Claims:1. A process for the treatment of a spent wash stream comprising:
a) providing a biomethanated spent wash stream comprising total solids up to 10% by weight;
b) subjecting said stream to evaporation forming a concentrated stream and a condensate stream;
c) treating said concentrated stream with desire quantity of phosphoric acid and adjusting pH with sulphuric acid forming a treated stream;
d) drying said treated stream to recover a dry powder and a condensate stream;
e) storing said dry powder for later use;
f) reusing said condensate streams as process water; and
g) using said dry powder as a soil conditioner.
2. The process of claim 1, wherein said biomethanated spent wash stream is evaporated using a multiple-effect evaporator or a mechanical vapour recompressor or a reverse osmosis system.
3. The process of claim 1, wherein said concentrated stream comprises total solids up to 30% by weight.
4. The process of claim 1, wherein phosphoric acid used is between about 0.5 % to about 10% by weight.
5. The process of claim 1, wherein sulphuric acid is used for adjusting pH between 5.5 to 6.5.
6. The process of claim 1, wherein said treated stream is dried using an agitated thin film drier or an oven.
7. The process of claim 1, wherein said dry powder is non-hygroscopic in nature and storable for at least six month without any changes in its powder properties.
8. The process of claim 1, wherein said dry powder has moisture content of no more than 5% by weight.
9. A dry powder produced according to the process of claim 1 for use as a soil conditioner.
10. A product comprising said dry powder prepared according to claim 1.
, Description:FIELD OF THE INVENTION
The invention relates to a method for the treatment and evaporation of a biomethanated spent wash [BMSW] produced in alcohol distilleries or chemical industries. More particularly to obtain from said BMSW, a less hygroscopic solid matter, capable of storage, with total recovery of water from it.

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 [BMSW]. Although BMSW 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 BMSW disposals and it is now imperative to sugar factories and distilleries to employ new methods of the treatment of BMSW that are more effective, economical and eco-friendly.
The BMSW 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 BMSW is provided in TABLE A. Presently, BMSW 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 A: Typical composition of a BMSW feed stream.
Sr. No. PARAMETER UNIT VALUE
1 pH - 7.0 – 9.0
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 BMSW 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 BMSW treatment is evaporation; herein BMSW from biogas reactors is stored in open lagoons to get rid of volatile matters present in it as various gases. Then this BMSW 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 BMSW faces severe problem of clogging of heat ex-changer 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 ºC of temperature. Higher temperatures thus worsen the problem in the BMSW evaporation equipment.
The invention presented herein discloses a method of the treatment of BMSW having several advantages over known methods. Besides it provides recycled water at the end of treatment that is usable in plant processes like in the fermentation of sugars by yeast.

DETAILED DESCRIPTION
To alleviate the problem of spent wash disposal of molasses based distilleries, the spent wash streams are 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 [BMSW]. The BMSW 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. A compositional analysis of a sample of BMSW is provided in Table 1. Presently, BMSW 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. Several technologies have been presented on the treatment of BMSW and recovery/ recycling of process water. However, these technologies have achieved limited success due to composition of recycled water obtained which is not suitable for the most water consuming step such as fermentation of sugars by yeast during making of alcohol. The invention presented herein discloses several advantages over known methods. Besides it provides recycled water at the end of treatment that is usable in plant processes like in the fermentation of sugars by yeast.
In one embodiment of the present invention, the steps of the said method are evaporation of the BMSW to concentrate it, mixing of mineral acid in the concentrated stream, drying said treated stream, storage of it for later use. Biomethanated spent wash stream having about 10% solids by weight are used. Said BMSW is fed to evaporator to form a concentrated stream having up to 30% solids by weight and a condensate stream. Said concentrated stream is acidified with a mineral acid to between about pH of 5.5 to 6.5 and dried at about 900 C in hot air tray dryer or using agitated thin film drier or in oven for about 15 hours to about 18 hours to produce dry powder and condensate stream. Said dry powder was stored for later use as a soil conditioner and said condensate stream is reused as process water without any discharge of liquid effluents from the processing plants. Said dry powder has moisture content of no more than 5% by weight and it is non-hygroscopic in nature and stored for at least six month without any changes in its powder properties.
In another embodiment of the present invention, mineral acid used for the treatment is phosphoric acid or a combination of phosphoric acid with sulphuric acid. Said concentrated stream is mixed with about 0.5% to about 10% phosphoric acid by weight and then pH is adjusted to between about 5.5 to 6.5 using sulphuric acid.
In yet another embodiment of the present invention, said BMSW is evaporated using a multiple effect evaporator, a mechanical vapour recompress or a reverse osmosis system.
In yet another embodiment of the present invention, the dry powder formed from BMSW has composition as shown in TABLE B.

TABLE B: The composition of dry powder.
Parameter Values Unit
Total Solids 97.80 %w/w
Ash 49.71 %w/w
pH 6.34
Conductivity 4.85 S/M
Total Nitrogen 3.07 %w/w
Potassium (available as K) 12.21 %w/w
Phosphorous as (Available as P) 0.76 %w/w
Sulphur 7.10 %w/w
Magnesium 2.21 %w/w
Calcium 1.99 %w/w
Sodium 0.45 %w/w

Examples provided below 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 experimental results is given in the examples, which demonstrate the advantageous and novel aspects of the method of using phosphoric acid or combination of phosphoric acid with sulphuric acid for the treatment of BMSW streams.

