wastewater treatment submerged, aerated filter
TRANSCRIPT
Microsoft Word - UK_SAF01_Submerged, aerated filter - Biological
treatment of Waste Water_09-06-201
Wastewater Treatment
Installation Instructions
Product information: As a result of many years of R&D and extensive experience with polyethylene extrusion techniques, EXPO-NET Danmark A/S has developed a structured filter media. The media has proven extremely efficient in biological treatment of domestic sewage, industrial wastewater and process water within aquaculture industry. The media is made from the environmentally friendly material polyethylene and consists of net tubes, which are welded together to form a square block. The unique surface structure of the many net tubes provides a large accessible surface area for enhanced biological growth on the filter media.
Table 1: BIO-BLOK® media – overview
Type Application Surface
structure Area of
BIO-BLOK® 100 BOD Rough 70% 90% 67.5mm 54x54x55cm
BIO-BLOK® 125 BOD Rough 67% 89% 55mm 55x55x55cm
BIO-BLOK® 150 Ammonia/BOD Rough 64% 88% 55mm 55x55x55cm
BIO-BLOK® 200 Ammonia/BOD Rough 60% 82% 55mm 55x55x55cm
BIO-BLOK® 300 Ammonia/BOD Rough 51% 72% 36.6mm 55x25x55cm
Due to the natural characteristics of extruded products, all measurements are approximate.
The filter media BIO-BLOK® is used for all kinds of biological treatment of industrial wastewater, domestic sewage and process water in the aquaculture.
Mode of Operation: Future construction, refurbishment or upgrading of biological wastewater treatment plants is a matter of optimizing living conditions for the micro-organisms. I.e., the bacteria etc. must thrive on the substrate in order to work well and "do the water treatment job". The surface of BIO-BLOK® filter media acts as substrate for specialised bacterial strains and other micro-organisms which in turn are able treat and degrade a wide range of wastewater qualities. The treatment capacity of a bioreactor generally depends on the quantity of bacteria that the filter media can sustain. The larger the specific biologically active surface area is the larger the bacterial population. When micro-organisms (biological film or biofilm) grow on a level surface, the specific surface area will remain constant even with the establishment of a thicker biofilm.
BIO-BLOK® filter media
2
The BIO-BLOK® media, however, is designed as a helical structure with oval threads. If the threads become thicker due to growth in the thickness of the biofilm, the specific biologically active surface increases correspondingly. The principle is illustrated below.
During high load periods on the filter media, the biofilm will grow thicker and the specific biologically active surface of the filter will increase considerably. Hence, the biological decomposition rate increases. In practice, this means that wastewater treatment plants constructed with BIO-BLOK® filter media do not only have larger capacity but also have enhanced resilience and flexibility towards fluctuations. Therefore, BIO-BLOK® reactors are able to adjust to the overloads which typically occur in most wastewater treatment plants.
Choice of BIO-BLOK® in connection with BOD reduction The bacteria that reduce and decompose organic substances always develop a thick biofilm. The thickness of the biofilm depends on how polluted the water is and the thickness of the hydraulic surface of the filter media in the actual system. The correct choice of BIO-BLOK® filter media therefore depends on the accessible area in the net mesh structure of the block when biofilm grows on the media. In connection with reduction and decomposition of organic substances (BOD), a biofilm thickness of approx. 2 mm usually develops and it is this thickness that is used in connection with dimensioning. The most effective types of BIO-BLOK® for this application are BIO-BLOK® 100 and BIO-BLOK® 125, as these two types allow for biofilm up to 4mm before the mesh hole clogs with biofilm. This means that you have to calculate with the values mentioned in Table 2, when dimensioning filters for BOD reduction. If you are certain that the biofilm will seldom grow to more than 2mm, you can naturally choose other BIO-BLOK® filter media types and thus get a smaller system or a higher decomposition and capacity. This means that you can calculate with the values mentioned in Table 2, when dimensioning filters for BOD reduction.
