DAIRY BIOTECHNOLOGY

Lesson 26. APPLICATION OF BIOTECHNOLOGY FOR DISPOSAL OF WHEY AND DAIRY EFFLUENTS

Module 5. Application of biotechnology in dairying

Lesson 26

APPLICATION OF BIOTECHNOLOGY FOR DISPOSAL OF WHEY AND DAIRY EFFLUENTS

26.1 Introduction

The dairy effluents including whey are quite rich in degradable organic matter and exert a high oxygen demand. The dairy effluents are peculiar as compared to other industrial wastes, because of relatively high concentrated effluent, particularly whey and butter washings. The processing of one litre of milk, yields about 8-10 litres of waste water depending on the type of products manufactured. More than 90 per cent of a dairy waste consists of milk components (lactose, proteins, and butterfat) that are lost and flow into floor drains during processing.

Whey is the major by-product, along with dairy effluents produced during the manufacture of cheese, paneer or casein from milk, representing 80 to 90% of the volume of milk transformed. It contains approximately 4.5% (w/v) lactose, 0.8% (w/v) protein, 1% (w/v) salts, and 0.1% to 0.8% (w/v) lactic acid. Proper disposal of whey is extremely important as it is considered as a pollutant due to its high biological oxygen demand (32, 000 to 60,000 ppm). Contaminating whey in natural water systems can quickly deplete oxygen levels due to the metabolic degradation of the organic constituents by the microbial population and hence disposing of whey has always been a major problem. Whey cannot be discharged into lakes or rivers for environmental reasons and at the same time, it is also not desirable to simply dump it to waste treatment facilities for economic reasons. Biotechnology offers ample opportunities in converting whey into numerous useful ingredients or product formulations reducing the burden on the effluent disposal.

26.2 Biotechnological Approaches in Treatment of Whey and Dairy Waste

The strength of whey pollution in dairy waste is determined by two parameters viz. Biochemical oxygen demand (BOD) and Chemical oxygen demand COD which are taken into consideration while designing the strategy for waste disposal.

Biochemical oxygen demand (B.O.D) is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. The BOD5 value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at 20°C.

Chemical oxygen demand (COD) is the amount of oxygen (in mg) required for the complete chemical oxidation of organic and inorganic material in 1 litre of an effluent

Before visualizing the application of biotechnological methods for treatment of whey and dairy effluents, it is important to be acquainted with the various processes involved in dairy product manufacturing and the pollution potential of different dairy products (Table 26.1)

Table 26.1 BOD and COD values for typical dairy products

26.2.1 Whey utilization and disposal

Whey is a complete protein, lush with amino acids and so it can be processed to produce a wide range of commercial products. In recent times the perception of whey from a “waste material” to an “opportunity'” for further processing is rapidly changing as recombinant DNA technology have offered a more direct way of manipulating the cell's metabolism for the production of specific biochemical products from whey. (Table 26.2)

Table 26.2 Some of the organisms used for utilization of whey for reducing the BOD

26.2.2 Dairy waste disposal

Dairy waste may be treated physically, biologically and chemically. The physical methods include, include screening, sedimentation, filtration, or flotation. Chemical processes comprises of disinfection, adsorption, or precipitation. Biological methods consist of aerobic systems such as activated sludge, trickling filter, oxidation ponds, lagoon technology and anaerobic systems.

However, genetically modified microbes can be produced by applying genetic engineering tools and used in several ways while dealing with different biological waste treatment methods for improving their efficiency and also generating useful end products for commercial use.

Recombinant DNA technology offers a more direct way of manipulating the cell's metabolism for the production of specific biochemical products. The technology has proved extremely useful for determining the nucleotide sequences of the DNA in and around genes and identifying those segments that are needed for the control of the genes or their products. These segments constitute prime targets that might be specifically mutated or deleted to alter the control of the genes. New genes might also be introduced into bacterial cells to give them novel synthetic capacities.

