Electrokinetic Remediation of Pentachlorophenol Contaminated Clay Soil

This paper presents a bench-scale experimental study performed to investigate the remediation of low permeable soil contaminated with pentachlorophenol (PCP) using the electrokinetic technique. A total of six electrokinetic tests were performed using kaolin soil spiked with 100 mg/kg of PCP. The first three tests were performed with an applied voltage gradient of 1 VDC/cm, where each test employed one of the three different flushing solutions: deionized water, electrolyte, or buffered electrolyte. The other three tests were performed using the same electrolyte solution, but each employed voltage gradient of 2 VDC/cm under constant and periodic application modes and constant voltage gradient with electrode liquid recirculation. The results of this study showed that PCP can be degraded in an electrokinetic system due to the direct electrochemical reduction process at the electrodes. The degradation of PCP ranged from 52% to about 78% depending on the conditions present. As the applied voltage gradient across the PCP-contaminated soil increased, the electroosmotic flow and PCP migration toward the cathode increased, resulting in higher PCP degradation by the direct reduction process. In the tests with electrolyte flushing solution, PCP degradation was about 58% and 65% under the applied voltage gradients of 1 and 2 VDC/cm, respectively. The mode of application of voltage potential across the PCP-contaminated soil showed noticeable effect on the system pH and electroosmotic flow and hence the PCP degradation. The highest PCP degradation (i.e., 78%) was in the test with constant 2 VDC/cm voltage gradient and recirculation application. Overall, this study demonstrated that electrokinetic technology has the potential to remediate PCP-contaminated clay soils by the direct reductive process. The electroosmatic flow as well as degree of PCP degradation during electrokinetics depend on the applied potential gradient and properties of the aqueous phase such as pH, ionic strength, and presence of carbonates.     

A Novel Laboratory Microcosm for Cocomposting Of Pentachlorophenol Contaminated Soil

A bench-scale composting system was constructed that relied on heat generation by microbial activity in the material rather than extraneous incubation. The system gave reproducible composting temperatures and eight microcosms could be operated simultaneously. These systems were used to investigate the feasibility of cocomposting pentachlorophenol (PCP) contaminated soil as a bioremediation strategy. Laboratory cocomposting of the contaminated soil successfully reduced PCP concentrations by 80%, from 68 mg/kg to 11 mg/kg in a six-week period. Losses of PCP from compost controls were minimal indicating that removal was due primarily to biotic processes. A comparison of residual PCP levels determined by dichloromethane (DCM) extraction and a methanolic potassium hydroxide (MeOH/KOH) digest prior to DCM extraction suggested that the residual PCP was bound to the compost matrix. Recovery of PCP at the end of a composting experiment using eight vessels simultaneously using the MeOH/KOH method indicated residual concentrations of 8-10 mg/kg.     

The Effect of Lignite and Comamonas testosteroni on Pentachlorophenol Biodegradation and Soil Ecotoxicity

Biodegradation of pentachlorophenol (PCP) in soil by autochthonous microflora and in soil bioaugmented by the bacterial strain Comamonas testosteroni CCM 7530 was studied. Subsequent addition of lignite, an abundant source of humic acids, has also been investigated as possible sorbent for PCP immobilization. Biodegradation of PCP and number of colony-forming units were determined in the three types of soil, haplic chernozem, haplic fluvisol, and haplic arenosol, freshly spiked with PCP and amended with tested sorbent. The enhancing effect of sorbent addition and bioaugmentation on PCP biodegradation depended mainly on the soil type and the initial PCP concentration. Microbial activity resulted in biotransformation of PCP into certain potentially toxic substances, probably lower chlorinated phenols that are more soluble than PCP, and therefore more toxic toward present biota. Therefore, it was necessary to monitor soil ecotoxicity during biodegradation. Addition of lignite resulted in a significant improvement of PCP biodegradation and led to a considerable decrease of soil toxicity especially in bioaugmented soils. The method could potentially serve as a promising technique in remediation technology for reducing high initial PCP content in contaminated soils.     

