Monday, 12 November 2012

To Recycle or Not To Recycle, That is The Question.

November 11th was the National Recycling day in Malaysia, a country which for the last 30 years has had one of the fast economic growing rates in south East Asia. However, according to the authorities, recycling in Malaysia is one of the lowest ones in the region by less than 10%. In this post, I would like to argue about the practice of recycling before finding out the reasons of low recycling rate and how to encourage people to start practicing it. We need to understand the advantages and disadvantages of recycling first and then decide if this practice is worth doing it or not.

It always happens to me when you talk about being green, sustainable life style, waste management and environment, the first reaction and focus of people is on recycling. Recycling without any doubt is our first action to do “something good for the Mother Nature”. It has always given us a great feeling. I still feel good and proud every time that I separate my wastes and dispose them into the specific waste bins. We all justify ourselves that because we do not litter and we do recycle, we have already paid our debt to the nature. I don’t want to talk about people’s mentality towards their wastes and how they deal with it but I would like to raise this question that “is recycling an environmental friendly practice?” Or when we proudly say that we purchase stuff that came from recycled materials, does that really make us someone who cares about the environment?

Let’s see what recycling can give us. The first benefit of recycling is conservation of material and energy. When we throw a plastic bottle, aluminium can, glass and so many other things, not only we are throwing those materials but also the energy that was used to produce those products. Therefore by recycling, we do not need to use virgin material to produce the same product (or use of less virgin materials). Studies have shown that by recycling one tonne of paper, we can save 17 trees; recycling one glass bottle would save energy to keep on a light bulb for four hours and recycled aluminium uses only 5% of the energy that it takes to create a new aluminium can.

When it comes to waste management, landfilling is the last option of waste management and another benefit of recycling is that it avoids sending the materials to the landfills. By doing that, we can increase the landfill lifespan (we can use the landfill for longer time). Recyclables like glass, plastics and aluminium take a long time to be naturally degraded as it takes 1 million years for glass and 100 years for aluminium to degrade naturally. Therefore, these items are better to be recycled than simply sent to landfills.

Due to lots of energy saving (by recycling instead of extract virgin materials), recycling reduces millions of tonnes of greenhouse gasses every year and as a result, it would mitigate the global warming impact. In addition to that, recycling makes it easier for those who are responsible for the waste disposal as they will have to deal with less amount of waste. It also causes less pollution. And the last and of course not least, recycling creates many jobs in much better environment than other options in waste management.

So recycling has pretty good environmental, economic and social benefits. But of course it doesn’t come without its dark side. Now it is good to know more about negative parts of recycling. First thing is the transportation. Anything we throw into the recycling bins needs to be transferred into the recycling facilities. The transportation itself consumes fuel which contributes to air pollution and global warming.

Recycling process consumes lots energy and resources too. When the recyclables reach to the facilities, depends on the process, it consumes water, chemicals, energy and generates greenhouse gases as well as wastewater and wastes. To have better picture we can take a quick look at a paper recycling facility. First cardboards and papers all will get mixed with water and different types of chemicals. As paper and cardboards got lots of inks, these chemicals would help to remove them and also turn them to a brighter colour. Next processes include removing the impurities and plating the paper pulp on a role and then drying. All these processes are very energy consuming and lots of water is also needed. Apart from the energy part, the wastewater from the processes contains lots of toxic and chemicals. Wastewater needs to be treated and the sludge (the leftover of the wastewater treatment) needs to be sent to special landfills (due to the existence of toxic material). It is eminent that many of these toxic and chemicals would also leak through the recycled papers; therefore the consumers will have to be careful for what purpose they should use the recycled papers. Unfortunately, I have seen that some of these papers are used to wrap food which can really threat the health of citizens. It is the same with other recyclables as well. For example, aluminium can recycling facilities consumes lots of energy to melt the used cans and turn them to aluminium bars. This type of recycling is also called up-cycling which is basically turns the recyclables back to its virgin material instead of the product itself.

