Bioremediation treatability studies of contaminated soils at wood preserving sites

Bioremediation has been used frequently at sites contaminated with organic hazardous chemicals where releases from processing vessels and the mismanagement of reagents and generated waste have contributed to significant impairment of the environment. At wood treater sites, process reagents such as pentachlorophenol (PCP), and creosote have adversely impacted the surrounding soil and groundwater. When PCP has been used at these sites, polychlorinated dibenzo‐p‐dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are typically found. Where creosote has been used as the wood preservative of choice, polynuclear aromatic hydrocarbons (PAHs) are commonly found. Many of these compounds are considered to be persistent, bioaccumulative, and toxic (PBT) and are particularly recalcitrant.     

Assessing detoxification and degradation of wood preserving and petroleum wastes in contaminated soil

This study was undertaken to evaluate in-situ soil bioremediation processes, including degradation and detoxification, for two types of wood preserving wastes and two types of petroleum refining wastes at high concentrations in an unacclimated soil. The soil solid phase, water soluble fractions of the soil, and column leachates were evaluated. Two bioassays, a mutagenic potential asay (Ames assay) and an aqueous toxicity assay (Microtox^™ assay) were used to evaluate detoxification; high performance liquid chromatography was used to evaluate chemical concentration and degradation for eight polynuclear aromatic hydrocarbons (PAHs). The group of non-carcinogenic PAHs studied demonstrated greater degradation, ranging from 54–90% of mass added for the four wastes; the carcinogenic group of PAHs studied exhibited degradation ranging from 24–53% of mass added. Although no mutagenicity was observed in waste/soil mixtures after one year of treatment, Microtox^™ toxicity was observed in water soluble fractions and in leachate samples. An integration of information concerning degradation of hazardous constituents with bioassay information represents an approach for designing treatability studies and for evaluating the effectiveness of in-situ bioremediation of contaminated soil/waste systems. When combined with information from waste, site and soil characterization studies, the data generated in treatability studies may be used in predictive mathematical models to: (1) evaluate the effectiveness of use of on-site bioremediation for treatment of wastes in soil systems; (2) develop appropriate containment structures to prevent unacceptable waste transport from the treatment zone; and (3) design performance monitoring strategies.     

Solvent extraction and soil washing treatment of contaminated soils from wood preserving sites: Bench‐scale studies

Bench‐scale solvent extraction and soil washing studies were performed on soil samples obtained from three abandoned wood preserving sites included in the National Priority List. The soil samples from these sites were contaminated with high levels of polyaromatic hydrocarbons (PAHs), pentachlorophenol (PCP), dioxins, and heavy metals. The effectiveness of the solvent extraction process was assessed using liquefied propane or dimethyl ether as solvents over a range of operating conditions. These studies have demonstrated that a two‐stage solvent extraction process using dimethyl ether as a solvent at a ratio of 1.61 per kg of soil could decrease dioxin levels in the soil by 93.0 to 98.9 percent, and PCP levels by 95.1 percent. Reduction percentages for benzo(a)pyrene (BaP) potency estimate and total detected PAHs were 82.4 and 98.6 percent, respectively. Metals concentrations were not reduced by the solvent extraction treatment. These removal levels could be significantly improved using a multistage extraction system. Commercial scale solvent extraction using liquefied gases costs about $220 per ton of contaminated soil. However, field application of this technology at the United Creosote site, Conroe, Texas, failed to perform to the level observed at bench scale due to the excessive foaming and air emission problem. Soil washing using surfactant solution and wet screening treatability studies were also performed on the soil samples in order to assess remediation strategies for sites. Although aqueous phase solubility of contaminants seemed to be the most important factor affecting removal of contaminants from soil, surfactant solutions (3 percent by weight) having nonionic surfactants with hydrophile‐lipophile balance (HLB) of about 14 (Makon‐12 and Igepal CA 720) reduced the PAH levels by an average of 71 percent, compared to no measurable change when pure deionized water was used. Large fractioza of clay and silt (<0.06mm), high le!ezielsof orgaizic contami‐ nants and hzimic acid can makesoil washing less applicable.     

