Dairy Effluent Polishing by Aquatic Macrophytes

DAIRY EFFLUENT POLISHING BY AQUATIC MACROPHYTES

B. D. TRIPATHI∗ and ALKA R. UPADHYAYDepartment of Botany, Banaras Hindu University, Varanasi-221005, India

(∗ author for correspondance, e-mail: [email protected])

(Received 9 November 2001; accepted 15 July 2002)

Abstract. In dairy industry, primary and secondary treatment methods are quite common for effluenttreatment. However, this type of treatment is not effective in filtering the nutrients from the dairywaste water. Nutrient removal capacity of some important macrophytes i.e. Eichhornia crassipes,Lemna minor and Azolla pinnata have been tested individually as well as in combinations undermicrocosm investigations. Percentage nitrogen removal values by E.crassipes, A.pinnata and L.minor were 71.8 ± 0.20, 62.5 ± 0.39 and 60.13 ± 0.48. Corresponding figures for phosphorus were63.2 ± 0.98, 58.8 ± 0.57 and 56.3 ± 0.51. Maximum removal was observed in combination studies,involving E. crassipes and L. minor (78.8 ± 0.18% nitrogen and 69.4 ± 0.11% phosphorus). Analysisof variance revealed significant (p < 0.001) variation among different incubation periods, both fornitrogen (F = 395985) and phosphorus (F = 196767) removal by a combination of E. crassipes,and L. minor. E. crassipes and A. pinnata removed 74.1 ± 0.11% of nitrogen and 68.7 ± 1.0%of phosphorus, whereas, it was recorded 70.0 ± 0.25% nitrogen and 66.7 ± 0.95% phosphorus bycombination of L. minor and A. pinnata.

Keywords: dairy effluent treatment, treatment by aquatic macrophytes

1. Introduction

Dairy industry in India has grown from an almost unorganized to a complex organ-ized industry of large magnitude during the last forty years. Nowadays India ranksfirst among milk producing countries. The industry is a significant contributor topollution. Its wastes are generally fractions of milk or milk products, together withdetergents, sanitizers, chemicals from boiler and domestic wastes (Tripathi et al.,2000).

It is true that the quantity of milk, lost to the drain, is reduced by adopting recentmethods of mechanized handling. However, hygienic requirements in the industryresults in huge amount of waste water generation. The dairy effluent is predomin-antly organic in nature (Kearney, 1973) and due to its biodegradable constituents, itis amenable to conventional (primary and secondary) treatment (Brown and Pico,1980). It is probably due to this reason that most of the existing dairies have treat-ment plants based on the efficient and dependable activated sludge process. Thistype of treatment method is not effective in filtering the nutrients from the dairywaste water.

Water, Air, and Soil Pollution 143: 377–385, 2003.© 2003 Kluwer Academic Publishers. Printed in the Netherlands.

378 B. D. TRIPHATI AND A. R. UPADHYAY

The capacity of vascular aquatic plants to assimilate nutrients from polluted wa-ters is well recognized (Rogers and Davis, 1972; Steward, 1970). Vascular aquaticmacrophytes such as water hyacinth, duckweed and cattails, cultured in ponds andreservoirs offer potential alternatives for treating sewage and industrial effluents(Boyd, 1969; Wooten and Dodd, 1976; Wolverton and McDonald, 1979) and agri-cultural effluents (Reddy et al., 1982). Many research workers have discussed thenitrogen and phosphorus removal capacity of different aquatic plants (Wolvertonand McDonald, 1979; Tripathi et al., 1991).

However, as most of these studies are restricted to one or very few plants,no comparative data among different plants and their combinations grown underthe same environmental condition are available. The purpose of this study was toevaluate the role of different types of aquatic macrophytes in removing nitrogenand phosphorus from dairy waste water and to establish their role in improvingwater quality.

2. Methods

Study was designed to evaluate the nutrient removal capacity of selected aquaticmacrophytes such as Eichhornia crassipes, Lemna minor and Azolla pinnata. Allthe three plants were cultured individually (monoculture) with 100% cover andin combinations with equal coverage of the total surface area of aquarium by thetwo partners in mixed cultures. Three replicates of each were maintained in 150 Lglass aquarium. Roots of all selected plants were washed thoroughly in tap waterand placed in separate glass aquariums. Control experimental sets contained onlydairy waste water without any macrophyte. During present investigation twentyone aquariums were used. In each aquarium, 95 L of waste water was poured.Physico-chemical properties of waste water used for aquaculture experiments wereanalysed weekly. However, plant analysis was done at initial and final stage of theexperiment.

Dairy effluent was collected from Ramnagar Dairy (Feeder Balancing Dairy)Ramnagar, Varanasi and transported to the laboratory in the dairy factory premises.Ramnagar dairy uses effluent treatment plant with surface aerators as the secondarytreatment. Effluent used in this study was collected from the discharge point.

