Objectives :

  1. Installing MBBR system for Hydroponics.
  2. Optimization Of Nitrate conversion.
  3. To optimize the formation of Calcium nitrate.
  4. To design MBBR system for proper growth of bacteria.

Introduction :

Nutrients required for the bacteria to grow.

The essential nutrients for a plant or any microorganism bacteria to stay alive are among Nitrogen, Phosphorous, Pottasium, Magnesium, Sulphur, Calcium, Boron, Chlorine, Manganese, Iron, Nickel, Copper, Zinc and molybdenum.

As we are working on wastewater treatment we want these microbes to grow and form a colony so that they can clear the waste in the water.Therefore we should provide them with nutrients as mentioned above.In order for the bacteria to eat these nutrients they should be water soluble.

MBBR Process :

Moving bed biofilm reactor (MBBR) is a biological technology used for wastewater treatment process suitable for municipal and industrial application. Another common name is moving bed film reactor. It was invented in the 1980s. MBBR offer an economical solution for wastewater treatment.

This method makes it possible to attain good efficiency results of disposal with low energy consumption. This process is used for the removal of organic substances, nitrification and denitrification.

The MBBR system consists of an activated sludge aeration system where the sludge is collected on recycled plastic carriers. These carriers have an internal large surface for optimal contact water, air and bacteria.

The bacteria/activated sludge grow on the internal surface of the carriers. The bacteria break down the organic matter from the wastewater. The aeration system keeps the carriers with activated sludge in motion. Only the extra amount of bacteria growth, the excess sludge will come separate from the carriers and will flow with the treated water towards the final separator.

The system can consist of a one stage or more stage system depending on the specific demands. The  specific bacteria remain in their own duty tank because of the fact that the carriers remain in only 1 tank, protected by screens.

The MBBR process can be used for a variety of different applications to attain the desired results, depending on the quality of the wastewater and the discharge regulations.

Industrial applications :
•    Capacity increase
•    Quality Improvement – BOD & Nitrogen Removal
•    Fast recovery from Process Upsets
•    Limited Footprint
•    Future Expansion
•    Minimize Process Complexity and Operator Attention

Benefits :
•    Economical very attractive
•    Compact (saves space)
•    Maintenance-friendly
•    Strong
•    High volume load
•    Simply to extend
•    Financial savings on discharge costs

The Nitrogen Cycle

Nitrogen, the most abundant element in our atmosphere, is crucial to life. Nitrogen is found in soils and plants, in the water we drink, and in the air we breathe. It is also essential to life: a key building block of DNA, which determines our genetics, is essential to plant growth, and therefore necessary for the food we grow. But as with everything, balance is key: too little nitrogen and plants cannot thrive, leading to low crop yields; but too much nitrogen can be toxic to plants, and can also harm our environment. Plants that do not have enough nitrogen become yellowish and do not grow well and can have smaller flowers and fruits. Farmers can add nitrogen fertilizer to produce better crops, but too much can hurt plants and animals, and pollute our aquatic systems. Understanding the Nitrogen Cycle—how nitrogen moves from the atmosphere to earth, through soils and back to the atmosphere in an endless Cycle can help us grow healthy crops and protect our environment.

The nitrogen cycle is a repeating cycle of processes during which nitrogen moves through both living and non-living things: the atmosphere, soil, water, plants, animals and The nitrogen cycle is a repeating cycle of processes during which nitrogen moves through both living and non-living things: the atmosphere, soil, water, plants, animals and bacteria microscopic living organisms that usually contain only one cell and are found everywhere. Bacteria can cause decomposition or breaking down, of organic material in soils.. In order to move through the different parts of the cycle, nitrogen must change forms. In the atmosphere, nitrogen exists as a gas (N2), but in the soils it exists as nitrogen oxide, NO, and nitrogen dioxide, NO2, and when used as a fertilizer, can be found in other forms, such as ammonia, NH3, which can be processed even further into a different fertilizer, ammonium nitrate, or NH4NO3.

Nitrogen Fixation

Process Design Calculation

The first questions that arose while designing were

1) What will the size of the reactor be?

2) Volume of the one MBBR?

3) Number of MBBR’s that fit in the reactor?

4) How much is the oxygen demand ?

5)What is the amount of mass transfer ?

6) Is there a stirring necessity?

