3.5 TDS: “Total dissolved solids” refer to any minerals, salts, metals, cations or anions dissolved in water. It comprises of inorganic salts and some minute amounts of organic matter that are dissolved in water 5, 6.3.11 Sodium: Sodium exists in almost all irrigation water and is not essentially a cause for concern unless high concentrations are present. High concentrations (> 70 mg/L) can be dangerous to both plants and soils. Sodium in irrigation water can be absorbed by roots and flora, and foliar burning can occur if excess amounts accumulate in leaf tissue 12. 3.13.1 Total viable countIn routine analysis the total number of bacteria present in 1 ml of sewage is determined by standard plate count method. One set of plates is incubated at 370 C for 48 h (mesophilic bacteria). Another set of plates is incubated at 220 C for 72 h (psychrophilic bacteria) and yet another set of plate is incubated at 550C for 72 h (thermophilic bacteria). After incubation the colonies are counted and the amount of cfu/ml (colony forming units) can be calculated 15.Plate count technique is useful in determining the efficiency of operation for removing or destroying organisms. A microbial count can be made before and after a specific treatment and results obtained indicate the degree to which the bacterial population has been reduced. A water sample containing less than 100 bacteria per ml is considered to be safe 5.The total number of psychrophilic bacteriaNon pathogenic bacteria grow mainly at lower temperatures. It is important that Gram-negative bacteria in water produce lipopolysaccharides in their cell wall which can be toxic – like endotoxins of pathogenic bacteria. Because of this, their numbers in water should be constantly monitored. A large increase in their numbers is evidence of the presence of easily available organic compounds in the water. Theoretically, the presence of 0.1 mg organic carbon in water can result in an increase of bacteria up to 108 cfu in 1 ml.Phosphorus is also a factor which stimulates the growth of psychrophilic microorganisms. Adding even small amounts of this element (i.e.,50mg/l) causes 10 times the acceleration of bacterial growth in a water treatment plant 15.The total number of mesophilic bacteriaMore dangerous are high numbers of bacteria growing at 370C, because among this high population, pathogenic forms may be found which are dangerous for human health. High number of bacteria in samples of water can prove that water treatment processes proceed badly or that polluted water is siphoned15.The total number of thermophilic bacteriaIt is an index of production of gases such as methane that elevate the temperature of sewage and allow the proliferation of thermophilic bacteria14. 3.13.2 Total coliform and fecal coliform (MPN – Most probable number)It is statistical method based on the probability theory. In this technique, the sample is serially diluted till the numbers of organisms reach the point of extension. From each of these dilutions several multiple tubes of a specific medium are inoculated. Presence of organism is indicated by acid and gas in the medium. Pattern of positive and negative test results are then used to estimate the number of coliforms in the original sample. Since the test gives the most probable number of organisms present in the sample. it is also known as MPN test220.127.116.11 Study of biological nitrogen fixersAzotobacter is a free living, non symbiotic nitrogen fixing bacterium that brings about biological nitrogen fixation 17. Since the sewage is SBT treated it is possible that these valuable microorganisms may enter the treated sewage by diffusion from the soil. Enrichment technique is used to increase the number of this organism as its number is very few in soil samples and hence in the treated sewage.4. Materials and methods:4.1 pH: pH was determined by pH metry using a pH meter18. 4.2 COD: 50.1N Pottasium dichromate, 0.1M sodium thiosulphate, 2M sulphuric acid, 1% starch solution. COD was determined by titrimetry by using procedure using Aneja.4.3 BOD: 50.5% Allyl thiourea, 1N sulphuric acid, sodium hydroxide. BOD was determined by titrimetry by using procedure using Aneja.4.4 TSS: APHA 2540 D Total Suspended Solids Dried at 103–105°C 19.4.5 Oil and grease: American Public Health Association (APHA) 5520 B. Partition-Gravimetric Method 20.4.6 Microbiological analysis:Raw and treated sewage effluent samples were incubated overnight at 370C, before analysis.The samples were sampled to enumerate total viable counts and total coliform counts. Also, the fungi and actinomycetes present in the samples were studied. The sample was also checked for the presence of nitrogen fixing bacteria, Azotobacter spp.The samples were 10-fold serially diluted and the total viable count was carried out using appropriate dilutions, sterile molten nutrient agar medium and incubation conditions by pour plate method15. Determination of total coliform count was carried out by MPN (three tube method) using single and double strength Lauryl tryptose broth16.For the study of fungi and actinomycetes, a loopful of each of the samples were streak isolated on sterile Sabouraud’s dextrose agar and sterile Kenkunight and munnair’s agar plates respectively5. Azotobacter spp was isolated by enrichment in Sterile Ashby’s mannitol broth medium and subsequent streaking on sterile Ashby’s mannitol agar plates5.