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 Provide 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 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 provides very adsorption capacity of activated carbon. This combination of high surface area and adsorption capacity of activated carbon leads to very quick 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 reduction 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 high internal porosity to structure with above statement 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 quick 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 efficiency.
What are the advantages of Levapor carriers?
- Faster process start ups
- Higher reduction efficiencies (50 to 400 %) compared to suspended growth based systems
- Lower degree of filling required ( 12-15 % )
- Remarkable process stability
- Degradation of persistence and difficult to bio degrade pollutants
- Lower energy consumption for mixing
- Smaller foot print
- Higher aeration efficiency due to application of fine bubble diffuser system
- Reduced head losses due to coarse retention screen designs
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:
- Anaerobic pre treatment of complex and persistent industrial effluents generating from pharmaceuticals, pesticides, herbicides manufacturing industries
- Nitrification-Denitrification of effluents containing high ammonia concentrations and inhibitory substances
- Treatment of hyper saline and high solvent containing effluents
- Treatment of AOX, BTX and PAHs from ground water and toxic effluents
- Treatment of landfill leachate
- MBBR/IFAS Wastewater Treatment plants
- Polluted Gas Treatment using Bio Trickling Filter
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 M m2/m3. However, a small fraction of this total surface area is colonized but still it is extremely higher than conventional plastic media.
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 provides 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 working cycle 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 reduction efficiencies within days of starting a new plant. However, the required COD reduction and nitrification establishment may take some time depending upon the effluent composition and site temperatures.
How biofilm thickness and reduction efficiency 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 functioning 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.
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
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 develop filamentous precipitate on the carrier material which is true for any 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 Wastewater
- 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
- Reduction 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 efficiency 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. 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.
Do LEVAPOR carriers enable specific biodegradation mechanism for specific pollutant reduction?
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 reduction.
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 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 reactor to achieve same amount of nitrification and COD reduction.
How stable is the LEVAPOR based biological reactor’s working 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 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 couldn’t recovered to the required efficiency while LEVAPOR carriers based reactors’ operation remain stable despite toxic shock loads (See Fig 7.)
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.
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 plastic media based bioreactors, coarse or large 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 provides distinct advantage of saving 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 for 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?
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 |
