Disinfection in the final effluent of wastewater, lead to high Ecoli

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Good day,

 

Am having a problem with the final effluent of one the biggest water treatment works of 16,5ml/d. The WWTWs disinfect with chlorine gas. The free chlorine and Total chlorine also monitored on shift basis, and it shows that chlorine is present in the effluent.  And both free and total are above 2.20 mg/l, on shift basis. My questions was:

I hope i will receive good responds from the forum.

 

Thank you,

 

Mr Mangena P

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16 Answers

  1. First of , please do not talk about chloroform being carcinogenic in wastewater, that is irrelevant. It isn't even carcinogenic in drinking water. see Cotruvo and Amato, Dose Response Journal, 2019. DOI: 10.1177/1559325818807781

    The issue from Mr Mangena  is proper wastewater treatment. We have inadequate information, so the speculations are just that, speculations. Something is fundamentally wrong, either with the treatment or the analysis.  So, please send some better information so we are not wasting time. 

    2 Comments

    2. Mr Cotruvo, due to your respect. what better information are referred to? If you are unable to answer me, please let me view others answer. I know that you, and the situation that you are working on. I don't want to waste your time, continue with your daily activities.

       

      Thank you,

      Mr Mangena P

  2. Hi

    If you are sure your residual  is 2.2 mg/l .... what is your turbidity?

    Are you sure your bacteriological testing is right? media sterile, not expired, 

    Carry out quality control check along with the testing like ...blanks, 

    check TSS, quality of your final effluent, etc

     

    Answered on by

    1 Comment

    1. Am talking about wastewater, it is necessary to analysis turbidity on wastewater? Bacteriological bottles are still on date. Quality control was conducted. The TSS of final effluent is 24mg/l  

  3. Are they confirmed E coli or coliforms or presumptive?  There are certain gram positive sporing rods, which can grow on the media used to detect coli providing false positive results.  I would expect these bacteria to be present at high levels in a WWT plant.  Chlorination kills the vegetative part of the cell leaving the resistant spore behind.  This then germinates on contact with the growth media.  As long as the water is clear and has no organic demand, 1 ppm of free chlorine at a pH of 7.2 will kill E coli and coliforms very quickly.  If the pH rises to 8.2, 1 ppm free chlorine has the equivalent kill rate of 0.1-0.2 ppm free chlorine.  The kill rate starts dropping dramatically above 7.5, so good pH control is important.  If there is ammonia present, chlorine reacts with the ammonia and  chloramines develop.  These are volatile and are rapidly lost from water, but even in water their bacterial effectiveness is much lower than chlorine.  I hope this is some help.

    1 Comment

    1. I  was not aware about chlorination kills the vegetative part of the cell and leaving the resistant spore behind. There is no ammonia dosage, and thank you for the information.

  5. Dear  PHETLA MANGENA,

     

    It is not easy answer it if we have no other data. But I will give you some tips that could help fond hte right answer.

     

    1) Any disinfetant will react with the BOD or even the COD, NH3 and other substances in that wastewater that you could have after your treatment. Then, you must remove all the substances that could react with that disinfectat used.

     

    2) The UV could beused justif you have a good transmitance.

     

    3) The chlorine or its compounds are good disinfetants. But ozone is a more powerful disinfectat than the chlorine or its compounds, and you will need smaller doses of ozone to obtain even better results compared with any other commertial disinfectant.

     

    Recomendations:

     

    1) Improve the biological treatment.


    2) Improve the micro-organism removal using a microfiltration that could remove micro-organisms and that does not use a membrane filtration technology (it is a patented filter).

     

    3) Use the ozone after this microfiltration to obtain a better removal.

     

    If you are interested in this excellent solution, you can contact me.

     

    Regards,

     

    Orlando D. Gutiérrez Coronado

    1 Comment

  6. I understand that chlorine is very popular and has been used for donkey's years. There are several drawbacks in treating effluents with chlorine.

    Firstly, chlorine is an oxidizing agent but absorbs only 2 electrons. Its residual presence in water is very short. This is because demand for chlorine is high and it is consumed rapidly in water.

    Secondly chlorine will react with organics in the wastewater producing chloroform, which is a trihalomethane and carcinogenic in nature.

    Even if the contact time is increased it will be ineffective as it is consumed very rapidly in water.

    Thirdly, as water biologists we always consider the effectiveness of chlorine in penetrating biofilms. While chlorine might partially treat the e. coli in the water it is unable to do so completely. Then there is the matter of biofilm that is formed in the tank or pond where the effluent is held. 

    Chlorine can never penetrate the biofilm and therefore after some time the chlorine gets exhausted, at which time the microorganisms break out from under the biofilm and increase the colony count of e.coli in the water.

    Chlorine is just not the right biocide to treat effluents with high microorganism counts. 

    While there has been suggestions by others to treat using UV or Ozone both have their limitations. While UV is good for disinfection at POU (Point of Use). This means at the point UV treatment is carried out it must be used either for irrigation or for discharge to the drain. If you store the water the e.coli will grow back as there is no residual presence of the UV in the water.

