FIELD OF THE INVENTION [001] The present invention relates in general to effluent treatment of wastewater. In particular it relates to a bio-augmentation composition for improving efficiency in effluent treatment for reduction of hydrocarbon content in wastewater generated from hydrocarbon processing industry. It further relates to a method of improving efficiency of treatment of waste water for reduction of hydrocarbons therein. The invention also relates to use of selective microorganisms as a microbial consortium in the composition for the purpose and their isolation. BACKGROUND OF THE INVENTION AND PRIOR ART [002] Basic wastewater treatment facilities reduce organic and suspended solids to limit pollution to the environment, however often they are not upto the satisfactory level. Lack of efficient waste water treatment may cause serious environmental damages and hence it is still a major concern for various industries. Depending on the type of industry and the nature of its wastes, industries have been utilizing various methods to purify wastewater containing pollutants such as heavy metals and toxic chemicals before it can be discharged, hi many parts of the world serious health problems and diseases have often been caused by discharging untreated or inadequately treated wastewater. Such discharges or water pollutants result in the spreading of disease and may cause destruction of other forms of aquatic life. [003] Petroleum processing industries use large quantity of water during various processing operations and produce large quantity of water contaminated with hydrocarbons, phenols, heavy metals and sulphides in varying amounts depending on the production processes. Besides that, accidental spillage of petroleum also causes contamination of water bodies. These pollutants, if left untreated can cause serious ill effects to the environment and human beings. Apart from that, if the water is to be re-used, it should be treated for removal of pollutants. The wastewater in a typical petroleum processing industry is treated in Effluent Treatment Plant (ETP) by various physico-chemical methods in which the economically recoverable products like hydrocarbons are recovered and the rest pollutants are degraded by mainly microbial action. [004] At present, wastewater treatment plants commonly utilize one or more processes for the treatment of wastewater. The most widely used wastewater treatment process is that of "primary treatment" which relies on plain sedimentation of settleable wastewater solids for Biochemical Oxygen Demand (BOD) and suspended solids removal. The efficiency of the primary process is in the 25-30% range. However, the results of primary treatment can be improved by the use of chemicals to enhance the settleability of wastewater solids. [005] In addition to the primary treatment process, there is a number of "secondary treatment" processes employed. These processes improve water quality by employing the growth of biological masses, which utilize the pollutants in the water for nutrients in their metabolic life cycles. The subsequent removal of the biological masses from the wastewater results in an effluent of an improved quality. [006] The "trickling filter" treatment is one secondary technique widely used in the treatment of wastewater. The filter is a packed bed of media, which provides a surface upon which a film of biological slime can grow and over which the wastewater is passed. The oxygen and organic matter in the wastewater diffuse into the film where the oxidation and synthesis of additional growth can occur. Plants using the trickling filter method can effect a carbonaceous BOD removal of 60 to 90 percent, depending mainly on the loading rate of the facility. In addition, the trickling filter process can effect an oxidation of the ammonia present in the wastewater, which is desirable. [007] The other and probably most widely used secondary treatment for wastewater is the "activated sludge" process. The activated sludge process can be defined as a process in which flocculated biological growths are continuously circulated and contacted with organic wastewater in the presence of oxygen. The oxygen is usually supplied by bubbling air into the sludge-liquid mixture in an aeration tank. This air can be introduced through air diffusers to develop a hydraulic motion of the contents of the aeration tank. A typical hydraulic motion involves a "spiral roll" of the contents of the aeration tank. The aeration step is usually followed by a solid-liquid separation from which a portion of the biologically active sludge is separated and recycled back to the aeration tank to provide an active source of bacterial growth to continue treatment. The activated sludge process under optimum conditions can be up to 90% effective in the removal of carbonaceous BOD. However, the "activated sludge" process is not without disadvantages as it can be readily upset by surges in the volume of wastewater and other circumstances which may prevent the attainment of the designed goals. [008] Microbial