The Most Common Problems in Water Treatment
The list of potential problems that water treatment managers face is almost endless. But there are a number of common problems that recur frequently and need to be addressed. At Water Care, we are dedicated to finding solutions to the most common and complex problems that water treatment professionals face. We have compiled a list of recommended solutions, which outline effective ways to overcome the challenges facing water treatment.
The five most common problems in water treatment are:
- Training problems
- Bacteria control
- Poor monitoring and record keeping
- Equipment design and specifications
- Maintenance problems
Technician training problems are common problems in water treatment
Most water treatment plants are small segments of a larger business system, such as a reverse osmosis system that supplies water to a 16-stage facility. The teams are large, and the process is highly technical. Managing the systems involved requires extensive and ongoing training for employees at every level within the team.
Without proper training, teams run the risk of misunderstanding the complex aspects of their sector. With high-quality, ongoing training, you can avoid this and help employees throughout your facility thrive as industry experts with up-to-date knowledge.
Regardless of job role or position, every team member in a water treatment facility should have a basic knowledge of the relevant subject. This includes:
- Identifying each piece of water treatment equipment, how it works and operating parameters.
- Understanding preventive maintenance procedures to reduce the risk of difficulties.
- Knowing which parameters to monitor and how to identify problems.
- More advanced knowledge is defined as the ability to troubleshoot and fix problems before they occur.
The most common water treatment problems that employees are likely to encounter are:
- Scaling
- Membrane fouling
- Bacteria
- Mechanical failure
- Device failure
Employees with advanced knowledge can provide on-the-job support to fill knowledge gaps. This creates a better opportunity to identify and resolve problems before they become more serious.
Most facilities rely on equipment suppliers for specialized knowledge rather than training employees in-house. However, by providing this high-level expert training in-house, employees will be able to quickly identify:
- Mechanical and device failures.
- Complex chemical, biological and bacterial problems.
Bacteria Control
Bacteria grow extensively under the following conditions:
- Presence of food for the bacteria
- Warm temperature
- Low flow rate
- Absence of bacteria control solutions
Most microorganisms feed on carbon-containing organic compounds. The ideal temperature range for most waterborne microorganisms is 30°-40° (86-105°F); this is where the fastest growth occurs.
The concentration of dissolved organic compounds in the feed water is measured as total organic carbon or total oxidizable carbon (TOC).
Microorganisms grow best when a steady supply of food is supplied at a low flow rate, giving the bacteria time to reproduce.
Increased flow rates reduce this due to the overwhelming force of the water. Chemicals that kill microorganisms are called biocides.
Common Practices
Common practice used to be to use oxidizing agents, such as chlorine, as biocides. However, with the introduction of stricter health, safety, environmental and chemical regulations, UV disinfectants have become the most common method of bacteria control used today. However, there are microorganisms that can tolerate UV radiation, making the use of UV disinfection a better choice for membrane filtration. Most nanofiltration and reverse osmosis membranes have a very limited tolerance to oxidizing agents. It is best to remove these oxidizing agents from the feed water above the membrane unit. This is done by passing the feed water through an activated carbon bed or water softener.
- Failure to remove these oxidizing agents will result in bacterial growth, which will foul the membrane.
- This reduces the flow and makes the problem progressively worse.
- The only solution was to add a biocide to this rinse section to reduce bacterial growth.
- A UV module system was proposed that would eliminate bacterial infection and reduce the use of biocide in the system.
- Once installed and operational, tests were conducted to ensure the units performed with tremendous results.
- Bacterial buildup was significantly reduced without the addition of any chemical biocide, and as a result, the client is now implementing the system throughout its global operations.
- UV Bacteria Control Exploration
Monitoring and Record Keeping
Many water treatment systems do not have enough instrumentation to check all parameters to catch problems at their most preventable stages or vice versa.
Even when adequate metering is in place, many facilities do not record data properly to allow them to see patterns in the data or plan preventative actions.
It may seem like if you have excellent feedwater coupled with an excellent membrane unit and pretreatment design, the system will just work on its own and take care of itself. However, this is not always the case.
It is essential to monitor certain parameters, such as:
- Monitoring and Record Keeping in Water Treatment Management
- Silt Density Index (SDI)
- Normal Permeability Flux (NPF)
- Pressure across each stage
- Salt Rejection Ratio (PSR) or Salt Passage Ratio (PSP)
- UV Intensity
- Silt Density Index (SDI) is a measure of the potential for contamination of feedwater. It is done by measuring contamination on a membrane filter pad after the feedwater has passed through for fifteen minutes.