So by knowing the fact that how recycling process is done, we can say that recycling is not a clean job especially when you’re dealing with toxic and chemical materials. Even though usually recycling facilities are cleaner environment in comparison with landfills (depend on the country of course) but workers are still exposed to toxics and it could seriously affect their health.

Another negative point of recycling is increasing of toxic concentration in recycled items. Unlike aluminium cans, plastic bottles for instance cannot be recycled forever as every time they are recycled, the concentration of toxic and heavy metals would increase in the new product. Therefore, it happens a lot that these items would be down-cycled which means instead of turning them to new plastic bottles they would make something with less value with lower quality. This action itself is against the spirit of recycling as it should be back into the cycle of the same product.

Now we already know some of the advantages and disadvantages of recycling. We know that recycling can save energy and material and create jobs and we are also aware that recycling also consumes energy and leaves pollution and waste behind. However, its advantages are far better than disadvantages. Recycling is in the waste management hierarchy, is though the 3rd favourable option after “reduce” which comes first and then “reuse”. Therefore, the main focus needs to be on the first two and if there is nothing we can do to reduce or reuse then recycling should be in place. As Annie Leonard the author of “The Story of Stuff” mentioned, by putting our main focus on recycling we are not changing anything as our main goal has to be on generating less waste, purchasing products that we know are environmental friendly and of course force the manufacturers to take responsibility to design products which can last much longer, be repaired easily and at the time of its disposal, gets recycled.

So always remember, we all have responsibility toward the environment we are living in. Everything we have comes from the nature and therefore, we need to be respectful to it. So first reduce, then reuse and at the end ALWAYS RECYCLE. 

Tuesday, 26 June 2012

Sustainable Production and Consumption: What is Cleaner Production and how to achieve it?

Industrial revolution without any doubt is the turning point that human conflict with the nature started. The economy growth was rapid and the hunger for consumption and production was unlashed. That caused so many disturbance and stress to the ecosystem due to the high volume of contaminants emission. In other words, the rate of polluting the nature started to overtake from the rate of degradation of the residues.

Environmental issues caused by productions and consumptions have given many people awareness to be more responsible in their life style and consumption patterns. For the last 40 years, many solutions for the emission controls have been offered and some of them have been taken seriously by many developed countries. People nowadays are familiar with green products, Eco-label, waste minimization, zero emission/waste, producer responsibility, environmental audit, environmental impact assessment, cleaner production, life cycle assessment and pollution prevention.

The first action to deal with industrial pollution was pollution control which also refers to the measurement taken to manage the pollution after it is generated. So many laws and regulations were made in order to control the pollution. However, wastes were still being generated, but the difference was that just before the release point, it got treated till the level it would meet the regulation requirements. Pollution control and waste treatment is becoming more difficult as the regulations have become more strict and tight, people are more aware of the risks and they can sue the factories. In addition the treatment and disposal cost are getting higher.

Years later, material and energy efficiency became industries and environmentalist centre of attention. So the focus was shifted from pollution control and treatment to pollution prevention also known as PP or P2. Pollution Prevention is defined as a multi-media environmental management approach which emphasizes the elimination and/or reduction of waste at the source of generation. In pollution prevention, wastes need to be eliminated or reduced from air, water, solid, time and energy. The concept is to look at all types of waste to protect the environment. Therefore, like in treatment, pollution should not shift from one medium to another but needs to be stopped at its generation source. 

There is another new term which is being used quite frequent as Cleaner Production. Pollution Prevention and Cleaner Production are slightly different but both share so many similarities. The similarity between pollution control and cleaner production is that both try to prevent waste generation at source instead treatment at the end. In addition, both should not be considered as absolute state but continuous improvement process. The only difference between P2 and CP is the sectors they are covering as CP usually applies to the manufacturing and P2 almost covers all sectors. Therefore, it can be said that PP is a broader concepts which CP is part of it.