degradation appears to be the most environment friendly approach of oil removal as these microbes transform the pollutants to CO2 and water. Typically, the biological treatment of the wastewater is carried out in the biological treatment section by the activated sludge process. In activated sludge process wastewater containing organic matter is aerated in an aeration basin in which micro-organisms metabolize the suspended and soluble organic matter. Part of organic matter is synthesized into new cells and part is oxidized to CO2 and water to derive energy. In activated sludge systems the new cells formed in the reaction are removed from the liquid stream in the form of a flocculent sludge in settling tanks. A part of this settled biomass, described as activated sludge is returned to the aeration tank and the remaining forms waste or excess sludge. The efficiency of microbes in activated sludge process depends upon the concentration of pollutants, presence of heavy metals, availability of carbon source, temperature, pH and process conditions like mixing regime, loading rate, and the hydraulic flow rate. Gram- negative heterotrophic bacteria mainly of Pseudomonas type constitute the majority of microorganisms present in activated sludge. [009] The biological treatment of industrial wastewaters by activated sludge process is, however, often disrupted by shock load from organic (e.g., chlorinated organics, phenolic compounds, surfactants, and herbicides) and inorganic (e.g., heavy metals, sulfides, and ammonia) chemicals present in the wastewater stream. This disruption of biological processes results in decreased carbon removal and modification of sludge compaction properties. Little is known about the composition of mixed microbial communities in reactors when biological processes are disrupted by or recovering from. Besides that, day by day, the statutory requirement for limit of hydrocarbons in effluent discharge is being decreased by statutory bodies. For example, in India the limit has been reduced from 10 ppm to 5 ppm for oil and grease (O&G) content effective by 2009. This also calls for the invention which can be used to meet the requirement by no change in the existing ETP configuration, which is a very cost intensive affair. [010] Petroleum refineries produce wastewater from their various processes. This water is treated in the ETPs. Bioremediation, using activated sludge is one option for the treatment of such wastes. Biological units (trickling filter and aeration chambers) reduce the O&G content by catabolic capacities of microbes. The extent of degradation depends on presence of required catabolic gene pool as well as in their numbers. ETPs are usually unable to completely degrade the wastewater being treated in the biological unit (the aerator chambers). By providing the desired catabolic potential in adequate numbers, the overall efficiency of the treatment system can be improved by bio-augmentation and/or bio-stimulation. Bio-augmentation of activated sludge systems with specialised bacterial strains could be a powerful tool to improve several aspects in wastewater treatment processes, such as improved degradation of recalcitrant compounds. [Oil] Bioremediation strategies rely on the catabolic capacities of microbes to transform harmful pollutants into harmless compounds. Wastewater generated from the petroleum industry finds its way into soil and water bodies causing pollution problems of increasing magnitude. Despite decades of research, successful bioremediation of petroleum wastes still remains a problem. Treatment of this wastewater in ETPs is carried out by microbial biomass in the activated sludge of the ETP. The efficiency of the microbial population depends on various factors, such as the concentration of pollutants, their availability as a carbon source, temperature, pH, etc. Due to adverse stress conditions, the ETP does not run at its maximum efficiency and the treated wastewater still contains high Chemical Oxygen Demand (COD) levels. Sometimes, the required gene pool for further degradation may not be present or its titer value could be too low for sustained expression. In such cases, methods like nutrient addition (bio-stimulation) or the addition of laboratory grown bacteria that have the desired degradation capacity (bio- augmentation) could be followed. The effects of bio-stimulation on total petroleum hydrocarbons have been extensively investigated in controlled conditions and in open field experiments under optimal conditions. It is reported that nutrient supplementation may speed up the process of bioremediation, since the addition of large quantities of oil results in a high C:N ratio which is unfavorable to microbial activity. In cases where natural communities of degrading bacteria are present in low numbers or even absent, bio-augmentation, i.e., the addition of contaminant- degrading organisms can speed up the degradation process. The main advantage of bio- augmentation is the addition of a different gene pool that complements the existing one