Mudanças químicas e fitodisponibilidade de zinco estimada por método isotópico, em solo tratado com lodo de esgoto

Zn availability in Red Latossol (Rhodic Ferralsol) of different pH amended with different rates of sewage sludge was studied by the isotopic 65Zn L value method. Soil chemical properties were found to be altered by SS addition. Zn concentration and Zn derived from SS (ZnpfSS) in plant, and Zn phytoavailability (L value), were increased with increasing SS rates. The linear correlation coefficient of plant Zn with SS rates and with L value was significant at 1% probability. The L value proved an efficient method for predicting Zn phytoavailability in sewage sludge-amended soil with different pH under the soil conditions studied.

Ex-situ bioremediation of Brazilian soil contaminated with plasticizers process wastes

The aim of this research was to evaluate the bioremediation of a soil contaminated with wastes from a plasticizers industry, located in São Paulo, Brazil. A 100-kg soil sample containing alcohols, adipates and phthalates was treated in an aerobic slurry-phase reactor using indigenous and acclimated microorganisms from the sludge of a wastewater treatment plant of the plasticizers industry (11gVSS kg-1 dry soil), during 120 days. The soil pH and temperature were not corrected during bioremediation; soil humidity was corrected weekly to maintain 40%. The biodegradation of the pollutants followed first-order kinetics; the removal efficiencies were above 61% and, among the analyzed plasticizers, adipate was removed to below the detection limit. Biological molecular analysis during bioremediation revealed a significant change in the dominant populations initially present in the reactor.

Caracterização de resíduos industriais visando a seu aproveitamento na fabricação de aço

Esse trabalho consiste na caracterização do resíduo de mármore, lama fina de aciaria e borra de alumínio, para averiguar a viabilidade técnica da utilização de tais resíduos na dessulfuração e desfosforação de ferro-gusa líquido. A caracterização desses resíduos foi feita através de análises químicas, granulométricas, difração de raios X e microscopia eletrônica de varredura (MEV) com micro análise por Espectroscopia por Energia Dispersiva de Raios X (EDS). A lama fina de aciaria apresenta um teor de FeO de 84,90%, o resíduo de mármore apresentou um teor de 61,5% de CaO e 33,9% de MgO e a borra de alumínio apresentou 36,5% de Al metálico e 62% de Al2O3. A granulometria do resíduo de mármore apresentou um tamanho de grão médio igual 42,810 µm. Já, na borra de alumínio, o tamanho médio foi de 101,803 µm. A lama fina de aciaria LD apresentou, em torno de 54,7% de sua granulometria, entre 0,15 e 0,075mm. Esses resultados apontam para a viabilidade técnica da utilização desses materiais na dessulfuração e desfosforação do ferro-gusa.

Lodo de esgoto como fonte de nitrogênio: concentração no perfil do solo e em plantas de milho

O objetivo deste trabalho foi avaliar a concentração de nitrogênio em plantas de milho e ao longo do perfil de um Latossolo Vermelho eutroférrico submetido a doses de lodo de esgoto e fertilizante mineral. O experimento foi instalado em delineamento experimental em blocos casualizados com 4 tratamentos (0,0; 55,0; 110,0 e 167,5 Mg.ha-1 de lodo de esgoto em doses acumuladas) e 5 repetições para um período de avaliação de 1 ano. A amostragem de solo foi realizada aos 60 dias após a emergência (d.a.e.) das plantas nas profundidades 0,0-0,1, 0,1-0,2, 0,2-0,4, 0,4-0,6, 0,6-0,8 e 0,8-1,0 m. Também aos 60, 80 e 128 d.a.e. foram coletadas, respectivamente, folha diagnose, planta inteira e grão. As maiores doses de lodo de esgoto proporcionaram maiores quantidades de nitrogênio no solo. O nitrogênio do solo, após a profundidade de 0,6 m, não diferiu entre as camadas avaliadas. Quanto maior a dose de lodo de esgoto, menor a proporção de nitrogênio em profundidade.

