Grantee Research Project Results
Final Report: Stacked Rapid Sand Filtration - A Robust Filtration Process for Sustainable Drinking Water Infrastructure
EPA Grant Number: SU835544Title: Stacked Rapid Sand Filtration - A Robust Filtration Process for Sustainable Drinking Water Infrastructure
Investigators: Weber-Shirk, Monroe , Lion, Leonard William
Institution: Cornell University
EPA Project Officer: Hahn, Intaek
Phase: II
Project Period: November 15, 2013 through November 14, 2015
Project Amount: $90,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2013) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Safe and Sustainable Water Resources , P3 Awards , Sustainable and Healthy Communities
Objective:
The AguaClara Program challenges in Phase I were to design an Enclosed Stacked Rapid Sand Filter (EStaRS) applicable to small communities, determine the feasibility of the lowflow unit for use as a standalone treatment (without pretreatment of water by flocculation and sedimentation), and to optimize operation and maintenance. Scaling down the original Open Stacked Rapid Sand (OStaRS) filter presented significant design challenges. The need for maintenance and assembly required that workable access to the internal pipes be retained. New methods had to be devised for connecting different sized piping and for fabricating leak free throughwall connections. To reduce the height of the EStaRS unit, a removable cap was needed to facilitate pressure changes in the filter and backwash operation under negative pressure. The presence of the cap that encloses the filter allows creating both positive and negative pressures within the unit at different stages of operation and required seal designs that were water and air tight.
Part of the effort in Phase II was devoted to resolving the operational weaknesses discovered in Phase I testing of the prototype EStaRS. Initial testing in Phase I revealed difficulty with sand removal, the need for a system to monitor sand fluidization inside the filter column, lack of strength of mechanical connections of distribution pipes, loss of small amounts filter sand during backwash and an air leak into the filter that interfered with initiation of backwash.
During Phase II the Cornell team collaborated with its implementation partner AguaClara LLC to test, evaluate, and deploy six 30 cm diameter EStaRS filters in two villages in Jharkhand, India. The EStaRS filters in India are used in direct filtration mode to treat well water that is under the influence of surface water. Shallow water wells are common in many developing countries and a long term project objective is to expand AguaClara technologies to other countries. The direct filtration systems deployed in India include an EStaRS interfaced with the linear flow orifice meter and chemical doser developed in prior EPA P3funded research. Doser regulated coagulant is added to the raw water prior to filtration and doser regulated chlorine is added after filtration for disinfection. Shallow well waters with relatively low turbidity (1 to 5 NTU) do not require the typical prefilter particle removal treatment processes of flocculation and sedimentation.
Performance monitoring of the initial field units in India has proven to be too difficult at this stage. The next generation of water treatment plant monitoring software including a custom designed app for SmartPhones will be released later in 2016. The goals of this next generation app is to simplify sending plant performance data to the server and to provide helpful summary data and advice.
Our implementation partner in Honduras, Agua Para el Pueblo, has now constructed 5 water treatment facilities with OStaRS filters. The OStaRS filters provide an additional barrier against particle and pathogen contamination. Agua Para el Pueblo has also designed two surface water treatment plants that each will have two 60 cm diameter EStaRS filters. Agua Para el Pueblo expects to build these facilities in 2016.
Figure 1. Performance data of the newest AguaClara plant in Honduras. The OStaRS filter is meeting EPA drinking water standards for turbidity.
Summary/Accomplishments (Outputs/Outcomes):
Stacked rapid sand filters (StaRS filters) were invented by the AguaClara program at Cornell University in the spring of 2010. The StaRS Filter invented by the AguaClara program consists of 6 sand filtration layers stacked on top of each other requiring less surface area than either slow or rapid sand filtration. During filtration the flow in a StaRS filter moves through six parallel paths within the filter. During backwash, the filter redirects all flow through the bottom inlet to the filter effectively increasing the flow through each layer by a factor of 6 and allowing the sand media to be fluidized for backwash. Two distinct versions of the StaRS filter have evolved over the past 6 years. The first design is an open (OStaRS) masonry tank that is suitable for flows above about 8 L/s. There are currently 7 OStaRS filters operating in Honduras serving 22,800 people and designed for a total flow rate of 94 L/s (Table 1). The OStaRS filters have a height of 4.5 m and can be designed for flow rates between 8 L/s and about 25 L/s. We recommend using at least two filters in all future water treatment plant designs to ensure that there is adequate flow for backwashing and to provide some flow capacity if a filter needs to be taken offline for maintenance.
