PHOSter is a soil and groundwater remediation process through bio-enhancement. It uses low-volume air sparge and chemical addition to maintain optimum aquifier conditions for native bacteria/archaea reduction/conversion of contaminants. PHOSter was developed in 1995 by the Department of Energy for reduction of trichloroethylene (TCE) in the Savannah River Plant and it is commercialized by Freeman and Vaughn.
Low-volume air sparge provides oxygen required to develop and sustain aerobic conditions and nitrogen as a macronutrient for cell growth. Since phosphate is required for cell division and the third most important macronutrient, triethyl-phosphate (TEP) is added through intermittent injections into the air stream. Application over two to four months is generally sufficient to provide cell counts better than 80,000,000 cells per mL. Sustained high cell counts under aerobic conditions allows quick contaminant reduction/conversion. Remediation to very low MCLs will occur within six months to two years of treatment.
PHOSter has been used to reduced TCE using methogenesis, providing direct reduction without formation of dichloroethylene or vinyl chloride. It is also used to directly reduce common, non-chloronated hydrocarbons (BTEX, naphthalene, total petroleum hydrocarbons (TPH), both gasoline range and diesel range organics), Methyl Tert-butyl Ethylene (MTBE) (under aerobic and anoxic conditions), Ethylene di-Bromide (EDB), Di-Chlorobenzene, Chlorobenzene, Tetra-ethyl Lead conversion to Lead Phosphate (precipitates), and ammonia conversion to nitrate then denitrification under anoxic conditions.
Each system is constructed to fit the site. Microprocessors allow independent control of total air and chemical injection. High quality and trusted components are used to provide optimum system runtimes. Mobile, trailer-mounting minimizes on-site construction and optimized site space utilization.
A typical six-point injector system uses $40 to $65/month in power and a typical twelve-point injector system uses $60 to $90/month in power.
'PHOSter Advanced' Design Improvements
The improvements include better chemical dosage control, higher duty ratings on compressors, improved oxygen transfer efficiency/capacity, remote process monitoring and control using cellular modem technology, and maintains radius/cone of influence through intermittent sparging.
PHOSter has been used in conjunction with the following technologies to speed up remediation in areas or product or near product concentrations:
- Soil Vapor Extraction/Dual-Phase Extraction
- Hydrogen Peroxide Injection
- Pure Oxygen Injection
- CoolOx Injection
- Site Monitoring/Process Control
- In-field analysis allows real-time process control. Monthly/Quarterly site sampling is conducted for the following parameters:
- pH - Process improves pH by scrubbing carbon dioxide
- Dissolved Oxygen - High DO (>3.0 mg/L) will maintain the high rate of oxygen consumption by the aerobic population
- Oxidation-Reduction Potential - ORP generally starts in the negative range (-250 mV to -100 mV) and increases over the coarse of remediation. By the end of the process the ORP is usually between +150 mV and +300 mV.
- Nitrate - Indicates sufficient oxygen addition when levels are greater than 2.0 mg/L
- Reactive Phosphate - Indicates sufficient TEP addition when greater than 2.0 mg/L
- Cell Counts - Process provides maximum contaminant reduction rates when greater than 20,000,000 cells per mL