|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|
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.
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.
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.
|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|
Surface area of Levapor carriers is the result of:
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.
Fig. 1. Delivery form of LEVAPOR Carriers
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.
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
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
The impregnation of PU foam with PAC results in superior properties providing many benefits for the application of Levapor carriers:
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.
YES, Due to high adsorbing capacity and porosity of LEVAPOR carriers:
Fig.5 Biodegradation of 1000 mg/L (7,8 mM) of 2-Chloroaniline (2-CA) by suspended LEVAPOR fixed microorganisms
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
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.
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.
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.
|Atribute||LEVAPOR||Unmodified PURfoam||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|
|wfull fluidization at gas upflow||4 to 7 (m³/m²xh)||n.d.||coarse bubble aeration|
|carrier retention||8-10 mm sieves||8-10 mm sieves||screens|
|aeration||fine bubble aeration||fine bubble aeration||coarse bubble aeration|
|more energy for fluidization||not required||yes, at > 20-25% filling)||yes, coarse bubble aer.|
|excess sludge removal||by fluidization||n.d.||by fluidization|
|variability of properties||very variable||quite narrow||negligible|