Page 54 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse: An Overview 37

The hydroxyl radical attacks the organic molecules by abstracting a hydro-
gen atom or by addition to the double bond, finally reducing them to carbon
dioxide and water.
The salient features of most AOPs are summarized below:
Fenton oxidation
• The oxidative decomposition and transformation of organic sub-
strates by H 2 O 2 /Fe 2+ (known as Fenton’s reagent)
– Produces OH radicals at acidic pH

– Ambient temperatures
– Optimal Fe/H 2 O 2 ratio is 1:10
– The OH radical attacks organic molecule and they are miner-
alized to CO 2 and H 2 O
• Emerging technology for wastewater treatment
• Useful for highly toxic and non-biodegradable wastes
• Employed successfully for black olive and mineral oil wastewaters
Oxidation with Ozone (O 3 )
• Removes organics in wastewater treatment
• Elimination of color, smell, and taste; disinfection
• An ozone molecule can react with many organic compounds, partic-
ularly those unsaturated or containing aromatic rings or heteroatoms
• Ozonation has been found to be very efficient for the decolori-
zation of textile wastewaters
Wet air oxidation
• For non-degradable or slowly degradable or toxic substances
○ Low pressure wet oxidation
– T<200 C

– P¼5–20 bar
– At COD>6 mg/L: heat recovery from enthalpy of oxida-
tion is comparable to the total energy requirement of the
process
2

–SO 3 /HSO 3 , phenol, amino and hydroxyl substituted
phenols, wastewater from dye manufacturing
– AOX decreases, COD decreases, BOD increases
○ High-pressure wet oxidation

– T>200 C
– P>20 bar
–AtCOD>50 mg/L:heatrecoveryfromenthalpyofoxidation
is comparable to the total energy requirement of the process
• Good for high concentrations of contaminants/may have corro-
sion issues.