Grantee Research Project Results
2011 Progress 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 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 - 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.
There were 6 project objectives:
- 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 and their nanoparticles for their ability to remove bacteria and viruses from rainwater collected by households in Thailand
- Screen a collection of different chitosans and their nanoparticles for their ability to remove metal ions from stormwater captured from green buildings in the U.S.
- Evaluate the user acceptability of chitosan and chitosan nanoparticles for treatment of collected rainwater in Thailand
- Measure the ability of metal ions and chitosans in combination to improve microbial quality of stormwater from green buildings in the U.S.
Progress Summary:
Rainwater Quality in Thailand
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
Efficacy of chitosans for turbidity and microbe removal
Commercially available chitosans were chosen to test a range of molecular weights, degrees of deacetylation (DD) and added functional groups for their effects on turbidity and microbe removal. Initial work to screen candidate chitosans focused on effective reduction of turbidity. Turbidity was created by the addition of kaolinite or bentonite.
Chitosan with MW 100,000 Da showed high efficiency for both kaolinite and bentonite coagulation. The highest reductions were 90.2% at dose 3 mg/L for kaolinite and 98.1% at dose 1 mg/L for bentonite. Chitosan 600K Da worked well with bentonite with the highest reduction 99.1% at dose 3 mg/L but exhibited poor performance on kaolinite; only 20.8% reduction at dose 1 mg/L. The % reduction of kaolinite decreased as chitosan doses increased. For the smallest MW chitosan, 5K Da, a high dose (30 mg/L) could remove up to 79.8% of kaolinite turbidity. The results showed that removal of kaolinite by chitosan 5K Da increased as chitosan doses increased, contrary to the higher MW polymers. Its effects on bentonite removal suggest diminishing returns, with removal of 46.2% at dose 10 mg/L dropping to 41.06% at dose 30 mg/L.
Removal of kaolinite reached a maximum of 87.6 - 92.7 % removal at dose 3 mg/L for all DD tested (70-95% DD). Chitosan with 70% DD gave the highest reduction (92.68%) whereas chitosan 95% DD gave the lowest reduction (87.59%). Although the optimum dose for all DD seems to fall around 3 mg/L, chitosan of 80% DD or greater exhibited a wider range of optimum doses. Degree of deacetylation (DD) appears to exert different effects on kaolinite and bentonite removal. The optimum dose for kaolinite removal was consistent, given the highest reduction at dose 3 mg/L for all DD tested. However, at the 3 mg/L dose, kaolinite reduction slightly decreased as DD of chitosan increased. At dose < 3 mg/L, lower DD chitosan (70 and 80%) showed better kaolinite removal while at dose > 3 mg/L, higher DD chitosan (85, 90, and 95%) showed better kaolinite removal. The highest bentonite removal was observed at dose 3 mg/L. At dose 1 and 10 mg/L, bentonite removal was also high for all DD, ranging from 84.5 % to 98.9%.
At dose 3 mg/L, reductions of kaolinite were 88.7, 87.9, and 91.3% for chitosan lactate, commercial chitosan lactate (stormKlear), and chitosan HCl. Optimal reduction occurred at dose 3 mg/L except chitosan HCl with 85.1% reduction observed at dose 10 mg/L. Chitosan acetate (StormKlear) had the optimum dose at 1 mg/L with 82.1% kaolinite removal; % reduction decreased as doses increased. Carboxymethyl chitosan showed very poor kaolinite removal with maximum reduction 1.46% at dose 10 mg/L. Chitosan acetate also showed poor kaolinite removal. Bentonite removal had a wide range of optimum doses; high removal was observed from dose 1 mg/l to 30 mg/L except carboxymethyl chitosan and chitosan acetate (StormKlear). Carboxymethyl chitosan exhibited only 59.6% bentonite reduction at dose 30mg/L. However, its reduction increased as dose increased. Chitosan acetate (StormKlear) showed high bentonite removal at doses of 1, 3 and 10 mg/L, but its removal dropped sharply at dose 30 mg/L (12.06 % removal). Chitosan lactate, chitosan lactate (stormKlear), chitosan acetate and chitosan HCl showed high bentonite reduction, ranging from 67.1 % to 98.8% across a dose range of 1 - 30 mg/L.
Chitosan polymers used as coagulants can be applied to water in two ways: directly as powder (the way chitosan is usually produced) or dissolved in acid solution (chitosan is readily acid-soluble). Both methods were evaluated here. Chitosan polymer of MW 100,000 daltons applied as powder showed almost no reduction of E. coli; the maximum reduction was 0.05 log10 at dose 300 mg/L. Water turbidity also increased as chitosan dose increased, since the chitosan powder itself adds turbidity: it went from 1.58 NTU at control (dose 0 mg/L) to 8.06 NTU at dose 10,000 mg/L (a 434% increase). Direct addition of powder also can have small pH effects; the pH of water after treatment with chitosan 100K Da powder was stable around neutral pH, but slightly increased at doses >1000 mg/L.
Chitosan was also applied as powder dissolved in a solution in 0.5% acetic acid. When dissolved in dilute acid before applied to water, chitosan 100K Da solution provided 4 log10 reduction of E. coli at dose 100 mg/L and 3.85 log10 reduction at dose 3 mg/L. Reduction of water turbidity was also highest (60% reduction) at chitosan dose 3 mg/L. The pH of water after treatment with chitosan 100K Da solution was stable around neutral pH, but decreased to below 6 at high doses of chitosan (>100 mg/L). The optimal doses for turbidity and microbial removal do not seem to change water pH even when chitosan is dissolved in acid solution. Chitosan of MW 100,000 daltons was applied in powder and solution forms. Chitosan solution (in 0.5% acetic acid) showed significantly higher efficacy for E. coli removal compared to chitosan powder. Chitosan solution could produce > 3 log10 reduction of E. coli starting at dose 3 mg/L whereas chitosan powder has almost no reduction.
Chitosan polymer of MW 600,000 daltons was applied as powder. Powdered chitosan 600K Da showed no reduction of E. coli at doses lower than 3,000 mg/L. E. coli removal occurred at high chitosan doses; maximum reduction was 1.34 log10 at dose 10,000 mg/L. Water turbidity slightly decreased as chitosan dose increased: the maximum turbidity removal was 29.9% at dose 10,000 mg/L. The pH of water after treatment with chitosan 600K Da powder was stable around neutral pH for all chitosan doses. When dissolved in dilute acid before application to water, chitosan 600K Da solution showed 3.76 log10 reduction at dose 3 mg/L, and the maximum reduction of E. coli was 4.17 log10 at dose 100 mg/L. Reduction of water turbidity was highest (57.31%) at chitosan dose 3 mg/L. The pH of water after treatment with chitosan 600K Da solution was stable around neutral pH, but decreased to pH 6 at high doses of chitosan (100 mg/L).
Comparing the efficiency of chitosan 600,000 daltons in powder and solution forms suggested that dissolving the polymer in dilute acid greatly increases microbial removal efficacy. For chitosan polymers of both small (100K Da) and large (600K Da) polymer size, a solution form gave better performance, with > 3 log10 reduction starting from dose 3 mg/L. The large chitosan (600K Da) produced slightly higher E. coli reduction than small (100K Da). The 100K Da chitosan worked better than large 600K Da at lower doses, around 1 and 3 mg/L. However, E. coli reductions were very close, particularly at the lowest optimum dose; 3 mg/L gave 3.76 and 3.85 log10 reduction for 600K Da and 100K Da chitosan, respectively.
Reduction of microbes in water by metal ions
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.
Future Activities:
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.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental 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.