Grantee Research Project Results
Final Report: Evaluation of Chitosan Coagulation as a Sustainable Method for Point of Use Drinking Water Treatment in Developing Countries
EPA Grant Number: SU834753Title: Evaluation of Chitosan Coagulation as a Sustainable Method for Point of Use Drinking Water Treatment in Developing Countries
Investigators: Sobsey, Mark D. , Ligon, Grant C. , Soros, Ampai , Knee, Jackie , Armstrong, Andrew , Casanova, Lisa
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Page, Angela
Phase: II
Project Period: August 15, 2010 through August 14, 2012 (Extended to August 14, 2013)
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 - Safe and Sustainable Water Resources , P3 Awards , Sustainable and Healthy Communities
Objective:
The purpose of this project is to evaluate the effectiveness of chitosan for improving the microbial quality of water, with the ultimate goal of applying it as a treatment for rainwater captured for recycling. The goal of Phase 2 was to determine whether coagulation using chitosan, both alone and followed by filtration, can reduce the numbers of bacteria and viruses in drinking water.
The project objectives were:
- Measure microbial quality of stormwater captured from green buildings in the U.S.
- Measure the microbial quality of rainwater collected by rural households in Thailand for use as drinking water
- Screen a collection of different chitosans for their ability to remove bacteria and viruses from water
- Measure the ability of metal ions and chitosans in combination to improve microbial quality of water.
Summary/Accomplishments (Outputs/Outcomes):
Overall, the quality of captured rainwater collected in a U.S. city from urban roofs and roof collection systems was good; although coliform bacteria were present in all samples, E. coli levels were low and present only in samples that were not part of a constructed rainwater capture system. To evaluate the quality of rainwater in Thailand, where it is captured for drinking, sixty households (HH) from the village of Wailum in the northeast province of Khon Kaen, Thailand were selected for this study. All HHs use stored rainwater as their primary source of drinking water. HHs were visited and sampled twice, once in the dry season (February - March) and once in the rainy season (July). During the dry season, 105 samples were collected, and 84 samples were collected during rainy season. Additionally, 59 samples from 35 HHs were tested for H2S-producing bacteria. Of all samples processed (collection tank, refillable container), 39% and 82% of households had E. coli present in at least one container during the dry and wet seasons, respectively. E. coli was present in 21% and 66% of RW collection tanks during the dry and wet seasons, respectively. Initial analysis suggests that no single factor related to RWHS setup (roof, pipe, or tank material) had a statistically significant impact on the presence of E. coli in RW collection tanks. These results suggest that stored RW microbiologic quality may be highly seasonal, may not always meet WHO guidelines for safe DW, and that deterioration of the microbiologic quality of stored RW is likely due to a combination of collection and use practices
Most of the chitosans (MW: 50,000, 100,000, 600,000 and 1,000,000 daltons) exhibited bentonite reduction > 90% at dose 1 and 3 mg/L. The smallest chitosan (MW 5,000 daltons) had lower bentonite reduction, with maximum reduction of 46% at dose 10 mg/L. At chitosan dose 1 mg/L, MW differences produced significant differences in the removal of turbidity from bentonite (p <0.0001). Different MW chitosans showed different effects on kaolinite removal (p < 0.0001). Chitosans with MW of 50,000, 100,000 and 1,000,000 Da provided kaolinite reduction, ranging from 87 - 90% at 1 and 3 mg/L doses. Chitosan 600,000 daltons had poor kaolinite reduction particularly at high dose of chitosan. Doses of chitosans affected kaolinite removal significantly (p <0.0001). All DD of chitosans exhibited bentonite reductions particularly between dose 1 - 10 mg/L.
All DD of chitosans showed the best bentonite reduction at dose 3 mg/L, with approximately 99% reduction. Kaolinite removal differed by DD; effects of DD on kaolinite reduction were significantly influenced by chitosan doses. Across all values of DD, optimal turbidity removal occurred at dose 3 mg/L. Modified chitosans, except carboxymethyl chitosan, produced bentonite reductions of 97-98% at doses of 3 and 10 mg/L. Carboxymethyl chitosan was ineffective for bentonite removal, with only 60% reduction. Modified chitosans affected kaolinite removal differently from bentonite removal. Results showed that both types and doses of modified chitosans influenced the removal of kaolinite from water (p < 0.0001). The effective doses for kaolinite removal were narrow. The optimum dose was 3 mg/L based on turbidity removal. Three modified chitosans, namely chitosan lactate (both general one and a commercial coagulant) and chitosan HCl, produced relatively high mean kaolinite removals of 88 - 91%.
Dose 10 mg/L appears to be the optimum dose for bacterial removal. At 10 mg/L, 100,000 Da exhibited 4.51 log10 reduction of E. coli, followed by chitosan HCl and chitosan acetate with 4.28 and 3.45 log10 but there was no statistical difference. Turbidity removal occurred at low chitosan doses (1 and 3 mg/L) with approximately 60 -70% removal.
