Transformation characteristics of refractory pollutants in plugboard wastewater by an optimal electrocoagulation and electro-Fenton process

The treatment of the plugboard wastewater was performed by an optimal electrocoagulation and electro-Fenton. The organic components with suspended fractions accounting for 30% COD were preferably removed via electrocoagulation at initial 5 min. In contrast, the removal efficiency was increased to 76% with the addition of H(2)O(2). The electrogenerated Fe(2+) reacts with H(2)O(2) and leads to the generation of (·)OH, which is responsible for the higher COD removal. However, overdosage H(2)O(2) will consume (·)OH generated in the electro-Fenton process and lead to the low COD removal. The COD removal efficiency decreased with the increased pH. The concentration of Fe(2+) ions was dependent on the solution pH, H(2)O(2) dosage and current density. The changes of organic characteristics in coagulation and oxidation process were differenced and evaluated using gel permeation chromatography, fluorescence excitation-emission scans and Fourier transform infrared spectroscopy. The fraction of the wastewater with aromatic structure and large molecular weight was decomposed into aliphatic structure and small molecular weight fraction in the electro-Fenton process.     

Coagulation and precipitation as post-treatment of anaerobically treated primary municipal wastewater.

The main objective of this study was to investigate the feasibility of coagulation as a post-treatment method of anaerobically treated primary municipal wastewater. Both mesophilic and ambient (20 degrees C) temperature conditions were investigated in a laboratory-scale upflow anaerobic sludge bed (UASB) reactor. In addition, optimization of the coagulant, both in terms of type and dose, was performed. Finally, phosphorus removal by means of aluminum and iron coagulation and phosphorus and ammonia nitrogen removal by means of struvite precipitation were studied. Anaerobic treatment of primary effluent at low hydraulic retention times (less than 15 hours) resulted in mean chemical oxygen demand (COD) removals ranging from 50 to 70%, while, based on the filtered treated effluent, the mean removals increased to 65 to 80%. Alum coagulation of the UASB effluent gave suspended solids removals ranging from approximately 35 to 65%. Turbidity removal reached up to 80%. Remaining COD values after coagulation and settling were below 100 mg/L, while remaining total organic carbon (TOC) levels were below 50 mg/L. Filterable COD levels were generally below 60 mg/L, while filterable TOC levels were below 40 mg/L. All coagulants tested, including prepolymerized aluminum and iron coagulants, demonstrated similar efficiency compared with alum for the removal of suspended solids, COD, and TOC. Regarding struvite precipitation, optimal conditions for phosphorus and nitrogen removal were pH 10 and molar ratio of magnesium: ammonia-nitrogen: phosphate-phosphorus close to the stoichiometric ratio (1:1:1). During struvite precipitation, removal of suspended solids reached 40%, while turbidity removal reached values up to 80%. The removal of COD was approximately 30 to 35%; yet, when removal of organic matter was based on the treated filterable COD, the removal increased to approximately 65%. In addition, nitrogen was removed by approximately 70%, while phosphorus removal ranged between approximately 30 and 45% on the basis of the initial phosphorus concentration. Finally, size fractionation of the organic matter (COD) showed that the various treatment methods were capable of removing different fractions of the organic matter.     

Chemical and bacterial changes during laboratory conditioning of formulated and natural sediments

Within the framework of toxicity testing using formulated sediment, a conditioning treatment prior to toxic contamination has been examined. This preliminary step enables the bacterial colonisation of the sediment, the initiation of organic matter degradation, and the establishment of stable biological and physico-chemical conditions. The treatment involved in keeping the formulated sediment under water in conditions similar to that chosen for toxicity tests. The behaviour of a formulated sediment was compared with a natural sediment. The monitoring of physico-chemical and biological parameters of sediment and water column was carried out over a 30-day incubation in two laboratories. The parameters of pH and redox, dissolved organic carbon (DOC), NH4 and NO2, total organic carbon (TOC) were measured. The bacterial community was characterised by the determination of bacterial density, in total bacteria number or colony forming units (CFU), several exoenzymatic activities (P-glucosidase, xylosidase, leucine-amino-peptidase phosphatase and sulfatase activities), and three gas productions (CO2, N2O and CH4). The same experiment was carried out with a natural sediment. A 10- to 15-day conditioning allowed a physico-chemical stabilisation and corresponded to kinetic changes in hydrolysis activities. As compared to data of the natural sediment, the biological activity of the formulated sediment showed a different dynamic with lower activity levels. For both sediments, an important decrease of activities levels was observed after 15 days because of a substrate limitation. The work showed that a preliminary conditioning treatment of a formulated sediment provides the stabilisation of parameters that can affect toxicant bioavailability. Additional research is needed to determine the real influence of conditioning on the bioavailability of contaminants. The possible advisability of organic matter input, to maintain the sediment bacterial activity, has to be studied.     

Laboratory study highlights the key influences of stormwater sediment thickness and bioturbation by tubificid worms on dynamics of nutrients and pollutants in stormwater retention systems

In urban area, the accumulation of polluted stormwater sediments (SWS) in retention ponds may be a source of dissolved pollutants and nutrients for the aquatic ecosystems. Our objective was to quantify the influence of the thickness of SWS layer and the occurrence of tubificid worms on organic matter processing (O(2) uptake and fluxes of NH(4)(+), NO(3)(-), PO(4)(3-), and dissolved organic carbon between sediment and water), releases of 17 PAHs and 4 heavy metals, and microbial characteristics. Results showed that oxidation of SWS organic matter (O(2) and NO(3)(-) uptakes) and releases of nutrients were significantly increased by the quantity of accumulated SWS and the worm bioturbation. Releases of acenaphtene and naphthalene from sediments were significantly increased by the thickness of the SWS layer. In contrast, tubificid worms did not promote the mobilization of pollutants. In conclusion, biological activities and stormwater sediment characteristics need to be assessed to quantify the fate of pollutants and nutrients in stormwater retention ponds.     