Also while designing, following are the considerations to be made:-

  • Flow Rate
  • BOD(biological oxygen demand)
  • Depth of the liquid in the tank
  • SALR(surface area loading rate)
  • Media surface area
  • Media fill volume

Experimentation:-

3 Experiments were set up at Vigyan ashram Soil testing lab. Each Experiment had Different Volume of the biofilm carriers and the consortium of bacteria. And in each experiment 1g/L(1000 ppm) Of urea was added.

The parameters that were taken into consideration while designing the MBBR experiment 1 are as follows

  1. Precise weight of One Biofilm Carrier = 1.093 gms
  2. Weight of one 1000 ml Beaker = 88 gms
  3. Volume of The biofilm carriers = 500 ml (50% by volume)
  4. No of biofilm carriers inside the reactor = 73
  5. Weight of reactor with the biofilm carriers = 168 gms
  6. Weight of biofilm carriers = 88 gms
  7. Volume of water added = 850 ml
  8. Volume of bacteria added = 150 ml

Experimental Data:-

Data as on 28 August 2020

  1. TDS (Total dissolved solids) = 185 ppm
  2. EC (Electrical Conductivity) = 395 microS/cm
  3. pH = 7.5
  4. Temperature = 27 degree celsius

Pump calculations:-

  1. Voltage supply = 230 V AC
  2. Frequency = 50 Hz
  3. Power supply (as mentioned on the pump) = 3W
  4. Power supply (Actual) = 2.5W
  5. Flow Rate =3L/min
  6. Pressure = 20 KPa
  7. Daily Energy consumption = 2.5 x 24 = 60 Wh
  8. Monthly Energy consumption = 60 x 30 = 1.8 KW
  9. Rate of One unit = 7 rupees
  10. Monthly Charges = 1.8 x 7 = 12.6 rupees

The parameters that were taken into consideration while designing the MBBR experiment 2 are as follows

  1. Precise weight of One Biofilm Carrier = 1.093 gms
  2. Weight of one 1000 ml Beaker = 88 gms
  3. Volume of The biofilm carriers = 300ml (30% by volume)
  4. No of biofilm carriers inside the reactor = 44
  5. Weight of reactor with the biofilm carriers = 136.092g
  6. Weight of biofilm carriers = 48.092 gms
  7. Volume of water added = 800 ml
  8. Volume of bacteria added = 200 ml

Experimental data for Experiment 2

Data as on 30 august 2020

  1. TDS (Total dissolved solids) = 337 ppm
  2. EC (Electrical Conductivity) = 699 microS/cm
  3. pH = 5.59
  4. Temperature = 25.2 degree celsius

The parameters that were taken into consideration while designing the MBBR experiment 3 are as follows

  1. Precise weight of One Biofilm Carrier = 1.093 gms
  2. Weight of one 1000 ml Beaker = 88 gms
  3. Volume of The biofilm carriers = 400 ml ( 30% by volume)
  4. No of biofilm carriers inside the reactor = 57
  5. Weight of reactor with the biofilm carriers = 153.15 gms
  6. Weight of biofilm carriers = 63.9 gms
  7. Volume of water added = 800 ml
  8. Volume of bacteria added = 200 ml

Experimental data for Experiment 3

Data as on 30 august 2020

  1. TDS (Total dissolved solids) = 354 ppm
  2. EC (Electrical Conductivity) = 755 microS/cm
  3. pH = 5.65
  4. Temperature = 25.2 degree celsius

Results:-

As seen from the table The Nitrate conversion for 50% by volume of biofilm carrier the nitrate conversion reaches to 100 ppm in 5 days. Now when we see the conversion it can be interpreted as follows:-

Weight of Urea is 60 g/mol . And urea has 46.66% of nitrogen in it. Now we have added 1g/L of urea in the solution. Therefore we have added 1000 ppm of urea in the solution out of which nitrogen is 460 ppm. The nitrate formed was 100 ppm. Now the % of nitrogen in nitrate is 22.5%. Therefore the conversion of nitrogen to nitrate is 4.891%.

Now for the other two experiments no formation of nitrate was seen . This may have happened because

  1. Lower amount of dissolved oxygen
  2. The consortium of bacteria in the solution was inactive
  3. Proper mixing of the biofilm carrier may not have happened.
  4. Biofilm detachment because of constant collision and attrition.
  5. The bubbler couldn’t provide adequate amount of turbulence needed.

