DESC:FIELD OF THE INVENTION:
The present invention relates to a process for coagulation and drying of sugarcane molasses based ethanol distillery bio-methanated spentwash (BMSW) to recover potash and to achieve zero liquid discharge status to ethanol distillery. Particularly, the present invention relates to a process for coagulation of BMSW by adding siliceous precursor and drying it at atmospheric pressure and lower temperature under sunlight or by using a slurry drying process to recover potash and other valuable nutrients. More particularly the present invention relates to coagulation of BMSW and its further drying to recover potash along with other minerals to obtain enriched organic fertilizer containing potash, silica, and ammoniacal nutrients as well as the to achieve zero liquid discharge status to meet the stringent environmental protection norms.

BACKGROUND AND PRIOR ART OF THE INVENTION:

Sugar manufacture from sugarcane generates large quantity of molasses as valuable by-product which contains 40-45% sugar which is being used for the manufacture of ethyl alcohol for its use as renewable fuel, raw material in chemical industry as well as for potable purpose. Sugarcane molasses based ethanol distillery generates large quantity of waste water called spentwash. One litre of ethyl alcohol manufactured generates about 10-12 ltrs of spentwash with dark brown color. The color is created by melanoidins, phenolics, caramels and furfurals and is dark enough to reduce photosynthesis in receiving waters. The melanoidins in particular are toxic to some microorganisms used in conventional wastewater treatment processes and difficult to remove.

Sugarcane molasses based distillery spent wash is one of the highly organically loaded material, with characteristic obnoxious smell, dark brown colour and low pH which makes it extremely difficult for treatment. The spent wash has a very high COD (about 1,30,000 mg/l) and high BOD (about 60000 mg/l) which needs to be treated to meet the stringent pollution control norms before it is discharged outside the distillery premises.

The high organic content of sugarcane molasses spent wash makes anaerobic treatment an attractive in comparison to direct aerobic treatment. Therefore bio-methanation is the most attractive primary treatment which recovers nearly 80% COD removal in the form of biogas which is used as fuel for the generation of steam in boilers or electricity using generators or recently for generation of Bio-CNG as described in publication by Bruna S, Moraes et. al. Renewable and Sustainable Reviews 44 (2015) 888-903.
The spentwash coming out from bioreactor called bio-methanated spentwash (BMSW) still has COD of about 30000 to 35000 and BOD of about 8000 to 9000 and needs to be treated before its disposal in the environment. The BMSW containing about 6-7% solids is a colloidal solution which is concentrated using multiple effect evaporator to obtain concentrated spentwash (35-40% solids) and then it is sprayed over the press mud from sugar industry in an open cement yard dried under sunlight i.e. open drying. The spentwash after biomethanation contains large quantity of dissolved CO2 and when the spentwash is taken in multiple effect evaporator, the dissolved CO2 starts coming out after heating and because of its viscous nature of spentwash generates lot of foam in the evaporator tubes hindering the flow of spentwash in the evaporator tubes which in turn it forms hard scaling on the inner tube surface affecting the heat transfer coefficient of the tubes. After the scaling of the inner surface of the tube the evaporator needs to stopped to remove the scale by chemical cleaning (clean in place, CIP) and needs to be started again. In normal practice the evaporators are operated for 18 to 20 hours in a day and 4 to 6 hours are stopped for cleaning making the operation of evaporators quite cumbersome as well as requires large amount of steam and chemicals for treatment. Apart from chemical cleaning frequent manual cleaning using hard steel wire brushing making the evaporation operation still difficult. The present treatment processes of BMSW to bio-compost has these limitations on large scale due to non availability of enough pressmud and distillery face problems to achieve zero liquid discharge.

