CN1335274A - Treatment method of textile printing industry effluent - Google Patents

Treatment method of textile printing industry effluent Download PDF

Info

Publication number
CN1335274A
CN1335274A CN 01130891 CN01130891A CN1335274A CN 1335274 A CN1335274 A CN 1335274A CN 01130891 CN01130891 CN 01130891 CN 01130891 A CN01130891 A CN 01130891A CN 1335274 A CN1335274 A CN 1335274A
Authority
CN
China
Prior art keywords
water outlet
aeration
woven fabrics
water
waste water
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
CN 01130891
Other languages
Chinese (zh)
Other versions
CN1156409C (en
Inventor
张瑛瑛
洪光前
高锡祯
张金铭
郑学侣
孔庆娴
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Xinlei Environment Protection Science & Technology Development Co Ltd Tangg
Original Assignee
Xinlei Environment Protection Science & Technology Development Co Ltd Tangg
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Xinlei Environment Protection Science & Technology Development Co Ltd Tangg filed Critical Xinlei Environment Protection Science & Technology Development Co Ltd Tangg
Priority to CNB011308915A priority Critical patent/CN1156409C/en
Publication of CN1335274A publication Critical patent/CN1335274A/en
Application granted granted Critical
Publication of CN1156409C publication Critical patent/CN1156409C/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Landscapes

  • Separation Of Suspended Particles By Flocculating Agents (AREA)
  • Removal Of Specific Substances (AREA)

Abstract

The treatment of textile and printing industry effluent is mainly one physical and chemical process and various dye pollutants are eliminated by the alkali system, acid system, oxidation system, oxidation and reduction system, flocculation system and adsorbing system. Treated water is colorless, smell-less, clear and transparent. According to different discharge requirement and different dye property, amount and sort, different treating units are combined. With chroma eliminating rate greater than 98 %, sulfide eliminating rate greater than 99 %, less residue and reused flocculant, the present invention is suitable for treating various printing effluent with various dyes.

