By Edward Koch
For many shuttered or abandoned chemical production sites, groundwater remediation is a requirement to address health, safety, and environmental issues. Remediation generally involves extracting groundwater from wells, processing it through various separation and purification process steps, and reinjecting the water back underground. Processing steps may include, among others, multistage particulate filtration, ozonation, air stripping, granular activated carbon adsorption, pH control, etc. Strict water quality standards must be met before reinjecting the water. The remediation process train is site-specific and the process design must depend on condition of water in the aquifers and local regulations.
In one such remediation site in southern California, it was mandated that the dissolved oxygen (DO) concentration of the water to be injected should approximately match the DO concentration of the water in the receiving aquifer, which was less than 1-2 mg/L. A Membrane Degasification (MDG) solution was considered because of the technology’s proven experience in many industries to achieve desired DO concentration levels. The technology enables building compact systems that are modular, mobile, and scalable, without the need to use chemicals for DO reduction. Membrane degassers are also called Membrane Contactors (MC) or Gas Transfer Membranes (GTM). A small-scale trial MDG DO removal system was designed and built using 3M™ Liqui-Cel™ 4×28 Membrane Contactors and operated for pilot demonstration. Specific trial objectives were: (a) to determine changes in water chemistry, TDS, hardness, and SDI before after MDG, and to assess the degree of fouling, if any, after processing about 90,000 gallons of treated water.