Water is a scarce source. The total amount of water on Earth is about 1.4 billion cubic kilometers, in which 97.2% are oceans. However, the total amount of freshwater resources only accounts for about 2.5% of the total water resources. Of all the freshwater, about 70 percent is locked up in the ice and permanent snow in the mountain, which cannot be used. Approximately 30% of the world's freshwater resources are stored underground in the form of groundwater. 97% of all potentially available freshwater resources for humans are either locked up in the ice and permanent snow in mountains or stored underground in the form of groundwater, including shallow and deep groundwater basins up to 2,000 meters deep, soil moisture, swamp water, and permafrost. Lastly, only about 0.3% of the world's freshwater resource are freshwater lakes and rivers that are accessible and safe to drink for human^[1].Given these limited amounts of usable freshwater, approximately 2 billion individuals globally lack access to clean drinking water, as highlighted in the SDG Report of 2022^[2]. Additionally, nearly 50% of the global population faces significant water scarcity during certain periods annually^[3]. This issue can worsen due to the effects of both climate change and population expansion.Also, because of human-induced contaminations and destructions, drinkable water is facing more damages and negatively affecting both human and animal health. According to a recent study conducted by Orb Media, the environmental scientists present a worldwide investigation of 159 tap water samples from six diverse regions spanning five continents. Among those samples studied, an overwhelming 83% were discovered to contain plastic particles, with the majority of the their lengths ranging from 0.1 to 5 mm, so tiny to be noticed when drinking^[4]. These plastics does not only impact humans, but also animal species. It is estimated that 90% of seabirds eat plastics, and plastics can rupture organs of animals, such as fish and turtles, leading to poisoning and starvation^[5].Water is highly a vital source of survival, both for human beings and for living organisms. When water pollution increases, it means that these creatures have less water to consume, not meeting their water demands, and they are pushed to the edge of life and death, and may even start competing for water. As human, and as a part of these living things, it is important to find ways to mitigate freshwater scarcity.

Shuhan Zhao. Comparative Study of Conventional and Biological Water Treatment. Academic Journal of Environment & Earth Science (2023) Vol. 5 Issue 9: 77-86. https://doi.org/10.25236/AJEE.2023.050910.

[1] Posner, A., & Covitt, B. (2023, August 2). Earth’s Fresh Water. National Geographic . https://education.nationalgeographic.org/resource/earths-fresh-water/

[2] United Nations, & Division. (n.d.). — SDG Indicators. United Nations-Department of Economic and Social Affairs . Retrieved September 13, 2023, from https://unstats.un.org/sdgs/report/2022/Goal-06/

[3] intergovernmental panel on climate change. (2022). Fact sheet - Food and Water. Sixth IPCC Assessment Report. https://www.ipcc.ch/report/ar6/wg2/downloads/outreach/IPCC_AR6_WGII_FactSheet_FoodAndWater.pdf

[4] Kosuth, M., V. Wattenberg, E., & Orb Invisibles Final. (2017, May 16). Invisibles Final Report — Orb Media. Orb Media. https://orbmedia.org/invisibles-final-report

[5] Parker, L., & National Geographic. (2015, September 2). Nearly Every Seabird On Earth Is Eating Plastic. National Geographic. https://www.nationalgeographic.com/science/article/15092-plastic-seabirds-albatross-australia

[6] Centers for Disease Control and Prevention. (2022, May 16). Water Treatment | Public Water Systems | Drinking Water | Healthy Water | CDC. CDC. https://www.cdc.gov/healthywater/drinking/public/water_treatment.html

[7] Water Resources Mission Area. (2019, January 3). Nutrients And Eutrophication | U.S. Geological Survey. USGS. https://www.usgs.gov/mission-areas/water-resources/science/nutrients-and-eutrophication

[8] Zheng, C., Zhao, L., Zhou, X., Fu, Z., & Li, A. (2013). Treatment Technologies for Organic Wastewater. In W. Elshorbagy & R. K. Chowdhury (Eds.), Water Treatment . IntechOpen. https://doi.org/10.5772/52665

[9] Activated Sludge Process, Design Criteria - Engineering Articles. (n.d.). Engineering Articles. Retrieved September 13, 2023, from https://www.engineeringarticles.org/activated-sludge-process-design-criteria-advantages-disadvantages/

[10] Karl-Uwe Schmitz. (2019, August 6). Activated Sludge Process And IFAS - Design Rules + Guideline. YouTube. https://www.youtube.com/watch?v=ciPFC3Y2rkg

