Journal of Scientific & Industrial Research Vol. 61, January 2002, pp 53-60

Chemical Industry Treatment Using A K A Rathi*

Technical Adviser (Chemi cal), Government of Gujarat, Industries Commissionerate, Udyog Bhavan, Gandhinagar 382017

and

SA Puranik VVP Engineering Coll ege, Rajkot 360 005

Received: 3 1 July 200 I; accepted: 02 November 200 I

In a typical wastewater treatment fl ow sheet used by several industri al units in Indi a. various stages of treatment include primary treatment. foll owed by second ary treatment . and terti ary treatment. The concentrati on of total dissolved solids increases during neutrali zation of the wastewater with acid/ alkali during primary treatment. which adversely affects the activity of microorgani sms during biological treatment. The present stud y aims at demonstrating that adsorption as th e Iirst stage of treatment shall increase efficiency of the subsequent bi ological treatment. Experiments were carried out on different wastewater sampl es from chemi cal pl ants on adsorbent s viz. ac ti vated carbon. bent onite. and li gnit e. The effecti veness of adsorbents in th e removal of refractory orga nics by way of reducin g chemical demand and colour is evaluated. The results of COD red uction are fitt ed into different models ava il ab le in literature including the new model Rat"i Puranik eq uation . which requires least experiment ati on for predicting COD va lues.

2 Introduction were reviewed . The use of activated carbon in and wastewater treatment, including the increasin gly A wide range of adsorbents (granulated as we ll important role of adsorption" for removal of specific as finely powdered) including activated carbon, clays, target compounds or classes of compounds from , tly as h, alumina, magnes ium ox id e, ferric . water and wastewater containing complex organi c oxide, silica, saw du st, zeo li tes , and activated substance mi xtures has also been reviewed. The anthrac ite vo lcanic ash so il s are used in wastewater wastewater was biologically treated, and the residual treatment for the removal of heavy metals, and BOD and COD were removed further with activated di ssolved organic compounds whi ch result in the ca rb o n~ . Powdered acti vated carbon and granular reducti on of COD, BOD, and colour. For treatin g acti vated carbon) were used for the terti ary treatment wastewater from multiproduct chem ical plants of wastewater from a petrochemical plant. It was containing organic chemi cal substan ces in varying inferred th at low COD and colour removal compositi on and concentration, which are difficult to effici encies were due to the presence of organic degrade biologicall y, adsorption process I in coll oid s. whi ch were not adsorbed by the carbon. combination with other processes is considered ve ry Granulated carbons prod uced colourl ess efflu ent from effective in reducing COD and colour. the am ber-coloured intluent. The results of removal Adsorbents in industrial wastewater treatment of phenols and cyanides6 by adsorption by acti vated with adsorptive properties of adsorbents, ac ti vated carbon in a pil ot-plant were presented. Some carbon, inorgani c adsorbents and effici ent ind ustrial act ive carbons were used as adsorbents in app li cati ons of activated carbon adsorption processes phenol and pyridine? removal processes and in adsorption of resins and oi ls from coki ng plant *A uth or for correspondence wastewater. It was observed that phenols were more Tcl: 079 3225837. Fax : 079 3225S2S. c-mail: env @ic.guj .nic.in easil y adsorbed than pyridines. It is reported that 54 J SCIIND RES VOL 6 1 JANUARY 2002 anionic, cationic, or nonionic polyelectrolytes or clay to be 90 per cent. The remaining sodium and minerals8 did not inhibit adsorption of phenol on sodium carbonate were recovered and reused in soda activated carbon. The phenol concentration In manufacture. wastewater9 was reduced to less than 0.5 mg/L by passing the wastewater through a three-stage­ Methodology adsorbing tank, each stage packed with activated The conventional flow sheet of wastewater carbon. treatment used by most of the nndu"trial units, More than 80 per cent COD removal was in c ludes primary treatment, followed by secondary obtained from wastewater containing benzene and tertiary treatments. derivatives. carboxylic acids, . and phenols During primary treatment , neutralizati on of the by sequential adsorption on sorbents combination of wastewater results into increase of salts (total activated anthracite PorolasT exchange resin di ssolved salts). Salts in hi gh concentration inhibit activated anthracite 10. oxide contai ning biological activi ty ' 6, and may cause an increase in ll adsorbents are reported to have been used for the nonsettleable suspended solids in the treated treatment of wastewater from pulp manufacturing wastewater I? The tlow sheet given sub equentl y is, plants. therefore,proposed, wherein adsorpti on with

Physico- Waste pH Chemical! Treatecl Water Adjustment .. Biological .. Adsorption wdSte Wolter ~ Treatment

