Distillery Condensate and Spent Leese Treatment for Complete Reuse An Approach towards Zero Intake

Transcription

1 Distillery Condensate and Spent Leese Treatment for Complete Reuse An Approach towards Zero Intake Apte S. S. 1, Hivarekar S. B. 2 1,2 Assistant Professor, Annasaheb Dange College of Engineering and Technology, Ashta. Abstract Distillery condensate is generated as a byproduct of Multi-Effect Evaporation of spent wash generated as wastewater stream from alcohol production process. This control is generated as an effluent has a very high amount of organic load and therefore can have a detrimental effect on the environment. Furthermore the stringent processes of the pollution control board and norms for disposal of the spent wash in the environment are extremely stringent and therefore it is necessary for the distillery to take up treatment processes for achieving zero effluent discharge in terms of spent wash. This had led to the advent of the process of volume reduction in which the spent wash volume is reduced to an extent where it can be utilized for press mud composting/bio-composting. A technique like Multi-Effect Evaporation is efficient alternative which achieves this volume reduction of up to 75%. The condensate which is generated because of the volume reduction technique contains large amounts of volatile organic components because of which the COD is increased very drastically and can be in the range of ,000 mg/l. However, the liquid is clear and hence if treated properly can be utilized as a source of raw water. The present study was carried out as a large-scale project at several distilleries and is working successfully. It deals with the treatment process which was selected and the observed results and problem troubleshooting. Keywords Distillery Condensate, Volume Reduction, Spentwash, Biological Treatment. I. INTRODUCTION Agro based industrial sector is a major contributor to the world economy since it is primarily responsible for the consumer based market. Due to this inherent advantage, the agro based industrial sector is one of the most important revenue generation sources in a country s economy. Sugar and distillery sector is one such division which has been responsible for the successful growth of the developing countries like Sudan, Philippines, Fiji, and India etc. In these areas, sugarcane is cultivated as a prime cash crop and has been dominating the country s economy. Moreover, this sector is not only generating revenue, but is creating employment for a large sector of the society. Distillery is an ancillary sector of the sugar complex and requires the raw materials from the sugar manufacturing process for most part. 312 There are about 295 distilleries in India, mostly concentrated in Maharashtra, Uttar Pradesh, Karnataka, Andhra Pradesh, Gujarat, Madhya Pradesh and Tamil Nadu. The distillery sector is based on the production of the different grades of alcohol suitable for the various processes like liquor production, medical preparations, fuel additives, cosmetics and drugs industries etc. The generation of alcohol takes place through a very complex process of fermentation of the raw material using some specific fungal cultures. The Indian fermentation industry is categorized mainly into Maltry, Brewery and Distillery. The processes run Majority of the units of distillery present in India are molasses based. This is due to the presence of a large number of sugar factories in close vicinity, which fulfill the requirement of molasses. The second reason for the presence of large number of molasses based units is the scarcity of food grains for grain based distillation processes given the requirement of food for the population, and the legal bindings in the countries like India. A. Raw material and water demand Molasses, a by product of the sugar industry, contains about 40 50% sugar content. In order to facilitate the fermentation process, this concentration is brought down in the range of 10 15% or brix by addition of fresh water. The molasses requirement for production of 1 KL of RS is between MT depending on type of process, i.e. Continuous or Batch Process. After dilution with fresh water, this diluted molasses solution then undergoes the various fermentation column processes, at each level of which the alcohol separated from the molasses is purified further. Water Use in Distillery A molasses based distillery requires fresh water for the following processes i. Process Application 1. Yeast Propagation 2. Molasses Preparation 3. Steam for Distillation

