Fixed film biomethanation of distillery spentwash using low cost porous media

ELSEVIER

Resources, Conservationand Recycling 14 (1995) 79-89

resources, conservation and recycling

Fixed film biomethanation of distillery spentwash using low cost porous media R. Seth, S.K. Goyal *, B.K. Handa National Enviromnental Engineering Research Institute, Nehru Marg, Nagpur, India 440 020

Received 1 September 1993;revised 26 August 1994;accepted 3 January 1995

Abstract Investigations were conducted using a low cost support media for microbial attachment and growth for the anaerobic treatment of sugarcane molasses based distillery spentwash employing fixed film reactor (FFR) technology. An HRT of 3 d corresponding to an OLR of 22 kg COD m-ad - t based on reactor liquid volume (VL) (VL ffi0.534 Vcb,empty bed volume) with COD reduction of 71.8% and gas yield of 0.45 m 3 kg- ~COD removed has been achieved in the methane phase. Volatile solids analysis has revealed that about 75% of the biomass is attached to the inert media surface leading to a major contribution in the performance of the methane reactor. Solids retention time (SRT) of 106 d has been calculated at an HRT of 3 d, thereby demonstrating superTority of FFR technology over other conventional anaerobic treatment methods. Further, the waste treatment is affected by the entire media height due to continuous effluent recycling. Comparison with granular activated carbon (GAC) has revealed that the media used in the present study has comparable or even better performance due to larger size of the pores in the media. Keywords: Distillery;Spentwash;Methane reactor;Sugarcanemolasses

1. I n ~ o d u c f i o n India is a major sugar producing country in the world. There am about 200 distilleries in India which mainly use molasses, a byproduct of the sugar industry, as a raw material. Distilleries are among the major polluters of the environment, generating spentwash which is characterized by high BOD, COD, low pH, high temperature and high concentrations of soluble organics and ions such as SO42- and K + (Table 1). Biomethanation using diphasic system is the most appropriate treatment meihod for high strength wastewaters because of its reported advantages [ 1,2 ], viz., possibility of maintain* Corresponding author. 0921-3449/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSD10921-3449 ( 95 ) 00003-8

80

R. Seth et al. / Resources, Conservation and Recyclhlg 14 (1995) 79-89

Table 1 Characteristics of distillery spentwash Sr. No.

Parameter

Range

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

pH total solids total suspended solids total dissolvedsolids total volatile solids chemical oxygendemand biochemical oxygen demand total nitrogen as N potash as K20 phosphate as PO4 sodium as Na chlorides as CI sulphates as SO4 acidity as CaCO3 temperature (after heat exchanger)

3.8-4.4 60 000°90 000 2000-14 000 67 000073 000 45 000-65 000 70 000098 000 45 000-60 000 1000-1200 5000-12 000 50001500 150--200 5000-8000 2000-5000 8000--16000 70-80*(2

All the values except pH and temperature, are in mg I- t. ing optimal conditions for buffering of imbalances between organic acid production and consumption, stable performance and higher methane concentration in the biogas produced. Considerable work has been reported on biomethanation using upflow anaerobic reactors with a variety of support media having porous and non porous structures [ 3 - 7 ] . A porous inert media enhances biofilm development considerably as compared to a more smooth media [8,9]. The present investigation was undertaken for the evaluation of a diphasic FFR technology for the treatment of sugarcane molasses based distillery spentwash, using a low cost support media.

2. Materials and methods 2.1. Experimental s c h e m e

The experimental scheme consisted of a diphasic process with an open facultative completely stirred acid reactor and an anaerobic fixed film methane reactor with clay brick granules (CBG)'as support media. All experiments were conducted in the laboratory under ambient conditions. Composited samples averaged over a day were used in the analysis. Total volatile acids (TVA) and also total and bicarbonate alkalinity were measured daily by the method of Dilallo and Albertson [ 10]. COD was analysed daily. Sulphate and solids were analysed once a week. All analyses, except those reported otherwise, were in conformity with the standard methods [ 11 ]. CO2 in the gas phase was measured thrice a week by Orsat apparatus, whereas H2S was measured fortnightly using Tutweiler burette.

R. Seth et al. / Resources, Conservation and Recycling 14 (1995) 79-89

M

.

1

81

....

~

p.