Description

The improvement method of wastewater in textile printing and dyeing industry
Technical field
The invention belongs to process for treating industrial waste water, particularly the improvement method of wastewater in textile printing and dyeing industry.
Background technology
The composition of printing and dyeing industrial waste water, character and colourity are different with textile properties, and also the variation with employed dyestuff kind, quantity and other chemical agent changes.Be generally that the water yield is big, colourity is high, alkalescence or acid strong or the like, generally based on Organic pollutants, wherein many materials are poisonous and harmful, directly do not enter the severe contamination that farmland or water body all can cause environment if do not handle.
Domestic and international at present improvement to printing and dyeing industrial waste water, the method that mainly adopts biochemical process, physico-chemical process, biochemical process and physico-chemical process to combine.Number of patent application is 97104496.1 invention, discloses a kind of treatment of dyeing and printing method and filter plant, is finished by coarse filtration, catalyzed oxidation flocculation and three processing units of millipore filtration.Dyeing waste water is entered the filtration that the remodeling strainer tube is housed in the tank body intercept and capture device, particle diameter is intercepted and captured at particle and suspended substance more than 5 microns, and form filter cake with filteration; Then in filtrate, add flocculant poly ferric sulfate, oxygenant and coagulant aids, make it the catalyzed oxidation flocculation.Entering millipore filter again filters.Application number is that the method for 99120641 a kind of pair of filtering layer filter bed treatment of dyeing and printing adopts A layer iron charcoal layer, and the two-layer filtering layer of B layer calcium hydroxide layer handled dyeing waste water.
Summary of the invention
Now the technology of report all is various dyestuff to be done as a whole, takes all factors into consideration its treatment process, and owing to different with textile properties of composition, character and the colourity of printing and dyeing industrial waste water, the result that obtains is widely different like this.
The present invention is that to overcome above-mentioned shortcoming be to handle respectively by the character of dyestuff, thereby solves the colourity of various dyeing waste waters and sulfide etc.
The present invention realizes with following method:
The present invention is according to the nature difference of dyestuff, use different steps respectively, pass through cascade filtration, from waste water, remove various relevant dyestuffs: be characterized in based on physico-chemical process, dyeing waste water respectively by alkaline system, acidic system, oxidation system, redox system, flocculation system and adsorption system, is removed various dyestuffs respectively.Waste water is transferred to slight alkalinity, remove dispersed dye and sour fuel, again under solutions of weak acidity, remove basic dyestuff and thioxine dyes etc., again under the strong oxidizer effect, remove the water-soluble reactive colour and the cationic dyestuff of easy oxidation, under the redox condition of iron filings, remove organism such as azoic dyestuff; The relevant dyestuff of under flocculating conditions, removing milkiness attitude, water-soluble attitude and easily being adsorbed by flocculation; Last again by the adsorption of slag, remove organism such as alkyl chloride, hydro carbons or the like.
Concrete steps of the present invention are as follows:
1. dyeing waste water being regulated pH value at equalizing tank with alkali is 8-9, filters through nonwoven fabric filter, removes matching stain and dispersed dye etc.;
2. in the acidifying aeration tank, regulating waste water with acid is about 3 to PH, and aeration filtered through non-woven fabrics again more than half an hour, removed most of sulfide and basic dyestuff, comprising thioxine dyes or title azoic dyestuff, if colourity is up to standard, can discharge after the neutralization;
3. as having water-soluble reactive colour and cationic dyestuff etc., waste water may be below standard, water is entered oxidation tank, add strong oxidizer, as clorox etc., aeration is placed more than 4-12 hour at oxidation pond more than half an hour then, filter through non-woven fabrics, remove multiple as soluble dye and sulfide such as reactive dyestuffs.At this moment, but water outlet qualified discharge.
4. if still below standard, then enter the redox jar that iron filings are housed, regulating PH with sulfuric acid is about 4, and aeration filtered through non-woven fabrics more than half an hour, further removed the above-mentioned azoic dyestuff that does not eliminate as yet etc., if see that colourity is up to standard, can discharge.
5. if above-mentioned water outlet is still below standard, then enters the flocculation jar and enter the flocculation stage, water outlet is filtered through non-woven fabrics, filters the back water outlet and gets final product qualified discharge;
6. also can be with waste water again through slag absorption, water outlet is after non-woven fabrics filters, and is colourless, tasteless, as clear as crystal, but complete qualified discharge.
In above processing step, 1 is that alkaline system processing unit, 2 is that acidic system processing unit, 3 oxidation systems are that processing unit, 4 is that redox system processing unit, 5 is that flocculation system processing unit, 6 is the adsorption system processing unit.The visual water quality of processing unit, dye species and quantity and increase and decrease and make up, unitary order is not a fixed, can design arbitrarily as required.
The combination of technique unit increases and decreases with kind, quantity and the character of dyestuff, but, general dyestuff: routine basic dyestuff, sour fuel, dispersed dye, reactive dyestuffs, neutral dye, vat dyes, cationic dyestuff or the like, after the improvement of this technology, sulfide, colourity etc. all can reach emission standard.The CDO clearance reaches 50~70%.
The water outlet of each processing unit all needs to filter with a kind of cotton non-woven fabrics that blending becomes with man-made fiber, and man-made fiber can be nylon, polypropylene fibre etc., and facility investment is reduced greatly, makes very difficult filtering floss be able to sharp separation.
