Journal of Scientific & Industrial Research
252 Vol. 68, March 2009, pp. 252-255
J SCI IND RES VOL 68 MARCH 2009
Optimization of organic loading rate for different fruit wastes during biomethanization R D Kirtane1*, P C Suryawanshi1, M R Patil1, A B Chaudhari2 and R M Kothari1 1
Jain Hi-Tech Agri Institute, Jain Irrigation Systems Ltd (JISL), Jalgaon 425 001, India 2 School of Life Sciences, North Maharashtra University, Jalgaon 425 001, India Received 27 January 2008; revised 15 December 2008; accepted 05 January 2009
Anaerobic microbial digestibility of three substrates [pomegranate shells (PS), mango peels and kernel (MPK) and banana peels (BP)] has been evaluated as a function of organic loading rate and conversion to methane. A direct correlation appears between C:N ratio and % lignin, and C:N ratio and % digestibility, placing BP topmost, MPK in middle and PS at the end. Accordingly, optimized organic loading rate (OLR) is: PS, 1.5; MPK, 3.5; and BP, 3.5 kg VS/day/m3. Keywords: Biogas, Biomethanization, Bioreactor efficiency, Fruit wastes, Organic loading rate, Methane
Introduction Jain Irrigation Systems Limited (JISL), Jalgaon, processes about 60,000 tons mango (Mangifera indica), 50,000 tons pomegranate (Punica granatum) and 15,000 tons banana (Musa paradisiaca), generating about 60,000 tons of solid wastes [mango peels and kernel (MPK), pomegranate shells (PS), banana peels (BP) and unripe/spoiled fruits]. Such a voluminous waste may be recycled for energy production to part furnace oil used at JISL as a source of energy, worth US $ 4000 per day. Present work assesses efficiency of these wastes for biogas and manure production.
plastic bags at 4°C until use. In 18 l substrate slurry (10% SS), 2 l inoculum [cattle dung (47.5%, v/v) + water (47.5%, v/v) + effluent (%, v/v) from ongoing biogas plant] was added, rendering 10% inoculum (v/v) in a total volume of 20 l. Experimental Procedure
Each of three circular, fixed-dome, PVC bioreactors with an inlet and outlet provision (Fig. 1), had: height, 32.0 cm; internal diam, 29.6 cm; and capacity, 25 l. Bioreactors were fitted with an agitator (100 rpm for 3 min after every 30 min) to provide uniformity of substrate slurry for pH, temperature and inoculum. Water displacement method1 was used for biogas collection.
Substrate [organic loading rate (OLR)= 0.25 kg of volatile solids (VS)/m3/day] was added and continued until 15 days, and then increased by 0.25 after every 15 days for steady increase in microbial count (except in case of BP) till it reached to 1.0. Then, it was increased by 0.5 after every 15 days. Anaerobic digestion2 was carried out at an ambient temperature (30-35°C) and pH (6.5-7.5). Chemical analysis of initial fruit waste and bioreactors’ slurry was performed as per standard methods3. Microbial analysis was carried out periodically using Bacteriological analytical manual4. Measurement of biogas was carried out after every 24 h using a calibrated transparent fiberglass container (20 l capacity). Methane analyzer (Technovation, Mumbai) analysed methane (%) of biogas.
