anaerobic digestion of cheese whey using up-flow anaerobic sludge blanket reactor

Biological Wastes 27 (1989) 289-305

Anaerobic Digestion of Cheese Whey Using Up-flow Anaerobic Sludge Blanket Reactor

J. Q. Y a n

Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, People's Republic of China

K. V. Lo* & P. H. Liao

Department of Bio-Resource Engineering, University of British Columbia, Vancouver, British Columbia, Canada V6T lW5

(Received 15 December 1987; revised version received 13 June 1988; accepted 17 June 1988)

A B S T R A C T

Anaerobic treatment o f cheese whey using a 17.5-1itre up-flow anaerobic sludge blanket reactor was investigated in the laboratory. The reactor was studied over a range o f influent concentration from 4"5 to 38.1 g chemical oxygen demand per litre at a constant hydraulic retention time o f 5 days. The reactor start-up and the sludge acclimatization were discussed. The reactor performance in terms o f methane production, volatile fa t ty acids conversion, sludge net growth and chemical oxygen demand reduction were also presented in this paper. Over 97% chemical oxygen demand reduction was achieved in this experiment. At the influent concentration o f 38.1g chemical oxygen demand per litre, an instability o f the reactor was observed. The results indicated that the up-flow anaerobic sludge blanket reactor process could treat cheese whey effectively.

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

With the increasing interest in anaerobic t reatment process of organic waste, new reactor technologies have been developed for improving the t reatment

* To whom correspondence should be addressed. 289

Biological Wastes 0269-7483/89/$03"50 © 1989 Elsevier Science Publishers Ltd, England. Printed in Great Britain

290 J. Q. Yan, K. V. Lo, P. H. Liao

efficiency. The up-flow anaerobic sludge blanket (UASB) reactor is one of the innovative reactor designs that permit high organic loading rates (Lettinga et al., 1979).

Although the application of UASB in the treatment of municipal and industrial wastewaters has been widely reported (Lettinga et al., 1985; Wang et al., 1985), few studies on treating acidic substrates are available (Wu & Zhang, 1983; Samson et al., 1984). In the acidic environment, a massive growth of filmentous bacteria may produce a bulky sludge with poor settleability resulting in a low treatment efficiency (Brummeler et al., 1985). Lettinga et al. (1979) suggested that improper procedures used in the UASB start-up period could lead to the development of sludge with low specific activity and poor settleability.

Cheese whey acidifies easily and frequently causes problems in the biological treatment process. Anaerobic digestion of cheese whey using different reactor configurations has been reported (Switzenbaum & Danskin, 1982; Nordstedt & Thomas, 1984; Samson et al., 1984; Williams, 1984; Wildenauer & Winter, 1985; Lo & Liao, 1986). The problems encountered in this process were assumed to be caused by inadequate buffering capacity and micronutrients deficiency. Examining the effects of medium and inoculum on the digestion of whey and cellulose in an anaerobic fixed-bed reactor, Norstedt & Thomas (1984) found that without pH control, the reactor could not achieve stable operation within 30 days. Marshall & Timbers (1982) reported that a 500-1itre pilot-scale fixed-film reactor receiving full strength whey needed the addition of NaOH for pH control. Lo & Liao (1986) observed that the anaerobic rotating biological contact reactor (AnRBC) fed with cheese whey could not sustain a stable operation at hydraulic retention times (HRT) shorter than 5 days. Similarly, a minimum retention time of 5 days was needed in a pH-controlled fixed-film reactor (Wildenauer & Winter, 1985).

In order to further investigate the anaerobic treatment of cheese whey, the UASB process was chosen for this study. The main objectives of this study were to (1) study the start-up of the UASB reactor and (2) evaluate the treatment efficiency in terms of COD reduction.

