Wet oxidative regeneration of activated carbon loaded with reactive dye

Wet Oxidative Regeneration (WOR) of powdered activated carbon (PAC) and granular activated carbon (GAC) loaded with the reactive dyes, namely chemictive brilliant blue R and cibacron turquoise blue G, was studied. Attempts were made to regenerate the loaded carbons designated now as spent carbon. A slurry (10% w/v) of spent carbon in distilled water was oxidized by wet oxidation in the temperature range of 150-250 degrees C using oxygen partial pressures between 0.69-1.38 MPa in an 1 1 SS 316 autoclave. The percent regeneration was determined from a ratio, X(RC)/X(VC), corresponding to an equilibrium adsorption capacity of regenerated carbon/equilibrium adsorption capacity of virgin carbon from an initial adsorption period of 3 h. It was observed that the regeneration mainly occurred due to the oxidation of the adsorbates taking place on the surface of carbon. It was possible to regenerate the spent GAC and PAC to the extent of more than 98% (approximately X(RC)/X(VC) > 0.98) by wet oxidation. After four consecutive cycles of adsorption and regeneration using the same stocks of GAC, carbon weight loss observed at 200 degrees C was about 40%. SEM studies of the regenerated carbon showed widening of the pores and loss of structure between the adjacent pores as compared with the virgin carbon. PAC was found to be more suitable as compared with GAC for the adsorption and wet oxidative regeneration processes to treat the aqueous solution containing lower concentration of unhydrolyzed reactive dye. The suitability of wet oxidative regeneration is demonstrated at a bench scale to treat the synthetic reactive dye solution.     

Bioremediation of Chlorobenzene-Contaminated Groundwater on Granular Activated Carbon Barriers

During the past decade, various promising technologies have been developed for the decontamination of groundwater insitu which do not require long-term pumping or high energy consumption. One approach is to use funnel and gate technology. In the case described here, the combination of adsorption of contaminants on granular activated carbon (GAC) and its biodegradation is applied to considerably extend the operating time of the filling material in the barrier system. Monochlorobenzene (MCB), a recalcitrant groundwater contaminant under anaerobic conditions, undergoes high-capacity adsorption on GAC up to about 450 mg per gram. Aerobic enrichment cultures, obtained from a contaminated aquifer, were able to mineralize initially adsorbed MCB. In respirometer experiments the rate of carbon dioxide formation was dependent on the equilibrium concentration of MCB. The oxygen consumption of activated carbon by means of autoxidative reactions may delay aerobic biodegradation in GAC filters. The oxygen uptake of pristine activated carbon amounted to 5.6 mg per gram GAC in laboratory column experiments. When GAC was pre-loaded with MCB, autoxidation rates were considerably reduced. Hence, it is advisable not to stimulate the biodegradation of MCB by oxygen supply in GAC biobarriers until after an initial period of solely sorptive MCB removal from the groundwater flow.     

Water quality impacts on sorbent efficacy for per- and polyfluoroalkyl substances treatment of groundwater

Per- and polyfluoroalkyl substances (PFAS) are a large group of synthetic compounds that have emerged as chemicals of concern in drinking water and groundwater. Typically, such waters are treated to remove PFAS by passing the water through a bed of sorbent material (e.g., activated carbon and anion exchange resins [AIX]). However, the efficacy of these sorbents varies depending on the types and concentrations of PFAS, in addition to water quality conditions such as organic matter content and conductivity (ionic strength). The choice of sorbent material to effectively treat PFAS in complex natural waters will, therefore, depend upon site water quality and PFAS conditions. To help inform these decisions, a series of evaluations using a rapid small-scale column test approach was conducted with two sorbent materials (a granulated activated carbon [GAC] and an AIX), individually and combined, under conditions where conductivity, pH, and organic carbon concentrations were varied in a semifactorial approach. Artificial groundwater batches were prepared to meet these test conditions and spiked with six PFAS compounds (perfluorobutane sulfonic acid [PFBS], perfluorobutanoic acid [PFBA], perfluorohexane sulfonic acid [PFHxS], perfluorohexanoic acid [PFHxA], perfluorooctane sulfonic acid [PFOS], and perfluorooctanoic acid [PFOA]), passed through small columns packed with ground sorbent material for ∼30,000 bed volumes of water for single sorbent treatments and ∼20,000 bed volumes for combined sorbent treatments, during which samples of effluent were captured and analyzed to quantify breakthrough of PFAS from the sorbent materials over time. AIX was found to be more effective than GAC at removing the tested perfluoroalkyl sulfonic acids (PFBS, PFHxS, and PFOS), but GAC was similarly or more effective than AIX at removing perfluorocarboxylic acids (PFBA, PFHxA, and PFOA) under high conductivity conditions. Overall, the efficacy of AIX at removing PFAS was more strongly impacted by organic carbon and conductivity than GAC, while pH had less of an effect on either sorbent's efficacy compared to the other test conditions.     