Conventional flowsheet

Wastewater containin g heavy metal s was treated in expensive adsorbents could be employed, prior to with fly ash ' 2 from coal combustion. resu lting in an the conventi onal primary treatment for in creasin g increase in pH to more than 8, a decrease in COD. efficiency of th e biological treatment. and removal of the metals . Methods for reducing This is expected to reduce refractory organi cs concentration of surface-active agents in industrial (COD) as well as BOD of the wastewater wastewater13 were examined and it was observed that substantially at the first stage of wastewater treatment adsorption on coal guaranteed a satisfactory itself, facil itating further treatment. From multi-stage concentration reduction for the carboxyli c and production processes used in the production of alkylsulphate surfactants but not the ami ne. which organic chemicals, wastewater stream is li kely to was best removed by adsorption on benton ite. The contain several organic as well as Inorganic performance of wood c h arcoa l' ~ for the removal or substances including products. intermediates. side DDT from the aqueous phase was in vestigated. The products , byproducts and unreacted raw materials. influence of partic le size, pH, and the time of contact. The industrial being hi ghl y complex and which affect the sorption process, was studied in varying widely in the adsorbability of the compounds batch experiments. present l ?, the detailed analysis of such wastewater

Adsorption 15 was employed to remove organic streams and study of their adsorption on d i fferent impuntles from wastewater contallllllt! sodium adsorbenrs was very complex. It was, therefore. chloride 5-15, sodium carbonate 1.5. and sodium decided to consider COD as the measure of organic nitrate O. I per cent and monochlorobenzene 0.3. solutes. The colour of the wastewater was also polyamines 0.3, 4,4' diaminodiphenylmethane 0. 3. measured. These parameters (COD and colour) and toluenediamine 2 mg/L for subsequent reflect the practical aspects of wastewater treatment recovery. The efficiency of the organi c impurity on the industrial scale. T hus. such a study should be removal from isocyanate manufacture was observed of much relevance to the industry in selecting cost- RATHI & PURANIK: CHEM ICAL INDUSTRY WASTEWATER TREATMENT 55

Physico- Waste pH Chemical! Treated Water Adsorption .. Adjustment ~ Bi ological ~ waste .. Treatment water

Proposed flowsheet

effective wastewater treatment technique for two from ethanol (before and after biogas generation; complying with the statutory regulation s. The sampl e no. 6 and 7), one from drug intermed iate approach fo ll owed in the evalu ati on of adsorption (diethyl malonate; sample no. 8), two from a complex performance of different adsorbents viz. acti va ted manufacturing vat dyes and intermediates (before and carbon, bentonite, and li gnite in the treatment of after neutralization ; sample no. 9 and 10). and one wastewater is thu s based on detection of COD and from a complex manufacturing various dyes and colour (optical ) in the wastewater with intermediates; sample no. 11 ). These samples were varying degree of treatment. This approach is entirely taken directly from the process plant streams, before different from that followed by many of the these had any chance of getting mixed with any other researchers who prepare wastewater samples from streams. In most of the cases these were concentrated known solutes in the laboratory and carry out streams, often referred as mother li quor. While chemi cal analysis of the treated sampl e. carryin g out experimental stud ies on the wastewater .J from each carboy the sample was analyzed for pH . The COD determination IX is a measure of the colour and COD. Then 500 mL of sample was taken oxygen equivalent of that portion of the organic from the respective carboy in a cylindrical tlask. 2. 5 g matter in a sample that is susceptible to oxidation by activated carbon (AC) was added into the flask and a strong chemical oxidant. It is an important, rap idl y magnetic stirrer was started. 5-10 mL sample was measured parameter for industrial wastewater studies drawn every 15 min from this mass, filtered on filter and for control of wastewater treatment processes. paper and the fi ltrate analyzed for pH, colour and The dichromate reflux method was used for the COD COD. At the end of 2 h, the stirring was stopped and determination because it has advantages over other the experiment was termin ated. The experiments were oxidants in oxidizabi lity, applicabi lity to a wide repeated wit h 5 g bentonite (WP) as well as 5 g variety of samples and ease of manipulation. The li gnite (BP). All the experiments were carried out at colour absorbance was measured as optical den sity in 0 the UV visible ran ge, with the help of room temperature of around 32 C. The properties of spectrophotometer at the wavelength of maximum adsorbents used are given in Table I . absorbance. The measurements were done on neat Results and Discussions undiluted wastewater samples. In the cases, where the absorbance readings went beyond the scale the Performance ofAdsorbents samples were diluted and the same dilution factor was app li ed to treated samples also. The performance of different adsorbents used in wastewater treatment with respect to COOl colour Experimental Procedure red uction has been analyzed by considering the fo llowing graded scale: For the contact time experiments, eleven wastewater samples from different production plants Performance Per cent reduction in were collected in labeled carboys and the carboys COOl colour were then sealed. These plants included dye Effective >40 intermediates (H-acid, dihydroxydibenzanthrone. Moderately effective 20- 40 dibenzyl oxybezaldehyde, dibenzanthronyl, and benzanthrone crude; sample nos. I to 5. respectively) , Not effective < 20 56 J SCIINO RES VOL 61 JANUARY 2002

