Modeling and interpreting bioavailability of organic contaminant mixtures in subsurface environments

Bioavailability often controls the fate of organic contaminants in surface and subsurface aquatic environments. Bioavailability can be limited by sorption, mass transfer, and intrinsic biodegradation potential and can be further altered by the presence of other compounds. This paper reviews current perspectives on the processes influencing subsurface contaminant bioavailability, how these processes are modeled, and how the relative role of the various processes can be assessed through bioavailability indices. Although these processes are increasingly well understood, the use of sophisticated models and indices often are precluded by an inability to estimate the many parameters that are associated with complex models. Nonetheless, the proper representation of sorption, mass transfer, biodegradation, and co-solute effects can be critical in predicting bio-attenuation. The influence of these processes on contaminant fate is illustrated with numerical simulations for the simultaneous degradation of toluene (growth substrate) and trichloroethylene (nongrowth cometabolite) in hypothetical, aerobic, solid-water systems. The results show how the relative impacts on contaminant fate of the model's various component processes depends upon system conditions, including co-solute concentrations. Slow biodegradation rates increase the inhibition effects of a cometabolite and suppress the rate enhancement effects of a growth substrate. Irrespective of co-solute effects, contaminant fate is less sensitive to biodegradation processes in systems with strong sorption and slow desorption rates. Bioavailability indices can be used to relate these findings and to help identify appropriate modeling simplifications. In general, however, there remains a need to redefine such indices in order that bioavailability concepts can be better incorporated into site characterization, remediation design, and regulatory oversight.     

Phenanthrene degradation in Arthrobacter sp. P1-1: initial 1,2-, 3,4- and 9,10-dioxygenation, and meta- and ortho-cleavages of naphthalene-1,2-diol after its formation from naphthalene-1,2-dicarboxylic acid and hydroxyl naphthoic acids

Arthrobacter sp. P1-1, isolated from a polycyclic aromatic hydrocarbon (PAH)-contaminated site in Hilo, HI, USA, can decompose phenanthrene (40 mg l⁻¹) completely within 7 days. A detailed phenanthrene metabolism map was constructed based on metabolite analysis and replacement cultures. Initial dioxygenation occurs on 1,2-, 3,4-, and 9,10-C of phenanthrene, dominantly on 3,4-C positions. Rapid accumulation of 5,6- and 7,8-benzocoumarin suggests that phenanthrene-1,2- and -3,4-diols mainly undergo meta-cleavage. However, a trace amount of o-carboxyvinylnaphthoates and diphenic acid indicates a limited extent of ortho-cleavage of the diols. Naphthalene-1,2-diol, as a common and converged metabolite, was formed from 1-[(E)-2-carboxyvinyl]-2-naphthoic acid, naphthalene-1,2-dicarboxylic acid, and 1-hydroxy-2-naphthoic acid in separate culture tests. Naphthalene-1,2-diol is then degraded in a dominant phthalic acid pathway and a minor salicylic acid pathway. Several metabolites of phthalic acid were found, while no salicylic acid metabolites were detected. The strain P1-1 likely has a very diverse set of PAH-degrading enzymes or the enzymes having relaxed substrate-specificity.     

The impact of the type and position of the halogen atom on the biodegradation of halosubstituted benzyl alcohols

The biodegradation of 2‐halosubstituted and 4‐halosubstituted benzyl alcohols was studied using two sources of biodegrative micro‐organisms: mixed culture from the ?TUDA waste water treatment plant, Dom?ale, and the white rot fungus Phanerochaete chrysosporium strain MZKI B‐223 (ATCC 24725). The results obtained by this study indicate the interrelationship between the types of micro‐organism used in the experiments and the type and position of the halogen element on the aromatic ring.     

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.     

Bioremediation of soils contaminated with explosives

The large-scale industrial production and processing of munitions such as 2,4,6-trinitrotoluene (TNT) over the past 100 years led to the disposal of wastes containing explosives and nitrated organic by-products into the environment. In the US, the Army alone has estimated that over 1.2 million tons of soil have been contaminated with explosives, and the impact of explosives contamination in other countries is of similar magnitude. In recent years, growing concern about the health and ecological threats posed by man-made chemicals have led to studies of the toxicology of explosives, which have identified toxic and mutagenic effects of the common military explosives and their transformation products (Bruns-Nagel et al., 1999a; Fuchs et al., 2001; Homma-Takeda et al., 2002; Honeycutt et al., 1996; Rosenblatt et al., 1991; Spanggord et al., 1982; Tan et al., 1992 and Won et al., 1976). Because the cleanup of areas contaminated by explosives is now mandated because of public health concerns, considerable effort has been invested in finding economical remediation technologies. Biological treatment processes are often considered, since these are usually the least expensive means of destroying organic pollution. This review examines the most important groups of chemicals that must be treated at sites contaminated by explosives processing, the chemical and biological transformations they undergo, and commercial processes developed to exploit these transformations for treatment of contaminated soil. We critically examine about 150 papers on the topic, including approximately 60 published within the past 5 years.     

Environmental Degradation of Biodegradable Polyesters: 3. Effects of Alkali Treatment on Biodegradation of Poly(ε-Caprolactone) and Poly[(R)-3-Hydroxybutyrate) Films in Controled Soil

The poly(-caprolactone) (PCL) and poly[(R)-3-hydroxybutyrate] (R-PHB) films with a hydrophilic surface were prepared by the alkali treatment of their as-cast films in NaOH solutions of different concentrations. The alkali-treated PCL and R-PHB films, as well as the as-cast PCL and R-PHB films, were biodegraded in soil controlled at 25°C and the effects of alkali treatment or surface hydrophilicities on their biodegradation were investigated by the use of gravimetry, gel permeation chromatography (GPC), scanning electron microscopy (SEM), and polarization optical microscopy. It became evident that the alkali treatment enhanced the hydrophilicities and biodegradabilities of the PCL and R-PHB films in soil. The biodegradabilities of the as-cast aliphatic polyester films in controlled soil decreased in the following order: PCL > R-PHB > PLLA, in agreement with that in controlled static seawater.     

