A high COD result and a darker outlet can point to different treatment problems. Trace the change upstream and compare tests made on the same basis before adjusting a dose.
Find what is driving the COD result
At ET-01, total outlet COD increases from 84 to 155 mg/L and total suspended solids (TSS) rise from 24 to 78 mg/L. Filtered COD changes from 60 to 63 mg/L. That pattern supports solids carryover as an important contributor to the total COD rise. Verify sample comparability, then check settling and the solids path.
Use a jar test to compare color treatment
For a color shift, check the production batch, EQ timing, pH, mixing, and actual chemical delivery. A supervised jar test compares a representative sample with an untreated control and approved trials under matched conditions. Record the method, pH, residual color, settling behavior, and sludge produced. The clearest-looking jar is one observation. A decision also uses measured quality, sludge handling, and the site’s approved operating procedure. The animation shows an illustrative comparison of jars after settling.
Further reading · IFC textile wastewater guidance
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