Microbial regeneration of spent activated carbon dispersed with organic contaminants: mechanism, efficiency, and kinetic models

Background and purpose

Regeneration of spent activated carbon assumes paramount importance in view of its economic reuse during adsorptive removal of organic contaminants. Classical thermal, chemical, or electrochemical regeneration methods are constrained with several limitations. Microbial regeneration of spent activated carbon provides a synergic combination of adsorption and biodegradation.

Methods

Microorganisms regenerate the surface of activated carbon using sorbed organic substrate as a source of food and energy. Aromatic hydrocarbons, particularly phenols, including their chlorinated derivatives and industrial waste water containing synthetic organic compounds and explosives-contaminated ground water are the major removal targets in adsorption?Cbioregeneration process. Popular mechanisms of bioregeneration include exoenzymatic hypothesis and biodegradation following desorption. Efficiency of bioregeneration can be quantified using direct determination of the substrate content on the adsorbent, the indirect measurement of substrate consumption by measuring the carbon dioxide production and the measurement of oxygen uptake. Modeling of bioregeneration involves the kinetics of adsorption/desorption and microbial growth followed by solute degradation. Some modeling aspects based on various simplifying assumptions for mass transport resistance, microbial kinetics and biofilm thickness, are briefly exposed.

Results

Kinetic parameters from various representative bioregeneration models and their solution procedure are briefly summarized. The models would be useful in predicting the mass transfer driving forces, microbial growth, substrate degradation as well as the extent of bioregeneration.

Conclusions

Intraparticle mass transfer resistance, incomplete regeneration, and microbial fouling are some of the problems needed to be addressed adequately. A detailed techno-economic evaluation is also required to assess the commercial aspects of bioregeneration.     

Co-transport of biochar colloids with organic contaminants in soil column

Environmental Science and Pollution Research - Co-transport of biochar (BC) colloids with coexisting organic contaminants (OCs) in soil involves complex interactions among BC colloids, OCs, and...     

Sorption of polar and nonpolar organic contaminants by oil-contaminated soil

Sorption of nonpolar (phenanthrene and butylate) and polar (atrazine and diuron) organic chemicals to oil-contaminated soil was examined to investigate oil effects on sorption of organic chemicals and to derive oil–water distribution coefficients (K_oil). The resulting oil-contaminated soil–water distribution coefficients (K_d) for phenanthrene demonstrated sorption-enhancing effects at both lower and higher oil concentrations (C_oil) but sorption-reducing (competitive) effects at intermediate C_oil (approximately 1 g kg⁻¹). Rationalization of the different dominant effects was attempted in terms of the relative aliphatic carbon content which determines the accessibility of the aromatic cores to phenanthrene. Little or no competitive effect occurred for butylate because its sorption was dominated by partitioning. For atrazine and diuron, the changes in K_d at C_oil above approximately 1 g kg⁻¹ were negligible, indicating that the presently investigated oil has little or no effect on the two tested compounds even though the polarity of the oil is much less than soil organic matter (SOM). Therefore, specific interactions with the active groups (aromatic and polar domains) are dominantly responsible for the sorption of polar sorbates, and thus their sorption is controlled by available sorption sites. This study showed that the oil has the potential to be a dominant sorptive phase for nonpolar pollutants when compared to SOM, but hardly so for polar compounds. The results may aid in a better understanding of the role of the aliphatic and aromatic domains in sorption of nonpolar and polar organic pollutants.     

