The problem
Currently, the continuous expansion of human activities in terms of scope and intensity has led to further stress on limited water resources worldwide, resulting in severe water shortages in numerous regions.
Water pollution refers to the phenomenon that pollutants entering a water body exceed its self-cleaning capacity, leading to the changes in the chemical, physical, biological, or radioactive characteristics of water body. Consequently, this hampers efficient utilization of water,pose risks to human health, and causes ecological harm that leads to degradation of water quality. According to the type of water body, it can be categorized as either surface water pollution or groundwater pollution. Moveover, depending on the type of pollutant present, it can be divided into organic pollution, aerobic pollution, nutrient pollution, pathogen pollution, heavy metal pollution, refractory organic matter pollution, thermal pollution, radioactive pollution, etc.
At present, over 420 billion tons of wastewater are discharged into rivers, lakes, and seas worldwide every year, polluting 5.5 trillion tons of fresh water, which is equivalent to more than 14% of the total global runoff. The United Nations World Assessment Report on Water Resources provided by the Fourth World Water Forum shows that around millions of tons of garbage are dumped into rivers, lakes, and streams worldwide every day, with each liter of wastewater polluting 8 liters of fresh water; All rivers flowing through Asian cities have been polluted; 40% of the water resources in the United States are polluted by processed food waste, metals, fertilizers, and pesticides; Only 5 out of 55 rivers in Europe have barely usable water quality. Water pollution poses a great threat to human health. About 1 billion people in developing countries drink unclean water, with over 25 million people dying every year. On average, 5000 children worldwide die every day from drinking unclean water, about 170 million people drink water contaminated with organic matter, and 300 million urban residents face water pollution. A survey of epidemics in areas with high incidence of liver cancer indicates that drinking water contaminated with algal toxins is the main cause of liver cancer. Statistics show that 1.2 billion people worldwide become ill each year due to drinking contaminated water, 15 million children under the age of 5 die from diseases caused by unclean water, and more than 5 million people die each year from diseases caused by water pollution such as cholera, dysentery, and malaria. Up to 6000 children and adolescents worldwide die every day due to poor drinking water hygiene. In developing countries, approximately 60 million people die from diarrhea each year, most of whom are children.
The measure
Wastewater treatment is urgent, and global wastewater treatment actions are underway
In the face of unprecedented environmental problems of, in order to have a better living environment in the future, mankind has started to save itself. Many countries and regions around the world have started to develop relevant wastewater treatment plans and carry out technical exchanges and cooperation related to wastewater treatment.
The currently popular wastewater treatment technology:
(1)Physical treatment: Removing suspended solids and particles from wastewater through physical processes. Common physical treatment methods include grids, sand settling tanks, air flotation systems, and filtration.
(2)Chemical treatment: The use of chemicals to treat and remove pollutants from wastewater. Common chemical treatment methods include coagulation, precipitation, adsorption, and oxidation.
(3)Advanced treatment technology: including reverse osmosis, ozone oxidation, ultraviolet disinfection, etc., used to treat special wastewater and improve treatment efficiency.
(4)Farmland utilization and resource utilization: The treated wastewater is used for farmland irrigation or the resource utilization of recycled water.
Among them, biotreatment technology is the most widely used, and the following are several common biological wastewater treatment methods:
·Activated sludge method: Contact and mix wastewater with activated sludge containing a large amount of bacteria and other microorganisms, and degrade organic substances through biodegradation. This method is commonly used in urban domestic wastewater treatment plants. The activated sludge method can be further divided into different operating methods such as oxidation ditch method, sequencing batch method, SBR method, etc.
·Immobilized biofilm method: Attach microorganisms to fixed media (such as filter media, membranes, etc.) to form a immobilized biofilm reactor. When wastewater passes through a biofilm, microorganisms degrade organic substances on the membrane surface or medium. The advantage of this method is that microorganisms are easy to fix and grow, and it has good stability against impact loads. It is suitable for high concentration organic wastewater treatment and limited treatment space.
·Biological filter method: Wastewater is passed through a layer of fillers (such as river sand and gravel) to provide a surface for attached organisms, which can degrade organic matter. The biological filter method is mainly used for the treatment of low concentration organic pollutants and pre-treatment processes.
