Grantee Research Project Results

2015 Progress Report: Smart Turbidimeters for Remote Monitoring of Water Quality

EPA Grant Number: SU835732
Title: Smart Turbidimeters for Remote Monitoring of Water Quality
Investigators: Ball, William P. , Kelley, Chris , Majithia, Vishwesh , Farhat, Michelle , Backer, Andrew , He, Ziwei
Current Investigators: Ball, William P. , Kelley, Chris , Backer, Andrew , Brunner, Logan , Burkland, Alison , Farhat, Michelle , He, Ziwei , Majithia, Vishwesh , Murphy, Sushant , Kahn, Daniel
Institution: The Johns Hopkins University
EPA Project Officer: Page, Angela
Phase: II
Project Period: October 1, 2014 through August 31, 2017
Project Period Covered by this Report: October 1, 2014 through September 30,2015
Project Amount: $89,995
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2014) Recipients Lists
Research Category: P3 Challenge Area - Safe and Sustainable Water Resources , P3 Challenge Area - Sustainable and Healthy Communities , Sustainable and Healthy Communities

Objective:

The unaided eye can distinguish cloudy water from clear water, but even visibly clear samples of water can have dangerous quantities of pathogens. Commonly, a chemical or physical disinfectant (such as chlorine, or ultraviolet light) is applied to water during treatment to inactivate pathogens so the water may be safely consumed. However, natural water sources typically contain suspended sediments (such as clay, silt, organic matter) which can interfere with drinking water disinfection by reducing chemical disinfectants in redox reactions (or by reflecting UV light) and by providing micro-refuges in which pathogens can be shielded from disinfecting light or chemicals. It is crucial that suspended sediments be removed to the best practicable extent during drinking water treatment, and that suspended sediment levels are taken into consideration when selecting disinfectant dosage levels. Engineers typically measure the suspended sediment levels indirectly, by measuring the turbidity, or “cloudiness” that these suspended sediments cause -- the device for this is known as a turbidimeter. The modern commercial turbidimeter is a complex piece of equipment that costs several hundred dollars, largely because it is designed to be an extremely accurate, general-purpose laboratory tool. This price is beyond the reach of many low-resource communities around the world. Without access to more affordable turbidimeters, such communities are unable to proactively assess the microbial risk of their drinking water or confirm levels of treatment they are hoping to achieve.  Alternative measures, such as microbial culturing, require equally great expense and time, such that they are impractical for daily use and real-time information processing. By contrast, turbidity measurements (once equipment is available) can be assessed in seconds and at negligible cost per measurement. An affordable, open-source turbidimeter designed specifically for water quality monitoring would therefore broaden access to the principal quality-assurance procedure in the drinking water treatment sector and remove a major roadblock to the sustainability of programs that seek to expand global access to treated drinking water.  

During Phase I of this project, the Johns Hopkins “Smart” Turbidimeters team developed opensource prototypes of a low-cost ($25) handheld turbidimeter, a low-cost ($115) inline turbidimeter for automated continuous sampling, and the means to integrate these devices to the web over Bluetooth and SMS. (Each of these objectives was accompanied by a set of design criteria – these are listed individually in the Phase I report and Phase II proposal.) The main outcome of Phase I was the demonstration that the essential engineering and public health task of routine turbidity monitoring can in principal be made significantly more affordable for lowincome communities around the world. 

Progress Summary:

In the first year of the Phase II project, we have worked to improve our Phase I outcomes by standardizing our prototype designs, lowering costs, reducing complexity, improving wireless communications capabilities, and making device designs that are easier to manufacture. We have collaborated with our main field implementation partner, the Honduran NGO Agua Para El Pueblo, to distribute our devices to field sites for evaluation. And, we have worked to expand our hardware design, integrating chlorine residual detection into our handheld turbidimeters.

 

The team produced several iterations of our handheld turbidimeter during 2015. Comparing the Phase I and current Phase II versions, we have reduced size by 80%, weight by 75%, and assembly time by 66%, while holding material costs at $25 per device. We have upgraded the device's display from a 4-digit “alarm clock” display to a 1.3" OLED screen -- this has greatly expanded the utility of the device's user interface, while reducing the complexity of the circuit board design and lowering passive power consumption by 20%. Disposable alkaline batteries were swapped for rechargeable lithium batteries, improving the environmental impact of the device while lowering the long-term operating costs. Battery life has been significantly improved (by, e.g., switching to a low-dropout linear voltage regulator), allowing 4,000-8,000 measurements per charge cycle. For an additional $5 in materials costs, a real-time clock with battery backup and 256Kb of onboard RAM can now be added to the turbidimeter, allowing automatic timestamping and backup of the most recent 1,000 readings taken. The next version of our handheld turbidimeter will make use of a "2.5-dimension" design plan, in which the case components are sandwiched together and secured with bolts or clips. This will allow case components to be easily cast from polyurethane rather than 3D-printed, which means that cases can be manufactured more quickly, will be stronger, and will be significantly easier to waterproof.

 

We have increased the accuracy of the handheld turbidimeter, particularly for low-turbidity measurements, beyond what was documented in our 2014 Sensors paper. Five key design choices helped us in this effort:

 

1)      The use of multiple infrared LEDs, both to increase total light available for scattering by suspended sediments of aqueous samples, and to allow for the generation of multiple overlapping calibration curves (corresponding to different combinations of lights).

