Natural attenuation of chlorinated ethene compounds: model development and field-scale application at the Dover site

A multi-dimensional and multi-species reactive transport model was developed to aid in the analysis of natural attenuation design at chlorinated solvent sites. The model can simulate several simultaneously occurring attenuation processes including aerobic and anaerobic biological degradation processes. The developed model was applied to analyze field-scale transport and biodegradation processes occurring at the Area-6 site in Dover Air Force Base, Delaware. The model was calibrated to field data collected at this site. The calibrated model reproduced the general groundwater flow patterns, and also, it successfully recreated the observed distribution of tetrachloroethene (PCE), trichloroethene (TCE), dichloroethylene (DCE), vinyl chloride (VC) and chloride plumes. Field-scale decay rates of these contaminant plumes were also estimated. The decay rates are within the range of values that were previously estimated based on lab-scale microcosm and field-scale transect analyses. Model simulation results indicated that the anaerobic degradation rate of TCE, source loading rate, and groundwater transport rate are the important model parameters. Sensitivity analysis of the model indicated that the shape and extent of the predicted TCE plume is most sensitive to transmissivity values. The total mass of the predicted TCE plume is most sensitive to TCE anaerobic degradation rates. The numerical model developed in this study is a useful engineering tool for integrating field-scale natural attenuation data within a rational modeling framework. The model results can be used for quantifying the relative importance of various simultaneously occurring natural attenuation processes.     

Biodegradation of acrylic acid polymers and oligomers by mixed microbial communities in activated sludge

The biodegradability (mineralization to carbon dioxide) of acrylic acid oligomers and polymers was studied in activated sludge obtained from continuous-flow activated sludge (CAS) systems exposed to mixtures of low molecular weight (Mw < 8000) poly(acrylic acid)s and other watesoluble polymers [poly(ethylene glycol)s] in influent wastewater. Dilute preparations of activated sludge from the CAS units were tested for their ability to mineralize acrylic acid monomer and dimer, as well as a series of model acrylic acid oligomers and polymers (Mw 500, 700, 1000, 2000, and 4500), as sole carbon and energy sources. Complete mineralization of acrylic acid monomer and dimer was observed in low-biomass sludge preparations previously exposed to the polymer mixture, based on carbon dioxide production and residual dissolved organic carbon analyses. Extensive (though incomplete) degradation was also observed for the low molecular weight acrylic acid oligomers (Mw 500 and 700), but degradation dropped off sharply for the 1000, 2000, and 4500 Mw polymers. Radiochemical (¹⁴C) data also confirmed the low degradation potential of the 1000, 2000, and 4500 Mw materials. Degradation of two commercial poly(ethylene glycol)s at 1000 and 3400 Mw was complete and comparable to that of the acrylic acid monomer and dimer. Our results indicate that mixed populations of activated sludge microorganisms can extensively metabolize acrylic acid oligomers of seven units or less. Complete mineralization, however, could be confirmed only for the monomer and dimer material, and carbon mass balance data suggested that the true molecular weight cutoff for complete biodegradation was significantly less than the 500–700 Mw range tested.     

17α-Ethynylestradiol biodegradation in different river-based groundwater recharge modes with reclaimed water and degradation-associated community structure of bacteria and archaea

This study investigated 17α-ethynylestradiol(EE2) biodegradation process and primary metabolic pathways associated with community structures of microorganism during groundwater recharge using reclaimed water. The attenuation rate is 1.58 times higher in wetting and drying alternative recharge(WDAR) than in continual recharge(CR). The primary biotransformation pathways of EE2 in WDAR system began with the oxidation of C-17 on ring D to form a ketone group, and D-ring was subsequently hydroxylated and cleaved. In the CR system, the metabolic pathway changed from the oxidation of C-17 on ring D to hydroxylation of C-4 on ring A, and ring A or B subsequently cleaved; this transition was related to DO, and the microbial community structure. Four hundred fifty four pyrosequencing of 16 s r RNA genes indicated that the bacterial communities in the upper layer of the WDAR system were more diverse than those found in the bottom layer of the CR system; this result was reversed for archaea. Unweighted Uni Frac and taxonomic analyses were conducted to relate the change in bacterial community structure to the metabolic pathway. Microorganism community diversity and structure were related to the concentrations of dissolved oxygen, EE2 and its intermediates in the system. Five known bacterial classes and one known archaeal class, five major bacterial genera and one major archaeal genus might be involved in EE2 degradation. The findings of this study provide an understanding of EE2 biodegradation in groundwater recharge areas under different recharging modes and can facilitate the prediction of the fate of EE2 in underground aquifers.     

