CHEMICAL UNIT PROCESS: PRECIPITATION, OXIDATION DR. MUNIR A. NAYAK

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1 CHEMICAL UNIT PROCESS: PRECIPITATION, OXIDATION DR. MUNIR A. NAYAK

2 CHEMICAL UNIT PROCESSES Coagu atio Precipitatio Oxidatio Disi fectio

3 Chemical Precipitation Defi itio : Cha gi g the state of co tami a ts (i to So id) by additio of chemica s to e ha ce their remova Wastewater + Soluble Chemical chemical reaction Insoluble Complexes + Water + Other Stuff Precipitate

4 Chemical Precipitation App icatio s: Improve the performa ce of sedime tatio ta ks For remova of Phosphorous For remova of Heavy Meta s I dustria Waste remova (Where bio ogica treatme t may be possib e)

5 Chemical Used For Chemical Precipitation

6 Alum Precipitation 3Ca HCO Al 2 SO H 2 O 2Al OH 3 + 3CaSO 4 + 6CO H 2 O Ca cium Bicarbo ate (So ub e) A umi um Su fate (So ub e) A umi um Hydroxide Ca cium Su fate (So ub e) A umi um Hydroxide (I so ub e): Ge ati ous f oc Requires A ka i ity (reported as CaCO 3 )

7 Lime Precipitation With A ka i ity Ca HCO Ca(OH 2 ) 2CaCO 3 + 2H 2 O Ca cium Hydroxide (Lime) With Carbo ic acid (Some hat I so ub e) H 2 CO 3 + Ca(OH 2 ) CaCO 3 + 2H 2 O

8 Ferric Chloride With A ka i ity 2FeCl 3 + 3Ca HCO 3 2 2Fe OH 3 + 3CaCl 2 + 6CO 2 A ka i ity Ferric Hydroxide (I so ub e)

9 Ferric Chloride with Lime Whe atura a ka i ity of aste ater is ess, Lime is added 2FeCl 3 + 3Ca OH 2 2Fe OH 3 + 3CaCl 2 Lime (A ka i ity) Ferric Hydroxide (I so ub e)

10 Ferric Sulfate with Lime 2Fe 2 SO 4 + 3Ca OH 2 2Fe OH 3 + 3CaSO 4 Lime (A ka i ity) Ferric Hydroxide (I so ub e)

11 Typical Dosages

12 How much alkalinity is required? For A um Precipitatio : 3Ca HCO Al 2 SO H 2 O 2Al OH 3 + 3CaSO 4 + 6CO H 2 O 3 (100 g/mole) g/mole Per Gram of A um If ess a ka i ity i the aste ater, you eed to add a ka i e chemica, such as Lime

13 Removal Efficiency Comparison For Sedime tatio ta ks Co tami a t Without Chemica Precipitatio (% remova ) With Chemica Precipitatio (% remova ) TDS BOD Bacteria Remova efficie cy depe ds o ma y factors: Qua tity of chemica used Mixi g times Co tro a d Care take Co stitue ts of aste ater etc.

14 Disadvantage Too much s udge, hich eeds care Eff ue t has high a ka i ity ph adjustme t Sca i g: CaCO 3 a d others accumu ate o surfaces

Phosphorous removal Objective: Co vert phosphorus to so id phosphate Lime: At high PH, excess io s react 10Ca 2+ + PO 3 4 + 2OH Ca 10 PO 4 6 OH 2 A umi

15 Phosphorous removal Objective: Co vert phosphorus to so id phosphate Lime: At high PH, excess io s react 10Ca 2+ + PO OH Ca 10 PO 4 6 OH 2 A umi um Sa t: Al HnPO 3 n 4 AlPO 4 + nh + Hydroxy apatite (SOLID) Iro Sa t: Phosphate Precipitate Fe HnPO 4 3 n FePO 4 + nh + Phosphate Precipitate

16 Dosages requirements

17 Dosages requirements 1. Dosage requireme ts based o mo es ot a ays accurate 2. Requireme ts based o Laboratory a d Fu -sca e tests 3. Sometimes, po ymers are a so added

18 Phosphorous Removal: Metal salts (Fe3+ or Al3+) and Lime applications

19 Heavy Metals removal Application of Lime, Aluminum or Iron Mostly Hydroxide and Sulfide precipitates formed For example, Cadmium hydroxide or Cadmium Sulfide

20 Dosage requirements Dosage depends on ph and Many other things

21 Chemical Oxidation Use oxidizing agents to change chemical composition Applications: Reduce Concentration of organics Control Odors (Especially used) Remove Ammonia Reduce Bacteria and Virus Reduce Toxicity of toxic compounds

22 Chemical Oxidation Oxidation-Reduction Reactions Oxidatio : Loss of e ectro s Reductio : Gai of e ectro s Zn 2e Zn 2+ Cu 2+ +2e Cu Oxidatio Reductio Cu 2+ + Zn Cu + Zn 2+ Redox reactio

23 Chemical Oxidation Common Oxidizing Agents Ozo e (O 3 ) Hydroge Peroxide (H 2 O 2 ) Perma ga ate (M O 4 ) Ch oride Dioxide (C O 2 ) Ch ori e (C 2 or HOC ) Oxyge (O 2 ) A d Others

24 Chemical Oxidation Standard Reduction or Oxidation Potential E Tendency of the reaction to occur towards right Zn 2e Zn 2+ Cu e Cu E =-.763 vo t E =+.34 vo t Reaction Potential E Whether the reactio i occur i the as ritte E reaction = E reduction E oxidation

25 Chemical Oxidation: BOD & COD removal Oraganic Molecules Cl,O 3,H Intermediate molecules Cl,O 3,H Simple end products BOD CO 2, H 2 O, etc.

26 Chemical Oxidation: Ammonia Removal 3HOC +2NH 4 + N 2 + 3HCl + 8H + +3H 2 O Ch ori e Ammo ia Gas Disadva tage Bui d up of HC, hich ca react ith a ka i ity bui d TDS, a d other products

27 Mid-Sem Score Distribution

General Chemistry. Contents. Chapter 5: Introduction to Reactions in Aqueous Solutions. Electrolytes. 5.1 The Nature of Aqueous Solutions

General Chemistry. Contents. Chapter 5: Introduction to Reactions in Aqueous Solutions. Electrolytes. 5.1 The Nature of Aqueous Solutions General Chemistry Principles and Modern Applications Petrucci Harwood Herring 8 th Edition Chapter 5: Introduction to Reactions in Aqueous Solutions Philip Dutton University of Windsor, Canada N9B 3P4