Kinetics of Indigenous Isolated Bacteria used for Ex-Situ Bioremediation of Petroleum Contaminated Soil

The bioremediation of petroleum contaminated soil was investigated using a laboratory scale aerated reactor. The Indigenous bacteria, Stenotrophomonas multophilia, were isolated from the contaminated sites near to Jordan Petroleum Refinery and used further in the bioremediation experiments. First order kinetic equation has been proven to satisfactorily describe the biodegradation of petroleum contained in soil in the presence of the isolated bacteria. The results also showed that the first order kinetic constants for the different bioreactors vary between 0.041 and 0.0071/day. The overall kinetic constant k′ was determined based on food-to-microorganisms ratio and found to be 0.02/day.     

Utilisation of Magnesium Phosphate Cements to Facilitate Biodegradation within a Stabilised/Solidified Contaminated Soil

Stabilisation/solidification (S/S) of heavy metals and a parallel biodegradation of an organic contaminant using magnesium phosphate cements (MPC) was investigated under laboratory conditions. The study was aimed at improving the robustness of S/S technology by encouraging biodegradation in order to bring about some form of contaminant attenuation over time. A silty sand soil, amended with compost was spiked with an organic contaminant, 2-chlorobenzoic acid (2CBA), and two heavy metal compounds, lead nitrate and zinc chloride. Two formulations of the MPC grouts based on different proportions of the cement constituents, with paste pH of approximately 6.5 and 10, were utilised for S/S treatment. The study involved treating the organic contaminant present in the soil with and without the heavy metals by employing the low and high pH MPC grout mixes, and using 10% and 25% compost content. Microbial activity was monitored using dehydrogenase assay, whilst the tests pertaining to the performance criteria such as contaminant concentration, unconfined compressive strength, elastic stiffness, permeability and batch leaching tests were evaluated at set periods. Contaminant recovery analysis after 140 days indicated a similar reduction in 2CBA concentration to approximately 56% in the different grout mixes. The cement constituents exhibited stimulatory and inhibitory effects on soil dehydrogenase activity. Heavy metal leachability as well as the engineering behaviour of the treated soils conformed to acceptable standards. The results of the investigations show considerable promise for the application of MPC in contaminated land remediation.     

An Assessment of the Biodegradation of Petroleum Hydrocarbons in Contaminated Soil Using Non-indigenous, Commercial Microbes

A study was conducted to determine the efficiency and effectiveness of two commercial microbial based bioremediation products compared to indigenous tropical microorganisms in a small-scale trial. The oil and grease content of the samples was monitored as an indication of the levels of petroleum hydrocarbon during the experiment. The indigenous enriched culture generally biodegraded the petroleum hydrocarbon to a greater extent than the commercial products and media controls early in the bioremediation process (0–5 days). However, as time progressed the extents of biodegradation were not significantly different between treatments until late in the bioremediation process (after 18 days). Of the two commercial products, one was more effective, reducing the level of oil and grease by 52.5% over the 3 week study. However, neither commercial product was able to meet the manufacturer’s stated level of 95% removal within three weeks. Commercial microbial-based bioremediation products may be used with some success in tropical environments, however location-specific trials may be required to ensure that the best commercial product is selected. As an alternative, the selective enrichment of indigenous microorganisms may result in similar performance at a reduced cost.     

Hot NTA Application Enhanced Metal Phytoextraction from Contaminated Soil

To increase the phytoextraction efficiency of heavy metals and to reduce the potential negative effects of mobilized metals on the surrounding environment are the two major objectives in a chemically enhanced phytoextraction process. In the present study, a biodegradable chelating agent, NTA, was added in a hot solution at 90°C to soil in which beans (Phaseolus vulgaris L., white bean) were growing. The concentrations of Cu, Zn and Cd, and the total phytoextraction of metals by the shoots of the plant from a 1 mmol kg^?1 hot NTA application exceeded those in the shoots of plants treated with 5 mmol kg^?1 normal NTA and EDTA solutions (without heating treatment). A significant correlation was found between the concentrations of metals in the shoots of beans and the relative electrolyte leakage rate of root cells, indicating that the root damage resulting from the application of a hot solution might play an important role in the process of chelate-enhanced metal uptake in plants. The application of hot NTA solutions did not significantly increase metal solubilization in soil in comparison with a normal application of solution of the same dosage. Therefore, the application of a hot NTA solution may provide a more efficient alternative in chemical-enhanced phytoextraction, although further studies of techniques of application in fields are sill required.     