Considering the above situation, pollution control authorities have made it mandatory to concentrate and incinerate the BMSW to achieve zero liquid discharge. Even after making very high capital investment for concentration using multiple effect evaporator (MEE) and a special expensive incinerator, it is difficult to operate it smoothly because of its operational problems as well as requirement of coal / bagasse as an additional fuel. The incinerator used for incineration of the concentrated spentwash is a special type of boiler (two stage) and costs about two to three times compared to normal boiler and very capital intensive equipment. Apart from higher costs of the required equipment, we need to use additional co-fuel such as bagasse or coal (about 25%) hence the operating cost also is very high. Since wet fuel is used (concentrated raw spentwash) the overall efficiency of this incinerator is about 50%. The incinerator needs to be cleaned frequently to remove the fine deposits (valuable potassium and other salts) on the tubes and furnace which gives thermal shocks to the boiler.
The BMSW contains 1.3 to 1.5% potassium which is one of the important constituent of a good fertilizer as well as contains other valuable micronutrients (K Sankarana et.al. Renewable and Sustainable Reviews 37 (2014) 634-643).The raw spentwash is acidic in nature whereas BMSW (pH-- 7.0 to 7.5) and the condensate obtained after evaporation is more alkaline (pH -- 9.0-9.5) contains ammonia indicating the presence of ammonia precursor in BMSW which would be a good nitrogen source if dried at lower temperature. The present mandatory process of spentwash concentration and incineration to achieve zero liquid discharge would destroy these valuable ingredients available in BMSW which needs to be recovered and used as good fertilizer.

Hence a cost effective drying procedure of bio-methanated spentwash to recover potassium and other valuable ingredients as well as to achieve zero liquid discharge is highly desired.

Indian patent 158/DEL/1999 describes an improved process for the treatment of the agro-industry waste water to produce colorless wastewater which comprises processing the agro-industry waste water to obtain colorless wastewater with precipitating the said waste water with divalent / trivalent coagulants, allowing the effluent to settle for a period of 6 to 120 min, separating the transparent yellow colored effluent by conventional methods, electrolyzing the said effluent optionally in the presence of 0.2 to 1% electrolyte at a current density of 35 to 100 ma/cm2, for a period of 3 to 15 min., separating the heavy precipitate formed by conventional methods and removing the traces of chlorine by conventional methods to obtain colourless waste water

Indian patent 102/DEL/2001 describes a process for the removal of colour of the spentwash after secondary treatment using ozone oxidation. Considering the pre-treatment process and the requirement of large quantity of ozone the process is not being used for spentwash treatment.

US patent 2002/0117455A1 describes a process for the treating an effluent comprising a mixture of spent wash and black liquor, Said process comprising mixing the effluent with a flocculating agent consisting of a mixture of Salts of Group III and transition metals, mixture of natural earth's along with an oxide of alkaline earth metal followed by treating with a combination of ion exchange resins.
Reference may be made to an article by Y. Satyawali, M. Balkrishnan, J. Environmental Management, Vol. 86, Issue 3, Feb. 2008, page 481-96. The review article describes molasses-based distilleries spentwash treatment processes covering anaerobic, aerobic as well as physico-chemical methods and their limitations.

Patent WO 2012077124A1 describes a method for co-processing of molasses distillery effluent comprising steps of: -neutralization of spent wash (optional), -concentration the spent wash, -co-processing of concentrated spent wash in a cement plant to achieve zero discharge.
WO 2012042524A1 patent describe a process and apparatus which uses multiple stages or unit processes to treat wastewater, such as distillery spent wash which may be molasses spent wash (MSW). The stages include one or more of anaerobic digestion, chemical treatment, electrocoagulation, aerobic treatment, physical separation, and RO or adsorbent based treatment. A chemical treatment for the effluent from an anaerobic digester treating MSW is described. In an electrocoagulation step, a stable cathode is used to also provide electrofloatation and hardness precipitation. Aerobic biological treatment and physical separation may be provided by a membrane bioreactor.

