High-rate ex situ and in situ treatment system for groundwater denitrification via membrane-based bacterial macro-encapsulatin

The main aim of this study was to develop a new biotreatment process for denitrification by using a small bioreactor platform (SBP) for macro-encapsulation of a bacterial consortium equipped with a slow-release organic matter core for ex situ and in situ treatment configurations. The biotreatment system in the continuous ex situ mode achieved a maximal nitrate removal load of 38.9 g nitrate/L/day with a short hydraulic retention time (HRT) of 1.3 h. The in situ configuration showed high performance for >50 days, with 85 % nitrate removal from an initial concentration of 110 mg/L. The capsules continuously removed nitrate at the same rate even when the organic matter level in the internal capsule was low. After 30 days of in situ experiments, the bacterial population composition set inside the SBP capsules presented dominant populations of well-known heterotrophic denitrifying bacteria. Thus, the encapsulated process not only demonstrated a short HRT necessary for high nitrate removal rates in ex and in situ configurations, but also potentially lower operational costs and no secondary environmental contamination caused by excess organic matter.