Zacatecas (Mexico) Companies Extract Hg from Surface Soil Contaminated by Ancient Mining Industries

In Zacatecas, Mexico, four plants are operating to extract Ag, Au, and Hg using CaS₂O₃ solution from surface soil containing tailings from the amalgamation method used during 1550–1900. The metal ions extracted are cemented by scrap Cu wires. Hg is separated by evaporation from the cemented amalgam and Ag and Au are obtained from the residue. A part of the soil to be leached was separated and leached as in the industrial process. Only 121 ppm of Hg was freed from 168 ppm of extractable Hg. About a half of the remaining Hg in the soil evaporated during 18 months. This confirms that the Hg in the soil is metallic. Pb and As are also freed in the same process. It is estimated that 13 000–34 000 t of Hg had been discarded in the extraction of Ag.     

Biodegradation of Diesel Oil in Soil by a Microbial Consortium

Biodegradation of diesel oil was performed using adiesel oil-degrading bacterial consortium, in bothlaboratory and pilot scale experiments. The bacterialconsortium was prepared in liquid for laboratory testsand for pilot scale experiments, it was prepared intwo steps, liquid and then in soil. The concentrationof diesel in soil treated with the bacterialconsortium was reduced to <15% of the initialconcentration, within a period of five weeks in bothlaboratory (135 to 19.32 g diesel kg (soil dryweight)^-1) and pilot scale (118 to 17.5 g dieselkg (soil dry weight)^-1) experiments, incomparison with controls (without bacterialconsortium), in which initial concentration of dieselwas reduced by only 5 and 15%, respectively. Dieselbiodegradation rate with the bacterial consortium was2.13 g diesel kg (soil dry weight)^-1 d^-1, itwas slightly enhanced by the addition ofNH₄NO₃ in the presence of bacterialconsortium 2.78 g diesel kg (soil dry weight)^-1d^-1. The enhancement of the microbial activity inhydrocarbon-contaminated soil can be achieved with thecombination of stepwise soil inoculation and nutrient additions.     

Characterization of Five Chromium-Removing Bacteria Isolated from Chromium-Contaminated Soil

In the mid-20th century, similar to many lakes in the vicinity of Sudbury, Canada, Middle Lake was severely acidified due to nearby smelting operations. However, this lake is of particular interest because it was limed in 1973, and later fertilized as part of a restoration effort. Here, we use paleolimnological methods to track cladoceran assemblage responses to acidification, liming, and subsequent recovery in a ～250-year lake sediment record. Cladoceran assemblage changes, notably increases in Chydorus brevilabris, coincided with the late 1800s establishment of open-pit ore roasting in the region. As acidification progressed, the Daphnia pulex complex was replaced by the Daphnia longispina complex. At the height of acidification, and with similar timing to the liming, C. brevilabris increased abruptly in relative abundance in the sediment record, followed by a rapid decline. Invertebrate predation was investigated using Bosmina mucro length; however, no significant trends were evident. Our results suggest that complete biological recovery has not occurred. Specifically, species richness (rarefied) is ～64 % lower after the onset of acidification, and many rare species present prior to the onset of acidification have not yet returned to pre-impact levels despite dispersal events of these rare taxa being observed during contemporary zooplankton monitoring. Factors impeding the complete biological recovery of the cladocerans in Middle Lake may include biotic resistance, ongoing metal contamination, and a warming climate.     

