Operation of Wastewater Treatment Works

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I am monitoring a 2ml of treatment works for a population of 19,500.

New growth is still continuing.

At peak hours flow increases 3 times the design capacity and treatment works operate with two process controllers.

At night no process controller is on-site and when is raining the WWTWs is overflowing, whereby screening is full of waste. Due to budget constraints we can not appoint extra process controllers.

In my case i have got some suggestion, and i need some advice too:

  1. I suggest to add a buffer/balancing tank, whereby flow it can overflow in it when is raining or absent of process controller.
  2. Add some bypass line to Primary settling tank, to avoid overflow in the inlet.

Your feedback much appreciated!

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9 Answers

  1. I agree with you for buffer tanks, and again you can add pump stations on site to control the flow. If pump A is pumping the pump B it will waiting water to reach switch level (balls). 

  2. Hi Phetla, my name is Keith Peters and my company is called SolEco Africa and we treat waste water with our flagship product called Solutek which is 100% Organic, fully biodegradable etc. I am based in Pretoria and you can contact me on 0839742168 or keith@solecoafrica.co.za. Please also visit our website www. solecoafrica.co.za. I look forward to hearing from you soon to be able to assist you with your water problems. Kind regards Keith

     

  3. Any STP which deals with combined sewage (foul and rainwater) should have an overflow tank. This assumes that you are not able to separate out the inflow to the sewer network during rainfall. The main process should be designed to deal with 3x average DWF. Inflow in excess of this should be diverted, via a screen to a balancing tank and returned to the main process when rainfall ceases. Any flow in excess of 6xDWF may be diverted direct to the environment after screening and may be designed as an overflow from the balancing tank or at the inlet.

  4. This problem should be consider with the plant design to have average and peak flow for such situation for the plant installation, whatever the peak flow is due to raining water or the process waste water, and normally raining water should by passed the plant if it clean free of debris and mud otherwise should treat to remove such mud and debris by screening and primary settling tanks and then discharged to the surface water streams straight, and no need to inter to the full treatment system. to avoid high hydraluic loads, and  currently I can advice to clean the screen regularly to avoid blocking the screen as well as new investment to add second screen to receive the extra loads due to the rain water then can bypassed by overflowing to surface water without treatment if not not mixed with the waste water otherwise should be go through the treatment plant cycle. 

      

  5. Phetla.  I agree with another respondent, that constructing an equalization tank to capture the overflow will not solve your problem and is more expensive than simpler solutions.  It's clear your collection system suffers badly from inflow, and the sewer is subject to considerable debris content.  Bypassing the screen and discharging directly to the primary clarifier risks sending debris to the primary clarifier and consequential damage to downstream mechanical equipment and pumps.  Overflowing to an equalization basin will result high expense and trash accumulation in the basin, and given the problem occurs during high flow events it is questionable as to whether you can build a basin large enough to capture the resulting overflow.  That being said, it could function as a trash basin, rather than equalization basin.  This would require a smaller volume and could overflow to the primary clarifier. It would still require effort and cost to clean out after overflow events.  A better approach may be to add a second upstream screen with a bypass to the existing screen, effectively providing double the screen area and half the probability of an overflow event.  Addressing the community growth issue, you could later consider an overflow to a trash tank as a contingency measure, or replacing the manual screens with mechanically cleaned screens.

  6. Can you flex time, let the operator come in at night and leave early the next day, if even to come clean the screens.  Like the other post recommend purchase automatic bar screens. It appears that this is where your issue resides

  7. Since, as you mentioned, screening is full in the night and water overflows,  It could be a obstruction in the screen channel.

    My suggestion is to  review this section and, in case, build at least a coarse screen before entering buffer balancing tank. Moreover, if flows during night is not greater than during the day (and process works good during rain) there is no reason to build a balancing tank (that is costly) only for night overflows. It is better to spend money for automatic screens and automatic flow controlling devices.

    Best regards

     

  8. We operate several systems that at times exceed design capacity. Some techniques we have used to treat the sewage and not change the physical plant, dealing with increase flow rates:

    1. Bio-augmentation

    We have achieved ~ over a 25% efficiency increase on biological reduction of BOD. A huge benefit when you consider the extremely low cost of the bacteria.

    2. Addition of microbubble surface aerators

    These are “Concentrated Oxygen Generators” that float on the surface. They can be installed in lift stations, channels, lagoons, any open area. Each COG-600 will infuse ~275 kg of O2 per day into .25 mm bubbles that collapse even smaller. Bubbles stay in suspension far longer than bottom diffusers. COGs can be moved, changed as needed. We have achieved an ~ 50% efficiency compared to bottom aeration.

    3. In one situation we added submerged membrane filters

    Submerged membrane filters (used in MBR) can increase efficiency by a factor of five.

    You would end up with a hybrid system using one or more of these techniques.