Waste­water Valori­sa­tion

Chemical Industry Digest - - What’s In? - Vikram Dhu­mal

- Vikram Dhu­mal, Head of Tech­nol­ogy, Geist Re­search Pvt Ltd.

Re­views how wastes can be ex­tracted from ef­flu­ent and other wa­ters and utilised. Var­i­ous valori­sa­tion meth­ods are de­scribed and the process of how to go about it.

Ab­stract

Waste is ma­te­rial which for some rea­son or the other we are not util­is­ing back in our man­u­fac­tur­ing pro­cesses. This ar­ti­cle re­views how wastes can be ex­tracted from ef­flu­ent and other wa­ters and utilised. Var­i­ous valori­sa­tion meth­ods are de­scribed and the process of how to go about it.

Man­u­fac­tur­ing came into ex­is­tence to pro­duce goods and meet the re­quire­ments of hu­mankind. Ex­plo­sive pop­u­la­tion growth lead to in­creas­ing the de­mand of al­most ev­ery ma­te­rial thing and this de­mand gave birth to in­dus­tri­al­iza­tion. In­dus­tri­al­iza­tion helped to meet the in­creased de­mand how­ever, the same In­dus­tri­al­iza­tion also ex­creted tremen­dous pres­sure on our nat­u­ral re­sources such as clean Air and Wa­ter. Re­source stressed sce­nario is seen world­wide. Ma­jor­ity of man­u­fac­tur­ing pro­cesses gen­er­ates waste­water with vary­ing quan­ti­ties and char­ac­ter­is­tics. Man­u­fac­tur­ing puts pres­sure on wa­ter cy­cle in two ways:

1. Con­sump­tion of Fresh Wa­ter

2. Pol­lu­tion in Wa­ter Bod­ies

In com­par­i­son to other fresh wa­ter con­sumers such as agri­cul­ture and do­mes­tic, con­sump­tion of fresh­wa­ter by man­u­fac­tur­ing in­dus­try is low but the tox­i­c­ity of waste­water gen­er­ated by man­u­fac­tur­ing in­dus­try espe­cially by chem­i­cal in­dus­tries is very high. Man­u­fac­tur­ing is nec­es­sary but at the cost of our nat­u­ral re­sources? That’s to­day’s dilemma.

In case of wa­ter, there is al­ways a pull be­tween In­dus­trial and Do­mes­tic de­mand. In most of the cases, the do­mes­tic de­mand is al­ways given pri­or­ity and wa­ter sup­ply is re­stricted to In­dus­try. This is the same pic­ture for many years near the In­dus­trial Belt.

Waste­water: It is re­ally a Waste ?

Waste is some­thing which does not have any use and hence a com­mer­cial value. As per the con­ven­tional un­der­stand­ing, wa­ter gen­er­ated dur­ing the course of man­u­fac­tur­ing does not have value hence the same is termed as “Waste­water”. “Waste­water” needs to be “man­aged” with the low­est cost, as there is no pos­si­bil­ity of rev­enue gen­er­a­tion from the same. Re­ports in­di­cate that pol­lu­tion lev­els are in­creas­ing. Dis­charg­ing of un­treated waste­water in wa­ter bod­ies had been re­ported. Apa­thy by man­u­fac­tur­ing in­dus­try to­wards In­dus­trial Waste­water is turn­ing Waste­water into a mod­ern day evil and the cost as­so­ci­ated with waste-

wa­ter treat­ment is the cause of this apa­thy.

The ques­tion is “Is waste­water re­ally a Waste?” Waste is a lim­i­ta­tion of our un­der­stand­ing or imag­i­na­tion. A Waste will re­main as a waste un­til we find out a bet­ter use of it. Once it has a use, a waste will be con­verted into a value or rev­enue.

Long time ago, a black, oily and vis­cous liq­uid was dis­cov­ered which we know to­day as crude oil. For a very long time, this black liq­uid was a source of nui­sance and had very lim­ited uses such as medicines and lu­bri­ca­tion etc. By mid of 19th Cen­tury petroleum re­fin­ing came into pic­ture and the whole world found a new source of en­ergy and raw ma­te­rial. Thus, a great tech­nol­ogy is able to con­vert a Waste into Wealth.

In­dus­trial Waste Wa­ter is an­other such re­source, which is wait­ing for a cor­rect tech­nol­ogy for its trans­for­ma­tion. Sus­tain­abil­ity will as­sured when prof­itabil­ity is as­so­ci­ated with waste­water.

