MOVING BED BIO-FILM REACTORS (MBBR) and INTEGRATED FIX ACTIVATED SLUDGE (IFAS) 

THE LEVAPOR ADVANTAGE

Wastewater treatment using moving bed bio-reactors (MBBRs) provide an advanced treatment technology for biological wastewater treatment operations.  Developed in the late 1980’s, MBBR’s have become increasingly popular throughout the world, currently an estimated 700 MBBR treatment systems are in operation to treat a variety of effluent types within a multitude of operating processes.  

BACKGROUND

The removal of pollutants from wastewater occurs through a required quantity of several different specialized microbial strains. Some of those special degrading organisms flocculate weakly, grow and settle slowly and will be washed out from treatment plants, resulting in damage to the natural process.

In the secondary treatment process, the aerobic biological process is able to biodegrade organic material. Bacteria and protozoa, referred to as beneficial microorganisms, feed on the contaminants within the wastewater. Microbial activity increases with an adequate supply of food and oxygen as does their  biomass (population).  An indication of a high level of microbial activity is determined by the biochemical oxygen demand (BOD), a measured indication of wastewater strength.

SUSPENDED-GROWTH SYSTEM

In a suspended-growth system, similar to that of an; activated sludge process, aerated lagoon or aerobic digestor, the wastewater is flowing freely amongst free-floating microorganisms and eventually settles out into a biological floc. Microorganisms will remain retained within these flocs and may be recycled for later treatment.

 

 

  

 

 

 

     

 
 
  
ATTACHED-GROWTH SYSTEM

An attached-growth system, in comparison to a suspended-growth system, will use a media to grow and retain the microorganisms, examples of an attached-growth system include a; rotating biological contactor (RBC), trickling filter, or biological aerated filters (BAF). The media can take the form of a variety of materials ranging from; plastic, textile, gravel, etc., all of which will enable microorganisms to become attached to the media and grow, creating a biofilm on the media. Upon reaching a certain thickness, the biofilm will become detached from the media, a process referred to as sloughing.

    Rotating biological contactor (RBC)                        Trickling Filter                                   Biological Aerated Filters (BAF)

Requiring less space than an activated sludge process, an attached growth system through the use of media generally maintains a greater concentration of microbial material and are less dependent of the final sludge separation. The, attached growth systems are advanced to the suspended biomass processes. Attached growth creates the biofilm on the support media to provide a better treatment efficiency due to accumulation of high microbial population in the presence of large surface area. The shape and size of biomass-supporting media can also play a significant role in the design of biofilm processes in order to meet an obligatory surface area for microbial growth.[1] Microorganisms will secrete a natural polymer which enables a firm adhesion to the media ensuring a bio-oxidation mechanism and the opportunity for biofilm growth.

The MBBR technology, which is comprised of both suspended and attached growth processes, provides greater removal of biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrogen and phosphorus. The MBBR technology thereby provides an increased treatment efficiency by providing greater capacity, low capital outlay as well as nominal operational costs, minimal maintenance and minimal replacement costs.

Allowing the adaptation into virtually any wastewater treatment system makes the MBBR technology beneficial for both new treatment systems and more commonly through modifications to existing wastewater treatment plants. The MBBR technology provides for ease of incorporation and a uncomplicated operating process. 

                      Visual description of MBBR process                                       Example of plastic bio-carrier

The MBBR process is favoured over numerous other treatment processes such as; activated sludge systems (AS), granular sludge, fixed film (RBC, Trickling Filter, etc.). For the purpose of nutrient and carbon removal the advantages of the MBBR technology are numerous, as indicated below;

  • more compact resulting in lower treatment costs and lower maintenance costs,
  • the biomass that requires separation achieves substantially lower concentration results, this enables a smaller footprint for solid separation systems, this provides greater efficiencies when compared to floatation or filtration methods,
  • operating in a bio-film process enables operation at higher wastewater concentrations of active biological effluent increasing the biological removal rate,
  • more resistant to overloading and toxic compounds,
  • the biomass can be tailored for specific treatment purposes, i.e. nitrification or de-nitrification,
  • no requirement for backwashing versus other biofilm reactors as they are not prone to clogging,
  • provide a high surface area for microbial growth and a low head loss,
  • compared to fixed media the MBBR provides for free circulatory movement within the water enabling the biomass to become fully grown on the media,
  • by remaining in suspension, some studies reveal that more than 90% of the biomass is trapped and cultivated within the media,
  • higher Solids Retention Time (SRT), this provides a lower cost of sludge disposal with MBBR technology versus a typical activated sludge process due to lower sludge production,
  • high specific surface area within the media accommodates biofilm growth, eliminating the requirement for the reactor to provide sludge recirculation for optimum biomass concentrations,
  • by providing an MBBR versus suspended growth systems, provides additional benefits; flexibility such as, smaller space requirements, lower hydraulic retention time, increased resiliency, greater biomass retention period, increased amount of biomass clusters, improved recalcitrant degradation of contaminates and a decreased rate in microbial proliferation,
  • ease of implementation when upgrading existing treatment systems,
  • more robust technology and resilient bacteria population,
  • ability to handle high loads or temporary limitations,
  • co-existence within aerobic or anerobic systems,
  • no clogging of bio-reactors