METHODS

Reactor

The schematic diagram of the UASB system is presented in Fig. 1. The reactor was made of acrylic plastic pipe with an inner diameter of 11"5 cm (4.5 in) and a height of 168 cm (60 in). The total volume and working volume

Anaerobic digestion of cheese whey 291

BIOGAS

BIOGAS

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FEED TANK

of the reactor were 17.5 and 14.3 litres, respectively. A series of sampling ports were fitted at intervals on one side of the reactor to permit sampling of the sludge. A three-phase separator was located at the top of the reactor. The whey stored in a refrigerator at 4°C was introduced continuously into the bottom of the reactor by a peristaltic pump and the effluent left the reactor at the top of the settling chamber. The gas bubbles produced rose to the top o f the reactor and were separated by the separator and then let out of the reactor. The biogas production was measured with a wet gas metre. Fermentation temperature was maintained at 33 -I- I°C using a thermostatic- ally controlled, external electric heater.

Feed substrate

Cheddar cheese whey was used in this study. The composition of the whey is shown in Table 1.


TABLE l Composition of Cheese Whey

TS 5.66-5.89% VS 4.52-4,70% COD 64-67 g litre- 1 TKN 2 750-3 050 mg litre- NH3--N 2-80-2"95 mg litre- 1 Nitrate 0.45-0-70 mg litre- 1 TP (Total phosphorus) 338-356 mg litre- 1 VFA 6-450 mg litre- t pH 4-6

In this study, sod ium b i ca rbona t e and po tass ium h y d r o g e n p h o s p h a t e were added to the cheese whey as a buffer and a nu t r ien t supplement , respectively. T h e compos i t i on o f the feed so lu t ion is p resen ted in Tab le 2. S o d i u m hyd r ox ide so lu t ion was used to adjust the p H value o f the whey (which ranged f rom 4.0 to 6.4) to 7-0.

Seed sludge

T he seed sludge was ob t a ined f r o m the effluent o f a l abora to ry - sca le anae rob i c ro ta t ing biological con tac t r eac to r (AnRBC) used for the t r e a tm e n t o f a mix tu re o f cheese whey and manure . This effluent was acc l imated by feeding with 200 ml o f cheese whey dai ly fo r 20 days in a glass bott le . T h e n 4 litres o f this subs t ra te con ta in ing 3 % T S a n d 2 .1% VS was seeded in to the U A S B reactor .

TABLE 2 Composition of Feed Solution

2 g NaHCO3 6.6 g K2HPO 4 1 g NH4CI 0.04 g F e 3 +

0"01 g Mg 2 + Cheese whey ° Tap-water ° NaOH (adjust feed pH to 7"0) Total volume: 14 litres

° The amount used depended on the influent concentrations that were chosen in the experiments.


Reactor operation

An H R T of 5 days was maintained throughout this study; however, the influent concentrations were increased step-wise from 5.0 to 9-93, 17.7, 28.8 and 38.1 g COD litre-1, then decreased to 7"30g COD litre-1. Finally the reactor was operated at the concentration of 21-5 g COD litre-1.

The reactor operation was commenced at an influent concentration of 5.0 g litre- 1 and the start-up period was ended at an influent concentration of 9.93 g COD litre- 1. The first 48 days are considered as a period of start-up in this study. An operating period of 2-3 HRT was maintained for each subsequent increment of influent concentration.

Analysis

Analyses conducted on the influent and effluent were total solids (TS), total suspended solids (TSS), volatile suspended solids (VSS) and ash content according to the Standard Methods (APHA, 1975). Chemical oxygen demand (COD) was determined by the colorimetric method (Knechtel, 1978). Both gas composition and volatile fatty acids (VFA) were analysed on a Hewlett Packard 5890A gas chromatograph. Total Kjeldahl nitrogen (TKN) and ammonia nitrogen (NHa--N) were determined using a block digestor and a Technicon Auto Analyzer II (Schulmann et al., 1973).

Effluents and biogas were collected and analysed daily. Influent was analysed once every 4 days, except N H 3 - - N and TKN were determined once for each loading rate. Biomass concentration was analysed twice for each loading rate.