WO201742832A1 describes a process for the recovery of potash from Molasses based alcohol distilleries highly contaminated, dark coloured and foul smelling effluent (bio-methanated spent wash, BMSW, also known as post methanated effluent). While the prevailing practices for treatment of alcohol distillery effluents operate on the premises of "liability management", high potassium content of spent wash (ca. 2% w/v in BMSW) offers an opportunity for its utilization in production of potash fertilizers – a major agricultural input. The invention provides process for potash recovery from BMSW with concomitant environmental remediation of effluent. The process involves pre-treatment of BMSW followed by potash recovery through selective precipitation technique to produce potash fertilizers and activated carbon while generating a relatively benign effluent (>80% remediation). It may further be possible for the alcohol distilleries to achieve ZLD status by incorporating commercially practiced water recovery techniques (viz., multiple effect evaporation/ nano-filtration/ reverse osmosis etc.) for downstream processing of the process effluent. The overall process involves a multistep process lowering the overall efficiency of the process and making it a costly process.

The objective of the present invention to provide a process for coagulation and drying of BMSW at room temperature and atmospheric pressure under sunlight or drying using a slurry drying process to recover potash, nitrogen source and other valuable micronutrients available in BMSW as well as to achieve zero liquid discharge status to ethanol distillery.

OBJECTS OF THE INVENTION:
The objective of the present invention is to provide a process for drying bio-methanated spentwash to recover potash and other valuable nutrients for its use as fertilizer as well as to achieve zero liquid discharge.

Another objective of the present invention is to provide a process for drying of BMSW at lower temperature under sunlight to recover potash and other valuable ammoniacal nutrients for its use as a good fertilizer.

Yet another objective of the present invention is to provide a process for coagulation of BMSW by addition of siliceous precursor and further drying at lower temperature under sunlight to recover potash and other valuable ingredients for its use as a good fertilizer.

Yet another objective of the present invention is to provide a process for coagulation of BMSW by addition of siliceous precursor and separating the solids either by settling, filtration or centrifugation and further drying the solids at room temperature under sunlight to recover potash and other valuable ingredients for its use as a good fertilizer.

Yet another objective of the present invention is to provide a process for coagulation of BMSW by addition of silica precursor as well as flocculating agent and drying the separated solids either at room temperature under mild vacuum.

Yet another objective of the present invention is to provide a process for coagulation of BMSW by addition of silica precursor and drying the separated solids using various types of dryers used for slurry drying process.
Yet another objective of the present invention is to provide a process for coagulation of BMSW by addition of silica precursor and drying the coagulated BMSW using hot solar drying with embedded water heater.

SUMMARY OF THE INVENTION:
In accordance to the objectives, present invention provides a process for drying of the bio-methanated spentwash, a dark brown color effluent to recover potassium and other nutrients as well as to achieve zero liquid discharge.

It also provides a process for coagulation of BMSW using siliceous precursors and drying of coagulated spentwash at lower temperature under sunlight.

It further provides a process for drying coagulated spentwash by separating the solids either by settling, filtration or centrifugation and further drying the solids at room temperature under sunlight to recover potash and other valuable ingredients for its use as a good fertilizer.

It further provides a process for coagulation of BMSW by addition of silica precursor as well as flocculating agents and drying the separated solids either at room temperature under mild vacuum.

It further provides a process for coagulation of BMSW by addition of silica precursor and drying the separated solids using various types of dryers used for slurry drying.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

In order to meet the objectives of the current invention, the inventor proposes a process wherein BMSW is mixed with silicious precursors to coagulate the BMSW as thick semisolid material. The initial colloidal BMSW is converted into a suspension and since the nature of water in changed in these two phases, its evaporation kinetics also changes and hence can be dried at lower temperature. The coagulated BMSW is dried under sunlight to obtain a solid product wherein the potash and other valuable ammoniacal nutrients available in BMSW are recovered in the form of dry solid material.