The dyestuff of collecting on the non-woven fabrics burns through washing to mix in the coal after concentrating, and non-woven fabrics can repeatedly use again repeatedly; Because of separating through multiple times of filtration, the dyestuff of staying in the last flocculation residue is few again, make inorganic flocculating agent recovery, recycle become feasible, thereby accomplish not have a large amount of residues dischargings, non-secondary pollution problem.
The add-on of oxygenant also becomes with the kind and the quantity of dyestuff.
The sorbing material of using in the adsorption system can be gac, slag etc., and particle diameter is generally 1-1.5mm, the coal dust that the above boiler tornado dust collector of also available 40 orders come out etc.
Iron filings in the redox jar can be pig scraps, also can be wrought iron bits, but need add 1/10th slag etc. when consider with wrought iron, and particle diameter is more preferably greater than 2mm during the usefulness pig scrap, otherwise air-flow is difficult for passing through during aeration, influences reaction effect.
The flocculation residue reaches about 8% with concentrated sulfuric acid dissolution to body iron content after drying.PH 2~3 promptly can be recycled.Waste water before handling: colourity 500~1000 extension rates are blackish green, dark red, blackyellow or the like;
S=is 5~10mg/L; SS is 200~500mg/L; Handle the back water outlet: colourity≤80 extension rates or as clear as crystal, colorless and odorless;
S=≤1mg/L or do not detect; SS≤70mg/L;
It is colourless, tasteless, as clear as crystal that water after the processing can reach, and also can only adopt the unitary combination of partially disposed to get final product according to the requirement of blow off levels.Dye property, quantity, kind difference, the combination of processing unit be difference to some extent also.Chroma removal rate 〉=98%, the clearance of sulfide 〉=99%, this technology does not have a large amount of residues, and flocculation agent recycles, and the present invention is applicable to various dyeing waste waters based on dyestuff.
Description of drawings Fig. 1: process flow sheet
Specific embodiment
Embodiment 1:
Hangu District a certain printing and dyeing workshop in Tianjin has 40 dyeing machines, 300~500 tons of day displacement. When 40 dyeing machines start simultaneously, cut the dyestuff composition, character of use, when quantity is different, useless Water meter is seen and is dark red, blackyellow, blackish green etc., and then its comprehensive discharge dyeing waste water uses 1~6 All processing procedures of six unit: waste water is flowed into collecting-tank, and transferring to PH with our factory's salkali waste is 8 About, filter the about 1M of net cage volume through the nonwoven net cage3, then waste water is squeezed into the acidifying aeration tank with pump, the about 20M in aeration tank3, it is 3 that adding sulfuric acid transfers to PH, aeration with the hydrogen sulfide that 40% isoconcentration alkali liquor absorption is emitted, was squeezed into the nonwoven net cage with pump and is filtered the about 1M of net cage volume more than 30 minutes3, enter again oxidation pond, the about 20M of oxidation pond3, adding volume ratio is 0.1~0.2% sodium hypochlorite solution, and it is about 3.5 that adding sulfuric acid transfers to PH, and aeration pumped into 140M more than 30 minutes3Oxidation is deposited the pond and is placed 12 About hour, filter through nonwoven fabric filter. Water outlet pumps into 20M3The redox tank, the iron plane flower of 1/3 volume is housed in the tank, use 1:1H2SO 4Transferring to PH is about 4, and aeration went out more than 30 minutes Water enters the flocculation tank after nonwoven fabric filter filters, add ferric sulfate to 20~50mg/L, again with being somebody's turn to do It is 8 that the spent lye of factory transfers to PH, and aeration agitation is even, adds immediately 0.05% polyacrylamide solution, The volume ratio of addition is 0.1%, and aeration stirs evenly the pump of namely stopping the supple of gas or steam, static about 20~30 minutes, and water outlet Filter through nonwoven fabric filter, through slag absorption, get final product qualified discharge again.
Waste water before processing: colourity 500~1000 extension rates, S=be 5~10mg/L,
SS is 200~500mg/L;
Water outlet after processing: colourity≤80 extension rates, S=≤2mg/L,
            SS≤70mg/L。
Embodiment 2:
When the dyestuff that uses has basic-dyeable fibre, sulfur dye and disperse dyes, at this moment this factory's workshop discharging It is main that the dyeing waste water of mouth is suspension black, and processing method is selected 1,2 unit combinations. It is useless to print and dye Water flows into collecting-tank, and transferring to PH with the spent lye of our factory is about 8, through the filtration of nonwoven net cage, net Casing amasss about 1M3, then waste water is squeezed into the acidifying aeration tank with pump, the about 20M in aeration tank3, add sulphur It is 3 that acid transfers to PH, and aeration absorbed the hydrogen sulfide of emitting with 40% isocyatic caustic soda more than 30 minutes After, to squeeze into nonwoven net cage filter with pump and filter, it is 6~7 that water outlet slightly is neutralized to PH with alkali lye, namely But qualified discharge.
Waste water before processing: colourity 500~1000 extension rates, S=be 5~10mg/L,
SS is 200~500mg/L;
Water outlet after processing: colourity≤80 extension rates, S=≤2mg/L,
            SS≤70mg/L。
Embodiment 3:
When the dyestuff that uses during as dyestuffs such as solubility reactive dye or cations, at this moment this factory's workshop discharging Mouthful dyeing waste water be bright-coloured large red, transparent, colourity up to 2000 extension rates about, no sulphur Compound is discharged and is put. Can adopt the 3rd, 6 unit combinations. This dyeing waste water is squeezed into oxidation pond, oxidation pond About 20M3, adding volume ratio is 0.1~0.2% sodium hypochlorite solution, and it is about 3.5 that adding sulfuric acid transfers to PH, and aeration pumped into 140M more than 30 minutes3Oxidation is deposited the pond and was placed about 12 hours, through nonwoven The cloth filter filters, and it is 6~7 that water outlet is neutralized to PH with aqueous slkali, after slag absorption, and can be up to standard Discharging.
Waste water before processing: colourity 200~2000 extension rates, SS are 200~500mg/L;
Water outlet after processing: colourity≤80 extension rates, SS≤70mg/L.