Produção de milho adubado residualmente com composto de lodo de esgoto e fosfato de Gafsa

Objetivou-se, com este trabalho, avaliar o efeito residual da adubação com composto de lodo de esgoto e fosfato natural de Gafsa sobre os teores de nutrientes no solo, na planta e na produtividade do milho. O trabalho foi realizado em Cambissolo Háplico. Os tratamentos, em esquema fatorial 2 x 4, corresponderam a 2 doses de fosfato de Gafsa (0 e 90 kg ha-1 de P2O5) e 4 doses de composto de lodo de esgoto (0; 25; 50 e 75 t ha-1, em base seca). O delineamento experimental utilizado foi em blocos casualizados, com 3 repetições. Em geral, a produtividade e os teores de nutrientes no solo e na planta no segundo cultivo sucessivo de milho não foram influenciados pela adubação com fosfato natural reativo. Entretanto, a produtividade de milho e os teores de nutrientes no solo e nas folhas de milho aumentaram com a dose de composto de lodo de esgoto ao solo, sendo a dose de 75 Mg ha-1, a de maior efeito residual. A produtividade do milho é menor no segundo cultivo sucessivo em razão do empobrecimento do solo em fósforo e potássio, recomendando-se novas adubações com lodo de esgoto, a cada cultivo realizado.

Fertilidade do solo, estado nutricional e produtividade de girassol, em função da aplicação de lodo de esgoto

O lodo de esgoto é um resíduo urbano-industrial que tem causado preocupação, quanto ao uso agrícola. Sua utilização pode ser viável, após a devida suplementação potássica, em substituição a fertilizantes minerais, especialmente em culturas como a do girassol. O presente trabalho objetivou avaliar a produtividade e nutrição mineral do girassol cv. CATISSOL 01, além da fertilidade de um Latossolo Vermelho eutroférrico adubado com lodo de esgoto, em comparação à adubação mineral, por dois anos consecutivos. O experimento utilizou delineamento em blocos casualizados, com 4 tratamentos (fertilização mineral, 5 t ha-1 ano-1, 10 t ha-1 ano-1 e 20 t ha-1 ano-1 de lodo de esgoto) e 5 repetições. Foram analisadas a produtividade de grãos de girassol, a concentração de macro e micronutrientes na folha diagnóstico e a fertilidade do solo. A produtividade de sementes do girassol adubado com o resíduo, em todas as doses, foi equivalente à adubação mineral, e os teores foliares situaram-se na faixa adequada, tanto para macro quanto para micronutrientes. O uso de lodo de esgoto, com suplementação potássica, mostrou-se eficiente na substituição total ou parcial da adubação mineral, sem prejudicar a produtividade da cultura do girassol.

Endotoxin exposure during sensitization to Blomia tropicalis allergens shifts TH2 immunity towards a TH17-mediated airway neutrophilic inflammation: role of TLR4 and TLR2

Experimental evidence and epidemiological studies indicate that exposure to endotoxin lipopolysaccharide (eLPS) or other TLR agonists prevent asthma. We have previously shown in the OVA-model of asthma that eLPS administration during alum-based allergen sensitization blocked the development of lung TH2 immune responses via MyD88 pathway and IL-12/IFN-γ axis. In the present work we determined the effect of eLPS exposure during sensitization to a natural airborne allergen extract derived from the house dust mite Blomia tropicalis (Bt). Mice were subcutaneously sensitized with Bt allergens co-adsorbed onto alum with or without eLPS and challenged twice intranasally with Bt. Cellular and molecular parameters of allergic lung inflammation were evaluated 24 h after the last Bt challenge. Exposure to eLPS but not to ultrapure LPS (upLPS) preparation during sensitization to Bt allergens decreased the influx of eosinophils and increased the influx of neutrophils to the airways. Inhibition of airway eosinophilia was not observed in IFN-γdeficient mice while airway neutrophilia was not observed in IL-17RA-deficient mice as well in mice lacking MyD88, CD14, TLR4 and, surprisingly, TLR2 molecules. Notably, exposure to a synthetic TLR2 agonist (PamCSK4) also induced airway neutrophilia that was dependent on TLR2 and TLR4 molecules. In the OVA model, exposure to eLPS or PamCSK4 suppressed OVA-induced airway inflammation. Our results suggest that B. tropicalis allergens engage TLR4 that potentiates TLR2 signaling. This dual TLR activation during sensitization results in airway neutrophilic inflammation associated with increased frequency of lung TH17 cells. Our work highlight the complex interplay between bacterial products, house dust mite allergens and TLR signaling in the induction of different phenotypes of airway inflammation.