Sorption of polar and nonpolar organic contaminants by oil-contaminated soil

Sorption of nonpolar (phenanthrene and butylate) and polar (atrazine and diuron) organic chemicals to oil-contaminated soil was examined to investigate oil effects on sorption of organic chemicals and to derive oil–water distribution coefficients (K_oil). The resulting oil-contaminated soil–water distribution coefficients (K_d) for phenanthrene demonstrated sorption-enhancing effects at both lower and higher oil concentrations (C_oil) but sorption-reducing (competitive) effects at intermediate C_oil (approximately 1 g kg⁻¹). Rationalization of the different dominant effects was attempted in terms of the relative aliphatic carbon content which determines the accessibility of the aromatic cores to phenanthrene. Little or no competitive effect occurred for butylate because its sorption was dominated by partitioning. For atrazine and diuron, the changes in K_d at C_oil above approximately 1 g kg⁻¹ were negligible, indicating that the presently investigated oil has little or no effect on the two tested compounds even though the polarity of the oil is much less than soil organic matter (SOM). Therefore, specific interactions with the active groups (aromatic and polar domains) are dominantly responsible for the sorption of polar sorbates, and thus their sorption is controlled by available sorption sites. This study showed that the oil has the potential to be a dominant sorptive phase for nonpolar pollutants when compared to SOM, but hardly so for polar compounds. The results may aid in a better understanding of the role of the aliphatic and aromatic domains in sorption of nonpolar and polar organic pollutants.     

水中有机污染物超声强化氧化技术研究进展

超声波技术在化学、环境、制药以及生物等领域有着广阔的应用前景。在降解水中难降解有机污染物方面 ,超声强化氧化技术有一定优势 ,降解效果显著 ,符合绿色环保技术的要求。超声强化氧化技术主要可分为超声空化技术、超声强化化学 (催化 )氧化技术、超声强化电化学 (催化 )氧化技术、超声强化光化学 (催化 )氧化技术、超声 生物降解等几大类 ,本文对各类技术的优缺点进行了评述。     

Grinding and sieving soil affects the availability of organic contaminants: a kinetic analysis

Field contaminated soils are often homogenized before application in bioassays and chemical assays that estimate the (bio)availability of their contaminants. The homogenization of the soil might affect the availability, and thereby the outcome of a bioassay might not reflect field situations. In this study, uptake kinetics of polycyclic aromatic hydrocarbons (PAH) by a negligible depletive passive sampler exposed to a ground and non-ground field contaminated soil were tested. The measurements illustrate how freely dissolved pore water concentrations of contaminants can be affected by soil treatment. It took more than a month, and over a year to reach steady state in the passive sampler exposed to the ground and non-ground soil, respectively. The uptake rate seemed to be limited by desorption from the soil, even though the fiber only extracted 0.2% of the soil-sorbed PAH at maximum. If these observations are translated to the field situation, where contaminants are not homogeneously distributed and disappear by (bio)degradation or physical transport processes, it is unlikely that pore water concentrations are solely determined by a thermodynamic equilibrium. Hence, exposure of organisms in these soils cannot always be estimated by sorption studies and an equilibrium partitioning approach.     

Cell absorption induced desorption of hydrophobic organic contaminants from digested soil residue

Oral ingestion of contaminated soil is an important pathway of human exposure to hydrophobic organic contaminants (HOCs), particularly for children in developing countries. The mobilization potential of various contaminants from ingested soil is often characterized using an in vitro gastrointestinal model, based on the quantities of contaminants remaining in digestive fluid after digestion and separation. Recently, it was experimentally demonstrated that a large fraction of mobilized contaminants sorbed on the digested residue could be released if the dissolved fraction was removed by intestinal absorption. This hypothesis was further tested in this study. Soil spiked with dichlorodiphenyltrichloroethane and its metabolites (DDXs) and polycyclic aromatic hydrocarbons (PAHs) was digested using an in vitro gastrointestinal model. A human colon carcinoma cell line (Caco-2) was cultured in digestive fluid with or without soil residue (pre-equilibrated with the soil) for 2 h. A large proportion of the contaminants (37-68%) was sorbed on the digested residue. Without this residue, 66 ± 13% of DDXs and 73 ± 14% of PAHs dissolved in the fluid, as means and standard deviations, were absorbed by the cell monolayer after exposure. With both digestive fluid and residue, the sorbed fraction of PAHs and DDXs decreased by 38-92%, while the ratios of the cellular to the dissolved concentrations were 2.7-2.8 times higher than those without the residue. This supported the hypothesis that the cell absorption of dissolved HOCs induces desorption of the sorbed fraction from digestive residue, and the desorbed HOCs can be absorbed as well.     

