Hi all,

I'm Anas from Kai Sik Towa, Malaysia. I operate wastewater treatment plant for our factory. We use coagulation and flocculation process to treat our wastewater. I would like to ask, what if the possible cause that makes turbidity and COD of the water inside our clarifier increased overnight? We only operate during the day.
Is it caused by BOD/COD exerted by sludge inside the clarifier? We manufacture rubber gloves, so our sludge is biodegradable in nature. But we don't have any biological process in our wastewater treatment plant.

I appreciate any opinion and positive feedback in this matter.

I would first check the concentration of the chemicals added to your clarifier. Secondly, I would check the output of the chemical addition pumps in the system. Finally, I would check with the manufacturing plant to see if they had any change in operations.

I would also run jar tests to determine the effectiveness of the chemical additions.

grrun

How much has the COD increased? Do you have flow measuring equipment on your influent (are you sure that there's no flow during the night)? Is there a change in pH in the clarifier overnight? Will additional PAC and polymer clear up the water that set overnight in the clarifier?

grrun

Hi Muhamad
It seems to me that there are three main aspects that should be given priority consideration, (separately and in combination), to help identify the cause of this problem:
1) Operation of the coagulant and/or flocculant addition to ensure that both of these are optimised.
2). Operation of the Clarifier to ensure that the hydraulic loading rate, (rather than just retention time), is optimised to prevent any carryout of solids in the discharge.
3). Operation of the sludge removal system from the clarifier to ensure that the sludge is not floating, or being disturbed during settling.

You have eliminated most of the conditions that I had considered as possibilities. I would do one more thing to confirm your hypothesis. Place in a beaker about 20% of the bottom sludge and 80% of the clarifier discharge and let it set overnight. If your hypothesis is correct, then you should be able to observe in the beaker the same sort of conditions that are occurring in your clarifier. You can check the supernatant COD in the beaker and see if it's increased from the previous days discharge. Also, you can determine if the supernatant has increased turbidity. This is one way to confirm your hypothesis. If it is correct, I would consider chlorinating the clarifier at the end of each day.

grrun