Avaliação comparativa entre custos dos processos MBBR/IFAS e lodo ativado para o tratamento de esgoto sanitário

O processo MBBR/IFAS, Moving Bed Biofilm Reactor/Integrated Fixed Film Activated Sludge, é uma tecnologia recente para o tratamento de esgoto que incorpora tanto biomassa em suspensão como aderida. Seus parâmetros de controle são os mesmos aplicados ao processo de lodo ativado, observadas algumas especificidades. Como objetivo principal deste trabalho, apresenta-se uma análise comparativa entre os custos de implantação de uma unidade IFAS e de lodo ativado operando sob alta taxa, na faixa convencional e com aeração prolongada, para populações de 50.000 e 500.000 habitantes. Os resultados mostraram que, sob as hipóteses assumidas para a implantação dos reatores, o custo do processo de lodo ativado foi de 36% até 100% do custo do processo IFAS, dependendo da carga orgânica aplicada, do preço do terreno ou do custo do meio suporte.

Phytostabilisation : use of wetland plants to treat mine tailings

Mine tailings can be rich in sulphide minerals and may form acid mine drainage (AMD) through reaction with atmospheric oxygen and water. AMD contains elevated levels of metals and arsenic (As) that could be harmful to animals and plants. An oxygen-consuming layer of organic material and plants on top of water-covered tailings would probably reduce oxygen penetration into the tailings and thus reduce the formation of AMD. However, wetland plants have the ability to release oxygen through the roots and could thereby increase the solubility of metals and As. These elements are released into the drainage water, taken up and accumulated in the plant roots, or translocated to the shoots. The aim was to examine the effects of plant establishment on water-covered mine tailings by answering following questions: A) Is plant establishment on water-covered mine tailings possible? B) What are the metal and As uptake and translocation properties of these plants? C) How do plants affect metal and As release from mine tailings, and which are the mechanisms involved? Carex rostrata Stokes, Eriophorum angustifolium Honck., E. scheuchzeri Hoppe, Phragmites australis (Cav.) Steud., Salix phylicifolia L. and S. borealis Fr. were used as test plants. Influences of plants on the release of As, Cd, Cu, Pb, Zn and in some cases Fe in the drainage water, and plant element uptake were studied in greenhouse experiments and in the field. The results obtained demonstrate that plant establishment are possible on water-covered unweathered mine tailings, and a suitable amendment was found to be sewage sludge. On acidic, weathered tailings, a pH increasing substance such as ashes should be added to improve plant establishment. The metal and As concentrations of the plant tissue were found to be generally higher in roots than in shoots. The uptake was dependent on the metal and As concentrations of the tailings and the release of organic acids from plant roots may have influenced the uptake. The metal release from tailings into the drainage water caused by E. angustifolium was found to depend greatly on the age and chemical properties of the tailings. However, no effects of E. angustifolium on As release was found. Water from old sulphide-, metal- and As-rich tailings with low buffering capacity were positively affected by E. angustifolium by causing higher pH and lower metal concentrations. In tailings with relatively low sulphide, metal and As contents combined with a low buffering capacity, plants had the opposite impact, i.e. a reduction in pH and elevated metal levels of the drainage water. The total release of metal and As from the tailings, i.e. drainage water together with the contents in shoots and roots, was found to be similar for C. rostrata, E. angustifolium and P. australis, except for Fe and As, where the release was highest for P. australis. The differences in metal and As release from mine tailings were mainly found to be due to the release of O2 from the roots, which changes the redox potential. Release of organic acids from the roots slightly decreased the pH, although did not have any particular influence on the release of metal and As. In conclusion, as shown here, phytostabilisation may be a successful technique for remediation of mine tailings with high element and sulphide levels, and low buffering capacity.