Degradation of Poly(3-hydroxybutyrate) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Some Soil Aspergillus spp.

Systematic screening of 45 soil fungi for degradation polyhydroxyalkanoic acids (PHAs) has led to the selection of 6 potent Aspergillus isolates belonging to A. flavus, A. oryzae, A. parasiticus, and A. racemosus. Degradation of PHAs as determined by tube assay method revealed that these Aspergillus spp. were more efficient in degrading poly(3-hydroxybutyrate) [P(3HB)] compared to copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid (P3HB-co-16% 3HV). Moreover, the extent of degradation in mineral base medium was much better than those in complex organic medium. For all the Aspergillus spp. tested, maximum degradation was recorded at a temperature of 37°C with significant inhibition of growth. The optimum pH range for degradation was 6.5–7.0 with degradation being maximum at pH 6.8. The extent of polymer degradation increased with increase in substrate concentration, the optimum concentration for most of the cultures being 0.4% and 0.2% (w/v) for P(3HB) and P(3HB-co-16%3HV) respectively. Supplementation of the degradation medium with additional carbon sources exerted significant inhibitory effect on both P(3HB) and P(3HB-co-16%3HV) degradation.     

Composition and Toxicity of Residual Bunker C Fuel Oil in Intertidal Sediments After 30 Years

In 1970, approximately 2000 m³ of Bunker C crude oil impacted 300 km of Nova Scotia’s coastline following the grounding of the tanker Arrow. Only 10% of the contaminated coast was subjected to cleanup, the remainder was left to cleanse naturally. To determine the long-term environmental impact of residual oil from this spill event, samples of sediment and interstitial water were recovered in 1993, 1997 and 2000 from a sheltered lagoon in Black Duck Cove. This heavily oiled site was intentionally left to recover on its own. Visual observations and chemical analysis confirmed that substantial quantities of the weathered cargo oil were still present within the sediments at this site. However, direct observations of benthic invertebrate abundance suggest that natural processes have reduced the impacts of the residual oil. To confirm this hypothesis, sediment and interstitial water samples from Black Duck Cove were assessed with a comprehensive set of biotests and chemical assays.Residual oil in the sediments had limited effect on hepatic CYP1A protein levels and mixed function oxygenase (MFO) induction in winter flounder (Pleuronectes americanus). No toxicity was detected with the Microtox solid phase test (Vibrio fischeri). Significant sediment toxicity was detected by the amphipod survival test (Eohaustorius estuarius) in four out of the eight contaminated sediments. Interstitial water samples were deemed non-toxic by the Microtox 100% test (Vibrio fischeri) and the echinoid fertilization test (Lytechinus pictus). Sediment elutriates were also found to be non-toxic in the grass shrimp embryo-larval toxicity (GSELTOX) test (Palaemonetes pugio).Recovery at this contaminated site is attributed to natural processes that mediated biodegradation and physical removal of oil from the sediments. In support of the latter mechanism, mineralization experiments showed that all test sediments had the capacity for hexadecane, octacosane and naphthalene degradation, while chemical analysis confirmed that the Bunker C oil from the Arrow had undergone substantial biodegradation.     

Biodegradation of Coproducts from Industrially Processed Corn in a Compost Environment

Information pertaining to biodegradability of renewable polymeric material is critical for the design and development of single-use biodegradable consumer products. The rate and extent of biodegradation of corn fiber, corn zein, cornstarch, distillers grain, and corn gluten meal were evaluated in compost environments under variable temperature, pH, and moisture conditions. Generally, composts with higher temperature (40°C), neutral pH (7.0), and 50%–60% moisture appeared to be ideal for corn coproduct biodegradation, particularly for corn gluten meal and corn zein. Low moisture conditions slowed biodegradation considerably, but degradation rates improved when moisture content increased up to 60%. Thereafter, increased moisture particularly slowed the degradation of corn gluten meal and corn zein, whereas cornstarch degradation remained unaffected. At low pH (4.0) and high pH (11.0) the rate of degradation of most coproducts was slowed somewhat. Cornstarch degradation was slower at pH 7.0, but degradation improved with increased temperatures. Increase in compost temperature from 25 to 40°C (in 5°C increments) also improved biodegradation of corn fiber and distillers grain. Addition of 1% urea to compost as a nitrogen source decreased the extent of biodegradation nearly 40% for corn gluten meal and corn zein, and 20% for cornstarch samples. Treatment of compost with 0.02% azide inhibited biodegradation of all coproducts, suggesting that the presence of metabolically active microbial cells is required for effective degradation of biobased materials in a compost environment.     

