Biomass 10 (1986) 319-322

Short Communication

Two-stage Anaerobic Digestion of Cheese Whey

ABSTRACT

A two-stage digestion of cheese whey was studied using two anaerobic rotating biological contact reactors. The second-stage reactor receiving partially treated effluent from the first-stage reactor could be operated at a hydraulic retention time of one day. The results indicated that two-stage digestion is a feasible alternative for treating whey.

Key words: Anaerobic digestion, two-stage, rotating biological contact reactors, cheese whey.

INTRODUCTION

Cheese whey is a by-product of cheese production. It has a chemical oxygen demand (COD) in the range of 60000 to 80000 mg litre-J which often causes problems for disposal. Anaerobic digestion offers an excellent approach from both energy conservation and pollution control considerations.

Using anaerobic biological fluidized bed reactors to generate methane from acid whey, Hickey and Owens ~ observed that total COD removal efficiencies were higher in a system with two reactors operating in series than that with one reactor at the same loading rate. Clanton et al., 2 also found that the digesters fed with the effluent from other digesters main- tained a pH greater than 8"0 without addition of base and produced biogas containing 90% methane. Once the digesters were switched back to raw whey, the pH gradually declined. Using an anaerobic rotating biological contact reactor (AnRBC) to treat cheese whey, Lo and Liao 3 demonstrated that stable operation and high treatment efficiency could be obtained utilizing two reactors in series (two-stage digestion system). This study was initiated to further investigate a two-stage digestion of cheese whey using AnRBC.

319 Biomass 0144-4565/86/S03.50- © Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain

320 K. V. Lo, f: H. Liao

MATERIALS A N D METHODS

Cheddar cheese whey was used in this study. The design and operation of the AnRBC reactors have been reported in detail previously?

Full strength whey was digested using both reactors (AnRBC 1 and 2) operated concurrently at a hydraulic retention time (HRT) of 6 days. Although the maximum methane production rate of 3-26 litres C H 4

litre-~ day-~ was obtained at a HRT of 5 days in a previous study, a stable and high effluent pH was maintained for the reactors operated at a HRT of 6 days. At the beginning of this study, both AnRBC 1 and 2 were operated as a single-stage reactor. Then the two reactors were operated in series. The effluents collected from both the AnRBC 1 and 2 (first-stage) were then fed into AnRBC 2 operated as the second-stage reactor.

Effluent and gas samples were collected for three consecutive days during steady-stage conditions at each HRT. The steady-state was defined as the period of time at which gas production rates were constant (+ 5%). Total solids (TS), volatile solids (VS), COD, pH, total Kjeldhl nitrogen (TKN) and ammonia-nitrogen (NH3-N) were determined according to 'Standard Methods'. 4 Gas samples and volatile fatty acids (VFA) contents were analyzed on a Hewlett Packard 5890 gas chromatograph.

RESULTS A N D DISCUSSION

Fed with screened dairy manure, the AnRBC could be operated at a HRT as low as one day. 5 However, steady-state operation could not be maintained for AnRBC reactors receiving either full strength or diluted whey at HRTs shorter than 5 days? Hence, a two-stage digestion system was set-up to further investigate the anaerobic digestion of cheese whey. Effluent from the first-stage reactors (AnRBC 1 and 2) was used as the substrate for the second-stage (AnRBC 2). Prior to the commencement of this study, both AnRBC 1 and 2 had been in operation for a period of 30 and 16 months, respectively. Sufficient microbial biomass was already present on the surfaces of the discs and inner walls of the reactors. The effective working volumes were 3"65 and 3.70 litres for AnRBC 1 and 2, respectively. The experimental conditions and steady- state performance data are summarized in Table 1. The results indicated that AnRBC 2 had better organic removal efficiency than did AnRBC 1 for the first-stage reaction. In a previous study, 3 methane production rates ranging from 2.83 to 3-10 litres C H 4 litre -~ day -~ and 0.304 to

Two-stage anaerobic digestion of cheese whey

TABLE 1 Methane Production From Two-Stage Digestion System

321

Operations, conditions First stage Second stage First stage Second stage and results (AnRBC 1) (AnRBC 2) (AnRBC 2) (AnRBC 2)

HRT (day) 6 1 6 1 Loading rate

(gVS l i t re- l day 1) 8"13 6'64 7"95 5"91 (g COD litre-~ day- i) 10-62 16.50 10.38 11.32

Methane production rate (litres CH 4 litre- 1 day- ~) 1-95 +- 0.23 0'98 _+ 0.02 2-56 +- 0.24 0.98 +_ 0.04

Methane yield ( l i t resCH4g - l VSadded) 0.240_+0.028 0.148+_0.003 0 .322+0.030 0-166+-0.007