Claims (4)

1. the improvement method of a wastewater in textile printing and dyeing industry, concrete steps of the present invention are as follows:
(1) dyeing waste water being regulated pH value at equalizing tank with alkali is 8-9, filters through nonwoven fabric filter, removes matching stain and dispersed dye etc.;
(2) in the acidifying aeration tank, regulating waste water with acid is about 3 to PH, and aeration is more than half an hour,
Filter through non-woven fabrics again, remove most of sulfide and basic dyestuff,,, can discharge after the neutralization if colourity is up to standard comprising thioxine dyes or title azoic dyestuff;
(3) as having water-soluble reactive colour and cationic dyestuff etc., waste water may be below standard, water is entered oxidation tank, add strong oxidizer, as clorox etc., aeration is more than half an hour, place more than 4-12 hour at oxidation pond then, filter, remove multiple as soluble dye and sulfide such as reactive dyestuffs through non-woven fabrics, at this moment, but water outlet qualified discharge;
(4) if still below standard, then enter the redox jar that iron filings are housed, regulating PH with sulfuric acid is about 4, and aeration filtered through non-woven fabrics more than half an hour, further removed the above-mentioned azoic dyestuff that does not eliminate as yet etc., if see that colourity is up to standard, can discharge;
(5) if above-mentioned water outlet is still below standard, then enter the flocculation jar and enter the flocculation stage, water outlet is filtered through non-woven fabrics, filters the back water outlet and gets final product qualified discharge;
(6) also can be with waste water again through slag absorption, water outlet is filtered through non-woven fabrics, and is colourless, tasteless, as clear as crystal, but complete qualified discharge.
In six above process steps, each step respectively is a processing unit.The visual water quality of processing unit, dye species and quantity and increase and decrease and make up, order also is transformable.
2. the improvement method of a wastewater in textile printing and dyeing industry as claimed in claim 1, the water outlet that it is characterized in that each processing unit all needs to filter with a kind of cotton non-woven fabrics that blending becomes with man-made fiber, man-made fiber can be nylon, polypropylene fibre etc., facility investment is reduced greatly, make very difficult filtering floss be able to sharp separation.
3. the improvement method of a wastewater in textile printing and dyeing industry as claimed in claim 1, it is characterized in that the sorbing material of using in the adsorption system can be gac, slag etc., particle diameter is generally 1-1.5mm, the coal dust that the above boiler tornado dust collector of also available 40 orders come out etc.
4. the improvement method of a wastewater in textile printing and dyeing industry as claimed in claim 1, it is characterized in that iron filings in the redox jar can be pig scraps, also can be the wrought iron bits, need add slag of 1/10th etc. when but considering to be worth doing with wrought iron, particle diameter is more preferably greater than 2mm during with pig scrap, otherwise air-flow is difficult for passing through during aeration, influences reaction effect.
CNB011308915A 2001-08-31 2001-08-31 Treatment method of textile printing industry effluent Expired - Fee Related CN1156409C (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CNB011308915A CN1156409C (en) 2001-08-31 2001-08-31 Treatment method of textile printing industry effluent

