Government, Membranes, Water, Water Reuse
Membrane Technology Advances Wastewater Treatment and Water Reuse
Recent developments in technology have resulted in breakthroughs in wastewater treatment and reclamation for water reuse. This progress includes membrane technology, which has emerged as a significant innovation for treatment and reclamation, as well as a leading process in the upgrade and expansion of wastewater treatment plants.
Recent technological breakthroughs in wastewater treatment and reclamation for water reuse include membranes, which have emerged as a significant innovation for treatment and reclamation, as well as a leading process in the upgrade and expansion of wastewater treatment plants.
Early use of membrane treatment for wastewater appeared nearly 30 years ago. However, over the past decade, there has been a rapid increase in the volume of wastewater that is treated with membranes to exceptionally high quality standards, typically for reuse purposes. In fact, today more municipal wastewater treatment facilities are using membrane technologies than ever, and this number is on the rise as the technology offers unparalleled capability in meeting rigorous requirements.
Membranes may be an option when they enable the removal of contaminants that other technologies cannot. They are also more economical than other alternatives, or require much less land area than competing technologies, since they may replace several unit treatment processes with a single one. For wastewater treatment applications, membranes are currently being used as a tertiary advanced treatment for the removal of dissolved species; organic compounds; phosphorus; nitrogen species; colloidal and suspended solids; and human pathogens, including bacteria, protozoan cysts, and viruses. Membrane technologies for wastewater treatment include:
- Membrane bioreactors—usually microfiltration (MF) or ultrafiltration (UF) membranes immersed in aeration tanks (vacuum system), or implemented in external pressure-driven membrane units, as a replacement for secondary clarifiers and tertiary polishing filters.
- Low-pressure membranes—usually MF or UF membranes, either as a pressure system or an immersed system, providing a higher degree of suspended solids removal following secondary clarification. UF membranes are effective for virus removal.
- High-pressure membranes—nanofiltration or reverse osmosis pressure systems for treatment and production of high-quality product water suitable for indirect potable reuse and high-purity industrial process water. Also, recent research has shown that microconstituents, such as pharmaceuticals and personal care products, can be removed by high-pressure membranes.
The biggest technical challenge with the use of membranes for wastewater treatment is the high potential for fouling. Membrane fouling—which can be caused by colloids, soluble organic compounds, and microorganisms that are typically not well removed with conventional pretreatment methods— increases feed pressure and requires frequent membrane cleaning. This leads to reduced efficiency and a shorter membrane life. Other technical barriers may include the complexity and expense of the concentrate (residuals) disposal from high-pressure membranes.
Treating wastewater with membranes is on the rise. It is not only a viable option, but often a smart one when considering plant upgrades and capacity expansion. This approach can be beneficial for a landlock situation; urban, agricultural, and industrial reuse; groundwater recharge and salinity barriers; and augmentation of potable water supplies, meeting very low effluent nutrient limits.
Khalil Z. Atasi, Ph.D., PE, BCEE, F.ASCE is a senior vice president specializing in process engineering for water, wastewater, and industrial wastewater treatment. He is editor in chief and contributing author of Membrane Systems for Wastewater Treatment and serves as CDM Smith’s wastewater discipline leader.