Substrates for Biogas Production and Inoculum
Results and Discussion
Solid wastes (PS, MPK and BP) from fruit processing plant of JISL were crushed as a paste and stored in
High rate Anaerobic Bioreactor
Materials and Methods Bioreactors
*Author for correspondence Fax: +91-257-2261155 E-mail:
[email protected]
Conversion of food processing wastes into biogas via anaerobic digestion is a feasible and eco-friendly practice1,5,6, and allows generation of biogas and organic
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KIRTANE et al.: OPTIMIZATION OF OLR IN FRUIT WASTE FERMENTATION
Table 1— Analysis of waste substrates
2 1
Substrates
Parameters* 4
3 7 5
8 6
9
Fig. 1—Bioreactor (1 = electric panel and timer, 2 = agitator motor, 3 = bioreactor inlet, 4 = biogas exit, 5 = bioreactor, 6 = bioreactor outlet, 7 = agitator, 8 = biogas holder and 9 = water bath)
manure from digested waste6-8. Successful anaerobic digestion is dependent on the development and use of high rate anaerobic bioreactors 7,9,10. Present set-up (Fig. 1) appears to be quite effective to treat large amount of solid waste of fruit processing plants, giving more methane (67-78 %) as compared to methane (55-60%) provided by KVIC (Khadi and Village Industries Commission, Mumbai) digesters in India. Substrate Analysis
Among fruit producing countries, India accounts for world’s (i) 60% mango production, (ii) 34% banana production and (iii) second largest pomegranate production after Iran. While mixed waste from vegetables and fruits has been subjected to biomethanation7,11,12, use of single feedstock of PS, MPK and BP is not reported13. An average composition of waste (Table 1) shows that: i) All wastes are rich in carbohydrates and moderate in % proteins; ii) Lignin (%) is more in PS, less in BP and least in MPK; iii) VS are 95.4% in PS, 95.2% in MPK and 87.8% in BP; and (iv) C:N ratio is maximum in MPK, less in PS and least in BP. Potential of PS for Digestion and Methane Generation
As OLR increased in PS, quantum of VS fed too increased (0.006-0.060 kg) in 120 days (Table 2). Initially, biogas production was 6.8 l, then it followed a zigzag path for quite some time. Biogas production was higher at 0.25 OLR; however, with an increase in OLR to 1.0, it has fallen down, may be due to either initial lack of critical requirement of inoculum to take load of additional OLR or lag period required proportionate to its growth inhibitor-rich recalcitrant chemical composition 14.
PS
MPK
BP
Total solids, %
32.3
23.6
13.9
Volatile solids, %
95.4
95.2
87.8
Total organic carbon, %
40.9
59.8
40.7
Total Kjeldahl nitrogen, %
1.1
1.3
1.2
C:N ratio
39.1
45.4
33.0
Total carbohydrates, %
30.5
34.5
32.0
Total proteins, %
5.1
5.0
7.9
Total phosphorus, %
2.1
0.6
1.8
Total lignin, %
29.4
10.3
16.3
All analysis are on dry weight basis and an average of 10 estimates *
However, regardless of zigzag profile of biogas, % methane was continuously increasing (started at 44.6 % and gradually rose up to 63.0 %), indicating an optimal performance of methanogens, presumably upon stabilization of bioreactor. However, at 2.0 OLR, % methane decreased with concomitant decrease in biogas production and this trend continued during 2.5 OLR. Decrease in % methane or biogas production results due to tannin, alkaloids, flavonoids and terpenoids, which are inhibitory to microbial growth and digestion14. This assumption is corroborated by aerobic and anaerobic TVC (Table 3). Therefore, bioreactor efficiency (kg of VS fed and its conversion to methane) as a function of OLR was optimal at 1.5 OLR, as also the digestion efficiency. Potential of MPK for Digestion and Methane Generation
In case of MPK, VS fed increased from 0.0056 to 0.077 kg over 150 days as OLR was increased; initially, biogas production was 11.0 l, slightly dropped at 0.50 and 0.75 OLR and again gradually increased to 11.0 l and higher at 1.5 OLR (Table 2). This trend continued up to 3.0 OLR with increase in % methane, showing stagnation at 3.5 OLR. Observed lag period to increase biogas production and its % methane is due to high C:N ratio, which facilitates more CO2 production and forbids metabolic pathway(s) leading to more methane production15. Each parameter (VS, biogas and methane production, % methane and bioreactor efficiency) has registered a consistent increase with an increasing OLR. Optimum OLR was in 3.0-3.5 range, as also digestion efficiency (72.8 %).
