Aerated Lagoon

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Hi everyone 

I have a municipal wastewater treatment plant with aerated lagoon process with capacity 1500 cm/d and with:

This plant built since 1991 receive now 2500 m3/d.

The main problem is the bad quality of treated water (SS > 120 mg/l and whitish look) and the sludge fails to settle

How to do ?

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14 Answers

  1. Hi there, clearly the system is overloaded, with incoming load now more than 65% than original design. This will lead to under aeration as the oxygen demand increases in the process due to the increased load, the installed aerators have a maximum installed oxygen transfer rate. The under aeration will encourage the proliferation of filamentous bacteria that will result in poor sludge settling, leading to sludge carryover that will affect the final effluent quality.

    In addition, the hydraulic retention will be compromised, contributing to poorer final effluent quality.

    An extension to the existing works will be necessary to improve on the final effluent quality under the current load.

    Regards

  2. Hi, Maymoun, 

    The Surface Load of clarifier is calculated as 0.2 m3/m2.h(2500/24/490), which is too low for the final clarification(normally it is more than 1.0 for active sludge process ). Hence, the hydralic settling process will not cause the high SS effluent in this case. Given the BOD effluent data was not provided, we cannot analyze if the BOD load and aeration is ok for the system. However, I guess that over-aeration and degration of active sludge could be the main reason responsible for the high SS effluent, especially the total Hydraulic Retention Time (HRT) of aeration lagoon is more than 2 days. You can make a SV30 (sludge Volume) test to see the settlement character of the active sludge(I guess the SV30 may beyond 70%). In this case, you may: 1) decrase the aeration and make sure the Dissolved Oxygen(DO) is not more than 2.0 mg/l; and 2) supply the fresh active sludge into the lagoon (the fresh active sludge could be got from the dewatering sludge of the similar treatment facility); 3) discharge the surplus sludge from the clarifier. The restoration of the sludge sytem may take more than one weeks, you need to check the Mixed Liquor Suspend Solid  (MLSS) and SV30 from time to time and make sure they are around 3000-5000 mg/l and 20-30% respectively. 

    Hope the above suggestion is helpful. 

    Regards, 

     

    Xujun

  4. Dear Maymoun,

    This analysis starts with the more simple question in aeration. The air mass balance comparing with the contaminants to remove and your budget, goals and economical projection for the project.

    How much is your organic load?
    Is the system well mixed?

    There are many techniques to solve this problem, but there are may questions to find the way.

    Please send a lab analysis to the posters can suggest a more accutare solution.

    Regards,

    Orlando D. Gutiérrez Coronado

  5. Hi Mymoun,

    We manufacture and sell a very inexpensive plant based product that will help your wwtp achieve less solids, no odor, and faster digestion.    

    Please see video at our website: scicorp.net

    Contact me for more info, samples, etc.

    enrique@scicorp.net

  6. Hello Maymoun, 

    Some good suggestions below but my advice is to call in an independent specialist waste water treatment plant process consultant who is not aligned with any particular product or technology. They need to have access to a good lab so that the failure of the current process is understood and then make recommendations.  A good consultant will provide you with several options and give you some idea of the OPEX/CAPEX cost for each. If you have a budget problem (who doesn't?) then the consultant should also be able to tell you what might be possible with the funding you have available and how it might be possible to stage the works. 

    Best wishes,

    Harry.

  7. El señor Constante está ofreciendo imposibles porque, convertir aguas residuales  en aguas potables, esto es,  apta para el consumo humano, incluyendo la ingestión, y aumentando la capacidad de 1500 m3/d a 4320 m3/d (50 L/s), "...con cero emisiones contaminantes y bajos costos operativos...." solo lo puede hacer el Man de Arriba, quien es el único que hace milagros. Algo parecido puede ser hecho con altísimos costos pero solo con  aguas residuales de características muy especiales, que requieren componentes de tratamiento también muy especiales , para poblaciones que no tienen ninguna otra alternativa para contar con agua potable.

    Jaime Logreira

  8. Dear Maymoun,

    We can purify your wastewater into potable and increase the plant capacity to 50 lps at least with zero pollutant emissions and low operating costs between another sustainable and economical advantages, if you are interested.

    Regards 

  9. Mr. Chaabouni, 

    You have measured a high effluent suspended solids of 120mg/L, but have you also measured the effluent BOD5 or COD? Often TSS and BOD are related, but not always, and the TSS to BOD ratio provide more information. 

    I have a few ideas about your system and what may be happening. If you would like to discuss further, please contact me at ARice@aqua-aerobic.com


    It is very possible your plant is overloaded, and requires more aeration in order to meet treatment, since you have expanded the flow rate 1500m3/day to 2500m3/day. If you have influent loading criteria (eg: BOD, TKN, etc), you can estimate if you have enough oxygen from your existing aerators.

    I am separating this into three different topics: poor effluent quality, poor settling in your clarifier, and a white color.

    Regarding the Poor Settling

    1. My first thought is that you do not have enough aeration in your basin for biological treatment. It is well understood that having a low dissolved oxygen level will lead to a biomass that is not able to flocculate effectively in lagoon systems ("High Performance Aerated Lagoon Systems" by Linvil Rich, pp. 204). The solution to this is to add additional aeration equipment.

