Levapor FAQ

What is Levapor ?

Levapor is the first synthetically modified carrier possessing ideal characteristics of a biocarrier (media) required for micro organism immobilization in MBBR/IFAS wastewater treatment process.

What is the material of construction (MOC) of Levapor carrier?

Levapor carriers are made of flexible, durable, high porous Poly Ether(PE) based Poly Urethane(PU).The PU foam is impregnated with fine activated carbon to render superior properties for the development of efficient biofilm for complex and difficult to biodegrade effluents.

What are the ideal properties of a carrier material for microbial immobilization in wastewater treatment?

Ideally a carrier material must offer higher adsorbent surface area for faster and stable colonization  of micro organisms on it. It should provide internal porosity to protect the microbes against toxic  and inhibitory substances and shear forces imparted due to mixing/aeration. It should also ensure  optimal mass transfer properties for the transport of substrate and nutrients making them available  for micro organisms growing in the biofilm. It should also possess good water affinity and higher  fluidization ability for economical and efficient mixing of the carriers with bulk liquid and thus  ensures optimal and user friendly operation of the biological treatment process.

PROPERTIES BENEFITS
Higher adsorbing surface and higher surface area Adsorption of inhibitory substances leading to better process stability and faster colonization
high internal porosity Prevention of biomass against excessive shear forces and formation of low DO zones
Fast wetting and water binding Homogenization of fluidised medium and maintenance of biological activity
Higher fluidization ability Reduction of power consumption
Faster colonization of bacterial mass with higher surface Faster process start up and higher efficiency

How does Levapor match above requirements?

Levapor carriers possess all the above mentioned properties of an ideal carrier: 

High Adsorption Surface:

PU foam has very high surface area compared to conventional plastic media. Moreover Levapor  carriers are impregnated with 15-40 kg of activated carbon per m3 of foam which increases the  surface area to thousand fold and also offers very adsorption capacity of activated carbon. This  combination of high surface area and adsorption capacity of activated carbon leads to very fast and  stable colonization of carrier material with micro organisms. The presence of activated carbon also  helps in adsorption of toxic and inhibitory substances on the activated carbon fixed on carriers  surface reducing its bulk liquid concentration. This eventually stabilizes the process in the reactor  and as Levapor facilitates development of specialized microbial strains for the degradation of these  toxic/inhibitory substances, their removal from the effluent stream becomes feasible and more  efficient compared to conventional suspended growth based and plastic media based processes.

Internal Porosity:

PU foam matrix provides higher internal porosity in the form of fine pore structure which enables  growth of micro organisms within the internal pores of Levapor carriers and thus prevents them  against toxic shock loads and excessive shear forces imparted due to aeration equipments.  

The fine pore structure of the foam also provides thinner film geometries compared to conventional  plastic media which allows for better diffusion gradients for substrate and nutrients resulting in  optimal mass transfer efficiencies. This in turn improves the transport of substrate and nutrients to  inner parts of the biofilm and thus increases the process performance.  

Fast wetting and water binding surface:

Levapor carriers have fast wetting and binding surface due to hydrophilic nature of PU foam which  provides faster colonization, better fluidization and homogenization capacity which results in faster  process start ups, lower energy consumption for mixing and maintenance of healthy biological  activity. The better fluidization also helps maintaining good mass transfer gradients across the  carriers.

The fine pore structure of the foam also provides thinner film geometries compared to conventional  plastic media which allows for better diffusion gradients for substrate and nutrients resulting in  optimal mass transfer efficiencies. This in turn improves the transport of substrate and nutrients to  inner parts of the biofilm and thus increases the process performance.  

What are the advantages of Levapor carriers?

What are the areas of application for Levapor carriers?

Over the years, Levapor carriers have been successfully utilised for the treatment of complex and  difficult to biodegrade effluents from different industries. The principle areas of applications are:

What are the physical properties of Levapor carriers ?

Various physical properties of Levapor carriers are summarised as below: 

Physical Property Value
Delivery Size 20 X 20 X 7 mm , 40 X 40 X 40 mm
Porosity 75 to 90%
Surface Area In excess of 20,000 m2/m3

What is the surface area of Levapor carriers?

Surface area of Levapor carriers is the result of:

  • Surface of PU foam which is 2500 m2/m3
  • Surface of the activated carbon which is 1000 to 2000 m2/g.

