High TDS in Treated water from MBR process

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Dear  all,

I found High TDS in treated water from Membrane bioreactor (MBR) process.

Analysis of TDS before MBR showed it was very low, 

For chemical injection consist of NaOH and HCl for pH adjusting in nitrification tank.

Pls  recommend  how to solve it?

Thank you

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6 Answers

  1. Share details of your process for a better solution.

    I hope you are dosing concentrated Acid & Caustic to control pH. Instead set your pH range (wide range) as required and dose dilute chemicals for a better control.

     

  2. Dear Panuwat,

     

    Please describe more detailed your process.

    As I understand you are elevating the TDS level using HCl and NaOH.

    Without know more details about the system, I think you could think in this two options:

    1) You could use an homogenization tank before the MBR.
    2) You could control the pH inside the MBR tank using the recommended uper and lower limits.

    Regards,

    Orlando D. Gutiérrez Coronado

  3. TDS is high in the membrane process, presumably because the membrane is unable to filter the water properly, there are several causes:
    1. The membrane filter is already full of flak and dirt from microorganisms and their carcasses, and the membrane may be stiff and hard.
    2. The membrane filter is not smooth enough and the pores are too big to filter.
    3. There is indeed a weakness of membrane filters, it cannot completely filter out all pollutants in water, especially heavy metals such as pesticides and others, as well as carcasses from microorganisms in the form of enzymes.
    There are many other factors that cause the membrane filter to not work, so it needs to be pre-treated before the water is filtered. Sorry, on this occasion I offer pre-treatment formulas and alternative systems to get clean water from sources: ground water, surface water (rivers, swamps, lakes) and from wastewater. See me at Linke dIn. Thank you.

    1 Comment

  4. It sounds like the target pH might be being continuously overshot and there could be several reasons for this. The most common reasons, in my experience are:

    1. the pH probe is located incorrectly and this sends the dosing system into a frenzy and/or
    2. the concentration of the dosing chemicals is too high to control the pH effectively (this is linked to your dosing pump).

    You shouldn't have to add both NaOH and HCl to meet the target pH unless the pH of your feedwater is highly variable.

    • Are you measuring pH inline or in the tank?
    • Are you dosing inline or in the tank?
    • What is the actual TDS/conductivity before and after?
    • What concentration of NaOH are you dosing?
    • What concentration of HCl are you dosing?

    2 Comments

    2. The pH probe is located  discharge nitrification recirculation pump and control pH at 6.8-7.0,  Concentrate of HCL 35% and NaOH 50%wt. I think I will check at stroke dosing pump. 

      1 Comment reply

      1. OK great. Your chemicals are quite concentrated so adding only a small amount can result in a significant change in pH. What is the flow of the plant (m3/hr or L/hr)? 

  5. Hi, this is a very good question. When you are using HCl and NaOH for pH adjustment then you will have NaCl as the result. This will increase the electrical conductivity of water. We usually use online TDS meters in industries that are working based on the electrical conductivity (EC) of water so you are experiencing high TDS values.

    Now, what to do? If you use an online pH meter that has two switches for low and high then you can control the pH with just a single material HCl or NaOH. Please make sure if you are having a stream in continues process, adjust the flow and put the pH meter prob in a proper place of tank or stream. In case you needed any more details please don`t hesitate and email me: alireza.reyhan@gmail.com

    Good luck

    1 Comment

    1. I will check NaCl at treated water,  The wastewater to system around 4-8 m3/hr. The pH probe is located  discharge nitrification recirculation pump and control pH at 6.8-7.0,  Thank you