    2. My second thought is perhaps you are short circuiting your basin. Although your theoretical detention time is 2.3 days, some of the water may be short circuiting and reaching your effluent in less time. A young sludge below 2 days does not flocculate well and would lead to high suspended solids. The solution to this would also be to add additional aeration equipment.

    3. You may be releasing dissolved gasses or denitrifying in your clarifier, which will float solids to the top similar to a dissolved air floatation system. This too may be an issue with aeration. 

    All three of these issues could occur directly from your increase in flow rate. There's other possible issues (eg: the placement of your aerators is shearing flocc by the effluent), but you would expect something like to have always happened rather than only happening recently.

    Regarding the poor effluent quality

    1. The high effluent suspended solids is clearly related to poor settling in your clarifier and facultative lagoon. 

    2. You may also be getting poor biological treatment in your lagoons, depending on your influent loading criteria.

    To achieve good treatment in an aerated lagoon, you usually want 5+ days of detention time. You have less than half of that. In order to get good treatment, you almost certainly need more aeration and mixing power to (1) transfer additional oxygen and (2) improve mixing, which will improve the kinetic removal rate of the biomass in your lagoon. 

    Regarding the white color - 
    In my experience, I have only seen three things that have caused a white effluent:

         i. You may have insufficient aeration that is leading to anaerobic decay on the bottom of your basin, and dissolved or undissolved gasses may be coloring the wastewater. 

        ii. Calcium carbonate or calcium phosphate could be  precipitating out of solution. You can measure your water pH, alkalinity, and Ca content in order to shed light on this. 

        iii. Certain industrial wastewaters - especially sugar beets. This is UNLIKELY in your case because it is a municipal system.

    I have also heard stories of cilates creating a milk-like effluent, but I have not seen that personally. 

    At any rate, please don't hesitate to email me at ARice@aqua-aerobic.com if you would like to discuss your application further. My expertise is in the design of aerated lagoon and facultative lagoon systems, and wastewater aeration systems, and I can help you predict how much additional aeration equipment you will need, and what the most effective aeration equipment will be for your basin. 

    Answered on by

  10. Bioaugmentation can help to product better results. I can suggest a product to use if you can provide additional information about the treatment system. Thanks.

    Jay Hill

    Bioscience, Inc.

    www.bioscienceinc.com

    Answered on by

  12. Hi Maymoun,

    I would kindly ask some more questions to help you better:

    What kind of aerators are you using? And how long are you running the aerators? 24/7 ? (The questions goes for the positioning to improve the treatment)

    General speaking the treatment can be improved by

    1. Checking the amount of sludge on the ground and if to high remove the sludge to get more active volume in the lagoons again!

    2. getting a better mixing (for example OLOID in Combination with your aerators), improvement of the flow inside the lagoons (use more of the volume in the lagoons to get better treatment results). The OLOID would also distribute the Oxygen better in the lagoons.

    3. If the oxygen level is to low in the aerated lagoons than you need more aeration or a bigger lagoon as Gary Brown said, because the load is too much. Please measure the oxygen level in the lagoons and you will see if it is enough (min. 1,5 mgO2/l until 2,5 mgO2/l) if you are always under 1,5 mgO2/l than the aerobic treatment will not work as good as it could be.

    One typical improvement and low energy solution if possible with the heights could be an rotating biological contactor before the lagoon treatment to reduce the load input in the lagoons.

    4. Improvement by splitting the lagoons for example with floating wetlands into parts will also improve the result, because the treatment will be in steps, short cut flow is eliminated and the roots of the plants will increase the surface for the bacteria to grow and do the work for you.

    5. The floating wetlands can also be positioned at the outlet of the lagoons to reduce the overflow of active bacteria from one lagoon to the next one (the roots will work as a filter).

    I you wish that I help you in a more specific way than please let me know and I would need some drawings, aerator information, load input and if you have some photos.

    Email: eric.schieblich@inversions-technik.ch

    All the best

    Eric Schieblich (CEO of Inversions-Technik GmbH, Switzerland)

     

  13. Hi Maymoun

    if the original capacity installed capacity was 1500 and you receiving 2500 then the process will be overloaded and you can expect poor effluent quality and bad sludge settling since aeration will be inadequate, encouraging filamentous bacteria growth, poor settling, smell, appearance etc

    in the long term you will need to increase your treatment process capacity, from inlet screens and grit removal across ponds and to the secondary settling. All of these, if receiving more load than designed for, will most likely fail and contribute to overall process performance failure

    Message me if you require additional inputs

    regards

    1 Comment

    1. I agree with Gary. From the given figures I do not think a quick fix would be possible, although some short term mitigation measures may be possible if more information is made available. One would need to consider more detailed design, actual loading and operational information to determine the way forward. Regards

  14. Put a poly baffle curtain around the inflow, 50m diameter, Relocate the aeration inside the curtain. Dose a proven bacteria product (Nitrogen Cycle) at inflow. Benefits - Ensures flow retained in aeration zone, Ensure correct bacteria present.

    1 Comment