Volatile organic air contaminants in plants

Comparative investigations of the sorption process of gaseous toluene were performed using fruit material (orange peel) and the mixture of chemically bonded phases (CBPs) as sorbents. For this study, a specially constructed system that allows exposure of sorbents to volatile air contaminants at constant concentrations was applied. The results for the prepared packings indicate a typical adsorption process described by Langmuir isotherm. In the case of orange peel, a mixed mechanism of the sorption process is suggested.     

Fugacity modelling to predict the distribution of organic contaminants in the soil:oil matrix of constructed biopiles

Level I and II fugacity approaches were used to model the environmental distribution of benzene, anthracene, phenanthrene, 1-methylphenanthrene and benzo[a]pyrene in a four phase biopile system, accounting for air, water, mineral soil and non-aqueous phase liquid (oil) phase. The non-aqueous phase liquid (NAPL) and soil phases were the dominant partition media for the contaminants in each biopile and the contaminants differed markedly in their individual fugacities. Comparison of three soils with different percentage of organic carbon (% org C) showed that the % org C influenced contaminant partitioning behaviour. While benzene showed an aqueous concentration worthy of note for leachate control during biopiling, other organic chemicals showed that insignificant amount of chemicals leached into the water, greatly reducing the potential extent of groundwater contamination. Level II fugacity model showed that degradation was the dominant removal process except for benzene. In all three biopile systems, the rate of degradation of benzo(a)pyrene was low, requiring more than 12 years for soil concentrations from a spill of about 25 kg (100 mol) to be reduced to a concentration of 0.001 microgg(-1). The removal time of 1-methylphenanthrene and either anthracene or phenanthrene was about 1 and 3 years, respectively. In contrast, benzene showed the highest degradation rate and was removed after 136 days in all biopile systems. Overall, this study confirms the association of risk critical contaminants with the residual saturation in treated soils and reinforces the importance of accounting for the partitioning behaviour of both NAPL and soil phases during the risk assessment of oil-contaminated sites.     

Microbial biomass, P-nutrition, and enzymatic activities of wheat soil in response to phosphorus enriched organic and inorganic manures

Compost was prepared from wheat straw enriched with Rajasthan rock phosphate and Aspergillus awamori. The resulting phospho-compost along with phosphorus enriched FYM, mineral fertilizer (rock phosphate) and super phosphate were evaluated for their individual contribution in improving organic matter status, P availability, and enzymatic activities of soil under wheat crop grown in a micro plot. The results showed that total organic carbon, nitrogen, microbial biomass, and humus content (an index of organic matter status of soil) of soil was highest when farm yard manure (FYM) after its enrichment with 12.5% rock phosphate was applied. Microbial enriched phospho-compost was the product yielding highest soil available phosphorus, phosphorus uptake, urease, and cellulase activities. However, FYM amended with 25% rock phosphate resulted in the greatest enhancement of beta- glucosidase. Measured parameters indicated a sure improvement of chemical and biological activities of soil after the application of phosphorus enriched organic amendments compared to the commercial fertilizer commonly used by the Indian farmers.     

