for PVC pieces and pumice stones. Judgment was based on constant gas production and constant COD of effluent. Flow rate was adjusted with the aid of a peristaltic pump so that all reactors could be operated at 1 d HRT. Reactors were run at 37°C under the same set of condi- tions height, width, total volume, and amount of bedd- ing material and their average size-5 X 5 X 5 mm. All reactors were operated for 30d after reaching the steady- state condition.

Gas was collected and measured from the displace- ment of acidified saturated salt solution making due cor- rection for atmospheric pressure and temperature. Gas composition was analyzed with a CIC gas-liquid chro- matogram equipped with stainless-steel Chromosorb 2 column and a thermal conductivity detector (9). Feed and effluent samples were routinely analyzed for pH, volatile fatty acids (VFA), COD, total solids (TS) and volatile solids (VS) as per standard procedure (10).

Among the reactors examined, the highest total gas production was obtained in the reactor packed with char- coal (6.01/d/l digester), and the lowest in the one pack- ed with pumice stones (Table 1). Methane content was the highest in the charcoal fixed film reactor. This may be because charcoal provides a better surface for attach- ment of methanogens and other anaerobic bacteria, resulting in good biofilm development on the supporting

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TABLE 1. Steady-state profile of fixed film reactors using different bedding materials

Bedding material Total gas production Methane Volatile fatty acids COD

(I/d/l digester) (%) (g/0 (g/l) Charcoal 6.0+0.011 7OkO.66 0.82 16.4 Brick pieces 5.1 LO.020 68f0.83 0.93 19.7 Gravel 5.4+0.008 681k1.33 0.87 18.4 PVC pieces 4.3kO.013 67kO.16 1.06 21.2 Pumice stone 3.8kO.013 64t0.83 1.23 22.8

COD in influent is 70 g/l. HRT fixed at 1 d.

COD removal (%)

76.6 71.9 73.7 69.7 67.5

TABLE 2. Steady state profile of fixed film reactor charcoal as bedding materials at different hydraulic retention times (HRT)

HRT Total gas production Methane Volatile fatty acids COD COD removal (d) (Z/d/l digester) (%) (g/l) (g/l) (%)

pH of effluent

1 6.OkO.013 7OkO.83 0.82 16.4 76.6 6.9 2 6.7kO.020 72t0.33 0.70 13.4 80.9 6.8 3 6.6kO.026 69kO.66 0.80 13.3 81.0 6.0 4 6.4f0.033 66k0.16 0.94 13.3 81.0 6.0 5 6.4kO.026 64kO.33 0.99 13.1 81.5 5.6

COD in influent is 70 g/l.

media. This could be observed visually in the reactor. VFA ranged from 0.82 g/l to 1.23 g/l. Process stability evidenced by lower VFA is high in the charcoal fixed film reactor. Under steady-state condition, COD of the charcoal fixed film reactor effluent is 16.4g/l (COD of influent =70 g/r) indicating better process performance as compared to the pumice stone bed reactor (COD is 22.8 g/l). Similarly COD removal is the highest (76.6%) in the charcoal fixed film reactor followed by those of gravel, brick pieces, PVC pieces and pumice stone. An overall best performance is exhibited by the charcoal fixed film reactor.

It is known that all anaerobic digesters have a pH optimum around 7, and that a pH below 6 adversely affects waste degradation and methane formation. In all reactors studied here, pH remained constant during the steady-state condition, an indication of improved proc- ess performance. In all reactors studied here, high COD removal was achieved in general as compared to COD removal in a conventional anaerobic digester at shorter HRT (11).

Since best performance was shown by the charcoal fixed film reactor, it was used to determine the optimum HRT from 1 to 5 d. Increasing HRT from 1 to 2 d led to improved total gas production with higher methane content and decreased VFA to 0.70 g/l (Table 2). However, further increase in HRT neither improved total gas production nor reduced VFA. Process performance can be judged from COD values which reduced considerably when HRT increased from 1 to 2 d. However, upon further increase in HRT, COD reduction was negligible. Similar to our results, Wildenauer and Winter (2) have achieved 95% COD reduction at 5 d HRT using porous clay beads, however, we succeeded in achieving rapid anaerobic digestion of cheese whey by using a charcoal fixed film reactor at very short HRT (2 d) corresponding to a COD load of 35 g/d/l digester. Moreover % COD removal was improved markedly when HRT increased from 1 to 2d, suggesting higher efficiency in the bac- terial conversion of COD to methane gas. With further increase in HRT, the increase in % COD removal was negligible. On the other hand, at longer HRT pH values

decreases affecting the overall biomethanation process even though pH of the feed was adjusted to 7.0 by lime. This may be due to accumulation of VFA at longer HRT.

Thus our study proves that the anaerobic fixed film reactor with charcoal bed can be utilized for high- strength dairy waste management and energy recovery at relatively short HRT.

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REFERENCES

Lo, K. V. and Liao, P. H.: Two-stage anaerobic digestion of cheese whey. Biomass, 10, 319-322 (1986). Wildenauer, F. X. and Winter, J.: Anaerobic digestion of high-strength acidic whey in a pH-controlled up flow fixed film loop reactor. Appl. Microbial., 22, 367-372 (1985). Callender, I. 3. and Barford, J. P.: Recent advances in anae- robic digestion technology. Process Biochem., 18, 24-30 (1983). Lo, K. V., Liao, P. H., and Bulley, N. R.: Two phase meso- philic anaerobic digestion of screened dairy manure using con- ventional and fixed film reactors. Agric. Wastes., 17, 279-291 (1986). van den Berg, L. and Kennedy, K. J.: Comparison of advanced anaerobic reactors. In Proceedings of the 3rd International Symposium on Anaerobic digestion, p. 14-18, Wenntworth, R. L. (ed.), Boston, Massachusetts, USA (1983). Liao, P. H. and Lo, K. V.: Methane production using whole and screened dairy manure in conventional and fixed film reactor. Biotechnol. Bioeng., 27, 266-272 (1985). Minami, K., Horiyama, T., Tasaki, M., and Tanimoto, Y.: Methane production using a bioreactor packed with pumice stone on an evaporator condensate of a kraft pulp mill. J. Ferment. Bioeng., 64, 523-532 (1986). Andrews, G. F. and Tien, C.: Bacterial film growth on adsorb- ent surfaces. Al. Che. Journal., 27, 396-402 (1981). Varel, V. H., Hashimoto, A. G., and Chen, Y. R.: Effect of temperature and retention time on methane production from beef cattle waste. Appl. Environ. Microbial., 40, 217-222 (1980). APHA: Standard methods for the examination of water and waste water, 14th ed. American Public Health Association, Washington, DC (1976). Desai, M., Patel, V., and Madamwar, D.: Effect of tempera- ture and retention time on biomethanation of cheese whey- poultry waste-cattle dung. Environ. Poll., 83, 311-315 (1994).