An assessment of the concentrations of pharmaceutical compounds in wastewater treatment plants on the island of Gran Canaria(Spain)

[EN] An assessment of the concentrations of thirteen different therapeutic pharmaceutical compounds was conducted on water samples obtained from different wastewater treatment plants (WWTPs) using solid phase extraction and high- and ultra-high-performance liquid chromatography with mass spectrometry detection (HPLC-MS/MS and UHPLC-MS/MS), was carried out. The target compounds included ketoprofen and naproxen (anti-inflammatories), bezafibrate (lipid-regulating), carbamazepine (anticonvulsant), metamizole (analgesic), atenolol (?-blocker), paraxanthine (stimulant), fluoxetine (antidepressant), and levofloxacin, norfloxacin, ciprofloxacin, enrofloxacin and sarafloxacin (fluoroquinolone antibiotics). The relative standard deviations obtained in method were below 11%, while the detection and quantification limits were in the range of 0.3 ? 97.4 ng·L-1 and 1.1 ? 324.7 ng·L-1, respectively. The water samples were collected from two different WWTPs located on the island of Gran Canaria in Spain over a period of one year. The first WWTP (denoted as WWTP1) used conventional activated sludge for the treatment of wastewater, while the other plant (WWTP2) employed a membrane bioreactor system for wastewater treatment. Most of the pharmaceutical compounds detected in this study during the sampling periods were found to have concentrations ranging between 0.02 and 34.81 ?g·L-1.

Messa a punto di processi biotecnologici per la produzione di biocombustibili da matrici organiche di rifiuto

The bioproduction of materials and energy from renewable sources (industrial biotechnology) is getting more and more interest in order to improve environmental sustainability of chemical industrial processes and to decrease their dependence from oil. Anaerobic digestion of organic waste matrices (agricultural and industrial wastes, organic fraction of municipal wastes, sewage sludges etc.) may play an important role in the implementation of industrial biotechnology being a well developed strategy in the valorization of complex matrices, as it can mineralize them while producing bioenergy in the form of a biogas rich in methane. In this research the potential of anaerobic digestion in the treatment of polluted sewage sludge was studied by developing three set of anaerobic microcosms with sludges differently contaminated by xenobiotic compounds. The effect of different incubating temperatures and of exogenous carbon and vitamine sources was investigated along with the role of the occurring microbial populations in the pollutant degradation activity. So, while confirming the potential of anaerobic digestion for the biomethanization of sewage sludges, this work proved the effectiveness of this technology in the removal of pollutants too. Moreover, since the degradation of lignocellulose appears to be a limiting step in the anaerobic treatment of a wide range of biomass, the possibility of optimizing anaerobic digestion of lignocellulosic substrates was also studied. To this aim a research was carried out at the BOKUUniversity of Natural Resources and Applied Life Sciences, Department for Agrobiotechnology, IFA - Tulln, where mixed cellulolytic cultures were isolated from biogas plants while assessing the metabolic pathway leading to cellulose degradation and verifying their capability to grow on lignocellulose too, proving that on the long term such bacterial cultures could be used as inoculum in order to improve the hydrolysis of lignocellulose in anaerobic digestion plants.

Processo biotecnologico a cellule immobilizzate per la produzione di acidi grassi volatili da acque di vegetazione