Competitive sorption of organic contaminants in chalk

In the Negev desert, Israel, a chemical industrial complex is located over fractured Eocene chalk formations where transfer of water and solutes between fracture voids and matrix pores affects migration of contaminants in the fractures due to diffusion into the chalk matrix. This study tests sorption and sorption competition between contaminants in the chalk matrix to make it possible to evaluate the potential for contaminant attenuation during transport in fractures. Single solute sorption isotherms on chalk matrix material for five common contaminants (m-xylene, ametryn, 1,2-dichloroethane, phenanthrene, and 2,4,6-tribromophenol) were found to be nonlinear, as confirmed in plots of Kd versus initial solution concentration. Over the studied concentration ranges, m-xylene Kd varied by more than a factor of 100, ametryn Kd by a factor of 4, 1,2-dichloroethane Kd by more than a factor of 3, phenanthrene Kd by about a factor of 2, and 2,4,6-tribromophenol Kd by a factor of 10. It was earlier found that sorption is to the organic matter component of the chalk matrix and not to the mineral phases (Chemosphere 44 (2001) 1121). Nonlinear sorption isotherms indicate that there is at least some finite sorption domain. Bi-solute competition experiments with 2,4,6-tribromophenol as the competitor were designed to explore the nature of the finite sorption domain. All of the isotherms in the bi-solute experiments are more linear than in the single solute experiments, as confirmed by smaller variations in Kd as a function of initial solution concentration. For both m-xylene and ametryn, there is a small nonlinear component or domain that was apparently not susceptible to competition by 2,4,6-tribromophenol. The nonlinear sorption domain(s) is best expressed at low solution concentrations. Inert-solvent-normalized single and bi-solute sorption isotherms demonstrate that ametryn undergoes specific force interactions with the chalk sorbent. The volume percent of phenanthrene sorbed at the liquid solubility limit is calculated to be 13% v:v in both the single and bi-solute experiments. This value exceeds what may be reasonably interpreted as partitioning of phenanthrene into organic matter, despite the relative linearity of the phenanthrene sorption isotherm (compared with other compounds) in both single and bi-solute systems.     

Effects of biochar and greenwaste compost amendments on mobility, bioavailability and toxicity of inorganic and organic contaminants in a multi-element polluted soil

Applying amendments to multi-element contaminated soils can have contradictory effects on the mobility, bioavailability and toxicity of specific elements, depending on the amendment. Trace elements and PAHs were monitored in a contaminated soil amended with biochar and greenwaste compost over 60 days field exposure, after which phytotoxicity was assessed by a simple bio-indicator test. Copper and As concentrations in soil pore water increased more than 30 fold after adding both amendments, associated with significant increases in dissolved organic carbon and pH, whereas Zn and Cd significantly decreased. Biochar was most effective, resulting in a 10 fold decrease of Cd in pore water and a resultant reduction in phytotoxicity. Concentrations of PAHs were also reduced by biochar, with greater than 50% decreases of the heavier, more toxicologically relevant PAHs. The results highlight the potential of biochar for contaminated land remediation.     

Microbial metabolism of N-Phenyl-1-naphthylamine in soil, soil suspensions, and aquatic ecosystems

N-Phenyl-1-naphthylamine (PNA) was degraded and mineralized in nonsterile aquatic and terrestrial samples. Degradation in unsupplemented sewage and lake water was detected in 3 to 6 days with half-lives of 5 and 10 days, respectively. In sewage and lake water supplemented with a readily degradable carbon source, degradation began in 1 and 5 days with half-lives of 2 and 8 days, respectively. Sewage samples converted between 20 and 30% of labeled [¹⁴C]-PNA to ¹⁴CO₂ in 35 days while lake water samples reached 10% conversion to ¹⁴CO₂ in 12 days. Soil samples and soil suspensions converted from 15 to 35% of [¹⁴C]-PnA to ¹⁴CO₂ in 11 days. PNA was microbiologically converted in lake water to two products that were tentatively identified by gas-liquid chromatography and mass spectroscopy as dihydroxy and N-acetyl derivatives.     