The economic, social and environmental benefits of CP are wide. By applying the concept, manufactures can reduce their wastes (material and energy) which it would decrease the cost of disposal, increase their productivity, energy efficiency and conserve the raw materials. Minimizing the waste (hazardous, solid, liquid, heat and gas), would turn the working place to be a cleaner, healthier and safer environment and that indirectly can increase the productivity. The public image of the company would improve and that would definitely increase the sales. A factory which already practices cleaner production can easily adopt itself to more strict regulations and it would decrease the civil and criminal liability. All these actions would help the economy to move towards sustainability.

Saying all these benefits of pollution prevention would not eliminate the need of treatment. Even in most efficient systems, there is always waste as endorsed by second law of thermodynamic. LeGrega has come up with an integrated method proposed which summarizes the pollution prevention techniques from higher efficiency and better environmental practice to the lower ones. Figure below gives the options from top to down.

As it can be seen above, efficiency and priority is with waste reduction and if that cannot be achieved next would be recycling. If there is neither option for waste reduction nor recycling then the generated wastes need to be treated and then released. Reduction at source is divided in two parts, by changing the product or source control.

Unfortunately, these days many products have been designed for dump not for long term usage. Customers use them for sometimes and then when the item is broken, most of the time there is no chance to fix it so it will be thrown away which easily can consider as solid waste with all its impact on the environment. The situation becomes worst if the thrown away product contains hazardous materials and heavy metals like mercury, lead, etc. Great example is electronic devices which sometimes have over 400 toxic chemicals in them. So to reduce the waste at source, one of the good practices is to change the product to more environmental friendly type. For example, in Denmark there are pens which are made by starch (or corn), so after they are thrown away, they will be degraded easily.

Another method is to have products which will not get broken easily and will last longer. There are tractors in India that can work for years due to the material they have been used in. Again, producing things which will break easily is part of sustaining a business so there is always a market for the products. Another method is to change the product composition like in paint, photo and film industry, different types of dyes can be used which are more environmental friendly and are not considered as hazardous materials and wastes.

Changes in input material are also another method that could prevent generation of waste at source. This can be done by making the material purer or switching to materials which are neither hazardous nor toxic. For example, if a process uses 70% pure alcohol and leaves some waste but by switching to 90% alcohol there would be no waste, then it is highly recommended to use the purer alcohol even though it might cost slightly more. Another option is to use water-based solvents instead of organic ones as they might need extra treatment or need to be disposed carefully.

Technology change is also another approach that could cause less waste generation. It can be achieved by changing the process such as installing a bridge between the tanks in electroplating industries as shown in picture below.

Bridge between two tanks collect the drips and send it back to the plating tank (Ref: P. Augumothu Cleaner tech slides)

Simple changes in the equipment can eliminate the waste even if that is few drops. According to the picture above, the materials go to the plating tank and then go for the next process. If that drain bridge and drip tank wouldn't exist then the drips would be wasted on the floor. Installing a bridge and drip tank can collect the drips and send it back to the plating tank.

Another method in technology change is changing the piping system. It can be extremely helpful in factories which have boilers. Changing the pipes in a way that hot water/steam leaving the boiler would be in counter current flow with cold water coming to the boiler. As the water with high temperature (usually above 40 0C) cannot simply be released, its temperature needs to be decreased and what a better way to exchange its heat with cold water which is on its way to the boiler. That would increase the temperature of ingoing water so the boiler needs to consume less energy as the water is already in higher temperature. This method in some factories has already saved over 70% on energy cost.

GOP or Good Operating Practice is also another approach that can make the factory processes and operation very efficient and smooth and also help to reduce the waste at source. GOP can be achieved by waste segregation (prevent mixing of hazardous and non-hazardous wastes, separation of solid and liquid wastes and separation of different solvents), having proper maintenance program, constant training and awareness to staff especially how to handle the material and operate the machine in a way that has the least generation of waste. Effective supervision, encourage employees and staff to participate in this kind of programs would also help a great deal.

As it was mentioned earlier, generation of waste is eminent. So it is needed to reduce the amount of waste generation as much as possible, but when the waste is generated, the best option is to recycle it.  Recycling can be done by recovery and reuse or by reclamation.

