Pervaporation for Treating Volatile Organic Compounds in Groundwater

Introduction

“Pervaporation is a process in which a liquid stream containing two or more components is placed in contact with one side of a nonporous polymeric membrane, while a vacuum or gas purge is applied to the other side. The components in the liquid stream sorb into the membrane, permeate through the membrane, and evaporate into the vapor phase” (Freeman 6.59). The term pervaporation is derived “from the two major operations, involved in the separation process, namely, permeation and evaporation” (Peng Ming 815-820). Pervaporation has become more common place in the recent years regarding environmental concerns; this is mostly due to its effectiveness in removing volatile organic compounds from large amounts of water. Conventionally, air stripping or activated carbon are used in these situations but pervaporation has certain advantages over these methods. “Air stripping is susceptible to fouling and merely turns a water pollution problem into an air pollution problem, and activated carbon treatment involves costly regeneration steps and may not be suitable for VOCs that are easily displaced by other organic compounds” (Freeman 6.59). There are also a number of other advantages to pervaporation. The process creates no fugitive emissions, so there is no air pollution created. On the permeate side of the membrane, volatile organic compounds are continuously removed, so there are no regeneration costs. Also, the process uses compact systems and there is potential to recycle or reuse the recovered volatile organic compounds. The theory behind pervaporation can be explained through mathematical equations and certain experimental parameters.

Theory

Membrane performance is evaluated by the experimental parameters of permea...

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...en used to meet NPDES limitations.

There are few limitations on the use of pervaporation technology. First, the pre-filter needs to be cleaned frequently to prevent solids from clogging it. Second, anti-scalents need to be added with influent streams of high alkalinity. Lastly, “highly soluble organics, such as alcohols, are not effectively removed by a single-stage pervaporation process” (Zenon Environmental, Inc. 4). Even with some limitations pervaporation has been proven to be an effective technology.

Pervaporation removes volatile organic compounds to near maximum contaminant levels. Pervaporation modules produce satisfactory results with minimal personnel in a compact design. With spiral-wound, hollow-fiber and plate and frame style modules there is a good amount of flexibility in the technology for treating various pollutants at various concentrations.