2)      Intentional misalignment of the LED paths: using three LEDs, one at 270 degrees to the sensor face and the other two offset slightly (at +/- 16 degrees) from 90 degrees, helps to correct for optical distortion of the cuvette glass due to anisotropy.

3)      Incorporating charge regulators for each LED, in addition to a voltage regulator for the circuit board, to minimize voltage and ambient temperature effects on LED brightness.

4)      Adding firmware code that automatically doubles the sampling period for very low turbidity readings, and halves the resulting sensor readings, to compensate for the “stair step” pattern of data produced by discrete sensors at very low signal levels.

5)      Smoothing low-turbidity readings with oversampling: For a given sample measurement, multiple readings are taken – each with a different fractional multiplier applied to a standard one-second reading interval (this multiplier then divided from the numerical reading). This “time stretching” of the sampling window is comparable to adding noise to the signal received by the sensor, and yields a significantly better averaged result at low turbidities than would be obtained from simple replicate sampling. (We have tried using equal-interval sampling window fractions (e.g. 9/8, 10/8, 11/8… seconds) and coprime sampling window fractions (e.g. 8/7, 6/5, 4/3… seconds); so far, these appear to perform equally well.)

 

Chlorine monitoring has been added to the handheld turbidimeter with the addition of a TCS3200RD color-to-frequency sensor placed directly below the turbidity sensor, and a green (515 nm wavelength) LED mounted opposite in the sample chamber. This colorimeter setup can be used to detect the presence of the DPD colorimetric indicator, which turns pink in the presence of chlorine. Results to date show that this colorimeter setup can detect chlorine concentrations in the range of 0.8-10 mg/L; work is ongoing to improve detection of lower chlorine concentrations.

The inline turbidimeter has been significantly improved during the first year of Phase II. The current design consists of two 30mA infrared LEDs placed on either side of the digital light sensor (which is covered by a visible-light filter). The device is enclosed in a commercial waterproof case (IP67-grade, manufactured by SERPAC) to which a Lexan viewport is epoxied. The current design performs very well at turbidities above 5 NTU – two cubic calibration curves yield a regression line with R-squared values greater than 0.99995 – and work is ongoing to improve detection accuracy at lower turbidities. Increasing the LED output (by increasing the charge regulators to 40mA, and/or adding a third light), implementing the “stretchy” sampling windows successfully employed in the current handheld turbidimeter, and if necessary protruding the LEDs through the water proof case, should significantly improve low-turbidity inline measurements. Implementing temperature compensation (probably with an externally mounted analog sensor such as an LM35, or a thermistor) is also a current priority.

Over the course of this year the team has improved their knowledge of and familiarity with lowcost GSM modems for SMS communication. This work has reduced the cost of drop-in GSM communications from $90 (with an Arduino Antenova unit) to $20 (with a custom-designed SIM800 board) per device. We have successfully tested an inline turbidimeter, immersed in three feet of water, relaying data with the OpenSourceWater SMS protocol via an internal SIM800 GSM modem, and adjusting its sampling parameters in response to remotely issued commands. We have also tested remote communication via Bluetooth paired to an Android phone, and over wifi (using a $3 ESP8266 wifi module). In collaboration with a Cornell computer science master’s student (Ethan Keller), we have begun the design of a smartphone app for transmitting and receiving device data, communicating the OpenSourceWater server, and providing real-time visualization of water quality data.

We learned during late 2015 that our implementation partner in India, AguaClara LLC, is currently experiencing a much higher-than-anticipated workload and would be unable to help us evaluate our technology. Thankfully, our Honduran partner Agua Para El Pueblo has been able to increase (to ten) the number of treatment plants at which we can evaluate our equipment. Handheld models of our turbidimeters are therefore currently being tested only in Honduras.  We will be shipping inline turbidimeters and handheld turbidity/chlorine residual combo meters to our partner in Honduras within the next four weeks. (We have had some preliminary feedback on our inline prototype from the Maine office of The Nature Conservancy, who tested the device at a project site in Kenya.) The software and hardware schematics for all of the Phase II deliverables are now publicly available in a GitHub repository, under the acronym AWQUA (for Affordable Water Quality Analysis).

Future Activities:

The Johns Hopkins “Smart” Turbidimeter team has built on the work produced during Phase I of this P3 grant. We have significantly improved our previous prototypes and made good progress towards our stated aims for Phase II: cost reductions, chlorine residual detection, improving sustainability of the technology by improving design scalability and marketability, and increasing the breadth and strength of the communications network. This work takes steps towards the ready availability of affordable, responsive, remotely accessible, real-time water quality monitoring with wide potential ramifications for the sustainability and public health of water treatment projects in developing regions around the world. We look forward to continuing this work and meeting other challenges in year two of Phase II. 

Journal Articles:

No journal articles submitted with this report: View all 2 publications for this project

Supplemental Keywords:

Turbidity, chlorine residual, water quality monitoring, open-source, low-cost technology, sustainable development

Relevant Websites:

AQWUA GitHub Repository Exit

Progress and Final Reports:

Original Abstract

2016 Progress Report

Final Report

P3 Phase I:

"Smart" Turbidimeters for Remote Monitoring of Water Quality  | Final Report