Introduction

Molasses (one of the important by- products of sugar industry) is the chief source for production of ethanol by fermentation method. In the year 1999, there were 285 distilleries in India producing 2.7 x 10⁹ l of alcohol and generating 4 x 10¹⁰ l of wastewater each year¹. This number has gone up to 319, producing 3.25 x 10⁹ l of alcohol and generating 40.4 x 10¹⁰ l of wastewater annually ². For every liter of ethanol production emerges about 8 liters of waste water called as raw spentwash (RSW). This RSW is known for   high BOD (5000-8000mg/L) and COD (25000-30000mg/L)³, undesirable color due to the presence of water soluble recalcitrant coloring compound called melanoidin⁴ and foul odor⁵. Besides a number of pathological pollutants. The chief among the notable pollutants, is melanoidin pigment which is brown in color that stains the superficial water sheet and in turn cuts off the light rays and dulls photosynthesis when RSW is let into water bodies (tanks, lakes, channels, Ponds, etc). The brown ting of melanoidin pigment is the outcome of mailard reaction between sugar and amino compounds⁹. The RSW contains pyrogenic compound like polycyclic aromatic hydrocarbons (PAHS) and benzo (a) pyrene, a known environmental carcinogen ^10-16.RSW is highly acidic and contains  easily oxidizable organic matter with very high BOD and COD, this untreated RSW is let into water courses could definitely cause a great strain on aquatic life. But by installing biomethonation plant in distilleries would positively reduces oxygen demand of RSW. Thus, the resulting spentwash is known as primary treated spentwash (PTSW). Even though, PTSW has adverse effect on the aquatic life.

Tilapia fish is originated from Nile valley and spread to entire globe. This group of fishes can be cultured under very basic conditions and  is ideal for rural subsistence farming, yet is minimal management and energy inputs. These fish have high reproductive and growth rates, are relatively disease free and hardy in nature.

Tilapia is the fifth most important fish in farming with production reaching 1,505,804 metric tons.¹⁷ Because of their large size, rapid growth, and palatability, tilapia are focus of major farming. Like other variety of fishes, tilapia   are a good source of protein and also tilapia have very low levels of mercury¹⁸ as they are fast growing and short lived with a primarily herbivorous diet and thus do not accumulate mercury found in prey ¹⁹_. Tilapia has low saturated fat, low calorie, low carbohydrate and low sodium protein source. It is a source of phosphorus, niacin, selenium, vitamin B12 and potassium. Tilapia is unable to survive in low temperature climates because they require warm water.

As a part of our ongoing studies of implication of distillery spent wash on the aquatic life²⁰ the present work is focused on the study of life sustainability of tilapia fishes (Oreochromis niloticus) on exposure to different concentrations of PTSW.

Material and Methods

Physico chemical parameters of PTSW (100%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%,.7%,0.8%,0.9%,1.0%,1.1%,1.2%,1.3%1.4%,1.5%,1.6%,1.7%,1.8%1.9%,2.0%2.1%,2.2%) were analyzed by standard methods (Table 1). Two hundred  and seventy six tilapia finger ling fishes obtained from  G.K.V.K Bangalore, Karnataka and divided into 23 groups,  and were set in  aquarium of 36” x 15” x 18” size. These were exposed to different concentration of PTSW (0.1% to 2.2%) with normal feeding. G1 was kept as control unit.  The mortality rate (MR) was recorded in each case up to 6 days of exposure (Table 2).     

Results and Discussion

In G23 (2.2% PTSW) the MR was 100% after 12h  exposure,50% in G22 (2.1%PTSW) and 16% in G21(2.0%PTSW) It was found that MR differs for G23, where as from G1 to G20 the MR was zero even after exposure for 6 days (Fig 1). The higher MR was noticed in G23 at higher concentration of PTSW with insufficient dissolved oxygen (DO). But in G1 to G20, DO was sufficient for respiration of the fishes as such they behaved normally and in higher concentration of PTSW fishes  get disturbed and were swimming rapidly with random moment . A thick coat of mucus was observed all over the body of the fishes making the fish slimier^21-23.The fishes was swimming with belly upward and zig-zag motion. There were also erratic and parallel movements observed in fish, indicating the loss of equilibrium.

Table 1: Physico-chemical parameters of different dilutions of spentwash

PTSW – Primary Treated spent wash

Table 1 Contd………

PTSW – Primary Treated spentwash

Table 2: Mortality rate (%) of tilapia fish exposed to different dilutions of spentwash

PTSW –   Primary Treated spent wash

Figure 1: Indicate Mortality rate, No of fish exposed, concentration of   PTSW, No of fish dead.   Click here to View figure

Conclusion

The discharge of distillery spent wash into water bodies at higher concentration leads to deficient of sunlight into water (due to dark brown color) and further the spent wash promotes   mucus formation on the gills of the fishes. Hence, there is a reduction of oxygen tension in gills of fishes, which makes them behave abnormal due to insufficient dissolved oxygen and finally leads to death.

The present study revealed that, higher the concentration of distillery spent wash lead into water bodies, the more the depletion of tilapia fishes.

Acknowledgement

Authors are grateful to the General Manager, Nijaveedu Sugars Ltd., Koppa, Mandya, Karnataka for providing spentwash.

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