Novel approach for the treatment and recycle of wastewater from soya edible oil refinery industry—An economic perspective
Introduction
Saving water to save the planet earth and to ensure a safe future for mankind is the ultimate need of the hour. With the growth of mankind, society, science, and technology our world is reaching to new high horizons but the cost which we are paying or will pay in near future is surely going to be too high. Environmental disorder with an increased pollution problem is one of the consequences of this rapid growth. Besides other needs, the demand for water (“Water for People Water for Life” United Nations World Water Development Report UNESCO) has increased tremendously with agricultural, industrial and domestic sectors consuming 70, 22 and 8% of the available fresh water, respectively and this has resulted in the generation of large amounts of wastewater containing a number of ‘pollutants’ (Helmer and Hespanhol, 1997, Lehr et al., 1980, Nemerrow, 1978). One of the important classes of the pollutants is edible oil refinery process, and once they are discharged into enter the water bodies it is no longer good and sometimes difficult to treat as the oil refinery wastewater have complex molecular structures which make them more stable and difficult to be biodegraded.
India has approximately 90 units of edible oil refineries located in different states. The sources of edible oil are soybean, groundnut, rapeseed, sunflower, safflower, cotton, sesame, coconut, palm, mustard, rice bran, watermelon, neem, etc. This crude oil is then refined in order to remove free fatty acids and other non-TAG (triacylglyceride) components which contribute to undesirable flavor, odor and appearance (Anderson, 1953). Crude oil is refined using several processes to remove undesirable components before making it available for human consumption (Dumont and Narine, 2007). The refinery process generates by-products produced after crude oil refining. Fig. 1 summarizes the conventional processing steps encountered from crude to refined rapeseed oil. The refining of crude edible oils generates large amounts of wastewater. The neutralization step, in particular, produces sodium salts of free fatty acids (“soapstocks”) whose splitting through the use of H2SO4 generates highly acidic and oily wastewater. Its characteristics depend largely on the type of oil processed and on the process implemented (Azbar and Yonar, 2004). Several successive physical processes are involved in depollution of such effluents before a final biological step in a waste treatment station. Oil and grease in oily wastewater may take various forms namely: free, dispersed and emulsified. Decantation and skimming are effective in removing free oil (Cheryan and Rajagopalon, 1998). For decades, aerobic treatment has been used to remove biodegradable organic pollutants present in the wastewater generated during various industrial processes.
The refined edible oil manufacturing units generate solid waste (spent earth) and wastewater which are of environmental concern and need proper treatment prior to their disposal (Pandey et al., 2003). In a vegetable oil industry, the effluent mainly comes from the degumming, deacidification, neutralization, bleaching, and deodorization steps, etc. (Kale et al., 1999). The blow-down of the boiler and wash water from de-oiling of the bleaching earth also contribute to the effluent in small amounts. Previously, effluent from a vegetable oil industry used to undergo primary treatment and then discharged directly into soil or ground water. But, due to the emergence of environmental consciousness, the Pollution Control Boards have become stricter and impose very stringent norms. The scarcity of water is also another incentive for recovering pure water from effluents. For the treatment of an effluent by conventional methods like aerobic or anaerobic digestion, the ratio of BOD to COD should be >0.6 (Chian and Dewalle, 1977). However, an effluent from the vegetable oil industry usually has a BOD/COD ratio around 0.2, which could cause the destruction of micro-organisms useful for the biodegradation. The combined wastewater from these sections of the refined edible oil manufacturing industry is acidic and contaminated with oil and colloidal particles. Generally, physico-chemical processes followed by biological processes are adopted for the treatment of such wastewater. The physico-chemical processes include air flotation, skimming of oil, flocculation and coagulation for colloidal pollutants followed by biological processes for dissolved organics (Pathe et al., 2000, Saha et al., 1998).
Flotation is a unit operation which is applied to separate solid or liquid particles from a liquid phase, the dissolved air flotation (DAF) for the removal of emulsified oils from oily wastewater. A dissolved air flotation unit has been designed for this purpose and the ultimate goal is to explore the technical viability of this technique. The design and construction of the dissolved air flotation pilot plant have been conducted to treat 1.0 m3 h−1 of oily wastewater. Separation is achieved by introducing fine gas (with help of compressor air) bubbles into the liquid phase. Being the bubble attached to the (oil) particulate matter, and the buoyant force of the combined particle and gas bubbles are great enough to cause the particle to rise to the surface. Particles that have a higher density than the liquid can be facilitated (e.g., oil suspension in water). Once the particles have been floated to the surface, they can be collected by a skimming operation (Rajkumar, 2006).