Microbial degradation of dissolved organic matter (DOM) and its influence on phenanthrene-DOM interactions

Microbial degradation-induced changes in the characteristics of dissolved organic matter (DOM), and the subsequent effects on phenanthrene-DOM interactions were investigated based on the microbial incubation of DOM collected from four different sources for 28 d. Partially biodegraded DOM presented higher specific UV absorbance (SUVA), lower protein-like fluorescence, higher humic-like fluorescence, lower aliphatic carbon fraction, and higher hydrophobic neutral fractions compared to the original DOM. Microbial changes in DOM led to an increase in the isotherm nonlinearity as well as the extent of phenanthrene binding. A negative relationship between SUVA and the Freundlich n values was established for the original and the biodegraded DOM, suggesting that aromatic condensed structures may play important roles in providing nonlinear strong binding sites irrespective of microbial degradation. In contrast, there were two separate slopes of the correlations between the percentage of hydrophobic acid (HoA) fraction and the n values for the original and the biodegraded DOM with a higher slope exhibited for the latter, implying that the microbial utilization of oxygen-containing structures in the HoA fractions may contribute to enhancing the associated isotherm nonlinearity.     

Heavy metal and organic contaminants in mangrove ecosystems of China: a review

China’s rapid economic growth has been accompanied by increasing environmental pollution. Mangrove ecosystems are now facing greater pollution pressures due to elevated chemical discharges from various land-based sources. Data on the levels of heavy metals and organic pollutants in mangrove compartments (sediments, plants, zoobenthos, and fish) in China over the past 20 years have been summarized to evaluate the current pollution status of the mangrove ecosystem. Overall, the Pearl River and Jiulong River estuaries were severely polluted spots. Concentrations of Cu, Zn, Cd, and Pb in mangrove sediments of Guangdong, Fujian, and Hong Kong were higher than those from Guangxi and Hainan. The pollution status was closely linked to industrialization and urbanization. The highest concentrations of polycyclic aromatic hydrocarbons (PAHs) were found in mangrove sediments from Hong Kong, followed by Fujian and Guangdong. Mangrove plants tend to have low-enriched ability for heavy metals and organic pollutants. Much higher levels of Pb, Cd, and Hg were observed in mollusks.     

Sorption of organic contaminants by biopolymers: role of polarity, structure and domain spatial arrangement

Sorption behavior of hydrophobic organic contaminants (HOCs) (i.e., pyrene, phenanthrene and naphthalene) by native and chemically modified biopolymers (lignin, chitin and cellulose) was examined. Lignins (native and treated) showed nonlinear sorption for all compounds studied, emphasizing their glassy character. Chitins and celluloses had linear isotherms for phenanthrene and naphthalene, illustrating the dominance of partitioning, while pyrene yielded nonlinear isotherms. Sorption capacity (K(oc)) of HOCs was negatively correlated with the polarity [(O+N)/C] of the biopolymers. Aromatic and alkyl+aromatic C percentages, rather than alkyl C content, demonstrated a better correlation with K(oc) values, indicating the importance of aromatic structures for HOC affinity. Hydrophobicity (K(ow))-normalized K(oc) values decreased sharply with increasing percentage of O-alkyl C versus total aliphatic C (O-alkyl C/total aliphatic C) or with polar C/(alkyl+aromatic C) ratio of the biopolymers until their values reached 80% and 4, respectively, illustrating the effect of surrounding polar groups on reducing affinity for HOCs. Overall, the results of this study highlight the role of spatial arrangement of domains within biopolymers in sorption of HOCs, and point to sorbent properties, such as functionality, polarity and structure, jointly regulating the sorption of HOCs in biopolymers.     