Ion exchange resin for PFAS removal and pilot test comparison to GAC

Amec Foster Wheeler and Emerging Compounds Treatment Technologies, Inc. tested pilot‐scale ex situ treatment technologies for treatment of poly‐ and perfluorinated alkyl substances (PFAS) in groundwater. The pilot test compared ion exchange resin to granular activated carbon (GAC) and evaluated in‐place regeneration of the resin to restore PFAS removal capacity. During the pilot test, both resin and GAC removed perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) below U.S. Environmental Protection Agency (USEPA) health advisories (HAs) of 0.070 micrograms per liter (μg/L) combined. Compared at a common empty bed contact time (EBCT) of five minutes, the resin treated over eight times as many bed volumes (BVs) of groundwater as GAC before PFOS exceeded the USEPA HA and six times as many BVs for PFOA. On a mass‐to‐mass basis, resin removed over four times as much total PFAS per gram as GAC before breakthrough was observed at the USEPA HA. A solution of organic solvent and brine was used to regenerate the resin in the lead vessel, which had treated water up to the point of PFOS and PFOA breakthrough exceeding the USEPA HAs. The pilot test demonstrated successful in‐place regeneration of the resin to near‐virgin conditions. The regenerated resin was then used to treat the contaminated groundwater up to the same breakthrough point. Compared to the virgin resin loading cycles, PFAS removal results for the regenerated resin were consistent with virgin resin.     

The treatment of contaminated water at remedial wood preserving sites

Contaminated groundwater and surface water have posed a great challenge in restoring wood preserving sites to beneficial use. Often contaminated groundwater plumes extend far beyond the legal property limits, adversely impacting drinking water supplies and crop lands. To contain, treat, and/or remediate these valuable resources is an important part of restoring these impacted sites. Various options are available for remediating the groundwater and other affected media at these sites. Frequently, pump and treat technologies have been used that can provide well‐head treatment at installed extraction wells. This approach has shown to be costly and excessively time consuming. Some of the technologies used for pump and treat are granular activated carbon (GAC), biotreatment, and chemical oxidation. Other approaches use in‐situ treatment applications that include enhanced bioremediation, monitored natural attenuation (biotic and abiotic), and chemical reduction/fixation. Ultimately, it may only be feasible, economically or practicably, to use hydraulic containment systems. Depending upon site‐specific conditions, these treatment approaches can be used in various combinations to offer the best remedial action. A comparison of water treatment system costs extrapolated from the treatability studies performed on contaminated groundwater from the McCormick/Baxter Superfund site in Stockton, California, yielded operation and maintenance costs of $1.19/1,000 gal. for carbon treatment and $7.53/1,000 gal. for ultraviolet (UV) peroxidation, respectively.     

