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Are you interested in how to use microalgae to treat wastewater?

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Our summary today works with the summary titled Extraction of microalgae as a form of wastewater treatment: Opportunities in biodiesel, biogas, biohydrogen, and volatile fatty acids production from 2023 by our next interviewee in ⁠⁠episode 144, Morley Muse about their current work. Since we are investigating the future of cities, I thought it would be interesting to see what we can do to treat wastewater better. This summary presents the use of microalgae in wastewater treatment for the production of other resources.

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Welcome to today’s What is The Future For Cities podcast and its Research episode; my name is Fanni, and today I will introduce a research paper by summarising it. The episode really is just a short summary of the original paper, and, in case it is interesting enough, I would encourage everyone to check out the whole paper. Stay tuned until because I will give you the 3 most important things and some questions which would be interesting to discuss.

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Before we jump into the summary, I would like to set the scene first because the following will be amazingly detail oriented. So we are talking about wastewater. What is wastewater? Wastewater is the used water that comes from homes, businesses, and industries, including everything from sewage to stormwater runoff, that typically needs to be treated before it can be released back into the environment. Why do we need to treat wastewater? Wastewater treatment is essential for protecting public health and the environment. It helps to remove harmful substances like bacteria, viruses, and pollutants from used water, preventing them from being released into natural bodies of water where they could harm aquatic life, contaminate drinking water sources, and contribute to disease spread among humans and animals.

Microalgae have been gaining attention as a sustainable source for waste water treatment as they can be used to polish secondary treated wastewater by removing nutrients and carbon without the addition of oxygen. Thus, it is a reduced energy treatment compared to traditional extended systems which circulate air in. The recovered microalgae in turn can be used for biofuels applications, such as biogas and biodiesel production. This provides an effective means in mitigating the environmental impacts of wastewater discharge.

Extracting microalgae waste as a form of wastewater treatment involves the cultivation of microalgae in wastewater which serves as a nutrient source for their growth. As the microalgae consume nutrients such as nitrogen and phosphorus from the wastewater, they effectively remove these pollutants from the water. Once the microalgae have reached their maximum growth potential, they are harvested and processes to extract valuable resources such as lipids, which can be used to produce biodiesel.

Microalgae waste can also be used to generate biogas via anaerobic digestion. Anaerobic digestion is a process where microorganisms break down organic materials, like food scraps or sewage, in an environment without oxygen, producing biogas (which can be used as a fuel) and a nutrient-rich material that can be used as a fertilizer. Here, anaerobic digestion involves the breakdown of organic matter in the absence of oxygen resulting in biogas, which is made up of biomethane and CO2. The biomethane then can be used as a renewable energy source for electricity and heat production, while the CO2 can be re-bubbled – meaning reused in the same system – as a carbon source, making the process carbon neutral. Besides biomethane and CO2, the anaerobic digestion results in the production of other intermediates, such as biohydrogen and volatile fatty acids. These can be applied across several industries including energy, food, plastics and pharmaceuticals. Moreover, the obtained biogas can further be used for biohydrogen production.

One of the benefits of using microalgae waste for wastewater treatment is that is can be a more sustainable and cost-effective option than traditional wastewater treatment methods. Conventional wastewater treatment methods, such as activated sludge treatment require significant energy inputs and can be expensive to operate and maintain. In contrast, microalgae-based wastewater treatment systems can reduce energy consumption and operating costs while producing valuable resources. Furthermore, the use of microalgae for wastewater treatment can help address the issue of nutrient pollution in waterways. Nutrient pollution from sources such as agricultural runoff and wastewater discharge can lead to harmful algal blooms. This can have negative impacts on aquatic ecosystems and human health. By using microalgae to remove excess nutrients from wastewater, the risk of nutrient pollution in waterways can be reduced.

However, one of the major challenges is the stubborn unwillingness of the microalgae’s cell walls during its further processing. To resolve this, a pretreatment process is required to disrupt the cell wall structure and improve the degradation of microalgae. There are several pretreatment options including mechanical, physical and thermal, but most result in a net or negative energy balance with the exception of biological pretreatment.

Biological pretreatment using enzymes and bacteria can offer several benefits for microalgae breakdown during anaerobic digestion or lipid extraction for biodiesel production. The biological pretreatment using enzymes and bacteria can help break down the complex carbohydrates, proteins and lipids in microalgae cell wall which can increase the availability of nutrients and improve the digestibility of microalgae during anaerobic digestion. By enhancing microalgae breakdown, biological pretreatment can increase the amount of methane produced during the anaerobic digestion. This can increase the energy yield and reduce the overall cost of producing biogas.

Biological pretreatment can also increase the amounts of lipids extracted from microalgae which can be used to produce biodiesel. Enzymes and bacteria can break down the cell walls of microalgae releasing the lipids of easier extraction. Biological pretreatment is a green and sustainable method for microalgae breakdown and lipid extraction. It does not require the use of harsh chemicals, and the enzymes and bacteria used in the process are biodegradable. Finally, biological pretreatment can be a cost-effective alternative to traditional chemical pretreatment methods. Enzymes and bacteria are often more affordable and easier to obtain than chemical reagents.

Extracting microalgae waste as a from of wastewater treatment offers a sustainable and cost-effective solution for mitigating the environmental impacts of wastewater discharge. The production of biogas, biohydrogen, volatile fatty acids and biodiesel from microalgae waste provides opportunities for renewable energy generation and can help address issues such as nutrient pollution in waterways. The use of microalgae waste for wastewater treatment and energy production offers a range of benefits of opportunities for a more sustainable and resilient future.

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What was the most interesting part for you? What questions did arise for you? Do you have any follow up question? Let me know on Twitter at WTF4Cities or on the wtf4cities.com website where the transcripts and show notes are available! Additionally, I will highly appreciate if you consider subscribing to the podcast or on the website. I hope this was an interesting paper for you as well, and thanks for tuning in!

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Finally, as the most important things, I would like to highlight 3 aspects:

1. Wastewater is basically any used water and its treatment is a public health and environmental issue which can be sustainably solved with microalgae.
2. Letting microalgae consume the nutrient pollutants from the water results in microalgae waste which then can be used to create other resources, like biodiesel and biogas.
3. The use of microalgae waste for wastewater treatment and energy production offers a range of benefits and opportunities for a more sustainable and resilient future.

Additionally, it would be great to talk about the following questions:

1. How do you think about your wastewater? What do you think happens to it?
2. What kind of wastewater treatment methods do you know?
3. Would you use this microalgae method? Why?

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