Author: Aiden

Oxygen Transfer in Stirred Fermenters


This study essay involves the measurement of the oxygen required by some plant that goes by the name P.pastoris. The experiment is carried out in the lab under controlled artificial conditions. P.pastoris needs the oxygen for aerobic reactions which are responsible for fermentation. (Silva, et al., 2012). A similar reaction occurs in plants that respire in the presence of oxygen. The specimen under observation is placed in a structure known as a fermenter while the oxygen is pumped in by a reactor which is fitted with a meter to measure the amount of oxygen being used.


The term kL.a stands for oxygen mass transfer coefficient. Oxygen mass transfer coefficient is a common term where the transfer of oxygen in stirred Fermenters is involved. It is therefore used fundamentally in facilitating the fermentation of the contents of the fermenter which more often than not contain aerobic organisms (Scargiali, Busciglio, Grisafi and Brucato, 2014).  Given the importance of the kL.a, its measurement should be done, and the outcome critically analyzed which is the aim of this experiment.


The setup of the experiment is a reactor containing oxygen and a fermenter with P.pastoris. The two apparatus are connected with pipes which are definitely small in diameter to increase the pressure of the gas. The air is then passed over the contents of the fermenter at given revolutions per minute using different impellers. An impeller is a blade that causes motion in a fluid. The rate of oxygen uptake entirely depends on the oxygen requirements of the plant. (Karimi, et al., 2013). Some plants grow massively as compared to others and as a result, require more oxygen for metabolic purposes. This is because they definitely show incredibly high rates of respiration.

The change in the rate of oxygen transfer can be varied using different impellers. One reason as to why that is done is because different organisms require different percentages of oxygen. Since the experiment is being carried out in the lab and on a small scale, there has to be a control experiment. A control experiment is usually set usually the counter of the primary test. As the name suggests, the research controls the main test by comparing the results of the primary experiment with those of the main experiment.

In the event of measurement of dissolved oxygen, oxygen electrodes do not measure the absolute amounts of dissolved oxygen instead they the partial pressure of the dissolved gas. The electrodes need to be calibrated in zero and oxygen saturated solutions to produce a scale from 0-100% dissolved oxygen tension. The experiment is executed all the conditions kept constant, and the results analyzed and interpreted accordingly. The results are calculated using a formula that will be eloquently explained under the results sections (Klein, Schneider, & Heinzle, 2013).

The above process is repeated this time using nitrogen gas in the place oxygen gas all the other conditions kept constant. The oxygen electrode is connected to an oxygen meter which still measures the rate of nitrogen being aerated. The dissolved oxygen tension is measured using a stopwatch. Working with your fermenter, you should aim to perform 3-6 runs under different conditions. Each run will involve purging the vessel before the run with nitrogen, establishing your experimental conditions, then aerating and recording the dissolved oxygen tension trace. This data will be used to estimate the kLa for that particular run.

For this to work, it is vital that you do a few things before beginning.

  • Become familiar with the actual controls at your disposal – stirrer speed and aeration rate.
  • “Zero” the system by purging with nitrogen until no further decrease is observed in the signal on the meter and on the chart recorder. If necessary, adjust the zero on the meter.
  • Now aerate the fermenter by connecting the air line. You should see the DO value on the meter begin to increase. Depending on the conditions you set, this could take 3- 10 minutes. Once there is no further increase, ensure the meter reading is 100% (adjust if necessary by adjusting the “span”).

In smaller groups, students should aim to move around the apparatus, so you get at least 3-4 measurements from at least three different fermenters. One will be a bubble column fermenter (you can only adjust flow rate of air), and the others will be stirred tanks (you can adjust stirrer speed and/or air flow rate)

For each run;

  • Zero the fermenter by purging it with nitrogen
  • Set-your experimental conditions. Record these clearly in your lab book
  • Switch air on and start your stopwatch
  • Record data until at least 80% of air saturation is reached. You will want to record DO data every 5 to 20s
  • One of your group adds this to the spreadsheet being collected on the lab computer. (Stanbury, Whitaker, & Hall, (2013).

