Regulatory pressure to provide better treatment for potable and waste waters (Clean Water Act, Safe Drinking Water Act, Enhanced Surface Water Treatment Rule), and water supplies with lower quality than those relied upon previously, contribute to the global increase in membrane use in environmental engineering applications. Membrane technology enhances Greeley and Hansen's foremost process engineering capability to better serve the firm's clients.
A membrane is a thin layer that can separate materials depending on their physical and chemical properties when a driving force (e.g., pressure) is applied across the membrane. Membrane processes may be used to treat wastewaters prior to discharge to surface waters, to recover materials used in industry before they enter waste streams, and to desalt oceans or brackish waters for potable use. Membrane processes can either provide a function unmet by conventional water treatment plants (e.g., salinity removal), or enhance filtration capability of conventional water treatment plants.
The raw water quality dictates the type of membrane to use, as well as its construction and O&M costs. For pressure-driven membranes, if particle removal is the primary objective, microfiltration (MF) and ultrafiltration (UF) are the membranes of choice. Nanofiltration (NF) is a type of membrane that can meet multiple water quality objectives (e.g., color removal, water softening, THM precursors, salinity removal for brackish waters). Finally Reverse Osmosis (RO) offers the highest rejection of total dissolved solids (TDS) and ionic species. Costs increase with selectivity and operating pressure.
