Why "COD Value" is Crucial for Thai Factories: From Legal Compliance to Treatment Cost Management

Meaning and the Big Picture

COD (Chemical Oxygen Demand) is the amount of oxygen required to chemically oxidize organic substances in wastewater into stable forms. It directly reflects the "treatment burden." When COD is high, the biological system must work harder, consuming more energy and chemicals, and increasing the risk of odors, floating sludge, or system imbalance. Generally, COD is higher than BOD because it includes substances that are difficult to biodegrade, making it suitable for monitoring the total load at the end of the pipe.

Impact on Law and Costs

For Thai factories, COD is not just a number in a report; it is directly related to environmental law compliance. Exceeding the limits risks fines, more frequent inspections, or even production shutdowns to improve the system. Simultaneously, hidden costs rise from increased energy for aeration, more chemicals, and sludge disposal. When a "shock load" occurs, the system requires recovery time, which immediately impacts opportunity costs.

What Often Spikes Costs

• Increased chemical/energy use to suppress COD values.
• Higher sludge volume and subsequent disposal costs.
• Downtime from system recovery after a shock load.
• Unplanned inspections or system improvements.

Real-World Causes of High COD

COD often spikes with production rhythms, such as major machine cleanings, highly concentrated first-rinse water, raw material spills, and peak loads. Without an EQ (Equalization) tank, this burden flows directly into the system, overwhelming it. Separating concentrated water for pre-treatment and spacing out discharge times can significantly reduce this risk.

How to Measure Reliably

The quality of decision-making starts with data quality. This includes choosing grab/composite samples that match production behavior; specifying appropriate times, temperatures, containers, and preservation methods; and conducting QA/QC (blank, standard, duplicate). Results should then be converted from individual readings into shift/daily trends to link operational events with value fluctuations.

Quick Checklist to Start Control (Bullet ~25%)

• Review wastewater routes; separate concentrated first-rinse for pre-treatment.
• Install an EQ tank to ensure a consistent load and reduce shock load opportunities.
• Adjust machine cleaning SOPs and seal leaks/spills.
• Update the lab's QA/QC plan and create trend graphs.
• Hold meetings with production shifts to link events to the COD graphs.

Conclusion

When measured correctly, trends are visible, and the root causes are addressed, the COD value will be "under control," both legally and financially. Readers wishing to review the basics can find more information on COD/BOD at https://www.ase-thai.com/th/category/11462/6699/cod-bod.