Integrated utilization of fruit-processing wastes for biogas and fish production

Biological Wastes 32 (1990) 243-251

Integrated Utilization of Fruit-Processing Wastes for Biogas and Fish Production

M. M a h a d e v a s w a m y & L. V. V e n k a t a r a m a n

Autotrophic Cell Culture, Central Food Technological Research Institute, Mysore--570013, India

(Received 29 May 1989; revised version received 20 August 1989; accepted 6 September 1989)

ABSTRACT

An integrated system for biogas production from mango-processing wastes and utilization of biogas effluent for production of major carp Rohu, ( Labeo rohita) and common carp (Cyprinus carpio) was studied. Mango peels produced 0"21 m 3 of biogas perkg of total solids. Biogas effluent of mango peels, when used at 34 kg/lO0 m z area in ponds as the sole source of feed for carps, yielded 8"35 kg/ lO0 m2 offish which had acceptable colour,flavour and taste every 120 days.

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

Waste from a fruit-processing operation constitutes a large untapped source of energy and proteins. In India, over 35 million tonnes of fruit and vegetables are processed annually and this results in about 10 million tonnes of wastes (Maheshwari et al, 1984). In this total, mango accounts for 9.2 million tonnes of processing wastes per annum (Mokshapathy, 1988). Processing of mango results in considerable quantities of wastes (50%), made up of peels (35%) and kernels (15%).

Possible uses of these wastes in animal feed preparation have been suggested by some workers (Patel et al., 1972; Bhatnagar & Subramanyam, 1973). Fruit- and vegetable-processing wastes have been used for methane generation (Lane, 1979, 1982). However, most of the mango-processing units merely dump these wastes in fields, causing pollution. There are reports on utilisation of agricultural and animal wastes for biogas generation and use

243 Biological Wastes 0269-7483/90/$03"50 © 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain

244 M. Mahadevaswamy, L. V. Venkataraman

of the digested effluent for fish production (Biswas,. 1977; Beszedits & Netzer, 1982; Martyshev, 1983; Mahadevaswamy & Venkataraman, 1988).

In the present study utilization of fruit processing wastes for biogas generation and subsequent use of biogas effluent for fish cultivation have been attempted.

METHODS

Fruit-processing wastes and chemical analysis

Mango peels were collected from food-processing units with 70% moisture. These wastes were sun dried and powdered.

Total and volatile solids, total nitrogen and ammonia concentration were determined by APHA (1985) procedures. Sugar, starch and lignin were determined by standard procedures (Kolmer et al., 1969). Cellulose and hemicellulose were estimated by the procedures of Updegraff (1969) and AOAC (1960), respectively.

Laboratory trials

Biogas production was studied in 5 litre digesters at room temperature (25-30°C) with 30 days' retention time. Initially, all digesters were filled with 5 litres of 6% (TS) cowdung slurry and incubated for two weeks for acclimatization. After acclimatization, 170 ml of slurry were removed from each digester and an equal amount of fresh slurry containing 6, 12 or 18% total solids was added daily. Continuous biogas production for a period of 24 weeks was studied in individual digesters.

Field trials

A flexible biogas digester (Swastik, Pune, India) made from rubber, with a capacity of 4 m 3, was used in outdoor field trials at ambient temperature (25-35°C). Cowdung (2 tonnes) was made into a slurry with 2000 litres of water and charged into the digester and left to acclimatize for a period of 2 weeks, after which biogas production started.

The fresh mango peels (27 kg) were made into a slurry with 114 litres of water and charged to the digester daily after the initial 15 days" incubation. In the first eight weeks, the digester contained a mixture of cowdung and mango peel effluent until cowdung was completely clear of the digester. After this, the biogas generation was monitored for a further period of four months. The effluent was collected and used for fish feeding trials for a

Fruit wastes for biogas and fish production 245

period of four months. The composition of the biogas was analyzed by gas-liquid chromatography.

