Enhanced microbial degradation of benzo[a]pyrene by chemical oxidation

Redox potential model for guiding moderate oxidation of polycyclic aromatic hydrocarbons in soils

In-situ chemical oxidation is an important approach to remediate soils contaminated with persistent organic pollutants, e.g., polycyclic aromatic hydrocarbons (PAHs). However, massive oxidants are added into soils without an explicit model for predicting the redox potential (Eh) during soil remediation, and overdosed oxidants would pose secondary damage by disturbing soil organic matter and acidity. Here, a soil redox potential (Eh) model was first established to quantify the relationship among oxidation parameters, crucial soil properties, and pollutant elimination. The impacts of oxidant types and doses, soil pH, and soil organic carbon contents on soil Eh were systematically clarified in four commonly used oxidation systems (i.e., KMnO4, H2O2, fenton, and persulfate). The relative error of preliminary Eh model was increased from 48-62% to 4-16% after being modified with the soil texture and dissolved organic carbon, and this high accuracy was verified by 12 actual PAHs contaminated soils. Combining the discovered critical oxidation potential (COP) of PAHs, the moderate oxidation process could be regulated by the guidance of the soil Eh model in different soil conditions. Moreover, the product analysis revealed that the hydroxylation of PAHs occurred most frequently when the soil Eh reached their COP, providing a foundation for further microorganism remediation. These results provide a feasible strategy for selecting oxidants and controlling their doses toward moderate oxidation of contaminated soils, which will reduce the consumption of soil organic matter and protect the main structure and function of soil for future utilization. ENVIRONMENTAL IMPLICATIONS: This study provides a novel insight into the moderate chemical oxidation by the Eh model and largely reduces the secondary risks of excessive oxidation and oxidant residual in ISCO. The moderate oxidation of PAHs could be a first step to decrease their toxicity and increase their bioaccessibility, favoring the microbial degradation of PAHs. Controlling the soil Eh with the established model here could be a promising approach to couple moderate oxidation of organic contaminants with microbial degradation. Such an effective and green soil remediation will largely preserve the soil's functional structure and favor the subsequent utilization of remediated soil.

Sulfur-containing iron carbon nanocomposites activate persulfate for combined chemical oxidation and microbial remediation of petroleum-polluted soil

In this study, sulfur-containing iron carbon nanocomposites (S@Fe-CN) were synthesized by calcining iron-loaded biomass and utilized to activate persulfate (PS) for the combined chemical oxidation and microbial remediation of petroleum-polluted soil. The highest removal efficiency of total petroleum hydrocarbons (TPHs) was achieved at 0.2% of activator, 1% of PS and 1:1 soil-water ratio. The EPR and quenching experiments demonstrated that the degradation of TPHs was caused by the combination of 1O2,·OH, SO4·-, and O2·-. In the S@Fe-CN activated PS (S@Fe-CN/PS) system, the degradation of TPHs underwent two phases: chemical oxidation (days 0 to 3) and microbial degradation (days 3 to 28), with kinetic constants consistent with the pseudo-first-order kinetics of chemical and microbial remediation, respectively. In the S@Fe-CN/PS system, soil enzyme activities decreased and then increased, indicating that microbial activities were restored after chemical oxidation under the protection of the activators. The microbial community analysis showed that the S@Fe-CN/PS group affected the abundance and structure of microorganisms, with the relative abundance of TPH-degrading bacteria increased after 28 days. Moreover, S@Fe-CN/PS enhanced the microbial interactions and mitigated microbial competition, thereby improving the ability of indigenous microorganisms to degrade TPHs.