Treating contaminated groundwater using a fluidized-bed reactor

Both biological treatment and carbon adsorption have inherent advantages for remediation of groundwater contaminated with compounds such as benzene, toluene, ethylbenzene, and xylenes (BTEX). Biological treatment destroys the contaminants and is extremely cost-effective. Carbon adsorption is a positive removal mechanism that ensures a product water of high quality, but the process is relatively expensive and requires frequent carbon replacement and/or regeneration. Coupling the two processes realizes the inherent advantages of both approaches. An additional benefit of combining these removal mechanisms in a biological fluidizedbed reactor (FBR) system is that no loss of BTEX from volatilization occurs, since predissolution of oxygen is used in place of conventional aeration for the fluidized-bed process. This article summarizes preliminary performance data from a laboratory, pilot-scale biological FBR, using granulated activated carbon (GAC) as the support media (GAC-FBR), operated at various BTEX concentrations and organic loading rates. Greater than 99-percent degradation of total BTEX was achieved at an organic loading rate of 3.0 kg COD/m³-day or less and an empty bed hydraulic retention time of 5.0 minutes. System performance was extremely robust, easily handling a tenfold step increase in loading due to the combined adsorptive capability of the biofilm-coated GAC and ability to subsequently bioregenerate the GAC. Monitoring verified that no off-gas was produced during treatment.     

Influence of groundwater conditions and co‐contaminants on sorption of perfluoroalkyl compounds on granular activated carbon

Per and polyfluoroalkyl substances (PFAS) are emerging and persistent organic pollutants that have been detected in many environmental media, humans, and wildlife. A common method to effectively remove PFAS from water is adsorption by activated carbon. Preliminary sorption experiments were conducted using five characterized Calgon Corporation coal‐based granular activated carbon (GAC; F100, F200, F816, F300, and F400), one coconut‐based GAC (CBC‐OLC 12 × 30), and one Jacobi Corporation coal‐based GAC (Omni‐G 12 × 40). Sorption of four representative PFAS onto each GAC was measured to select the most favorable carbon sources. F400 and CBC were chosen based on their performance in preliminary PFAS sorption experiments and contrasting properties. Freundlich and Langmuir isotherm models were developed for perfluorooctanoic acid (PFOA) and perfluorooctanoic sulfonate (PFOS) at an initial concentration of 1 mg/L. Sorption capacities were determined for PFOA and PFOS individually and in the mixture. Individual compounds showed higher sorption than when present in the mixture for both PFOA and PFOS. PFOS showed higher sorption than PFOA both individually and in the mixture and F400 showed higher sorption capacity than CBC. The presence of co‐contaminants (kerosene, trichloroethylene, and ethanol), and variations in groundwater conditions (pH, presence of anions, naturally occurring organic matter, and iron oxides) demonstrated limited impact on the sorption of PFAS onto GAC under the experimental conditions tested.     

Applications of mulch biowalls—three case studies

Mulch biowalls are proving to be an effective means of generating reducing conditions for the in situ anaerobic reduction of contaminants in groundwater that are amenable to the reduction process. Mulch is an inexpensive and readily available substrate that provides a long‐lasting carbon and electron donor source for the stimulation of the anaerobic reduction process in groundwater. Examples of contaminants that are amenable to the biotic anaerobic reduction process include: chlorinated alkenes and alkanes, explosives, perchlorate, some metals, and petroleum hydrocarbons. The microbial degradation of cellulose fibers (mulch) is arguably the oldest reduction process known and is evident anywhere that plant material, soil, and water are present together. This article presents three case studies discussing three different uses of mulch biowalls to stimulate the anaerobic bioremediation of contaminants in shallow soils and groundwater. © 2009 Wiley Periodicals, Inc.     