Recovery and reuse according to the LeGrega model, the waste can go back to the original process or be the raw material in another process. An example of waste going back to the same process is like in candy factories and the shape they give to sweets. Whatever is left from the dough or other things can be used again. As it can be seen in figure below, the tray of dough is ready and the heart shape cookies are taken out. What is left of dough can be used again.

Reusing the Dough in sweet factory

Unlike the example above, some wastes cannot be used in the same process unless some treatment is done prior to reuse. Good practice is to find out if the generated waste can be used as raw material for another process. For example, if the used solvent can be used for other processes. This method is very common in industrial ecology as waste of one factory is raw material for another factory. Fly ash generated in industries can be used in the cement factory as a raw material.

Reclamation of waste is another valuable approach which extracts the valuable materials from the waste. Good example is reclamation of copper and silver from wastewater in photo industry as well as well recovery of spent nickel in oil palm industry. Sometimes by removing some toxic material and heavy metals the waste is no longer hazardous and can be disposed with much less cost.

When waste reduction and recycling is no longer possible, waste treatment comes very helpful. However, this method has its own hierarchy. First it is highly recommended to do waste separation and concentration. By separation, the volume of the hazardous waste (which requires special treatment and disposal) is reduced and then the disposal cost would be less. It also requires less recourses and energy for its treatment. Reducing the concentration of waste (removing the toxic from wastewater for example) would also change the characteristics of the waste from hazardous to non-hazardous. Waste exchange is another way when waste cannot be recycled. Waste to energy is also another method that is being practiced in different countries. Waste instead of going to the landfills will be sent to the places to be burnt and produce heat for the boilers. Generated steam from the boilers is used to generate electricity. If the quality and quantity of waste is not desirable to be used as fuel then waste can be incinerated as the volume would be significantly reduced. The last step in treatment is ultimate disposal which is sending the waste to the landfills. Of course landfills have their own environmental impacts which will be explained in other posts.

Picture below gives the best conclusion to this article.
Waste Management Hierarchy (Ref: P. Augumothu Cleaner tech slides)

It is always ideal to start from the top which is prevention, to minimize, recycle, treat and at the end dispose. Cleaner Production is any practice which stands on top of this pyramid. 

Thursday, 26 April 2012

Advantages and Disadvantages of Water Reuse and Recycle

Water is a vital element of life and there is no life without water. Life itself over 3 billion years ago miraculously started in the water. When scientists explore the other planets, they are looking for water as without it there would be no life. About 70% of the earth is covered by water and only 2.5% of it is fresh water but only 0.01% is potable. By considering the positive rate of population growth in the world, it can be said that there might not be enough water in the future for human consumption, plants and animals.  31 countries in Asia and Africa are in absolute water shortage and this number will increase to 48 in 2025. Still 2.5 billion people do not have any sewage facility. Over 80% of sickness in developing counties is caused by water pollution. These numbers are indeed shocking but they put more attention to the water issue. When I was a child, I was told that the third World War would be because of the water shortage.

People in big cities with always access to water have taken this essential element of life as granted and maybe that is the reason that even in very developed countries with material recycling rate above 60%, water recycling still has a very small percentage. There have been so many awareness campaigns regards to wiser water consumption around the world but personally I feel, till people do not experience or understand the water shortage they cannot be really wise consumers. The amount of water that we in big cities let it run from our tabs when we wash dishes, shave our face or brush our teeth might be the same amount of water a family use in a village in Africa for a week. The sad point is that the water that is being wasted in our houses has reached there at the first place with difficulties. The water was collected in catchment areas, then it was treated and next through the pipes and pumps which covers the whole city it came to our homes. After usage, through different pipes it would go back to a treatment plant and then released to the river. The fact is that still in many developed countries the same clean water goes to the toilet flush. As both water and wastewater is not cheap, there has been some recommendations and suggestion to reclaim and recycle the wastewater. There are different methods like decentralized treatment plants in building to treat the water not for drinking but for using it in the toilet for flushing. In this short paper, it is tried to discuss the advantaged and disadvantages of water reclamation and reuse.