A bioreactor will be operating in the lab with a P.pastoris culture. These will be operated under controlled temperature and with oxygen measured. You will be required to estimate the specific oxygen uptake (QO2 in mg O2 gX-1h-1) of the yeast using the following protocol

  1. Record the temperature, dissolved oxygen, stirrer speed and air flow rate
  2. Sample as shown, dilute and estimate the OD600 of the sample. Use your data from lab 1 to convert this into g DCW per liter
  • With stopwatch ready, shut off the air supply and briefly sparge the headspace with nitrogen if possible. Record the DO levels every 10s
  1. Convert the %DO readings into concentration (mg/l) values using the chart below.
  2. To estimate the QO2, you need to do the following:
  3. Estimate the bioreactor OCR (oxygen consumption rate) (mg O2 l-1h-1) (average data when the DO appears to be declining linearly.
  4. Convert the OD600 reading into gX.l-1 using the data from your other lab (as a guide, 1 OD600 should be equal to approx. 0.25-0.30 gX.l-1 for P.pastoris (Gullo, Verzelloni, and Canonico, (2014).
  5. QO2 = OCR/X
  6. Repeat the calculation for other data collected by other groups.


The rate of mass oxygen transfer is given by the formula;

(1)        OTR=dCo2,l/ dt= kLa(Co2,l*-C02,l) integrating gives the following relationship.

(2)        -ln(1-C02,l/C02,l*)=kLat

Where;                                     t = time period of measurement (h)

CO2,l* = saturated [O2] in the liquid (mM or mg l-1)

CO2,l = actual [O2] in the liquid (mM or mg l-1)

kLa = O2 mass transfer coefficient (h-1)


The measure of dissolved oxygen tension is given by the formula;

DOT=100*C02,l/C02,l* , therefore





The results that were obtained after the experiment were fed into an excel sheet. Using the formula given above the rate of oxygen transfer and dissolved oxygen transfer can be calculated by merely substituting the results into the equation. In this case, the following results were used to calculate the rate of oxygen uptake by the P.pastoris.


Table 1: Oxygen Uptake; Best Group in the World

Time3.00 P.M 078.3
OD14.1 1078.2
WCW22.1 2076.6
pH5.8 3073.2
Temperature28.2 4068.4
Airflow Rate (L/min)2 5062.4
Stirrer Speed (rpm)900 6055.8

Substituting the corresponding values in the formula elaborately estimates the rate of oxygen transfer. As for the dissolved oxygen tension, the following results carried the day.


Table 2: Dissolved Oxygen Tension (DOT); Best Group in the World


Airflow Rate (L/min333
Stirrer Speed (rpm)10007031150
Time (s)dO2 (%)dO2 (%)dO2 (%)
50 69.2 
55 75.8 
60 81.1 


Using the formula, DOT=100*C02,l/C02,l* the estimated value of the dissolved oxygen tension can be estimated.



Oxygen supports life in that the gas is involved in many important processes that is crucial for life in this case fermentation. Fermentation takes place through aerobic respiration in the presence of oxygen. On a few occasions agents like yeast are used to speed up the process as catalysts (Stanbury, Whitaker, & Hall, 2013).  In the world today is applicable in many manufacturing and food processing industries such as those that brew wine and bake bread. The fact that fermentation is crucial for living gives rise to need to study it and find out how the process takes place hence such experiments as the one discussed above.


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Air Pollution Problem in South Korea

Air Pollution Problem in South Korea

The air pollution problem in South Korea is very prominent in such a way that it supersedes other issues or causes of concern in the country like economic stagnation, natural disasters, and the threat of nuclear-armed North Korea. South Korea’s polluted air is in extents that outmatch its industrialized peers, and this is a result of domestically coal-fired power plants and vehicle emissions, as well as pollutants that come from other neighboring countries like China and North Korea.

The level of air pollution in the Asian country is so high that workers have to wear masks and sometimes remain indoors to avoid inhaling particulate matter. The high levels of concentrated pollutants in the air also mean that people cannot move around freely, or even walk their pets, or even spend a lot of time outside.

Fine Dust

The issue of fine dust has weighed in on South Koreans, thanks to industrial emissions from China and within that continue to pollute the air. The upper air stream of the country remains heavily contaminated with fine dust, and there have been discussions on creating artificial rain to address the heavy pollution in the country.

Early this year, the country witnessed high levels of fine toxic dust and particulate matter. The issue has only continued to get worse, and authorities in major cities across the Asian industrial power have instituted emergency measures with the goals of reducing emissions. Further, discussions are in progress which could lead to research on how to arrest the pollution problem.

Sources of Emissions and Pollutants

The high levels of concentrated pollutants, fine dust, and particulate matter in South Korea raise some very critical questions about how these emissions get into the atmosphere. A significant source of these emissions is China since most of the particulate matter and emissions come from industrial clusters that are on China’s east coast. Increases in industrial activity on these clusters correspond with increases in pollutants in South Korea.

The industrial activity in South Korea also remains a key source of the particulate matter in the upper airstream. Further, continued investment in China’s companies by South Korea has exacerbated the situation, since emissions and pollutants find their way back to South Korea.

