4 replies to this topic

[KingStrijder]

Hello everyone.
I'm new to the forums and I come with 2 problems that exceed both my theoretical and practical knowledge.

I work at a water treatment plant for industrial efluents. We deal mainly with chrome and cyanide in water, but we also treat some other metals, mostly iron.

We are a team of 2 chemists in a factory that has very few chemical engineers, and we treat around 5 to 10 m³ per day.

The water treatment plant in question was specifically designed for Cr+6 and Cyanide, but because most people here dont understand chemistry this plant is also used for treating other types of efluents. They just go "you are chemists, you do chemistry, deal with this dirty water".

The crown jewel of the plant is the 30m³ decanter we have at the end of the process. It has a pH between 7.5~8.5 for the precipitation of Cr+3 solids and Fe(OH)3. Everything works out, except when we deal with detergents.
These detergents have a high concentration of phospates and we have no equipment nor method to deal with them. We just try to dilute them and hope for the best.

The problem that brought me here happened a few weeks ago when about 18m³ of detergents got in the system in 4 days. The pH and phospates created the perfect environment for the proliferation of algae in the decanter. The water became green and now is of a greyish color. We tried killing them with about 6 liters of NaClO, just like if it was a swimming pool but nothing happened. What else could we try?



On the other hand, the week after the algae formed, iron-rich water came into the system too. We have some back-up tubs to deal with that. Iron is meant to precipitate when in alkaline pH as Fe(OH)3 but for some reason is not precipitating. Our method is to add NaOH until the pH goes to 9.5, add floculant and an adjuvant solution and agitate with air. It usually precipitates really fast (about 4hs) but right now it's been 5 days and nothing happens.

I'd really like to hear your opinions on the matter. And please feel free to ask for more details.

[Pilesar]

A few thoughts: The phosphate/algae problem may not be related to the iron precipitation trouble. Lab experiments might be useful for testing. Swimming pool algaecides often use copper sulfate. Some types of fish and snails eat algae.

[breizh]

Hi,

You may find pointers in the link attached:

https://www.intechop.../chapters/62471

note: You should contact the supplier of chemicals for your WWT plant, he may have experience to share with you.

Good luck

Breizh 

[horatorres]

Algas must be treated with copper sulphate..  first a shotk concentration, later a maintenance concentration.

 

horacio

[KingStrijder]

Thanks for all your answers. 

 

In the end the NaClO we used on friday did actually work, it killed the algae and the greyish color were the dead algae in suspension. After running some water to drag them out of the system, everything started getting clear again and they haven't returned.

 

In the future we will try to prevent the situation with Copper Sulfide.