Silt Density Index (SDI) means that measurement may only be required monthly.
However, for surface water, it should be measured once a day. The data should then be recorded and graphed weekly to allow you to see emerging patterns.
Normalized permeability flux is a measure of how membrane units are performing now, versus when they were new. Normalized permeability flux takes into account changes in temperature, flow rate, salt concentration, and operating pressures. If normalized permeability flux decreases, it indicates membrane scaling or fouling. If it increases, it indicates membrane damage or bypass.
Many membrane units operate on a pressure drop. This is a measure of the inlet pressure to the membrane pressure vessel, minus the outlet pressure. It is related to the flow through the membranes. With higher membrane fouling, there is less space for water to travel, causing more resistance and increased pressure drop. Salt rejection rate measures the percentage of conductive material that the membranes reject, known as the concentration. Relative salt passage rate (PSP) is the opposite, measuring the percentage of conductive feedwater molecules that pass through the membranes. A conductivity meter measures the value in real time. 10 micro Siemens is the most common.
Operating a UV disinfection system does not mean it will work without further attention. The flow of water passing through the UV lamp requires a certain amount of UV intensity to deliver the correct disinfection dose (mg/cm²). Monitoring the UV intensity will indicate when the quartz shell is becoming dirty and delivering the incorrect UV dose.
Poor Specifications in Equipment Design
Industrial water treatment is booming. As more OEMs enter the market, many of them inexperienced, it is important to understand what the ideal design specifications should look like to minimize problems.
- Designs should include the following components:
- Conservative water flow rates
- Relatively high crossflow rates
- Sufficient metering for adequate monitoring
- Adequate cleaning facility
Water flow (known as GFD, gallons of permeate produced, per square foot of membrane per day) is the amount of permeate that passes through the membrane area in a given period of time.
Acceptable water flow rates are:
- Surface water
- A treatment plant with adequate pretreatment – 10-14 GFD
- Well water treatment plant with adequate pretreatment – 15-20 GFD
- Highly pretreated feedwater, such as ultra-filtered water – 20-30 GFD
To reduce costs, a new inexperienced OEM may specify fewer membrane elements and pressurized vessels than a fully experienced OEM. The result is the same amount of permeability produced through a smaller square area of membrane resulting in a higher GFD resulting in a higher fouling rate. Crossflow rates refer to the rate at which feedwater passes through the membrane surface. The higher the crossflow rate, the greater the shear force. This means a lower fouling rate.
To monitor these parameters, the following monitoring instruments will be required within the unit:
- Feed water temperature
- Feed water pressure
- Feed water conductivity
- Permeate flow rate
- Permeate pressure
- Permeate conductivity
- Concentrate flow rate
- Concentrate pressure
- Pressure drop between each stage
- UV intensity
Most units have their own built-in cleaning system including:
- A cleaning tank that can hold 2 – 2.5 times the volume of water in the first stage pressure vessel
- A proper mixing system for the cleaning tank so that all chemicals required for the cleaning process are dissolved prior to the cleaning process.
- A heating element, temperature indicator and control unit.
- A cleaning pump that can deliver up to 40 gallons per minute per pressure vessel of cleaning solution for each stage being cleaned, at a pressure of less than 60 psi (4 bar).
- A cartridge pre-filtration system to remove any particulate matter prior to membrane cleaning.
- A flow indicator and flow control valve for cleaning solutions.
- Inlet and outlet pressure indicators to monitor pressure drop and control flow rate.
- Sample point so that pH, conductivity and other parameters can be monitored.
Poor maintenance
Poor maintenance of a water treatment facility can have serious impacts on performance. The Poor maintenance can lead to increased costs, significant damage to systems and financial losses to customers. It is important to have regular maintenance in water purification systems because:
- A preventive maintenance schedule for changing pre-filter cartridges and bags helps extend the life of the membranes within the system
- Reduces the build-up of sediment and dirt on the membranes
- Money is saved due to reduced unit downtime because leaks are found and repaired faster
- Customers can predict flow trends, pressure and purified water quality to enable the best results by keeping detailed maintenance records
- The unit remains in good condition, giving the best results for the longest period of time
Conclusion
The five most common water treatment problems can be solved through expert facility management to protect the customer and the facility itself from losses, damaged reputation and regulatory violations. With proper bacteria management and maintenance, as well as excellent record keeping, monitoring, and employee training, facilities can leverage the excellent resources available to them to dominate their industry as water treatment experts. At CareWater, we are happy to help you avoid these common mistakes and find the right solutions.