Controllable chemical redox reactions to couple microbial degradation for organic contaminated sites remediation: A review

Global environmental concern over organic contaminated sites has been progressively conspicuous during the process of urbanization and industrial restructuring. While traditional physical or chemical remediation technologies may significantly destroy the soil structure and function, coupling moderate chemical degradation with microbial remediation becomes a potential way for the green, economic, and efficient remediation of contaminated sites. Hence, this work systematically elucidates why and how to couple chemical technology with microbial remediation, mainly focused on the controllable redox reactions of organic contaminants. The rational design of materials structure, selective generation of reactive oxygen species, and estimation of degradation pathway are described for chemical oxidation. Meanwhile, current progress on efficient and selective reductions of organic contaminants (i.e., dechlorination, defluorination, -NO2 reduction) is introduced. Combined with the microbial remediation of contaminated sites, several consideration factors of how to couple chemical and microbial remediation are proposed based on both fundamental and practical points of view. This review will advance the understanding and development of chemical-microbial coupled remediation for organic contaminated sites.

Remediation of crude oil contaminated soil through an integrated biological-chemical-biological strategy

A plausible approach to remediating petroleum contaminated soil is the integration of chemical and biological treatments. Using appropriate chemical oxidation, the integrated remediation can be effectively achieved to stimulate the biodegradation process, consequently bolstering the overall remediation effect. In this study, an integrated biological-chemical-biological strategy was proposed. Both conventional microbial degradation techniques and a modified Fenton method were employed, and the efficacy of this strategy on crude oil contaminated soil, as well as its impact on pollutant composition, soil environment, and soil microorganism, was assessed. The results showed that this integrated remediation realized an overall 68.3 % removal rate, a performance 1.7 times superior to bioremediation alone and 2.1 times more effective than chemical oxidation alone, elucidating that the biodegradation which had become sluggish was invigorated by the judicious application of chemical oxidation. By optimizing the positioning of chemical treatment, the oxidization was allowed to act predominantly on refractory substances like resins, thus effectively enhancing pollutant biodegradability. Concurrently, this oxidating maneuver contributed to a significant increase in concentrations of dissolvable nutrients while maintaining appropriate soil pH levels, thereby generating favorable growth conditions for microorganism. Moreover, attributed to the proliferation and accumulation of degrading bacteria during the initial bioremediation phase, the microbial growth subsequent to oxidation showed rapid resurgence and the relative abundance of typical petroleum-degrading bacteria, particularly Proteobacteria, was substantially increased, which played a significant role in enhancing overall remediation effect. Our research validated the feasibility of biological-chemical-biological strategy and elucidated its correlating mechanisms, presenting a salient reference for the further studies concerning the integrated remediation of petroleum contaminated soil.

Adaptation strategies and functional transitions of microbial community in pyrene-contaminated soils promoted by lead with Pseudomonas veronii and its extracellular polymeric substances

Pyrene was designated as a remediation target in this study, and low contamination of lead (Pb) was set to induce heavy metal stress. Pseudomonas veronii and its extracellular polymeric substances (EPSs) were chosen for biofortification, with the aim of elucidating the structural, metabolic, and functional responses of soil microbial communities. Community analysis of soil microorganisms using high-throughput sequencing showed that the co-addition of P. veronii and EPSs resulted in an increase in relative abundance of phyla associated with pyrene degradation, and formed a symbiotic system dominated by Firmicutes and Proteobacteria, which involved in pyrene metabolism. Co-occurrence network analysis revealed that the module containing P. veronii was the only one exhibiting a positive correlation between bacterial abundance and pyrene removal, indicating the potential of bioaugmentation in enriching functional taxa. Biofortification also enhanced the abundance of functional gene linked to EPS production (biofilm formation-Pseudomonas aeruginosa) and pyrene degradation. Furthermore, 17 potential functional bacteria were screened out using random forest algorithm. Lead contamination further promoted the growth of Proteobacteria, intensified cooperative associations among bacteria, and increased the abundance of bacteria with positive correlation with pyrene degradation. The results offer novel perspectives on alterations in microbial communities resulting from the synergistic impact of heavy metal stress and biofortification.