Residual organic fluorinated compounds from thermal treatment of PFOA,PFHxA and PFOS adsorbed onto granular activated carbon (GAC)

Perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA) and perfluorooctane sulfonate (PFOS) adsorbed onto granular activated carbon (GAC) were thermally treated in N₂ gas stream. The purpose was to assess the fate of perfluoroalkyl and polyfluoroalkyl substances (PFASs) during thermal regeneration of GAC, which had been used for water treatment. Mineralized F, residual PFASs including short-chained species, and volatile organic fluorine (VOF) were determined. In a temperature condition of 700 °C, VOF were 13.2, 4.8, and 5.9 % as for PFOA, PFHxA, and PFOS. However, the VOF decreased to 0.1 %, if the GAC and off-gas were kept at 1000 °C. No PFASs remained in GAC at 700–1000 °C; at the same time, short-chained PFASs were slightly detected in the aqueous trapping of off-gas at 800 and 900 °C conditions. The destruction of PFASs on GAC could be perfect if the temperature is higher than 700 °C; however, the process is competitive against volatile escape from GAC. Destruction in gaseous phase needs a temperature as high as 1000 °C. Destruction of PFASs on the surface of GAC, volatile escape from the site, and thermolysis in gas phase should be considered, as to thermal regeneration of GAC.     

Adsorption of Geosmin and MIB on Activated Carbon Fibers–Single and Binary Solute System

The adsorption of two taste- and odor-causing compounds, namely MIB (2-methyl isoborneol—C₁₁H₂₀O) and geosmin (C₁₂H₂₂O) on activated carbon was investigated in this study. The impact of adsorbent pore size distribution on adsorption of MIB and geosmin was evaluated through single solute and multicomponent adsorption of these compounds on three types of activated carbon fibers (ACFs) and one granular activated carbon (GAC). The ACFs (ACC-15, ACC-20, and ACC-25) with different degrees of activation had narrow pore size distributions and specific critical pore diameters whereas the GAC (F-400) had a wider pore size distribution and lesser microporosity. The effect of the presence of natural organic matter (NOM) on MIB and geosmin adsorption was also studied for both the single solute and binary systems. The Myers equation was used to evaluate the single solute isotherms as it converges to Henry’s law at low coverage and also serves as an input for predicting multicomponent adsorption. The single solute adsorption isotherms fit the Myers equation well and pore size distribution significantly influenced adsorption on the ACFs and GAC. The ideal adsorbed solute theory (IAST), which is a well-established thermodynamic model for multicomponent adsorption, was used to predict the binary adsorption of MIB and geosmin. The IAST predicted well the binary adsorption on the ACFs and GAC. Binary adsorption isotherms were also conducted in the presence of oxygen (oxic) and absence of oxygen (anoxic). There were no significant differences in the binary isotherm between the oxic and anoxic conditions, indicating that adsorption was purely through physical adsorption and no oligomerization was taking place. Binary adsorptions for the four adsorbents were also conducted in the presence of humic acid to determine the effect of NOM and to compare with IAST predictions. The presence of NOM interestingly resulted in deviation from IAST behavior in case of two adsorbents, ACC-15 and F-400.     

Thermally enhanced hydrolysis for treatment of pesticides and explosives

Thermally enhanced hydrolysis of halogenated alkanes such as 1,1,1‐trichlorethane has become a proven method of in situ soil and groundwater remediation. Electrical resistance heating is commonly used to heat soil and groundwater to accelerate the rate of hydrolysis. This article provides practical information to extend the hydrolysis remediation toolkit to include treatment of common pesticides and explosives. Sites with comingled volatile compounds, pesticides, and/or explosives can also be treated via a single solution.     

The in situ treatment of PFAS within porewater at the air–water interface of a PFAS source zone