Evaluation of a soil‐amendment process demonstration for reducing the bioavailability of lead

The U.S. Environmental Protection Agency (EPA) evaluated an in‐situ application of a soil‐amendment process at a residential site that was contaminated with lead. The goal of the evaluation was to determine if the soil‐amendment process resulted in lower concentrations of bioavailable lead in the contaminated soils. The relative bioavailability of lead (bioaccessible lead) was measured by an in vitro test procedure that uses a highly acidic extraction procedure to simulate human digestive processes. The soil‐amendment demonstration showed that the 11.2 percent mean reduction in bioavailable lead concentration between untreated and treated soils was not statistically different. © 2002 Wiley Periodicals, Inc.     

Bioremediation of PCP-contaminated soil: Bench to full-scale implementation

Pentachlorophenol (PCP) is a widely used wood treatment agent and pesticide that is often listed among the contaminants at hazardous waste sites. Bench-scale studies were performed to develop a microbial culture and biodegradative process that could treat PCP at higher concentrations than previously reported. Several substrate formulations and culture techniques were evaluated. Ultimately a “self-feeding” (pH auxostat) continuous culture system (pH auxostat) was used to select for biodegradative activity with PCP as the carbon and energy source. After a period of 50 days, influent PCP concentrations reached 3,500 mg/liter at a dilution rate of 0.066 H^?1. Of the total theoretical chloride that could be released from PCP, 99% was detected as free chloride in the reactor effluent. PCP analysis of the effluent verified complete degradation by the microbial consortium. The reactor was converted to a constant PCP feed. At steady state conditions, the dilution rate was 0.05 H^?1 with an influent PCP concentration of 2,560 mg/liter and a biomass yield of 018 mg (dry weight) per mg of PCP. Mineralization studies performed with the microbial consortium using [U-14C1]-PCP indicated that 36.5% of the label was released as 14C-carbon dioxide.     

Enhanced land treatment of petroleum-contaminated soils using solid peroxygen materials

A pilot field study evaluated whether adding solid peroxygen materials during land treatment could cost effectively accelerate cleanup at a site contaminated with petroleum-related compounds. Five test cells were constructed containing approximately five cubic yards of soil contaminated with 300–400 mg/kg of total petroleum hydrocarbons (TPH). Three cells received treatment with solid peroxygen materials (either MgO₂ or CaO₂), while the other two cells served as controls (no peroxygen amendment). Adding solid peroxygen compounds effectively reduced the hydrocarbon contamination in the soils and decreased the treatment time. During this time, the concentration of TPH in soil in the three treatment cells decreased. In contrast, there was little loss of TPH from the two control cells simulating traditional land treatment. Adding the solid peroxygen materials reduced the total site remediation time, thereby reducing the overall costs.     

The Use of Zero‐Valent Iron (ZVI) Technology to Promote DDT and Dieldrin Degradation at Point Pelee National Park

Point Pelee National Park (PPNP) is highly contaminated with dichlorodiphenyltrichloroethane (DDT) and dieldrin due to the historical use of these two persistent organochlorine pesticides. Zero‐valent iron (ZVI) technology with and without amendments has been successfully used in the past to promote organochlorine pesticides degradation in several locations in North America and Europe. In this study, the use of two commercially available ZVI products, DARAMEND^® and EHC^®, to promote DDT and dieldrin degradation in PPNP's soil and groundwater were investigated. DARAMEND^® was applied to PPNP's soil in a laboratory experiment and in an in situ pilot‐scale plot. In both cases, DARAMEND^® did not significantly increase DDT or dieldrin degradation in treated soils. The effectiveness of EHC^® was tested in a laboratory experiment that simulated the park's groundwater environment using PPNP's pesticide contaminated soil. The result was consistent with the one reported for DARAMEND^®, in that there was no significant increase in DDT or dieldrin degradation in any of the samples treated with EHC^®. These results demonstrate that both of these ZVI commercially available products are not suitable for in situ remediation at PPNP.  ©2017 Wiley Periodicals, Inc.     