Transport of reactive colloids and contaminants in groundwater: effect of nonlinear kinetic interactions

Transport of reactive colloids in groundwater may enhance the transport of contaminants in groundwater. Often, the interpretation of results of transport experiments is not a simple task as both reactions of colloids with the solid matrix and reactions of contaminants with the solid matrix and mobile and immobile colloids may be time dependent and nonlinear. Further colloid transport properties may differ from solute transport properties. In this paper, a one-dimensional model for coupled and contaminant in a porous medium (COLTRAP) is presented together with simulation results. Calculated breakthrough curves (BTC's) during contamination and decontamination show systematically the effect of nonlinear and kinetic interactions on contaminant transport in the presence of reactive colloids, and the effect of colloid transport properties that differ from solute transport properties. It is shown that in case of linear kinetic reactions, the rate of exchange of mobile and immobile colloids have a large impact on the shape of BTC's even if the solid matrix is saturated with respect to colloids. BTC's during the contamination and decontamination phase have identical shapes in this case. Moreover, the slow reactions of contaminants and colloids may lead to unretarded breakthrough of contaminants. Independent of reaction rates, nonlinear reactions lead to BTC's that are steeper during contamination than in the linear case. A characteristic aspect of nonlinear sorption is that shapes of BTC's differ during the contamination and decontamination phase. It has been observed that shapes of some of the simulated adsorption and desorption curves are similar as shapes found in experiments reported in literature. This stresses the importance of incorporating both kinetics and nonlinearity in models for coupled colloid and contaminant transport and the capability of COLTRAP to interpret experimental results. Finally, to figure out whether nonlinear processes play a role, it is very important to consider both contamination and decontamination in transport experiments.     

Modelling the extraction of soil contaminants with supercritical carbon dioxide

Extractions of volatile organic compounds (VOC’s) in contaminated soil from petroleum site were performed with supercritical carbon dioxide at different temperatures, pressures, extraction times, solvent flow rates, soil moisture contents and soil acidity. Three soil systems were investigated in order to compare the best parameters for extraction. A central composite rotatable design has been used to evaluate the influence of operation conditions on the extraction efficiency to generate model equations representing the types of soil. The results indicate that at least 70-80% of the initial amount of VOC’s can be removed at moderate temperatures even at very high moisture content. Supercritical extraction is best suited to silt type soils which have a low adsorption capacity. VOC’s recoveries from the artificial contaminated soil samples were higher in comparison with real contaminated soils. At moderate temperatures, the extraction efficiency for real soils is low because pollutants bind strongly to the soil.     

Tidal salt marsh sediment in California, USA. Part 1: occurrence and sources of organic contaminants

Surface sediment samples (0-5 cm) from five tidal marshes along the coast of California, USA were analyzed for organic pollutants to investigate their relationship to land use, current distribution within marshes, and possible sources. Among the study areas, Stege Marsh, located in San Francisco Bay, was the most contaminated. Compared to San Francisco Bay, Stege Marsh had much higher levels of organic contaminants such as PCBs (polychlorinated biphenyls), DDTs, and chlordanes. At reference marshes (Tom's Point and Walker Creek in Tomales Bay), organic contaminants in sediments were very low. While PAHs (polycyclic aromatic hydrocarbons) were found at all of the study areas (22-13,600 ng g(-1)), measurable concentrations of PCBs were found only in the sediments from Stege Marsh (80-9,940 ng g(-1)). Combustion related (pyrogenic) high molecular weight PAHs were dominant in sediments from Stege and Carpinteria Marshes, while in sediments from Tom's Point and Walker Creek petroleum related (petrogenic) low molecular weight PAHs and alkyl-substituted PAHs were much more abundant than pyrogenic PAHs. PCB congener patterns in all of the Stege Marsh samples were the same and revealed that Aroclor 1248 was a predominant source. In all marshes, the sum of DDE and DDD accounted for more than 90% of total DDTs, indicating that DDT has degraded significantly. The ratios of p,p'-DDE to p,p'-DDD in sediments from Stege Marsh provide evidence of possible previous use of technical DDD. Chlordane ratios indicated that chlordanes have degraded slightly. Bis(2-ethylhexyl)phthalate (280-32,000 ng g(-1)) was the most abundant phthalate. The data indicates that Stege Marsh may be a source of contaminants that continue to be discharged into San Francisco Bay.