Aquaculture

The Indian major carp Rohu (Labeo rohita) and common carp (Cyprinus carpio) were used in mixed culture (1:1) in 10m x 10m x 1 m cement ponds with a water depth of 80 cm. Initially, the experimental pond was fertilized with 190 litre digested mango peel biogas effluent (4.5% TS) and filled with water up to 80 cm. A week after the initial fertilization, stocking was carried out with uniform-sized fingerlings of major carp (Rohu) and common carp at 50 each per 100 m 2 in the two porrds. Subsequently the pond was fertilized with the addition of 190 litres of mango peel slurry after every 30 days.

A control pond was maintained and supplied with a standard feed containing 30% protein which contains 24% groundnut cake, 25% fish meal, 40% rice bran and 10% rice powder and 1% vitamin and mineral mix cooked with water 1:2 w/v for 15 min and extruded as noodles and dried. The feed was provided at 5 % of the fish body weight during the four month study. Fortnightly samples were collected from the ponds for analysis of dissolved oxygen, bicarbonate and total alkalinity by using standard procedures (APHA, 1985). Fishes were collected once a month for measurement of growth rate.

Organoleptic evaluation

On completion of the 4-month experimental period, uniform-sized fish of the two species were collected and dressed separately for organoleptic evaluation. Fishes from the control group were used for comparison. They were cooked in 1.5% salt for 3 min and evaluated by a trained panel of ten people using standard proforma. Grades obtained were statistically analyzed (Harter, 1960).

RESULTS AND DISCUSSION

Biogas production

The composition of sun-dried maiago peels is shown in Table 1. In the 5 litre laboratory digesters the biogas production was studied for a period of 24 weeks. The average rate of biogas production at 2, 4 and 6 kg/m a per day loadings (corresponding to 6, 12 and 18% total solids) was found to be 2.2, 4.0 and 1.5 litre/day, respectively. The biogas generation attained


TABLE 1 Composition of Sun-dried Mango Peels (% Dry Matter) a

Constituents Mango peels

Moisture 6.4 Crude protein 10.3 Ether extractable 8"9 Starch 16'2 Cellulose 10"2 Hemicellulose 10.8 Total reducing sugar 4-0 Pectin 7"0 Lignin 20.0 Ash 5'5

Values are a mean of three estimations.

steady/states after the first 12 weeks. Though biogas production was high at 4 kg/m 3 per day loading rate, it was not proportional to the total solids in the system. However, 2 kg/m 3 per day loading was found to be most suitable for biogas production per kg of total solids used in digesters.

Biogas production was initially higher at 6 kg/m 3 per day, but steeply decreased after three weeks. This can be attr ibuted to a shift in pH to acidic range (5-6) requiring adjustment of pH to make the digester functional. However, this did not improve biogas digestion. Increases in ammonia, volatile acids and alkaline metals concentration which inhibit methane production has been reported in higher loading rates (Stafford et al., 1978; Kirimhan, 1982).

The methane content o f biogas produced from mango peels at 2, 4 and 6 kg/m 3 per day loading rates was 65, 60 and 40%, respectively. It was found

TABLE 2 Composition of Digested Mango Peels from the Field Digesteff

Constituents Grams per cent

Volatile solids (% of total solids) 80-5 Total solids (% of slurry) 4-5 Total nitrogen (% of total solids) 1"3 Phosphorus 0-40 Sodium 0-20 Potassium 0.25

a Values are a mean of three estimations. Detail constituents not estimated.


that higher loading rates reduces the methane content due to acidification of the digester. In the field trials, after an initial incubation period of 8 weeks, 3-3.5 ma/day of biogas was produced continuously from the 4 m a digester during the 4 month study. The methane content was between 60-65%. The composition of the effluent is shown in Table 2.

Aquaculture

The water temperature of the fish tank was 23-26°C and the dissolved oxygen 6.5-9.0 mg/litre in both ponds throughout the experimental period. The total alkalinity was comparable in ponds fed with biogas effluent (140 mg/litre) and ponds maintained on the control feed (155 mg/litre). The total alkalinity of the tanks, pH and oxygen were within the optimal range for fish growth (Umasharma & Grover, 1982).