The combination of PU foam and activated carbon thus results in a total BET surface area of 3.34  million m2/m3. However, only a small fraction of this total surface area is colonized but still it is  extremely higher than conventional plastic media. 

faq
Fig. 1. Delivery form of LEVAPOR Carriers

What degree of filling is required for LEVAPOR Carriers ?

Due to high adsorption capacity and surface area of LEVAPOR carriers, the degree of filling required  will vary between 12-15%. 

What is the stability of Levapor carriers against mechanical and chemical resistance?

Levapor carriers are made of reinforced, abrasion resistant PU foams with a bulk density higher than  usual foams used in packaging or furniture industry and thus offer excellent mechanical resistance.  

However, during the plant operation, due to pitting against one another and reactor walls and also  depending upon the aeration intensity, the carriers could loss 1-3% of carbon pigments and foam  matrix after several years of operation. We have observed an average life of 10-12 years for Levapor  carriers based on the above mentioned factors and effluent composition.  

PU foams are basically of two types : 1) Poly Ether based and 2) Poly Ester based. The Poly Ether  based PU foam are very much stable against hydrolysis while poly ester based foams are less stable  against hydrolysis.  

Levapor carriers are based on Poly Ether based PU foams which are very much stable against  hydrolysis. However, certain solvents like chloroform and DCM cause swelling of the PU foams and  affect their dimensional stability. While treating effluents containing such solvents, enough care  must be taken to provide enough HRT so that they can be effectively biodegraded and thus their  enrichment/precipitation on the surface could be avoided. 

How long will it take for complete wetting, fluidization and colonization of Levapor carriers?

Normally it takes 1 to 3 days for complete wetting and fluidization of dry carriers. Once they are wet,  using inoculation of acclimatized sludge or micro organisms, the colonization of carriers takes place  within hours. We have observed good COD removal efficiencies within days of starting a new plant.  However, the required COD removal and nitrification establishment may take some time depending  upon the effluent composition and site temperatures.

Fig. 2 : Fluidized LEVAPOR Carriers in reactor

How biofilm thickness and performance is controlled with Levapor carriers?

The thickness of the biofilm will depend on the concentration and structure of the dissolved  substrate present in the effluent. Apart from biofilms, micro organisms also grow as discrete  colonies within the internal pores of Levapor carriers. However, the performance of biofilm does not  depend on the thickness of the film but rather on the activity of the fixed micro organisms present in  the biofilm. Due to specific properties of Levapor carriers, a very high amount of active micro  organisms are retained on the carrier material which results in higher process efficiencies and  performance.  

Biofilms are controlled due to turbulent energy of fluidization and aeration intensity. As the biomass  becomes dead, it can’t stay on the carrier material and will be washed out with the bulk liquid  leaving the reactor

Fig. 3 SEM View of Colonized Carriers with immobilized micro organisms on it As the PU foam has very fine pore structure, Will it not get clogged due to biofilm?
Fig. 3 SEM View of Colonized Carriers with immobilized micro organisms on it As the PU foam has very fine pore structure, Will it not get clogged due to biofilm?

As mentioned above, the dead biomass can’t remain in the biofilm and thus will be washed out with  the bulk liquid which subsequently will be removed in the secondary clarifier.

Will inorganic salts like Fe,Ca precipitate on the carrier material and clog it?

Depending upon their concentration in the effluent, in organic salts like Fe,Ca will become part of  the bio film and will wash out with the dead biomass. Based on excessive concentration and effluent  pH, they could precipitate on the carrier material. It has been observed that, the presence of calcium  aids biofilm settling properties when present in sufficient quantity and at desired pH range of  biological wastewater treatment. However, when present in excessive quantity of 2000 mg/lit or  more, it will form filamentous precipitate on the carrier material which is true for all type of carriers.

What is the role of Powdered Activated Carbon (PAC) in Levapor carriers?

The impregnation of PU foam with PAC results in superior properties providing many benefits for the application of Levapor carriers:

  • Faster microbial colonization and biofilm generation
  • Adsorption of toxic pollutants and reducing the toxicity of the medium
  • Faster process start up and stable processes over long period of time which can withstand shock loads
  • Lower filling (12-15%) compared to alternative plastic and unmodified PU carriers ∙ Better degradation of difficult to bio degrade pollutants
  • Removal of odour and foul smell from the reactor

As the pollutants adsorb on the activated carbon, Will it not reduce the adsorbing capacity of the PAC and also the biological activity?