Reusing wastewater would improve sustainability and secure the water with much less pressure on environmental sources in addition to many economic benefits. If wastewater is treated enough it can be reused for agriculture, landscaping irrigation, industrial processes, toilet flush and cooling water in power plants. The water used for agriculture and landscaping irrigation might not be proper for drinking but according to the United States EPA, there have not been any human health problems due to contact with recycled water that has been treated to the required standards. By reusing treated wastewater, of course the cost will decrease as for the mentioned examples there would not be necessary to treat the water in its highest quality. It is also great method for a country to reduce its carbon footprint as it would need less treatments and transportation of wastewater to the treatment plants. Recycling water is a great method for regions with less annual rainfall as they can conserve more water. In addition to the benefits above, it decreases the use of fresh water which can conserve the balance in ecosystem as well as less water to treat and as a result less water to discharge into the sensitive waters.

However, reusing wastewater is not without risks and it can have negative impacts on human and the environment around it. The most important factor in water reuse is hygiene and as it was mentioned earlier, water is the source of life and that includes life of so many pathogens. Pathogens are the major concerns when it comes to human health. Usually reverse osmosis is a great method as it can remove the chemicals and pathogens from the wastewater and then expose it to UV light or oxidation for disinfection. Nutrients, organics and heavy metals in wastewater are the contaminants that if not properly treated can seriously threat the human’s health and his surrounding ecosystem. Other characteristics of wastewater such as salinity, chloride, nitrogen and phosphorus are other factors than need to be considered for different purposes of water recycling. Usually household wastewater does not contain any heavy metal but the concentration of new types of chemicals like hormones and residue of the contraceptives is increasing in the wastewater and it can also have unknown impacts on the ecosystem. Another problem could be different infrastructure to separate the fresh water from the flush water in a building which would end up in higher costs.
By considering the pros and cons, water reuse would be much better even though in some aspects it might increase the costs. Water is the most important element of life and there would be no life without it. As a result, human has to do anything in its power to keep this valuable resource always available and clean. Wise man said once that we did not inherit the world from our ancestors but borrowed from our children.

Thursday, 16 February 2012

Cleaner Production (session 1)

Today I am going to start discussing the cleaner production (cleaner technology) a little bit. Of course today’s post is just a little introduction and I will expand this interesting topic in coming weeks little by little. This post is sort of the summary of the Prof Aga’s lecture and from his slides.

We usually discuss the cleaner production when it comes to the industry and industrial wastes. In a factory wastes can be divided to process waste (waste produced during the process) and non-process waste such as canteen waste (municipal solid waste characteristics), office and workshop wastes. Interesting point in process waste is that this kind of waste is also produced like the product. In other words, in addition to the product, we have also spent energy and material to produce wastes. I will explain about this in future posts.

The source of industrial waste could be material itself (when it gets expired), during the process (cutting, splitting, etc), production itself (defected ones), residual and wastes from sanitary uses which is not our discussing topic.

It was also discussed that usually cleaner production is mainly focused inside the factory and if there is anything for outside, then it is considered as EPR or Extended Producer Responsibility which means that the factory is responsible from the production till the disposal of the product. This issue will also be covered in my future posts.

It can be said that the whole issue with cleaner production is to prevent waste generation rather than treat it at the end of the pipe. The concern in the past was to treat the waste (if any treatment) at the end without considering where and how the waste was being generated. While in cleaner production, it is very important to have the exact details of the process and how to prevent waste generation either by inventory management, improved operation, equipment modification, process change or by recycling and reuse. Sometimes a very tiny change in the factory (covering the boiling tank with isolator layers or fixing the leaking pipes) can save up to 60% of the energy and make the working environment a better place for employees.

We discussed about how throwing a recyclable item can be throwing the material and energy at the same time (it is said if one aluminium can is thrown out, equivalent of half can petrol is wasted). In addition, it was discussed how to reduce the cost of treatment by volume and toxicity reduction. Also sometimes a waste of a company could be used as raw material for another process.

Stay with me and I will bring more examples and case studies. This was just a simple introduction of what we are going to discuss in the next few coming weeks.

