Regular Sampling Days vs. Intensive Sampling Days
During the length of the HMGA Water Project, two types of sampling days were developed to give a clear picture of the water quality over a day and over three hour intervals.  Regular sampling days involved taking one set of samples at each point of the treatment process with auto-samplers placed at the pre-treatment and post-treatment positions.  Intensive sampling days were often bordered by regular sampling days and grab samples were taken every three hours along with the collection of the composite samples from the auto-samplers. ​

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. 
​
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.  

Some solids are too small to be captured by solid removal techniques. They need to be compounded together in order to make them large enough to be efficiently separated from water. This process is referred to as coagulation and flocculation.

​Electrocoagulation is a method of coagulation and flocculation which applies an electrical charge to make the particles come together by changing the charge on the particles’ surfaces. The wastewater is held in an area where an electrical field is created using charged metal surfaces called anodes and cathodes. Applying the charge to the water destabilizes the bonds holding compounds such as solids and nutrients to water molecules. It will also strip the charge from colloids. These destabilized particles now come together to form a mass. This process will create a stable floc of particles that rises to the surface, a sludge layer on the bottom, and clarified water in the middle. The waste can be removed by skimming from the surface and collecting from the bottom; it can then be dewatered and composted. The clarified water is removed from the center and brought to its next destination.

The alternative to electrocoagulation is using chemicals to coagulate and flocculate. The advantage of electrocoagulation is the waste stream is free of any added compounds. Chemical dosing systems are also greatly dependent on the pH, composition of the water to be treated, and the flow rate. The dose may need to change regularly in response to these factors in order to be fully effective. The disadvantage of electrocoagulation is that it is reliant on a sufficient electrical supply and will require a sludge de-watering system. Both versions of coagulation require on-going inputs, whether be chemicals or electricity.

​Problem: A greenhouse facility wants to reuse water from a flood floor which is used to water potted plants. The water collected has vermiculite and organic matter clouding the water which would clog nozzles and settle in pipes.
 
Solution: The operator looked at two different technologies, a self-indexing filter and a parabolic filter screen (Figures 1 & 2). Both are recommended units that filter coarse material from water.

​Discussion: The infrastructure required for either technology is similar; both will need some plumbing and a pump to move water through the treatment system. The technologies are compared in the table below. Both systems will complete the task; the self-indexing filter is more hands-off but requires more inputs. The parabolic filter screen must be supervised but has minimal on-going costs.

​Decision: The operator choses the self-indexing filter as it requires less regular supervision. The additional energy costs, on-going need of paper rolls, and disposal of paper was preferable to increased labour requirements and disposal of waste.
 
Lesson Learned: When there are multiple technologies that could fit in a treatment system it is important to investigate all aspects. Decisions should be made based on more factors than merely cost.

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.

The HMGA Water Project evaluated coagulation and flocculation systems for removing fine solids from washwater. They were used in conjunction with large solid removal technologies and compared to other systems with no added chemicals. A summary of the tests and results are available in the article below.

This project has produced an array of factsheets on a range of topics. Below is the list grouped into topics and arranged in a suggested reading order. The documents can be found here, unless otherwise noted.
 
Water Qualities
#012 Water Quality Standards in Agriculture
#001 Water Quality Parameters for Vegetable Washwaters
 
Regulatory Considerations
#004 Considerations when Determining Discharge Limits
#018 Selecting a Laboratory
#006 Water Sampling & Proper Procedures
#009 Regulatory Permitting & Compliance
 
Technology Considerations
#016 Design Considerations for Vegetable Washwater Treatment Systems
#007 Choosing Washwater or Water Treatment Technologies
#002 Impact of Muck Soils on Water Treatment Systems
 
Large Solid Removal
#014 Large Solid Removal for Effective Treatment
Technology Investigation: Filter Bags (available here)
#005 Settling Ponds & Tanks
#008 Drum Filters
#010 Hydrocyclones & Centrifuges
 
Small Solid and Nutrient Removal
#003 Coagulation & Flocculation
#013 Biofiltration
Technology Investigation: Ultrafiltration & Capacitive Deionization (available here)

Polishing and Dosing
#011 Bottom Aeration
#017 Surface Aeration
#015 Water Treatment Technology Options for Washing Vegetables