"

-'-,'to,:ND--

I?/./////2

PUMP ~PERISTALTIC )

~'//////~

®EF,LUENT [NT

~////II,A

(,p) SUPPORr

,,L FILM REACTOR

® )RECIRCULATION e s c iR uL , PUMP PERISTALTIC )

"--~B

~SAS

COLI COLLECTION UNI'I~

4

Fig. I. Schematicdiagramof methanereactor. 2.2. Neutralization

Distillery spentwash is highly acidic in nature and requires neutralization before acid phase treatment. Therefore, spentwash with pH ranging between 3.8-4.4, was first neutralized using 10% lime slurry. 2.3. Acid phase

The continuously stirred acid reactor consisted of a Borosil® bottle and was fed with neutralized spentwash using a Watson-Marlow peristaltic pump. The optimum conditions for maximum rate of acid production in acid phase are pH 7.0 and HRT 1.2 d (unpublished data) corresponding to an organic loading rate (OLR) of 55-61 kg COD m-ad - i. Total volatile acids formed in this phase were in the range of 17-22 g 1- t and nearly 10% COD reduction was observed. 2.4. Methane phase

The schematic diagram of the upflow fixed film methane reactor is shown in Fig. !. The reactor was made of perspex and filled with CBG. The details of reactor geometry and specifications of support media (CBG and GAC) are given in TablesTable 2 Table 32 and 3, respectively. Initially, the methane reactor (MR) was seeded with the methanogenic culture (TVA, 3.42 g 1-i; TVA/T.ALK, 0.37) being maintained in the laboratory on acid phase effluent in a completely stirred methane reactor. The experimental protocol consisted of several phases. Up to an HRT of 15 d, the methane reactor was operated on once a day feeding with acid reactor (ART effluent basis. At 15 d HRT it was changed to continuous feeding

82

R. Seth et al. / Resources, Conservation and Recycling 14 (1995) 79--89

Table 2 Methane reactor details Notation

Description

Height (cm)

G

gas outlet effluent port hole support media sampling port sampling port sampling port sampling port distribution plate reactor base

92.5 82.5 77.5 77.5 57.5 37.5 17.5 2.0 0.0 Volume (1) 5.25 4.68 4.40 2.20 2.20 2.50

E

M P4 P3 P2 P1 D B

between B&G (empty bed) between B&E (empty bed) between D&M (empty bed ) between D&M (media) between D&M (liquid) between B&E (liquid) Reactor diameterm 8.5 cm. Distributionplate thicknessffi0.5 cm. All the heights are measured from base. Media porosity ffi50%.

mode, which was continued until the end o f the study. The rate of recirculation was five reactor liquid volume per day during the entire study. At the end o f the present study, total biological solids were determined in the methane reactor. Accordingly, first the liquid volume inside the reactor was removed separately from all port holes starting from the top and VSS were determined. Since the VSS values, ranging between 1.6 to 2.0 g 1- I (avg. 1.76), were low, the same were not considered for the calculation o f SRT. Representative samples were drawn from all the port holes. The support media was segregated from the suspended matter and washed with minimum quantity of water. The washings were added to the suspended matter to make a uniform suspension. Volatile solids were determined on support media and VSS were determined in the suspensions. SRT was calculated at the end o f the study as: total volatile solids in M R (attached and suspended) (g)

SRT (d) ffi

total volatilesuspended solids in M R effluent(g d -l)

Table 3 Characteristicsof supportmedia Sr. No.

l 2 3 4

Parameter

particle size (ram) bulk density (kg m -s) porosity (%) surface area (m2 m -s) (apparent)

Support media CBG

GAC

4.76--9.51 950 50 100

1.19-2.38 590 49 1600

R. Seth et al. / Resources, Conservation and Recycling 14 (1995) 79-89

I 0 13

t OLR " 0 TVA :" o BALK "

83

• COD,Redudlon r'. Gol Yield - TVA/T,ALK

75 70

.6

-4

o

i!

8 2~ o

I-

I t 20

L~

~ I 40

I 60 No. of Ooys

I 80

I I00

Fig. 2. Startup of methane reactor.

3. Results and discussion

3.1. startup of MR Acid reactor effluent (ARE) was fed to MR only after 3 weeks of startup. Later, 10 ml ARE, along with 40 ml methane culture, was fed daily. Slowly, the feed volume of ARE was increased and within a 10-week period of reactor startup, 100 ml ARE was fed. At this stage, the effluent TVA, bicarbonate alkalinity and TVA/T.ALK ratio were estimated as 1.38 g 1- ~, 5.52 g 1- ~and 0.214, respectively, with gas yield of 0.364 m3/kg COD. Various parameters monitored during startup of MR are presented in Fig. 2. It is evident that the reactor started taking load only after 68 d of the startup period.