Biodegradation of soil‐applied endosulfan in the presence of a biosurfactant

Abstract

Biodegradation of endosulfan isomers in soil‐applied and flask‐coated conditions was studied, by an isolated bacterial coculture. The degradation in soil‐applied form was 20–30% slower than in flask‐coated condition. Addition of a biosurfactant, isolated from Bacillus subtilis MTCC 1427, enhanced the rate of biodegradation by 30–45% in both the conditions. It also mobilized the residual endosulfan towards biodegradation, that otherwise remains undegraded.     

Aliphatic hydrocarbons in an oil-contaminated soil

Microbial decontamination of hydrocarbon-polluted soil was paralleled with soil respiration measurements. About 1,500 tons of a loamy top soil were found to be contaminated with approximately 2000 mg/kg of aliphatic hydrocarbons, mainly oleic (C18:1) and linoleic acid (C18:2) found in the vicinity of a linoleum manufacturing and then a car dewaxing plant. The contaminated soil was analysed for dry matter, pH, dehydrogenase activity, electrical conductivity and nutrient content viz. nitrate, phosphorus and potassium, as well as a number of indigenous microbes. The soil was low in salt and nutrients. This paper describes the procedure and measures to decontaminate this bulk soil on site from approx. 2,000 to 500 mg of aliphatic hydrocarbons/kg dry matter by use of a nutrient emulsion, indigenous micro-organisms and aeration over 13 months. This 75% reduction in aliphatic hydrocarbons resulted in a concomitant carbon efflux, measured as soil respiration, and was used to calculate carbon fluxes.     

Method of Producing Biodegradable Reference Material and its Biodegradability Based on International Standard Evaluation Method (ISO 14855-2)

Returnable cups made of poly(lactic acid) (PLA) are employed as an example of products made of biodegradable plastics. Two kinds of PLA samples plates and powders with different shapes were prepared from PLA cups. The plates were cut from a cup using nippers. Powders were prepared using a rotation mechanical mixer for 45 min. PLA powders were separated by sieves with 60 meshes (250 μm) into a size ranging from 0 to 250 μm. An average diameter of powders separated by a sieve is 169 μm. Biodegradation tests of PLA plates, PLA powders and cellulose powders in controlled compost at 58 °C were performed using a Microbial Oxidative Degradation Analyzer (MODA) instrument according to ISO 14855-2. PLA powders showed almost the same biodegradation curve as that of cellulose powders. PLA plates biodegraded at a slower rate than PLA powders.     

Simultaneous pyridine biodegradation and nitrogen removal in an aerobic granular system

Simultaneous pyridine biodegradation and nitrogen removal were successfully achieved in a sequencing batch reactor(SBR) based on aerobic granules. In a typical SBR cycle, nitritation occurred obviously after the majority of pyridine was removed, while denitrification occurred at early stage of the cycle when oxygen consumption was aggravated. The effect of several key operation parameters, i.e., air flow rate, influent NH_4~+-N concentration,influent p H and pyridine concentration, on nitritation, pyridine degradation and total nitrogen(TN) removal, was systematically investigated. The results indicated that high air flow rate had a positive effect on both pyridine degradation and nitritation but a negative impact of overhigh air flow rate. With the increase of NH_4~+ dosage, both nitritation and TN removal could be severely inhibited. Slightly alkaline condition, i.e., pH 7.0–8.0, was beneficial for both pyridine degradation and nitritation. High pyridine dosage often resulted in the delay of both pyridine degradation and nitritation. Besides, extracellular polymeric substances production was affected by air flow rate, NH_4~+ dosage, pyridine dosage and p H.In addition, high-throughput sequencing analysis demonstrated that Bdellovibrio and Paracoccus were the dominant species in the aerobic granulation system. Coexistence of pyridine degrader, nitrification related species, denitrification related species, polymeric substances producer and self-aggregation related species was also confirmed by highthroughput sequencing.