Choice of BIO-BLOK® in connection with ammonia reduction
Bacteria that reduce ammonia always develop a thin biofilm. The precondition for ensuring these bacteria developing is that as much BOD load as possible is removed; the reason for this is that the nitrifying bacteria grow much slower than the BOD reducing bacteria. As only a thin biofilm then develops, it is possible to choose a BIO-BLOK® type with more mesh strings and consequently
3
smaller holes in the mesh “wall”. The most efficient types of BIO-BLOK® for this application are BIO- BLOK® 150, BIO-BLOK® 200 and BIO-BLOK® 300. This means that you should calculate with the values mentioned in Table 2 when dimensioning filters for BOD reduction or nitrifying filters: Table 2: Specific biologically active surface area for BIO-BLOK® filter media
Filter type Application Thickness of biofilm
1mm 2mm 3mm 4mm
BIO-BLOK® 200 Ammonia/BOD 312m2/m3 426m2/m3
BIO-BLOK® 300 Ammonia/BOD 360m2/m3 460m2/m3 560m2/m3
Due to the natural characteristics of extruded products, all measurements are approximate.
Sludge Production Above Table 2 shows that when applying BIO-BLOK® filter media, there will always be a big, active biomass in the treatment plant with a relatively thick biofilm, depending on where in the process the actual filter media is placed. This means that the sludge age will be considerably higher than in activated sludge systems, resulting in a significantly lower sludge production. Estimated sludge production in these systems would be 0.1 – 0.33kg SS/kg decomposed BOD. Since the sludge age in the BIO-BLOK® media is high, it will also result in development of bacteria in the biofilm, which can decompose organic matters that decompose slowly such as medical residues etc., which is difficult in activated sludge systems. By comparison, the sludge production in an activated sludge plant is about 0.8kg SS/kg decomposed BOD.
Installation of BIO-BLOK® Filter Media: In submerged aerated reactors BIO-BLOK® filter media is always installed with the net tubes placed vertically.
BIO-BLOK® is easily cut into the desired shape with a saw since the net tubes are welded together only at the tube ends. BIO-BLOK® filter media can therefore be adjusted to any tank design.
4
Bio-Reactor Design: It is an advantage for the biological processes to divide the bio-reactor into compartments connected in series. Depending on the size of the reactor this is normally between 3 and 8 compartments. In the compartments different bacterial cultures will develop depending on the composition of the supplied waste water. E.g. in the first compartments upstream, bacteria which decompose organic matter will have preference. In the later compartments nitrifying bacteria will normally dominate. Air supply system and grating on which the BIO-BLOK® is positioned is installed at the bottom of the compartments. Each compartment should have separate air supply in order to adjust the quantity of air supply for the individual compartment. The possibility to aerate the filter media heavily is convenient from an operational point of view and will also provide the means for easy backwash of the media should this prove necessary. The height of filter media may vary from two to many layers of BIO-BLOK®. As a rule of thumb, BIO- BLOK® filter media installed in four layers, corresponding to 2.2 m, will provide the best operational economy for the air blower. In order to make sure that the tube ends of the BIO-BLOK® are positioned straight over each other, connection kits can be used. Normally two connection kits are used in each joint/BIO-BLOK® in the edge of the bioreactor.
Plan of bio-reaktor, example
5
The top of the BIO-BLOK® is normally minimum 20cm below water level.
Please note that the partition walls of the basin must be placed to the bottom and placed above the water surface. In this way, the waste water can achieve the best contact with the filter media. The inlet and oulet should usually be placed in top and bottom as far apart as possible. The size of the inlet and outlet should be about twice of the main inlet size. The distance from the air diffusers to the bottom of the BIO-BLOK® material depends on the type of air diffusers (and the quantity of air) being used. It is important that the bottom of the BIO-BLOK® is positioned at a distance where the air bubbles are spread efficiently and distributed over as much of the BIO-BLOK® surface as possible. The distance is typically from 10 to 25cm.
Uplift Pressure and Weight: BIO-BLOK® filter media is made from the environmentally friendly material polyethylene. The type of BIO-BLOK® is decisive for the uplift pressure and the weight of the filter media. The uplift pressure can be counteracted with a girder system in order to keep the BIO-BLOK® units in place.
Water surface
The distance depends on the choice of air diffusers.
The filter height appears by using whole, vertically positioned BIO-BLOK®. Standard height is 55cm. Can be produced in heights from 40 to 120cm as per agreement.
Bottom
Bottom grating
Top grating
Example of installation of BIO-BLOK® units by means of a bottom grating and top girders.