After obtaining the following results What I interpreted as the factors affecting the MBBR performance would be:-

1) Percentage of Reactor Volume comprised of Biofilm Carrier:-

With an increasing fill fraction the suspended growth concentration decreases. However low suspended biomass can lower the MBBR removal efficiency. Since they have a major role in enzymatic hydrolysis and bio flocculation in the reactor. It is observed that a fill fraction of 35% had a higher COD removal . Whereas a 66% fill fraction had slightly better nitrification due to higher concentration of slow growing nitrifiers which could be retained in the reactor.

2) Specific Surface Area:-

Typical biofilm concentration ranges from 3000 to 4000 TSS/m3. The effective area of the MBBR carrier medium is reported to be 70% of the total surface area due to less attachment of biofilm on the outer perimeter of media.

3)Presence of Dissolved Oxygen:-

DO should be kept higher than 2 mg/L for efficient COD removal. By decreasing the DO from 2 to 1mg/L can bring down the COD removal efficiency by 13%. On the other hand Increase in the DO from 2 to 6 mg/L increases the COD removal efficiency by 5.8%.

4)Flow and mixing conditions:-

The nature of the carrier media used requires development of a thin evenly distributed and smooth biofilm to enable transport of substrate and oxygen to the biofilm surface. Adequate turbulence also maintained the flow velocity necessary for effective system performances. Collision and attrition of media in the reactor causes biofilm detachment from outer surface of the media . Therefore fins are provided.

5)Biofilm Development:-

The diff between biofilm growth and attachment on one hand and detachment processes on the other can be defined as biofilm development. Which depends on adsorption and desorption of microorganisms to the solid surface, biofilm growth, thickness, biofilm adhesion as well as detachment to and from the solid surface or media. . The microorganisms grow on a small carrier element that move freely with water in the reactor. Due to erosion caused by frequent collision between the carrier elements very little biofilm grows on the outside surface of the carriers.

After finding these factors two new experiments were set up for 30 and 40% by volume of biofilm carriers by changing the consortium of bacteria and keeping the parameters same.

The parameters that were taken into consideration while designing the MBBR experiment 4 are as follows

  1. Precise weight of One Biofilm Carrier = 1.093 gms
  2. Weight of one 1000 ml Beaker = 88 gms
  3. Volume of The biofilm carriers = 300ml (30% by volume)
  4. No of biofilm carriers inside the reactor = 44
  5. Weight of reactor with the biofilm carriers = 136.092g
  6. Weight of biofilm carriers = 48.092 gms
  7. Volume of water added = 800 ml
  8. Volume of bacteria added = 200 ml

Experimental data for Experiment 2

Data as on 3 september 2020

  1. TDS (Total dissolved solids) = 680 ppm
  2. EC (Electrical Conductivity) = 1302 microS/cm
  3. pH = 8.56
  4. Temperature = 27.1 degree celsius

The parameters that were taken into consideration while designing the MBBR experiment 3 are as follows

  1. Precise weight of One Biofilm Carrier = 1.093 gms
  2. Weight of one 1000 ml Beaker = 88 gms
  3. Volume of The biofilm carriers = 400 ml ( 30% by volume)
  4. No of biofilm carriers inside the reactor = 57
  5. Weight of reactor with the biofilm carriers = 153.15 gms
  6. Weight of biofilm carriers = 63.9 gms
  7. Volume of water added = 800 ml
  8. Volume of bacteria added = 200 ml

Experimental data for Experiment 3

Data as on 3 september 2020

  1. TDS (Total dissolved solids) = 395ppm
  2. EC (Electrical Conductivity) = 835 microS/cm
  3. pH = 5.52
  4. Temperature = 27.2 degree celsius

Results:-

Possible reasons for the Low conversion of Ammonia to Nitrate could be incorporated as follows

Anaerobic Ammonia Oxidizing (Annamox) Bacteria

These Bacteria can oxidize Ammonia Using Nitrite as the oxidant and form Nitrogen gas as an end product.

  • First Nitrite is reduced to Nitric oxide by nitrate reductase.
  • Hydrazine synthase combines with ammonia and nitric oxide to form highly volatile and reactive hydrazine.
  • Hydrazine is oxidized to nitrogen gas by hydrazine dehydrogenase releasing four electrons that are used to provide energy to the early steps of the pathway.