2 ii. International Journal of Emerging Technology and Advanced Engineering Non Process Application 1. Cooling Tower Water 2. Treated Water for Liquor Preparation 3. Water and Steam for Washing The average water requirement of a molasses based distillery ranges between m 3 / KL of Rectified Spirit. An additional 50 m 3 /day of soft treated water is required for other purposes. However, in practical context, the amount of fresh water required per day for a distillery ranges between 11 13% of total RS Production capacity. II. WASTEWATER GENERATION IN DISTILLERY The process of distillation results in release of large quantities of wastewater which has a considerable environmental impact. The distillery is therefore one of the most critical sectors which are listed among the 17 High Pollution Potential Industries in India. The major sources of wastewater in a molasses based distilleries are listed below. Process Waste Streams o Spentwash from Analyzer Column o Fermenter Sludge o Spent leese from Rectifier Column o Condensate from Spentwash Volume Reduction Unit Non Process Waste Streams o Cooling Tower Blowdown o Waste wash water o Water Treatment Plant Maintenance Water o Cooling Water etc. Out of these, most of the non process streams are recycled to ancillary units, or used for washing purposes, gardening etc. The various types of process effluents are as described below. A. Distillery spentwash Distillery spentwash is one of the 17 most high strength wastewater streams which are described by the Central Pollution Control Board. It is a wastewater stream generated from the primary column of the distillation process, i.e. the Analyzer column. The average generation of the spentwash in a distillery ranges between L/L of alcohol produced. The average characteristics of spentwash are as given below. TABLE I CHARACTERISTICS OF DISTILLERY SPENTWASH Sr. Characteristics Range No. 1. ph Total Solids (mg/l) Total Suspended Solids (TSS) (mg/l) 4. Total Dissolved Solids (TDS) mg/l 5. Total Volatile Solids (TVS) mg/l 6. COD BOD Total Nitrogen as N Potash as K 2 O Phosphate as PO Sodium as Na Chlorides as Cl Sulfates as SO Acidity as CaCO Temperature (After Heat 70 0 C 80 0 C Exchange) B. Distillery condensate Spentwash volume is reduced through the process of spentwash concentration. This process is carried out through multi effect evaporation techniques. A variety of volume reduction techniques are available for spentwash concentration like Reverse osmosis, multi-effect evaporation (MEE) etc. The widely used method of spentwash concentration is multi-effect evaporators, which compared to the reverse osmosis techniques, are more efficient and have lesser recurring costs. The efficiency of the multi-effect evaporators ranges between 60 75%, thereby reducing the spentwash volume significantly. In the process, the vapors which are generated as a by product undergo condensation in the condensers and this water stream is called as Distillery Condensate. Theoretically, this water is more or less pure. However, since the MEE process works under vacuum, any changes in the vacuum settings can cause significant entrainment in the vapors. Also, spentwash contains large amount of volatile products, because of which, the condensate is often entrained by the volatile organics which cause increase in the COD of the water. The general characteristics of the distillery condensate are as given below. 313

3 TABLE II CHARACTERISTICS OF DISTILLERY CONDENSATE For A 300 KLPD Distillery Sr. No. Parameter Value 1. Volume (m 3 ) C.O.D. (mg/l) B.O.D.5 (mg/l) C. Distillery spentleese Spentleese is another type of effluent which is generated from the Recovery columns of the distillation process. The effluent is mainly characterized by rogue alcohols, which get entrained in the spentleese due to change in the conditions of the columns, which thereby affect the parameters of the stream significantly. The parameters of the spentleese are as given below. TABLE III CHARACTERISTICS OF DISTILLERY SPENTLEESE For A 300 KLPD Distillery Sr. No. Parameter Value 1. Volume (m 3 ) C.O.D. (mg/l) B.O.D.5 (mg/l) III. DISTILLERY EFFLUENT TREATMENTS A. Distillery spentwash The spentwash quantity generated from the process varies from distillery to distillery. The quantity can also depend on the type of process changes which may have been implemented in a unit as well. It was seen from practical observations at the study site that the spentwash generation in the distillery (having a production capacity was in the range of 4 6 L / L of alcohol because of a change in the process which was implemented, wherein spentwash recycle for certain columns was being carried out for an undisclosed process. However, even this quantity is still higher, and the treatment cost and the required end results may not yet be achieved. The Ministry of Environment and Forests (MoEF) has now prescribed 5 specific treatment methods for the proper disposal of the spentwash generated. The methods are as given below: 1. Concentration and incineration 2. Concentration and composting 3. Anaerobic digestion followed by two stage aeration and composting. 4. Anaerobic digestion followed by controlled land application. 5. Raw spentwash composting. Method 4, 5 and 6 are now more or less discontinued because of higher land requirement and lesser treatment efficiencies. Method 1 and 2 are now the methods now in practice in the distillery sector. However, concentration and incineration is now being slowly rejected because of its higher capital and recurring cost and therefore concentration and composting is now dominantly practiced. Concentration of spentwash is critical as the immense volume of raw spentwash requires extremely extensive treatments which are not only financially challenging but are also very high maintenance and less efficient. Concentration of spentwash significantly reduces the treatment expenditures and also reduces the land requirement to a great extent whenever an industry is planning to adopt composting as an option. B. Distillery condensate and Spentleese The characteristics of the condensate and Spentleese depict the need of biological treatment in order to effectively reduce the organic matter content. Several methods were discussed, and after detailed brainstorming on design considerations for the volume in question, i.e 1200 m 3 /day, a conventional mode of Anaerobic Digestion followed by Aerobic System was adopted. The process flow of the method adopted is as given below: FIGURE I TREATMENT PROCESS FOR DISTILLERY AND SPENTLEESE TREATMENT 314