Water inlet
Water outlet
Air diffusers
Weight/m3 BIO-BLOK® 100 62.00kg/m3 BIO-BLOK® 125 66.00kg/m3 BIO-BLOK® 150 69.00kg/m3 BIO-BLOK® 200 74.00kg/m3 BIO-BLOK® 300 100.00kg/m3 BIO-BLOK® Weight without Biofilm Coating:
Weight Weight/m3 BIO-BLOK® 100, 54 x 54 x 55 cm 7.43kg 46.00kg/m3 BIO-BLOK® 125, 55 x 55 x 55 cm 9.01kg 54.00kg/m3 BIO-BLOK® 150, 55 x 55 x 55 cm 9.97kg 60.00kg/m3 BIO-BLOK® 200, 55 x 55 x 55 cm 11.41kg 69.00kg/m3 BIO-BLOK® 300, 55 x 25 x 55 cm 8.03kg 106.00kg/m3 As it is a matter of extruded products, all measurements are approximate.
In order to design and calculate the bottom grating system, it is recommended to use a BIO-BLOK®
maximum weight (including biofilm) of 300kg/m3. This weight, however, will only occur in situations where the BIO-BLOK® units are clogged due to operational accidents and the water in the reactor has to be pumped out for maintenance purposes. To optimise the self-cleaning properties of the BIO-BLOK® media, the carrying girders of the bottom grating system should not be so wide that they cover a BIO-BLOK® tube opening (Ø 55mm). As top grating in smaller reactors, 20 x 20cm steel grid fixed onto the side walls can be used. In larger reactors, girders which further absorb the upward forces (uplift pressure) can be used in combination with a steel grid.
Air Diffusers: In most biological wastewater treatment plants air diffusers frequently cause problems. Air diffusers are expensive and periodical replacement is necessary, often with relatively short intervals. In order to exploit the oxygen in the air as much as possible air diffusers have been developed to produce micro- bubbles. Today this type of air diffusers is successfully used in traditional activated sludge systems. The same type of air diffusers has also been applied in systems with fixed film technology, however, without showing the same good results. The reason for this is that micro-bubbles do not transport as much water as desired upward through the filter media. Consequently, the waste water does not get in contact with the bacteria on the filter and treatment capacity is therefore reduced. It is well documented in numerous wastewater treatment plants and aquaculture systems that the phenomenon is reinforced in reactors based on fixed film technology. These generally use approx. 30% less air when compared to activated sludge systems. It is important that the BIO-BLOK® media function optimally. In this context, choice of air diffuser system must be emphasised. Choosing the wrong type of air diffuser could prove expensive both to buy and to operate and air diffusers have substantial influence on the treatment capacity of the BIO- BLOK®.
7
Stirring: It is extremely important that the waste water is properly stirred so that the water gets in contact with the bacteria on the filter media. Therefore, air diffusers developing so big bubbles that this requirement is meet should always be applied.
Examples of good stirring
Grating made of stainless steel and PVC air diffuser system
Example of Aromatic air diffuser system
8
Content of Oxygen: The concentration of oxygen in an aerobic filter should always be higher than 6mg/l. If the oxygen concentration is under 4mg/l, the efficiency of the wastewater treatment plant will deteriorate considerably.
Temperature: Temperature has a significant influence on biological processes. Further, at temperatures above 35 °C, nitrification is more difficult. At temperatures above 40 °C, aerobic heterotrophic decomposition of organic matter and de- nitrification cannot take place. Temperatures between 35 and 40 °C might cause big problems, as the bacteria populations that cannot be decomposed thermophilic will be completely inhibited.
The curves in fig. 1 and 2 describe Biological Oxygen Demand (BOD) and Ammonia (NH4+) degradation rates with BIO-BLOK® media as a function of temperature. The process water must not contain critical levels of biologically toxic substances, and the BOD:N:P ratio should be approx. 100:5:1.
pH: The pH value in the wastewater should be between 6.5 and 8.25. At pH values below 6 and above 9 decomposition rates are inhibited.