The benefits of MBBR technology have been well proven over the past 4 decades, however it’s important to note that not all MBBR technology is the same.  An article provided by the Faculty of Engineering and Built Environment, University of Kebangsaan in Malaysia indicates that the bio-carrier used for the MBBR process is vitally important for the effectiveness of the wastewater treatment process. They cite that,

“an important aspect about the MBBR technique to note is the choice of the carrier; this plays the most vital and critical part in the systems achievement. Therefore, selecting efficiency carriers is vital for optimal results in the MBBR method.”[2]

The relentless search for the most optimal bio-carrier have involved scientists and researchers around the globe seeking the optimal biocarrier so that wastewater treatment performance can be optimized, “more research testing for a carrier that is economical with the combined advantages of having surfaces that can enhance microbial growth and hence improvement of MBBR performance.” [3]

Research findings have revealed that the specific area of the carrier used in the MBBR process is one of the most important factors of the MBBR bio-carrier. A high specific area will directly relate to the performance due to the high biofilm concentrations capable of forming in the relatively small reactor area.  The surface area of some bio-carriers are well below 1,000 m²/m³, some may reach a surface area of 3,000 to 4,000 m²/m³, this area however still falls short of the area found in the Levapor bio-carrier.  

The Levapor bio-carrier reveals a surface area in excess of 20,000 m²/m³, this extensive surface area compared to other biocarriers provides extensive benefits for the treatment of wastewater.

Research work performed by M. Maurer, C. Fux, M. Graf and H. Seigrist in 2001 on moving bed biological treatment and published in Water Science and Technology, 43(11). 337-344, revealed studies of two different types of carriers, plastic tubes and sponge cubes.  Although both carriers revealed similar results for denitrification capacity, temperature dependency, maximum nitrate and COD removal there was significant differences with respect to the amount of substrate.  Further studies by D. Robescu in 2009 emphasized the importance of good design and surface to enable greater mass transfer of nutrients to microorganisms.

Research results published by H. Odegaard, B. Gisvold and J. Strickland in Water and Science Technology, 41, (-4) 383-391 with respect to the carrier size and shape in the moving bed biofilm process revealed, “the MBBR organic loading rates per carriers area (i.e. COD/m² •d) plays a crucial role within the treatment efficiency of MBBR reactors. Higher area was shown to considerably improve the performance of those systems.”[4] 

In the same research article a researcher by the name of D.V. Vayenas concluded that,

“the attachment of organism to the surface and the resulting growth of the biofilm community rely upon the surface of the biofilm carriers that are rougher, more hydrophobic and coated with surface-conditioning films.”[5]

It has been consistently proven by researchers that the bio-reactor surface area is a significant factor in determining the effectiveness of the MBBR technology.  Additionally it has also been indicated that foam versus plastic creates a greater substrate enabling a greater mass transfer of nutrients to microorganisms.

Impact of Bio-Carrier Percentage Fill of Water Volume

What remains key to the MBBR’s performance however is, “The high specific area of the carrier media, which permits very high biofilm concentrations due to a small reactor volume, controls the system performance.”[6] With surface area of the bio-carrier being a key element in the promotion of biofilm concentrations, it would seam logical that an increase in the concentration of bio carriers within the designated volume of water would increase the overall surface area for the biofilm to attach itself.  Although true to a certain point, the fill percentage of bio-carriers to water volume, does provide a marginal increase in nitrification, however eventually diminished performance is exhibited, this in part is due to enzymic hydrolysis reaction and bio-flocculation within the reactor. 

Research has indicated, “fluid turbulence and mechanical collision among the biocarriers in MBBR are the main detrimental factors restricting the biomass attachment to carriers”.[7]

Adhering to the prescribed volume fill of bio-carrier ratio to water volume recommended from numerous bio-carrier manufacturers’ increases the likelihood of bio-reactor collision and shear stress. This is ultimately detrimental to the MBBR process and may present challenges to achieving optimal performance. According to H. Odegaard and his research team they had determined through their research, “the optimum carrier concentration ascertained was approximately 50%.”[8] Many bio-reactor suppliers however may recommend fill ratios as high as 60% or 70%.