Fenton氧化—微生物法降解土壤中石油烃

以长期被苯系物污染的活性污泥为菌源,采用液相“诱导物-中间产物-目标污染物”驯化模式驯化出专性混合石油降解菌群,并将其用于Fenton氧化—微生物法处理模拟石油污染土壤。高通量测序结果表明,产黄杆菌属（Rhodanobacter）、分支杆菌属（Mycobacterium）和根瘤菌属（Rhizobiales）为主导菌属。实验结果表明：接种混合菌群后降解50 d,土样的总石油烃（TPH）去除率较土著菌提高了13.4~20.5百分点;对于TPH含量（w）分别为4%,8%,11%的土样,Fenton氧化的最佳H₂O₂加入量分别为3,4,4 mol/L（Fe²⁺加入量0.04 mol/L）,TPH总去除率分别可达88.8%,65.0%,47.7%,较单独Fenton氧化或单独微生物法均有很大程度的提高,且缩短了降解时间,增加了土壤有机质。     

A simple and convenient empirical survey method with a soil electrical conductivity meter for incineration residue-derived soil contamination

To facilitate field surveys for identifying areas of incineration residue-derived soil contamination, a simple and convenient method with a soil electrical conductivity meter was examined. First, the leaching test specified by Notification No. 13 of the Ministry of the Environment, 1973, was conducted on 506 samples of 11 types of wastes and compost, and the relationship between the concentrations of toxic elements [total Hg (T-Hg), Cd, Pb, Cr⁶⁺, and As] and values of electrical conductivity (EC) was examined. The results showed that bottom ash and fly ash were wastes with high EC values and that these wastes indicated higher levels of toxic elements. Second, an estimation method for the soil EC value of contaminated soil (ECc) was proposed based on the EC values of noncontaminated soil, and its usefulness was examined. The results of field surveys conducted at sites whose soils were suspected of contamination by dioxins and other pollutants derived from incineration residues showed that the contaminated spots and areas were identified by using ECc values. Moreover, comparison of the elemental contents of soils in terms of Cr, Ni, Zn, Na, K, Ca, Fe, Mn, and others, in addition to the above-mentioned toxic elements (excluding Cr⁶⁺), with those of the potential sources of pollution was verified to be effective for identifying the source of soil contamination.     

Methane oxidation at a surface-sealed boreal landfill

Methane oxidation was studied at a closed boreal landfill (area 3.9 ha, amount of deposited waste 200,000 tonnes) equipped with a passive gas collection and distribution system and a methane oxidative top soil cover integrated in a European Union landfill directive-compliant, multilayer final cover. Gas wells and distribution pipes with valves were installed to direct landfill gas through the water impermeable layer into the top soil cover. Mean methane emissions at the 25 measuring points at four measurement times (October 2005–June 2006) were 0.86–6.2 m³ ha^?1 h^?1. Conservative estimates indicated that at least 25% of the methane flux entering the soil cover at the measuring points was oxidized in October and February, and at least 46% in June. At each measurement time, 1–3 points showed significantly higher methane fluxes into the soil cover (20–135 m³ ha^?1 h^?1) and methane emissions (6–135 m³ ha^?1 h^?1) compared to the other points (<20 m³ ha^?1 h^?1 and <10 m³ ha^?1 h^?1, respectively). These points of methane overload had a high impact on the mean methane oxidation at the measuring points, resulting in zero mean oxidation at one measurement time (November). However, it was found that by adjusting the valves in the gas distribution pipes the occurrence of methane overload can be to some extent moderated which may increase methane oxidation. Overall, the investigated landfill gas treatment concept may be a feasible option for reducing methane emissions at landfills where a water impermeable cover system is used.     