Fig.2: BIO-BLOK fixed film technology, NH4
reduction as a function of water temperature
0
0.2
0.4
0.6
0.8
1
1.2
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25
Temperature (degrees Celsius)
reduction as a function of water temperature
0
5
10
15
20
25
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25
Temperature (degrees Celsius)
9
Decomposition in a Submerged, Aerated Filter Depends on the Following: * Temperature of the waste water. * The biological capacity of the waste water to decompose. * The residence time of the waste water in the filter. * The biological accessible area of the filter media per m3. * The oxygen stress in the waste water (type and number of air diffusers). * The wastewater flow through the filter. Depending on above, the following decomposition speeds can be expected by a temperature of waste water from 15 – 25 o C: * Decomposition of BOD7 without nitrification 10 – 15gr BOD/m2 x d * Decomposition of BOD7 with nitrification 4 – 8gr BOD/m2 x d * Decomposition of ammonia under oxygen limitation 1 – 2gr NH4-N/m2 x d
Indicative Decomposition Speeds for Biological Processes: Water Ammonia (> 3mg/l) BOD5 Temperature (gr/m2 x day) (gr/m2 x day) 0 0 0 2.5 0.15 3.9 5.0 0.30 7.8 7.5 0.40 10.4 10.0 0.50 13.0 12.5 0.60 15.0 15.0 0.70 17.0 17.5 0.80 18.5 20.0 0.90 20.0 25.0 1.00 22.3 Above figures show the decomposition speeds that, based on the wastewater temperature, can be expected in the BIO-BLOK® filter media provided that the optimum conditions are present in the filter. We draw your attention to the fact that for ordinary waste water, optimum biological decompositions rarely occur for a long period of time. Therefore, depending on the physical and biological conditions in the wastewater treatment system in question, a slower biological decomposition can be expected in practice. The optimum conditions for a well-functioning filter are as follows:
1. That the filter media has a large accessible surface on which the actual bacteria can grow (m2 filter surface / m3 filter media).
2. That the waste water has a sufficiently good contact to the filter media, which can be created through good aeration or good irrigation.
3. That there are no toxic matters or other matters in the supplied waste water which might inhibit the biological decomposition.
10
4. That the waste water, as required, has been pre-treated, i.e. sedimentation, filtration or another form of pre-treatment.
5. That the volume of waste water corresponds to the volume for which the treatment plant has been dimensioned.
6. That the waste water’s retention time in the treatment plant is sufficient.
7. That the wastewater load on the biological filter is as uniform as possible – i.e. there should be compensation basins in the plant or the waste water should be recirculated.
8. That the factual waste water temperature is the temperature for which the wastewater treatment plant has been dimensioned.
9. That the waste water contains the right ratio of organic matters, nitrogen and phosphorus so that the wanted bacteria can establish: (BOD : N : P = 100 : 5 : 1)
10. If the waste water contains big volumes of salt, this will result in a considerably lower biological decomposition.
Nitrification: Nitrification is not easily achieved; many factors have an important impact on the actual decomposition rate for the specific effluent - * Temperature * Organic load * Composition of the effluent * Level of oxygen in the effluent * The level of ammonia in the effluent, which influences the decomposition per m2. If the ammonia
level > 3mg/l, the decomposition will be higher per m2 surface than if the ammonia level is < 3mg/l.
Speed of nitrification as function of the ammonia concentration in the outlet in a clean nitrification trickling filter,
which follows biological treatment for removal of BOD5.
Georg Jensens Vej 5 – DK-9800 Hjørring – Phone: +45 98 92 21 22 – E-mail: [email protected] – www.expo-net.com
If it is a matter of ammonia reduction, the following additional conditions also have to be fulfilled:
11. That the wastewater load on the biological nitrifying filter is less than 10mg BOD / l.
12. That the content of oxygen in the waste water is as high as possible, i.e. the content of oxygen has to be higher than 4mg/l.
All the above conditions have to be fulfilled in order to achieve the previously mentioned indicative decompositions. If increased decompositions are requested, more of the mentioned conditions have to be improved considerably. If these decomposition figures should be upgraded, it should be the owner or the project supervisors who are responsible for doing this, because they have the ability of changing and controlling the above 12 conditions.
Sludge Production: In submerged, aerated filters in which the bio-reactor is constructed of minimum 4-6 compartments connected in series, the following sludge production can be expected: Maximum 0.1 – 0.333kg SS/kg decomposed BOD. By comparison a sludge production of approx. 0.8kg SS/kg decomposed BOD is estimated for activated sludge systems.