The growth of carp is shown in Table 3. The survival rates were 84-86% in the control and 80-84% in the experimental group. Common carp and major carp had control weights of 150g and 115 g compared to 120 g and 85g on biogas effluent. The yields of both fishes in the control and experimental ponds were 11-24 and 8-35 kg/100 m 2 in the 4-month period. The extrapolated yields are 3372 and 2505 kg/ha per year, respectively. However, these are lower than those reported for intensive operations of 4000 kg/ha in Malaysia and 3000 kg/ha in the People's Republic of China and Taiwan (Bardach et al., 1972).

TABLE 3 Average Growth of Fish on Control Feed and Biogas Effluent (in grams)

Growth period (days)

Control Biogas

Common carp Major c a r p Common carp Major carp

Initial 9"5 10"5 10 15 (7-12) (8-14) (8-10) (10-20)

30 16 12"2 30 25 (13-35) (9"5-17) (22-40) (20-30)

60 45 43"5 72 40 (30-58) (34-53) (55-80) (35-55)

90 70 59-0 90 60 (40-95) (47-75) (95-110) (65-85)

120 150 115 120 85 (98-195) (88-150) (100-148) (90-115)

Weights shown are mean of forty fishes. Values in parentheses show the range of fish weight (g).

248 M. Mahadevaswamy, L. II. Venkataraman

TABLE 4 Sensory Evaluation of Fish Meat Raised on Control Feed (A) and Mango Waste Biogas

Effluent (B). Analysis of Variance of Mean Scores __+ SEM (3"27 df)

Qualities Common carp Rohu +_ SEM

(3"27 df) A B A B

Colour 4'3 3"8 3"7 3"5 0"29 Taste 4-1 3"8 3"9 3"7 0"40 Flavour 3"8 3'6 3"5 4'0 0"28 General quality 4"2 3"8 3"9 3"6 0"25

No significant difference (P = 0"5). Mean score: 1 - 1 ' 5 = n o t acceptable; 4.6-6 = very good.

1"6-2.5 = poor; 2"6-3-5 = fair; 3.6--4.5 = good;

Organoleptic qualities

The rank sum analysis of the individual sensory quality attributes and the overall quality are given in Table 4. Both the species of fish (Rohu and common carp) raised in the biogas effluent showed better 'juiciness', had comparable quality to the control in all other attributes and were acceptable

I ~ STEAM MANOO P SS'NG " ' TONS

1 ,8oo

FRUIT WASTE (720 TONS)

WATER J BIOGAS PLANT J BIOGAS -I (3600 M 3) 900M 3 (43200M 3) I BIOOAS (540 TONS)

WASTE

Fig. 1.

WATER _ JFISH PONDS I (675600 M 3) ~ 42 ha

ELECTRICITY (35820 UNITS)

[ 31' TONS I OF FISH

Model integrated system for biogas and fish production for a 15 tonnes/day mango- processing plant operating during the season of four months.


to the panel. Good organoleptic qualities have been reported also on fish grown on organic wastes and biogas effluent (Nandeesha et al., 1984; Mahadevaswamy & Venkataraman, 1988).

Though this study has been only exploratory in nature, a rough com- putation of energy values will illustrate the efficiency of such waste- utilization. For processing 15 tonnes day of mango, 5 tonnes of steam is required costing about US $150-200. (Anon., 1986). An equivalent amount of energy can be obtained from 1500m 3 of biogas.

TABLE 5 Project Costing for Integrated Utilization of Fruit-Processing

Waste for Biogas and Fish Production ° (for 15 t/day plant)

(I) Capital cost (a) Biogas plant (900 m a) $46 900 (b) Boiler (50 kg/h) $1 900 (c) 5 HP pump set (2 No:S) $1 200 (d) Land development for

fish ponds $10000

$60000

(II) Operating cost (a) Depreciation of plant

and machinery (20%) $10000 (b) Lease towards land $5 250 (c) Production cost

1. Electrical energy $2460 2. Labour $800 3. Fruit waste $4000 4. Miscellaneous $500

Savings on steam production from biogas plant

$23010

$4500

23010 - 4 5 0 0

18510

Net operating cost

Annual fish production = 34 tonnes Cost of production

per kg of fish 18 500

34 000 = $0"54

Costing done for Indian context--cost in Rupees converted to US $.