Isolation and Optimization of PAH-Degradative Bacteria from Contaminated Soil for PAHs Bioremediation

The aim of the present study was to determine the amount ofcoal fly ash required to stabilize sewage sludge, without causing an adverse effect on the growth of Zea mays L. seedlings (corn) in a loamy soil receiving the ash-sludge mixtures amendment. Sludge was stabilized by mixing with fly ash at an amendment rate of 0, 5, 10, 35 and 50% (w/w) beforeundergoing a short fermentation period to produce a range of ash-sludge fertilizer product. Each mixture was then mixed with a loamy soil at either 1:1 or 1:5 ash-sludge mixture:soil(v/v). Soil pH, electrical conductivity (EC), and solubleCa, Mg and B contents increased while soluble NH₄-N,PO₄-P, K, Cd, and Ni contents decreased with anincrease in ash amendment rate. Dry weight yields of potsreceiving 1:5 ash-sludge:soil mixture (v/v) weresignificantly higher than their counterparts with asoil-mixing ratio of 1:1 (v/v). The highest yields were obtainedat 5 and 10% ash-sludge mixture amended soil at 1:5 soilmixing ratio. Nevertheless, the yield at 35% ash-sludgeamended loamy soil at 1:1 v/v was still higher than that ofthe control soil with fertilizer treatment. The nutrientcontent of corn seedlings was higher at 35% and 10% ash-sludge mixture amended soil at 1:1 v/v, and 5% and 10% at1:5 v/v than other treatments. Zinc concentrations of cornseedlings increased while B decreased with the decreasingamounts of fly ash added. Hence, the present experimentdemonstrates the beneficial effects of the ash-sludgemixture on soil nutrient status and plant root growthenvironment. An ash amendment rate of up to 35% in theash-sludge mixture would not have any adverse effects onplant production even at a high soil-mixing volume of 1:1(v/v), but an addition of 5% to 10% ash-sludge mixture at1:5 (v/v) produced the optimum condition for corn seedlingsgrowth. The results support the use of coal fly ash as astabilizing agent for sewage sludge and the product couldbe used for land application.     

Assessment of Metal Availability in a Contaminated Soil by Sequential Extraction

A contaminated soil from Pieve Vergonte (Piedmont, Italy) has been investigated in order to point out the availability and extractability of a series of metal ions and consequently their potential release into other environmental compartments. A sequential extraction procedure has been adopted in order to subdivide total concentrations into five operational fractions with different potential toxicity. A chemometric analysis has been used for the characterization of similarities or differences of behaviour. High concentrations of the main pollutants, namely Cu, Pb and Zn, were extracted into the exchangeable, carbonate-bound/specifically adsorbed and Fe-Mn oxide bound fractions, showing the risk of release of these metals into the environment. A remobilization of Cr, Mn and Ni could also take place, but to a lesser extent. The other investigated metals (Al, Fe, La, Sc, V, Ti and Y) were mainly bound to the residual and, in some samples, to the Fe-Mn oxide bound fractions. The high availability of several potentially toxic metals shows that the soil needs remediation.     

Fungal Generation of Organic Acids for Removal of Lead from Contaminated Soil

The use of solid-state fermentation (SFF) of low cost substrates by fungal species to generate organic acid solutions for washing of lead from a contaminated soil was evaluated in this study. SFF filtrates were generated by fermentation of four substrates (corn cobs, apple pomace, rice and hay) with three fungal species (Aspergillus niger NRRL 2001 (A. niger 1), Aspergillus niger ATCC 64065 (A. niger 2), Aspergillus foetidus NRRL 337) at three fermentation times. The concentration and speciation of organic acids of the filtrates was found to be a function of the substrate type, the fungal species and the fermentation time. Fermentation of rice resulted in the highest concentrations of citric acid while fermentation of corn cobs, apple pomace and hay tended to generate oxalic acid with an increasing fraction of this acid as the fermentation progressed. Batch extraction tests that employed the SSF filtrates revealed that soluble lead concentrations as high as 35 mg/l could be achieved. Filtrates containing elevated concentrations of citric acid resulted in the greatest lead extraction while oxalic acid inhibited solubilization. Due to the buffering of pH that was provided by the soil in the batch tests this factor did not appear to influence lead extraction. Lead extraction was observed over an extended period of time in a column test. Lead extraction was strongly influenced by the pH of the soil column and less strongly influenced by the organic acid content of the SSF filtrate. The speciation of organic acids was substantially modified from primarily citric acid in the SSF filtrate to gluconic acid in the soil column discharge.     

