Rice Husks as an Effective Means of Denitrification

1. ENVS 001: INTRODUCTION TO ENVIRONMENTAL SCIENCE, FALL 2013 Rice Husks as an Effective Means of Denitrification BRENDA CAM, PEDRO CHANG, WARREN HE, KEVIN LAU, ERIC LEE and RUSSELL E. DI FIORI Pasadena City College, Pasadena, CA USA Discussion Introduction Figure 1 Figure 1a.A model of our design. In order for our bacteria to survive, they must dwell on a nutritious carbon source (rice husks) and have a second source of nutrition. In essence, the main food source for our bacteria is oxygen because it is so abundant and nutrient-dense; when we starve the bacteria of oxygen (by keeping it enclosed and sealed), its secondary food source becomes nitrate (NO3-). When nitrate-filled water passes through our system, the bacteria will take the nitrate in the water, break it down, and convert it to N2 gas. In doing so, nitrate breaks free from the water, thus reducing the amount of nitrates in the water6. Based on the data collected from this project, it can be concluded that rice husks are in fact effective in removing nitrates from water. In our data, it is seen that there was slight increase in nitrate levels on Day 9 and 10. This may be because the tube responsible for water flow was clogged, which affected our results. Future research can implement larger husk-filled systems or multiple husk-filled components to observe and test quicker flow rates. Also, other organic compounds such as charcoal, sawdust, or wood chips can be used in conjunction with rice husks to test for denitrification efficacy. We are confident that rice husks are capable of greatly reducing the amount of nitrates in water, and can be used in actual storm water runoff treatments. A. Living in Los Angeles today, there are many issues that arise regarding the health of individuals as well as other living organisms, such as the use of genetically modified crops or what to do with electronic waste; however, one important issue that is often overlooked is the cleanliness of the water being used by everyone in the city. It may be difficult to believe, but there are an abundance of contaminants in L.A.'s drinking water, which in effect cause a number of different ailments in those who drink the water. In 1974, the Environmental Protection Agency passed the Safe Water Drinking Act (SWDA) which, over the years, has worked to disinfect water from various waterborne pathogens1. Although effective, there are still a number of disease-causing chemicals present in today’s water supply. In this project, one particular contaminant – nitrate – is studied extensively and treated accordingly from water. According to a fact sheet posted by Colorado State University, nitrate (a chemical commonly found in fertilizer and feces) is known to cause methemoglobinemia, a disorder that afflicts red blood cells and causes oxygen deprivation over time2. Also, increased nitrate intake cause individuals to be at a greater risk of thyroid disease and thyroid cancer3. Other symptoms include (but are not limited to) shortness of breath, dizziness, and stomach aches. Currently, it costs over $6 billion in water investment, conservation, and purification for Los Angeles, so it is imperative to find cheap but effective alternatives to the city’s overall water management4. B. Figure 1b.A plastic bottle was cut into four sections, and each section was tightly packed with rice husks. Each section was separated by a platform of Gorilla Tape (punctured with a small hole for water to pass through); the Gorilla Tape was sealed with the sectioned bottle using a hot glue gun. This method of sealing minimizes oxygen exposure to the rice husks. Three more layers were then stacked onto the existing platform. D. C. Figure 1c.An additional layer of metal mesh was added to the top and bottom of the bottle to prevent leakage of the rice husk. We inverted our system for convenience. References Figure 1d.The husk-filled system was placed over a bottle containing nitrate-filled water, and both systems were connected via a tube and a pump to allow for a cyclical flow of water. Water flowed through the system at around 8.2 liters per day, 24/7. We measured this using a graduated cylinder and stopwatch. The denitrifying bacteria in the system (present in the rice husks) were given 18 days to cultivate (occasionally switching out the nitrate-filled water with a new batch of water containing 50 mg/L nitrate), and samples were collected from that point. • "Fact Sheet: Stage 2 Disinfectants and Disinfection Byproducts Rule ." United States Environmental Protection Agency. Office of Water, n.d. Web. 23 Nov. 2013. <http://www.epa.gov/safewater/disinfection/stage2/pdfs/fs_st2_finalrule.pdf>. • Self, J.R., and R.M. Waskom. "Nitrates in Drinking Water." Nitrates in Drinking Water. Colorado State University, 13 Nov. 2013. Web. 24 Nov. 2013. <http://www.ext.colostate.edu/pubs/crops/00517.html>. • Ward, MH, et al. "Nitrate intake and the risk of thyroid cancer and thyroid disease." NCBI. U.S. National Library of Medicine, 21 May 2010. Web. 26 Nov. 2013. <http://www.ncbi.nlm.nih.gov/pubmed/20335813>. • "Los Angeles Department of Water and Power." Los Angeles Department of Water and Power. KPMG LLP, 30 June 2012. Web. 23 Nov. 2013. <http://www.ladwp.com>. • Shao, L, et al. "Rice Husk as Carbon Source and Biofilm Carrier for Water Denitrification." Polish Journal of Environmental Studies. N.p., 8 Dec. 2008. Web. 1 Dec. 2013. <http://www.pjoes.com/pdf/18.4/693-699.pdf>. • "Bioreactors, Water Table Management, and Water Quality." How Bioreactors Work. University of Illinois Extension, 2013. Web. 1 Dec. 2013. <http://web.extension.illinois.edu/bioreactors/bioreactors.cfm>. Results Figure 2 A. B. Methods In order to reduce/eliminate nitrates in water, we created a miniature system to simulate a real-life application of water treatment. Because the general movement of water is a continuous directional flow, we used a pump to simulate a continuous flow of water into our system. In our model, our system acts as a filter and a porous medium by which water passes through, which is highly applicable to the many lakes and streams scattered throughout Southern California. We used rice husks as the main component in removing nitrates from our water because it is highly productive. It works two-fold: rice husk serves as both a carbon source (where bacteria is cultivated) and a source of denitrifying bacteria5. Acknowledgements We would like to thank Professor Di Fiori for attentively assisting us throughout the poster process and providing much needed insight on our project. We would also like to thank Matthew Cui, Lizzie Beuyukian, and Natalie Melgoza for tremendously helping us get started with our design and our search for an efficacious carbon source. Figure 2b.After 18 days of allowing the bacteria present in the rice husks to cultivate, there is a noticeable decrease in the amount of nitrates in our water. It is clear that rice husks are effective in removing nitrates from water. Figure 2a.A numeric representation of the efficacy of the rice husks. Within 10 days, nitrate levels decreased from 50 mg/L to 2.4 mg/L.