Particulate matter, fine dust, and the aggregate concentrated pollutants often lead to haze and smog, which is not only detrimental to the South Korean populace, but also the country’s attractiveness to other citizens and visitors.

The Problem Is Cyclical

There are times when air pollution becomes extreme, and the atmosphere becomes full of haze and smog, and there are times when all settles down, and the level of fine dust and particulate matter reduces. When the atmosphere is full of concentrated pollutants and smog is all over, there is a lot of outrage from the citizenry, who demand government action. The situation becomes the mainstay of many media outlets.

After some time, the situation eases, and the public stops the outrage against the issue. This, coupled with other factors, has hindered concrete action against the air pollution problem in South Korea. The government also goes with the public tide and announces steps to curb the problem when there is a lot of haze and smoke and poor atmospheric conditions.

Air Purifiers and Masks

South Korea citizens have taken steps to reduce the inhalation of fine dust and particulate matter. Among the actions taken is the use of air purifiers and masks. There has been a spike in business activity associated with the manufacture of air purifiers and masks in South Korea, and companies that engage in this business have witnessed increased revenues and performing shares.

Most employees who go to work in the morning and the evening use masks to reduce the inhalation of fine dust and particulate matter.

Health Hazards

The health risks associated with air pollution in South Korea are numerous. South Koreans risk contracting lung complications and other diseases like cancer. Some particulate matter and fine dust find its way through the skin, and this results in skin ailments, and could also result in other diseases associated with the skin.

Other complications like inflammation in the brain arise from the toxic and polluted air, and folks who have to deal with it daily, due to work or other outdoor activities face the risk of contracting different assortments of diseases and complications.

In summary, the industrial activity in South Korea and more so China is contributing significantly to the air pollution problem in South Korea. South Korea, which is a member country of the Organization for Economic Cooperation and Development – a bloc of countries that stimulates global trade and economic progress. In this particular bloc, South Korea leads in terms of countries with the worst air quality.

Folks in South Korea continue to directly breath toxic air and polluted air as days go by, and this situation may lead to complications in the health of these folks, which may come to have a toll on the country’s health infrastructure.

The air pollution problem continues to inconvenience workers and other people in different capacities and stature in society since they have to live with the problem. Government efforts have not adequately addressed the issue, though continued efforts give citizens hopes of better days to come.

Three Biggest Problems With Marine Pollution

Three Biggest Problems With Marine Pollution

Marine pollution is the biggest threats to life in the ocean, and by extension, a threat to a key source of food for the human population. Plastics, discharged industrial effluent, residential waste, oil spills from tankers in the high seas and chemicals are the major pollutants in the oceans. Worth noting is that a significant portion of these pollutants is entirely the work of man and that they originate from land. There’s a lot information about earth pollutions you can read in the essay on pollutions.

Marine pollution has a devastating impact on marine life since it makes the ocean inhabitable for marine life. The result is that most marine life die due to extreme conditions, which has ripple effects in the ecosystem that lives underwater.

These areas where marine life is unsustainable are referred to as dead-zones since these regions lack of oxygen, and without oxygen, marine life cannot survive. Statistics indicate that these dead zones, cumulatively, are in the order of 500, and projections suggest that the number is highly likely to increase due to wanton marine pollution.

Disruption and Loss of Marine Life

A lot of marine pollution comes from the land. Plastics form the most significant portion of marine pollutants in the ocean. With the rise of large cities with proximity to the oceans, more and more plastics are finding their way to the oceans and seas day in day out. The numbers indicate that an upwards of eight million tons of plastic find its way to the oceans every year. What exacerbates the situation is that the disposal of plastic in the ocean is exponential, while there are intangible efforts to clean and get rid of the plastic in the polluted oceans and seas.

Microplastics in the sea are the result of washed up particles of plastics when it rains. Plastics and microplastics hugely disrupt marine life. Plastics choke aquatic flora and fauna by blocking airspaces that allow for the efficient exchange of respiratory gases. Like other living things, marine life cannot survive without air. In some cases, these plastics clog the digestive tracts of marine animals, and in some cases, turtles, in particular, become entangled in plastic debris, which inhibits their movement, thus leading to death.

Risks to Humans

The oceans and seas are a critical resource for humans. Humans depend on the oceans for fish and other aquatic food. Marine pollution affects humans in two dimensions. When microplastics or plastics find their way to the oceans and seas, they choke marine life, fish included, causing them to die and reduce in number. In such cases, there is a disruption in the supply of fish in the human food chain, and humans get little fish to consume.