RESULTS AND DISCUSSION

Reactor start-up

When the UASB reactor was started at an influent concentration of 5 g COD litre- 1 and a H R T of 5 days, the organic loading rate to the reactor was 1-01 g COD litre- 1 day- 1. Four litres of the seed sludge were introduced into the reactor, the corresponding sludge loading rate was 0.164 g COD g VSS- 1 day- 1. The organic loading rates were increased step-wise, after the VFA concentrations were well eliminated in the digestion system. The first 48 days were considered as the start-up period, two influent concentrations (5-0 and 9.93 g COD litre-1) were used in this period.

Results of the UASB performance during the start-up period are shown in Fig. 2.


Fig. 2.

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Reactor performance data during start-up period. Key to Fig. 2(A): O = acetic acid; /~ = propionic acid; • = total VFA.

Anaerobic digestion of cheese whey 2 9 5

Figure 2(a) shows the effluent VFA concentration vs the time of reactor operation. The contents of acetic and propionic acids decreased significantly with time of reactor operation. For example, acetic acid reduced from 180 to 60 mg litre- ~ from day 2 to day 20. In the same period of time, propionic acid decreased from 360 to 260 mg litre- z. As a result of VFA reduction, effluent pH gradually increased from 6-4 to 6.7.

The same trend of increasing efficiency in terms of COD removal and gas production was also observed, as shown in Fig. 2(B), (C) and (D). Within the first 40 days, effluent COD was reduced from 1500 to 110 mg litre- 1, and the COD removal efficiency increased from 70 to 97%. In the meantime, methane composition increased from 48 to 57%. The gas production rate reached a value of 2.5 litres CH 4 litre feed -~ day - t within 15 days and remained at approximately the same level under the same loading rate.

Figure 2 also shows that the lowest effluent VFA, the highest CH 4 content of the biogas and the highest COD removal were reached after 40 days of operation. However, the highest gas production rate was reached much earlier at day 15.

The amount of sludge was monitored by measuring the VSS profile along the height of reactor and VSS content in the effluent. The effluent VSS concentrations are shown in Fig. 3. Due to the poor settling quality of the seed sludge, a large amount of sludge left the reactor at the beginning of the operation. After 15 days of operation, the amount of sludge remaining in the reactor was reduced from 86 to 60 g VSS. However, the sludge settleability improved gradually. At day 15, 67.2 g VSS of seed sludge were added to the

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reactor to maintain specific activityofthe sludge. At day 30, the TSS content in the effluent was as low as 0-1 g litre -1.

The use of the UASB process is dependent on good sludge floc formation. The procedure of start-up was important for the development of active sludge with both high specific activity and settleability. Considerable attention has been directed to the start-up ofa UASB reactor (Lettinga et al., 1979, 1985; De Zeeuw & Lettinga, 1980; HulshoffPol et al., 1983; De Zeeuw, 1985; Wu et al., 1985). Starting with a poor quality digested sewage sludge, De Zeeuw (1985) was able to cultivate a highly active biomass (specific activity of 0.75 g COD g VSS-x day-1) within a period of 6 weeks (organic loading rate of 7.5 g COD litre- 1 day- a).

Compared to the sewage sludge used by De Zeeuw (1985), the seed used in this study had a lower VSS content and poorer settleability. This was demonstrated by the loss of the sludge (Fig. 3), high FVA concentrations and low gas production (Fig. 2) in the beginning of the start-up. However, the seed was able to degrade acetate and propionate resulting in very low effluent VFA concentrations within a period of 40 days, reaching 0.711 g COD g VSS - 1 day- 1 of specific activity after an operation period of 70 days. The results indicated that the initial sludge loading rate (range of 0.2-0"4 kg COD kg VSS -1 day -1) and the organic loading increment sizes were important parameters for start-up. Too rapid an increase of the organic loading may result in the loss of specific activity of the sludge. The loading rate can be increased only after the VFA concentration is well removed by the process. The indicators of primary adaption of sludge were the effluent acetic and propionic acids contents (Fig. 2). The results indicated that the highest specific methane production rate as well as the highest methane content in gas appeared at the points where acetic and propionic acid content dropped to the lowest level (Fig. 2).

