FORM 2
THE PATENT ACT 1970
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION TREATMENT OF BIOMETHANATED SPENT WASH
2. APPLICANT
(a) NAME: PRAJ INDUSTRIES LIMITED
(b) NATIONALITY: Indian Company
(c) ADDRESS: PRAJ House, Bavdhan, Pune - 411021, INDIA
3. PREAMBLE TO THE DESCRIPTION
The following specification describes the invention and the manner in which
it is to be performed.

4. DESCRIPTION
FIELD OF THE INVENTION
The invention relates to a method for the treatment and evaporation of a biomethanated spent wash [BSW] produced in alcohol distilleries. More particularly to removing gaseous and heat labile volatile matters present in said BSW, making it more amiable to concentration along with partial recovery of reusable water for utility applications.
BACKGROUND
Sugar industry is one of the largest agro based industry, which contributes substantially to the economic development of several communities worldwide. The sugar factories in India produce about 15 million tons of sugar by crushing about 150 million tons of sugarcane. The annual by-product production is about 7 million tons of press mud and about 8 million tons of molasses. Molasses is utilized in distilleries for the production of ethanol. These distilleries producing alcohol generate billion litres of spent wash annually. The spent wash and press mud cause disposal and pollution problems. The raw spent wash contains very high values of BOD and COD, beside solids. Therefore, to alleviate the problem of spent wash disposal it is subjected to biomethanation process where significant reduction of BOD and COD occurs along with production of bio-gas as an energy source. The effluent discharged from biomethanation process is known as biomethanated spent wash [BSW]. Although BSW has significant fewer BOD and COD values and solids, it is still a biological hazard if left to open disposal sites as presently done, creating significant air, water and soil pollution. Recently, regulators have also tightened the requirements of BSW disposals and it is now imperative to sugar factories and distilleries to

employ new methods of the treatment of BSW that are more effective, economical and eco-friendly.
BSW is made up of solid materials left unused in biomethanation process; these solids are mostly in the form of organic and inorganic complexes having very high BOD and COD demands for its degradation in natural environment creating pollution everywhere. A compositional analysis of a sample of BSW is provided in Table 1. Presently, BSW is left in open fields to compost and then remains are used as fertilizer, etc. At some large factories it is evaporated to partially recover water that is disposed off in natural streams and the concentrated part is left for composting or drying.
TABLE 1: Typical composition of a BSW feed stream

Sr. No. PARAMETER UNIT VALUE
1 PH - 7.0-8.0
2 COD ppm 30000 - 70000
3 BOD mg/L 10000-32000
4 Volatile Acids mg/L 700-1200
5 Alkalinity mg/L 12000-22000
6 Total Solids % by weight 1.5-8.0
7 Suspended Solids % by weight 0.2-1.0
8 Ammoniacal Nitrogen [NH3-N] mg/L 1500-3000
In recent times due to increased need of preservation of water and its use for more important agricultural applications than alcohol production, there is significant pressure on sugar factories to reduce water consumption and

recycle the process wastewater generated in plants more effectively. To this end, several technologies have been presented on the treatment of BSW and recovery / recycling of process wastewater. However, these technologies have achieved limited success due to composition of recycled water obtained and which is not suitable for the most water consuming step, that is, fermentation of sugars by yeast during making of alcohol.
One current method of the BSW treatment is evaporation; herein BSW from biogas reactors is stored in open lagoons to get rid of volatile matters present in it as various gases. Then this BSW from lagoons is fed to a multiple effect evaporation process wherein it is concentrated up to - 35-40% of total solids by weight. The process condensate water generated from this evaporation process is either disposed off or used for gardening or any other non-process applications due to high ammoniacal nitrogen [NH3-N] content with other associated impurities of varying nature, rendering it not suitable for process and utility applications. Besides, the evaporation stage of BSW faces severe problem of clogging of heat exchanger surfaces due to fouling and scaling. This leads to significant expenditures on the cleaning of the evaporators and its working efficiencies. The reasons behind fouling and scaling in this process have been studied. The spent wash [vinasse] from molasses based ethanol plant contains nitrogenous compounds like proteins etc. During anaerobic digestion of proteins in biogas reactor ammonia is formed as a by-product and gets dissolved in the reactor liquid. The anaerobic digestion process of vinasse also produces methane and carbon dioxide. Carbon dioxide and ammonia react to form bicarbonates which maintain pH in the reactor at about 7.0 and it is required to ensure better reactor efficiencies. When evaporated, alkalinity is reduced due to the thermal degradation with concurrent release of ammonia, carbon dioxide and some dissolved gases. This causes a sudden shift in pH to alkaline range due to the loss of H+ ions during thermal degradation and pH increases to about 9.0 - 9.5. At this pH the inorganic salts present in the liquid get affected as their solubility