Spatial distribution and risk assessment of polycyclic aromatic hydrocarbons in soils from contaminated sites in Eastern China

A total of 16 polycyclic aromatic hydrocarbons (PAHs) were measured in 28 soil column samples from two contaminated industrial sites in Eastern China. The total concentration of 16 PAHs (∑PAHs) in the surface soil (0-20 cm) was measured up to 52,600 ng/g (dry weight basis) with a remarkable spatial difference in the studied contaminated sites. The concentrations of the ∑PAHs in soils decreased with the increase in soil depth (0-10 m). The surface and subsurface soil presented a tenfold higher concentration than the soil with depth greater than 4 m. Additionally, the vertical migration tendency of the PAHs was found to be correlated significantly with their hydrophobicity (R2 = 0.79, P < 0.01). Naphthalene (with lowest octanol-water partition coefficient among the studied PAHs) showed the greatest average soil depth at which its peak concentration occurred. Furthermore, risk quotient analysis by using benzo[a]pyrene as reference compound showed that 71.4% of the samples exhibited high ecological risk for soil. Moreover, the total carcinogenic risk of the PAHs in the surface soil samples was assessed at 5.61 × 10-5-1.28 × 10-4 and 4.41 × 10-6-9.43 × 10-5 for male and female workers, respectively, in which 67.9%-71.4% of the samples showed potential risk. Generally, these results suggest a further consideration of ecological and health risks associated with PAHs in contaminated sites in Eastern China.

Remediation of benzo[a]pyrene contaminated soils by moderate chemical oxidation coupled with microbial degradation

Chemical oxidation is a promising technology for the remediation of organics-contaminated soils. However, residual oxidants and transformation products have adverse effects on microbial activities. This work aimed at moderate chemical oxidation coupled with microbial degradation (MOMD) for the removal of benzo[a]pyrene (BaP) by optimizing the type and dosage of oxidants. Potassium permanganate (KMnO₄), Fe²⁺ + sodium persulfate (Fe²⁺ + PS), Fenton's reagent (Fe²⁺ + H₂O₂), and hydrogen peroxide (H₂O₂) were compared for BaP removal from loam clay and sandy soils. Overall, the removal efficiency of BaP by a moderate dose of oxidant coupled indigenous microorganism was slightly lower than that by a high dose of relevant oxidant. The contributions of microbial degradation to the total removal of BaP varied for different oxidants and soils. The removal efficiency of BaP from loam clay sandy soil by a moderate dose of KMnO₄ (25 mmol/L) was 94.3 ± 1.1 % and 92.5 ± 1.8 %, respectively, which were both relatively higher than those under other conditions. The indirect carbon footprint yielded by the moderate dose of oxidants was 39.2-72.8 % less than that by the complete oxidation. A moderate dose of oxidants also reduced disturbances to soil pH and OC. The microbial communities after MOMD treatment were dominated by Burkholderiaceae, Enterobacteriaceae, Alicyclobacillaceae, and Oxalobacteraceae. These dominant microorganisms promoted the removal of BaP through the expression of polycyclic aromatic hydrocarbon-ring hydroxylated dioxygenase gene. Compared with complete chemical oxidation, MOMD is also a promising technique with the utilization of indigenous microorganism for remediating BaP-contaminated soils.

Effects of combined remediation of pre-ozonation and bioaugmentation on degradation of benzo[a]pyrene and microbial community structure in soils

The combination technique of pre-ozonation and bioaugmentation is promising for remediating benzo[a]pyrene (BaP)-contaminated soil. However, little is known about the effect of coupling remediation on the soil biotoxicity, soil respiration, enzyme activity, microbial community structure, and microbial in the process of remediation. This study developed two coupling remediation strategies (pre-ozonation coupled with bioaugmentation by addition of polycyclic aromatic hydrocarbons (PAHs) specific degrading bacteria or activated sludge), compared with sole ozonation and sole bioaugmentation, to improve degradation of BaP and recovery of soil microbial activity and community structure. Results showed that the higher removal efficiency of BaP (92.69-93.19%) was found in coupling remediation, compared with sole bioaugmentation (17.71-23.28%). Meanwhile, coupling remediation significantly reduced the soil biological toxicity, promoted the rebound of microbial counts and activity, and recovered the species numbers and microbial community diversity, compared with sole ozonation and sole bioaugmentation. Besides, it was feasible to replace microbial screening with activated sludge, and coupling remediation by addition of activated sludge was more conducive to the recovery of soil microbial communities and diversity. This work provides a strategy of pre-ozonation coupled with bioaugmentation to further degrade BaP in soil by promoting the rebound of microbial counts and activity, as well as the recovery of species numbers and microbial community diversity.