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CNB011308915A CN1156409C (en) 2001-08-31 2001-08-31 Treatment method of textile printing industry effluent

Publications (2)

Publication Number Publication Date
CN1335274A true CN1335274A (en) 2002-02-13
CN1156409C CN1156409C (en) 2004-07-07

Family

ID=4670217

Family Applications (1)

Application Number Title Priority Date Filing Date
CNB011308915A Expired - Fee Related CN1156409C (en) 2001-08-31 2001-08-31 Treatment method of textile printing industry effluent

Country Status (1)

Country Link
CN (1) CN1156409C (en)

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1296296C (en) * 2004-08-03 2007-01-24 李双民 Textile printing and dyeing waste water processing system and method
CN101962218A (en) * 2010-09-27 2011-02-02 浙江大学 Method for degrading azo dyes waste water
CN102050535A (en) * 2010-11-10 2011-05-11 浙江大学 Processing method for resource recovery of acidic dye waste water
CN101412571B (en) * 2007-10-17 2011-06-01 上虞市金冠化工有限公司 Technique for reclaiming waste water of azoic dye production
CN102557298A (en) * 2012-01-06 2012-07-11 绍兴文理学院 Method for decoloring printing and dyeing waste water of reactive dye
CN102774995A (en) * 2012-07-24 2012-11-14 吴江市聚力机械有限公司 Dyeing wastewater treatment device
CN102826673A (en) * 2011-06-15 2012-12-19 浙江龙盛化工研究有限公司 Cleaning treatment method of dying industrial acidic wastewater
CN103149184A (en) * 2013-02-04 2013-06-12 山西大学 Fluorescence detection method for hypochlorite
CN103964600A (en) * 2013-02-05 2014-08-06 浙江龙盛集团股份有限公司 Recycling method for azo disperse dye waste water
CN104071920A (en) * 2014-08-07 2014-10-01 南通润启时装有限公司 Printing and dyeing wastewater treatment process
CN105692952A (en) * 2016-01-22 2016-06-22 南通海陵环境检测有限公司 Treatment method of textile wastewater
CN105948318A (en) * 2016-06-08 2016-09-21 浙江奇彩环境科技股份有限公司 Recycling treatment method for positive ion dye wastewater
CN108751495A (en) * 2018-06-11 2018-11-06 河南新野纺织股份有限公司 A kind of wastewater in textile printing and dyeing industry processing method
CN109368861A (en) * 2018-11-20 2019-02-22 韩涛 A kind of textile printing and dyeing sewage-treatment plant
CN109384333A (en) * 2018-11-20 2019-02-26 韩涛 A kind of textile printing and dyeing sewage treatment process
CN109665547A (en) * 2019-02-28 2019-04-23 仲恺农业工程学院 A kind of method that sodium sulfate crystal is precipitated in induction high-salt wastewater