The treatment of per- and polyfluoroalkyl substances (PFAS) within groundwater is an emerging topic, with various technologies being researched and tested. Currently, PFAS-impacted groundwater is typically treated ex situ using sorptive media such as activated carbon and ion exchange resin. Proven in situ remedial approaches for groundwater have been limited to colloidal activated carbon (CAC) injected into aquifers downgradient of the source zones. However, treatment of groundwater within the source zones has not been shown to be feasible to date. This study evaluated the use of CAC to treat dissolved PFAS at the air–water interface within the PFAS source zone. Studies have shown that PFAS tends to preferentially accumulate at the air–water interface due to the chemical properties of the various PFAS. This accumulation can act as a long-term source for PFAS, thus making downgradient treatment of groundwater a long-term requirement. A solution of CAC was injected at the air–water interface within the source zone at a site with PFAS contamination using direct push technology. A dense injection grid that targeted the interface between the air and groundwater was used to deliver the CAC. Concentrations of PFAS within the porewater and groundwater were collected using a series of nine lysimeters installed within the vadose and saturated water columns. A total of six PFAS were detected in the porewater and groundwater including perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), and perfluorononanoic acid (PFNA). Detectable concentrations of PFAS within the pore and groundwater before treatment ranged from values greater than 300 µg/L for PFPeA to less than 3 µg/L for PFNA. Following the injection of the CAC, monitoring of the porewater and groundwater for PFAS was conducted approximately 3, 6, 9, 12, and 18 months postinjection. The results indicated that the PFAS within the porewater and groundwater at and near the air–water interface was effectively attenuated over the 1.5-year monitoring program, with PFAS concentrations being below the method detection limits of approximately 10 ng/L, with the exception of PFPeA, which was detected within the porewater during the 18-month sampling event at concentrations of up to 55 ng/L. PFPeA is a five carbon-chained PFAS that has been shown to have a lower affinity for sorption onto activated carbon compared to the longer carbon-chained PFAS such as PFOA. Examination of aquifer cores in the zone of injection indicated that the total organic carbon concentration of the aquifer increased by five orders of magnitude postinjection, with 97% of the samples collected within the target injection area containing activated carbon, indicating that the CAC was successfully delivered into the source zone.     

Treatment of poly- and perfluoroalkyl substances in groundwater using a carbon-based micro-adsorbent and ceramic membrane filtration

This article presents the results of an Environmental Security Technology Certification Program (ESTCP) demonstration conducted at Horsham Air Guard Station and the former Willow Grove Naval Reserve Station in Horsham, Pennsylvania. The ESTCP project information can be found here: https://www.serdp-estcp.org/projects/details/568c0487-f182-40c1-9d4d-9297f4bbedda/er19-5181-projcet-overview . The technology demonstrated, identified as the AquaPRS™ system, employs a carbon-based micro-adsorbent suspension to adsorb polyfluoroalkylated substance (PFAS), which is subsequently filtered using a ceramic membrane filter. A prototypical AquaPRS system was specifically designed and implemented to treat per- and PFAS-contaminated water resources at a fidelity level that could be replicated at other US Department of Defense sites. The objective of the project was to demonstrate and validate the application of the adsorption and separation treatment approach to reduce the total life-cycle cost of treating PFAS-impacted groundwater. The results of the demonstration showed that the AquaPRS technology provides an alternative to granular activated carbon (GAC) and ion exchange (IX) systems based on treatment efficacy and cost performance using lifecycle cost analyses. Pretreatment included cloth media filtration with a nominal 5 µm particulate rejection rating to remove sediment from the surface water treated during the Horsham evaluation. Prefiltration was not necessary for treating the Willow Grove groundwater due to the lower raw turbidities. The micro-adsorbent was added to the system to maintain a suspension between 1 and 50 g/L in the sorbent chamber at reaction times from 5 to 20 min. Treated effluent was separated from the sorbent slurry matrix using the ceramic membrane filter, with the slurry returned to the sorption reactor. The first study conducted at Horsham Air Guard Station demonstrated and validated the AquaPRS treatment approach using a mobile pilot system, while the second study (conducted at the former Naval Reserve Air Station at Willow Grove) provided further optimization of cost, performance, and scalability. At Horsham, 13 tests were conducted over 9 months using a dual-train pilot with each test evaluating two separate conditions. The first 10 tests were conducted with treatment systems in parallel and the remaining three were conducted in series. At Willow Grove, five tests were conducted over a 6-month period for a total of 10 individual test conditions. Three tests were performed in parallel with two operated in series. Tests conducted at Horsham evaluated the performance of the AquaPRS system at different hydraulic detention times (5–120 min), sorbent mass (10–430 g), sorbent densities (0.5–40 g/L), and flowrates (0.1–1 L/min). At Willow Grove, the range of these parameters was further narrowed with hydraulic detention times from 10 to 20 min, sorbent mass from 100 to 200 g, sorbent density from 10 to 25 g/L, and flowrate from 0.67 to 1 L/min. AquaPRS was validated by quantifying the specific adsorption rate (SAR) of various PFASs on the micro-adsorbent and comparing it to values derived for GAC and IX from the same water matrix. The costs of the three treatment systems were compared to estimate a payback period for the AquaPRS system compared to GAC and IX. At 10% breakthrough, the SAR of AquaPRS for the combined concentration of the United States Environmental Protection Agency's Third Unregulated Contaminant Monitoring Rule (UCMR3) PFASs was nearly 300 times higher compared to those treated with GAC. At 40 ng/L breakthrough for combined UCMR3 compounds, a single-stage AquaPRS system at Horsham achieved 146 µg PFAS/g sorbent SAR, while a dual-stage system at Willow Grove achieved 2128 µg PFAS/g sorbent. The AquaPRS system showed a breakeven period of 8 months compared to a similarly designed GAC system in the Horsham evaluation using the observed adsorption rates. In the Willow Grove test case, a 24–36-month breakeven period was determined for the AquaPRS technology when compared to the highest sorption rates observed among five previously tested IX resins. The AquaPRS benefits in comparison to GAC/IX include effective performance in the presence of co-contaminants, adaptability to changing conditions, limited downtime for sorbent replacement, resistance to biofouling, small footprint, and reduced disposal requirements. The lower waste production rates are due to the AquaPRS' ability to dewater the spent sorbent resulting in a waste generation of just 0.002% of the total volume of water treated. Based on the treatment efficacy and cost performance, the AquaPRS system is positioned as an alternative to GAC and IX systems.     