Biochar loaded with cobalt ferrate activated persulfate to degrade naphthalene

Considering the simple preparation of biochar and the excellent activation performance of cobalt ferrate material, a biochar supported cobalt ferrate composite was synthesized by a solvothermal method. The material was used to activate persulfate (PS) to degrade naphthalene (NAP) in water. The structure and morphology characterization showed that the composite (CoFe₂O₄-BC) was successfully prepared. Under the conditions of 0.25 g L^-1 CoFe₂O₄-BC and 1 mM PS, 90.6% NAP (the initial concentration was 0.1 mM) was degraded after 30 minutes. The degradation kinetics of NAP followed the pseudo-first-order kinetic model with a rate constant of 0.0645 min^-1. With the increase of the dosage of activator and PS, the removal rate of NAP could be increased to 99.5%. The coexistence of anions and humic acids inhibited the removal of NAP. The acid environment promoted the removal of NAP while the alkaline environment inhibited it. After four cycles of CoFe₂O₄-BC material, the removal rate of NAP decreased from 90.6% to 79.4%. The removal of TOC was about 45% after each cycle. After the first cycle, the concentration of leached cobalt ion and leached iron ion was about 310 μg L^-1 and 30 μg L^-1 respectively. The free radical quenching experiments showed that SO₄ ^-˙ and OH˙ were the main causes of NAP removal, and the possible degradation path of NAP was elucidated by DFT calculation.

Newly isolated halotolerant Aspergillus sp. showed high diesel degradation efficiency under high salinity environment aided with hematite

The contamination of saline soil with hazardous petroleum hydrocarbons is a common problem across coastal areas globally. Bioaugmentation combined with chemical treatment is an emerging remediation technique, but it currently shows low efficiency under high saline environments. In this study, we screened and used a novel halotolerant lipolytic fungal consortium (HLFC) combined with hematite (Fe₂O₃) for the bioremediation of diesel contaminated saline soils. The changes in total petroleum hydrocarbons (TPH) concentrations, enzyme activity, and microbial diversity were compared among different treatments (HLFC, hematite, hematite-HLFC, and control). The results showed that TPH degradation was significantly (P < 0.05) enhanced in hematite-HLFC (47.59-88.01%) and HLFC (24.26-72.04%) amended microcosms across all salinity levels, compared to the treatments of hematite (23.71-66.26%) and control (6.39-55.20%). TPH degradation was positively correlated with lipase and laccase enzyme activities, electrical conductivity, and the water holding capacity of the soil. Analyses of the microbial community structure showed that microbial richness decreased, while evenness increased in HLFC and hematite-HLFC treatments. The relative abundances of Alicyclobacillus, Sediminibacillus, Alcanivorax, Penicillium, Aspergillus, and Candida genera were significantly high in hematite-HLFC and HLFC amended microcosms. Our findings provide a promising new microbial-based technique, which can degrade TPH efficiently in saline soil.

Insights into the effects of Fenton oxidation on PAH removal and indigenous bacteria in aged subsurface soil