EXAMPLE 1
About 1025 g of biomethanated spent wash (BMSW) from stream molasses based distillery containing about 15.5% solids by weight [without any acid treatment] was fed to a hot air tray dryer for evaporation at about 90 ºC for about 15 to about 18 hours. This process produced solids which were then crushed to a fine dry powder. The total weight of said dry powder was about 140 g. Said dry powder showed significant moisture uptake of about 10% by weight when exposed to humidity in a humidity chamber at about 30 ºC and about 60% of relative humidity [RH] for up to 48 h as shown in Table 1.
TABLE 1:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.04 0
24 5.58 10.84
48 5.57 10.59

EXAMPLE 2
About 1025 g of BMSW stream from molasses based distillery containing about 15.5% solids by weight was acidified with about 1.66 g of phosphoric acid [about 1% of the solids] before feeding it to a hot air tray dryer for evaporation at about 90 ºC for about 15 to about 18 hours. This process produces solids which were crushed to a fine dry powder. The total weight of said dry powder was about 142 g. Said dry powder was stable at room temperature; however showed significant moisture uptake of about 10% by weight when exposed to humidity in a humidity chamber at about 30 ºC and about 60 % humidity for up to 48 h as shown in Table 2.
TABLE 2:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.04 0
24 5.58 10.78
48 5.60 11.03

EXAMPLE 3
About 1025 g of BMSW stream from molasses based distillery containing about 15.5% solids by weight was acidified with about 3.32 g of phosphoric acid [about 2% of the solids] before feeding it to a hot air tray dryer for evaporation at about 90 ºC for about 15 to about 18 hours. This process produces solids which were crushed to a fine dry powder. The total weight of said dry powder was about 143 g. Said dry powder was stable at room temperature and but also showed significant moisture uptake as compared to acid untreated BMSW, when exposed to humidity in a humidity chamber at about 30 ºC and about 60 % humidity for up to 48 h as shown in Table 3.
TABLE 3:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.04 0
24 5.55 10.15
48 5.57 10.50

EXAMPLE 4
About 1025 g of BMSW stream from molasses based distillery containing about 15.5 % solids by weight was acidified with about 6.65 g of phosphoric acid [about 4.3% of the solids] before feeding it to a hot air tray dryer for evaporation at about 90 ºC for about 15 to about 18 hours. This process produces solids which were crushed to a fine dry powder. The total weight of said dry powder was about 145 g. Said dry powder was stable at room temperature and showed reduced moisture uptake as compared to acid untreated BMSW when exposed to humidity in a humidity chamber at about 30 ºC and about 60 % humidity for up to 48 h as shown in Table 4.
TABLE 4:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.04 0
24 5.47 8.52
48 5.45 8.23

EXAMPLE 5
About 1025 g of BMSW stream from molasses based distillery containing about 15.5 % solids by weight was acidified with about 13.2 g of phosphoric acid [about 8.5% of the solids] before feeding it to a hot air tray dryer for evaporation at about 90 ºC for about 15 to about 18 hours. This process produces solids which were crushed to a fine dry powder. The total weight of said dry powder was about 148 g. Said dry powder was stable at room temperature and showed significantly reduced moisture uptake as compared to acid untreated BMSW (EXAMPLE 1) when exposed to humidity in a humidity chamber at about 30 ºC and about 60% humidity for up to 48 h as shown in Table 5.
TABLE 5:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.04 0
24 5.39 6.84
48 5.34 5.90

EXAMPLE 6
About 1025 g of BMSW stream from molasses based distillery containing about 15.5% solids by weight was acidified to about 5.8 pH with about 10.5 g of sulphuric acid [about 6.5% of the solids] before feeding it to a hot air tray dryer for evaporation at about 90 ºC for about 15 to about 18 hours. This process produces solids which were crushed to a fine dry powder. The total weight of said dry powder was about 149 g. Said dry powder was stable at room temperature and showed significant moisture uptake as compared to acid untreated BMSW (EXAMPLE 1) when exposed to humidity in a humidity chamber at about 30 ºC and about 60% humidity for up to 48 h as shown in Table 6.
TABLE 6:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.00 0
24 5.44 8.79
48 5.44 8.77

EXAMPLE 7
About 1025 g of BMSW stream from molasses based distillery containing about 15.5% solids by weight was acidified to about 5.8 pH with about 1.58 g of phosphoric acid [about 1% of the solids] and about 9.5 g of sulphuric acid [about 6% of the solids] before feeding it to a hot air tray dryer for evaporation at about 90 ºC for about 15 to about 18 hours. This process produces solids which were crushed to a fine dry powder. The total weight of said dry powder was about 146 g. Said dry powder was stable at room temperature and showed insignificant moisture uptake as compared to acid untreated BMSW (EXAMPLE 1) when exposed to humidity in a humidity chamber at about 30 ºC and about 60% humidity for up to 48 h as shown in Table 7.
TABLE 7:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.04 0
24 5.47 8.51
48 5.45 8.11