Phytoextraction and Accumulation of Lead from Contaminated Soil by Vetiver Grass: Laboratory and Simulated Field Study

A soil-culture study was conducted to investigate the phytoextraction of lead (Pb) in two species of vetiver grass (Vetiveria zizanioides and V. nemoralis) irrigated with an increasing level of Pb(NO₃)₂ (5, 7, 9 and 11 g L^-1) for 12 weeks. In a laboratory study, the removalof lead from soil was correlated with lead accumulation by roots and shoots of both species of vetiver grass. High concentration of lead (9—11 g L^-1) resulted in decrease of growth, total chlorophyllcontent and biomass of V. zizanioides, while V. nemoralis died after one week of application. Toxicity symptoms (e.g., burning leaf margins, shoot die back) occurred in vetiver grass at a high concentration of lead. Based on the data V. zizanioides tolerated and accumulated the greatest amount of lead most effectively. A simulated field experiment was conducted to examine the efficiency of vetiver grass in removing lead from contaminated soil. The vetiver grasses, V. zizanioides and V. nemoralis, were grown in soil contaminated with Pb(NO₃)₂ (5, 7, 9, and 11 g L^-1) for 3 months. The removal of lead from soil was correlated with lead accumulation by roots and shoots of both grass species. The grass roots took up more lead than the shoots. V. zizanioides could uptake more lead from soil than V. nemoralis. The effects of lead on the biomass of V. zizanioides and V. nemoralisshowed that in both species, the biomass was decreased when the lead concentration was increased. In comparison, V. zizanioidesshowed greater biomass than V. nemoralis.     

Immobilization of Heavy Metals by Co-pyrolysis of Contaminated Soil with Woody Biomass

We investigated the potential application of pyrolysis treatment to a mixture of woody biomass and a metal-contaminated soil as an alternative eco-friendly option to stabilize metals in soils. Our specific objective was to test the optimum combination of high heating temperature (HHT) and heating time to effectively encapsulate metals in a contaminated soil into a biochar. For this purpose, we used a laboratory bench batch reactor to react a mixture of multi-element metal contaminated soil with 0% (control) 5%, 10%, and 15% (w/w) sawdust. Each mixture was reacted at 200°C and 400°C HHT for 1 and 2 h heating times. Physicochemical and morphological characterization along with standard EPA Synthetic Precipitation Leaching Procedure (SPLP) test were conducted to assess the effectiveness of the heat treatment to immobilize the metals in the contaminated soil. Compared to controls, we recorded up to 93% reduction in Cd and Zn leachability after 1 h heat treatment at 400°C, with the addition of 5–10% biomass. Pb leaching was reduced by 43% by the same treatment but without the addition of biomass. At lower pyrolysis temperature (200°C), however, there was a substantial increase in both As and Zn leaching compared to the untreated controls. Our study suggests that several factors such as the type of metal, heating temperature, heating period, and the addition of biomass influence the efficiency of pyrolysis to immobilize metals in the contaminated soil.     

Phosphorus Runoff from Coastal Plain Forest Soil in Louisiana

Although not a common practice, poultry litter (PL) may be used for forest fertilization. Despite usually low soil phosphorus (P) and runoff under forest, repeated or high rates of PL application may cause appreciable P loss. Phosphorus in natural runoff under loblolly pine (Pinus taeda L.) fertilized with PL, downslope P enrichment of surface soil, and P runoff during simulated rainfall (a) 5 years post-application and (b) where straw was harvested were measured. Relationships of runoff P (dissolved reactive, dissolved, and total) concentration and load to soil P (Bray 2 and water-extractable in two depths) and hydraulic conductivity were examined. Post-application loss of P was lower than reported for pasture. There was little downslope P movement. Runoff P was related to the corresponding form of soil P (R² = 0.28–0.48) but likely affected by P leached from the O horizon. Loads could be estimated from regressions.     