Table 1- Properties of adsorbents Activated carbon Bentonite Lignite .. Appearance Fine hlack powder. free from Fine white powder. free Fine black powder. gritty matter from gritty matter free from gritty matt er Acidity! alkalinity 3g boiled in 60 mL water should pH : 8.76 give a neutral and colourless tiltrate Moisture. per cent by oven at 100" C 5 10.2 10 - 20 Volatile matter. per cent 30 - 35 Fixed carbon. per cent 20 - 22 Adsorption on kerosene, mLiI 00 g 28 Porosity, per cent 19 .5 Melting point, "c 1550 Specil1c surface. sq m! g 220 Refracti ve index 1.502

Ash content , per cent. 2 - 3 12 - 20 Oecolourization capacit y. per cent 40 Parti cle size. mi cron 10 - 100 10 - 100 10 - 100 Mesh size. per cent -BS 72: 100 -BS 100 90 \ +BS 100 0.45 -BS 100 + BS 200 27 .22 -8S 200 + BS 300 11 .77 -8S 300 60.56

COD Reduction for wastewater from H-acid. BP is effective for wastewate r from dihydroxydibenzanthrone and The COD reduction by the three adsorbe nts over ethanol (both before and after bi ogas gene.ratiun). and time for sample nos. I to 5 and 6 to II is plotted in the complex manufacturing different dyes (othe r than Figure I and 2, respecti vely. It can be observed that vat) and inte rmedi ates, and moderately effecti ve for for COD reduction, AC is effecti ve for wastewate r dibenzanthronyl, benzanthrone crude and di ethyl from H-acid, dihydroxydibenzanthrone, ethanol malonate, and the complex manufacturi:lg vat dyes (before biogas recovery) and di ethyl malonate, and and their intermediates. BP is not effectiv" for H-acid moderate ly effecti ve for wastewater from the plants and dibenzyl oxybenzalde hyde. manufacturing dibenzanthronyl , benzanthrone crude and ethanol (after biogas recovery), and the complex Thus the performance of all the three adsorbents manufacturing vat dyes and their intermediates. AC is is comparable for reducing COD of the wastewater not effective for wastewate r from dibenzyl from the plants manufacturing dihydroxy­ oxybenzaldehyde. WP is effecti ve for wastewate r dibenzanthrone, dibenzyl oxybenzaldehyde, diben­ d ihydroxydibenzanthrone, ethanol (both before and zanthronyl. benzanthrone crude and ethanol (both after biogas generati on) and from diethyl malonate. before and after biogas recovery). AC is obse rved to and the complex manufacturing different dyes (other perform better than both WP and BP for wastewater than vat) and intermediates, and moderately effective from H-acid. In the case of wastewater from diethyl for dibenzyl oxybezald ehyde, dibenzanthronyl and malonate p lant, the performance of AC and WP is benzanthrone crude, and the complex manufacturing comparable. and better than BP. The performance of vat dyes and their intermediates. WP is not effective WP and BP is comparable for mi xed wastewater from RATHI & PURANIK: CHEMI CAL INDUSTRY WASTEWATER TREATM ENT 57

----_._----- _ ._------1 --+--lAC ...-lWP -.-1I1P -M-2AC _+_2WP __ 2SP -+-3AC -2WP -3BP - ·:·- ~c ':.j-. 4WP -'\- 48P -+t-- SAC - lII-&WI' ___ _ 0.8

0.5

~ 1" 0.3 8U

0.2 .r_ ;'j '-

0.1

Figure I - COD red ucti on over time

--+--SAC _+_SWP -'-6BP ~7AC -+-7WP --+--7BP -+-SAC -8WP -SBP ..., - SAC -Jc"' gWp -'-A- IIBP -H'- 10AC ""·:r. .. 1OWP -·",- ·1011P -- -i- llAC -llWP -11BP 0.6

0.5

I 0.4 I" § 0.3

0.2

0.1

0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 t,h

Figure 2 - COD red uction ove r time the complexes manufacturing di fferent dyes and the ir benzanthrone crude, and the complex manu factu ring intermediates and it is better th an AC for wastewater vat dyes and their intermediates, and it is moderately from the complex manufacturing different dyes (other effecti ve for ethanol (both before and after biogas th an vat) and intermediates. recovery. W P is effecti ve for wastewater of dibenlyl oxybezaldehyde and moderately effective for CoLour Reduction dihydroxydibenzanthrone, benzanthrone crude and For colour reducti on, AC is foun d to be eth anol (both before and after biogas recovery). and effecti ve for wastewater of dihydroxydibenzanthrone. the complex manufacturing different dyes (other than dibenzyl oxybezaldehyde. di benzanthronyl and vat) and intermediates. WP is not effective fo r 58 J SCIIND RES VOL 61 JANUARY 2002

wastewater from dibenzanthronyl, and the complex """'" manufacturing vat dyes and their intermediates. BP is effective for wastewater from dihydroxy­ dibenzanthrone and benzanthrone crude dibenzyl oxybezaldehyde, and the complex manufacturing vat dyes and their intermediates, and is moderately effective for and ethanol (both before and aft