The water crisis is one of the biggest challengesin the 21st century. With the development of economy, nitrogen and phosphorus and other nutrients discharged into the water, causing water eutrophication, which leading to abnormal algal breeding and deterioration of water quality. At the same time, 40% of countries and regions in the world are facing water shortages now. Thesustainability of water resources is imminent. Therefore, to develop an efficient, low-cost water purification technology is the key to solve the current water crisis.
In recent years,population growth and industry development around the world brought about the excessive consumption of resources and energy. It is expected that the global energy gap will be 403 EJ·a and will reach 488 EJ·a in 2020. While the utilization of new energy is no more than the 10% of the insufficient gap. On the other hand, the burning of fossil fuels exacerbates greenhouse gas emissions. C02 concentration levels and global temperatures increased significantly since 1950s. Therefore, looking for sustainable regeneration, environmentally-friendly energy is imperative.
Microalgae has the characteristics of fast growth rate, short harvest period and high photosynthetic rate. The annual C02 yield of Micro-algaeis about 40% of the world's net photosynthesis yield. It is the only substitute for fossil energy. At the same time, microalgae will absorb a large number of nitrogen and phosphorus in growth process , so it can be used as a processor in sewage treatment plant. Combined with the above advantages, the application of microalgae technology get more and more attentionin recent years.
Controllingthe content of nitrogen and phosphorus inthe wateris the key to preventwater eutrophication. Domestic and foreign research shows that although theconventional sewage biological treatment can remove most of the organic and inorganic pollutants in the sewage, but the effect to remove nitrogen and phosphorus nutrients is poor. Chemical method of phosphorus removal can work well, but the drawback is its high cost and the resulting sludge. Since the concept of using algal cells to remove nitrogen and phosphorus proposed by Oswaldin 1958, the sewage disposal technology based on microalgae cultivationhas been greatly improved.High-efficiency algae pond (all photosphere reactor (Algal Photobior c% APBR) and other microalgae culture devices have emergedand gradually put into application.
The mechanism of removal of nitrogen and phosphorus by microalgae in thetreatment of sewage including direct and indirect effects. Microalgae cells can use a variety of inorganic nitrogen and organic nitrogen compounds as nitrogen source, use carbon dioxide and carbonates as carbon source for photoautotrophical growth. Nitric acid, nitrite and ammonium salts absorbed by algal cells can be synthesized by amino acids and proteins. Phosphorus in water can be directly absorbed by algal cells and transformed into organic matter such as ATP and phospholipids through a variety of phosphorylation routes. At the same time, the photosynthesis of microalgae rise the pH value in water, which leading to removal of orthophosphate and NH3.H20 in the form of precipitation and volatile, thus to remove nitrogen and phosphorusindirectly. In addition, the high pH in water caused by microalgae photosynthesis can also have a certain degree of disinfection effect. Therefore, microalgae cells can remove nitrogen, phosphorus and other nutrients in sewage by transforming them in the form of organic matter in algae cells.
In the new sewage treatment system in future, the concerns are not limited to the removal of pollutants, but should combine the treatment with re-utilization of sewage, transform the "treatment"to "production". It is not only a new concept to obtain "new" resources and "new" energy from sewage, but a solution to alleviate the lack of resources and energy shortage. As a result, the technology of wastewater regeneration based on microalgae cultivation has a broad development prospect.