    In case of Ozone it is slightly better. While it has the oxidation capacity of O3 this also is one of its drawbacks. At the point of entry of Ozone in the wastewater you will get very good disinfection but as the gas dissipates its efficacy drops and once there is no more residual left in your wastewater the e.coli will grow back.

    Ideally you should be using chlorine dioxide, and chlorine dioxide is not chlorine. Chlorine dioxide is a gas and is more powerful than chlorine. It is able to break the biofilm in the system and completely sanitize the water system, thus not allowing any e.coli to remain. If the cell wall and the nucleus of the e.coli are removed there is no way for the e.coli to grow or mutate. This is what chlorine dioxide does, which neither chlorine, ozone or UV cannot do. Besides this chlorine dioxide will remain as a residual in the water thus if there is any re-contamination of the wastewater it will continue to disinfect. 

    3 Comments

    1. Having come across biofilms where the water was treated with chlorine dioxide, the statement that ClO2 breaks down biofilm is not always true.  The problem with ClO2 is that it is volatile and is lost due to pressure changes, turbulence and pressure changes and it is more hazardous to produce than hypochlorite.  Chlorine dioxide residuals can rapidly disappear and there are organisms, which can develop in levels 0.1-0.2 ppm frequently found in waters.

    3. It is a very idealistic and somewhat exaggerated statement. I wrote the first disinfection byproducts THM regulation at USEPA, so I know chlorine and DBPs very well. The THM regulation has often been misunderstood. Bladder cancer incidence in the US and Canada  has not changed in the 40 years since the regulations, and the  repro/developmental speculation is not supportable by the many studies in animals and human epi. . I looked at 6 other countries too. THMs is really a surrogate indicator regulation. The THMs are not carcinogenic in animal bioassays in water. I have a couple of papers on it coming out soon  in JAWWA and Dose-Response Journal, and I am presenting tomorrow at the Water Quality Technology Conference in Toronto.  All disinfectants have limitations.  Chlorine has saved millions of lives since its introduction in the early 20th century. Chlorine dioxide has a lot more problems than you suggest.  Read my coming papers or contact me.

  7. The Coliform count of >2419600 per 100 ml or >24196 /ml is not countable in Laboratory.   Please recheck the results. I trust of 2.2 mg/l residual chlorine is determined after 30 minutes contact time. If not then chlorine get consumed by the residual organic matter present in waste water.

    Residual chlorine of 2.2 mg/l with 30 minutes contact time ensures killing of Coliform. Presence of coliform may be due to inadequate contact time, presence of turbidity. Ozonization or UV treatment may be better alternative. For further details you may contact me on sarafrv@virajenvirozing.com

    Prof. Rajendrakumar V Saraf

    1 Comment

  8. For chlorine to disinfect several conditions have to be present. 

    Low turbidity, for drinking water disinfection below 1 NTU 

    Contact time with chlorine free residual at the end of the time.  The contact time is also temperature and pH dependent for a particular residual.

    Are you achieving these?

    You may be better off with UV as is used for many effluent discharges 

    1 Comment

    1. Thank you Steve i was referring to Wastewater effluent not drinking water

      2 Comment replies

      2. I think that you will find that the mechanisms of disinfection are the same across wastewater and drinking water. It is the required effectiveness that differs.

  9. hI, do you sure of your analysis ?

    if yes probably you haven't a correct time of contact and/or right point of inlet of chlorine 

    Gianfranco 

    1 Comment

  11. At a glance it's evident the WWT is not efficient to reduce the BOD at permissible minimal levels, so coagualation if you have is defficient and consequently floculation; don't worry you case is not the only one but you need a better WWT to eliminate any virus and pathogen if you are reusing for human contact.

    The solution is in your previous processes to chlorine disinfection although I'd sugest a more efficient and low costly WW purification process for your 191 lps plant.

    Regards.

    2 Comments

  12. Something is seriously wrong. 2.4 million E.coli/100 is raw sewage. It could not be that high if you had free chlorine present. Probably not even with combined, unless you have high turbidity and lots of particulates that are protecting aggregations of E. coli.  Has it been filtered? It is very difficult  (maybe impossible) to maintain a free chlorine residual in the presence of all the ammonia. Did you really get to breakpoint? Not likely. What test methods are you using for chlorine residuals and E coli counts. Maybe you need a different analyst or different metering.

    1 Comment

  14. Chlorine gas disinfection, if correctly controlled, is highly effective. One would need a good idea of the treated effluent quality before one could venture a response, for example effluent COD, suspended solids, ammonia and pH. Furthermore one would need to confirm where and how the gas (solution) is dosed (adequate mixing upstream of the chlorine contact tank, etc), the size of the chlorine contact tank, the condition of the chlorine contact tank (is settled sludge regularly cleaned out) and where the sample is taken for the residual chlorine test.

  15. I manufacture a device that can reduce or eliminate e-coli,  legionnaire's and other bacteria.  Is your system a single pass or are you circulating the water?

    1 Comment

  16. What is the pH value of effluent? 

    What is the turbidity and how much is the suspended solids? 

    2 Comments

    2. Check your  turbidity and check your media... and your treatment system.

      one of them or all are out of shape

      N

       

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      1 Comment reply