09-06-2020
Wastewater Treatment
Installation Instructions
Product information: As a result of many years of R&D and extensive experience with polyethylene extrusion techniques, EXPO-NET Danmark A/S has developed a structured filter media. The media has proven extremely efficient in biological treatment of domestic sewage, industrial wastewater and process water within aquaculture industry. The media is made from the environmentally friendly material polyethylene and consists of net tubes, which are welded together to form a square block. The unique surface structure of the many net tubes provides a large accessible surface area for enhanced biological growth on the filter media.
Table 1: BIO-BLOK® media – overview
Type Application Surface
structure Area of
BIO-BLOK® 100 BOD Rough 70% 90% 67.5mm 54x54x55cm
BIO-BLOK® 125 BOD Rough 67% 89% 55mm 55x55x55cm
BIO-BLOK® 150 Ammonia/BOD Rough 64% 88% 55mm 55x55x55cm
BIO-BLOK® 200 Ammonia/BOD Rough 60% 82% 55mm 55x55x55cm
BIO-BLOK® 300 Ammonia/BOD Rough 51% 72% 36.6mm 55x25x55cm
Due to the natural characteristics of extruded products, all measurements are approximate.
The filter media BIO-BLOK® is used for all kinds of biological treatment of industrial wastewater, domestic sewage and process water in the aquaculture.
Mode of Operation: Future construction, refurbishment or upgrading of biological wastewater treatment plants is a matter of optimizing living conditions for the micro-organisms. I.e., the bacteria etc. must thrive on the substrate in order to work well and "do the water treatment job". The surface of BIO-BLOK® filter media acts as substrate for specialised bacterial strains and other micro-organisms which in turn are able treat and degrade a wide range of wastewater qualities. The treatment capacity of a bioreactor generally depends on the quantity of bacteria that the filter media can sustain. The larger the specific biologically active surface area is the larger the bacterial population. When micro-organisms (biological film or biofilm) grow on a level surface, the specific surface area will remain constant even with the establishment of a thicker biofilm.
BIO-BLOK® filter media
2
The BIO-BLOK® media, however, is designed as a helical structure with oval threads. If the threads become thicker due to growth in the thickness of the biofilm, the specific biologically active surface increases correspondingly. The principle is illustrated below.
During high load periods on the filter media, the biofilm will grow thicker and the specific biologically active surface of the filter will increase considerably. Hence, the biological decomposition rate increases. In practice, this means that wastewater treatment plants constructed with BIO-BLOK® filter media do not only have larger capacity but also have enhanced resilience and flexibility towards fluctuations. Therefore, BIO-BLOK® reactors are able to adjust to the overloads which typically occur in most wastewater treatment plants.
Choice of BIO-BLOK® in connection with BOD reduction The bacteria that reduce and decompose organic substances always develop a thick biofilm. The thickness of the biofilm depends on how polluted the water is and the thickness of the hydraulic surface of the filter media in the actual system. The correct choice of BIO-BLOK® filter media therefore depends on the accessible area in the net mesh structure of the block when biofilm grows on the media. In connection with reduction and decomposition of organic substances (BOD), a biofilm thickness of approx. 2 mm usually develops and it is this thickness that is used in connection with dimensioning. The most effective types of BIO-BLOK® for this application are BIO-BLOK® 100 and BIO-BLOK® 125, as these two types allow for biofilm up to 4mm before the mesh hole clogs with biofilm. This means that you have to calculate with the values mentioned in Table 2, when dimensioning filters for BOD reduction. If you are certain that the biofilm will seldom grow to more than 2mm, you can naturally choose other BIO-BLOK® filter media types and thus get a smaller system or a higher decomposition and capacity. This means that you can calculate with the values mentioned in Table 2, when dimensioning filters for BOD reduction.