Treatment of effluent containing micropollutants by means of activated carbon

Different amounts of granular activated carbon (GAC) have been tested for the removal of aliphatic and aromatic micropollutants contained in a liquid stream coming from an industrial plant. Tests have been carried out in a JAR-Test apparatus, using plugged flasks, in order to eliminate the oxygen influence on the adsorption process and to obtain information for studying the process in a pilot plant. The removal of aliphatic compounds resulted better than aromatic ones, probably because these substances are enveloped by water molecules which make adsorption on the GAC surface easier; in contrast, aromatic compounds show a lower affinity for the GAC, owing to their steric conformation. The good results obtained confirm that the proposed system is applicable to the examined effluent, even when the concentration of the pollutant load varies. In the latest part of this work, a plan for the construction of a full-scale plant to treat the examined wastewater has been developed.     

Carbon isotope forensics for methane source identification

Methane (CH₄) in ecosystems originates from ancient petroleum formed deep within the earth and/or via microbial fermentation of organic carbon and subsequent reduction of carbon dioxide (CO₂). Given the complexity of different ecosystems, origins of CH₄ present can be difficult to determine. This issue was realized in a situation where an antimethanogenic in situ chemical reduction (ISCR) remedial amendment containing organic carbon plus zero‐valent iron was applied to treat chlorinated solvents in groundwater at a former dry cleaner facility. The technology rapidly and effectively reduced the concentration of tetrachloroethene in groundwater thus meeting project goals without the stoichiometric accumulation of catabolites such as trichloroethene (TCE), cis‐1,2‐dichloroethene, or vinyl chloride and without excessive methanogenesis (e.g., <2 mg/L) in the treated area. However, approximately 9 months after treatment, increased levels of CH₄ (from 5 to 10 mg/L) were observed downgradient from the treated area. The applied remedial amendment contained approximately 60% (weight basis) fermentation organic carbon and was therefore a potential source of this CH₄. However, there was <500 mg/L total organic carbon in groundwater emanating from the upgradient treatment area which was unlikely sufficient to produce that much CH₄. Moreover, the soil gas also contained benzene, toluene, ethylbenzene, and xylenes and other gasoline constituents. These data suggested that the presence of three gasoline/diesel underground storage tanks that were previously closed in place with no active remediation performed could be the source of elevated CH₄. Thirdly, there were sewer lines, utilities, multiple gasoline stations, and industrial activities in the immediate area. With an initial assumption that CH₄ source(s) could include the ISCR amendment over stimulation of production, gasoline sourced CH₄ from nearby leaking lines, or sewage from local fractured pipes, carbon isotope analyses—radiocarbon (Δ¹⁴C) and stable carbon (δ¹³C)—were coupled with CH₄ and CO₂ concentration data from groundwater samples to determine the origin of respired carbon. The δ¹³C range for carbon sources respired in the process would be approximately ?26.5‰ to ?33.0‰ for the ISCR amendment and total petroleum hydrocarbons (TPH) residuals, respectively. Δ¹⁴C is approximately 0‰ and ?999‰ for the ISCR amendment (young carbon) and TPH (old carbon), respectively. The isotopic signature of respired gasses confirmed that elevated CH₄ downgradient of the treated area originated primarily from sewer gasses (or fermentation of liquids released from sewer lines). This study provides an overview of the capability to apply carbon isotope geochemistry to confirmation of remedial protocols and sources of anthropogenic carbon pools that conclusively identify the origin of CH₄ in a complex ecosystem undergoing a remedial action.     