3.2. Performance of MR The performance characteristics of MR with respect to HRT are presented graphically in Figs. 3 and 4 and have been tabulated in Table 4. During the entire period of reactor operation, the influent COD was in the range of 66 to 72.8 g 1- t (avg. 69.4). MR could be operated at an HRT of 3 d with COD and TVA reduction effieiencies of 71.8 and 88.5%, respectively.

R. Seth et al, /Resources, Conservation mid Recycling 14 (1995) 79-89

84

--• -"

-- TVA REDUCTION , CO0 REDUCTION = GAS YIELD

~. : OLR -.= --= GPV ~ "~_ CO2

14C 25

120 -J20

I00

10

v z 0 v- 80

B

,.q n.

i-r !o< 0'4[

'E

4C O

~(>2 L

2,0

5

.v

/~

,~

g

g

~,

~

b

2

~-

HaT (dGys)

Fig. 3. Performancecharacteristicsof methanereactor. MR was operated at 25, 15, 10 and 6 d HRT for a total period of 16, 15, 14 and 30 d, respectively. The HRT was changed when the performance of the reactor was found satisfactory. Apparently, the reactor did not reach steady state at 25, 15 and 10 d HRTs, but steady-state conditions were observed at 6 d HRT due to prolonged operation, leading to the improvement in performance of the reactor. The performance of the reactor improved appreciably on reduction of HRT from 10 to 6 d. Marginal improvement in the performance of MR was further observed on reduction of HRT to 4 d which may be attributed to the rise in the reactor temperature from 24-27°C to 26--30"C. On further reduction in HRT to 2 d, the reactor performance was found to deteriorate with COD and TVA reductions reducing to 61 and 78%, respectively, and hence the studies were discontinued. Depending upon the influent substrate concentration, 20 to 23 m a of biogas was produced per cubic meter of spentwash with CO2 and H2S contents varying between 20 to 30 and 0.8 to 2.2%, respectively. The empirical relationship between gas yield (m 3 k g - l COD removed) and COD removal rate (CODr in kg d - I ) has been derived by statistical method of curve fitting as:

Gas yield = 0.435 CODr- 0.353 with regression coefficient (R) and coefficient of correlation (r) values of 0.97 and 0.98, respectively.

R. Seth et al. /Resources, Conservation and Recycling 14 (1995) 79--89

! c

~ TVA

I

I

OLR

/~1. /

85

35

/-

12

3O

)'4

.-". IC I j

25

02 ~

< 8

20

,1I

.6 O

ff o 5

.t3--O

o --.¢/ HRT (doys)

Fig. 4. P e r f o r m a n c e characteristics o f methane reactor.

3.3. Sulphate and solids reduction During the entire period of MR operation, SO42- concentration in influent and effluent was in the range of 2 to 6 g 1-~ (avg. 3.90) and 1 to 3 g 1-~ (avg. 1.71), respectively. Approx. 56% reduction is achieved in methane phase. However, with the change in OLR or HRT, no specific trend was observed. Similarly, the concentration of TSS and VSS in the influent was in the range of 7 to 25 g 1- t (avg. 15.03) and 5 to 14 g 1- ~ (avg. 10.87), respectively, whereas in treated effluent, these concentrations were in the range of 1 to 4 g I- i (avg. 1.6) and 0.6 to 2 g 1- t (avg. 0.98), respectively, with corresponding average reduction of about 90% both in TSS and VSS. However, with change in OLR or HRT, no specific trend was observed. Total solids in the influent and effluent were in the range of 60-95 g 1- ~ (avg. 75.34) and 30-38 g 1- t (avg. 36.62) with approx. 50% inorganic fractions in both the streams. About 51% reduction is observed in the methane phase. 3.4. Biomass estimation Table 5 depicts the distribution of biomass along the reactor height at the end of the study. From the table it is evident that the biomass attached to the support media played a major role in the performance of the reactor which is contrary to the results reported by some researchers [ 6,12] who concluded that the major contribution is due to the biological solids held loosely in the interstitial void spaces within the media. This may be attributed