4 C. Treatment process description a. Equalization Tank: The condensate and Spentleese generated in the distillery process is collected in a 1 day lagoon near the distillery, and from here, the effluent is pumped to the Condensate Treatment Plant. Here, the effluent ph is neutralized using Caustic Soda or Lime. Preferably, lime is utilized as a first preference as the end use of water does not rely on the TDS of the water and therefore, moderate TDS in the water is acceptable. The Equalization tank is designed for a retention time of 8 hrs. The main aim of the equalization tank is to equalize the flow and characteristics and load the effluent to the further treatment at a constant uninterrupted rate. b. Anaerobic Digester: In order to limit the energy requirement for the treatment process, an initial phase of biological treatment in the form of Anaerobic digester was provided. This digester was a Completely Stirred Type Reactor (CSTR). However, instead of the conventional agitator based mixing system, a newer advanced mode of Pump Sparging was applied. The system was designed keeping in mind the mixing speed required which is approximately 4 times that of the inlet flow. This flow was confirmed through practical studies on site. The digester was commissioned and stabilized by the procedure discussed later, and then, it was continuously fed with the effluent for more than 190 days. The digester dimensions were 12 m dia x (10+1) m Height. c. Degasser Tower: The effluent after the biodigestion process contains mainly remaining organic solids and gases like Ammonia, Hydrogen sulfide etc, which are entrapped in the effluent. If this effluent is directly subjected to the aerobic treatment, it can result in toxic effects on the aerobic bacterial culture. Therefore, it is necessary to provide a treatment mode suitable for dispersion of these gases. In order to achieve this, a degasser system based on diffused air diffusion was provided. This system proved effective for the complete removal of the entrapped gases to the maximum extent. d. Lamella Clarifier: This settling system is utilized in order to maintain the biomass culture in the anaerobic digester. The recirculation pattern of the lamella clarifier was kept at 100%. Due to this, the balance of the microbial mass in the digester was kept constant. Biodigester sludge i.e. anaerobic sludge is naturally light in nature nd therefore, does not settle easily. Therefore, a specialized treatment scheme wherein aided settling is necessary without coagulant addition. For this purpose a specialized settling scheme in the form of Plate based settling is utilized. e. Two Stage Aeration Clarification System: The effluent after anaerobic treatment contains significantly reduced amounts of organic load. This effluent is then further treated in an Aerobic process scheme. In generalized terms, the system used in the present process is called commonly as Activated Sludge Process. However, in order to have a better efficiency and reduced economic burdens, an advanced ASP mode in the form of Extended Aeration, which works on the principle of low F: M Ratio, was utilized in two stages. Utilization of two stages was carried out because of the end use requirement of the water. Therefore, the second stage of extended aeration system acted more like a polishing treatment rather than an extensive biological treatment. f. Tertiary Treatment: As a polishing treatment for confirmation of consistent efficiency, a Multimedia filtration unit for removal of any trace suspensions, and an Activated Carbon filter to cope with any colour or trace organics was provided. The backwash frequency for the units was regularized to once in 2 days, which was effectively practiced and gave satisfactory results. IV. TREATMENT STABILIZATION PHASE Any biological treatment requires a phase of stabilization before actual loading of the effluent. Similarly for this project, a stabilization phase for the commissioning of the biological units was carried out. The phases involved in the stabilization are as given below: A. Digester Charging: In this phase, the digester was loaded with cowdung, nutrients and enriched culture. The quantity of the cowdung loading (in Tons) was typically 2 4% of the digester volume. The nutrient addition was carriedut only on requirement of the process. The total cowdung that was used in the stabilization of the above digester was approximately 30 Tons, and the nutrients used in the stabilization phase were approximately 500 Kgs all together. The charging phase of the digester consisted of loading the ingredients in the unit, and keeping the unit under constant agitation without external additions for 2 3 days. B. Digester Loading: After 2 3 days steady period, the effluent loading based on the COD load was initiated. The loading was on the basis of COD Load because of the fact that in anaerobic reactors, quantity of organic load supplied is more critical than the volume of the effluent. The loading phase continued for 30 days wherein the COD load was increased gradually keeping a constant difference between the increases, and thereby avoiding any shockloads. 315