As the pollutants adsorbed on the Levapor carriers would be continuously biodegraded by the micro  organisms present in the biofilm, the adsorbing capacity of the PAC will be continuously self  regenerated by the activity of these micro organisms. However, due to adsorption of salts and non  biodegradable metabolites, after certain time the adsorption capacity of PAC present on LEVAPOR  may partially reduced but due to higher biological activity within the Bio film present on the carriers,  We have not observed performance losses due to adsorption of salts on the carriers.

How can one determine whether the carriers are colonized and performing well or not? How do I measure the activity of biofilm in the reactor?

Due to presence of higher amount of live and active micro organisms in the biofilm developed on LEVAPOR carriers, the amount of oxygen consumed by carriers + suspended biomass will be higher than that of suspended phase biomass only. By measuring Oxygen Uptake Rate(OUR) with and without carriers for the MLSS present in the aerobic reactor, the activity of the biomass present on the LEVAPOR carriers can be quantified.The OUR of carriers + suspended phase biomass shall be higher than the OUR of suspended phase biomass only.

Fig 4: OUR comparison between LEVAPOR+ suspended Biomass versus suspended phase biomass only.

Do LEVAPOR carriers enable specific biodegradation mechanism for specific pollutant removal?

YES, Due to high adsorbing capacity and porosity of LEVAPOR carriers: 

  • Hazardous, inhibitory pollutants become adsorbed on the carriers surface and reducing their  bulk liquid concentration and thus their inhibitory effects on the micro organisms  
  • Further, within the biofilm developed on LEVAPOR carriers, specialized strains of micro  organisms are developed responsible for the degradation of the pollutant enabling their  removal. 
Fig.5 Biodegradation of 1000 mg/L (7,8 mM) of 2-Chloroaniline (2-CA) by suspended LEVAPOR fixed microorganisms

How effective is the application of LEVAPOR Carriers in reducing the foot print of the biological wastewater treatment process?

Depending upon the type of effluent, its composition, treatment targets and temperature, the application of LEVAPOR carriers can reduce the size of biological wastewater treatment plant significantly. 

During our application with a Pulp and Paper Mill Effluent anaerobic treatment, We observed that to achieve a COD of 1000 mg/lit for the effluent from anaerobic reactor, the size of the anaerobic reactor with LEVAPOR carriers was reduced to just 15,000 m3 compared to 65,000 m3 for suspended growth only Anaerobic reactor to achieve desired COD reduction. (See Fig. 6 ) 

For, our NINGAN , China, 20 MLD installation for municipal wastewater nitrification, We have observed that just with 3200 m3 of reactor volume, We are able to achieve stable and efficient nitrification under adverse winter conditions with lowest water temperature of 5 Degree C (-24 Degree C ambient temperature) with greater than 85% COD reduction for the plant. The plant is consistently meeting Grade-I requirement of Chinese nutrient and COD discharge standards. The above application would require atleast 15,000-20,000 m3 of suspended growth based only reactor to achieve same amount of nitrification and COD reduction.

Fig 6: Impact of LEVAPOR Carriers on the size of Anaerobic reactor for Pulp and Paper Mill Bleaching Effluent

How stable is the LEVAPOR based biological reactor’s performance against toxic shock loadings?

Due to higher adsorption capacity and internal porosity, LEVAPOR carriers protect the micro  organisms immobilized on the carriers very well against toxic shock loading.  

During the full scale start up of Anaerobic plant for Pulp and Paper Mill Bleaching effluent, two of  the three reactors were started using LEVAPOR carriers while the third reactor was started without  carriers in it with suspended growth biomass only so that the effectiveness of carrier addition could  be confirmed further.  

After few days of start up, a toxic shock loading event occurred at the plant with high amount of AOX  concentration in the bleaching effluent. The suspended growth based reactor was collapsed totally  and never recovered to the required performance while LEVAPOR carriers based reactors’ operation  remain stable despite toxic shock loads (See Fig 7.) 

Fig. 7 Impact of toxic shock loads on the performance of LEVAPOR based Anaerobic Reactor and suspended growth only reactors.

Our NINGAN, China 20 MLD installation which is in operation from last four years, observed very  high fluctuation of COD and TKN loading during summer 2013. For a period of 10 days from May 5 to  May 22nd 2013, the COD at the inlet increased in the range of 401.4 to 516 mg/lit which is almost 1.3  to 1.5 times higher than the designed COD values. Despite such higher fluctuations the overall COD  values of effluent remained between 38-42 mg/lit which corresponds to 90-91.8% COD reduction.  