Further, when these fish and aquatic animals consume these microplastics, they are ingested, and they remain in their bodies. The non-biodegradable nature of these plastics and microplastics make them stay in the animal’s body without degradation for some time, and when this gets to humans in the form of food, it could pose health risks to humans.

This could result in the emergence of unforeseen outbreaks and diseases, which could lead to poor health on the part of humans.

Disruption of Coral Reefs

Oil spills disrupt coral reefs since the thick layer of oil keeps floating on the water surface. Oil prevents air from getting into the water and equally prevents sunlight from effectively penetrating to the lower beds of the sea. Since coral reefs are essentially huge structures under the water that consist of skeletons of corals, these reefs face massive disruption in the event of oil spills, since the resources that allow for their effective growth become unavailable or little in supply.

Also, oil and toxic spills get in the feathers of birds that are part of the marine ecosystem, as well as gills of other marine animals. Oil spills are destructive to marine life, and whenever they occur, the chances are high that a lot of aquatic life will die due to the disruption of the supply of crucial resources like air and sunlight, which impairs their ability to make food and to live.

In summary, marine pollution has significant effects on marine life as well as humans. However, these effects have not been a deterrent to marine polluters. Increasingly, pollution in the oceans and seas increases daily, and the steps taken to clean the oceans do not match the rate at which these oceans take in pollutants.

Marine pollution has a substantial economic, health, and social cost to humans, and these costs, with time, will weigh in on humans. Significant drops in marine food will result in shocks and disruptions in human food, since fish and aquatic animals remain an abundant large source of food, protein in particular, for a significant number of humans.

The other effect that humans will have to bear is the emergence of diseases and outbreaks due to contaminated marine food. When oil spills happen, fish are affected. The oil sticks on their gills, and in some cases, they ingest the oil. When that fish makes its way into human food, the chances of falling ill from stomach complications or getting cancer are high.


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World Cultures

World Cultures

In a means to illustrate the different perceptions of culture, the author draws an analogy from the domesticated and undomesticated animals. Culture is the common explanation people give for the differences between societies. For instance, when two societies differ regarding material possessions, societies, historians, and anthropologists have the propensity to attribute the variances on cultural differences. According to the Anna Karenina principle, there are several qualities animals ought to satisfy to make them domesticable. As such, it is imperative to comprehend the aspects the author strived to communicate regarding civilization and culture.

Drawing from the Anna Karenina theory, there are six distinct features of domesticable animals, i.e., not carnivorous, must proliferate, comfortable living in captivity, nasty disposition, tend to panic in danger, and used to herding. Following these characteristics, the number of domesticated in quite small at around 14. Human beings can take advantage of the accessible resources. As such, if given a chance, they could breed the available animals irrespective of region. The author tries to explain why their more domesticated animals in Eurasia than Sub-Saharan Africa. It is not about the cultural variances or beliefs; instead, the difference emanates from the material differences. In other words, Eurasia was home to many animals, most of which are not available in Africa. Therefore, the fact that people from one region domesticated more animals than others does not revolve around cultural differences but the availability of the animals.

The writer purports that availability of large, domesticable animals can be ascribed to the geographical “luck of the draw” and not individual human capabilities. On the other hand, the lack of these large domesticable animals in Africa led to limited agricultural practices. As such, the author wants the reader to comprehend the fact that the variances in possessions across the globe were stimulated by the absence of some resources. Regarding civilization, some countries prospered more than others due to the accessibility of resources. Therefore, civilization and culture did not develop along the same lines.

The article is structured into three main sections. The first part dwells on the qualifications of domesticated animals, the second addressing why some animals and practices thrive in specific regions more than others, and the final part shows why civilization and culture development varied in the areas. As elucidated above, there are six key features utilized from the ancient days to identify a domesticable animal. The main reason agriculture thrives in Eurasia is due to the favorable climate. Evidently, agriculture is contingent on climate and tends to diffuse faster in areas that lie within the same latitude, since they have a similar environment. As such, farmers adopt identical techniques making the diffusion process much quicker. The author manages to merge all these three aspects to convey the central notion that material differences are to be accredited for the different practices across the globe.

Drawing from the six features of domesticable animals, all civilizations and cultures domesticated the same animals depending on whether they were available. The different domestication practices also led to the diverse agricultural activities. In the millennia that followed, countries continued to vary regarding the farming methods and types of crops among others. Evidently, some regions benefitted from a favorable climate that attracted a wide range of animal and plant species. In the process, they thrived in both practices, i.e., domestication and agriculture.