2011 Progress Report: Virus Removal in Biosand Filters for Rural Mayan CommunitiesEPA Grant Number: SU834754
Title: Virus Removal in Biosand Filters for Rural Mayan Communities
Investigators: Nguyen, Thanh (Helen) H.
Institution: University of Illinois at Urbana-Champaign
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: August 15, 2010 through August 14, 2012
Project Period Covered by this Report: August 15, 2010 through August 14,2011
Project Amount: $75,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2010) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Materials & Chemicals , P3 Challenge Area - Pollution Prevention , P3 Challenge Area - Water , P3 Awards , Sustainability
Engineers Without Borders (EWB) at the University of Illinois at Urbana-Champaign (UIUC) was contacted by Wuqu' Kawoq, a non-profit medical NGO that works with the indigenous people of Guatemala. Wuqu' Kawoq identified the Mayan village of Socorro as suffering from medical conditions that could be easily alleviated by clean drinking water. With 450 people, Socorro was plagued with water- and soil-borne pathogens that cause problems such as scabies, diarrhea, dysentery, hepatitis A, giardiasis, shigellosis, amoebiasis, and soil transmitted helminthes infections. EWB-UIUC assessed multiple water purification and distribution alternatives in order to identify the most effective remediation option. Ultimately, it was concluded that point-of-use biosand filters (BSFs) installed in individual family homes would be the most effective.
A travel team for EWB-UIUC consisting of five students in Environmental Engineering and Spanish Studies and a professional engineer specializing in concrete arrived in Socorro on December 29th, 2009. Prior to EWB-UIUC’s arrival, four albañiles (professional concrete workers) received training in the construction and maintenance of concrete biosand filters from a partner NGO, Servants 4 Him. Having built several filters on campus, the EWB team shared their own construction techniques to augment the knowledge of the concrete workers and Servants 4 Him. All materials needed in the construction of the filters are available locally.
EWB-UIUC trained two social workers on sanitary and hygienic practices including the disposal of waste, hand washing techniques, procedure to boil water, BSF maintenance and use, and proper storage of clean water. With the aid of the social workers, a specialized educational program was developed for the community that utilizes educational images developed by the Center for Affordable Water and Sanitation Technologies (CAWST). The social workers discuss hygiene and filter use with every new family that receives a filter. Additionally, the principal and teachers at a local school were given information on proper sanitation, hygiene, and the biosand filter and are teaching these topics to their students.
At the University of Illinois, research efforts are being made to improve the overall efficiency and design of the BSF. Considering the criteria of water quantity produced, water quality, ease of use, and ease of access, BSFs have been identified as the point-of-use technology having the most potential to deliver sustainable potable water treatment to the developing world. However, as our experimental results show, the filters are not effective in removing viruses, which are much smaller than other pathogens and can easily pass through the sand grains. Additionally, sand and viruses are both negatively charged in neutral water so there is less of a chance of a virus sticking to the surface of a sand particle as it passes through the filter. A novel technology being investigated is the use of iron oxides to enhance virus removal. Negatively charged viruses are expected to adsorb to positively charged iron oxide surfaces at neutral pH.
Studies conducted by the team investigated the removal of virus by zerovalent iron. Small-scale studies with glass columns simulating the average use of a biosand filter were used as a proof of concept and to test different orientations of iron placement. Large-scale studies were then performed with both plastic and concrete filters, comparing virus removal between commonly found mild steel nails, steel wool, and commercially available zerovalent iron particles. Lastly, studies were performed to determine whether locally available iron materials would sufficiently remove viruses from source water. The research objective is to design a modification that can improve filters being built in Socorro and, potentially, the over 200,000 BSFs used worldwide.
Figure 1. Long Term MS2 Removal in Columns
Small-Scale Glass Columns Simulating BSFs
Long Term Removal of MS2 Bacteriophage
To simulate the normal operation of a BSF, 4 glass columns (Fig. 1) packed with different iron orientations were charged daily with 1 PV of aquifer water containing ~108 pfu/mL of MS2 bacteriophage, a commonly used surrogate for enteric virus, and 2.5% pasteurized primary effluent (PE). While the sand column averaged only 1-log10 (90%) removal, all three iron columns had greater than 5-log10 (99.999%) removal for the duration of the experiment.