百菌清污染土壤生物修复研究进展

针对百菌清具有在土壤中药效稳定、不易分解、代谢周期长、长期大量施加导致土壤严重污染等特点和问题,简要介绍了百菌清的毒性作用机制。总结了降解土壤中百菌清的物理法、化学法和生物法的原理及优缺点。重点阐述了生物修复百菌清污染土壤的主要降解菌株及其效果、降解途径以及降解产物及其毒性,分析了土壤性质、微生物种类、温度、土壤含水率等因素对百菌清降解效果的影响。指出今后的研究重点应为降解中间产物的毒性分析及其进一步的降解与转化问题,而复合菌制剂或多酶复合体系可实现百菌清的彻底降解和无害化。     

In Situ flushing of contaminated soils from a refinery: Organic compounds and metal removals

This article demonstrates the applicability of in situ flushing for the remediation of soil contaminated with petroleum hydrocarbons at a Mexican refinery. The initial average total petroleum hydrocarbon (TPH) concentration for the demonstration field test was 55,156 g/kg. After six weeks of in situ flushing with alternate periods of water and water/surfactant, an average concentration of 1,407 mg/kg was reached, achieving a total removal efficiency of 98 percent. At the end of the process, no hydrocarbons such as diesel; gasoline; benzene, toluene, ethyl benzene, and xylene (BTEX); or petroleum aromatic hydrocarbons (PAHs) were found. Iron washing achieved a removal efficiency of 70 percent, and for vanadium, the removal efficiency was 94.4 percent. The volume of soil treated was 41.6 m³ (38 m²), equivalent to 69.5 tons of soil. A rough calculation of the process costs estimated a total cost of $104.20/m³ ($114.00/m²). Our research indicates that there are a few studies demonstrating in situ flushing experiences under field conditions where both organic (TPH, diesel, gasoline, PAHs, BTEX) and metal (iron and vanadium) removals are reported. © 2004 Wiley Periodicals, Inc.     

Enhanced biodegradation of creosote-contaminated soil

Bioremediation, a viable option for treatment of cresote-contaminated soil, can be enhanced by the use of surfactant. A study was conducted to investigate the effect of a non-ionic surfactant, Triton X-100, on biodegradation of creosote-contaminated soil. Abiotic soil desorption experiments were performed to determine the kinetics of release of selected polynuclear aromatic hydrocarbon (PAH) compounds. Respirometric experiments were also conducted to evaluate the effect of nonionic surfactant on biodegradation. The N-Con system respirometer was used to monitor the oxygen uptake by the microorganisms. The abiotic experiments results indicated that the addition of surfactant to soil/water systems increased the desorption of PAH compounds. It was also observed that the desorption rate of PAH compounds depended on their molecular weight. The 3- and 4-ring PAH compounds showed higher and faster desorption rates than the 5- and 6-ring PAHs. The respirometric experiments indicated that an increase in soil contamination level from 112.5 to 771.8 mg/kg showed an increase in oxygen uptake. But for a soil contamination level of 1102.5 mg/kg, the oxygen uptake was similar to the contamination level of 771.8 mg/kg. This might be due to toxicity by the surfactant or the solubilized PAHs at high concentration or interference with contaminant transport into the cell or to reversible physical-chemical interferences with the activity of enzymes involved in the PAH degradation. The increase in PAH availability to the microorganisms in the aqueous phase produced an increase in oxygen consumption that is proportional to the biodegradation of organic compounds.     