86

R. Seth et al./ Resources, Co.sen,ation and Recycling 14 (1995) 79-89

Table 4 Performance characteristics of methane reactor St. No. Parameters

1 2

3

4

5 6 7 8 9 10

II

HR'I~ feed vol. (ml) OLR (kg COD m-3d-I) based on empty bed

Hydraulic retention time (HRT) (d) 25

15

10

6

4

3

2

46.8 100 2.78

28 167 4.65

18.7 250 6.83

11.2 415 12.13

7.5 630 17.41

5.6 833 22.02

3.7 1250 33.97

1.48

2.48

3.65

6.48

9.30

11.76

18.15

69.56 19.49 71.98

69.80 20.43 70.73

68.26 21.21 68.93

72.79 18.28 74.89

69.62 18.20 75.74

66.06 18.82 71.75

67.94 26.50 61.00

20.42 1.71 91.60 6.84 5.70

21.48 1.94 91.00 7.46 6.17

17.11 1.76 89.71 8.00 6.83

20.83 2.77 86.70 8.68 6.83

19.54 2.42 87.62 8.38 6.77

17.22 1.98 88.50 8.39 7.07

24.58 5.41 78.00 7.88 4.27

0.25 2.10

0.26 3.37

0.22 5.67

0.32 9.05

0.29 12.63

0.24 17.58

0.69 19.68

0.42

0.41

0.48

0.40

0.39

0.45

0.38

0.84

1.35

2.27

3.62

5.05

7.03

7.82

0.45

0.72

1.21

1.93

1.93

3.76

4.21

21.00

20.40

22.68

21.80

20.05

21.11

15.74

20.00 28-30

22.00 26-28

26.00 26-28

29.00 24-27

24.70 26-30

28.20 28-30

24.80 30-33

COD

influent (g 1-~) effluent (g 1-~) reduction (%) TVA influent (gl - j ) effluent ( g 1- ~) reduction (%) total alk. (g I- ~) biearb, alk. (gl - I ) TVA/T. alk. gas procln. (ld -I) gas yield (m 3 kg- ~COD,) GPV (m 3 m -3 d-') based on empty bed gas pmdn. (m 3 m -3 of

12 13

feed) COz (%) temperature

14

pH

(*c) ~

7.5-8.0

~

t

7.6-8.4

°Based on empty bed volume. tO t h e p o r o u s n a t u r e o f the i n e r t s u p p o r t m e d i a u s e d in the p r e s e n t i n v e s t i g a t i o n w h i c h e n h a n c e s b i o f i l m d e v e l o p m e n t c o n s i d e r a b l y . F u r t h e r , it h a s b e e n o b s e r v e d that w i t h the v a r i a t i o n in r e a c t o r h e i g h t , the b i o m a s s a n d b i o m a s s a t t a c h e d to the m e d i a d e c r e a s e s in u p f l o w reactors. T h e d i s t r i b u t i o n o f b i o m a s s a l o n g the e n t i r e r e a c t o r height, as d e p i c t e d in Fig. 5 is d u e to effluent r e c y c l e w h i c h e n s u r e s a b e t t e r d i s t r i b u t i o n o f s u b s t r a t e w i t h i n the reactor.

3.5. Media comparison Studies have also been conducted previously on biomethanation of distillery spentwash using GAC as support media. The comparative performance of the two support media is

87

R. Seth et al. / Resources, Conservation and Recycling 14 (1995) 79-89

Table 5 Distributionof biomass in methane reactor (as g of volatile solids) Description (Fig. 1)

Height (cm)

Biomass attached to media (g)

Loosely bound biomass (g)

Total biomass Total biomass (g) per unit height (g/cm)

Biomass attached to media per unit height (g/era)

From D to PI From PI to P2 From P2 to P3 From P3 to P4 Total (from D to P4)

15 20 20 20 75

30.54 35.25 27.95 24.01 117.75

4.14 9.35 13.18 11.29 37.96

34.68 44.60 41.13 35.30 155.71

2.04 1.76 1.40 1.20

2.31 2.23 2.06 1.76

presented in Fig. 6. The performance o f G A C is seen to be better than C B G up to HRTs o f more than 10 d, but at lower HRTs CBG has shown better performance. The maximum OLR achieved with G A C was 21.3 kg COD m -3 d - i, corresponding to an HRT o f 4 d with COD and T V A reductions o f 67% and 82%, respectively, whereas O L R achieved with CBG is 22 kg COD m - 3 d - i, corresponding to an HRT of 3 d with COD and T V A reductions of 71.8 and 88.5%, respectively, even though the surface area provided by G A C is much more than CBG (Table 3). The better performance of G A C in the initial phase may be due to faster initial attachment of biomass and better adsorptive capacity. SEM analysis o f the two support media have revealed that a majority o f the pores on G A C are < 5 / z m in size, whereas those on CBG are between 20--40 btm. Hence, the better performance o f C B G at lower HRTs may be due to its better support characteristics [4].