drastically reduces. The carbonate undergoes immediate precipitation and other salts achieve their saturation points. Again subsequent rise in concentration during evaporation leads to precipitation of more of respective salts and hence uncontrolled scaling and fouling of heat exchange surfaces occurs. Hence at the operating conditions used in typical evaporation processes, the salts of calcium and magnesium precipitate over heat exchange surfaces and result in heavy scaling. The increased temperature also plays a major role in the scale formation as the calcium sulphate which is the major scaling component has inverse solubility above 90 °C of temperature. Higher temperatures thus worsen the problem in the BSW evaporation equipment.
The invention presented herein discloses a method of the treatment of BSW having several advantages over known methods. Besides it provides recycled water at the end of treatment that is directly usable in plant processes like in the fermentation of sugars by yeast without any further need of conditioning as is presently required.
BRIEF DESCRIPTION OF THE DRAWINGS
Particular examples of a method in accordance with this invention will now be described with reference to accompanying drawings, in which:
FIGURE 1 is a schematic diagram of the mass flow in the disclosed process. A BSW feed stream is subjected to pretreatment steps in first part, which is one novel aspect of the invention. In second part, said pretreated stream is fed to evaporation process leading to 5 - 10 times concentration of solids present over initial BSW feed stream. In third part, which is a second novel aspect of the invention, said evaporator condensate is treated in a polishing process to obtain reusable water without any BSW associated contaminants in it.

FIGURE 2 is a block diagram of the energy flow of the disclosed process. The pretreatment unit is supplied energy in the form of fresh steam or as vapours of gaseous streams formed. The evaporation unit gets energy in the form of unused energy recovered from other steps of distillery plant like main ethanol distillation steps or alternately gets fresh steam as energy source. The polishing unit is supplied energy in the form of fresh steam.
FIGURE 3 is an exemplary plan of the invention showing several features that control the process of concentration of BSW feed stream and production of process reusable water from the aqueous part of BSW. The whole system is divided into three units, namely: 1] pretreatment unit, 2] evaporation unit, and 3] polishing unit. Each unit has several elements that significantly contribute to the process of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In one embodiment of the present invention, as illustrated in FIGURE 3 the three parts of said process are: 1] pretreatment unit having several elements to perform various steps, 2] evaporation unit and 3] polishing unit. Herein a BSW stream (1) with at least 1.5% total solids by weight is preheated to desired temperature of about 60 °C to 80 °C by heat exchangers (41) and enters into said flash tank (30) leading to separation of a gaseous part (16) and formation of a first stream (3). The said flash tank (30) is operated under vacuum pressure of about 0.3 to 0.8 bar absolute [bar(a)]. The said first stream is directed to a stripper column (31) operating at a desired temperature of about 75 °C to 95 °C. This step strips said first stream of another gaseous part (11) while remaining part forms a second stream (4). This second stream is directed to a reactor tank (33), where acidification of said stream is performed using sulphuric acid or other mineral acid (19) supplied by a storage tank (34) to decrease the pH of said stream to about 6.5 from about 9.5 leading to formation of a third stream

(5). These steps form the part of pretreatment process, wherein substantial amount of matters from said BSW feed stream is removed in the form of gaseous and volatile matters leading to significant reduction on the alkalinity in said third stream. In an evaporation unit (35) employing a system like multiple effect evaporators, said third stream is concentrated to achieve up to 10 times of the initial solid concentration obtained from said evaporation unit. This evaporation unit is run by fresh steam or using high energy vapours (15) of process plant left unused at the time of distillation or concentration of alcohol and operates at about 80 to 110 °C. This evaporation process leads to formation of a fourth stream (7) containing no solids and clear of most of the impurities present in said BSW stream. That is the heat labile volatile components present in said spent wash are removed by sequential action of said flash tank, stripping column and polishing column. In the next part, in a polishing unit said fourth stream (7) is subjected to a polishing column (37) operating at a desired temperature of about 100 °C to 150 °C, wherein said fourth stream is heat treated at a boiling temperature to split the ammoniacal impurities present in said stream leading to separation of a gaseous stream (12) and formation of a reusable water stream (9), which has no impurities that prevents its use as such in fermentation steps of production of ethanol from sugars. In this system said stripper column (31) is supplied with fresh steam and/ or a gaseous stream (12) as a heat source. Also said preheater (41) is supplied with a gaseous stream (11) obtained from said stripper column (31) as a heat source. Further a gaseous stream (12) obtained from said polishing column (37) supplies heat to said stripping column (31). Secondly, said stripper column (31) is operated under vacuum pressure of about 0.3 to 0.8 bar absolute and vacuum in the system is maintained by a vacuum pump (39), which also removes a gaseous stream (11) from the system. Below atmospheric pressure operation of said pretreatment unit is essential part of this invention leading to effective operation of the system as such. The tray arrangement in said stripping column is preferably of disk and donut