Biodegradation of Agricultural Plastic Films: A Critical Review

The growing use of plastics in agriculture has enabled farmers to increase their crop production. One major drawback of most polymers used in agriculture is the problem with their disposal, following their useful life-time. Non-degradable polymers, being resistive to degradation (depending on the polymer, additives, conditions etc) tend to accumulate as plastic waste, creating a serious problem of plastic waste management. In cases such plastic waste ends-up in landfills or it is buried in soil, questions are raised about their possible effects on the environment, whether they biodegrade at all, and if they do, what is the rate of (bio?)degradation and what effect the products of (bio?)degradation have on the environment, including the effects of the additives used. Possible degradation of agricultural plastic waste should not result in contamination of the soil and pollution of the environment (including aesthetic pollution or problems with the agricultural products safety). Ideally, a degradable polymer should be fully biodegradable leaving no harmful substances in the environment. Most experts and acceptable standards define a fully biodegradable polymer as a polymer that is completely converted by microorganisms to carbon dioxide, water, mineral and biomass, with no negative environmental impact or ecotoxicity. However, part of the ongoing debate concerns the question of what is an acceptable period of time for the biodegradation to occur and how this is measured. Many polymers that are claimed to be ‘biodegradable’ are in fact ‘bioerodable’, ‘hydrobiodegradable’, ‘photodegradable’, controlled degradable or just partially biodegradable. This review paper attempts to delineate the definition of degradability of polymers used in agriculture. Emphasis is placed on the controversial issues regarding biodegradability of some of these polymers.     

An insight into the removal of fluoroquinolones in activated sludge process: Sorption and biodegradation characteristics

The detailed sorption steps and biodegradation characteristics of fluoroquinolones(FQs)including ciprofloxacin, enrofloxacin, lomefloxacin, norfloxacin, and ofloxacin were investigated through batch experiments. The results indicate that FQs at a total concentration of 500 μg/L caused little inhibition of sludge bioactivity. Sorption was the primary removal pathway of FQs in the activated sludge process, followed by biodegradation, while hydrolysis and volatilization were negligible. FQ sorption on activated sludge was a reversible process governed by surface reaction. Henry and Freundlich models could describe the FQ sorption isotherms well in the concentration range of 100–300 μg/L. Thermodynamic parameters revealed that FQ sorption on activated sludge is spontaneous, exothermic, and enthalpy-driven. Hydrophobicity-independent mechanisms determined the FQ sorption affinity with activated sludge. The zwitterion of FQs had the strongest sorption affinity, followed by cation and anion, and aerobic condition facilitated FQ sorption. FQs were slowly biodegradable, with long half-lives( 100 hr). FQ biodegradation was enhanced with increasing temperature and under aerobic condition,and thus was possibly achieved through co-metabolism during nitrification. This study provides an insight into the removal kinetics and mechanism of FQs in the activated sludge process, but also helps assess the environmental risks of FQs resulting from sludge disposal.     

微生物燃料电池表观内阻的构成和测量

将微生物燃料电池内部各种阻力用表观内阻统一表征,在建立其等效电路的基础上将表观内阻分为欧姆内阻和非欧姆内阻2部分.通过稳态放电法测量微生物燃料电池表观内阻,在改变外电阻后稳定时间需要60 s以上方能保证测定准确性,通过稳态放电法测定一室型微生物燃料电池的表观内阻为289 Ω,当外电阻等于表观内阻时微生物燃料电池对外输出功率达到最大,为241 mW/m²;通过电流中断法测量一室型微生物燃料电池的欧姆内阻为99 Ω,测定结果与断电前电流强度无关;当一室型微生物燃料电池对外供电分别处于活化极化区、欧姆极化区和浓差极化区时,非欧姆电阻占总内阻的比例分别为93％、66％和75％,在电池对外供电达到最大时非欧姆占总内阻比例最低.提高微生物燃料电池产电能力需要同时降低电池的欧姆内阻和非欧姆内阻.     

Comparing the removal of polycyclic aromatic hydrocarbons in soil after different bioremediation approaches in relationto the extracellular enzyme activities

A 120-day experiment was conducted to compare the removal of polycyclic aromatic hydrocarbons(PAHs) from agricultural soil after natural attenuation(NA), phytoremediation(P), mycoremediation(M), and plant-assisted mycoremediation(PAM) approaches in relation to the extracellular enzyme activities in soil. The NA treatment removed the total soil PAH content negligibly. The P treatment using maize(Zea mays) enhanced only the removal of low and medium molecular PAHs. The Pleurotus ostreatus cultivated on 30–50 mm wood chip substrate used in M treatment was the most successful in the removal of majority PAHs. Therefore,significantly(p 0.05) highest total PAH removal by 541.4 μg/kg dw(dry weight)(36%) from all tested M treatments was observed. When using the same fungal substrate together with maize in PAM treatment, the total PAH removal was not statistically different from the previous M treatment. However, the maize-assisted mycoremediation treatment significantly boosted fungal biomass, microbial and manganese peroxidase activity in soil which strongly correlated with the removal of total PAHs. The higher PAH removal in that PAM treatment could be reflected in the following post-harvest time. Our suggested M and PAM approaches could be promising in situ bioremediation strategies for PAH-contaminated soils.