Perchlorate bioremediation: Controlling media loss in ex-situ fluidized bed reactors and in-situ biological reduction by slow-release electron donor

The main concern of perchlorate exposure through drinking water is its effects on the production of thyroid hormone, which is important for human metabolism and child's brain development. The US Environmental Protection Agency (EPA) has listed perchlorate in the contaminant list as well as in the Unregulated Contaminant Monitoring rule.;The extent of perchlorate contamination can be categorized by the level of contamination into parts per million (ppm) levels, typically in locations where perchlorate was manufactured, and parts per billion (ppb) levels where perchlorate was used for various purposes. Ion-exchange is generally adopted for treating ppb levels of perchlorate while biological reduction, bioremediation, is preferred for treating ppm level contamination.;This dissertation focuses on two important but not completely researched issues related to ex-situ and in-situ perchlorate biodegradation: (a) Use of digital image as a tool to determine appropriate backwashing frequency for fluidized bed reactor (FBR) used to treat perchlorate contaminated waters, (b) Feasibility of using a slow release electron donor, emulsified oil, to support in-situ degradation of perchlorate in groundwater with slow and fast hydraulic conductivities.;To address the first issue, two FBRs were built using five feet long and half inch diameter transparent plexiglass columns. Activated carbon was used as media and synthetic solutions containing 100 ppb, 100 ppm, and 10 ppm perchlorate were used. A high resolution camera was mounted targeting the operating zone of the FBR and pictures were taken at interval of 1.5 hours. The digital pictures were analyzed using the image processing tool, ImageJ. A biofilm model was developed and its simulated results were used to determine theoretical frequencies to backwash the filters so to avoid media loss. To address the second issue, four 5-foot long and 2.5-inch diameter column bioreactors were used to simulate saturated groundwater zones with fast and slow groundwater velocities. Soil and plastic rings were used as media to simulate slow and fast velocities, respectively.;The results revealed that the biofilm model predicted backwashing times that were very close to those observed using digital imaging. For the first FBR run, backwashing time forecasted using biomass growth, in perchlorate fed batch bioreactors, was in agreement with the other two methods used. However, the biomass growth data was unable to simulate similar backwashing for the second and third runs in the FBRs. The result of FBR operation indicates that images processed with the ImageJ closely represented the height of the expanded media in the FBR, and hence it can be used to decide backwashing frequency. A good agreement was found between the backwashing needs encountered in the FBR runs and those forecasted using the biofilm model.;For the testing of slow release electron donor, emulsified oil was proven to be an effective slow release electron donor to degrade nitrate and perchlorate in saturated groundwater zones. The removal of perchlorate required acclimation time while nitrate degraded almost immediately. Perchlorate degradation was highly impacted by high hydraulic conductivities (i.e. smaller contact time). Perchlorate degradation commenced after nitrate levels decreased to less than 0.5 mg/L. On the other hand, once a significant amount of biomass has been built into the system, degradation of both perchlorate and nitrate took place. It was found that the extent of degradation is dependent upon the relative amounts of perchlorate and nitrate present, the amount of electron donor present, and the residence time.