Reactor performance

The steady-state performance of whey digestion as a function of influent concentration is summarized in Table 3. It can be seen that a COD removal efficiency over 97% was maintained after 45 days of reactor operation. A 98% COD reduction with gas production rate of 9"57 litres CH4 litre feed- l day-1 was obtained at a loading rate of 5"96 g COD litre-~ day-~ and an influent concentration of 28"8 g COD litre-x.

Figure 4 clearly illustrates the effects of influent concentration on gas composition, gas production rate and the quality of effluent refected in terms of COD, VFA and pH.

The CH4 content in biogas diminished with the increase of influent concentration up to a certain level (Fig. 4(A)). After the influent


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concentration was increased to 17.7 g litre-1, there was little change in gas composit ion with further increase of effluent concentration up to 38.1 g COD litre-1. The average methane production rate was about 0.32 litre g C O D - 1 (Fig. 4(B)). In spite of the high influent COD of 28.8 g COD litre- 1, the effluent COD were between 400 and 500 mg litre- 1, and a higher COD removal efficiency of 97-99% was maintained. Effluent pH increased with the increase of influent concentration. VFA contents were in the range of 76-16 mg litre-~. However, the process became unstable 14 days after the reactor was fed the influent concentration of 38.1 g COD litre- ~. This was demonstrated by a decrease of gas production from 70 to 61 litres day-1, and an increase of effluent COD from 505 to 643 mg COD litre- 1 and also an increase of effluent acetic acid and propionic acid to 80 and 64 mg litre- 1, respectively. This might be due to sludge overloading and an unbalance between the acidogenesis and methanogenesis by increasing the influent concentration from 5 to 38.1 g COD litre- 1 within 70 days. Similar findings were reported by Switzenbaum & Danskin (1982) using an expanded bed reactor. In their experiments at a constant influent concentration of 10 g COD litre-~, the COD reduction reached 77% at loading of 27 g COD litre- 1 day- 1. However, the COD reduction was decreased from 83 to 58% when the influent strength was increased from 5 to 20 g COD litre-1. The process became unstable at the influent concentration of 20 g COD litre- 1 and the loading rate of 22 g COD litre- ~ day- 1. It was suggested that in treating high strength whey the physiological balance between the methane- producing organism and the hydrogen and acid-producing organisms is more easily upset in this system.

It was also very interesting to compare the behaviours of the UASB with the fixed-film reactor in cheese whey treatment system. It appears that the growth rate and bacterial activity are somewhat different between the suspended-growth system (UASB system) and the attached-growth system such as fixed-film (Lettinga e t al., 1979; Kelly & Switzenbaum, 1984; Nordstedt & Thomas, 1984; Wildenauer & Winter, 1985; Lo & Liao, 1986). Lower effluent VFA was reported in the UASB reactor than in the fixed-film system. The VFA concentration has proven to be a good indication of the condit ion of an anaerobic reactor, and the changes in the VFA concentration reflect changes in the bacterial population of the anaerobic process (Grady & Lim, 1980). This comparison revealed that a higher activity of biomass was developed in the UASB reactor than in the attached growth system with respect to the degrading of VFA.

There was a net increase in VSS concentration in the reactor as shown in Table 4 as sludge net growth. Th~ small amount of biomass formation at the beginning was attributed to the low food/sludge ratio of 0-164g COD g VSS- ~ day-~. A significant increase of VSS in the lower regions of the


T A B L E 4 Sludge in the U A S B Reac tor

Organic loading Influent Sludge in Ratio of Sludge lost in Sludge rate concentration digester foodandsludge effluent sample net growth

(gCODlitre -1 (gCODlitre -t) (g VSS) (gCODgVSS -1 (gVSS) day- 1) day- 1) (g VSS) (g VSS)