In agri­cul­ture-based in­dus­try, many ex­am­ples of Waste Valori­sa­tion can be seen and now a days they have been stan­dard norms e.g com­post­ing, bio­gas etc.

How­ever, the same con­cept is new in tech­no­log­i­cally ad­vanced Man­u­fac­tur­ing In­dus­try.

Waste­water is a typ­i­cally a mix­ture of var­i­ous chem­i­cals. Most of these chem­i­cals are known. In­ter­est­ing point to be notes that the chem­i­cals, which are present in waste­water, have sig­nif­i­cant value/mar­ket price when they are present in pure form. How­ever, in waste­water, be­cause of the mixed na­ture, these chem­i­cals lose their value.

Waste­water Valori­sa­tion aims at gen­er­at­ing value from waste­water by three ways:

1. Re­cover Chem­i­cals in pure form: Re­cov­ered chem­i­cals can be re­cy­cled to the par­ent process thus re­duc­ing the cost of fresh chem­i­cal pur­chase or these chem­i­cals are sold thus gen­er­at­ing ad­di­tional rev­enue 2. Re­duce the cost of treat­ment: Once these chem­i­cals are re­cov­ered, the treat­ment cost of waste­water re­duces.

3. Re­duce the cost of fresh wa­ter pur­chase: In cases where post chem­i­cal re­cov­ery wa­ter re­cy­cle is pos­si­ble, the cost of fresh wa­ter can be saved. Waste­water valori­sa­tion not only gen­er­ates rev­enue from waste but also helps to min­i­mize the en­vi­ron­men­tal im­pact of toxic waste. In­vest­ment in Waste Valoriza­tion can give at­trac­tive pay­back. In few cases, es­ti­mated pay­back of 3 to 5 years is pos­si­ble.

Present Waste Wa­ter Man­age­ment Sce­nario

To­day most of the tech­nolo­gies of waste­water treat­ment are cost cen­tric. These tech­nolo­gies treat par­tic­u­lar type of waste­water in­vari­ably re­sult­ing into a cost. Al­most all newer tech­nolo­gies talks about how the lat­est tech­nol­ogy will lower the cost in com­par­i­son to the ex­ist­ing tech­nolo­gies.

Lets take a closer look at the ex­ist­ing tech­nolo­gies which are con­sid­ered as In­dus­try Stan­dards.

A. In a con­ven­tional biomass based sys­tems, a low TDS & mod­er­ate COD con­tain­ing waste­water streams are first con­di­tioned for cor­rect pH etc. The stream is then sentto mi­crobes for con­sump­tion of COD and pro­duce the biomass, which again has to be dis­posed off.

B. In case of waste­water streams with mod­er­ate con­cen­tra­tion of dis­solved solids, first, the stream goes to Re­verse Os­mo­sis for in­creas­ing the con­cen­tra­tion of dis­solved solids. The re­ject ob­tained goes to evap­o­ra­tion sys­tem. In case of high TDS stream, the stream di­rectly goes to evap­o­ra­tion sys­tem. Evap­o­ra­tion Sys­tem helps to re­cover wa­ter but in the process gen­er­ates mixed salts. As the mixed

salts does not have any value, they has to be dis­posed off to se­cured land­fills.

C. In case of high Or­gan­ics con­tain­ing streams, the ma­te­rial is in­cin­er­ated. Incin­er­a­tion process gen­er­ates gaseous pol­lu­tants and residue/ash. Gaseous pol­lu­tants needs to be con­tained by ab­sorp­tion this gen­er­at­ing sec­ondary waste­water and residue/ash needs to be dis­posed off.

As can be seen, most of the present tech­nolo­gies con­vert one type of waste to other type of waste at the ex­pense of en­ergy. An un­man­age­able waste is con­verted to a man­age­able waste at cost. Since cost is a pain, many small scale in­dus­tries could not af­ford these so­lu­tions and end up adopt­ing “Short-Cuts”. Sce­nario of un­treated waste­water go­ing in wa­ter bod­ies are per­fect ex­am­ples of these “Short-Cuts”.

If tech­nol­ogy can gen­er­ate profit from waste­water then the same can be­come sus­tain­able. Waste­water valori­sa­tion aims for the same.