[11] Zheng, C., Zhao, L., Zhou, X., Fu, Z., & Li, A. (2013). Treatment Technologies for Organic Wastewater. In W. Elshorbagy & R. K. Chowdhury (Eds.), Water Treatment . IntechOpen. https://doi.org/10.5772/52665

[12] Wetland Functions And Values: Surface And Ground Water Protection | Department Of Environmental Conservation. (n.d.). Agency of Natural Resources-Department of Environmental Conservation. Retrieved September 13, 2023, from https://dec.vermont.gov/watershed/wetlands/functions/water-quality

[13] Zheng, C., Zhao, L., Zhou, X., Fu, Z., & Li, A. (2013). Treatment Technologies for Organic Wastewater. In W. Elshorbagy & R. K. Chowdhury (Eds.), Water Treatment . IntechOpen. https://doi.org/10.5772/52665

[14] Jurenka, R., S. Martella, and R. Rodriguez. 2001. “Water Treatment Primer for Communities in Need.” Available at: http://www.usbr.gov/pmts/water/media/pdfs/ report068.pdf. Accessed on 1 September 2023.

[15] Buffalo Water Authority. 2005. “2004-2005 Annual Water Quality Report.” Available at: http://www.buffalowaterauthority.com/water_quality_report.htm. Accessed on 1 September 2023.

[16] Sturdivant, A.W. (2006.) Extension Associate Economist. Texas AgriLife Extension Service. Weslaco, TX. Provided photographs of McAllen Northwest facility.

[17] Rogers, C. (2008). Economic Costs Of Conventional Surface-Water Treatment: A Case Study Of The Mcallen Northwest Facility.

[18] Environmental Protection Agency. (2008.) “Drinking Water Contaminants.” http://www.epa.gov/safewater/contaminants/index.html.

[19] McAllen Public Utilities Water Systems. (2002.) “Initial Construction Budget-Pay Estimate for McAllen Northwest Water Treatment Plant.” Copy provided by Javier Santiago, McAllen, TX.

[20] CASE STUDY: PUERTO RICO WTP SAVES THOUSANDS WITH UV254. (2018, January 5). Real Tech Water. https://realtechwater.com/blog-post/case-study-puerto-rico-wtp-saves-thousands-with-uv254/

[21] Cáceres Acosta, N M. (2013). “Monitor Source Water UV254 to Enhance Operations in WT Plant [22] Los Filtros Guaynabo”. 19th Drinking Water Seminar Puerto Rico. May 23, 2013.

[22] Encarnación Martínez, T. Y., & Rosa Rosado, L. (2022). Analysis of Rehabilitation of the Sludge Treatment System at Guaynabo Water Treatment Plant, “Los Filtros.” http://hdl.handle.net/20.500.12475/1615

[23] Learn About UV Water Purification | ESP Water Products. (n.d.). ESP Water Products. Retrieved September 14, 2023, from https://www.espwaterproducts.com/understanding-uv-water-filtration-sterilization/

[24] California Climate: Average Temperature, Weather By Month, California Water Temperature. (n.d.). Climate Data. Retrieved September 14, 2023, from https://en.climate-data.org/europe/united-kingdom/england/california-657474/

[25] Climate In California. (n.d.). Best Places. Retrieved September 14, 2023, from https://www.bestplaces.net/climate/state/california

[26] Reusing On-Site Water At Emory University | Better Buildings Initiative. (n.d.). Better Buildings-U.S. Department of Energy. Retrieved September 14, 2023, from https://betterbuildingssolutioncenter.energy.gov/implementation-models/reusing-site-water-at-emory-university

[27] The WaterHub at Emory University. (n.d.). Sustainable Water. Retrieved September 14, 2023, from https://cliftoncommunitypartnership.org/documents/emory-waterhub-case-study-1.pdf

[28] Emory Magazine. (2020). Smarter Water: Emory’s WaterHub. Emory University-Water. https://news.emory.edu/features/2020/04/waterhub/#group-Study-and-Research-0mBShHER1V

[29] Sofwan, N. M., Idris, J., Azir, K. M. A. K., Hadi, N. A., Ali, S. N. A. M., Hassan, N. A., Wakimin, N. D., Francis, L. D., & Abdullah, M. F. (2020). Process Design and Physicochemical Characterization of Extended Aeration Activated Sludge Treatment Plant: A Case Study. Journal of Asian Scientific Research, 10(3), 121–130. https://doi.org/10.18488/journal.2.2020.103.121.130

[30] Karl-Uwe Schmitz. (2019, August 6). Activated Sludge Process And IFAS - Design Rules + Guideline. YouTube. https://www.youtube.com/watch?v=ciPFC3Y2rkg