and helps in further degradation of pollutants. [012] Bio-augmentation, the addition of bacterial products that increases the biological activity in the system and addition of optimized nutrients could be beneficial to enhance the degradation efficiency. This helps to reduce the contaminants in faster manner. Bio- augmentation products can be either liquid or dry. Because of ease of handling, liquid products are generally preferred and can be added by a liquid metering pump drawing on a container that is replenished on a periodic basis. However, dry formulations are preferred for other applications such as waste treatment facilities. Strains used in bio-augmentation of hydrocarbons should have efficient hydrocarbon degrading ability to produce hydrocarbon solubilizing surface active agents and should have tolerance/detoxification methodology for heavy metals like vanadium, nickel and chromium etc. Since, the activated sludge operates in ambient conditions, changing seasons, particularly in tropic countries like India, where all extremes of three seasons i.e., winter, summer, rainy seasons are observed, the bio-augmentation formulation should have ability to grow and effectively remove toxicants. Bio-augmentation product should also have the ability to stabilize in aeration tank and multiply in appropriate numbers. The growth of the added microbes should also not be inhibited by already present in activated sludge and vice versa. When Gram-negative microorganisms are used for bio-augmentation, they are present as vegetative cells and as such they may be killed by chemicals, such as surfactants, heavy metals which often remain present in the wastewater. The spore forming Gram-positive bacteria are more resistant to the toxic substances. [013] Accordingly, there is a need to develop bio-augmentation formulations that can effectively and efficiently degrade oil and grease and which should have environment-tolerant features to work in seasonal variations. There is a further need for increasing tolerance level of the microbial consortium which can detoxify/tolerate heavy metals present in the wastewater and the process should work without any change in the existing ETP configuration. [014] US Patent 4,093,539 discloses a method for operating an activated sludge wastewater treatment plant, which utilizes rotating contactors that are partially submerged in the wastewater in the aeration tank of the activated sludge plant. The rotating contactors provide a fixed film media for the growth of biological life that is present in the recycled activated sludge in the aeration tank. The result is a more active biological coating on the fixed film media than is found on such media when used as a separate secondary treatment. In the preferred embodiment, the energy to rotate the contactors is supplied by the same compressed gas that is normally introduced below the surface of the wastewater in the aeration tank of the conventional activated sludge system [015] US Patent 5,705,072 discloses a process for bio-treatment of effluent from waste gas scrubbing systems of hydrocarbon processing facilities and for the biotreatment of sulfide and ammonia containing wastewater streams from other sources. Sulfides are minimized by bacteria cultures, particularly Thiobacillus. COD, TKN and BOD are concurrently minimized by co-cultures of the bacteria with various heterotrophs. In a version of the process, the co-cultures of the bacteria with various heterotrophs are also capable of performing nitrification, without application of nitrifiers. Acclimation of the heterotrophs to the species to be removed is accomplished by biological acclimation and enrichment reactors which reduce mycell toxicity to the heterotrophs. To control pH of the heterotrophic reaction with sulfides, magnesium oxide (MgO) and caustic are used separately or in combination. With adequate removal of the COD, TKN and BOD, nitrification and removal of ammonia can be accomplished by nitrifying bacteria cultures, particularly nitrosomonas and nitrobacters. Enrichment of the nitrosomonas and nitrobacters is accomplished by using a biological enrichment reactor. To control pH and provide a carbon source for the nitrosomonas and nitrobacters, a combination of magnesium oxide and sodium bicarbonate is utilized. [016] US Patent 6,818,211 discloses a Gram-positive microorganism, Bacillus megaterium that effectively and efficiently degrades fatty acids. A composition comprising said microorganism and a method for degrading fatty acids and grease are also disclosed. Availability of glycerol to the biodegrading microorganism was discovered to enhance biodegradation. [017] US Patent 6,25,1657 discloses an apparatus and method for anaerobic biodegradation, bioremediation or bioprocessing of hydrocarbon dissolved in aqueous matrix, such as wastewater, ground water, or slurry and dissolved alkanes, aromatic hydrocarbons and/or halogenated hydrocarbons that are metabolized or co-metabolized by denitrifying bacteria. [018] US Patent 7,560,027 discloses a method and an