Methane content (%) 39-3 _+ 1 "8 57.5 _+ 0"5 42.2 _+ 1 "2 63"4 +- 1"8 Influent characteristics

pH 4-4 +_ 0-1 TS (%) 5.76 +_ 0-07 VS (%) l i tre- 1 4.97 _+ 0"28 COD (rag litre- ') 64'9 +_ 0"55 VFA (mg l i tre- l)

Acetic 346 _+ 75 Propionic 207 +_ 120 Butyric

Effluent characteristics pH 7"0 _+ 0"3 TS (%) 1.54 + 0.01 VS (%) 0-91 _+0.02 COD (mg li tre- L) 22.3 + 2.8 VFA (mg li tre- i)

Acetic 1460 +_ Propionic 530 +_ Butyric 717 _+

7-0+0-3 4"4+-0-1 7'3-+0"3 1 "54 -+ 0"01 5'76 -+ 0"07 1"43 _+ 0"02 0'91+-0-02 4"97+_0-28 0"83+_0'03 22"3_+2"8 64"9_+0-55 15"3+_ 1"3

1460+-127 346+-75 1780+_476 530_+ 141 207+_ 120 406.3+_ 126 717 +339 - - 478 +_ 112

7"3_+0'1 7-2+-0'3 7'4+_0"1 1'42 +_ 0"09 1'43 _+ 0'02 1"34 +- 0'04 0'80+_0.10 0"83+0"03 0"74+0 '04 16'8+_3.2 15.3_+1.3 12.5+2.3

127 1249_+370 1780+476 7 4 9 + 6 3 141 289_+33 406.3+_ 126 187+2-1 339 290+ 106 478+ 112 29.3_+6-6

0"328 litres C H 4 g- ~ VS added were achieved for AnRBC 1 at a HRT of 6 days, loading rates of 9.28 to 9"60 g VS litre- ~ day -~. Similar methane production rates were obtained for AnRBC 2, however, much lower gas was produced for AnRBC 1 in this study. This might have been due to the biofilm age. Studying the AnRBC process, Laquidara, Blanc and O'Shaughnessy ~' indicated that the amount and type of microbial biomass is a function of the biofilm age, temperature, substrate composi- tion, differential velocities between support media and bulk fluid, abra- sion by foreign particles and media material. The amount and type of microbial biomass also influences mass loading rate and performance of reactors.

322 K. V. Lo, P. H. Liao

AnRBC 2, receiving partially treated anaerobic reactor effluents, resulted in improved stability and higher biogas methane composition. AnRBC receiving either full strength or diluted whey could not be operated at HRTs shorter than 5 days? It is significant that the second- stage reactor (AnRBC 2) receiving partially treated effluent could be operated at a HRT of one day. This result also indicated that better gas production and treatment efficiency could be obtained with an appro- priate pH adjustment in the digestion process.

It is concluded that two-stage anaerobic digestion of whey using AnRBC reactors could provide a commercial process for rapid waste treatment and energy production.

ACKNOWLEDGEMENT

The authors express their gratitude to Fraser Valley Milk Producers Association at Abbotsford, British Columbia, Canada, for supplying cheese whey. The technical assistance of Adeline Chen is gratefully acknowledged.

REFERENCES

t. Hickey, R. F. & Owens, R. W. ( 1981 ). Methane generation from high-strength industrial wastes with the anaerobic biological fluidized bed. Biotechnology and Bioengineering Symposium, 11,399-413.

2. Clanton, C. J., Goodrich, P. R., Morris, H. A. & Backus, B. D. (1985). Anaerobic digestion of cheese whey. Proceedings oflnternational Symposium on Agricultural Wastes, 5,475-82.

3. Lo, K. V. & Liao, P. H. (1986). Digestion of cheese whey with anaerobic rotating biological contact reactors. Biomass. (in press).

4. APHA American Public Health Association (1975). Standard Methods for the Examination of Water and Wastewater, 14th edition, APHA, AWWA, WPCF, Washington, DC.

5. Lo, K. V., Chen, W. Y. & Liao, E H. (1986). Mesophilic digestion of screened dairy manure using anaerobic rotating biological contact reactor. Biomass, 9, 81-92.

6. Laquidara, M. J., Blanc, F. C. & O'Shaughnessy, J. C. (1986). Development of biofilm, operating characteristics and operational control in the anaerobic rotating biological contactor process. Journal of Water Pollution Control Federation, 58, 107-14.

K. V. Lo and P. H. Liao Department of Bio-Resource Engineering, University of British Columbia, Vancouver, B.C. V6 T1 W5, Canada

(Received 1 August 1986; accepted 3 August 1986)