5 Sr. No. International Journal of Emerging Technology and Advanced Engineering Flow (m 3 /hr) TABLE IV DIGESTER LOADING CYCLE COD (mg/l) COD Load (Kg/m 3.hr) Remarks Loading Initiated Increased by approx. 30Kg/m 3.d Flow decreased suitably so that consistent loading 30Kg/m 3.d is maintained Loading decreased due to sudden ph drop. Loading rate decreased to <120Kg/m 3 d D. End use of the treated water: The water after this extensive treatment was enough to replace the water demand of the distillery by almost 80% wherein the water was used in fermenter makeup, cooling tower makeup and other non critical processes in the distillery. This significantly decreased the financial load, and also, reduced the dependence of the distillery on the external water source by a large extent. V. RESULTS AND OBSERVATIONS Regular analysis of the effluent was carried out in order to observe the health of the Condensate and Spentleese treatment scheme. The cumulative results analysis is as given below. C. Aeration Tank Charging: The charging / commissioning of the Aerobic phase was initiated on the 5 day of the digester loading phase. The day was calculated using the amount of time required for the digester to overflow and the time required for the same effluent to reach the Aeration Tank I. The charging phase for aeration tank comprised of filling the tank to 40% capacity with fresh water on the 3 rd Day of the digester loading and addition of the enriched aerobic microbial culture in sufficient quantity along with nutrients. This steady stage continued uptil the 5 th day when the digester effluent began to reach the unit. Similar calculations and additions were carried out on the second stage aeration phase, which began on the 9 th day of the digester loading phase. FIGURE II VARIATION IN COD FROM INLET TO OUTLET FIGURE III COD REMOVAL EFFICIENCY VARIATION 316

6 Water after this extensive treatment was enough to replace the water demand of the distillery by almost 80% wherein the water was used in fermenter makeup, cooling tower makeup and other non critical processes in the distillery. This significantly decreased the financial load, and also, reduced the dependence of the distillery on the external water source by a large extent. Furthermore, since the water requirement dropped significantly, the dependence of the factory on the external water source was negligible, and the internal usages were also controlled through in plant measures, utilizing which, the factory made a significant monetary profit. The photographs of the Distillery and Spentleese treatment unit are given below: VI. CONCLUSIONS The study that was conducted in the project was based on actual data generated through practical operations of the treatment scheme employed. The design was carried out by the primary author and the plant erected on the same basis. The treatment proved to be a critical initiative for the proper disposal of the spentwash from the distillery which is a major environmentally dangerous wastewater stream. The amount of investment required for the project is roughly 1 2% of the capital cost of the distillery, and which can reduce the expenditure of the factory on water significantly. This is a ground breaking design which has been incorporated by the authors firm in more than 10 distilleries in India. REFERENCES [1] Apte S. S., 2011, Anaerobic Filter for Distillery Condensate Treatment Optimization of Anaerobic Filter System for Distillery Condensate Generated from Volume Reduction of Spentwash, LAP Lambert Academic Publishing GmbH & Co. KG, ISBN: [2] Baez Smith C., 2006, Anaerobic Digestion of Vinasse for Production of Methane in the Sugar Can Distillery, Proceedings of SPRI Conference on Sugar Processing [3] Bortone G., 2009, Integrated anaerobic / aerobic biological treatment for intensive swine production, Bioresource Technology, Elsevier Publication, Vol. 100, pp [4] Chen Y. and Cheng J. J., 2005, Anaerobic Processes in Waste Treatment, Water Environment Research, Water Environment Federation Publication, Vol. 77(6), pp