Daniel P. Cassidy

Use of calcium peroxide to provide oxygen for contaminant biodegradation in a saturated soil

Laboratory studies were conducted in solid-phase reactors on a silty loam contaminated with bis-(2-ethylhexyl) phthalate (BEHP) to determine the conditions under which calcium peroxide (CaO(2)) would promote the aerobic bioremediation of water-saturated soil. Closed 500 ml solid-phase reactors were operated to determine whether CaO(2) stimulated the biodegradation of BEHP in saturated soil. Ex situ bioremediation conditions were then simulated by mixing water-saturated soil for 6 h before placing the soil in three vented, 2 l solid-phase reactors for 50 days. Biodegradation of BEHP was quantified using four different measurements of microbial activity: (1) oxygen concentrations in the reactor gas; (2) bacterial colony-forming units (CFU); (3) fungal CFU; and (4) 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride dehydrogenase activity (INT-DHA). CaO(2) released molecular O(2), which retarded dewatering but substantially enhanced BEHP biodegradation. After 20 days, BEHP in the amended reactor was reduced from 20.3 to roughly 5 g kg(-1) vs. 15 g kg(-1) in the reactor without CaO(2). Bacterial growth was favored over fungal growth at elevated moisture and BEHP levels.

The Effects of LNAPL Biodegradation Products on Electrical Conductivity Measurements

Field geophysical studies have identified anomalously high conductivities in and below the free product zone at many sites with aged contamination by light, non-aqueous phase liquids (LNAPL). Laboratory experiments were conducted to test the hypothesis that these anomalously high conductivities can result from products of LNAPL biodegradation. Soil from a hydrocarbon-impacted site with anomalously high conductivities was washed repeatedly to remove soluble constituents, recontaminated with diesel fuel (DF), and the pores filled with water to simulate a saturated smear zone. Nutrients were provided at levels observed at the site, which resulted in anaerobic conditions due to DF biodegradation. Within 120days, the increase in specific conductivity from microbial activity was 2,100μS∕cm, caused by an increase in total dissolved solids (DS) of over 1,700mg∕L. The increase in DS was due to mineral (mostly carbonate) dissolution and to the production of organic acids and biosurfactants. Under aerobic conditions...

Microorganism selection and biosurfactant production in a continuously and periodically operated bioslurry reactor

A continuous-flow reactor (CSTR) and a soil slurry-sequencing batch reactor (SS-SBR) were maintained in 8l vessels for 180 days to treat a soil contaminated with diesel fuel (DF). Concentrations of Candida tropicalis, Brevibacterium casei, Flavobacterium aquatile, Pseudomonas aeruginosa, and Pseudomonas fluorescens were determined using fatty acid methyl ester (FAME) analysis. DF removal (biological and volatile) and biosurfactant concentrations were measured. The SS-SBR encouraged the growth of biosurfactant-producing species relative to the CSTR. Counts of biosurfactant-producing species (C. tropicalis, P. aeruginosa, P. fluorescens) relative to total microbial counts were 88% in the SS-SBR and 23% in the CSTR. Biosurfactants were produced in the SS-SBR to levels of nearly 70 times the critical micelle concentration (CMC) early in the cycle, but were completely degraded by the end of each cycle. No biosurfactant production was observed in the CSTR. DF biodegradation rates were over 40% greater and DF stripping was over five times lower in the SS-SBR than the CSTR. However, considerable foaming occurred in the SS-SBR. Reversing the mode of operation in the reactors on day 80 caused a complete reversal in microbial consortia and reactor performance by day 120. These results show that bioslurry reactor operation can be manipulated to control overall reactor performance.

Production and accumulation of surfactants during the chemical oxidation of PAH in soil.

A soil contaminated with polycyclic aromatic hydrocarbons (PAH) was treated in laboratory slurry reactors with three chemical oxidants: (1) modified Fenton chemistry (MFC) with hydrogen peroxide (HP), (2) MFC with calcium peroxide (CP) (Cool-Ox), and (3) sodium persulfate activated with Fe chelated using ethylenediaminetetraacetic acid (EDTA). A bioreactor served as a control. Samples of slurry filtrate were tested to quantify emulsification of PAH and concentrations of bulk surfactants, using the critical micelle dilution method. All three oxidants produced surfactants reaching levels above the critical micelle concentration (CMC), though the surfactants were removed at the end of treatment. The surfactants emulsified the PAH, and resulted in greater overall removal of 5- and 6-ring PAH than biodegradation alone. Treatment with CP-MFC resulted in the highest concentration of surfactants (four times the CMC), the most emulsification of PAH, and the highest removal of 5- and 6-ring PAH. None of the chemical treatments significantly reduced counts of culturable heterotrophic microorganisms.