Ba­sics of Waste­water Valori­sa­tion Step-1: Seg­re­ga­tion of Waste­water streams:

As per the con­ven­tional treat­ment phi­los­o­phy, all waste­water stream are col­lected in equal­iza­tion tank prior to treat­ment. How­ever this step is against the waste­water valori­sa­tion con­cept. Im­ple­men­ta­tion of Waste­water valori­sa­tion af­ter equal­iza­tion tank cre­ate fol­low­ing tech­ni­cal dif­fi­cul­ties

a. Con­cen­tra­tion Re­duc­tion: Waste­water Valori­sa­tion Tech­nolo­gies are gen­er­ally sep­a­ra­tion pro­cesses, which works bet­ter with higher con­cen­tra­tion of tar­geted chem­i­cal. When the con­cen­tra­tion re­duces, sep­a­ra­tion be­fore chal­leng­ing thus in­creas­ing the op­er­at­ing cost of Waste­water Valoriza­tion Tech­nolo­gies b. In­creased Hy­draulic Load: Post equal­iza­tion, the com­pos­ite stream vol­ume goes up. Again im­ple­men­ta­tion of Waste­water Valori­sa­tion Tech­nolo­gies af­ter equal­iza­tion leads to larger equip­ment re­sult­ing in higher cap­i­tal ex­pen­di­ture.

Step-2: Com­plete Char­ac­ter­i­za­tion of Waste­water:

Con­ven­tion­ally waste­water is the most ne­glected part of the man­u­fac­tur­ing process. The waste­water is gen­er­ally char­ac­terised from treat­ment point of view such as Chem­i­cal Oxy­gen De­mand (COD), To­tal Dis­solved Solids etc. In or­der to un­der­stand the value as­so­ci­ated with the waste­water, its cor­rect char­ac­ter­i­za­tion i.e es­ti­ma­tion of chem­i­cal com­po­si­tion and iden­ti­fi­ca­tion of chem­i­cals present is waste­water is the de­cid­ing fac­tor for suc­cess­ful im­ple­men­ta­tion of valo- riza­tion tech­nolo­gies.

Step-3: Iden­ti­fi­ca­tion of Cor­rect Tech­nolo­gies

Waste­water valori­sa­tion tech­nolo­gies are sep­a­ra­tion process based on chem­i­cal en­gi­neer­ing prin­ci­ples. Chem­i­cal En­gi­neer­ing Unit Op­er­a­tions are ba­sics of Valori­sa­tion Tech­nolo­gies. Some of the ex­am­ples of Waste­water valori­sa­tion tech­nolo­gies are as fol­lows: a. Se­lec­tive Crys­tal­liza­tion of Sodium Sul­phate from

Tex­tile ef­flu­ent b. Se­lec­tive Ex­trac­tion of Acetic Acid from mixed

waste­water streams c. Re­cov­ery of Sol­vents from mixed sol­vents or waste­water

Large amount of lit­er­a­ture is avail­able which is pub­lished by Academia for chem­i­cal re­cov­ery from waste­water. A thor­ough lit­er­a­ture search pro­vide in­sight about the avail­able al­ter­na­tives for waste­water valori­sa­tion.

New Think­ing

Con­ven­tion­ally the bound­ary of man­u­fac­tur­ing ends at pro­duc­tion of re­quired ma­te­rial. Ef­flu­ent treat­ment is a sep­a­rate sec­tion in man­u­fac­tur­ing setup and Pro­duc­tion Team is not much con­cerned about the same. How­ever, ev­ery Pro­duc­tion Man­ager, Tech­ni­cal Team should look at Waste­water for its valori­sa­tion po­ten­tial. Top Man­age­ment of the man­u­fac­tur­ing com­pany, Man­u­fac­tur­ing Heads, Ef­flu­ent Plant Man­agers should look at waste­water stream closely and ex­plore the pos­si­bil­ity of valori­sa­tion. The strate­gic plan­ner should choose sus­tain­able Valori­sa­tion Tech­nolo­gies rather than quick-fixes such as Treat­ment Tech­nolo­gies.

Man­u­fac­tur­ers pro­duc­ing sim­i­lar prod­ucts can join hand to cre­ate a Waste Valori­sa­tion Fa­cil­ity. This is par­tic­u­larly help­ful for small-scale man­u­fac­tur­ing com­pa­nies. The part­ners along with the rev­enue gen­er­ated can share the CAPEX bur­den.

Waste­water Valori­sa­tion has a po­ten­tial change the ap­proach of the man­u­fac­tur­ing in­dus­try to­wards waste­water and make its man­age­ment sus­tain­able.

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