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J SCI IND RES VOL 68 MARCH 2009
Table 2 — Profile of methane production and bioreactor efficiency as a function of substrates Days
VS fed kg
OLR kgVS/ day/m3
pH
Alk: acid % TS ratio
% VS (TS)
C: N ratio
Biogas generation l
Methane CH4 production content l %
Bioreactor efficiency %
6.8±0.6 6.0±0.3 6.0±0.4 6.0±0.4 8.0±0.7 9.0±0.4 7.0±0.6 5.0±0.7
3.0±0.3 3.0±0.1 3.2±0.3 3.1±0.1 4.3±0.4 5.7±0.3 3.7±0.3 2.3±0.3
44.6±0.7 50.7±0.9 52.6±1.0 51.2±0.7 53.8±1.1 63.0±0.5 52.2±0.7 45.0±0.3
16.9±1.2 16.9±0.7 36.8±1.1 43.7±0.9 50.3±1.2 57.9±0.6 48.6±1.0 37.8±1.1
11.0±0.4 11.0±1.4 8.0±0.9 8.0±0.8 9.0±1.8 11.0±1.2 15.0±1.1 17.0±0.8 19.0±1.1 20.0±1.0
5.9±0.6 6.3±0.7 4.3±0.7 5.0±0.5 6.0±0.3 7.7±0.9 10.5±0.4 11.7±0.7 13.7±0.9 15.4±0.5
53.8±1.0 57.0±0.7 54.0±0.3 63.0±0.8 67.0±1.0 70.0±0.8 70.0±0.9 69.0±0.4 72.0±0.2 77.0±0.6
19.3±0.6 19.3±0.3 40.2±1.6 44.5±0.3 54.7±1.0 63.8±0.6 63.4±1.1 61.7±0.5 65.2±0.9 72.8±0.4
5.0±0.6 7.0±0.9 7.0±0.8 8.0±1.2 9.0±0.9 13.2±0.8 13.2±0.6 17.2±0.5 20.0±1.8 20.0±1.8
2.8±0.8 4.4±0.6 4.8±0.7 5.8±1.1 7.1±0.9 11.0±0.9 10.7±0.7 14.6±0.8 16.8±0.6 17.0±0.5
55.5±1.4 62.8±1.0 68.5±0.3 72.9±1.5 78.6±0.9 83.0±0.4 81.0±0.7 85.0±0.8 84.0±0.6 84.0±0.3
47.4±0.2 56.1±0.7 56.2±0.4 78.1±0.9 81.6±0.3 89.8±0.7 85.2±0.6 92.7±0.9 90.8±0.8 90.6±0.8
Pomegranate shell (PS) 00-15 16-30 31-45 46-60 61-75 76-90 91-105 106-120
0.006 0.006 0.012 0.018 0.024 0.036 0.048 0.060
0.25 0.25 0.50 0.75 1.00 1.50 2.00 2.50
7.4 7.3 7.3 7.2 7.1 6.9 6.9 6.8
7.2 3.8 3.4 4.6 3.5 2.9 2.6 2.7
10.2 10.5 9.8 8.0 7.0 6.7 6.3 6.9
78.8 78.5 76.0 79.2 76.8 75.5 75.3 76.2
16.6 18.1 16.8 17.7 11.4 14.0 15.5 14.6
00-15 16-30 31-45 46-60 61-75 76-90 91-105 106-120 121-135 136-150
0.0056 0.0056 0.011 0.017 0.022 0.033 0.044 0.055 0.066 0.077
0.25 0.25 0.50 0.75 1.00 1.50 2.00 2.50 3.00 3.50
7.4 7.4 7.4 7.4 7.3 7.1 7.0 6.9 6.5 6.3
7.8 3.6 3.2 5.3 3.7 2.6 4.0 5.9 4.1 2.6
Mango peel kernel (MPK) 12.6 76.7 21.6 10.5 76.6 16.0 7.2 72.0 13.1 7.2 72.9 17.1 6.1 71.6 11.3 5.7 73.2 11.4 5.6 72.7 16.0 6.7 75.0 20.3 6.5 77.5 15.0 4.8 80.0 8.3
00-15 16-30 31-45 46-60 61-75 76-90 91-105 106-120 121-135 136-150
0.006 0.011 0.017 0.022 0.033 0.044 0.055 0.066 0.077 0.077
0.25 0.50 0.75 1.00 1.50 2.00 2.50 3.00 3.50 3.50
7.0 7.0 7.1 7.0 7.0 7.0 6.9 7.0 6.9 7.1
5.0 4.3 3.7 2.5 5.1 5.2 5.2 4.2 4.1 4.2
7.4 5.5 4.8 5.1 5.2 6.1 5.6 5.3 4.7 4.7
Banana peel (BP) 80.8 14.1 78.7 13.2 77.7 11.2 74.4 13.6 74.9 15.0 76.0 17.4 76.9 16.9 74.8 18.9 73.4 14.7 73.7 15.3
VS = volatile solids, TS = total solids
Table 3 — Average comparative performance of PS, MPK and BP for methane production over 150 days Substrate
pH
Alk: acid ratio