The refinery uses chemical and physical methods for the refining of oils (soybean). The entire process involved is summarized in Fig. 1. On an average, the refinery and other process generate around 200 m3 of wastewater daily, which includes acid wastewater (60–80 m3/day) and technological wastewater (90–120 m3/day). In view of the present emphasis placed on environmental pollution control, new legislations and regulations, and changes in economic factors, the company installed a physico-chemical and biological wastewater treatment plant. The process flow diagram with sources of wastewater discharged is shown in Fig. 2. The Principle parameters of concern are pH, oil and grease (solvent extractable), suspended solids and organic constituents expressed as 5-day biochemical oxygen demand (BOD5) and chemical oxygen demand (COD). Other wastewater components of concern are sulphates, phosphates and chlorides. The wastewater treatment plant, like any other, is to reduce the pollution level prior to discharge to the environment to avoid breaking the eco-balance.
The high costs associated with the plant and its operation require a wise optimization of the process. A typical ETP is usually defined by a primary treatment, a secondary treatment and in some cases a tertiary treatment. The primary treatment is a physical process which aims to eliminate the gross solids and grease, so avoiding the blocking up of the secondary treatment. As its cost does not depend Considerablly on the characteristics of the wastewater, we chose not to include it in the optimization procedure. The secondary treatment is a biological process and is the most important treatment in the plant because it eliminates the soluble pollutants. Major opportunities for wastewater reuse exist in industry because most water is used for processing activities (washing, rinsing, etc.). In recent years various systematic design approaches to wastewater reuse across complex manufacturing operations have been developed (Wang and Smith, 1994, El-Halwagi, 1997, Kuo and Smith, 1998, Almato et al., 1999, Dunn and Wenzel, 2001). Because economic benefits are undoubtedly a major driver for industry to implement wastewater reuse programs, recent research in this area has focused on the economic optimization of wastewater reuse systems (Hallale and Fraser, 1998, Jodicke et al., 2001, Parthasarathy, 2001, Koppol et al., 2003). Bruggen and Braeken (2006) cited suggest that reusing wastewater streams as an input for less demanding installations is a step towards a zero discharge system.
Hence, we aimed to characterize the wastes generated from soya edible oil refinery and the objective of this study was to evaluate the physico-chemical treatment process removal of the mentioned parameters and to assess the biodegradability of the wastewater and also to recycle and reuse the waste for economic profits.
Section snippets
Waste samples
Wastewater samples from vat house, soap splitting, solvent extraction, floor washing, boiler and cooling system were collected together as received finally by the ETP through a single drain. Samples of solid waste (spent earth) were also collected. The parameters such as pH, TDS, COD ect. were monitored at inlet and outlet. All the samples were analyzed using analytical grade chemicals and all the analyses were performed in accordance with adopting standard methods (APHA, 1995).
Process details
The specific raw material requirement and process details with respect to manufacture of refined edible oil are presented in Table 1. In short, soya edible oils are individually pre-refined with caustic soda to remove free fatty acid (FFA) and with citric acid or phosphoric acid to remove gummy matters. The oils are then bleached with bleaching earth to remove the colour and residual matter.
The main wastewater generating sources are from vat house after soap splitting (60 m3/day), floor washing
Economic study
Based on the above results, effluent treatment plant economic study for 200 m3/day wastewater treatment plant for the soya oil refinery industry was conducted. Maximum design parameters of wastewater samples for soya oil refinery industry are illustrated in Table 3. Fig. 2 shows the schematic block flow diagram of the effluent treatment system, which consists of: equalization tank, flocculate, D.A.F. clarifier, oil separator, aeration tank, and secondary clarification. The economies of the plant
Conclusions
The waste from soya edible oil refinery included solid wastes viz. spent earth, chemical and biological sludge and wastewater from solvent extraction, soap splitting unit, floor washing, and cooling and boiler sections. The combined wastewater from soap splitting and floor washing had high concentration of oil and COD. The wastewaters produced are amenable to physical, chemical, and biological treatment. It is clear that the degree and type of treatment are influenced by local circumstances.
Acknowledgements
The authors are thankful to Dr. N. Mahalingam, Chairman of Sakthi Group of Companies, Sri M. Manickam, Vice Chairman and Managing Director, Sakthi Sugars Limited and Mr. M. Ponnuswami, Senior President of Sakthi Sugars Limited, Tamilnadu, India.
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