]

ATI'ACHEDBK~IASS

[]

L00~

~

o

Z

E O

=S O

Pt SAMPLING PORT

Fig. 5. Status of biomass in methane reactor.

...~ss

R, Seth et al./ Resources, Conservation and Recycling 14 (1995) 79-89

88

c8c; • • • •

GAC V

O o A

COOl TVAI CO0 REOUCTION TVA I~OUCTION

J

~

i

-

P

1-

9o~ 9c

zSO

0

7o

60

f ~r° I 60 ~ HRT (doyt) Fig. 6. Comparative pe~ommnce o f methane reactors.

4. Conclusions The efficacy of anaerobic diphasic system has been demonstrated in the present investigation with low cost clay brick granules as support media in the methane phase. The reactor startup period was observed to be 68 d in the FFR system. An HRT of 3 d, corresponding to an OLR of 22 kg COD m -a d - t with COD reduction of 71.8% and gas yield of 0.45 m3 kg- ~COD removed has been achieved in the methane phase. Volatile solids ahalysis has revealed that the biomass attached to the inert media surface played a major role in the performance of the methane reactor. SRT of 106 d has been calculated at an HRT of 3 d, thereby confirming the superiority of FFR technology over conventional anaerobic treatment methods. Further the biomass is distributed along the entire media height due to continuous effluent recycle. The better performance of CBG over GAC as support media may be attributed to its better support characteristics which is confirmed by SEM analysis.

Acknowledgements This study was supported by the Department of Nonconventional Energy Sources, Ministry of Energy, Government of India. The authors express their gratitude to Ms. Geetanjali

R. Seth et al. / Resources, Conservation and Recycling 14 (1995) 79--89

89

Naik and Ms. N.R. Shanti for their assistance in carrying out experimental work, and Director, N E E R I for e n c o u r a g e m e n t and kind permission to publish this work.

References [ 1] Ohosh, S. et al., 1975. Anaerobic acidogenasis of wastewater sludge. J. WPCF, 47( 1): 30--45. [ 2 ] Cohen, A., et al., 1979. Anaerobic digestion of glucose with separated acid production and methane formation. Water Res., 13: 571-80. [ 3 ] Young, LC. and Mc Catty, P.L., 1967. The anaerobic filter for waste treatment. In: Proceedings of the 22nd Industrial Waste Conference, Purdue University, Lafayette, IN, pp. 559-574. [4] Huysman, P., Van Meanen, P., Van Asscbe, P. and Verstraete, W., 1983. Factors affecting the colonization of non porous and porous packing. Biotechnol. Lett., 5 (9): 643--648. [5] Carrondo, M.J.T. et al., 1983. Anaerobic filter treatment of molasses fermentation wastewater. Water Sci. Technol., 15:117-126. [6] Young, J.C. and Dahab, M.F., 1982. Effect of media design on the performance of fixed bed anaerobic reactors. Water Sci. Technol., 15: 369-383. [7] Handa, B.K. and Seth, R., 1990. Waste management in distillery industry. L IJEM, 1(7): 44-54. [8] Murray, W.D. and Van den Berg, L., 1981. Effect of support material on the development of microbial fixed films converting acetic acid to methane. L Appl. Baeteriol., 51: 257-265. [9] Salkinoja-Salonen, M.S. et al., 1982. Biodegradability of recalcitrant organochlorine compounds in fixed film reactors. Water Sci. Technol., 15:309-319. [ 10] Dilallo, R., and Albertson, O.E., 1961. Volatile acids by direct titration. J. WPCF, 33(4): 356-65. [I1] APHA, AWWA, andWPCF, 1976. Standard methods for theexaminationofwaterand wastewater.American Public Health Association, Washington, DC. [ 12] Van den Berg, L. and Lentz, C.P., 1979. Comparison between up-and down flow anaerobic fixed film reactors of varying surface-to-volume ratios for the treatment of bean blanching waste. In: Proceedings of the 34th Industrial Waste Conference, Purdue University, Lafayette, IN, pp. 319-325.