Trickling Filter Filling issue

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The filling of a trickling filter with a diameter of 53 m2 and a reactor volume of 320 m3 has to be renewed. To comply with new effluent standards in the future it is considered to enhance its performance by using filling elements with very high specific surface volumes. In this case, 165 m2/m3 is chosen instead of the actual 100 m2/m3.
This filter has to treat daily 480 m3 industrial effluent which represents 250 kg BOD. The usual recirculation is 80-100 m3/hr. The influent contains TSS at 5-10 mg/l.

My questions:
1. Are more clogging risks to be expected by using these new fillings?
2. What can be done to reduce or to avoid these risks?
3. Are there other aspects to be considered in the new situation?

Thank you, TheWaterNetwork!

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14 Answers

  1. Dear Cees, the higher surface area of the new media means that you also have reduced channel sizes. Smaller channel sizes mean a higher risk of clogging. 

    However there are different ways to still reduce the risk of clogging: 

    1. Choice of the right fill media design and considering a mix of different fill media types depending on the layer depth. 

    2. Correct operation of the rotary distributor and more frequently flushing. 

    3. Biofilm thickness monitoring e.g. with weight stations 

    More information on trickling filters can also be found here: Trickling filter video

  2. Dear Cees.

    You seem to have an intermediate-rate filter between 40 and 64 KgBOD/100m3 per day. As some say below the void space would be an important factor. Overall you seem OK to go.

    Regards

  3. In addition to the comments below about organic loading, flushing rates and consequential hydraulic capacity of the system, including drains, there will need to be a review of the air movement. With less porosity more slime will grow and it will be easier to block the pores. Equally there will be more oxygen required from the air supply so make sure that the current fan system can handle both changes in pressure and perhaps increased recirculation rates. There will also be more solids transport from flushing and slightly greater solids loading on the downstream clarifier.

  4. I hereby want to thank all of you who has participated in this issue. It helped me a lot to continue in finding the best fitting solution. Btw. this TF has only to treat BOD/COD and was originally filled with PVC fillings.

  5. The clogging of bio media is depending on theporosity of media and organic loading rate BOD g/m2d. Prem is right if you had used a rock as media before and has replaced by a plastic media. However, if the previous media were a plastic media, there would be an increased risk of clogging. Because with an increased specific area of plastic media, normally the porosity would be reduced! So please check your organic loading rate and porosity to make sure there is no risk.  

  6. Dear  Cees Vallentgoed 

    No more clogging risks expected by using these new fillings.
    Your new filling as per design criteria no doubt,you may increase the circulation rate as well as flushing frequency.

    A material with a specific surface area between 45 and 60 m2/m3 for rocks and 90 to 150 m2/m3 for plastic packing is normally used. Larger pores (as in plastic packing) are less prone to clogging and provide for good air circulation . Primary treatment is also essential to prevent clogging and to ensure efficient treatment. Trickling filters are designed primarily for  BOD removal. A structured ​plastic media ​comprising ​corrugated ​layers on a ​diagonal angle​will be much ​more resistant ​to clogging ​than mineral ​media ​ Treatment performances depend on wastewater characteristics, hydraulic and organic  loading, medium type, maintenance of optimal dissolved oxygen levels, and recirculation rates. A BOD  reduction of 60 to 85 % can be expected with loading rates of 1 kg BOD /m3/day  Bacterial reductions have been reported to be 1 to 2 logs of faecal respectively 60 to 90 % of total Coliforms

    A trickling filter, also called trickling bio filter, bio filter, biological filter and biological trickling filter, is a fixed-bed, biological reactor that operates under (mostly) aerobic conditions. Pre-settled wastewater is continuously ‘trickled’ or sprayed over the filter. As the water migrates through the pores of the filter, organics are aerobically degraded by the biofilm covering the filter material.

    Organisms that grow in the thin biofilm  over the surface of the media oxidize the organic  load in the wastewater  to carbon dioxide and water, while generating new biomass . This happens mainly in the outer part of the slime layer, which is generally of 0.1 to 0.2 mm thickness

    The primary factors that must be considered in the design of trickling  filters  include

     

    1. The type of filter media to be used.
    2. The spraying system, and
    3. The configuration of the under-drain system.
    4. The flushing rate (or ​Spulkraft ​number) is also ​important.
    5. ​Recirculation ​rate will ​normally help ​to reduce ​clogging. 

