Micro-Bubbles Oxygen Injection in Groundwater Contaminated by Organic Biodegradable Compounds and Metals

Site is a pharmaceutical facility located in Milan Province with main contamination by TPH and BTEXS (about 100–120 mg/L). The results of pilot test were great (100% of degradation in 5–6 month). At the moment the Emergency Measures Project design is currently in progress (about 33 points of oxygen delivery). Contaminants are not transferred from one media to others, but are biodegraded to CO2 and Water, so this technology is in accordance with AECOM global vision on Sustainable Remediation technologies. S̲p̲e̲c̲i̲a̲l̲ d̲i̲f̲f̲u̲s̲e̲r̲ used allows the minimization/elimination of contaminant volatilization due to no bubbles or micro-bubbles (max Ø less than 0.1 mm) and low flow (0.5 – 1 NL/h); on site these diffuser is able to dissolve up to 50 mg/L oxygen. L̲a̲b̲ s̲c̲a̲l̲e̲ b̲a̲t̲c̲h̲ t̲e̲s̲t̲: The test objective is to evaluate, under controlled conditions, the feasibility of bioremediation, by injection of pure oxygen; Batch tests was performed in controlled microcosm with continuous monitoring of pH, Red-Ox and dissolved oxygen, periodic monitoring of chemical parameters on both the matrix: on water and in air line (by activated carbon) and microbiological analysis; batch test show the complete degradation of organics in 20 days. F̲i̲e̲l̲d̲ P̲i̲l̲o̲t̲ T̲e̲s̲t̲ (one injection well, two lateral monitoring wells and one downgradient monitoring well): The test objective is to assess the feasibility of remediation @ field-scale using bio-stimulation with pure oxygen; first period of injection of a mixture of oxygen and tracer nobles gas (Krypton and Neon) in order to highlight the effectiveness of removal of the contamination and to identify the range of influence of the technology. B̲a̲s̲e̲l̲i̲n̲e̲: Total hydrocarbons and toluene, at maximum concentrations equal to 100 – 120 mg/L; main contaminant is Toluene, the chlorinated organic compounds (low concentrations) are also present upstream site; due to reducing condition there was presence of dissolved iron (5 to 32 mg/L) and manganese (4 and 9 mg/L). After 8 month Removal efficiency (due to aerobic degradation) for organics are: 95 to 99.99%; in addition due to recreation of natural oxidizing condition also metals (Fe, Mn and As) re-precipitate. Bacteric count (general and oxidizing specific bacteria) grow from baseline 10^+1/+2 UFC/mL to 10^+5/+6 UFC/mL due to correct growing substrate and electron acceptor (O₂). Results: Lateral ROI is estimated to be at least 4 m (diffusion of approximately 2 m/month), oxygen influence downstream of at least 25 m (diffusion of approximately 8–9 m/month). These results show that pure oxygen diffused into the groundwater in the area has stimulate indigenous biomass and thus promote the biological aerobic removal of pollutants so contamination can be removed with yields close to 100%. N̲o̲t̲e̲: in one area of site at the end of Pilot test we found also Tetrahydrofuran and Dichloromethane, we perform a fast batch test and we note that also these contaminant are quickly degraded (75% and 97%) due to aerobic co-metabolism in presence of toluene as growing substrate.