Le acque di vegetazione (AV) costituiscono un serio problema di carattere ambientale, sia a causa della loro elevata produzione sia per l’ elevato contenuto di COD che oscilla fra 50 e 150 g/l. Le AV sono considerate un refluo a tasso inquinante fra i più elevati nell’ambito dell’industria agroalimentare e la loro tossicità è determinata in massima parte dalla componente fenolica. Il presente lavoro si propone di studiare e ottimizzare un processo non solo di smaltimento di tale refluo ma anche di una sua valorizzazione, utlizzandolo come materia prima per la produzione di acidi grassi e quindi di PHA, polimeri biodegradabili utilizzabili in varie applicazioni. A tale scopo sono stati utilizzati due bioreattori anaerobici a biomassa adesa, di identica configurazione, con cui si sono condotti due esperimenti in continuo a diverse temperature e carichi organici al fine di studiare l’influenza di tali parametri sul processo. Il primo esperimento è stato condotto a 35°C e carico organico pari a 12,39 g/Ld, il secondo a 25°C e carico organico pari a 8,40 g/Ld. Si è scelto di allestire e mettere in opera un processo a cellule immobilizzate in quanto questa tecnologia si è rivelata vantaggiosa nel trattamento continuo di reflui ad alto contenuto di COD e carichi variabili. Inoltre si è scelto di lavorare in continuo poiché tale condizione, per debiti tempi di ritenzione idraulica, consente di minimizzare la metanogenesi, mediata da microrganismi con basse velocità specifiche di crescita. Per costituire il letto fisso dei due reattori si sono utilizzati due diversi tipi di supporto, in modo da poter studiare anche l’influenza di tale parametro, in particolare si è fatto uso di carbone attivo granulare (GAC) e filtri ceramici Vukopor S10 (VS). Confrontando i risultati si è visto che la massima quantità di VFA prodotta nell’ambito del presente studio si ha nel VS mantenuto a 25°C: in tale condizione si arriva infatti ad un valore di VFA prodotti pari a 524,668 mgCOD/L. Inoltre l’effluente in uscita risulta più concentrato in termini di VFA rispetto a quello in entrata: nell’alimentazione la percentuale di materiale organico presente sottoforma di acidi grassi volatili era del 54 % e tale percentuale, in uscita dai reattori, ha raggiunto il 59 %. Il VS25 rappresenta anche la condizione in cui il COD degradato si è trasformato in percentuale minore a metano (2,35 %) e questo a prova del fatto che l’acidogenesi ha prevalso sulla metanogenesi. Anche nella condizione più favorevole alla produzione di VFA però, si è riusciti ad ottenere una loro concentrazione in uscita (3,43 g/L) inferiore rispetto a quella di tentativo (8,5 g/L di VFA) per il processo di produzione di PHA, sviluppato da un gruppo di ricerca dell’università “La Sapienza” di Roma, relativa ad un medium sintetico. Si può constatare che la modesta produzione di VFA non è dovuta all’eccessiva degradazione del COD, essendo questa nel VS25 appena pari al 6,23%, ma piuttosto è dovuta a una scarsa concentrazione di VFA in uscita. Questo è di buon auspicio nell’ottica di ottimizzare il processo migliorandone le prestazioni, poiché è possibile aumentare tale concentrazione aumentando la conversione di COD in VFA che nel VS25 è pari a solo 5,87%. Per aumentare tale valore si può agire su vari parametri, quali la temperatura e il carico organico. Si è visto che il processo di acidogenesi è favorito, per il VS, per basse temperature e alti carichi organici. Per quanto riguarda il reattore impaccato con carbone attivo la produzione di VFA è molto ridotta per tutti i valori di temperatura e carichi organici utilizzati. Si può quindi pensare a un’applicazione diversa di tale tipo di reattore, ad esempio per la produzione di metano e quindi di energia.

Prove di ozonolisi sui fanghi biologici prodotti da impianti di depurazione delle acque reflue urbane

La tecnica di ozonolisi viene applicata ai fanghi biologici derivanti da impianti di depurazione acque reflue urbane, e consiste nell'ottenere, grazie all'ozono, una minor massa fangosa da smaltire e una miglior trattabilità del fango residue. In questo elaborato si prendono in esame le sperimentazioni effettuate a Marina di Ravenna e si estraggono le prime conclusioni gestionali, economiche e ambientali sull'applicabilità del metodo a questo tipo di fango.