Physico-chemical analysis of waste water was done by using standard methodsfor the examination of water and waste water (1995). The plants were analysedfor total nitrogen-N by microKjeldahl (Peach and Tracey, 1956). Wet oxidationmethod was used to determine the total phosphorus-P content of the plant tissues(Jackson, 1962).

DAIRY EFFLUENT POLISHING BY AQUATIC MACROPHYTES 379

Figure 1. Removal of nitrogen by aquatic macrophytes (± 1 SE)

2.1. NUTRIENT REMOVAL CAPACITY

The nutrient removal capacity of each plant species and its combination was cal-culated by using the formula C = I − F

T (Tripathi et al., 1991), where C = nutrientremoval capacity of the plant, I = Initial concentration of nutrient in the water, F =Final concentration of the nutrient in the water, and T = Time taken for the removal.

Study was conducted from 15 September, 1999 to 9 November, 1999 (56 daysincubation period). A constant water level was maintained during this time byreplacing it with distilled water. Diluting effect of distilled water on the N andP was recorded to calculate the actual removal by the macrophytes.

3. Results

Removal of nitrogen and phosphorus from dairy waste water by aquatic macro-phytes are shown Figures 1 and 2. Table I shows physico-chemical characteristicsof dairy waste water used for study. Tables II and III show plant tissue contents.

Nitrogen as well as phosphorus removal was found to be faster in E. crassipesfollowed by L. minor and A. pinnata in monoculture. N removal by E. crassipes,Lemna minor and Azolla pinnata were 71.8 ± 0.20, 62.5 ± 0.39 and 60.1 ± 0.48%,


Figure 2. Removal of phosphorus by aquatic macrophytes (± 1 SE)

TABLE I

Physico-chemical characteristics of waste water used forstudy (± 1 SE)

Temperature (◦C) 21.3 ± 0.8

PH 6.97 ± 0.2

TDS (mg L−1) 1420.7 ± 12.2

TSS (mg L−1) 70.4 ± 1.5

Oil and grease (mg L−1) 2.7 ± 0.09

BOD5 (mg L−1) 29.1 ± 1.0

COD (mg L−1) 209 ± 2.5

Phosphate (mg L−1) 3.7 ± 0.05

Total Kjeldahl nitrogen as N (mg L−1) 43.9 ± 1.2

Chloride (mg L−1) 76.4 ± 1.32

Sulphate (mg L−1) 79.8 ± 1.1


Figure 3. Removal of nitrogen by aquatic macrophytes (combination studt) (± 1 SE)

respectively. Similarly, 63.2 ± 0.98, 58.8 ± 0.57 and 56.3 ± 0.51% of P have beenremoved by the three macrophytes.

During present investigation highest removal of nitrogen (78.8 ± 0.18%) wasrecorded in mixed culture of E. crassipes and L. minor, followed by 74.1 ± 0.11%in mixed culture of E. crassipes and A. pinnata, and 69.9 ± 0.25% in L. minor andA. pinnata (Figures 3 and 4). Statistical analysis revealed significant variation (F =395985, p < 0.001) among different incubation periods. Similarly highest removalof phosphorus (69.4 ± 0.11%) was noted in mixed culture of E. crassipes and L.minor followed by 68.7 ± 1.0% in E. crassipes and A. pinnata and 66.7 ± 0.95%in L. minor and A. pinnata. Analysis of variance revealed significant variation (F= 196767, p < 0.001). In the control experimental set (without any macrophytes)slight removal of 13.1 ± 0.02% nitrogen and 8.4 ± 0.05% phosphorus were alsodetected.

In plant tissue content analysis for total nitrogen, maximum 58.2% increasewas recorded in E. crassipes in case of individual experimental sets (Table II).E. crassipes and L. minor in combination experimental sets were recorded withhighest increase in E. crassipes (59.2%) as well as L. minor (31.4%) (Table II) fortotal nitrogen content in plant tissues at the end of retention period. Combinationexperimental sets containing E. crassipes and A. pinnata were also observed withremarkable increase in plant tissues content with 58.4 and 18.1% total nitrogenrespectively.


Figure 4. Removal of phosphorus by aquatic macrophytes (combination studt) (± 1 SE)

TABLE II

Total nitrogen content in plant tissues (g kg−1) (± 1 SE)

Initial Final % increase

Individual study

E. crassipes 15.1 ± 0.01 23.9 ± 0.02 58.2

L. minor 20.3 ± 0.20 26.0 ± 0.15 28.1

A. pinnata 22.7 ± 0.43 26.7 ± 0.14 17.8

Combination study

Eichhornia + Lemna

E. crassipes 15.1 ± 0.01 24.1 ± 0.07 59.2

L. minor 20.3 ± 0.20 26.7 ± 0.25 31.4

Eichhornia + Azolla

E. crassipes 15.1 ± 0.01 24.0 ± 0.05 58.4

A. pinnata 22.7 ± 0.43 26.8 ± 0.08 18.1

Lemna + Azolla

L. minor 20.3 ± 0.20 26.4 ± 0.05 29.8

A. pinnata 22.7 ± 0.42 26.7 ± 0.05 17.4


TABLE III

Total phosphorus content in plant tissues (g Kg−1) (± 1 SE)