Effective dose range for virus removal was wide, starting at dose 3 mg/L with approximately 2 log10 reduction. Generally, higher MW and DD chitosans showed better virus removal. Chitosan 100,000 Da and 1,000,000 Da had similar effects on MS2 removal (3-4 log10 reductions starting at dose 3 mg/L) and provided better virus removal compare to chitosan 50,000 Da (2-3 log10 reductions). Chitosan 85 and 95DD also gave similar MS2 removal with 4 log10 virus removal at dose 10 mg/L and were more effective than chitosan 70DD (1 log10 reduction at dose 10 mg/L). Chitosan acetate was significantly better than other modified chitosans on virus removal tested in this study. Chitosan MW 100,000 Da and chitosan acetate exhibited > 3 log10 reduction of MS2 starting at dose 3 mg/L and both chitosans were dose independent from this point. Their effects on virus removal were significantly similar at every dose. At dose 10 mg/L chitosan 100,000 Da, chitosan 85DD, chitosan 95DD and chitosan acetate exhibited similar effects on MS2 removal (> 3 log10 reductions) (p > 0.05).
The inactivation kinetics of E. coli and MS2 in water by copper ions were examined. Maximum reductions of E. coli and MS-2 coliphage were achieved after 6 hours with 3.0 mg/L Cu (8.5 and 2.4 log10, respectively). Reductions by 1.0 and 3.0 mg/L doses were statistically similar. Reductions of bacteria appeared to follow exponential kinetics. Definitive conclusions could not be drawn about inactivation kinetics of MS-2 with Cu because the inactivation curves showed significant tailing and the mathematical models returned varying estimates for the inactivation rate constant. However, the ChickWatson model was found to provide best estimates of rate constants for inactivation of all test organisms with Cu.
Conclusions:
Our results show that chitosan has enormous potential as an effective, low-cost water treatment. It can be used at household or community scale, and combined with other point-of-use technologies to enhance effectiveness. Chitosan is an important potential water treatment technology because even drinking water sources that are perceived as being of good quality, like collected rainwater, may not be safe. Stored rainwater may not be a microbiologically safe source of drinking water, as E. coli was present in drinking water storage containers in 39% and 82% of surveyed households in Thailand in the dry and rainy seasons, respectively. E. coli concentration in HH water seemed to increase during the rainy season. Because E. coli were detected in collected rainwater and stored household water at levels considered unsafe, larger scale water quality surveys should be performed to confirm this finding and investigate causes and interventions. The detection of E. coli in harvested rainwater, an improved water, has implications for the achievement of the UN safe water access target of the Millennium Development Goals (MDGs) because this "improved" water was often microbiologically unsafe.
Users of these water sources could benefit immensely from point-of-use water treatment. POU treatment can be applied using a multibarrier approach, where multiple types of treatment are used to achieve maximum removal of undesirable constituents in water. Metal ions and chitosan polymers are one such multibarrier combination that might be used. The WHO classifies POU technologies that are capable of achieving at least 2 log10 reductions of bacteria in water as "protective". Based on this criterion, ionic copper was shown to be an adequate disinfectant for stored drinking water in a model system under controlled conditions at doses greater than or equal to 0.3 mg/L, well below the 2.0 mg/L WHO guideline value for drinking water. Chitosans may be effective in two ways in combination with copper: it can remove additional microbes above and beyond those inactivated by copper, and it may be sufficient for removing copper ions from water that has been disinfected with dissolved copper ions.
The goal of this project was to measure the effectiveness of chitosan for removing bacteria and viruses from water, both alone and in combination with metals. We have gathered novel data that give insight into the mechanisms that determine how chitosan works as a water coagulant. We have identified both the types and doses of chitosan that are effective for the removal of microbes and turbidity. Microbial removal improves the safety of water; turbidity removal can help increase the effectiveness of other treatment methods, such as chlorine and filters. The determination of doses and types of chitosans is the most difficult element of the work; the chitosans we have identified can now be applied to a wide range of water types and tested in conjunction with other disinfectants, particularly metals, for a multibarrier approach to water treatment at the household level. The work done has been successful in meeting project goals
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 2 publications | 1 publications in selected types | All 1 journal articles |
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Soros A, Amburgey J, Stauber C, Sobsey M, Casanova L. Turbidity reduction in drinking water by coagulation-flocculation with chitosan polymers. WATER AND HEALTH 2019;17(2):204-218 |
SU834753 (Final) |
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Supplemental Keywords:
drinking water, treatment, health effectsProgress and Final Reports:
Original AbstractP3 Phase I:
Evaluation of Chitosan Coagulation as a Sustainable Method for Point of Use Drinking Water Treatment in Developing Countries | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.