Table 1. OStaRS Filters installed in Honduras as of February 2016
| Location | Inauguration Date | Population Served | Filters | Design flow (L/s) |
| Tamara, F.M. | June 15, 2008 | 3500 | 1 | 12 |
| San Nicolas, Santa Barbara | April 5, 2014 | 6000 | 2 | 32 |
| Moroceli, El Paraiso | Jan 16, 2016 | 4500 | 1 | 16 |
| Jesus de Otoro, Intibuca | Jan 2015 | 5000 | 2 | 20 |
| San Matias, El Paraiso | Jan 2016 | 3800 | 1 | 14 |
The second version of the StaRS filter is Enclosed (EStaRS). The enclosed version is fabricated in a pipe and because it is enclosed it can operate under positive or negative pressure . EStaRS filter are only 1.8 m tall and have been deployed in two villages in India. The EStaRS Filter retains the AguaClara design principles of operation without the use of electricity within the water treatment plant as well as fabrication without the use of expensive or difficult to obtain components.
Both the EStaRS in India and OStaRS in Honduras require maintenance to clear the injection slots that deliver water into the sand bed. The filters in India needed to be taken off line during an algae bloom in one of the open wells. The clogging of the injection slots led to a concerted innovation effort to invent an improved method of injecting water into the sand beds. An initial design was created in the fall of 2014 and then tested at laboratory scale in the spring of 2015. The new design was deployed in the San Matias filter in Honduras in the fall of 2015. The inlets have sand guards (Figure 2) that created a clear interface between the fluidized sand and water to prevent sand from entering orifices. The orifices replace the slots that were used previously and the orifices are large enough in diameter to completely eliminate any concerns with clogging.
Figure 2. Section of an inlet manifold showing the sand guards and orifices that replace the slotted pipes.
An AguaClara StaRS team spent a semester evaluating the feasibility of using an orifice and sand guard system to extract filtered water from a StaRS filter. They concluded that it was too difficult to fabricate an extraction system that had a sufficiently large sand/water interface to prevent sand fluidization. Thus the StaRS filters will continue to use slotted pipes for filter effluent.
The AguaClara team will continue to improve the StaRS technologies. During the spring of 2016 we will be developing an improved manifold support system for OStaRS. The manifolds experience significant vertical forces during the transitions between settled sand and fluidized bed. Our goal is to devise support structures that are easy to install and that provide long term stability for the plumbing that is embedded in the sand.
We are also continuing to investigate particle removal in StaRS filters with a goal of better understanding the role of filter bed depth and the role of floc size distribution entering the filter.
Conclusions:
StaRS filters have solved the century old problems of filtered water storage and backwash pumping associated with conventional rapid sand filters. By using high quality settled water to backwash filters and by using a stacked geometry it is possible to backwash the StaRS filter without even changing the flow rate to the filter.
EPA P3 has provided critical support for the development of StaRS filters. The EPA funding has made it possible to develop an innovative flow injection system that eliminates the inlet clogging that the first generation of StaRS filters experienced. EPA funding also enabled the team to develop, test, and iterate on the design of an Enclosed StaRS filter.
The deployment of StaRS filters continues with a current global installed capacity of 100 L/s and a new 70 L/s plant under construction for the town of Las Vegas, Honduras. It is likely that the global installed capacity of StaRS filters will more than double in 2016.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
| Other project views: | All 2 publications | 2 publications in selected types | All 2 journal articles |
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Adelman MJ, Weber-Shirk ML, Will JC, Cordero AN, Maher W, Lion LW. Novel fluidic control system for stacked rapid sand filters. Journal of Environmental Engineering 2013;139(7):939-946. |
SU835544 (2014) SU835544 (Final) SU835307 (Final) |
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Adelman MJ, Hurst MW, Weber-Shirk ML, Cabrito TS, Somogyi C, Lion LW. Floc roll-up and its implications for the spacing of inclined settling devices. Environmental Engineering Science 2013;30(6):302-310. |
SU835544 (2014) SU835544 (Final) |
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Supplemental Keywords:
Sand filtration, community scale water treatment, gravity powered, zero electricityRelevant Websites:
Progress and Final Reports:
Original AbstractP3 Phase I:
AguaClara Stacked Rapid Sand Filtration – A Robust Filtration Process For Sustainable Drinking Water Infrastructure | 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.