% TS
% VS (TS) C:N ratio
Microbial analysis cfu x 105/g
Biogas Methane CH4 generation, l production, l content
PS
7.1
4.0
8.4
77.2
15.7
7.4±0.5
4.3±0.3
52.6±0.7
4.3
7.3
74.8
15.0
12.9±1.0
8.2±0.6
65.3±0.6
4.4
5.5
76.4
15.0
Aerobes >25 Anaerobes 0.8 Aerobes 77 Anaerobes 13 Aerobes 23 Anaerobes 45
MPK
7.1
BP
7.0
11.1±1.0
8.5±0.7
72.3±0.8
%
KIRTANE et al.: OPTIMIZATION OF OLR IN FRUIT WASTE FERMENTATION
Potential of BP for Digestion and Methane Generation
BP has shown steadily improving digestion efficiency, biogas production and its methane content (Table 2). Bioreactor efficiency (90.6%) reflects easy microbial digestibility of BP due to soft texture, in spite of relatively lower % VS (Table 1); lowest C:N ratio enhanced amenability to microbial degradation. Optimum OLR was in 3.0-3.5 range, as also digestion efficiency.
2
3
4
5 Correlation between Microbial Count, Digestion Efficiency And Methane Content
Possible cause for initial fluctuation in biogas production, regardless of substrate, might be due to need for equilibration period by methanogens. All bioreactors performed well (Table 3) as pH remained in optimal range. Similarly, alkalinity: acidity ratio too maintained during biomethanization. Variation in % total solids (TS) and % VS was as per the substrate fed and its digestion efficiency. Microbial analysis for total aerobes and anaerobes in respective bioreactors clearly showed that: i) PS had very low population of anaerobes; ii) MPK showed increased number of anaerobes; and iii) BP providing the maximum. Accordingly, it directly affected biogas and % methane production16.
6
7
8
9
10 Organic Manure as Soil Conditioner
Since organic manure has emerged after meaningful conversion of organic carbon of wastes into methane, its C:N ratio (16-20) is for immediate utilization as soil conditioner. Due to production of methane and CO2, effluent is richer in micronutrients17. Finally, its rich consortium of aerobes and anaerobes enriches soil for productivity and pest control18.
11
12
Conclusions Based on methane content of biogas, BP has given optimal (84.0%), followed by MPK (77.0%) and PS (63.0%) in the order of bioreactor efficiency (Table 3). Thus, anaerobic digestion has converted waste efficiently into value-added methane and manure leaving sustainable pollution-free environs.
13
Acknowledgment Authors thank Mr B H Jain, Founder Chairman, JISL for providing state-of-the-art R & D facilities to undertake the present work.
16
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18
1
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14 15
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