Application of recombinant DNA technology to waste treatment procedures involve two steps

• Finding a microorganism that has the desirable function (e.g., ability to degrade a pesticide)

• Transferring this desirable function to a suitable host, preferably a microorganism with some relevance from an environmental viewpoint

Some of the notable areas of applications of specially designed or genetically manipulated strains of microbes for utilization of whey or disposal of dairy waste in more economical way are summarized below:

1. BOD Reduction

Lactose utilizing yeasts such as Kluyveromyces sp. are important sources for the production of β-galactosidase enzyme. It is one of the most promising enzymes for biotechnological applications for treating whey and dairy waste for reducing the lactose concentration and BOD content

2. Single cell proteins

Conversion of whey and useful components form dairy waste into single cell protein serves two functions (i) for reduction in pollution and (ii) creation of edible protein. The Kluyveromyces species have been most widely studied for SCP production by converting lactose to protein into microbial biomass. The mixed culture of K. lactis and K. marxianus with S. cerevisiae was reported to be viable and an attractive alternative for removal of BOD and obtaining a valuable biomass yield.

3. Bio-ethanol

Several metabolic engineering approaches have been used to construct lactose-consuming S. cerevisiae strains, specifically involving the expression of the lactose genes of the phylogenetically related yeast Kluyveromyces lactis, and also from Escherichia coli and Aspergillus niger for the production of bio-ethanol from lactose.

4. Exopolysaccharides (EPS)

Modified lactic acid bacteria (LAB) such as Lactobacillus helveticus or Lactococcus lactis subsp. cremoris are being successfully employed for the production of EPS for use in various food formulations

5. Removal of toxic metals

Extracellular polymers produced by microorganisms commonly found in activated sludge display a great affinity for metals. Several bacterial types (e.g., Zooglea ramigera, Bacillus licheniformis) produce extracellular polymers that are able to complex and subsequently accumulate metals such as iron, copper, cadmium, nickel, or uranium. The accumulated metals can be easily released from the biomass by treatment with acids.

6. Biological fuel cells

Microorganisms can be used as electron donor in biological fuel cell (BFC) for the conversion of organic matter into power. One of the microbes exploited in this area is Rhodoferax ferrireducens. BFC generates electrical energy through the oxidation of biodegradable organic matter in the presence of either fermentative bacteria or enzyme under mild reaction conditions like ambient temperature and pressure

7. BOD Sensors

Biofilm-based biosensors consist of immobilized microorganisms trapped between a porous membrane and a gas-permeable membrane. Biosensors using pure microbial cultures (e.g., Bacillus subtilis, Klebsiella oxytoca, Clostridium butyricum, Pseudomonas putida, Trichosporon cutaneum) or mixtures of activated sludge microorganisms have been considered and are commercially available.

8. Biodegradation of oil

Biodegration of oil spills is a major problem. Moreover, a single bacterium cannot degrade all the components of oil which are petroleum products. Anand Chakrabarty, an Indian scientist, genetically engineered a strain of Pseudomonas putida that can degrade more than 3-4 compounds of petroleum.

9. Application of Immobilized cell technology can be used in the treatment of supernatant liquor which is a by-product of sewage sludge processing having high concentrations of ammonia. This high load of ammonia can be reduced by nitrifiers which convert ammonia to nitrate and this ammonia is oxidised to nitrite by Nitrosomonas, and then the nitrite is oxidised to nitrate by Nitrobacter.

Further Reading

Advanced Dairy Science and Technology, First Edition, Trevor J. Britz and Richard K. Robinson (Eds) Blackwell Publishing Ltd, UK, 2008

Biotechnology for Waste and Wastewater Treatment, Nicholas P. Cheremisinoff Noyes Publications, USA, 1996.

Environmental Biotechnology-Theory and Applications, Gareth M. Evans and Judith C. Furlong, John Willey and Sons Ltd, 2003

Handbook of Industrial and Hazardous Wastes Treatment, Lawrence K Wang, Yung-Tse Hung, Howard H Lo and Constantine Yapijakis (Eds) Marcel Decker Inc, USA 2004