apparatus for treating organic wastewater and sludge which remarkably reduce the generated amount of sludge at a much lower running cost, and which reduce the size and the capacity of the solubilization tank. The method and apparatus for treating the sludge employs a biological treatment system, wherein a biological treatment of wastewater is carried out, and a solid-liquid separation unit for separating a solid from a liquid in the wastewater after the biological treatment gives a treated wastewater and a sludge. The apparatus has a means for obtaining a withdrawn sludge from a part of the sludge and an alkali-treatment tank, wherein an alkali-treatment of the withdrawn sludge is carried out. The apparatus also has a biological solubilization tank which solubilizes the sludge after the alkali-treatment under an anaerobic, anoxic or microaerophilic condition, and a means for recycling the solubilized sludge to the biological treatment system. [019] US Patent 6,653,120 discloses generally biodegrading volatile organic compounds found in refinery liquid waste streams and, in particular, a process and apparatus for removing volatile organic compounds from refinery liquid waste streams. Volatile organic compound content of liquid refinery waste stream is reduced by using aqueous solutions containing microbes. [020] US Patent 7,547,394 teaches about a wastewater treatment system using aerobic granules which has a large number of sequencing batch reactor tanks with high volumetric exchange rate, a variable cycle length and constant batch volume. The batch reactors are operated for C, N removal and P is removed chemically, optionally under BioP enhanced conditions. SS are removed in a downstream separation step. [021] US Patent 7,344,643 discloses a process which utilizes an activated sludge tank, a solid-liquid separator, and a bioreactor to significantly reduce, or eliminate, waste activated sludge (WAS) within a sludge stream. A sidestream reactor is employed downstream from the bioreactor to remove soluble phosphates left in the sludge stream by the low WAS process. Within the sidestream reactor, a source of multivalent metal ions is added to a slightly alkaline sludge stream to precipitate the phosphates. The solid phosphates have a specific gravity higher than that of the organic matter in the sludge stream and may be separated from the sludge stream based upon differential settling velocity. [022] Burgess et al. 2000 (JE Burgess, J Quarmby and T Stephenson Vitamin addition: an option for sustainable activated sludge process effluent quality; Journal of Industrial Microbiology & Biotechnology (2000) 24, 267-274) describe the process wherein performance and metabolic rates of samples of activated sludge dosed with vitamin supplements have been compared. After initial screening, four vitamins and two metals as single supplements and in pairs were dosed continuously into the mixed liquor of an activated sludge simulation. Toxicity, oxygen demand removal, respiration rates and suspended solids were measured to monitor the effect on process efficiency. It was confirmed experimentally that an industrial wastewater stream did not contain a sufficient supply of micronutrients for efficient biological treatment. This was concluded from the observation that control sludge batches (receiving no supplements) averaged chemical oxygen demand removal efficiency of 58%. Dosing micronutrients into the mixed liquor produced removal efficiencies of up to 69%. Some of the supplements increased the respiration rate of the sludge while some decreased it, indicating a range of stimulatory and inhibitory effects. Complex interactions between micronutrients that were dosed simultaneously were evident. Several positive effects led to the conclusion that micronutrients have the potential to optimise process performance of activated sludge plants treating industrial wastewater. The addition of phosphorus/niacin and molybdenum/lactoflavin removed wastewater components that were toxic to nitrifiers as indicated through toxicity testing, thus protecting downstream nitrification/denitrification treatment processes. [023] Pala and Sponnza 1996 (A. I. Pala; D. T. Sponza Biological Treatment of Petrochemical Wastewaters by Pseudomonas Sp. Added Activated Sludge Culture. Environmental Technology, Volume 17, Issue 7 July 1996, pages 673-685) isolated a Pseudomonas sp. from the activated sludge of a petrochemical industry treatment plant and used as an inoculum culture for biological treatment of petrochemical wastewaters. The objective was the comparison of biological treatment efficiencies between Pseudomonas sp. added activated sludge and normal activated sludge taken from the full scale treatment plant. Experiments were carried out both in batch and continuous operations using a laboratory scale activated sludge system. Monod kinetic was used to determine kinetic coefficients from the experimental data of continuous operations. The maximum COD utilization rate constant (k), saturation constant (Ks), microbial decay rate (k