Settling Difficulties

We have been encountering settling problem in our clarifiers recently. 

The flocs become flaky and light weight. This has been happening at night only. In the day time, they easily settle.

I tried several dosages using the jar test but still couldn't fix it. 

any suggestions much appreciated

Taxonomy

• Purification
• Water Supply
• tube settler
• plate settler

12 Answers

1. As you know biological treatment process is very unstable and its reliability in the best of the cases is not higher than 65%.

   pH and temp are key factors with direct influence in water treatment but most in wastewater, so are missing more data to supply.

   I suggest you our ionic process with reliability is ~95% to solve since root your problem which doesn't have critical parameters from pH neither temp while saving money.

2. I would check the DO night vs day. I had a problem at night not enough loading and DO shot right up the high DO and polymer made the tank work like a DAF

   Kevin

3. It may due to the temperature, in low temperatures the polymer may not mix properly. 

4. Can you check the pH of the feed water during day & night time. There might be a variation in pH due to presence of algae. Temperature could be the another reason for difference in performance.

5. is there a big difference of ther water temperature during day-time and during the night ?

   a lower temperature means that the reaction time of the flocculant will become longer = it needs more time to coagulate the flocs , add some extra lengths of piping to have a longer retention time that allows the flocculant to ract properly

6. For the last few days I tried desludging the clarifier throughout the night by trotting the valve as to lose less water. 

   The turbidity has improved significantly, even though it's not the best. 

7. Paul Gaydon 

   1.the source is from a dam 

   2.yeah, there is algae 

   3.we are using polymer 

   4.yeah, the flow is controlled 

8. sampling the wastewater and store in the Lab., and check the different between the sample in Lab. and the wastewater in the plant, is other wastewater into the plant in the night?

   1 Comment

   1. Actually it's not waste water 

      1 Comment reply

      1. sorry, but you might sampling the MLSS and store in the Lab, and check the different between Lab and plant, you might also check the SV30 of your samples.

9. I would also consider diurnal oxygen content. If oxygen deficiencies are being experienced overnight, this could create toxic shock, as well as off-gassing with anoxic / anaerobic  processes. Generally experienced in wastewater, but not unheard of in water treatment. More info as Paul suggest would help.

   1 Comment

   1. Actually it's not waste water 

10. Of course temperature affects coagulation processes. You may see the option of polymers to enhance the coagulation.

11. Please can you give us some more information:

    1. Is the source water from a bore, river or dam?
    2. If it from a dam, is there algae present?
    3. What coagulant are you using
    4. Is the coagulant dosing flow controlled?

12. could be water temp or ph change at night