Figure 1 shows a model system for the production of biogas using all the waste from a mango industry (720 tonnes) obtained during a season of four months. Forty-two hectares of fish ponds are required to use the biogas effluent of 540 tonnes, giving a production of 34 tonnes of fish in four months. The cost computations for a full-scale plant utilizing the wastes are shown in Table 5; the costing have been based on Indian conditions. For ease of understanding, Indian rupees have been converted to US $. The cost of fish per kg raised on biogas will be US $ 0,54 while at the present market rate it sells at nearly US $1.00. The whole system looks promising. However the cost-benefit analysis of such an integrated system needs more detailed and careful analysis in view of the seasonal nature of the waste.

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

The authors thank M/s. Globe Food Pvt. L td and M/s. Frutin Exports (P) Ltd, Mysore for supplying the wastes. They are grateful to Mr S. Dhanraj for the statistical analysis.

REFERENCES

Anon. (1986). Information from Fruit Processing Industry. Frutin, Mysore. AOAC (1960). Official Methods of Analysis. Association of Official Analytical

Chemists, Washington, DC. APHA (1985). Standard Methods for the Examination of Water and Waste Water

(16th edn). American Public Health Association, New York. Bardach, J. E., Ryther, J. H. & McLarney, W. O. (1972). Aquaculture. The Farming

and Husbandry of Fresh Water and Marine Organisms. Science Editions, New York.

Beszedits, S. & Netzer, A. (1982). Protein Recovery from Food Processing Waste Water. B and L Information Service, Toronto, Ontario, Canada.

Bhatnagar, H. C. & Subramanyam, H. (1973). Some aspects of preservation, processing and export of mango and its products. Indian Food Packer, 27(4) 33-52.

Biswas, T. D. (1977). Biogas plants--prospects and limitation.. Invention Intelligence, 12, 77-80.

Harter, H. L. (1960). Critical values for Duncan's new range test. Biometric, 16, 671-5.

Kolmer, J. A., Spaulding, E. H. & Robinson, H. W. (!969). Approved Laboratory Techniques (5th edn). Scientific Book Agency, Calcutta, India.

Kirimhan, S. (1982). Methane generation from live stock waste. In Biomass utilization. Life Science Vol. 67, ed. W. A. Cote. Plenum Press, New York, pp. 511-27.

Lane, A. G. (1979). Methane from anaerobic digestion of fruit and vegetable processing waste. Food Tech. Aust., 31, 201-7.


Lane, A. G. (1982). Prospects for anaerobic treatment of food processing effluent. Food. Tech. Aust., 34, 410-11.

Martyshev, F. G. (1983). Pond Fisheries. American Publishing Co., Pvt. Ltd, New Delhi, India.

Maheshwari, R. C., Bohra, C. P. & Srivastava, P. K. (1984). Energy demand and biomass energy potential. Changing Villages, 6(5) 337-41.

Mahadevaswamy, M. & Venkataraman, L. V. (1988). Integrated utilization of rabbit dropping for biogas and fish production. Biological Wastes, 25, 249-56.

Mokshapathy, S. (1988). Handbook of Complete Statistics on Processed Fruits & Vegetables Exported from India (1977-1985). CFTRI Press, Mysore, India.

Nandeesha, M. C., Keshavanth, P. & Udupa, K. S. (1984). Evaluation of organoleptic qualities of fish grown in ponds treated with different organic manures. Fishery Technology, 21, 94-7.

Patel, B. M., Patel, C. A. & Talpada, P. M. (1972). Evaluation of mango seed kernels and tomato waste in the ration of bullocks. Indian. J. Nutr. and Dietet., 9(6), 347-50.

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Integrated utilization of fruit-processing wastes for biogas and fish production