When to use a pilot treatment system
Deciding on how to treat a new water or waste source can be very challenging. Piloting, or employing a small-scale test plant, gives you system, cost and operational details that prove the concept of the full scale system.
While not being required for most water sources, piloting will:
- save significant money if water quality falls on the borderline between clearly defined treatment technologies
- provide info on consumable and operational costs
- demonstrate if an operator is comfortable with the technology and is able to effectively operate the plant
- show if the technology chosen can work and/or meet long-term monetary requirements
Piloting is especially useful:
- Where difficult water exists,
- When there is no detailed water analysis
- When the analysis was not done during freshet or summer heat
- When operations and maintenance data is needed
- The water analysis does not clearly indicate one treatment method or another
- When multiple water sources are used, ie ground water and surface water, or multiple wells (blending).
When piloting IS NOT required is when a series of detailed water analyses taken over a few years are conclusive as to the treatment method.
When designing a pilot treatment plant you will need to:
- gather information on pre-filtration, dosing rates and filtration alternatives
- determine the operational characteristics of membrane systems
- compare the performance of RO membranes supplied by different manufacturers
- verify disinfection operational performance
- obtain data to predict operational costs of a full scale plant
The pilot equipment needs to be scalable up to the eventual drinking water flow rate required. A flow rate of 0.1 to 2.0 percent of plant design is normal. The pilot should represent reality as close as possible.
Typical Types of Pilots and Frequency
Filtration: It is important to select the right water treatment technology for the specific water available at a site. If nano-filtration can be used rather than reverse osmosis, capital costs and pumping/power costs will be reduced. Testing out disinfection technologies — ultraviolet as primary disinfection, advanced oxidation and chlorination as residual disinfection — will show if the filtration selected has improved the turbidity and UVT enough.
Data Collection: A full water sampling and analysis program is required. On site sampling is normally carried out manually through analog signals or every 4-8 hours to obtain:
- Raw and treated water pH
- raw and treated water turbidity
- raw and treated water iron and manganese content
- raw and treated water hardness
- flow consistency and consistent pressure trends
The water analysis reveals:
- Major and minor contaminants
- Potable or process water quality objectives
- Flow rate – peak and average
- Project budgets
- Future expansion possibilities
Costs associated with piloting
The cost can range from $3500 to $250,000. A pilot system can be rented or owned depending on the length of piloting time; pilots can be over 1 month or several years.
The challenges of pilots and designing treatment systems is typically there is 1) a lack of data for new water sources. 2) A few chemical analyses do not necessarily define a water source. 3) Piloting a source helps to define and log trends in water quality.
Without understanding the water chemistry or trending over an extended period of time it is difficult to optimize a water treatment design. BI Pure Water designs pilot systems all the time for our final treatment plants and has a wide variety of systems available to rent.
Case Study 1: Pilot test shows different results at two nearby sources
For the Columbia Valley a small filtration plant was pilot tested a few years ago to determine O&M cost, UV and chlorine disinfection. The results during spring melt showed raw water quality remained acceptable for self cleaning and cartridge filtration. Enough data was collected in the testing to design for a full-scale plant, and showed that the system design was cost effective and met Canadian Drinking Water (CDW) guidelines.
However when the same pilot was moved to another location three hours away to Windemere Lake, the 1 micron absolute filters became plugged every 6 days and the water quality objective of less than 1 NTU couldn’t be consistently met. It was found that the piloted equipment was wrong for that source: it was too expensive to operate and didn’t consistently conform to CDW turbidity guidelines. The next step was to pilot a different technology.
Step 2: Testing an ultrafiltration membrane on the water sourcePilot testing was carried out to determine the efficacy of different ultrafiltration membranes. Results showed the ultrafiltration membrane effectively removed small particle (diatoms) that were plugging the previous cartridge filter pilot, without having to use acid or caustic; this was an important O&M detail. It was also demonstrated that whether the water source was from Williston Lake or ground water, with differing chemistry, the technology could meet performance goals over the long term. The pilot also determined what the flux rate was going to be for the full-scale ultrafiltration plant.
Case Study 2: Reverse Osmosis Pilot Test
Case Study 3: Larger pilot plant prevents large scale errors in system design
For a very challenging water source, a larger mobile pilot in a 10 foot container was employed. In warm July and August months the 1 micron absolute cartridge filter was fouled by algae growth. It seemed the RO technology was too expensive on consumables and didn’t effectively reduce TOCs. But the data provided for the design of the alternate slow sand filtration system, saving money and time in the final system.