Choice of BIO-BLOK® in connection with ammonia reduction
Bacteria that reduce ammonia always develop a thin biofilm. The precondition for ensuring these bacteria developing is that as much BOD load as possible is removed; the reason for this is that the nitrifying bacteria grow much slower than the BOD reducing bacteria. As only a thin biofilm then develops, it is possible to choose a BIO-BLOK® type with more mesh strings and consequently
3
smaller holes in the mesh “wall”. The most efficient types of BIO-BLOK® for this application are BIO- BLOK® 150, BIO-BLOK® 200 and BIO-BLOK® 300. This means that you should calculate with the values mentioned in Table 2 when dimensioning filters for BOD reduction or nitrifying filters: Table 2: Specific biologically active surface area for BIO-BLOK® filter media
Filter type Application Thickness of biofilm
1mm 2mm 3mm 4mm
BIO-BLOK® 200 Ammonia/BOD 312m2/m3 426m2/m3
BIO-BLOK® 300 Ammonia/BOD 360m2/m3 460m2/m3 560m2/m3
Due to the natural characteristics of extruded products, all measurements are approximate.
Sludge Production Above Table 2 shows that when applying BIO-BLOK® filter media, there will always be a big, active biomass in the treatment plant with a relatively thick biofilm, depending on where in the process the actual filter media is placed. This means that the sludge age will be considerably higher than in activated sludge systems, resulting in a significantly lower sludge production. Estimated sludge production in these systems would be 0.1 – 0.33kg SS/kg decomposed BOD. Since the sludge age in the BIO-BLOK® media is high, it will also result in development of bacteria in the biofilm, which can decompose organic matters that decompose slowly such as medical residues etc., which is difficult in activated sludge systems. By comparison, the sludge production in an activated sludge plant is about 0.8kg SS/kg decomposed BOD.
Installation of BIO-BLOK® Filter Media: In submerged aerated reactors BIO-BLOK® filter media is always installed with the net tubes placed vertically.
BIO-BLOK® is easily cut into the desired shape with a saw since the net tubes are welded together only at the tube ends. BIO-BLOK® filter media can therefore be adjusted to any tank design.
4
Bio-Reactor Design: It is an advantage for the biological processes to divide the bio-reactor into compartments connected in series. Depending on the size of the reactor this is normally between 3 and 8 compartments. In the compartments different bacterial cultures will develop depending on the composition of the supplied waste water. E.g. in the first compartments upstream, bacteria which decompose organic matter will have preference. In the later compartments nitrifying bacteria will normally dominate. Air supply system and grating on which the BIO-BLOK® is positioned is installed at the bottom of the compartments. Each compartment should have separate air supply in order to adjust the quantity of air supply for the individual compartment. The possibility to aerate the filter media heavily is convenient from an operational point of view and will also provide the means for easy backwash of the media should this prove necessary. The height of filter media may vary from two to many layers of BIO-BLOK®. As a rule of thumb, BIO- BLOK® filter media installed in four layers, corresponding to 2.2 m, will provide the best operational economy for the air blower. In order to make sure that the tube ends of the BIO-BLOK® are positioned straight over each other, connection kits can be used. Normally two connection kits are used in each joint/BIO-BLOK® in the edge of the bioreactor.
Plan of bio-reaktor, example
5
The top of the BIO-BLOK® is normally minimum 20cm below water level.
Please note that the partition walls of the basin must be placed to the bottom and placed above the water surface. In this way, the waste water can achieve the best contact with the filter media. The inlet and oulet should usually be placed in top and bottom as far apart as possible. The size of the inlet and outlet should be about twice of the main inlet size. The distance from the air diffusers to the bottom of the BIO-BLOK® material depends on the type of air diffusers (and the quantity of air) being used. It is important that the bottom of the BIO-BLOK® is positioned at a distance where the air bubbles are spread efficiently and distributed over as much of the BIO-BLOK® surface as possible. The distance is typically from 10 to 25cm.
Uplift Pressure and Weight: BIO-BLOK® filter media is made from the environmentally friendly material polyethylene. The type of BIO-BLOK® is decisive for the uplift pressure and the weight of the filter media. The uplift pressure can be counteracted with a girder system in order to keep the BIO-BLOK® units in place.
Water surface
The distance depends on the choice of air diffusers.
The filter height appears by using whole, vertically positioned BIO-BLOK®. Standard height is 55cm. Can be produced in heights from 40 to 120cm as per agreement.
Bottom
Bottom grating
Top grating
Example of installation of BIO-BLOK® units by means of a bottom grating and top girders.