Short Term Removal of Rotavirus
To ensure that MS2 bacteriophage was an accurate indicator of human pathogenic viruses, column experiments were also performed with rotavirus, a human enteric virus responsible for hundreds of thousands of deaths annually. Two additional glass columns (identical to Figure 1) were tested. One contained only sand and one was a mixture of sand and iron particles. The columns were charged with aquifer water and 104-105 FFU/mL of rotavirus. While the sand only column obtained a 1.1-log10 removal, the iron column achieved complete removal of rotavirus on each daily charge. Additionally, the iron column experiment was repeated with treated wastewater effluent that contained 10 times higher total organic carbon (TOC). This was performed to evaluate the effect of natural organic matter on virus removal, which competes with viruses for adsorption sites. Even with high levels of NOM, the iron column achieved 5.2-log10 removal of rotavirus.
Long Term Removal of MS2 Bacteriophage
Initially, plastic BSFs were used to study virus removal of filters amended with iron nails. The nail filter started with a 6.5-log10 removal (99.99997%) but retention of virus particles quickly declined as independent flow paths formed around the large iron nails, short circuiting the filter. To avoid this problem, sources of iron smaller in size were used in three new concrete BSFs built to specifications provided by CAWST.
One filter was amended with iron by mixing zerovalent iron particles evenly throughout the top 20 cm of the filter media. Another filter was packed with extra fine steel wool, also mixed evenly throughout the top 20 cm of media, while the third filter contained only sand media.
Figure 2. Long term removal of MS2 by concrete BSFs.
The concrete sand filter achieved between 4-log10 removal and no removal, with an average of about 2-log10 (99%) removal (Figure 7) for the first 150 days. In comparison, the two filters packed with iron (particles and steel wool) achieved between 7-log10 (99.99999%) and >5-log10 removal, with an average of 6-log10 (99.9999%) reduction of virion particles for the first 170 days of filter use. The iron particles and steel wool resulted in filters with a more even media grade than in the filters containing nails. This promoted uniform, steady flow throughout the entire cross-sectional area of the filter, allowing sufficient contact time between each filter charge and the iron media. The corresponding increase in MS2 removal shows that iron-amended BSFs can effectively remove select viruses, with removal rates that exceed U.S. Environmental Protection Agency (USEPA) drinking standards (4-log10 removal).
However, removal in the steel wool filter decreased significantly after day 170, dropping to an average of 2-log10 removal. Sorption of viruses to the steel wool stopped once its adsorption sites were exhausted, and remaining removal of viruses was due only to the sand media. The reduction in removal capacity to levels below those observed in the sand-only filter may indicate that the addition of steel wool to the sand media adversely affected the traditional filter’s removal efficacy.
The sand only BSF saw a steady increase in removal from 2-log10 to >4-log10. Previous research has shown that biofilm ripening and media aging contribute significantly to the MS2 removal capacity of the traditional sand BSF, but long term studies (>2 months) have not been previously conducted. However, it is well-known that filter ripening plays a crucial role in particle removal during granular filtration. The results from this study suggest that traditional BSFs may experience significant virus removal (>2 log10) once filters have been in use for several months. If this is the case, filters would only need to be amended with an appropriate iron source for the initial ripening period.
Continued Technical Innovation
Our findings show that amending the BSF’s sand media with grain-sized iron particles results in effective MS-2 bacteriophage removal. Before applying this technology to Socorro’s BSFs, the research team is testing the filters on-site using the community’s water supply and typical running practices. The team has established a secure location within the community to act as an on-site laboratory. Four filters are being tested, two standard BSFs, and two with the sand/iron particle mixture. Filters are run daily with the help of Wuqu’ Kawoq, and analysis of microbial reductions is performed every few months when UIUC is able to seed influent water with MS2 according to the procedures established above. Microbial analysis is performed using lab facilities at Universidad del Valle de Guatemala as part of a continuing collaboration between our two institutions.
The source water used in the experimental filters is distributed from a local river, so the proposed studies will give insight into surface water quality fluctuations and the BSF’s buffering capacity. Additionally, the different sand media used in Socorro may affect microbial removal. These less controlled testing parameters reflect conditions existent in filters worldwide and are imperative to ensure that the final design of iron-amended filters is effective in real world scenarios. This research is the first to evaluate the removal capabilities of a BSF packed with a mixture of sand and low-cost iron oxide materials in the developing world.