·Artificial wetland method: Utilize wetland plants, roots, aquatic microorganisms, etc. to purify and treat wastewater. Wetland plants absorb organic matter and provide a surface for biofilm growth, while microorganisms can further degrade and remove pollutants. The artificial wetland method is usually used for the treatment of rural wastewater and rainwater, while also beautifying the environment and protecting the environment.
Despite the continuous advancements in wastewater treatment technology driven by scientific progress, imperative to minimize avoidable pollution. Embracing of green and sustainable development should be an obligatory commitment for every enterprise.
The study of Algae & Bacteria system
The engineered mutualistic consortia of microalgae and bacteria offer a promising approach to combine unique metabolic capabilities, thereby presenting potential biotechnological advantages. At present, relevant studies have shown that in the symbiotic system of bacteria and microalgae, microalgae can provide nutrients for bacteria through photosynthesis, such as lipid, polysaccharide, organic phosphorus, polypeptide, TEP and some essential growth factors, which can effectively promote the bacterial metabolism and growth. Moreover, the oxygen generated by photosynthesis facilities aerobic respiration and enhances bacterial productivity. Conversely, bacteria contribute vitamin B12 to compensate for its deficiency in microalgae within the symbiotic system. The inorganic salts produced during bacterial metabolism serve as nitrogen and phosphorus sources for algal growth. Furthermore, carbon dioxide released from bacterial aerobic respiration provides raw materials for the photosynthesis of microalgae. These bacteria-microalgae interactions encompass the exchange of nutrients, signals, and genes, exerting profound impacts on the growth, metabolism, and productivity of both partners.
We are confident that the implementation of such bacteria-microalgae interaction systems hold immense potential for achieving exceptional outcomes in wastewater treatment, prompting our team to adopt this innovative approach.
P. tricornutum & Q. aquimaris
In our project, we selected the unicellular oil-producing diatom P. tricornutum as the substrate material for our experiments due to its prevalence in marine environments. The selection was based on the exceptional properties commonly associated with diatoms, such as a high oil content and an abundance of fucoxanthin, rendering it a material of significant environmental and economic potential.
Fucosidase plays a crucial role in the degradation of fucosan, a major constituent of the cell wall in P. tricornutum. Fucosamine is formed through alternating linkage of fucosuronic acid and fucosamine. The degradation of fucosan serves as a carbon source and energy for P. tricornutum, while also regulating the physical and chemical properties of cell wall. Although the precise impact of fucosidases on lipid synthesis, fucoxanthin synthesis and absorption of elements such as nitrogen and phosphorus, remains unknown, it is evident that they play a pivotal role in the formation and cleavage of fucose-containing glucoside bonds. These enzymatic activities potentially influences the synthesis of various biomolecules, including some types of polysaccharides and glycoproteins as well as possibly other molecules like fucoxanthin.
Our team selected P. tricornutum as a chassis organism, and overexpressed fucosidase-related genes in it by using relevant techniques of synthetic biology, subsequentl constructing corresponding engineered algae strains. Q. aquimaris with a highly similar environment to P. tricornutum, can interact more effectively with microalgae without compromising its own growth. So, we opted for Q. aquimaris as the bacterium utilized in the project.
The gelation of sodium alginate occurs under mild conditions, thereby preventing the inactivation of sensitive drugs, proteins, cells, enzymes, and other active substances. Considering the exceptional properties of sodium alginate, we made the decision to use it for embedding P. tricornutum. Additionally, Q. aquimaris were introduced into this system to form a relatively stable symbiosis relationship whit P. tricornutum, which is beneficial for maintaining the stability and efficiency of wastewater treatment in the system.
Due to the utilization of genetically modified microalgae strains in our research, we have implemented an immobilization approach to address concerns related to biosafety, thereby effectively mitigating the potential escape of microalgae and bacteria.
Summary
In summary, we developed an engineered strain of P. tricornutum that exhibits enhanced oil production and improved efficiency in nitrogen and phosphorus removal for this project. Subsequently, we successfully embedded it into sodium alginate microspheres together with wild Q. aquimaris, establishing a stable bacteria-microalgae interaction system. Consequently, we exploit the interaction system of microalgae and bacteria to purify wastewater.
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