Title of Invention

"AN IMPROVED PROCESS FOR PRODUCING COLORLESS WATER FROM THE AGRO-INDUSTRY EFFLUENTS"

Abstract

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 characterising in that 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 coloured effluent by conventional methods, electrolysing 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

Full Text

An improved process for producing colorless water from the agro-industrial waste water. from agro-industry effluents. More particularly it relates to an electrochemical decolouration of the agro-industry waste like spent wash from alcohol distillery and black liquor from paper mill, wherein the high COD (Chemical Oxygen Demand) comprising colouring matter along with the dissolved salts are removed by electro-coagulation and electro-oxidation, so that the treated colourless water can be recycled in the process itself or let into ecosystem since it meets norms laid down by statutory bodies. The present invention thus relates to an environmental friendly process for colour removal from the sugarcane based alcohol distillery effluent and papermill effluent after biomethanalion and/ or activated sludge process. More specifically the effluent containing mainly of lignin, caramels, melanoidins, and dissolved inorganics, is decolourized by electro-coagulation and electro-oxidation using electrochemical cell. Distillery effluent or spent wash is generated after molasses fermentation to ethyl alcohol and its recovery by distillation. Normally the process produces about 15 liters of the spent wash per liter of the alcohol. This discharged effluent has obnoxious odour, dark brown colour, acid pH and COD of about 1,20,000 and is difficult to treat. Biomethanation is the first treatment, wherein some organics are converted into methane rich gas, which is used as fuel for boiler. Biomethanation of the effluent reduces the COD upto 60 to 80% and the wastewater after biomethanation needs further treatment. This effluent still has COD about 25,000 to 30.000mgl-1. Activated sludge is the secondary treatment, which generates the bacterial sludge using organic matter as a carbon source to give an effluent with COD ranging from 6,000- 8,000mgl'1 and has a dark brown colour. Electrolysis or electrochemical oxidation is a novel technique useful to treat wastewater containing difficult (refractory) organics. Its use has been restricted to laboratory scale only as seen from the review discussed here. Electrolysis or electro-oxidation technique has been used as a "front-end" technology ahead of biological treatment with the objective of detoxifying biorefractory contaminant(s) like chlorophenols (Polcaro and Palmas, in, Ind. Eng. Chem. Res. 36,1791-1798,1997). Simple effluents coming out from metal plating unit have been subjected to electrolysis to remove heavy metals and toxic organic materials (Kim, in, US patents No. 4445990,1984 and US patent 4556469, 1984). Kotz, (US patent, 4839007, 1988) attempted electrochemical oxidation of organic material from wastewater with different metal electrode doped by different ions to oxidize organic pollutants. Guaglianoni, L., (Papel, 55, 21-50, 1994) reports use of the Al and Fe or Carbon and Steel electrodes to treat high COD effluent. Free metal gets dissolved or highly corroded and should be replaced for the next batch. Electrochemical oxidation technique has been applied in the treatment of distillery spent wash. Berchman et al., (C.L.J. Berchman and Vijayavalli, in Indian J. Environ Hlth, 31, 309, 1989) diluted high COD raw spent wash 10 times with water and added 2-5 % sodium chloride before electro-oxidation. The colourless treated effluent had negligible COD/BOD values. Vijayaraghavan et al., (K. Vijayaraghavan, T. K. Ramanujan and N. Balasubramanium, in Ind. Eng. Chem Res. 38, 2264, 1999) also used high COD raw spent wash for electro-oxidation. They diluted spent wash to 10 to 20 times and carried out electro-oxidation in the presence of 2.5 to 3.0 % sodium chloride. The hypochlorous acid formed has been responsible for oxidation of organic matter present in spent wash. Presence of high amount of sodium chloride, current density of the order of 34 mA/cm2 and high residence time of 240 min will be account for high cost of treatment requiring huge : amount of energy of the order of 27-36 KWh/Cubic meter of spent wash. This technique will remain as a laboratory curiosity due to its requirement of high residence time and presence of too much salt in the treated effluent. Both these investigations have been tried using raw spent wash before recovery of energy via biomethanation technique (which has been made mandatory on the part of distilleries by central pollution control board). Thus this technique is not practical under Indian context. All other reports disclosed so far have following disadvantages, 1. use of high residence time 2. use of expensive electrodes 3. lack of employing effluent containing bio-refractory colouring matter like melanoidins, caramels and lignin, after spent wash is given primary and /or Secondary treatment, 4. Negligible removal of dissolved solids like Ca, Si etc. Hence for the applicability of the electro-chemical oxidation technique to industrial scale, the above mentioned drawbacks are to be addressed. Physico chemical treatment proves advocated by our copending patent (disco closed by Gokaran et al., (A.N. Gokarn, A.P. Joshi, N.V. Sankapal and B.D. Kulkani. Patent application No. 203/DEL/96 193284) also suffers from following drawbacks. 