In extension of the existing research, EWB-UIUC proposes to expand into studying the removal of viruses under additional water quality and filter usage conditions. The goal is to more concretely define the capabilities of the BSF, highlight best operation practices, and test the removal efficacy of human enteric pathogens. This research will be valuable to NGOs and international communities where people can adopt practices to enhance BSF’s water treatment without requiring additional treatment that can be burdensome or costly.
The NGO CAWST has recently developed a newer version of the BSF, Version 10.0, and has started to promote its use in international projects. Previous publications analyzed removal efficacy of an earlier filter design, and no current publications focus on the Version 10.0 design. UIUC is investigating the removal of surrogate organisms MS2 and Escherichia coli, and the human pathogen rotavirus, using the new Version 10.0 filter.
Furthermore, the exact mechanisms for removal within the BSF are still unknown. In a BSF, viruses and bacteria are removed through a combination of physical, chemical, and metabolic processes in the biofilm and granular filtration in the sand media. However, the exact mechanisms or removal due to each type of mechanism is not known. To determine the effect that each mechanism has on bacteria and virus removal, UIUC is analyzing the microbial communities present throughout the filter and beginning to correlate the areas where viruses or bacteria are reduced with specific microbial communities and mechanisms for removal. This research affects not only our knowledge of BSFs, but of removal in slow sand filters used throughout the world. Such research could lend an understanding never before achieved for these technologies.
Continued Social Innovation
The EWB team is collaborating with the community of Socorro, our NGO partners in the area such as Wuqu’ Kawoq and Servants 4 Him, and international NGOs such as CAWST, to develop a successful and sustainable educational series that builds upon past BSF endeavors. Beyond the direct benefits for Socorro, which include improved community health through enhanced water treatment, the partnership will examine the feasibility of expanding amended BSFs to other communities.
UIUC has also collaborated with the Universidad del Valle de Guatemala (UVG) to obtain lab space for microbial studies and expert knowledge necessary to perform health surveys. With the help of UVG our team will be able to evaluate the effectiveness of the amended filters, both in terms of microbial reductions and community health. If our studies support expansion to other communities, CAWST will disseminate our findings around the world to the hundreds of non-profit organizations that they work with.
Continued Educational Innovation
Education and personal advancement has always been a vital component of the project. In Urbana-Champaign, approximately 20 undergraduate engineering students have been introduced to the Environmental Engineering Laboratories to take part in BSF experiments. They have learned about biosand functionality, laboratory techniques, and advanced problem solving, and continue to be a driving component of our research. In addition to their lab work, the students present at local schools to educate students and teachers about international water projects and basic drinking water treatment practices. Working with Wuqu Kuwoq partners in the Urbana-Champaign area, project members are currently involved in hosting a lecture series highlighting the importance of collaboration between engineers and social workers in international development.
An NSF-funded group investigating international service projects continually monitors student progress and learning in the project. By understanding how students learn, they hope to be able to strengthen the capabilities of our university and other institutions.
Implementation of BSFs has improved the health of those living in Soccoro. The project’s strong collaboration with local NGOs and leaders within the community led to widespread acceptance of the filters. It has also established knowledgeable, local leaders that will sustain the project in the future, independent of foreign assistance. Additionally, individuals involved in the Socorro project have gone on to introduce more filters to new communities in Guatemala.
The extensive laboratory studies performed by the team demonstrated effective removal of viruses using BSFs amended with inexpensive, locally available iron materials. Concrete filters utilizing sand media amended with commercially available iron shavings displayed an average of ~6-log10 removal of MS-2 phage, greater than the US-EPA standard. As research continues in-country, students have been actively promoting awareness about Socorro and water-related projects. Frequent presentations are given to elementary and high school students, and a multi-disciplinary group of students has been formed to aid research in the lab. In addition to learning to build and run the filters, the teams learn the theory and application of pertinent lab techniques and are presenting their work to both the academic and scientific community through conferences, presentations, and open houses. These productions are often the first time students have had the opportunity to actively present to the academic and scientific community, allowing them to practice their public speaking and presentation skills.
With a focus on community-based implementation, laboratory research, student advancement, and education outreach, the project continues to build upon past success to benefit Socorro, the student team, and the general public. With strong collaborations internationally and locally, the team is poised to expand new and innovative BSF technologies around the world.