Soil washing treatability tests for pesticide-contaminated soil

The 1987 Sand Creek Operable Unit 5 record of decision (ROD) identified soil washing as the selected technology to remediate soils contaminated with high levels of organochlorine pesticides, herbicides, and metals. Initial treatability tests conducted to assess the applicability of soil washing technology did not effectively evaluate the removal of the elevated contaminant concentrations that were found. To further evaluate the applicability of soil washing at this industrial site, a second more comprehensive pilot-scale treatability test was conducted. Twenty-three test runs were conducted over a two-week period in late September 1992, using a pilot-scale soil washing device called the volume reduction unit (VRU). The experimental design evaluated the effects of two wash temperatures, two pH levels, three surfactants, four surfactant concentrations, and two liquid-to-soil ratios on the contaminant removal efficiency of the soil washing process. Site soils from layers at three different depths were used in the study. Results from the pilot-scale treatability test indicated that the VRU could achieve contaminant reduction efficiencies of 97 percent for heptachlor and greater than 91 percent for dieldrin in the uppermost contaminated soils (surface to 1-ft. depth). Residual concentrations of heptachlor and dieldrin in the treated soil ranged from 50 ppm to less than 1.6 ppm, and 6.8 ppm to less than 1.6 ppm, respectively. However, the analytical method detection limit of 1.6 ppm was not low enough to provide residual concentration data at the risk-based action levels of 0.55 ppm for heptachlor and 0.15 ppm for dieldrin.     

Optimum Dose Of Lime And Fly Ash For Treatment Of Hexavalent Chromium–Contaminated Soil

The presence of hexavalent chromium, Cr(VI), in soil is an environmental concern due to its effect on human health. The concern arises from the leaching and the seepage of Cr(VI) from soil to groundwater. In this paper, a stabilization technology to prevent this problem was simulated on an artificial soil contaminated with hexavalent chromium. The process is a physico-chemical treatment in which the toxic pollutant is physically entrapped within a solid matrix formed by the pozzolanic reactions of lime and fly ash to reduce its leachability and, therefore, its toxicity. This paper presents the optimum ratio of fly ash and lime in order to stabilize artificial soils contaminated with 0.4 wt.% of Cr (VI) in a brief term process. The degree of chromium released from the soil was evaluated using a modified Toxicity Characteristic Leaching Procedure (TCLP) by US Environmental Protection Agency (EPA). Overall, experimental results showed reduced leachability of total and hexavalent chromium from soils treated with both fly ash and quicklime, and that leachability reduction was more effective with increasing amount of fly ash and quicklime. Stabilization percentages between 97.3% and 99.7% of the initial chromium content were achieved, with Cr(VI) concentration in the TCLP leachates below the US EPA limit for chromium of 5 mg/l. Adequate treatment was obtained after 1 day of curing with just 25% fly ash and 10% quicklime.     

Phytoremediation of lead-contaminated soil at a New Jersey Brownfield site

Phytoremediation is a new technology that uses specially selected metal-accumulating plants as an attractive and economical method to clean up soils contaminated with heavy metals and radionuclides. The integration of specially selected metal-accumulating crop plants (Brassica juncea (L) Czern.) with innovative soil amendments allows plants to achieve high biomass and metal accumulation rates. In a recent study conducted at a lead-contaminated site in Trenton, New Jersey, the soil was treated with phytoremediation using successive crops of B. juncea combined with soil amendments. Through phytoremediation, the average surface soil lead concentration was reduced by 13 percent. In addition, the target soil concentration of 400 mg/kg was achieved in approximately 72 percent of the treated area in one cropping season.     

Ex‐situ efficacy analysis of brine remediation products in clay loam soil

This study evaluated the effectiveness of gypsum and three proprietary products to remediate brine‐contaminated soil. The research objective was to determine if additives could increase plant cover germination in soils without costly prior soil‐washing or dilution techniques. The soil was shredded using a soil shredder equipped with a spray bar to apply the individual treatments of DeSalt Plus, SoilTech, Chlor*rid, and calcium sulfate (gypsum). Treatments were placed in 40‐mm high‐density polyethylene cells and small drainage systems were installed to allow removal of excess water. An initial 10‐point soil composite was taken from bulk untreated soils at a depth of more than 2.5 cm. Five‐point composite samples were collected from the same depth at weekly intervals and analyzed for: electrical conductivity, sodium adsorption ratio, cation exchange capacity, sodium, calcium, magnesium, potassium, chlorides, and pH. The Gapon selectivity coefficient was calculated and utilized to quantify the affinity for binding between ionic alkali salt constituent groups Na⁺, Ca ⁺⁺, and Mg ^++. Soil analysis indicated product‐related improvements in and bioavailability of salts. The nature of the products requires some prior treatment such as soil washing or dilution using clean soil to lower electroconductivity levels and allow the site to vegetate.     