     The ideal filter material is low-cost and durable, has a high surface to volume ratio, is light, and allows air to circulate

    .Physical adsorption of virus  on the biofilm  or elimination by predation are additional factors in pathogen elimination in trickling filters Total suspended solids  (TSS) removal is expected to be very low (due to the down-flow regime  and pre-settling  as well as removal of the solids from the effluent  is recommended. Because aerobic bacteria convert ammonia to nitrate some nitrification can also be achieved, depending on the organic loading rate to the filter, the temperature and the aeration. Total nitrogen removal varies from 0 to 35 %  while phosphorus removal of 10 to 15 % might be expected  However, the capacity for nutrient  removal of trickling filters  depends strongly on the operation conditions, and while some sources indicate a high removal of ammonia other indicate no capacity of trickling filters  for nutrients.

     

    Regards,

    Prem Baboo  

     

  7. Hi Cees,

    I hope all is well. In response to your questions the following.

    1. To answer this we need to know the type of media used at the moment. We have a filter media with a specific surface are of ~160 m2/m3  (http://www.qmes.nl/products/biofill/)  which is very open. Also the type of industry play a role. If it is food industrial containing FOG and there is not a properly working FOG removal system like a DAF for example than these solids can clog the media. 

    2. Answered above, install a properly working solids removal system.

    3. You only talk about BOD removal, what about nutrient removal. You have to take this into account as well when dimensioning the system.

    I hope these answers are of help.

    Best regards,

    Robert Wagenveld

     

  8. Triple7 Colloidal Concentrate https://envirofluid.com/worksafe-environmental-chemistries/accessories/spill-control/triple7-colloidal-concentrate works very well in filter maitenance to remove and prevent blockin - be free to email sales@envirofluid.com for further details

  10. Since this is an industrial application, it may be quite different than municipal wastewater. To prevent clogging, the first thing is to have a good pretreatment. Some Industrial wastes may not need any, some may need a lot. This is especially true if you are dealing with grease. There are a number of things to consider, also. The media size. The plastic media offers more area for the microbes to attach and may be a good alternative to rock. The TSS may actually increase at the effluent to a trickling filter due to sloughing of the microbes. Therefore a settling tank or clarifier is needed afterwards. These should settle vey easy and only require 3-4 hrs of detention.

    1 Comment

    1. This is not a particularly "strong" used water, with average BOD of only about 520 mg/l., and with a Total Suspended Solids of only 5 to 10 mg/L., so pre-treatment would not be expected to be a serious issue.

  11. How does the void space in the proposed new media compare to the void space in the existing media? If the void space is greater in the proposed new media then the risk of "more clogging" is likely to be reduced.

    Based on the limited information that you provide about the used water to be treated, I would not expect that clogging would be a significant isssue.

    Regards

    Tom Keenan

  12. Jeremy has some good points, but I don't understand Guy McGowen's observations in this context. Random packed media will create not flushed pockets, with all the consequences, mainly loss of effective surface and anaerobic conditions. Higher specific surface, also for structured media, reduces the free passage and increases the clogging risks.

    An interesting option, absolutely clog-free (!) and with high flexibility in m2/m3 variation are the SESSIL®  film strips from NSW (Germany).

  13. Treat the effluent with an Archaea microbial group species. Toxins will be chelated, pathogens will be zero, all effluent will be biodegraded into its elemental/nutritional state. Chlorine and filters no longer needed.  It becomes part of the circular economy.   Technology is a wonderful thing.  You only have to ask.  

  14. You haven't mentioned the type of filling material. I guess that you mean that your filter has a plan area of 53 m2, so it is 6m deep, in which case it will be a plastic media. A structured plastic media comprising corrugated layers on a diagonal angle will be much more resistant to clogging than mineral media and I personally believe structured plastic media are more resistant to clogging than random packed media too.

    The flushing rate (or Spulkraft number) is also important. You don't mention whether your filter has a rotating distributor or a fixed distribution system, but you may be able to adjust the flushing rate. It is not always easy to predict how the system will respond; you might think that increasing the flushing rate will reduce the risk of clogging but actually it will also reduce the population of higher organisms (flies and snails) living in the filter, which graze on the biofilm and can help to keep it under control. Air temperature has a big effect on trickling filters and you may need to adjust parameters according to the season.

    A higher recirculation rate will normally help to reduce clogging (by increasing flushing and by diluting the influent) but of course it will increase operating costs too.