pH Buffering – Overview
Acidity Testing – Avoid pH complications before they happen
Every organism has a pH range within which growth is possible and typically a well-defined optimum pH for maximum growth rates and activity. Although organisms that thrive in low pH (acidophiles) and high pH (alkaliphiles) environments have been isolated, most microorganisms are classified as neutrophiles with pH optimums between pH 6 and 8. Many important bacterial groups responsible for biodegradation of chlorinated solvents belong to this neutrophile category. For example, the pH for optimal growth of Dehalococcoides ethenogenes strain 195, the only known bacterium capable of complete reductive dechlorination of PCE to ethene, is between pH 6.8 and 7.5. Likewise, optimal pH ranges for several Desulfitobacterium species capable of reductive dechlorination of chlorinated ethenes and ethanes are near neutral. Thus maintenance of a circum neutral pH in subsurface environments can be an important factor in promoting reductive dechlorination.
In pristine aquifer systems, low groundwater pH is relatively uncommon although oxidation of sulfides can lead to pH values as low as 4 to 5 under natural conditions. More often, pH excursions are a direct result of site activities including:
Aquifer pH can be increased by the subsurface circulation or injection of a dissolved base or alkaline material. The added alkalinity, however, will be consumed by groundwater acidity and acidic mineral surfaces in the aquifer matrix. Consequently, determination of groundwater and soil acidity is a key component of remediation system design. The acidity and buffering analysis provides the equivalents of base needed to overcome aquifer acidity and maintain a near neutral pH required for optimum biological activity.