Initial Final % increase

Individual study

E. crassipes 3.43 ± 0.03 5.83 ± 0.04 70.0

L. minor 6.86 ± 0.05 9.29 ± 0.09 35.4

A. pinnata 6.89 ± 0.09 9.63 ± 0.03 39.7

Combination study

Eichhornia + Lemna

E. crassipes 3.43 ± 0.03 5.86 ± 0.04 70.8

L. minor 6.86 ± 0.05 9.38 ± 0.01 36.9

Eichhornia + Azolla

E. crassipes 3.42 ± 0.03 5.83 ± 0.01 70.5

A. pinnata 6.89 ± 0.09 9.64 ± 0.03 39.2

Lemna + Azolla

L. minor 6.86 ± 0.05 9.32 ± 0.03 35.8

A. pinnata 6.89 ± 0.09 9.62 ± 0.02 39.6

Phosphorus content in plant tissues was also analysed and the results are shownin Table III. It is evident from the data that E. crassipes showed an increase of PO4-P by 70.5 and 70.8% in mixed culture and 70.0% in pure culture. But the percentincrease of PO4-P ranged between 35.4 and 36.9% in case of L. minor and 39.2and 39.7% in A. pinnata.

4. Discussion

An increasing content of nitrogen and phosphorus in the E. crassipes and L. minortissues (Tables II and III) and decreasing concentration of N and P in waste waterat the end of experiment reveals that nitrogen and phosphorus are absorbed by theplants from the waste water.

Dissolved oxygen content of the water under large-leaf floating plant was low,similar findings were observed by Reddy, 1981. In L. minor containing experi-mental sets oxygen content of the water was found to be the highest. Eichhor-nia forms a dense mesh on the water surface which reduces oxygen diffusion atair-water interface while Lemna allows a greater oxygen diffusion.

The deficient supply of O2 (by surface aeration) did not affect the purificationprocess. Sculthorpe (1967) reported that some O2 produced during photosynthesis


is transported to the plant roots. Whereas, Dinges (1982) has reported that atmo-spheric oxygen enters the stomata of the hyacinth stems/leaves, which is transpor-ted down into the roots. However, this oxygen release keeps the microorganismson the roots metabolizing aerobically, even though the surrounding water is anaer-obic. In a study of nitrifier distribution in rivers, Matulewich and Finstein (1978)reported that greater numbers of nitrifiers colonized submerged roots and stemsof aquatic plants than other potential attachment sites (rocks, bottom sediments,etc.). In aquatic systems with dense cover of floating plants (water hyacinth orpennywort), denitrification can possibly occur in the root zone of floating plants(Reddy, 1983).

Considerable variability in the phosphorus content of the dairy waste water wasobserved. Phosphorus content of aquatic macrophytes was closely related to thephosphorus content of the dairy waste water. Loss of phosphorus in the control(with no macrophytes) was probably due to precipitation with Ca compounds athigh pH levels. Diel variations in water pH can play an important role in controllingP availability in calcareous water bodies (Reddy, 1983). Higher accumulation per-centage of phosphorus in the tissues of water hyacinth was detected in comparisonto the nitrogen (Tables III and IV).

Highest removal of nitrogen and phosphorus in mixed culture of E. crassipesand L. minor in comparison to their nutrient removal capacity when grown indi-vidually, indicates synergistic effect. There seems to be a possibility of biochem-ical and physico-chemical processes functioning (Johnson and Schroeffer, 1964;Wuhrman, 1964).

5. Conclusions

E. crassipes and L. minor was found to be the best possible combination for re-moval of nitrogen and phosphorus from the dairy waste water. With the help ofE. crassipes and L. minor about 78.8 ± 0.18% N and 69.4 ± 0.11% P may beremoved. Combinations of large leaf and small leaf aquatic macrophyte removedhigher nitrogen and phosphorus. E. crassipes and L. minor combination may beused for the treatment of dairy waste water as tertiary treatment. After harvestingwater hyacinth plants may be used for the production of biogas, rough qualitypapers and insulators etc., where as both the plants may be used for productionof manure.

Acknowledgement

We thank Prof. R. S. Ambasht, Emeritus Scientist, Department of Botany, BanarasHindu University, Varanasi-221005, India for valuable comments on the manu-script. The staff at the Ramnagar Dairy (Feeder Balancing Dairy), Ramnagar, Vara-nasi are gratefully acknowledged for their technical assistance.


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Dairy Effluent Polishing by Aquatic Macrophytes