The process of drying of BMSW comprises following steps.
1) Take the BMSW in mixing tank with agitator / stirring provision.
2) Add liquid alkaline sodium silicate, siliceous precursor, slowly to BMSW under constant stirring.
3) Continue the stirring and addition of siliceous precursor and flocculating agent till coagulated thick slurry is formed.
4) Transfer the slurry to drying tray / drying vessel with a layer of 1- 10 cms thickness.
5) Keep the drying tray with thick BMSW under sunlight in open air for about 6 to 7 hours to obtain dry solid containing potassium and other valuable ingredients as well to achieve zero liquid discharge.
6) Keep the drying pan with external heating by circulating hot water in the jacketed pan with thick BMSW under sunlight in open air for about 6 to 7 hours to obtain dry solid containing potassium and other valuable ingredients as well to achieve zero liquid discharge.
According to present invention the BMSW is dried at lower temperature to recover potash and other valuable nutrients as well as zero liquid discharge status is achieved to meet environmental norms.
According to the present invention the BMSW is dried by coagulating the BMSW by addition of siliceous precursor and the thick BMSW is dried under sunlight.
According to the present invention the solids from coagulated spentwash are separated by settling, decantation, filtration and centrifugation and further dried under sunlight.
According to the present invention the coagulated spentwash is dried by using various drying techniques for solid slurries.
According to present invention the coagulated spentwash is dried at room temperature under vacuum.
The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.
Examples: Following examples are given by way of illustration therefore should not be construed to limit the scope of the invention.
Example-1
1.00 litre of biomethanated spentwash with 6% solid was taken in plastic container of 5.00 litres capacity. 50.00 ml of alkaline sodium silicate was added slowly to BMSW with constant stirring using magnetic stirrer. The BMSW started getting coagulated and a thick slurry was formed. The thick slurry was transferred to a circular plastic trough forming a thick layer of 1-2 cms in the trough. The trough containing thick slurry was kept in open air under sunlight for 7 hours (10.00 am to 5.00 pm). The dried BMSW powder was collected and stored in closed plastic container.
130 g. of dry of BMSW was obtained which was analysed for its potassium content.
The potassium content in the dry BMSW was analysed using EDAX as well by chemical analysis.
The potassium content found was 13%.
The Nitrogen content was 8%
Example : 2

1.00 litre of biomethanated spentwash with 6% solid was taken in plastic container of 5.00 litres capacity. 50.00 ml of alkaline sodium silicate was added slowly to BMSW with constant stirring using magnetic stirrer. Flocculating agent Magnaflock LT-27 was added to the thick slurry formed. The thick slurry was transferred to a circular plastic trough forming a thick layer of 1-2 cms in the trough. The trough containing thick slurry was kept in open air under sunlight for 7 hours (10.00 am to 5.00 pm). The dried BMSW powder was collected and stored in closed plastic container.
130 g. of dry of BMSW was obtained which was analysed for its potassium content.
The potassium content in the dry BMSW was analysed using EDAX as well by chemical analysis.
The potassium content found was 14%.
The Nitrogen content was 8%
Example: 3
One litre of biomethanated spentwash with 6% solid was taken in 5.00 ltrs. Plastic container. 50.00 ml of alkaline sodium silicate was added slowly to BMSW with constant stirring using magnetic stirrer. The BMSW started getting coagulated and a thick slurry was formed. The thick slurry was transferred to centrifuge tubes and the solids were separated by using centrifugal separation. The separated solids were in open under sunlight for 7 hours (10 am to 5 pm). The dried BMSW was collected.
Dry amount of BMSW obtained was 120 grams which was analysed for its potassium content.
The potassium content in the dry BMSW was analysed using EDAX as well by chemical analysis.
The potassium content found was 15%.
The Nitrogen content found was 8.5%