5-00 86"54 0' 164 - - - - - - 0'91 4"56 133"6 a 0"099 22"36 - - 3"06 1"97 9"93 107"4 0"262 20"11 13-58 7"37 3"54 17"7 91"7 0"547 4"87 17"87 7"05 5"96 28"7 114"2 0"711 2"32 13"72 38"46 7"77 38-1 164"9 0"654 2"52 13"92 67"14

° Add 67.23 g VSS of sludge to digester at day 15.

reactor took place only after the influent concentration was increased to 17"7 g COD litre-1, corresponding to sludge loading rate of 0.547 g COD g VSS- 1. This is very close to the favourable value of 0"6 g COD g VSS- 1 for biomass growth (Wu et al., 1985).

The rate of sludge growth can be expressed as follows:

where

dX ds d--? = r

dX d-t- = net growth rate of sludge (g VSS litre- 1 day- 1)

Y = growth yield coefficient (g VSS g C O D - 1)

d_s = rate of substrate utilization by sludge (g COD litre- 1 day- 1) dt

Ka = sludge decay coefficient (day- 1)

X = concentration of sludge in the reactor (g VSS litre- 1)

A plot of (dX/dt)/X vs (ds/dt)/X would yield Y and K a as the slope and intercept, respectively. Based on the data in Table 4, the sludge growth yield coefficient (Y) and decay rate (Ka) obtained in this experiment were 0"058 g VSS g C O D - 1 and 0-02 day- 1, respectively (with a correlation coefficient of 0"90). This indicated that the sludge yield in the UASB reactor was low.

The COD balances were determined for the four experimental conditions. A mass balance of the system enables the sludge formed in the reactor to be

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calculated (Table 5). The sludge accumulation factor appeared to be within a reasonable range for this type of waste which is primarily carbohydrate (Switzenbaum & Danskin, 1982; Henze & Harremoes, 1982).

Anaerobic digestion of whey using different reactor configurations has been investigated by many researchers. The treatment efficiency in terms of COD, TS and VS reductions varied with reactor types, waste strength and experimental conditions (Table 6). Compared to other treatment systems, very high COD removal ,efficiencies (over 97% COD reduction) were achieved in this study (Table 4). The UASB reactor had the highest COD removals among the different reactor systems. The UASB with a built-in three-phase separator was able to accumulate active biomass inside the reactor, and hence a high treatment efficiency was obtained. This also implies that the settling of the active biomass was quite efficient. It was evident that a high VSS concentration was obtained in the reactor, and a low VSS concentration was found in the effluent.

CONCLUSIONS

The start-up of a UASB reactor could be initiated at a low influent concentration. The influent concentration could be increased step-wise as long as the VFA concentrations were well removed in the reactor.

The UASB reactor should be maintained at certain sludge loading rates, preferably around 0.6 g COD g VSS- t, to ensure a favourable condition for biomass growth.

The anaerobic digestion using UASB reactor can be an efficient treatment method for the diluted cheese whey. Over 97% COD removals can be achieved.

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

The authors express their gratitude to The Fraser Valley Milk Producers' Association in Abbotsford, British Columbia, Canada, for supplying cheese whey.

REFERENCES

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

Boening, P. H. & Larsen, V. F. (1982). Anaerobic fluidized bed whey treatment. Biotechnol. Bioeng., 24, 2539-56.


Brummeler, E. Ten, Holshoff Pol, L. W., Dolfing, J., Lettinga, G. & Zehnder, A. J. B. (1985). Methanogenesis in an UASB-reactor at pH 6 on an acetate-proprionate mixture. Appl. Environ. MicrobioL, 49, 1472-7.

De Zeeuw, W. & Lettinga, G. (1980). Acclimatization of digested sewage sludge during start-up of an up-flow anaerobic sludge blanket (UASB) reactor. In Proceedings of the 35th Industrial Waste Conference, Purdue University, pp. 39-47.

De Zeeuw, W. (1985). Acclimatization of anaerobic sludge for UASB reactor start- up. Neth. J. Agric. Sci., 33, 81-4.

