In one of our previous articles on ultrafiltration, we had talked about some of the common problems associated with UF water purification. Some of these issues are avoidable and others can be mitigated with proper systems management. Knowing how to deal with such problems is key to optimizing a membrane filtration process. When designing ultrafiltration systems, it is imperative to keep these issues in mind so that they are dealt with beforehand to avoid any substantial O&M costs. However, they can also be dealt with as they happen whether or not appropriate measures are in place.

Addressing potential issues before they happen is something Genesis Water Technologies, Inc. prides itself in. With our years of prior experience designing, engineering, and working with UF water purification, we know how to minimize the occurrence of these common problems. This includes, knowing what indicators to look for to identify these issues, and how to address these common problems before they happen.

In this article, we will look at some of the more common issues of ultrafiltration systems and how GWT identifies and handles them to keep these units running optimally for our commercial, industrial and municipal clients.

The Problems:

Membrane Fouling

The term membrane fouling refers to a buildup of biological matter, solids, or scale on the membrane and within its pores. It is understood, that particulate matter will adhere to a grow on the membrane due to the nature of the process. However, if developed in excess, fouling leads to decreased membrane flux, and an increased pressure difference across the membrane. This fouling process can also cause lower permeate flow rates and increased energy use from over utilized pumps.

Waste Stream Disposal

In membrane separation systems, up to 15 % of the feed water volume ends up as a secondary waste stream. This filtrate water contains the concentrated collective of the retained pollutants from the process. Due to the fact, UF water purification is a physical process, no chemical additives contribute to the composition of the wastewater stream. The issue presents itself when the system user must decide what to do with the secondary waste. Not all cases can be solved by simply discharging it, if it contains harmful contaminants.

Permeate Contamination

UF water purification systems efficiency is determined in part by the consistent quality of the permeate water. However, on occasion a facility may experience a decrease in that quality with contaminants found in the permeate. It fact, it may even reach a level that is unacceptable in the scope of the system design and treated water quality regulations. This contamination can happen when a membrane is torn or damaged in such as way to allow larger particulate matter to leak into the permeate stream.

Identifying the Problems at Hand:

The effects of these kinds of issues aren’t so obvious as a smoking engine, therefore, careful monitoring of operational parameters and particulate is strongly recommended..

There are a few key performance indicators in UF water purification systems, that can provide warnings to an operator in the event a problem may be occurring, namely fouling and permeate contamination:

• System pressure drop

  • Pressure changes will indicate flow restriction which is a side effect of membrane fouling.

• Permeate turbidity

  • Increased permeate turbidity would typically signify the membrane has been compromised.

• Permeate flow

  • If the flow of the permeate slows down, it is quite likely that the membrane has been fouled by some contaminant. Of course, measurements of this indicator should be corrected for factors like temperature and pressure drop to get the normalized flow rate.

• Feed water composition

  • Particularly look out for hardness minerals and high suspended solids and organic matter concentrations.These elements could be possible causes of membrane fouling.

Solving these Issues:

Fouling

Membrane fouling has a few potential solutions available depending on the situation. GWT takes preventative measures in system design optimization to minimize the occurrence of fouling for clients new or existing UF water purification systems. This includes proper pretreatment measures such as coarse filtration, coagulation and flocculation, and antiscalants. For reduction of fouling during operation, GWT systems can include air scouring, using bubbles to scrub off buildup as the system runs based on water quality. Cross flow system configurations will also prevent excessive buildup by using shear forces to remove organic matter. Regular back washing is also one of the vital mechanisms to fouling prevention. Cleaning with certain chemicals can also ensure the removal of any stubborn particulate matter from the membrane surface.

Disposal

In some applications, the secondary waste is safe enough to simply discharge or inject into a deep well if available and regulatory permitted. In those cases, it may even be possible to dilute the solution and use it for irrigation. Other cases may require a filter press to remove the suspended solids so that the water may be discharged. If there is a high presence of organic matter, the waste could be disposed on in a municipal sewer.

However, disposal usually is enforced according to local regulations in place and therefore, the facility should have a plan in place prior to system installation to handle this appropriately.

Contamination

As permeate contamination is a result of a compromised membrane, regular integrity testing and careful membrane selection is absolutely imperative. Over time, membrane integrity can typically degrade. However, the rate of degredation depends on the feed water composition (i.e. high pH or other contaminant) therefore, operators should be careful to monitor this parameter over time. In addition, selecting the proper membrane material for a particular application will minimize degredation as well. Genesis Water Technologies assists our clients in recommending proper membrane material for the specific application and the associated pretreatment to reduce client operating costs.

Do you need to remediate these issues with your current UF water purification system? Are you encountering another problem not listed here with your system? Contact the water treatment experts at Genesis Water Technologies, Inc. at 1-877-267-3699 or email us at customersupport@genesiswatertech.com to discuss your application with one of our qualified representatives for a free consultation.