1. three steps process means a costly operations 2. large amount of sludge formed creates a problem of disposal of solid waste. Considering the above limitations it is evident that there is dire need of a simple and economic process for the treatment of distillery spent wash with a view to remove color and make it suitable for recycle or discharge in the ecosystem as a harmless effluent. It has been found for the first time in this invention that primary treated or secondary treated spend wash can be treated by electro-oxidation technique in the short time using catalytic amounts of flocculants and/or electrolytes. Accordingly the present invention provides an improved process for producing colorless water from the agro- industry effluents which comprises processing the agro-industrial waste water to obtain colorless water characterised in that precipitating the said agro-industrial waste water with di/tri-valent coagulants, allowing the effluent to settle for a period of 6 to 120 min, separating the transparent yellow coloured effluent by conventional methods, electrolysing 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 water. In one of the embodiments of the present invention the di / trivalent coagulants used may be selected from Feds, FeS04, A1C13, or polychlorides of aluminum, or iron such as polyaluminium chloride. In another embodiment the electrolytes used to adjust the conductivity may be selected from inorganic salts such as sulfates, nitrates, chlorides of alkali metals, preferably sodium or potassium, and / or mineral acids such as dilute H2S04/ HCL. In still another embodiment the electrodes used for the electrolysis may be nonoxidizable and reusable electrodes, made of iron, aluminum, or triple oxide coated titanium. In a feature of the present invention the electrodes are sieve or rod shaped and or circular fashion with centered cathode. In, another feature, reactor used for the electro-coagulation is, with single compartment, where cathode and anode are at the distance of 2 to 20 mm. To bring. the effective reaction, further the reactor configuration can be modified for continuous mode operation. In still further feature the current used for the electrolysis may be either DC or AC having a current density of 35 to 100 ma/cm2'preferably DC current. In yet another feature, the iron and aluminium salts used could be obtained from the waste or as by-products from the other industries to reduce the cost of treatment. In another feature, low the residence time of 3 to 15 min. helps in making the process continuous and using a small size reactor. In yet another feature electro-coagulated clean water being acidic, may be neutralized using base in the form of oxide, hydroxide or carbonate of calcium, sodium, potassium at small concentration of the order of 0.2 to 2.0 g 1" . In yet another feature the spent wash and black liquor to be treated (after biomethanation and/ or activated sludge process) may preferably have characteristics as given in table-1 given below: TABLE-1 (Table Removed) The invention is described herein below with examples, which are illustrative only and should not be construed to limit the scope of the present invention in any manner. EXAMPLE-1 Spent wash after second stage activated sludge process with a COD of 6,500 was partially coagulated with 4.5 g T1 of ferric chloride and filtered to get yellow coloured liquid, after that it was mixed with 1.2 ml I'1 of the 30% HCL and 500 ml of that was subjected for electrolysis with the following parameters: Current density: 50 ma\cm2 Residence time: 6 minutes. Electrode: Expanded mesh type triple oxide coated titanium, with mesh size of 5mmX 12mm. Volume to be treated: 500 ml. Electrochemical oxidation was carried out in a single compartment cell of 1000-ml capacity. Anode and cathode were separated at a distance of 15 mm, and dipped vertically at 70 mm to meet effective reaction. Effluent being less conductive, 5.0 gm the sodium chloride was separately added to the effluent. DC power was provided to the electrode over a period of 6 minutes. After electrolysis it was neutralized with calcium oxide or hydroxide at a level of 500 mgl"1, aerated for 10 minutes and decanted to get the effluent of characteristics as shown in table-2 TABLE-2 (Table Removed) EXAMPLE-2 Mixed flocculation and decolonisation: A spent wash sample of COD 20,600 was subjected to partial flocculation with 3-0gl'1 of ferric chloride, 4-0gT-1 aluminium sulfate and 100 mgl'1 of the cationic polyelectrolyte and mixed using a