Combined chemical oxidation and bioremediation is a promising method of treating polycyclic aromatic hydrocarbon (PAH) contaminated soil, wherein indigenous soil bacteria play a critical role in the subsequent biodegradation of PAHs after the depletion of the oxidant. In this study, different Fenton conditions were applied by varying either the oxidation mode (conventional Fenton (CF), Fenton-like (LF), modified Fenton (MF), and graded modified Fenton (GMF)) or the H₂O₂ dosage (0%, 3%, 6%, and 10% (v/v)) to treat PAH contaminated soil. The results revealed that when equal dosages of H₂O₂ are applied, PAHs are significantly removed following oxidation treatment, and the removal percentages obeyed the following sequence: CF > GMF > MF > LF. In addition, higher dosages of H₂O₂ improved the PAH removal from soil treated with the same oxidation mode. The ranges of total PAHs removal efficiencies in the soil added 3%, 6%, and 10% of H₂O₂ (v/v) were 18.04%∼59.48%, 31.88%∼71.83%, and 47.56%∼78.16%, respectively. The PAH removal efficiency decreased with increasing ring numbers for the same oxidation treatment. However, the negative influences on soil bacterial abundance, community composition, and function were observed after Fenton treatment. After Fenton oxidation, the bacterial abundance in the soil received 3%, 6%, and 10% of H₂O₂ (v/v) decreased 1.96-2.69, 2.44-3.22, and 3.09-3.42 orders of magnitude compared to the untreated soil. The soil bacterial abundance tended to be impacted by the oxidation mode and H₂O₂ dosage simultaneously. While the main factor influencing the soil bacterial community composition was the H₂O₂ dosages. The results of this study showed that different oxidation mode and H₂O₂ dosage exhibited different effects on PAHs removal and soil bacteria (including abundance, community composition, and function), and there was a trade-off between the removal of PAHs and the adverse impact on soil bacteria.

Recent Developments in Advanced Oxidation Processes for Organics-Polluted Soil Reclamation

Soil pollution has become a substantial environmental problem which is amplified by overpopulation in different regions. In this review, the state of the art regarding the use of Advanced Oxidation Processes (AOPs) for soil remediation is presented. This review aims to provide an outline of recent technologies developed for the decontamination of polluted soils by using AOPs. Depending on the decontamination process, these techniques have been presented in three categories: the Fenton process, sulfate radicals process, and coupled processes. The review presents the achievements of, and includes some reflections on, the status of these emerging technologies, the mechanisms, and influential factors. At the present, more investigation and development actions are still desirable to bring them to real full-scale implementation.

Remediation of polycyclic aromatic hydrocarbons by sulfate radical advanced oxidation: Evaluation of efficiency and ecological impact

Remediation of polycyclic aromatic hydrocarbon (PAH) contamination in soil remains expensive and difficult. Sulfate radical advanced oxidation processes (SR-AOPs) can be used for in situ PAH oxidation but their efficiency and ecological impacts require evaluation. Here, we tested the remediation efficiency and ecological impacts of an SR-AOP combining sodium persulfate and ferrous sulfate (FS), the FS SR-AOP with the chelating agent citric acid (FS+CA), and the FS SR-AOP with chelating agent and the surfactant IGEPALCA-720 (FS+CA+IG) compared with natural attenuation (control, CK). We measured PAH, soil physicochemical properties (pH, soil organic matter [SOM]), and soil biological properties (polyphenol oxidase [PPO] activity, peroxidase [POD] activity, soil microbes) in contaminated soil samples after incubation with FS, FS+CA, FA+CA+IG, or CK for 1, 15, and 30 d. Compared with CK, all SR-AOPs significantly decreased PAH after 1 d, with FS+CA+IG showing the highest efficiency (80.8%) and PAH removal peaking at 15 d. FS+CA+IG treatment reduced SOM the least and soil pH the most; after 30 d, SOM recovered to ~80% of the level observed in CK, but soil pH decreased further. PPO and POD activities were highest after 15 and 30 d of FS+CA+IG treatment. Real-time quantitative PCR demonstrated that SR-AOPs significantly decreased quantities of PAH-degrading bacteria, soil bacteria, fungi, and actinobacteria at 1 d, but after 30 d, the microbes recovered to levels similar to those observed in CK, with no significant differences among SR-AOPs. SR-AOPs reduced bacterial diversity and changed the dominant phylum from Acidobacteria to Firmicutes. In summary, SR-AOP treatment with both the chelating agent and the surfactant produced the best PAH removal and least SOM destruction but the largest pH decrease, although some factors recovered with longer incubation. This study provides key information for improving PAH remediation and evaluating its ecological impact.