During the month of June the Total Nitrogen Concentration at the plant spiked to as high as 55  mg/lit during most of the days with an average TKN value of 40 mg/lit at the inlet. However, despite  such a high increase in the TKN values, the NH4.N values at the outlet remained < 3-5 ppm with a  lowest value of 0.72 mg/lit NH4.N. The TKN values were always observed between 10 to 17 ppm at  the outlet which indicated simultaneous nitrification and denitrification occurring at the plant. 

Fig 8 Inlet COD fluctuation and effluent COD trend at NINGAN plant during may 9 to 22nd 2013.
Fig. 9 Inlet TN Concentration and NH4.N,TN trend in the effluent During June 2013 at NINGAN.

What type of Aeration system We can use with LEVAPOR carriers?

We can use fine bubble diffuser aeration system with LEVAPOR carriers. Due to the larger size of  plastic carriers which cause coalescence of air bubbles, even if one uses fine bubble diffuser system  with them, the overall efficiency of the aeration system is reduced. Thus, for all type of plastic media  based biological reactors, coarse or medium sized diffuser systems are used for aeration which are  low in efficiency. While due to fine pore structure and physical shape of the LEVAPOR carriers along  with lower degree of filling, fine bubble aeration system can be used without loss of aeration  efficiency due to loss of bubble size. 

Is LEVAPOR application in Biological wastewater treatment energy saving?

Due to better fluidization properties and light weight of colonized carriers, the amount of mixing  energy required for LEVAPOR carriers is quite less compared to conventional plastic based media  and thus LEVAPOR offers distinct advantage of saving in terms of aeration energy. Moreover, due to  better mass transfer efficiency across fine pore structure of the carriers, the aerobic reactors based  on LEVAPOR carriers can be operated at bulk DO concentration as close as to that of Conventional  Activated Sludge system while conventional plastic media based aerobic reactors require bulk liquid  DO concentrations in the range of 3-5 mg/lit to facilitate efficient COD reduction and Nitrification.  The amount of higher bulk DO requirement increases the aeration capacity significantly and thus  also increases the power consumption. 

What type of clarifiers can be use with LEVAPOR based reactors?

The excess sludge generated from LEVAPOR based reactors has excellent settling properties and  thus conventional secondary clarifiers can be utilised with LEVAPOR based aerobic reactors to  achieve good quality of effluent in terms of solids separation. However, if space is restraint then  advanced clarifiers like Lamella/Plate and Tube type settlers also can be incorporated with LEVAPOR  based systems. 

What size of retention screens required for LEVAPOR Carriers?

Using a retention screen of 8-10 mm sieve, LEVAPOR carriers can be retained within the reactor. The  shape of the retention screen would depend upon the type of reactor design and flow configuration.  Due to larger size of sieve energy loss due to headloss is minimal with LEVAPOR carriers compared to  plastic media which requires fine screens of 5- 7 mm size.

What is the difference between LEVAPOR and other carriers offered in the market?

Fig 10. Settling Properties of Sludge Biomass from LEVAPOR Based aerobic reactor

The comparison between LEVAPOR, plastic and other material based carriers can be made on the  basis of their size, surface area, internal porosity, adsorption and adhesion capacity, weight and thus  fluidization energy required along with type of aeration system which can be used with the carrier  material. During the development of LEVAPOR carriers various organic and in organic materials with  varying degree physical properties and their applicability for biological wastewater treatment was  compared and it was found that modified PU foam based LEVAPOR carriers are the most efficient  carriers for biological wastewater treatment application.

Attribute LEVAPOR Unmodified PUR foam Plastic carriers
total surface (m²/m³) up to 20.000 up to 2500 300 to 900
adsorbing capacity very high moderate low
required reactor filling 12 to 15 % 20 to 40 % 30 to 70 %
porosity 75 to 90 % 75 to 90 % 50 – 75 %
wetting 0 - 3 days several weeks several weeks
water uptake up to 250 % - remarkably lower - negligible
ionic charge + to - - non variable - no
colonisation by microbes 60 to 90 min. - several weeks - several weeks
full fluidization at gas 4 to 7 (m³/m²xh) n.d. coarse bubble
upflow carrier retention 8-10 mm sieves 8-10 mm sieves aeration screens
aeration fine bubble fine bubble aeration coarse bubble
more energy for aeration not yes, at > 20-25% aeration yes, coarse
fluidization excess required filling) n.d. bubble aer. by
sludge removal by fluidization quite narrow fluidization
variability of properties very variable negligible