Monday, 13 February 2012

Water Pollution Control Technolgies (session 1)

I am back after such a long time. I have been really busy whole summer and then my third semester started and ended really well. Now I am in my last semester and I have decided to write down everything I am learning after each lecture so I can share it with all my readers.

The first session of our water pollution lecture started in an interesting way. Lecturer explained different levels as to remember, to understand and to apply. In top level we should do analysis, evaluation and create. For example, we might know what COD (Chemical Oxygen Demand) is. It is the amount of oxygen needed for chemical reaction in the wastewater. Higher COD means more organic matter in water. On the other hand, COD means pollutant in water and that’s the definition and understanding. But for application it is referred to organic matter (Carbon, Hydrogen and Oxygen). Another way to measure the organic matter in wastewater if we don’t have any equipment (such as Spectrophotometer and Digester) is to use BOD (Biochemical Oxygen Demand) determination. Definition of BOD is amount of oxygen that organisms in wastewater need to oxidize the organics matters in water. To do analysis we should be able to differentiate between COD and BOD.

We know that BOD and COD mean organic matter in water. But BOD is there when there are organisms in the water. So it can be said that amount of COD is always higher than BOD because no matter what, we have chemical actions but depend on type of organic matters (Biodegradable or non-degradable) we might have BOD as well. So if in our analysis, we have high COD and low BOD that simply means that organic matters in wastewater are non-degradable. If we have the other way around, then there must have been a mistake in our test.  High BOD without any shred of doubt means high COD too.

So that was the end of first part of the lecture. For the second part, we went through the three future topics: water chemistry, water governance and water pollution control which is going to take more than 50% of the semester.

Examples of water governance are EQA 1974 (Environmental Quality Act), WQI (Water Quality Index), Water Quality Standard, WHO drinking water and MASMA (flood control).

Water chemistry is more on water characteristic parameters and why they are important to be considered in wastewater treatment. These parameters are listed below:

  • COD (amount of organic pollutant)
  • BOD (amount of organic pollutant)
  • pH (above 8 and below 6 is not suitable for aquatic life and it can affect the enzymes)
  • Colour (very quick indicator and also aesthetic reason)
  • Temperature (above 40 is considered polluted as it affects enzymes)
  • Turbidity (mostly aesthetic related)
  • Odour
  • Solids (suspended and dissolved)
  • Conductivity and Salinity (direct relationship between these two as high salinity means high conductivity but high conductivity doesn’t mean high salinity as it could be due to existence of heavy metals)
  • Alkalinity /  Acidity
  • Nutrients (Phosphorus and Nitrogen and cause of eutrophication. Important factor for aquatic life)
  • Dissolved Oxygen (vital for aquatic life. There is a limit for DO and after that it is not possible to dissolve more oxygen).
  • Heavy metals (could cause illness due to their characteristics and also affects enzymes)
  • Oil and Grease
  • Faecal Coliform
  • Xenobiotic (Related to the antibiotic and they cannot be treated)
  • EDC (Endocrine Disturbing Chemicals like pregnancy pills which is slowly becoming an issue)
So that was actually all of it for the first session. It is going to be an amazing course and we all look forward to the future sessions.

Keep visiting this blog as I do my best to keep it updated all the time.

Saturday, 25 June 2011

Biological Treatment - Part III

Hello again!

Today, I would like to finish the biological treatment by explaining the Pond System which mostly is used in decentralized treatment facilities. However, some centralized treatment plants might use this method as well. Pond system or Lagoon could be really big as big as a football pitch. There is two types of pond system: aerobic or anaerobic. If the pond is about 1 meter, then it is considered as aerobic but if it is more than one meter, then top of it is aerobic and bottom would treat the wastewater with anaerobic bacteria. There is a middle level which is considered as facultative zone. This zone, bacteria can live with or without oxygen. Figure below shows a typical example of a pond system.

