INDUSTRIAL WASTE WATER TREATMENT : ZERO DISCHARGE? Professor (Dr) V. V. Mahajani Contact : 0251 249 68 85 +91 900 4266 456, Email: vv@gamil.com 1
ZERO DISCHARGE : A MYTH! Near zero discharge = Distinct Possibility Question : At What Cost? Cost to Project Owner Cost to Society Cost to Environment 2
Industrial waste water contains: Priority Pollutants, BOD biodegradable waste, COD non biodegradable waste, Metals. Discharge specifications are discharge point specific. The State Industrial Development Corporations designs specifications. 3
WAR for WATER is a common local phenomenon. Water precipitation on our planet Earth and in India is almost constant Water demand is growing; Population is growing & so Water demand for human Consumption Agriculture Industrialization 4
AGRICULTURE & INDUSTRIALIZATION, BOTH MUST GROW TOGETHER FOR OUR SUSTAINABLE DEVELOPMENT. Both need WATER vnearly 90 % of water used in Industry results in an effluentindustrial waste. Diverse nature of industry results in wide variation in effluent quality. Water conservation results in concentrated waste resulting in very high COD / BOD ratio. 5
WE NEED A PROCESS WHICH CAN MINERALIZE ALL COD TO MAKE IT POSSIBLE TO RECOVER GOOD QUALITY WATER. THE OBVIOUS CHOICE IS ADVANCED OXIDATION PROCESS 6
ADVANCED OXIDATION PROCESSES: All Processes dealing with oxidation with OH* (hydroxyl radicals) are Advanced Oxidation Processes. LIMITATIONS OF BIO PROCESSES: SLOW RATES, LARGE VOLUME. HENCE, MORE FLOOR AREA IS REQUIRED. OFTEN NEED ENGINEERED MICRO-ORGANISMS DO NOT PERMIT, INVARIABLY, SHOCK LOADS NEEDS ELABORATE POLISHING TREATMENT FOR WATER RECYCLE 7
ADVANCED OXIDATION PROCESSES: Wet Air Oxidation Fenton Chemistry Ultra Violet (UV) Ozonation Sonication Electro destruction 8
OXIDATION POWER OF COMMON OXIDIZING AGENTS RELATIVE TO OXYGEN O 2 1.00 Cl 2 1.06 ClO 2 1.06 HOCl 1.24 H 2 O 2 1.48 H 2 SO 5 1.51 O 3 1.68 OH* (hydroxyl radical) 2.33 F 2 2.50 9
HIGHER OXIDATION POWER MEANS A RELATIVE LACK OF SELECTIVITY. This property IS USELESS for organic synthesis but the mostdesirable in waste treatment. SHE management does not allow use of F. Hence next automatic choice is OH* hydroxyl radical. Advanced Oxidation Technologies are centered around OH* radical as non- Selective but powerful oxidizing agent. 10
WET AIR OXIDATION MORE APPROPRIATELY : THERMAL PROCESS. IT IS A SUBCRITICAL OXIDATION PROCESS IN AN AQUEOUS MEDIUM Water T c = 374 o C & P c = 217.6 atm OXIDATION OF ORGANIC SUBSTRATE IN PRESENCE OF MOLECULAR O 2 T = 100 _ 250 o C & Pressure: O 2 pressure 5 to 20 atm O 2 Solubility in water is minimum at near about 100 o C. Above 100 o C it is increasing with increase in temperature. 11
OXIDATION REACTION FREE RADICAL MECHANISM via OH* radical formation NON SELECTIVE OXIDATION TO MINERALIZE OXIDIZABLE CONTAMINANTS O 2 C a H b N c P d X e S f O g C CO 2 H 2 O N N 2 or NH 4 + or NO 3 - H H 2 O -3 P PO 4 X HX (halogen) S SO 2-4 Inorganic substances O 2 Na 2 S Na 2 SO 4 Na 2 SO 3 Na 2 SO 4 12
KINETICS: The waste stream consists of complex and simple molecules The waste is characterized as BOD (bio-chemical oxygen demand) COD ( chemical oxygen demand) TOC (total organic carbon) Kinetics is presented in terms of COD / TOC reduction Instead of having complex kinetics representing series and parallel reactions, a series reaction approach is considered 13
REACTION MECHANISM Large molecular wt. + O 2 organic substrate k 1 k 2 k 3 CO 2 + H 2 O low mol. wt organic acids (Acetic, Propionic, Glyoxalic, Oxalic) Complex Reactions; Intermediates are formed and can be slow to oxidize or mineralize to CO 2 14
We have found that a lumped parameter series reaction in terms of COD / (TOC) is more design friendly: k 1 k 2 (COD) (COD) CO 2 and H 2 O Original low mol. wt Waste intermediates In majority of cases, the second reaction step (k 2 ) is the rate limiting step. 15
The kinetic expression is then: d( COD) dt = k ( COD) m ( O n 2 ) = k 2 ( COD) m ( P O2 ) n m 1 n varies with 0.5 to 1.0 This is applicable to homogeneous reaction 16
CATALYSTS Wet air oxidation reactions can be catalyzed by homogeneous catalysts heterogeneous catalysts to reduce operating conditions. 17