Persulfate Oxidation Coupled with Biodegradation by Pseudomonas fluorescens Enhances Naphthenic Acid Remediation and Toxicity Reduction

The extraction of bitumen from the Albertan oilsands produces large amounts of oil sands process-affected water (OSPW) that requires remediation. Classical naphthenic acids (NAs), a complex mixture of organic compounds containing O₂^- species, are present in the acid extractable organic fraction of OSPW and are a primary cause of acute toxicity. A potential remediation strategy is combining chemical oxidation and biodegradation. Persulfate as an oxidant is advantageous, as it is powerful, economical, and less harmful towards microorganisms. This is the first study to examine persulfate oxidation coupled to biodegradation for NA remediation. Merichem NAs were reacted with 100, 250, 500, and 1000 mg/L of unactivated persulfate at 21 °C and 500 and 1000 mg/L of activated persulfate at 30 °C, then inoculated with Pseudomonas fluorescens LP6a after 2 months. At 21 °C, the coupled treatment removed 52.8-98.9% of Merichem NAs, while 30 °C saw increased removals of 99.4-99.7%. Coupling persulfate oxidation with biodegradation improved removal of Merichem NAs and chemical oxidation demand by up to 1.8× and 6.7×, respectively, and microbial viability was enhanced up to 4.6×. Acute toxicity towards Vibrio fischeri was negatively impacted by synergistic interactions between the persulfate and Merichem NAs; however, it was ultimately reduced by 74.5-100%. This study supports that persulfate oxidation coupled to biodegradation is an effective and feasible treatment to remove NAs and reduce toxicity.

Succession of microbial communities and synergetic effects during bioremediation of petroleum hydrocarbon-contaminated soil enhanced by chemical oxidation

Biotechnologies integrated with chemical techniques are promising in treating the soils contaminated by petroleum hydrocarbons. Experiments by applying the degrading consortium and the modified Fenton (MF) with the chelator sodium citrate simultaneously were carried out to investigate the effects of the MF reagents on the degradation of total petroleum hydrocarbons (TPHs), changes in enzyme activities and the succession of microbial communities at the 0, 20, 100 and 500 mmol/kg hydrogen peroxide concentration levels. The ratio between hydrogen peroxide, ferrous sulfate and sodium citrate in the MF reagents was 100:1:1. The results indicated that the degradation of TPHs conformed to first-order kinetics and MF treatments increased the total removal rates of TPHs (4.73-24.26%) and activated dehydrogenase and polyphenol oxidase activities. A shift in microbial communities from Proteobacteria to Bacteroidetes was observed during the enhanced bioremediation, and the predominant genus shifted from Pseudomonas with an average relative abundance (ARAs) of 76.61% at the beginning to Sphingobacterium with ARAs of 52.06% at the later stage. The MF reagents at the proper level could simplify the relationship among the community populations, alleviate their competition and strengthen their associations, which would optimize the removal efficiency.

Polycyclic Aromatic Hydrocarbons: Sources, Toxicity, and Remediation Approaches

Polycyclic aromatic hydrocarbons (PAHs) are widespread across the globe mainly due to long-term anthropogenic sources of pollution. The inherent properties of PAHs such as heterocyclic aromatic ring structures, hydrophobicity, and thermostability have made them recalcitrant and highly persistent in the environment. PAH pollutants have been determined to be highly toxic, mutagenic, carcinogenic, teratogenic, and immunotoxicogenic to various life forms. Therefore, this review discusses the primary sources of PAH emissions, exposure routes, and toxic effects on humans, in particular. This review briefly summarizes the physical and chemical PAH remediation approaches such as membrane filtration, soil washing, adsorption, electrokinetic, thermal, oxidation, and photocatalytic treatments. This review provides a detailed systematic compilation of the eco-friendly biological treatment solutions for remediation of PAHs such as microbial remediation approaches using bacteria, archaea, fungi, algae, and co-cultures. In situ and ex situ biological treatments such as land farming, biostimulation, bioaugmentation, phytoremediation, bioreactor, and vermiremediation approaches are discussed in detail, and a summary of the factors affecting and limiting PAH bioremediation is also discussed. An overview of emerging technologies employing multi-process combinatorial treatment approaches is given, and newer concepts on generation of value-added by-products during PAH remediation are highlighted in this review.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.