Irrespective of the fill ratio required, when the percentage of bio-carrier fill to water volume increases, collision amongst the bio-carriers and resulting shear stress increases as well creating more challenges for achieving optimum performance.  Studies have revealed that, “plastic biocarriers are freely floating and moving in the bioreactors, which are normally equipped with mechanical mixing or air pumping, the high fluid shear stress on the biocarrier surface can greatly hinder microbial colonization, thereby slowing the biofilm development on the moving carriers.”[9]

Levapor provides the ultimate solution; a very high surface area on the bio-carrier (20,000+ m2/m3) and a low ratio of bio-carrier fill to water volume, (10% to 15%) reducing the likelihood of shear stress to nearly non-existent.

It is important to note that the higher the percentage of bio-carriers required withing the volume of water increases the likelihood of collision amongst the bio-carriers and ultimately creates shear stress. 

Levapor believes achieving the best of both models is preferential. An extremely high surface area provided by the Levapor bio-carrier, 20,000+ m²/m³, significantly higher than virtually any other bio-carrier on the market. The higher the surface area reduces the required water volume fill, typically a 30% to 60% requirement with most bio-carriers to only 10% to 15% fill with the Levapor bio-carrier. Ample surface area on the individual bio-carrier to create biological growth and ample area within the volume of water to avoid colliding with other carriers and incurring loss of attached growth. Not to mention of course, the cost per cubic metre of the bio-carrier when acquiring manufacturers required volumes.

 Ceramics                       Polyethylene                 Polyurethane Foam                        LEVAPOR

  400 m²/m³                    780 m²/m³                           1,500 m²/m³                       > 20,000 m²/m³

What Results Can Be Achieved With MBBR Technology Using the Levapor Bio-Carrier

 
 

10.

 

Summary of Levapor Advantages

 

PROPERTY

LEVAPOR

plastic bio-carrier (PE)

Material

Reticulated Poly Ether based PU Foam impregnated with activated carbon

High Density Polyethylene (PE)

Individual Cube Size

20 x 20 x 7 mm

15 mm +/-0.76 mm Diameter

9.5 mm +/-0.76 Height

Weight of media

65-80 kg / m3 of colonized carriers

143 – 176 lbs. per 1.3yrd3

170 kg – 1 m3

374 lbs – 1.3 yrd3

Surface Area

Ø  20,000 m2 / m3

780 m2/m3

Specific Gravity

1.1g / cm3

Unknown

Porosity

Ø  90%

Unknown

% of Reactor Filling Required

10 – 15%

25% to 65%

Full Fluidization energy

4 – 7 Nm3 / m2.hr air

Unknown

Wetting Period

1 – 3 days

Unknown

Colonization

60 – 90 minutes

Unknown

 

Learn more out about the many advantages with the Levapor Technology at

www,wettechenvironmental.com  / www.levapor.com

Ken Parke                                                              Robert Woodward

780-933-5104                                                        403-437-20-30

k.parke@wettechenvironmental.com                woodwardr645@gmail.com

Website: www.wettechenvironmental.com

[1] Scientific World Journal, Nov. 12, 2013, Evaluation of Different Wastewater Treatment Processes and Development of a Modified Attached Growth Bioreactor as a Decentralized Approach for Small Communities

[2]´3´4  A Review On Sewage Treatment and Polishing Using Moving Bed Bioreactor (MBBR), Jamal Ali Kawan, Hassimi Abu Hasan, Fatihah Suja, Othman Bin Jaafar, Rakmi Abd-Rahman, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia

 

 

 

[6]´8 A Review On Sewage Treatment and Polishing Using Moving Bed Bioreactor (MBBR), Jamal Ali Kawan, Hassimi Abu Hasan, Fatihah Suja, Othman Bin Jaafar, Rakmi Abd-Rahman, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia

[7] Use of a packed-bed biofilm reactor to achieve rapid formation of anammox biofilms for high-rate nitrogen removal.

Author links open overlay panel Ying-yu Li a, Xiao-wu Huang a, Xiao-yan Li 

 

[9] Use of a packed-bed biofilm reactor to achieve rapid formation of anammox biofilms for high-rate nitrogen removal.

Author links open overlay panel Ying-yu Li a, Xiao-wu Huang a, Xiao-yan Li