Biometanazione della frazione organica di rifiuti solidi urbani da raccolta indifferenziata mediante codigestione con refluo zootecnico o addizione di solfuro di sodio

Il presente elaborato è stato finalizzato allo sviluppo di un processo di digestione anaerobica della frazione organica dei rifiuti solidi urbani (FORSU oppure, in lingua inglese OFMSW, Organic Fraction of Municipal Solid Waste) provenienti da raccolta indifferenziata e conseguente produzione di biogas da impiegarsi per il recupero energetico. Questo lavoro rientra nell’ambito di un progetto, cofinanziato dalla Regione Emilia Romagna attraverso il Programma Regionale per la Ricerca Industriale, l’Innovazione e il Trasferimento Tecnologico (PRRIITT), sviluppato dal Dipartimento di Chimica Applicata e Scienza dei Materiali (DICASM) dell’Università di Bologna in collaborazione con la Facoltà di Ingegneria dell’Università di Ferrara e con la società Recupera s.r.l. che applicherà il processo nell’impianto pilota realizzato presso il proprio sito di biostabilizzazione e compostaggio ad Ostellato (FE). L’obiettivo è stato la verifica della possibilità di impiegare la frazione organica dei rifiuti indifferenziati per la produzione di biogas, e in particolare di metano, attraverso un processo di digestione anaerobica previo trattamento chimico oppure in codigestione con altri substrati organici facilmente fermentabili. E’ stata inoltre studiata la possibilità di impiego di reattori con biomassa adesa per migliorare la produzione specifica di metano e diminuire la lag phase. Dalla sperimentazione si può concludere che è possibile giungere allo sviluppo di metano dalla purea codigerendola assieme a refluo zootecnico. Per ottenere però produzioni significative la quantità di solidi volatili apportati dal rifiuto non deve superare il 50% dei solidi volatili complessivi. Viceversa, l’addizione di solfuri alla sola purea si è dimostrata ininfluente nel tentativo di sottrarre gli agenti inibitori della metanogenesi. Inoltre, l’impiego di supporti di riempimento lavorando attraverso processi batch sequenziali permette di eliminare, nei cicli successivi al primo, la lag phase dei batteri metanogeni ed incrementare la produzione specifica di metano.