mechanical stirrer. After 1 hour it was decanted or precipitated mass was scummed out to get a dark transparent liquid of COD 2790. Electrolysis was carried with the following parameters: Current density: 52 ma\ cm2 Residence time: 10 minutes. Electrode: As in example: 1 Volume to be treated: 500 ml Before electrolysis 2 g. sodium chloride was added and transferred to the electrolytical reactor provided with a stirred at 800 rpm and allowed to electrocoagulate and oxidize for 10 mins and then kept for two hours under steady condition for settling. In order to remove the trace chlorine, supernant liquid was aerated for 10 minutes, neutralized with 0.6 gl"1 calcium hydroxide and decanted to meet the following characteristics as disclosed in table-3 TABLE-3 (Table Removed) EXAMPLE-3 A sample after activated sludge process with a COD of 20,600 was partially flocculated with 8.2 gl~' feme chloride and 100 mgf1 of the cationic polyelectrolyte to form the big clogs of the precipitate. It was then subjected for electrochemical process in the reactor discussed above in the presence of 3.0 g Sodium Chloride with following parameters. Current density: 52 ma\cm2 Residence time: 9 minutes Electrode: As discussed in example: 1 Volume of treatment: 500 ml It was neutralized with Ig I'1 Calcium hydroxide and aerated for 10 minutes and decanted to get the treated effluent of the following characteristics: TABLE-4 (Table Removed) EXAMPLE-4 Treatment of the black liquor: 500 ml of the black liquor after activated sludge process was directly subjected to the eletro-coagulation in the same reactor as described above in the, presence of 2.0-g Sodium chloride. The parameters of the reactor were as follows: Current density: 51 ma\ cm2 Residence time: 12 minutes. Electrode: Anode: As described in example: 1 Volume of treatment: 500 ml After electrolysis colourless liquid was neutralized with 400 mgl'1 lime, aerated for 10 minutes and decanted to meet the following characteristies: TABLE-5 (Table Removed) EXAMPLE-5 Black liquor, after activated sludge process had a COD of 5400. This was partially coagulated with 3.0 gl-1 commercial alum and 1.0 gl"1 of the ferric sulfate, and allowed to settle for one hour and decanted to get transparent liquid. 500 ml of this was mixed with 2.0 g sodium chloride and subjected for electrolysis process with following parameters. Current Density: 50 ma\cm2 Residence time: 8 minutes. Electrode: As described in example: 1 Volume of treatment: 500 ml After this stage the colourless liquid was neutralized with 300 mgl"1 calcium hydroxide and aerated for 5 minutes, to get the treated effluent with the following characteristics: TABLE-6 (Table Removed) EXAMPLE - 6 Treatment using different electrodes: Black liquor after activated sludge process was directly subjected for electro-coagulation with the following parameters. Current density: 51 ma\ cm2 Residence time: 8.5 minutes. Electrode: Anode: mild steel, Cathode: triple oxide coated Ti, with mesh size 5mm x 12mm. Volume of treatment: 500 ml TABLE – 7 (Table Removed) The main advantages of the present invention are as follows: 1. Use of the one compartment cell to carry out electro-oxidation and electro- coagulation, 2. Short residence time to oxidize the high molecular weight colouring bodies, makes process suitable for continuous operations 3. Efficient removal of COD, BOD and inorganics with less power input, 4. Safe and non-hazardous technique. We Claim: 1. An improved process for producing colorless water from the agro-industrial waste water which comprises processing the agro-industry effluents to obtain colorless water characterised in that precipitating the said agro-industrial waste water with di/tri-valent coagulants, allowing the effluent to settle for a period of 6 to 120 min, separating the transparent yellow coloured effluent by conventional methods, electrolysing 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 water. 2. An improved process as claimed in claim 1 wherein, the di/tri-valent coagulants used is selected from FeCI3, FeSO4, ALCb, or polychlorides of aluminum or iron such as poly aluminum chloride . 3. An improved process as claimed in claim 1 to 2 wherein, the electrolytes used to adjust the conductivity are selected from inorganic salts such as sulfates, nitrates, chlorides of alkali metals, preferably sodium or potassium, mineral acids such as dilute H2S04, HCL. 4. An improved process as claimed in claim 1 to 3 wherein, the electrodes used for the electrolysis is selected from non-oxdisable metal, iron, aluminum, or triple oxide coated titanium. 5. An improved process for producing colorless water from the agro- industry effluents substantially as described herein before with reference to examples.

Documents:

1580-del-1999-abstract.pdf

1580-del-1999-claims.pdf

1580-del-1999-correspondence-others.pdf

1580-del-1999-correspondence-po.pdf

1580-del-1999-description (complete).pdf

1580-del-1999-form-1.pdf

1580-del-1999-form-19.pdf

1580-del-1999-form-2.pdf

1580-del-1999-form-3.pdf