Development of Water and Wastewater Biofiltration Technologies for the Developing World using Locally Available Packing Media: Case Studies in Vietnam and Haiti
Water and sanitation are two of the world's most urgent current challenges (Elimelech, 2006). With a population racing towards seven billion people, over one sixth of the human population does not have access to adequate water and sanitation. Drinking water is inaccessible for approximately 783 million people living in the developing world (WHO, 2014). This is especially critical for people at risk of exposure to deadly pathogens such as <italic>Vibrio cholerae</italic>, <italic>Shigella</italic>, and <italic>Salmonella</italic>, such as those living in Haiti as <italic>Vibrio cholerae</italic> is now ubiquitous (Enserink, 2010). On the sanitation side, more than 2.5 billion people in the world still lack access to adequate resources (WHO, 2014). Almost half of these people have access to no sanitation facilities at all and practice open defecation (WHO, 2014). Thousands of small children still die every day from preventable diseases caused by inadequate sanitation (WHO, 2014). As global climate change is expected to exacerbate these issues, there is an urgent need for the development of sustainable treatment technologies to ensure a better tomorrow for our world (Ford, 1999). Safe water and sanitation technologies, while often disjointed, should be considered together as pathogens transmitted via drinking water are predominantly of fecal origin (Ashbolt, 2004; Montgomery, 2007).
In this dissertation project, I explore the use of both drinking water and wastewater treatment technologies which are cost effective and rely on locally available materials in low-income countries. For the drinking water treatment side, I focus on the use of biosand filters in Haiti with a specific interest in understanding their ability to remove the pathogen <italic>Vibrio cholerae</italic>, the causative agent for cholera. The wastewater treatment technology consists of biofilters packed with cocopeat, a waste product generated during coconut husk processing, and I investigate their use for the treatment of septic tank effluent in Vietnam. Both of these projects combine lab and field work. The specific objectives of this dissertation project are to 1) compare the removal efficiency of <italic>V. cholerae</italic> to indicator bacteria in field biosand filters and determine the parameters controlling removal; 2) investigate the correlation between removal efficiency of pathogens in field biosand filters having operated for varying lengths of time to schmutzdecke bacterial composition and influent water characteristics; 3) determine the effect of number of charges, total organic carbon loading, and schmutzdecke composition on <italic>V. cholerae</italic> removal efficacy; 4) isolate the effect of biological removal mechanisms and physical/chemical removal mechanisms on <italic>V. cholerae</italic> removal efficiency and determine the correlation to TOC concentration in water; 5) evaluate cocopeat as a packing medium for biofilters in terms of nitrogen, phosphorus and biological oxygen demand removal from simulated wastewater as compared to other traditional packing media; and 6) conduct an assessment of cocopeat-packed, vertical flow constructed wetlands treating septic tank effluent in the Mekong Delta of Vietnam.
In the first part of this dissertation, biosand filters in the Artibonite Valley of Haiti, the epicenter of the cholera epidemic, were tested for total coliform and <italic>V. cholerae</italic> removal efficiencies. In addition, schmutzdecke samples were collected in order to measure the amount of EPS in the biofilm, as well as characterize the microbial community. Total coliform and <italic>V. cholerae</italic> concentration were measured using novel membrane filtration technique methods. It was found that total coliform concentration does not indicate <italic>V. cholerae</italic> concentration in water, and total coliform removal efficiency does not indicate <italic>V. cholerae</italic> removal efficiency within biosand filters. Additionally, parameters controlling biosand filter performance include: schmutzdecke composition, time in operation, and idle time.
In the second part of this dissertation, <italic>V. cholerae</italic> challenge tests were performed on laboratory-operated biosand filters receiving high, medium or low TOC influents in order to determine the effect of number of charges, total organic carbon loading, and schmutzdecke composition on <italic>V. cholerae</italic> removal efficacy, as well as to isolate the effect of biological removal mechanisms and physical/chemical removal mechanisms on <italic>V. cholerae</italic> removal efficiency and determine the correlation to TOC concentration in water. To this end, three biosand filters were operated in the lab. Each received lake water or diluted lake water with high, medium or low concentrations of TOC. After being charged once per day for 6 days, the filters were charged with four consecutive charges of pure cultures of <italic>V. cholerae</italic> suspended in PBS buffer, at concentrations of 10<super>2</super>, 10<super>3</super>, 10<super>5</super>, and 10<super>7</super> cfu/mL. This challenge was repeated each time the filters received an additional 6 charges, up to 66 total charges. This was done to determine how number of charges, TOC loading, and schmutzdecke composition affects removal efficiency. Schmutzdecke was analyzed for amount of EPS and microbial community. It was found that parameters controlling biosand filter performance include: TOC loading, schmutzdecke composition, time in operation, and physical/chemical attachment. Additionally, it was shown that physical/chemical attachment is critical during startup, especially at low TOC concentrations. At steady state, physical/chemical attachment is more important than schmutzdecke effects in filters receiving low TOC, and schmutzdecke effect is more important than physical/chemical attachment in filters receiving high TOC.
For the third section of this dissertation, columns packed with cocopeat, celite, or sphagnum peat were charged with simulated wastewater and removal efficiencies of nitrogen, phosphorus, and biological oxygen demand were measured. Additionally, different redox zones were tested to determine if cocopeat could successfully accomplish nitrification and denitrification. It was found that cocopeat is comparable to traditional packing media and can successfully accomplish nitrification and denitrification in the treatment of synthetic wastewater.
In the final section of this dissertation, constructed wetlands were built and packed with cocopeat to determine if cocopeat is a suitable packing media in constructed wetlands treating wastewater in Vietnam. Removal efficiencies of nitrogen, phosphorus, and biological demand were measured. Microbial community samples were collected periodically in order to analyze community shifts between wetlands and over time. This work concluded that cocopeat can be used successfully as a packing media in constructed wetlands treating wastewater for the removal of nitrogen, phosphorus, and total coliform.
Overall, this dissertation work contributes to the body of knowledge on point-of-use water and wastewater technologies. The biosand filter was studied in both lab and field conditions and it was found that total coliform is not a reliable indicator for <italic>V. cholerae</italic>, and that there are several factors controlling biosand filter performance, including idle time, TOC, filter time in operation, physical/chemical attachment, and schmutzdecke composition. Cocopeat was studied for its ability to promote nitrification and denitrification in lab-scale vertical flow columns treating synthetic wastewater. It was shown that cocopeat achieved similar levels of nitrification and denitrification as traditional packing media. Finally, cocopeat packed vertical flow constructed wetlands were operated in Vietnam for the treatment of septic tank effluent. This setup proved effective for the removal of nitrogen, phosphorus, and total coliform in the treatment of wastewater.
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