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1296296C (en) * 2004-08-03 2007-01-24 李双民 Textile printing and dyeing waste water processing system and method
CN101412571B (en) * 2007-10-17 2011-06-01 上虞市金冠化工有限公司 Technique for reclaiming waste water of azoic dye production
CN101962218A (en) * 2010-09-27 2011-02-02 浙江大学 Method for degrading azo dyes waste water
CN102050535A (en) * 2010-11-10 2011-05-11 浙江大学 Processing method for resource recovery of acidic dye waste water
CN102826673B (en) * 2011-06-15 2016-01-06 浙江龙盛集团股份有限公司 A kind of cleaning method of dyestuffs industries acid waste water
CN102826673A (en) * 2011-06-15 2012-12-19 浙江龙盛化工研究有限公司 Cleaning treatment method of dying industrial acidic wastewater
CN102557298A (en) * 2012-01-06 2012-07-11 绍兴文理学院 Method for decoloring printing and dyeing waste water of reactive dye
CN102774995A (en) * 2012-07-24 2012-11-14 吴江市聚力机械有限公司 Dyeing wastewater treatment device
CN103149184A (en) * 2013-02-04 2013-06-12 山西大学 Fluorescence detection method for hypochlorite
CN103964600A (en) * 2013-02-05 2014-08-06 浙江龙盛集团股份有限公司 Recycling method for azo disperse dye waste water
CN103964600B (en) * 2013-02-05 2016-08-17 浙江龙盛集团股份有限公司 A kind of recoverying and utilizing method of azo dispersion dyes waste water
CN104071920B (en) * 2014-08-07 2015-10-28 南通润启时装有限公司 Printing-dyeing waste water treatment process
CN104071920A (en) * 2014-08-07 2014-10-01 南通润启时装有限公司 Printing and dyeing wastewater treatment process
CN105692952A (en) * 2016-01-22 2016-06-22 南通海陵环境检测有限公司 Treatment method of textile wastewater
CN105692952B (en) * 2016-01-22 2018-06-01 南通海陵环境检测有限公司 The processing method of textile waste
CN105948318A (en) * 2016-06-08 2016-09-21 浙江奇彩环境科技股份有限公司 Recycling treatment method for positive ion dye wastewater
CN105948318B (en) * 2016-06-08 2019-06-11 浙江奇彩环境科技股份有限公司 A kind of recycling processing method of cationic dye wastewater
CN108751495A (en) * 2018-06-11 2018-11-06 河南新野纺织股份有限公司 A kind of wastewater in textile printing and dyeing industry processing method
CN109368861A (en) * 2018-11-20 2019-02-22 韩涛 A kind of textile printing and dyeing sewage-treatment plant
CN109384333A (en) * 2018-11-20 2019-02-26 韩涛 A kind of textile printing and dyeing sewage treatment process
CN109665547A (en) * 2019-02-28 2019-04-23 仲恺农业工程学院 A kind of method that sodium sulfate crystal is precipitated in induction high-salt wastewater

Also Published As

Publication number Publication date
CN1156409C (en) 2004-07-07

Similar Documents

Publication Publication Date Title
CN1156409C (en) Treatment method of textile printing industry effluent
CN102092879B (en) Dye wastewater cyclic utilization device and method based on electrolysis and lamination technologies
CN108558140A (en) A kind of dyeing fabric sewage water treatment method
CN105692952B (en) The processing method of textile waste
CN208995266U (en) A kind of polluted underground water apparatus for extracting
CN105776726A (en) Treatment process of printing and dyeing wastewater in textile industry
CN111548850B (en) Method for treating and recycling cutting fluid and recovering precipitated sludge product
CN207243633U (en) A kind of dyeing and printing sewage filtering and purifying
CN109592853A (en) A kind of wastewater treatment method
CN207958039U (en) A kind of pickle liquor Treatment and recovery utilizes device
CN106241833A (en) A kind of method of the recycling of light alkali wasteliquid regeneration high alkali liquid
CN207468386U (en) A kind of zero-discharge treatment system of mixed electroplating wastewater
CN212924728U (en) Printing and dyeing wastewater pretreatment device
CN109626725A (en) A kind of method of sewage purification
CN213266036U (en) Industrial wastewater vibrating membrane treatment device
CN105692859B (en) Strong oxidizer and its application
CN209906563U (en) Processing system for processing antioxidant wastewater
CN209619070U (en) A kind of printing development waste liquid processing system
CN1583608A (en) Comprehensive treatment of cotton-dreg black liquid and waste water from production of viscose fiber
CN208454670U (en) A kind of printing ink wastewater processing integrating device
CN101525440B (en) Preparation method of high molecular compound polyacrylamide flocculant
CN102417270A (en) Printing and dyeing wastewater treatment system
CN104016527A (en) Textile dyeing wastewater treatment method
KR100483694B1 (en) Adsorption Reaction Unit Using Power Active Corbon and Method Thereof
CN205773683U (en) A kind of meat-packing industry Waste Water Treatment

Legal Events

Date Code Title Description
C10 Entry into substantive examination
SE01 Entry into force of request for substantive examination
C06 Publication
PB01 Publication
C14 Grant of patent or utility model
GR01 Patent grant
C17 Cessation of patent right
CF01 Termination of patent right due to non-payment of annual fee

Granted publication date: 20040707

Termination date: 20110831