重金属污染土壤生物毒性的发光菌法测定及评价

向土壤中人为投加重金属污染物,制备了重金属含量不同的一系列污染土壤,对土壤重金属浸提条件进行了探究,并应用明亮发光杆菌T3（Photobacterium phosphoreum T3）对单一Cu、Cd和Pb污染及Cu-Cd和Cu-Pb复合重金属污染土壤的生物毒性进行了测定。实验结果表明,土壤重金属的最佳浸提剂为0.1 mol/L HCl溶液,最佳浸提时间为2.0 h。在单一重金属污染条件下：Cu表现出低浓度促进生长、高浓度抑制生长的双重生物效应,而Cd和Pb则表现出浓度与生物毒性的正相关性;3种重金属污染土壤的毒性强弱顺序为Cd>Pb>Cu。在复合重金属污染条件下,由于重金属之间的相互作用,污染土壤的生物毒性增强。     

A research note on the assessment of optimum conditions for preparing soils for bioremediation feasibility testing

In this applied study, the effects of short‐term storage at 22°C, 6°C, and ?25°C on the numbers of microorganisms enumerated were examined with soils collected from a petrochemical contaminated soil containing multiple contaminants including phenol, polycyclic aromatic hydrocarbons, and petroleum hydrocarbons. Short term storage of soils at refrigerator temperature did not significantly change the number of microorganisms compared to those in the fresh soil (0 days of storage); however, at ?25°C there was a slight decrease in the phenol utilizers and total viable count (TVC). Long‐term storage caused a significant decrease in the number of phenol utilizers in the petrochemical‐contaminated soil samples. Chemical dispersing agents were used in an attempt to increase the extraction of microorganisms from naphthalene contaminated soil which were predominantly clay soils. These did not significantly change the enumeration of naphthalene utilizers or TVC. While these results are not unexpected from current research and knowledge of microbial community succession in laboratory environments, the results from the applied nature of this study confirm that it is best practice to keep soil samples designated for bacterial enumeration for the shortest possible time, and not longer than 1–2 weeks, and at refrigerated temperature (6°C) in preference to room (22°C) or deep freezer (?18°C) temperatures.     

Contaminated land clean-up using composted wastes and impacts of VOCs on land

This paper describes experiments that demonstrate the effects and potential for remediation of a former steelworks site in Wales polluted with polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs). Under field conditions, PAH-contaminated soil was composted in-vessel, with or without organic feedstocks, receiving forced aeration for 80 days followed by 4 months maturation. Treatments compared PAH removal in contaminated soil to contaminated soil mixed with three different organic waste mixes after composting and after composts were spread to land. After composting, PAH concentrations declined in all treatments, by up to 38%. Sixteen months after the composts were landspread and vegetation was established, only those containing contaminated soil with organic additions exhibited further PAH removal, by up to 29%. Composting resulted in a decline in the relative concentration of small PAHs, whereas the landspreading-vegetation phase saw a decline in the relative concentration of medium PAHs in two of the three composts exhibiting PAH removal. Under controlled glasshouse conditions, vegetated soil columns of differing depths were exposed to VOCs from beneath. VOC vapour affected both shoot and root growth and soil microbial activity; effects varied with distance from the VOC source. This work demonstrated that on-site remediation of aged PAH-contaminated land can be successfully initiated by in-vessel co-composting followed by land spreading and vegetation, within a practical timeframe.