Example : 4
One litre of biomethanated spentwash with 6% solid was taken in 5.00 litres. Plastic container. 50.00 ml of alkaline silicate was added slowly to BMSW with constant stirring using magnetic stirrer. The BMSW started getting coagulated and a thick slurry was formed. The thick slurry was sprayed as a thick bed of 1.00 cms thick on agricultural black cotton soil kept in flower pot. No percolation of water from soil in flower was observed whereas untreated BMSW percolated down from the flower pot showing the safe disposal of coagulated BMSW on agricultural soil. The flower pot with coagulated BMSW was kept in the sunlight which was nicely dried forming dried flakes of BMSW.
Example :5
1.00 litre of biomethanated spentwash with 6% solid was taken in plastic container of 5.00 ltrs capacity. 50.00 ml of alkaline sodium silicate was added slowly to BMSW with constant stirring using magnetic stirrer. The BMSW started getting coagulated and a thick slurry was formed. The solids from the slurry were separated using pressure filter and filter cake was kept in a plastic tray forming a thick layer of 1-2 cms in the tray. The tray containing thick slurry was kept in open air under sunlight for 7 hours (10 am to 5 pm). The dried BMSW powder was collected and stored in closed plastic container.
130 g. of dry of BMSW was obtained which was analysed for its potassium content.
The potassium content in the dry BMSW was analysed using EDAX as well by chemical analysis.
The potassium content found was 13%.
The nitrogen content found was 8%.

Example: 7
1.00 litre of biomethanated spentwash with 6% solid was taken in plastic container of 5.00 ltrs capacity. 50.00 ml of alkaline sodium silicate was added slowly to BMSW with constant stirring using magnetic stirrer. The BMSW started getting coagulated and a thick slurry was formed. The thick slurry was transferred to a rectangular stainless steel tray with provision of embedded hot water circulation forming a thick layer of 1-2 cms in the trough. The tray containing thick slurry was kept in open air under sunlight for 7 hours (10 am to 5 pm) along with hot water circulation. The dried BMSW powder was collected and stored in closed plastic container.
130 g. of dry of BMSW was obtained which was analysed for its potassium content.
The potassium content in the dry BMSW was analysed using EDAX as well by chemical analysis.
The potassium content found was 13%.
The nitrogen content found was 8%.

Advantage of the invention
1) A simple process for drying of bio-methanated spentwash which is challenging task for sugarcane based ethanol distillery to meet the stringent environment norms.
2) A simple process for recovery of potassium, ammoniacal nitrogen and other valuable nutrients from BMSW.
3) A simple process for coagulation of BMSW by adding liquid silicious precursor and a flocculating agent to obtain thick slurry which can be dried at lower temperature under sun light.
4) A simple process for drying of BMSW without concentration by using multiple effect evaporator which is a cumbersome process, requires costly equipment as well as steam for evaporation making overall operation expensive and tedious.
5) A simple process for drying of BMSW without concentration and incineration by using multiple effect evaporator and special boiler which is a cumbersome process, requires costly equipments as well as steam for evaporation making overall operation very expensive and tedious.
,CLAIMS:We claim:
1) A process for coagulation of biomethanated spentwash to obtain enriched organic manure comprising the following steps:
a. Addition of silica precursor coagulant 4.0-5.0% to biomethanated spentwash under stirring conditions to obtain coagulated spentwash.
b. Spreading of coagulated biomethanated spentwash on a concrete floor in open under sunlight for two days to obtain dried powder for its use as organic fertilizer which contains about 13-15% potassium, 20-23% organic carbon and 2-3% ammoniacal nitrogen.
2) A process as claimed in claim 1, wherein silica precursor and flocculating agent Magnaflock LT-25 is added in to coagulate BMSW
3) A process as claimed in claim 1, wherein the biomethanated spentwash is coagulated by addition of silica precursor and 20-30% pressmud under stirring conditions to obtain coagulated spentwash which is dried under sunlight to obtain dried powder.
4) A process as claimed in claim 1, the biomethanated spentwash is coagulated by addition of silica precursor, flocculating agent along with pressmud and further dried using industrial rotary dryer to obtain dried powder which can be used as organic manure.
5) A process as claimed in claim 1-4, wherein the coagulated BMSW is dried in open air under sunlight by circulating hot water from solar heater.

6) A process as claimed in claim 1-4, wherein the coagulated BMSW is dried using various slurry drying process dryer.

7) A process as claimed in 1-6, wherein the solids from coagulated BMSW are separated using filtration, centrifugation and the separated solid is dried in open air under sunlight.