Water inlet
Water outlet
Air diffusers
Weight/m3 BIO-BLOK® 100 62.00kg/m3 BIO-BLOK® 125 66.00kg/m3 BIO-BLOK® 150 69.00kg/m3 BIO-BLOK® 200 74.00kg/m3 BIO-BLOK® 300 100.00kg/m3 BIO-BLOK® Weight without Biofilm Coating:
Weight Weight/m3 BIO-BLOK® 100, 54 x 54 x 55 cm 7.43kg 46.00kg/m3 BIO-BLOK® 125, 55 x 55 x 55 cm 9.01kg 54.00kg/m3 BIO-BLOK® 150, 55 x 55 x 55 cm 9.97kg 60.00kg/m3 BIO-BLOK® 200, 55 x 55 x 55 cm 11.41kg 69.00kg/m3 BIO-BLOK® 300, 55 x 25 x 55 cm 8.03kg 106.00kg/m3 As it is a matter of extruded products, all measurements are approximate.
In order to design and calculate the bottom grating system, it is recommended to use a BIO-BLOK®
maximum weight (including biofilm) of 300kg/m3. This weight, however, will only occur in situations where the BIO-BLOK® units are clogged due to operational accidents and the water in the reactor has to be pumped out for maintenance purposes. To optimise the self-cleaning properties of the BIO-BLOK® media, the carrying girders of the bottom grating system should not be so wide that they cover a BIO-BLOK® tube opening (Ø 55mm). As top grating in smaller reactors, 20 x 20cm steel grid fixed onto the side walls can be used. In larger reactors, girders which further absorb the upward forces (uplift pressure) can be used in combination with a steel grid.
Air Diffusers: In most biological wastewater treatment plants air diffusers frequently cause problems. Air diffusers are expensive and periodical replacement is necessary, often with relatively short intervals. In order to exploit the oxygen in the air as much as possible air diffusers have been developed to produce micro- bubbles. Today this type of air diffusers is successfully used in traditional activated sludge systems. The same type of air diffusers has also been applied in systems with fixed film technology, however, without showing the same good results. The reason for this is that micro-bubbles do not transport as much water as desired upward through the filter media. Consequently, the waste water does not get in contact with the bacteria on the filter and treatment capacity is therefore reduced. It is well documented in numerous wastewater treatment plants and aquaculture systems that the phenomenon is reinforced in reactors based on fixed film technology. These generally use approx. 30% less air when compared to activated sludge systems. It is important that the BIO-BLOK® media function optimally. In this context, choice of air diffuser system must be emphasised. Choosing the wrong type of air diffuser could prove expensive both to buy and to operate and air diffusers have substantial influence on the treatment capacity of the BIO- BLOK®.
7
Stirring: It is extremely important that the waste water is properly stirred so that the water gets in contact with the bacteria on the filter media. Therefore, air diffusers developing so big bubbles that this requirement is meet should always be applied.
Examples of good stirring
Grating made of stainless steel and PVC air diffuser system
Example of Aromatic air diffuser system
8
Content of Oxygen: The concentration of oxygen in an aerobic filter should always be higher than 6mg/l. If the oxygen concentration is under 4mg/l, the efficiency of the wastewater treatment plant will deteriorate considerably.
Temperature: Temperature has a significant influence on biological processes. Further, at temperatures above 35 °C, nitrification is more difficult. At temperatures above 40 °C, aerobic heterotrophic decomposition of organic matter and de- nitrification cannot take place. Temperatures between 35 and 40 °C might cause big problems, as the bacteria populations that cannot be decomposed thermophilic will be completely inhibited.
The curves in fig. 1 and 2 describe Biological Oxygen Demand (BOD) and Ammonia (NH4+) degradation rates with BIO-BLOK® media as a function of temperature. The process water must not contain critical levels of biologically toxic substances, and the BOD:N:P ratio should be approx. 100:5:1.
pH: The pH value in the wastewater should be between 6.5 and 8.25. At pH values below 6 and above 9 decomposition rates are inhibited.
