Engineered bio-remediation is a promising, cost- and energy-saving, in-situ method for the treatment of soils contaminated with volatile organic compounds. In a pilot project, a combination of pump and treat and engineered bio-remediation is evaluated for the remediation of chlorinated hydrocarbons. In order to speed up the remedial work, the microbial activity is stimulated by raising the groundwater temperature to 30°C and by phased injection of an organic substrate, while the water from the recovery wells is treated before reinjection. The groundwater is routinely sampled to monitor the distribution of the substrate, the microbial activity, and the development of the contaminant concentration.
In order to reduce the amount of manual sampling, the potential of fluorescent dye tracers as surrogates for monitoring the organic substrate distribution was evaluated. The fluorescent dye Eosin Y was mixed with the substrate solution before the injection, and its distribution was monitored for a period of one year: periodically, by weekly sampling at up to 16 observation wells, and continuously, by using a prototyped, in-line, fiber-optic fluorescence sensor connected to four of the observation wells. The obtained data shows a correlation between the development of the dye concentration and the substrate concentration. Furthermore, decomposition of Eosin Y to an Uranine like fluorescing substance was observed.
This presentation aims to elaborate on the data obtained during the long-term field experiment on tracing engineered bio-remediation: firstly, how automated, in-line fluorescence sensing can improve the management of contaminated site treatment, and secondly, the prospects of dye decomposition as an additional process parameter in engineered bio-remediation.