Inhibition due to Free ammonia(FA) and Free nitrous acid(FNA)

High concentration of Free ammonia can inhibit nitrification. In Aerobic nitrifying reactors operated under constant aeration and agitation. Ammonia can be lost from the system by volatization. On the other hand the ammonia oxidation to nitrate produces protons and leads to acidification of environment. this decrease in pH value can inhibit nitrification by diminishing the availability of ammonia. The ammonia will be in the solution as the ammonium ion (NH4+) and unionized ammonia (NH3). This will be in equilibrium that is affected by pH of the solution. When pH increases the concentration of ammonia increases

The oxidation of ammonia to nitrite is a relatively fast process then the oxidation of nitrite to nitrate. Nitrite depresses both respiration and growth of nitrosomonas. Nitrobacter is sensitive to ammonium ion but even more to free ammonia. As nitrite oxidation occurs there is a release of H+ ions that decrease the pH to an extent related to the buffering capacity of the system. The nitrite formed will exist in equilibrium with unionized Nitrous acid (FNA). As the pH decreases the concentration of (FNA) increases.

Two processes work to reduce (FA) inhibition. As the pH decrease the ammonia equilibrium will adjust and concentration of (FA) will decrease. In addition the total ammonia concentration decreases as it is oxidized to nitrite. These reductions relieve inhibition of nitrobacters caused by (FA) promoting oxidation of Nitrite to nitrate.

The ranges of (FA) concentration that begin to inhibit the nitrifying organisms are

  • (FA) inhibition to nitrosomonas 10 to 150 mg/l
  • (FA) inhibition to nitrobacter 0.1 to 1 mg/l

The inhibition of nitrifying bacteria initiates at concentration of (FNA) between 0.22 and 2.8 mg/l

Effect of HRT (Hydraulics retention time)

As seen from the results it is clear that the oxygen uptake by bacteria is less (Day1 to Day3) due to the less nitrate conversion. As the acclimatization time for 30% by volume of biofilm carriers increased the autotrophic nitrifying bacteria started to flourish and started to convert the free ammonia to nitrate. This optimum growth phase was observed during ( Day4 to Day 7/8). After 7/8 days bacteria entered the declining phase as there was lack of sufficient organic matter for their survival resulting in a gradual decrease in the trend line.

Nitrogen loss by Ammonia volatization

Aeration and mixing increase the volatization rate especially when the pH of solution is above 8. Ammonia volatization rate depends on the Ammonia concentration. Since the pKa of ammonia is 9.25 at 25 degree celsius ammonia concentration is relatively low at neutral pH . At high pH ammonia volatization rate is affected by Total ammonia nitrogen(TAN) i.e the ammonium ion and ammonia molecules together, concentration, temperature, aeration rate. Alkaline pH and higher temperature favours the unionized gaseous form. At pH 9.3 50% of ammonia is unionized at pH 8.3 about 10% and pH 7.3 about 1% is unionized. Volatization is thus enhanced at elevated pH due to equilibrium relationships and the resultant increase in the partial pressure of ammonia gas.

Nitrogen loss via Denitrification

Denitrification is carried out by various archaea and facultative heterotrophic bacteria such as achromobacter, aerobacter, acinetobacter, bacillus, brevibacterium, flavabacterium, pseudomonas, protus and microocus. These use nitrate as an electron acceptor and utilize the dissolved organic carbon in the water. Carbon limitation affects the activity of denitrifying bacteria which causes the accumalation of intermediate product such as NO and N2O and also results in Nitrate reduction to ammonium ion via the dissimilatory nitrate reduction to ammonia(DNRA).

Nitrogen loss via assimilation of heterotrophic bacteria

Heterotrophic bacteria co exist with nitrifiers and become dominant when organic carbon concentration or C:N ratio increases leading to generation of high quantity of nitrogen loss in anoxic condition and excess microbial biomaas in the form of sludge. Heterotrophs utilize Ammonium ion, nitrate, and organic carbon for cell growth so that they will be more dominant when organic carbon is available due to higher growth rate than the autotrophs. The high growth rate results in dominance of heterotrophs over autotrophs at high C:N ratio. Heterotrophs grow by consuming dissolved organic carbon under aerobic conditions. In a system where heterotrophs and nitrifiers coexist the rates of nitrate production,(TAN) consumption were reduced by 24%,56%,73% at C:N ratios of 0.5, 1, 1.5 respectively.