Fig.2: BIO-BLOK fixed film technology, NH4
reduction as a function of water temperature
0
0.2
0.4
0.6
0.8
1
1.2
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25
Temperature (degrees Celsius)
reduction as a function of water temperature
0
5
10
15
20
25
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25
Temperature (degrees Celsius)
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Decomposition in a Submerged, Aerated Filter Depends on the Following: * Temperature of the waste water. * The biological capacity of the waste water to decompose. * The residence time of the waste water in the filter. * The biological accessible area of the filter media per m3. * The oxygen stress in the waste water (type and number of air diffusers). * The wastewater flow through the filter. Depending on above, the following decomposition speeds can be expected by a temperature of waste water from 15 – 25 o C: * Decomposition of BOD7 without nitrification 10 – 15gr BOD/m2 x d * Decomposition of BOD7 with nitrification 4 – 8gr BOD/m2 x d * Decomposition of ammonia under oxygen limitation 1 – 2gr NH4-N/m2 x d
Indicative Decomposition Speeds for Biological Processes: Water Ammonia (> 3mg/l) BOD5 Temperature (gr/m2 x day) (gr/m2 x day) 0 0 0 2.5 0.15 3.9 5.0 0.30 7.8 7.5 0.40 10.4 10.0 0.50 13.0 12.5 0.60 15.0 15.0 0.70 17.0 17.5 0.80 18.5 20.0 0.90 20.0 25.0 1.00 22.3 Above figures show the decomposition speeds that, based on the wastewater temperature, can be expected in the BIO-BLOK® filter media provided that the optimum conditions are present in the filter. We draw your attention to the fact that for ordinary waste water, optimum biological decompositions rarely occur for a long period of time. Therefore, depending on the physical and biological conditions in the wastewater treatment system in question, a slower biological decomposition can be expected in practice. The optimum conditions for a well-functioning filter are as follows:
1. That the filter media has a large accessible surface on which the actual bacteria can grow (m2 filter surface / m3 filter media).
2. That the waste water has a sufficiently good contact to the filter media, which can be created through good aeration or good irrigation.
3. That there are no toxic matters or other matters in the supplied waste water which might inhibit the biological decomposition.
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4. That the waste water, as required, has been pre-treated, i.e. sedimentation, filtration or another form of pre-treatment.
5. That the volume of waste water corresponds to the volume for which the treatment plant has been dimensioned.
6. That the waste water’s retention time in the treatment plant is sufficient.
7. That the wastewater load on the biological filter is as uniform as possible – i.e. there should be compensation basins in the plant or the waste water should be recirculated.
8. That the factual waste water temperature is the temperature for which the wastewater treatment plant has been dimensioned.
9. That the waste water contains the right ratio of organic matters, nitrogen and phosphorus so that the wanted bacteria can establish: (BOD : N : P = 100 : 5 : 1)
10. If the waste water contains big volumes of salt, this will result in a considerably lower biological decomposition.
Nitrification: Nitrification is not easily achieved; many factors have an important impact on the actual decomposition rate for the specific effluent - * Temperature * Organic load * Composition of the effluent * Level of oxygen in the effluent * The level of ammonia in the effluent, which influences the decomposition per m2. If the ammonia
level > 3mg/l, the decomposition will be higher per m2 surface than if the ammonia level is < 3mg/l.
Speed of nitrification as function of the ammonia concentration in the outlet in a clean nitrification trickling filter,
which follows biological treatment for removal of BOD5.
Georg Jensens Vej 5 – DK-9800 Hjørring – Phone: +45 98 92 21 22 – E-mail: [email protected] – www.expo-net.com
If it is a matter of ammonia reduction, the following additional conditions also have to be fulfilled:
11. That the wastewater load on the biological nitrifying filter is less than 10mg BOD / l.
12. That the content of oxygen in the waste water is as high as possible, i.e. the content of oxygen has to be higher than 4mg/l.
All the above conditions have to be fulfilled in order to achieve the previously mentioned indicative decompositions. If increased decompositions are requested, more of the mentioned conditions have to be improved considerably. If these decomposition figures should be upgraded, it should be the owner or the project supervisors who are responsible for doing this, because they have the ability of changing and controlling the above 12 conditions.
Sludge Production: In submerged, aerated filters in which the bio-reactor is constructed of minimum 4-6 compartments connected in series, the following sludge production can be expected: Maximum 0.1 – 0.333kg SS/kg decomposed BOD. By comparison a sludge production of approx. 0.8kg SS/kg decomposed BOD is estimated for activated sludge systems.
09-06-2020