type trays; however, use of other types of trays may be anticipated by a person skilled in the art in conjunction with the novel aspects of the invention disclosed herein.
In another embodiment, about 35500 L of BSW coming out of 60 KLPD molasses based distillery was subjected to method disclosed herein. This BSW contained about 4% total solids by weight with pH 7.5 at about 30 °C. The alkalinity was of about 15000 PPM. The level of ammoniacal nitrogen was about 2500 mg/L with other associated impurities of varying nature. This BSW was preheated to about 75 °C using a preheater and subjected to vacuum flashing in a flash vessel maintained at a vacuum pressure of about 0.6 bar(a) in the pretreatment part of the invention. This first step removed gaseous volatile matters from the feed stream creating a first stream having pH of about 8.5. Next, said first stream was subjected to a stripping column operating at temperature of 95 °C and at vacuum pressure of about 0.75 bar(a), this step further degraded the components of said first stream leading to temperature labile matters to decompose and separate as gases forming a second stream with pH of about 9.5. This said second stream was further subjected a reactor vessel and acidified with one or more of concentrated sulphuric acid, hydrochloric acid, nitric acid or phosphoric acid till pH of about 6.5 was achieved. Here non condensable vapours and foam were separated to form a third stream. This said third stream was subjected to an evaporation process using a multiple effect evaporator operating at about 100 °C in the evaporation part of the invention. This step concentrated total solids present in said third stream to about 20% by weight with pH of about 7 forming a concentrated stream. This said fourth stream obtained from the evaporator was further subjected to a polishing process in a polishing column operating at about 140 °C in polishing part of the invention. Here vapours of said polishing column were heat integrated with the stripper column of the pretreatment unit and reusable water stream was collected to be used in the process of

fermentation or utility applications. In a further step, said concentrated stream was optionally used as a boiler fuel to generate energy to run other plant processes.
Embodiments provided above give wider utility of the invention without any limitations as to the variations that may be appreciated by a person skilled in the art. A non-limiting summary of various embodiments is given in the examples and tables, which demonstrate the advantageous and novel aspects of the process disclosed herein.

5. CLAIMS
WE CLAIM:
1. A method for concentration of biomethanated spent wash
comprising:
(a) providing a biomethanated spent wash;
(b) preheating said biomethanated spent wash to a desired temperature using a preheater;
(c) flashing said preheated biomethanated spent wash in a flash tank at a desired vacuum leading to formation of a first stream;
(d) stripping said first stream in a stripping column working at a desired temperature and a desired vacuum leading to formation of a second stream;
(e) acidifying said second stream with a mineral acid in a reactor to reduce pH to a desired number leading to formation of a third stream;
(f) evaporating said third stream in an evaporator unit working at a desired temperature leading to formation of a concentrated stream and a fourth stream; and
(g) polishing said fourth stream in a polishing column working at a desired temperature leading to formation of a reusable water stream.
2. The method of claim 1, wherein said biomethanated spent wash is a
waste product of distillery unit comprising at least 1.5% total solids
by weight.

3. The method of claim 1, wherein said biomethanated spent wash is preheated to about 60 °C to 80 °C.
4. The method of claim 1, wherein said flash tank operates at a vacuum pressure of about 0.3 bar{a) to 0.8 bar(a).
5. The method of claim 1, wherein said stripping column operates at a temperature of about 75 °C to 95 °C and at a vacuum pressure of about 0.3 bar(a) to 0.8 bar(a).
6. The method of claim 1, wherein said stripping column is constructed preferably with a disc and donut type tray arrangement.
7. The method of claim 1, wherein said mineral acid used is one or more of sulphuric acid, hydrochloric acid, nitric acid or phosphoric acid.
8. The method of claim 1, wherein said evaporation unit is a multiple effect evaporator.
9. The method of claim 1, wherein said polishing column operates at a temperature of about 100 °C to 150 °C.
10.The method of claim 1, wherein said preheater, stripping column and polishing column are thermally integrated with each other such that minimum input energy is required to operate said method.
11. The method of claim 1, wherein said evaporation unit is thermally integrated with alcohol vapours obtained from an alcohol distillation unit used in distillery.
12. The method of claim 1, wherein said concentrated stream comprises at least 20% total solids by weight.

13. The method of claim 1, wherein heat labile volatile components present in said spent wash are removed by sequential action of said flash tank, stripping column and polishing column.