In situ rhamnolipid production at an abandoned petroleum refinery

A simple screening method was developed to detect in situ biosurfactant production by exploiting the relationship between surface tension (ST) and surfactant concentration. Filtered groundwater from contaminated wells with ST values of 60 to 70 dynes/cm decreased to 29 dynes/cm after being concentrated 10 to 15 times in a rotary evaporator, indicating that biosurfactants in the sample reached the critical micelle concentration (CMC). Samples from uncon-taminated groundwater concentrated 25 times showed no decrease in ST below 72 dynes/cm, suggesting that biosurfactants were not present. Microorganisms from soil cores were cultured on diesel fuel and identified using fatty acid methyl ester (FAME) analysis. Pseudomonas aeruginosa was found at very low numbers in uncontami-nated soil but was the dominant species in contaminated soil, indicating that hydrocarbon release impacted microbial diversity significantly. High-performance liquid chromatography (HPLC) was used to quantify rhamnolipids, biosurfactants produced by P. aeruginosa, in concentrated ground-water samples. Rhamnolipid concentrations in samples from contaminated soil were observed equal to their CMC (50 mg/L), but were not detected in samples from un-contaminated wells. We conclude that biosurfactant production may be an indicator of intrinsic bioremediation.

Combining in situ chemical oxidation, stabilization, and anaerobic bioremediation in a single application to reduce contaminant mass and leachability in soil

Laboratory batch reactors were maintained for 32 weeks to test the potential for an in situ remedy that combines chemical oxidation, stabilization, and anaerobic bioremediation in a single application to treat soil from a manufactured gas plant, contaminated with polycyclic aromatic hydrocarbons (PAH) and benzene, toluene, ethylbenzene, and xylenes (BTEX). Portland cement and slaked lime were used to activate the persulfate and to stabilize/encapsulate the contaminants that were not chemically oxidized. Native sulfate-reducing bacteria degraded residual contaminants using the sulfate left after persulfate activation. The ability of the combined remedy to reduce contaminant mass and leachability was compared with NaOH-activated persulfate, stabilization, and sulfate-reducing bioremediation as stand-alone technologies. The stabilization amendments increased pH and temperature sufficiently to activate the persulfate within 1 week. Activation with both stabilization amendments and NaOH removed between 55% and 70% of PAH and BTEX. However, combined persulfate and stabilization significantly reduced the leachability of residual BTEX and PAH compared with NaOH activation. Sulfide, 2-naphthoic acid, and the abundance of subunit A of the dissimilatory sulfite reductase gene (dsrA) were used to monitor native sulfate-reducing bacteria, which were negatively impacted by activated persulfate, but recovered completely within weeks.

Modified Fenton oxidation of diesel fuel in arctic soils rich in organic matter and iron.

Modified Fenton (MF) chemistry was tested in the laboratory to treat three diesel fuel-contaminated soils from the Canadian arctic rich in soil organic matter (SOM) and Fe oxides. Reactors were dosed with hydrogen peroxide (HP), and treatment was compared in reactors with SOM as the only chelate vs. reactors to which ethylenediaminetetraacetate (EDTA) was added. Concentrations of diesel fuel and HP were measured over time, and the oxidation of both diesel fuel and SOM were quantified in each soil. A distinct selectivity for oxidation of diesel fuel over SOM was observed. Reactors with EDTA showed significantly less diesel fuel oxidation and lower oxidant efficiency (diesel fuel oxidized/HP consumed) than reactors with SOM as the only chelate. The results from these studies demonstrate that MF chemistry can be an effective remedial tool for contaminated arctic soils, and challenge the traditional conceptual model that SOM reduces the efficiency of MF treatment through excessive scavenging of oxidant.

Biodegradation of sulfur mustard hydrolysate in the sequencing batch reactor

The United States Army is currently examining chemical neutralization followed by biodegradation for disposal of the chemical warfare agent sulfur mustard. The acidic hydrolysis of sulfur mustard (“mustard gas”, 2,2′-dichlorodiethyl sulfide), yields a detoxified and biodegradable product typically containing from 80 to 95% thiodiglycol. The hydrolyzed product was typically amended with 1,450 mg/L of ammonium chloride (NH 4 Cl), 280 mg/L of potassium phosphate monobasic (KH 2 PO 4 ), and mineral salts and fed to aerobic Sequencing Batch Reactors (SBRs). The SBRs were operated with 3-5 hour aerated Fill, 17-18 hour React, 1 hour Settle and 1 hour Draw periods. The efficiency of carbon removal was greater than 90% and the effluent was non-toxic as determined by aquatic toxicity tests.

Activated Carbon Preconditioning to Reduce Contaminant Leaching in Cement-Based Stabilization of Soils

AbstractAdding powdered activated carbon (PAC) with cement can enhance stabilization and solidification (S/S) by adsorbing organic contaminants. Simultaneous addition of PAC and cement reduces soil-handling costs, but cement-hydration reactions coat PAC with Ca(OH)2 before contaminants can be adsorbed onto PAC. Laboratory studies were done on four aged, contaminated soils from manufactured gas plant sites to compare S/S performance with simultaneous addition of PAC and cement versus cement addition after preconditioning with PAC. Ordinary (Type I) portland cement, quicklime, and class C fly ash were the cementing agents tested. Leaching of benzene, toluene, ethylbenzene, and xylenes and naphthalene was quantified using the synthetic precipitation leaching procedure, and unconfined compressive strength was measured. Allowing a 20-week PAC preconditioning time dramatically enhanced leaching and strength compared with adding cement and PAC simultaneously. Adding cement at the same time as PAC resulted in onl...