巨大/胶冻样类芽孢杆菌对印度芥菜修复Cd污染土壤的影响

采用盆栽试验方法,研究了接种巨大芽孢杆菌和胶冻样类芽孢杆菌的混合发酵液对印度芥菜修复Cd污染土壤的影响。结果表明,接种混合菌发酵液可显著增加印度芥菜的生物量,接种20d、接种量为50ml时,总生物量较对照组增加了50.44%;在接种30d时,50ml混合菌发酵液处理的印度芥菜地上部P、K的含量显著高于对照组,分别增加了48.84%和74.90%,同时接种50ml混合菌发酵液可显著提高根际和非根际土壤中有效态Cd含量,使其较对照分别增加了39.29%和32.52%。接种混合菌发酵液可促进印度芥菜对土壤Cd的吸收,接种40d接种量为50ml时Cd吸收总量较对照组显著增加了60.36%。综上所述,接种混合菌发酵液50ml时,可促进印度芥菜的生长,增加土壤有效态Cd含量,从而提高了印度芥菜对Cd污染土壤的修复效率。     

三种无机萃取剂去除土壤中PbCd的条件研究

通过对重金属污染土壤的萃取实验,比较了HCl、Na2S2O3、CaCl2 3种常用无机萃取剂对重金属Ph和cd的萃取效果,并通过改变萃取条件（萃取剂浓度、时间、固液比、萃取次数和温度）,以期找到各种萃取剂达到最大萃取效率时所需的萃取条件。结果表明,萃取剂浓度对于萃取效率的影响最大,随着浓度的提高,3种萃取剂对Ph、Cd的去除作用增强;固液比和萃取次数对Ph、Cd的去除率也有较大的影响;时间对两金属的去除率也有一定的影响,但在本实验条件下,达到萃取平衡所需时间很短;温度对萃取效率的影响很小。本实验中,HCl去除Pb、Cd的能力远远大于其他两种萃取剂。对Cd进行萃取时,需增加萃取次数才能达到较好的萃取效果。     

Production and Characterization of Siderophores and its Application in Arsenic Removal from Contaminated Soil

Siderophores are small molecular weight extracellular organic compounds secreted by microorganisms under iron-starved conditions, used by them to chelate and solubilize iron. Though they are specific ferric iron chelator, but is reported that they bind other metals also, such as divalent heavy metals and actinides because of potentially high metal-siderophore stability constants. Thus metal contaminant fate and transport in subsurface environment can be heavily influenced by siderophores. This approach can be successfully used in removing many toxic metals off the soil which poses a serious health threat. Our research focuses on the correlation between cell growth and siderophore production and chemical characterization of the siderophore type. Its also documents the development of an assay method for the screening of different metals for complexation with siderophores based on the Chrome Azurol S (CAS) assay. The present research aims at batch scale mobilization of arsenic from arsenic contaminated soils using siderophore produced by P. azotoformans and thus evaluating its efficiency as compared to Ethylene Diamine Tetra Acetic Acid (EDTA), Citric Acid (CA) for the same. FT-IR spectroscopic studies were carried out to determine the interaction between soil, arsenic and siderophore. Results have shown that the cell growth and siderophore production are inversely related. Characterization of siderophore produced by P. azotoformans has revealed that it is of mixed-type catecholate and hydroxamate. Siderophore was found to complex with heavy metals like Cadmium, Lead, Nickel, Arsenic (III, V), Aluminium, Magnesium Zinc, Copper, Cobalt, Strontium other than Iron. Five washings by siderophore, EDTA, CA removed almost 92.8%, 77.3%, 70.0% arsenic respectively as compared to only 33.8% removal by control. Washing of arsenic contaminated soil with tap water revealed that ≈ 65.8% of arsenic in contaminated soil is in freely available or weakly bound form. The IR spectra revealed that hydrogen bonding exists between siderophore, arsenic and soil. Encouraging results of arsenic removal by biomolecule-siderophore can lead to an emerging tool brimming with opportunities for environmental clean up.