COMPARATIVE ANALYSIS OF SPECTROPHOTOMETRIC RESIDUAL PEROXIDE MEASUREMENT METHODS IN A SLAUGHTERHOUSE WASTEWATER

Slaughterhouse wastewater treatment by advanced oxidation processes (AOP) is encouraged

to increase the overall quality and reusability of the discharge water. And several AOPs such

as Fenton oxidation, UV radiation, ozone, and photocatalytic oxidation involves the use of

hydrogen peroxide (H2O2) for the production or intensification of hydroxyl radicals (OH●

). In

some cases, a quick measurement of H2O2 is required to track the concentration of residual

H2O2 in a sample, for optimization and evaluation of the performance of the applied AOPs. In

this study, two commonly used spectrophotometric residual H2O2 measurement options,

potassium titanium (IV) oxalate (PTO) and iodometric-colorimetric (I3

-

method by Klassen

1994) were compared for a slaughterhouse wastewater matrix. Slaughterhouse wastewater

was prepared in the laboratory by mixing a known amount of blood with tap water. The

pH of all samples was adjusted to 3.00, and 50 mg/L H2O2 was added. Reaction time, organic

matter concentration, and dilution factor (DF) were used for the comparative analysis of the two

methods. In the PTO method, color development is instantaneous and stable while the I3

method required ~5 minutes of reaction time. Both methods were stable and unaffected by

organic matter concentration. Cod of 2000 to 100 mg/L were used for organic matter

presence evaluation. PTO method residual H2O2 recovery was between 95-98% and recovery

by I3 method was between 104-110%. Slaughterhouse wastewater is highly colored and can

include turbidity which is a problem for spectrophotometric measurements. Such samples

usually demand pre-processing like dilution or filtration before measurement. Increasing the

dilution factor decreases the color intensity and background color interference in the sample.

The PTO method can directly measure the residual H2O2 with 102-105% recovery in DF1 (no

dilution) to DF5. On the other hand, the I3 method required at least DF 50 for direct

measurement. A sample blank can be used in both methods to minimize color interference.

When sample blank was used in the I3 method for DF50 to DF2, 103-105% recovery was

achieved but for DF1, recovery was only 80%. The use of sample blanks in an ongoing

experiment can be time-consuming along with necessary dilutions to meet the calibration

range of the method (10 mg/L for I3 and 100 mg/L for PTO). PTO method with rapid color

change, higher measurement concentration range was able to measure residual H2O2 within 2

minutes. So, a practical method (PTO) with high precision is preferable.