EXAMPLE 8
About 1923 g of BMSW stream having about 15.5% solids by weight was acidified to pH 5.6 using about 5.65 g of phosphoric acid [about 3.5% of the solids] and about 20 g of sulphuric acid [about 14% of the solids]. Next, said mixture was fed to hot air trey drier for evaporation at about 90 ºC. This process produced solids which were crushed to a fine dry powder. The total weight of said dry powder was about 275 g. Said dry powder was stable at room temperature and showed significantly reduced moisture uptake as compared to acid untreated BMSW (EXAMPLE 1) when exposed to humidity in a humidity chamber at about 30 ºC and about 60% humidity for up to 72 h as shown in Table 8.

TABLE 8:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.02 0
24 5.34 6.43
48 5.32 5.92
72 5.29 5.43

EXAMPLE 9
About 1784 g of BMSW stream having about 15.5 % solids by weight was acidified to pH 5.7 using about 10 g of phosphoric acid [about 6.5% of the solids] and about 10 g of sulphuric acid [about 6.5% of the solids]. Next, said mixture was fed to hot air trey drier for evaporation at about 90 ºC. This process produced solids which were crushed to a fine dry powder. The total weight of said dry powder was about 262 g. Said dry powder was stable at room temperature and showed significantly reduced moisture uptake as compared to acid untreated BMSW (EXAMPLE 1) when exposed to humidity in a humidity chamber at about 30 ºC and about 60% humidity for up to 72 h as shown in Table 9.

TABLE 9:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.03 0
24 5.35 6.41
48 5.35 6.29
72 5.33 5.93

EXAMPLE 10
About 1784 g of BMSW stream having about 15.5% solids by weight was acidified to pH 5.7 with about 15.6 g of phosphoric acid [about 10% of the solids] and about 5.2 g of sulphuric acid [about 3.5% of the solids]. Next, said mixture was fed to hot air trey drier for evaporation at about 90 ºC. This process produced solids which were crushed to a fine dry powder. The total weight of said dry powder was about 258 g. Said dry powder was stable at room temperature and showed significantly reduced moisture uptake as compared to acid untreated BMSW (EXAMPLE 1) when exposed to humidity in a humidity chamber at about 30 ºC and about 60% humidity for up to 72 h as shown in Table 10.

TABLE 10:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.02 0
24 5.34 6.42
48 5.33 6.24
72 5.32 5.94

EXAMPLE 12
The treatment of a BMSW stream was carried out with different mineral acids. The experiment was carried out with five BMSW stream samples each about 1000 g having 5.6 % solids by weight. Said stream were acidified with different mineral acids to about pH 6.3 and then fed to rotary evaporator to obtain thick flowable syrup. Next, said syrup was poured in a tray and dried in a vacuum oven to obtain powder. All these powders which were exposed to different mineral acids have different compositions. Said powders were then exposed to air at about 50% to 60% if humidity for up to 16 h and examined for the moisture uptake and results are shown in Table 12.

TABLE 12:
Duration [h] Control
[% by Weight] Phosphoric acid
[% by Weight] Oxalic acids [% by Weight] HCl
[% by Weight] Nitric acid
[% by Weight]
0 0 0 0 0 0
2 1.20 9.65 12.50 28.83 29.75
4 2.53 7.59 6.91 32.36 31.74
6 19.17 7.79 6.91 33.82 32.80
16 17.84 7.32 7.51 44.21 39.76

EXAMPLE 13
About 7520 g of BMSW stream from molasses based distillery containing about 6% solids by weight was evaporated at 70 ºC. About 5350 g of condensate stream and 1880 g of concentrated stream were recovered and then said concentrated stream having about 24% solids by weight was acidified to about 5.5 pH with about 18 g of phosphoric acid [about 4% of the solids] and about 40 g of sulphuric acid [about 9% of the solids] before feeding it to a hot air tray dryer for evaporation at about 90 ºC for about 15 to about 18 hours. This process produces solids which were crushed to a fine dry powder. The total weight of said dry powder was about 378 g. Said dry powder was stable at room temperature and showed significantly reduced moisture uptake as compared to acid untreated BMSW (EXAMPLE 1) when exposed to humidity in a humidity chamber at about 30 ºC and about 60% humidity for up to 72 h as shown in Table 13
TABLE 13:
Duration [h] Gross Weight [g] Weight Gain [% by Weight]
0 5.02 2.0
24 5.18 3.1
48 5.17 2.9
72 5.17 2.9

EXAMPLE 14
To determine the flowability of the dry powder batched produced in the above examples after treatment by various acids, the method of angle of repose [AOR] was used. AOR is used for measuring the flowing characters of fine powdery materials as a physical method. The protocol of XXX was used for taking AORs for the samples listed in Table 14 and the average of three measurements is reported.
TABLE 14:
Humidification AOR
Non-treated Sample Treated Sample
Before 38.6 27.8
After [60% for 24 h] 42.5 31.2

Embodiments and examples 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.