Homogeneous catalysts The catalyst should be such that complete oxidation of substrate to CO 2 and H 2 O is possible It should be compatible with MOC of the reactor. It should be easily recoverable It should be easily available It should be cheap It should be possible to meet SHE compliance with ease. 18
HETEROGENEOUS CATALYSTS: ADVANTAGE: EASE OF SEPARATION. REACTOR CAN be : Slurry reactor (Mechanical Agitated Contactor) Bubble column ( Circulating Bubble Column) Packed bed (Adiabatic) Limitations: Slower rate, (?) Possibility of the catalyst leaching in the solution. At prevailing high temperatures, t > 200 o C, intermediate acetic acid formed can react with catalyst metal elements forming water soluble metal acetates thereby reducing active centres on the catalyst Please note homogeneously catalyzed reaction will effectively enhanced the rate. 19
THE CATALYST CHOICE IS WASTE SPECIFIC. Bench Scale Screening is highly recommended. EVERY WASTE IS HAVING RADICALLY DIFFERENT CHARACTERISTICS. BENCH SCALE PAPRAMETER OPTIMIZATION IS ALWAYS DESIRED 20
Advantages It can handle concentrated waste COD 10,000-500,000 mg/l. It can handle toxic chemicals such as cyanides, sulfides, chlorophenols, amines, metals and priority pollutants. Waste with TDS can be handled. Energy integration is possible via Gas turbine and hydraulic turbine. Very less space, even it can be underground. 21
Lower operating cost. Valuable low molecular weight acids such as acetic acid could be produced. When used as pretreatment to anaerobic bio process, higher yields of CH 4 (say 30-40 %) possible. Total mineralization of the waste is possible. Treated water can be recycled / reused. WATER CONSERVATION (WATCON) is possible 22
Limitations: Capital intensive due to exotic MOC (often titanium ). How to cope? Lining or cladding will help! (only wetted parts) To reduce volume of the waste, membranes can be used upstream The residence time can be reduced by using bio treatment at downstream. MBR for water recycle. However, depreciation benefit makes it attractive! 23
Effluent Compressed air Product Gas AQUEOUS STREAM for Water Recovery Heat transfer Fluid Wet Air Oxidation: Schematic Diagram 24
HYBRID PROCESSES SONIWO Sonication - Wet Oxidation WO MEM Wet Oxidation- Membrane MEMWO Membrane - Wet Oxidation 25
A SYSTEMATIC APPROACH FOR WATER TREATMENT for RECYCLE We can use following guidelines for water recycle in chemical plant Identify contribution of water bill in the cost of production. Identify the scenario around your project with special reference to availability of water in future, considering your future requirements due to expansion. Take water balance in your plant. Identify all water outlets such as plant effluent, utility blow downs, water used in administrative block, canteen etc. Please note that one can do little to evaporation loss in a cooling tower. 26
Have detailed analysis of each effluent stream and decide which can be used for recycle and which can be used for purging. It may be possible to use purge water for gardening and horticulture. Have specifications for water use at all process blocks in the project. For instance, specifications for water used for washing filters would be totally different from that used as boiler feed water generating steam for captive power generation also. Decide on treatment strategy. 27
Since each effluent stream is unique, carry out bench scale studies. Carry out detailed techno - economic feasibility study to ensure that set goals or targets could be achieved / realized. Implement the project without any delays. WATER MANAGEMENT IS MUST for SUSTAINABLE DEVELOPMENT 28
Recommended Readings : Wet air oxidation. Mishra, V. S.; Mahajani, V. V.; Joshi, J. B. Ind. Eng. Chem. Res. 1995, 34, 2. A novel way to treat refractory waste: Sonication followed by Wet Oxidation(SONIWO) Ingle, M. N.; Mahajani, V.V.; Journal of Chemical Technology Biotechnology. 1995, 64, 80. Studies in treatment of disperse dye waste : membranewet oxidation process. Dhale A. D.; Mahajani, V. V. ; Waste Mgmt. 2000, 20, 85. 29
Interactive Session Begins now INNOVATION IS ANYTHING THAT PRODUCES MONEY 30