Modeling of water quality downgradient of a mulch biowall

Groundwater treatment biowalls may be located close to a surface water body to prevent contaminant discharge from a groundwater plume into the surface water. Groundwater contaminants passing through the biowall are treated within the biowall or immediately downgradient of the biowall. Biowalls designed and constructed for the treatment of chlorinated solvents typically contain either a solid and/or liquid source of organic carbon to promote contaminant degradation by enhanced anaerobic reductive dechlorination. Common solid organic materials in biowalls include wood mulch or similar waste plant material, and common liquid organic materials are vegetable oil (possibly emulsified) or other long‐chain fatty acids. Such biowalls then develop anaerobic conditions in the constructed biowall volume, and potentially downgradient, as dissolved oxygen originally present in the aquifer is consumed. This groundwater condition can lead to the appearance of sulfide if groundwater influent to the biowall contains moderate to high sulfate concentrations. Other researchers have presented evidence for groundwater conditions downgradient of a biowall or a permeable reactive barrier (PRB) that are altered in relation to groundwater quality, besides the desired effect of contaminant degradation or removal by precipitation. The objective of this work was to investigate with modeling the changes in downgradient groundwater species chemistry as a result of a constructed biowall. This was accomplished with a chemical species model to predict levels of sulfate and sulfide present in groundwater in close downgradient proximity to the biowall. The results indicate that downgradient chemical changes could impact a surface water body to which groundwater discharges. The model described could be enhanced by incorporating additional design variables that should be considered in biowall feasibility assessments.     

Submerged Membrane System with Biofilter as a Treatment to Rainwater

Rainwater has been used as drinking water in Thailand for centuries especially in the rural parts and is accepted as an important water resource. From past to present, the quality of rainwater has changed with the landuse of the landscape, and its water quality is influenced by a diverse range of conditions such as the management of pollutant sources, the catchment condition, wind and meteorological conditions, and the location of rainwater collection points. In this study, the quality of rainwater collected off roofs at several locations was examined. Granular activated carbon (GAC) filtration was used as a pretreatment to microfiltration (MF) to remove the dissolved organic matter (DOC). After an initial adsorption period, the biofilm that formed on the GAC (biofilter) was found to remove DOC by up to 40%, 35%, and 15% for bed filter depths of 15, 10, and 5 cm, respectively. Biofilters also removed nitrate and phosphate by more than 80% and 35%. The hollow fiber membrane microfiltration with pore size of 0.1 μm was used to treat the effluent from biofiltration to remove the microorganisms/pathogens in the rainwater. Although there was no significant additional removal of DOC by MF, the biofilter removed all microorganisms. The use of biofilters as pretreatment to MF/UF could remove a higher amount of DOC, remove microorganisms, increase the membrane treatment efficiency, and reduce membrane fouling.     