Pond System

What actually happens in pond system is that they let the wastewater to get settled for few days (could be 3-4 days or 40 days) then the organics get consumed by aerobic and anaerobic bacteria and the nutrients is absorbed by algae and bacteria. According to the figure above, the wastewater goes to the pond and settles. If there is any settleable solids then they go to the button and accumulate as sludge. As the pond could be mixed of aerobic and anaerobic, then this part is usually anaerobic zone so the bacteria here cannot with in presence of oxygen. The top surface has interaction with CO2 and O2, so having CO2 plus nutrients such as nitrogen (Ammonia) and phosphorus then it makes it a good environment for algae growth. More nutrients and more CO2 mean more algae and more oxygen. If algae dies, in goes to the bottom of the pond. Oxygen also can get mixed with hydrogen sulphide and produces sulphuric acid. So the pH of the pond is usually acidic. If there is lack of oxygen, then H2S is released as gas which could cause odder problem. Also as pond system is open, there is always issues of flies around. In order to remove the sludge they have to empty the pond. Then the sludge will go for further processing which has been already explain in this post.

I think we can finish the wastewater treatment here. There are still more things to discuss like advanced treatment (the water can be used for drinking) and leachate treatment. I may come back to them later but for the next post, I am still thinking to write about hazardous waste, Basel convention or waste minimization. I would like to keep my main focus on waste minimization and cleaner production but I very much like to discuss the hazardous waste treatment as well as it is one of the most important issues that most countries in the world are dealing with. I will decide what to write later.

Monday, 20 June 2011

Biological Treatment - Part II

Hello again, hope the last post was interesting for you. Today I would like to continue the biological treatment. What I forgot to mention in my previous post was the nitrification. In aeration we provide the oxygen for the aerobic bacteria but we also do the nitrification which means conversion of ammonia to nitrates. The process is done as below:

NH3 + O2 --> NO  +  O2 --> NO2 --> NO3
I explain what will happen after this step but before that, I am about to go for the next biological treatment which is anoxic treatment. This method is very useful for the wastewater with very high amount of nitrogen. This method also has suspended growth and attached growth.

Anaerobic process is the third method of biological treatment which like the first two has attached and suspended growth. Anaerobic process is very important as it can remove the nitrogen from the wastewater. In anaerobic process, there is no aeration nor oxygen and therefore it would be methane as output of the organic consumption by the anaerobic bacteria. If we already have the nitrification process, in anaerobic treatment the oxygen in nitrates and nitrites would be used and the nitrogen itself is released as gas. The process is shown below:

NO3 --> (reduction) NO2 --> NO -->

The next method is combination of aerobic, anoxic and anaerobic and is the most effective one. This method not only removes the organic and reduces BOD, it also removes phosphorous and nitrogen from the wastewater. It could be suspended or attached growth. 

Here, I would like to explain a little bit more about nitrogen and phosphorus removal. As it was mentioned earlier, mixed methods would also remove nitrogen and phosphorous from the wastewater. The process is not difficult. There is a slight difference between nitrogen removal and removing of phosphorus. In order to remove nitrogen you need to nitrify first in aerobic process and then you have to put the wastewater in anaerobic process so the nitrogen will be released as gas. To remove the phosphorus, it is the other way around as first wastewater should go through anaerobic process and then aerobic. Phosphorus is consumed by bacteria and when the bacteria die, they go at the bottom of the settlement tank as sludge. By removing the sludge, phosphorus is also removed. The figure below shows the removal of nitrogen and phosphorus.

Nitrogen and Phosphorus Removal
According to the figure above, the wastewater goes for anaerobic process first and then anoxic. In this level, nitrogen is removed. Now you may ask, how come nitrogen is removed from anaerobic to anoxic while we said, it would be removed if there is aerobic and then anaerobic processes? The point is that the wastewater is coming back in again as  influent. So according to the figure above, the last level before the settlement tank is aerobic process, so after that if we have anaerobic process, the nitrogen is removed through de-nitrification and reduction process. From anaerobic to aerobic, the phosphorus is absorbed by bacteria and in the settlement tank, by removing the sludge, we remove the phosphorus. Therefore, we can say one of the main purpose of aeration is to remove the nutrients as well as reducing the BOD by organic consumption.

In the next post, I will explain the pond system.