About Bacterial Culture

Autotrophic And Heterotrophic bacteria

Chemosynthetic autotrophic bacteria derive their energy from inorganic compounds . And heterotrophic bacteria derive their energy from organic compounds, Nitrifying bacteria are primarily autotrophs which consume Carbon di oxide and obligate aerobes which require oxygen to grow. In the autotrophic nitrification process as opposed to heterotrophic processes very small amount of bacterial biomass are produced. And because of the relatively slow maximum growth rate of nitrifying bacteria in a suspended growth process it becomes very easy to wash out the nitrifying bacteria as opposed to a fixed film system.

Systems having a consortium and C:N ratios high, heterotrophs are capable of outperforming and significantly inhibiting nitrification. At C:N ratios between 1 and 2 there is a 70% reduction of (TAN) removal rate as compared to C:N =0

High concentration of heterotrophs in biofilters drastically lowers the Dissolved oxygen and promotes anoxic condition which causes denitrification and nitrogen loss via N2O and N2 gas.

Nitrifying bacteria Require Alkaline pH (7 to 8.5) for optimal growth. At pH > 8.5 nitrobacter may be inhibited more than nitrosomonas resulting in accumalation of nitrite.

Effect of pH, Do, HLR on the system

Closed system:-

As the reasons stated above and the results obtained give us a clear indication that the amount of ammonia that was in the system has been mostly lost due to volatization. And the bacterial cultures need to be optimized. And therefore there was a major need for us to shift to a closed system. And since there are heterotrophic bacteria in the solution which rely on the organic carbon source, the nitrogen source of changed from urea to liquor ammonia.

Experimentation:-

An experiment was setup at Vigyan ashram soil testing lab, Pune. A pressure cooker of 3L capacity was chosen as a reactor. The complete setup was of 1L . And the pump with a diffuser at the end of it were kept inside the reactor so that the pump generates the air that is inside the reactor. And therefore it forms a completely closed system. 500 ppm of liquor ammonia was added to the system.

Experimental data:-

  1. Precise weight of One Biofilm Carrier = 1.093 g
  2. Volume of The biofilm carriers = 500ml (50% by volume)
  3. No of biofilm carriers inside the reactor = 61
  4. Weight of biofilm carriers = 66.673 gms
  5. Volume of water added = 820 ml
  6. Volume of bacteria added = 150 ml

Experimental data as on 27/9/20

  1. TDS(Total Dissolved solids)=696
  2. EC( Electrical Conductivity)=1490
  3. pH=8.11
  4. Temperature=26.3 degree celsius

Amount of oxygen In the reactor:-

As discussed earlier the pump will produce the air that is inside the reactor. Therefore the amount of oxygen in the system would fall short in some amount of time. And the amount of oxygen in the reactor that should brought inside the reactor for proper nitrification is as follows

The reaction of ammonia reacting with oxygen is as follows

  1. The amount of oxygen required for complete oxidation of ammonia to nitrate is = 1881mg
  2. The amount of air inside the reactor is = 2 Lit
  3. The amount of air inside the reactor in grams = 2*1.22=2.44 gms
  4. The amount of oxygen inside the reactor= 2.44*0.21 =0.5124gms=512.4mg
  5. Therefore to cover the amount of oxygen in the reactor for complete nitrification = 1881/512.4mg=3.67 times.

Results:-

As seen from the table there is no significant formation of nitrate in the reactor. And the amount of ammonia in the reactor is huge and is not deteriorating with time. Therefore as discussed earlier the inhibition of ammonia to nitrate forming bacteria starts around 10 to 150ppm. So we decided to check that and so a new setup was done with just 100 ppm of ammonia in it and check the results.

As seen from the above table the nitrate formed was significant on the first day and then slowly goes down with ammonia. The possible reason could be that the nitrifying bacteria have a very slow growth rate and require some time to adapt to the surrounding conditions and then form nitrate. We have also seen in the previous open systems that the bacteria don’t take in oxygen on the first 2-3 days . Therefore there should be some acclimatization time for their proper growth.