A study of treatment options to remediate explosives and perchlorate in soils and groundwater at Camp Edwards,Massachusetts

The Army National Guard initiated an Innovative Technology Evaluation (ITE) Program in March 2000 to study potential remedial technologies for the cleanup of explosives‐contaminated soil and groundwater at the Camp Edwards site on the Massachusetts Military Reservation. The soil technologies chosen for the ITE program were: soil washing, chemical oxidation, chemical reduction, thermal desorption/destruction (LTTD), bioslurry, composting, and solid phase bioremediation. The technologies were evaluated based on their ability to treat both washed and untreated soil. A major factor considered was the ability to degrade explosives, such as RDX, found in particulate form in the soils. The heterogeneous nature of explosives in soils dictates that the preferred technology must be able to treat explosives in all forms, including the particulate form. Groundwater remediation technologies considered include: in situ cometabolic reduction, two forms of in situ chemical oxidation, Fenton‐like oxidation and potassium permanganate. This article presents the results of each of the remedial technologies evaluated and discusses which technologies met the established ITE performance goals. © 2003 Wiley Periodicals, Inc.     

Chemical investigations of aquifers affected by pyrite oxidation in the Bitterfeld lignite district

In a large area around the former open-pit lignite mines near Bitterfeld, Germany, groundwater taken from wells was analyzed for the major cations, anions, and trace elements. Quaternary and Tertiary sediments were collected from aquifers exposed on the sides of the pits and from boreholes outside the mines and analyzed for major and trace elements, as well as for carbonate, pyritic sulfur and total organic carbon. The pH and electrical conductivity of the sediments in suspension were measured. Significant differences were determined between the Tertiary sediments of the aquifers that were exposed to atmospheric oxygen during the lowering of the groundwater table and those outside the cone of depression. The greatest differences were found in the pyrite content, the pH values, and the electrical conductivity. In order to map the degree to which the mining of the lignite has affected the quality of the groundwater in the study area, the water samples were divided into six classes on the basis of their sulfate content. The neutralization potential was calculated to estimate the potential for acidification. Prediction of future groundwater quality is based on both (i) the present composition of the groundwater, surface water, and Quaternary and Tertiary aquifer sediments and (ii) the present and future groundwater flow directions. These studies have shown which parameters are important for future groundwater monitoring.     

Production of Poly(3-hydroxyalkanoate)s by Pseudomonas putida Cultivated in a Glycerol/Nonanoic Acid-Containing Medium

The biosynthesis of poly(3-hydroxyalkanoate) (PHA) by Pseudomonas putida (JCM6160) cultivated in a medium containing glycerol, nonanoic acid, or a glycerol/nonanoic acid mixture as the sole carbon sources was investigated. The PHA content was ~20 % when glycerol was the carbon source. This relatively low content can be attributed to the glycerol end-cap effect and the absence of enzymes that can directly synthesize PHA from acetyl CoA, which is the major metabolite of glycerol. Fatty acids, containing even numbered carbons, are synthesized from acetyl CoA, and they can be used as substrates for PHA synthesis. However, this process also results in decreasing PHA content as fatty acids are siphoned off into other pathways. However, addition of 5 mM nonanoic acid into a 20 mM glycerol-containing medium dramatically increased the PHA content in P. putida, which was 1.3 times larger than the sum of the values found when glycerol and nonanoic acid were each used as the sole carbon source. The PHA, synthesized in the glycerol/nonanoic acid medium, contains 3-hydroxy alkanoate units that have 5, 6, 7, 8, 9, or 10 carbons. The units that contain the even numbered carbons are derived from fatty acids that were produced from glycerol; whereas, the PHA units with the odd numbered carbons are derived from nonanoic acid. Pentanoate units were also found in the polyester derived from glycerol and nonanoic acid, and must have been synthesized indirectly via β-oxidation of nonanoic acid with the assistance of glycerol because pentanoate units were not found in PHA when P. putida was cultivated in the presence of only nonanoic acid.