Bioremediation of PAHs - Limitations and soultions

Introduction 1.1 Occurrence of polycyclic aromatic hydrocarbons (PAH) in the environment Worldwide industrial and agricultural developments have released a large number of natural and synthetic hazardous compounds into the environment due to careless waste disposal, illegal waste dumping and accidental spills. As a result, there are numerous sites in the world that require cleanup of soils and groundwater. Polycyclic aromatic hydrocarbons (PAHs) are one of the major groups of these contaminants (Da Silva et al., 2003). PAHs constitute a diverse class of organic compounds consisting of two or more aromatic rings with various structural configurations (Prabhu and Phale, 2003). Being a derivative of benzene, PAHs are thermodynamically stable. In addition, these chemicals tend to adhere to particle surfaces, such as soils, because of their low water solubility and strong hydrophobicity, and this results in greater persistence under natural conditions. This persistence coupled with their potential carcinogenicity makes PAHs problematic environmental contaminants (Cerniglia, 1992; Sutherland, 1992). PAHs are widely found in high concentrations at many industrial sites, particularly those associated with petroleum, gas production and wood preserving industries (Wilson and Jones, 1993). 1.2 Remediation technologies Conventional techniques used for the remediation of soil polluted with organic contaminants include excavation of the contaminated soil and disposal to a landfill or capping - containment - of the contaminated areas of a site. These methods have some drawbacks. The first method simply moves the contamination elsewhere and may create significant risks in the excavation, handling and transport of hazardous material. Additionally, it is very difficult and increasingly expensive to find new landfill sites for the final disposal of the material. The cap and containment method is only an interim solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability. A better approach than these traditional methods is to completely destroy the pollutants, if possible, or transform them into harmless substances. Some technologies that have been used are high-temperature incineration and various types of chemical decomposition (for example, base-catalyzed dechlorination, UV oxidation). However, these methods have significant disadvantages, principally their technological complexity, high cost , and the lack of public acceptance. Bioremediation, on the contrast, is a promising option for the complete removal and destruction of contaminants. 1.3 Bioremediation of PAH contaminated soil & groundwater Bioremediation is the use of living organisms, primarily microorganisms, to degrade or detoxify hazardous wastes into harmless substances such as carbon dioxide, water and cell biomass Most PAHs are biodegradable unter natural conditions (Da Silva et al., 2003; Meysami and Baheri, 2003) and bioremediation for cleanup of PAH wastes has been extensively studied at both laboratory and commercial levels- It has been implemented at a number of contaminated sites, including the cleanup of the Exxon Valdez oil spill in Prince William Sound, Alaska in 1989, the Mega Borg spill off the Texas coast in 1990 and the Burgan Oil Field, Kuwait in 1994 (Purwaningsih, 2002). Different strategies for PAH bioremediation, such as in situ , ex situ or on site bioremediation were developed in recent years. In situ bioremediation is a technique that is applied to soil and groundwater at the site without removing the contaminated soil or groundwater, based on the provision of optimum conditions for microbiological contaminant breakdown.. Ex situ bioremediation of PAHs, on the other hand, is a technique applied to soil and groundwater which has been removed from the site via excavation (soil) or pumping (water). Hazardous contaminants are converted in controlled bioreactors into harmless compounds in an efficient manner. 1.4 Bioavailability of PAH in the subsurface Frequently, PAH contamination in the environment is occurs as contaminants that are sorbed onto soilparticles rather than in phase (NAPL, non aqueous phase liquids). It is known that the biodegradation rate of most PAHs sorbed onto soil is far lower than rates measured in solution cultures of microorganisms with pure solid pollutants (Alexander and Scow, 1989; Hamaker, 1972). It is generally believed that only that fraction of PAHs dissolved in the solution can be metabolized by microorganisms in soil. The amount of contaminant that can be readily taken up and degraded by microorganisms is defined as bioavailability (Bosma et al., 1997; Maier, 2000). Two phenomena have been suggested to cause the low bioavailability of PAHs in soil (Danielsson, 2000). The first one is strong adsorption of the contaminants to the soil constituents which then leads to very slow release rates of contaminants to the aqueous phase. Sorption is often well correlated with soil organic matter content (Means, 1980) and significantly reduces biodegradation (Manilal and Alexander, 1991). The second phenomenon is slow mass transfer of pollutants, such as pore diffusion in the soil aggregates or diffusion in the organic matter in the soil. The complex set of these physical, chemical and biological processes is schematically illustrated in Figure 1. As shown in Figure 1, biodegradation processes are taking place in the soil solution while diffusion processes occur in the narrow pores in and between soil aggregates (Danielsson, 2000). Seemingly contradictory studies can be found in the literature that indicate the rate and final extent of metabolism may be either lower or higher for sorbed PAHs by soil than those for pure PAHs (Van Loosdrecht et al., 1990). These contrasting results demonstrate that the bioavailability of organic contaminants sorbed onto soil is far from being well understood. Besides bioavailability, there are several other factors influencing the rate and extent of biodegradation of PAHs in soil including microbial population characteristics, physical and chemical properties of PAHs and environmental factors (temperature, moisture, pH, degree of contamination). Figure 1: Schematic diagram showing possible rate-limiting processes during bioremediation of hydrophobic organic contaminants in a contaminated soil-water system (not to scale) (Danielsson, 2000). 1.5 Increasing the bioavailability of PAH in soil Attempts to improve the biodegradation of PAHs in soil by increasing their bioavailability include the use of surfactants , solvents or solubility enhancers.. However, introduction of synthetic surfactant may result in the addition of one more pollutant. (Wang and Brusseau, 1993).A study conducted by Mulder et al. showed that the introduction of hydropropyl-ß-cyclodextrin (HPCD), a well-known PAH solubility enhancer, significantly increased the solubilization of PAHs although it did not improve the biodegradation rate of PAHs (Mulder et al., 1998), indicating that further research is required in order to develop a feasible and efficient remediation method. Enhancing the extent of PAHs mass transfer from the soil phase to the liquid might prove an efficient and environmentally low-risk alternative way of addressing the problem of slow PAH biodegradation in soil.