Grady, C. P. L. & Lim, H. C. (1980). Biological Wdste Treatment. Marcel Dekker, New York.

Henze, M. R. & Harremoes, P. (1982). Anaerobic treatment of wastewater in fixed- film reactors, a literature review. Water Sci. Technol., 15, 1-101.

Hulshoff Pol, L. W., De Zeeuw, W., Dolfing, J. & Lettinga, G. (1983). Start-up and sludge granulation in UASB-reactor. Paper at Agricultural University, Department of Water Pollution Control, Wageningen, Netherlands.

Kelly, C. R. & Switzenbaum, M. S. (1984). Anaerobic treatment: temperature and nutrient effects. Agric. Waste, lfl, 135-54.

Knechtel, J. R. (1978). A more economical method in the determination of chemical oxygen demand. Water Pollut. Control 116, 25-7.

Lettinga, G., Van Velsen, A. F. M., De Zeeuw, W. & Hobma, S. W. (1979). The application ofanerobic digestion to industrial pollution treatment. Proceedings of the 1st International Symposium on Anaerobic Digestion, University College, Cardiff, Wales, pp. 167-87.

Lettinga, G., De Zeeuw, W., Holshoff Pol, L. W., Wiegant, W. & Rinzema, A. (1985). Anaerobic wastewater treatment based on biomass retention with emphasis on UASB-process. Proceedings of the 4th International Symposium on Anaerobic Digestion, Guangzhon, China, pp. 279-302.

Lo, K. V. & Liao, P. H. (1986). Digestion of cheese whey with anaerobic rotating biological contact reactor. Biomass, 10, 243-52.

Marshall, D. & Timbers, G. E. (1982). Development and testing of a prototype fixed- film anaerobic digester. Paper No. 82-6519, Winter Meeting, ASAE, St Joseph, Michigan.

Nordstedt, R. A. & Thomas, M. V. (1984). Inoculum requirements for start-up of anaerobic fixed bed reactors. Paper No. 84-4090. Summer meeting of ASAE. University of Tennessee, Knoxville.

Samson, R., Van den Berg, B., Peters, R. & Hade, C. (1984). Dairy waste treatment using industrial scale fixed-film and up-flow sludge bed anaerobic digestors: design and start-up experience. Proceedings of the 39th Industrial Waste Conference, Purdue University, pp. 235-41.

Schulmann, G. E., Stanley, M. A. & Knudsen, D. (1973). Automated total nitrogen analysis of soil and plant samples. Proc. Soil Sci. Soc. America., 37, 480-81.

Switzenbaum, M. S. & Danskin, S. C. (1982). Anaerobic expanded bed treatment of whey. Agric. Waste, 4, 411-26.

Wang, Zuxuan, Chen, Zepang & Qian, Zeshu (1985). Status quo and prospects on the study of anaerobic disposal for industrial wastewater. Proceedings of the 4th International Symposium on Anaerobic Digestion, Guangzhou, China, pp. 259-77.

Wildenauer, F. X. & Winter, J. (1985). Anaerobic digestion of high-strength acidic


whey in a pH-controlled up-flow fixed-film loop reactor. Appl. Microbiol. Biotechnol., 22, 367-72.

Williams, D. W. (1984). Fixed-film anaerobic digestion of cheese whey. 84-4095. Summer Meeting of ASAE. University of Tennessee, Knoxville.

Wu, Wei-min, Hu, Ji-Cui & Gu, Xia-sheng. (1985). Properties of granular sludge in up-flow anaerobic sludge blanket (UASB) reactor and its formation. Proceedings of the 4th International Symposium on Anaerobic Digestion, Guangzhon, China, pp. 339-51.

Wu, Youg fen & Zhang, Wanting (1983). Report on pilot-scale experiment disposing monosodium glutamate wastewater with up-flow anaerobic digestor. Annual report at Guangzhon Institute of Energy Conversion, Chinese Academy of Sciences.

anaerobic digestion of cheese whey using up-flow anaerobic sludge blanket reactor

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