Collecting water samples is a key component to the HMGA Water Project as it provides data necessary to compare treatment processes. Samples are taken before anything was added as well as after the installation of new treatment technologies.  By comparing the results, the efficiency of the new technology was determined.

Auto-samplers were introduced during the project in order to collect samples throughout a given production day. They are used to collect samples at various times without the user needing to be present.  Grab samples were collected along with composite samples to provide a clear image of a day’s worth of washing.

HMGA Water Project & Auto-Samplers
The project utilized two types of auto-samplers: the Hach Sigma 900 and the MasterFlex E/C Composite Sampler.  These two auto-samplers were utilized due to their ease of use and reliability. Both types of auto-samplers use peristaltic pumps to pull the water from the collection point through the hose to the bottle. All samples collected using the auto-samplers are composite samples; composite samples are a multitude of single samples combined.  The composite samples were compared to results from manual grab samples.

The auto-samplers were set at varying intervals based on requirements of the day.  On regular sampling days, the auto-samplers were set to take samples every half hour for twelve hours. Alternatively, the auto-samplers were set to draw a sample every ten minutes for three hours during the project’s intensive sampling days.

Peristaltic pumps
As discussed previously, the auto-samplers use peristaltic pumps to draw the water up the hose or tube.  The pump works by pinching a flexible tube around rotors which rotate creating a suction on the water.  As shown in Figure 1, the rotors move in a counter-clockwise rotation, creating suction, thus pulling the water up the tube. 
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Conclusion
The use of auto-samplers was integral to the success of the HMGA Water Project.  They offer a user-friendly method to take samples that can be used in a variety of situations.  

The Hach Flo-Tote 3, installed in a pipe, acts as the sensor which measures velocity and level of water. The sensor sends velocity and depth measurements through the cable to the Hach FL900AV meter which calculates flow and acts as a data logger. The data is stored for several days until it is downloaded to a computer. The Hach FL900AV meter is powered by four 6V lantern batteries. The unit is based on the principals of Faraday’s Law of electromagnetic induction. As the water moves through a magnetic field created by the sensor, it produces a voltage which is then recorded. The faster the water, the higher the voltage produced. Using the voltage, a velocity is determined. Flow is calculated by multiplying the velocity by the area of the pipe (Q=AV). The level of water in the pipe is measured using a pressure transducer. The transducer is made up of a thin diaphragm which converts exerted pressure to an electronic signal.

​The software used to compile data, FSData Desktop Instrument Manager, allows the user to graph flow, velocity, and water level. An exporting function is also available to convert data to a .csv file which is compatible with Microsoft Excel.  FSData is also used to calibrate the instrument at installation.
 
Limitations
The flow sensors could not be placed in pipes with a diameter less than 8” due to the width of the sensor, water would flow beneath the flow sensor due to the curve of the pipe. It can operate between -18°C to 60°C. The accuracy of the Flo-Tote 3 sensor was ±2% of reading.
 
Installation and Use
An appropriate band is chosen based on the pipe diameter. The Flo-Tote 3 sensor is attached to the band using screws and the cable from the sensor is affixed to the back of the band using zip-ties with ends snipped in order to have minimal effect on the flow. The sensor and band are then placed into the outlet pipe as far in as possible to minimize turbulence and create a streamlined flow. Lastly the sensor is connected to the logger.

The logger is then connected to the computer using FSData Desktop Instrument Manager. The Set-Up Wizard found within FSData requires the pipe diameter and current water level measurements be manually measured and inserted into the program. This is required once at initial start-up.

​Logging measurements can be set at variable time intervals to suit the application; for example, readings can be taken every 60 seconds. In such cases, there is a need for greater program memory to capture data over longer periods of times. The data is collected by connecting the Hach FL900AV meter to a laptop computer via a cable.

Taking flow measurements in regular intervals provides a clear description of a set period of flow. Peak flows will be displayed as well as regular flow conditions.

Reference

• Hach Company (2013). Flo-Tote 3 sensor: Open channel flow sensor – User manual. Retrieved from http://www.hachflow.com/pdf/Flo-Tote3Man.pdf on 22 June, 2016.