Effect of physical forms of soil organic matter on phenanthrene sorption

The sorption coefficient, K(OC), of phenanthrene (PHE) has been reported to vary with different types of organic matter, leading to uncertainties in predicting the environmental behavior of PHE. Among the studies that relate organic matter properties to their sorption characteristics, physical conformation of organic matter is often neglected. In this work, organic matter samples of different physical forms were examined for their sorption characteristics. Dissolved humic acids (DHA) showed significantly higher K(OC) than the corresponding solid humic acids (SHA) from which the DHAs were made. The K(OC) of DHAs was found to be related to polarity, whereas K(OC) of SHAs increased with aliphatic carbon content. Soil particles were treated with H(2)O(2) to remove organic matter, and humic acid was coated on H(2)O(2)-treated soil particles to make organo-mineral complexes at pH 4, 7 and 10. Although the nonlinear sorption was apparent for SHAs and H(2)O(2)-treated soil particles, the organo-mineral complexes formed using these two components at pH 4, 7 and 10 exhibited relatively linear sorption at organic carbon content, f(OC)>0.5%. These results indicate that organic matter of the same composition may have different sorption properties due to different physical forms (or conformations). Nonlinear sorption for the complexes formed at pH 4 with lower f(OC) (<0.5%) was also discussed.     

Modification of chemical oxygen demand monitoring in the Yellow River, China, with a high content of sediments.

This paper presents a modification of chemical oxygen demand (COD) monitoring giving a better indication of the pollution level compared with the conventional COD method for rivers with a high content of sediments. The correlation between the sediment organic carbon and COD was investigated using sediments sampled in the middle Yellow River, China. Partitioning of the sediment organic carbon between the water and sediment phases was also investigated using batch experiments, with the sediment concentration varying from 20 to 400 g/L. As a result, the COD modification equations are proposed for both turbid water (mixture of water and sediment) and supematant water (filtrate using a 0.45-microm membrane). The modified COD in turbid water and supernatant water could be 40 and 10% less than the monitored COD values, respectively. These results may have a significant influence on the assessment of water quality class in the Yellow River.     

Do tubificid worms influence the fate of organic matter and pollutants in stormwater sediments?

In urban area, management of stormwater leads to the accumulation of polluted sediments at the water-sediment interface of various aquatic ecosystems. In many cases, these sediments are colonised by dense populations of tubificid worms. However, the influence of tubificid worms on the fate of stormwater sediments has never been tackled. The aim of this study was to measure in sediment columns the influence of tubificid worms on sediment reworking, organic matter processing (O(2) uptake and release of NH(4)(+), NO(3)(-), PO(4)(3-), and dissolved organic carbon), release of hydrocarbons and heavy metals, and microbial characteristics. Results showed that tubificid worms increased the release of NH(4)(+), PO(4)(3-), and dissolved organic carbon by 2-, 4-, and 3-fold, respectively. O(2) uptake also increased by more than 35% due to tubificid activity. The increase in the percentages of active bacteria and hydrolytic activity in the presence of worms indicated that the higher sediment respiration was caused by the stimulation of microbial communities. A reduction of the number of sulphate-reducing bacteria in the uppermost layers of the sediment was attributed to the penetration of O(2) due to worm activity. These significant effects of tubificid worms were probably linked to the dense network of burrows, which enhanced the exchange surface between the water column and the sediment. No release of heavy metals and hydrocarbons to the water phase was detected in the sediment columns. Understanding the fate and effect of organic stormwater sediments in the natural environment requires the integration of the role of bioturbation in urban pollution studies.     

Experimental in situ chemical peroxidation of atrazine in contaminated soil

Lab-scale experiments of in situ chemical oxidation (ISCO), were performed on soil contaminated with 100 mg kg(-1) of atrazine (CIET). The oxidant used was hydrogen peroxide catalysed by naturally occurring minerals or by soluble Fe(II) sulphate, added in aqueous solution. The oxidation conditions were: CIET:H2O2=1:1100, 2 PV or 3 PV reaction volume, Fe(II):H2O2=0, 1:22, 1:11. Stabilized (with KH2PO4 at a concentration of 16 g l(-1)) or non-stabilized hydrogen peroxide was used. The pH of the reagents was adjusted to pH=1 with sulphuric acid, or was not altered. Results showed that the addition of soluble Fe(II) increased the temperature of the soil slurry and the use of stabilized hydrogen peroxide resulted in a lower heat generation. The treatment reduced the COD of the soil of about 40%, pH was lowered and natural organic matter became less hydrophobic. The highest atrazine conversion (89%) was obtained in the conditions: 3 PV, Fe(II):H2O2=1:11 with stabilized hydrogen peroxide added in two steps. The stabilizer only increased H2O2 life-time significantly when soluble Fe(II) was added. Results indicate as preferential degradation pathway of atrazine in soil dechlorination instead of dealkylation.     

Effects of black carbon and montmorillonite clay on multiphasic hexachlorobenzene desorption from sediments

The desorption kinetics of hexachlorobenzene (HCB) in four freshly spiked artificial sediments were determined using a polymeric adsorbent Tenax-mediated desorption. The sediments included a standard sediment (SS) prepared as per Organisation for Economic Cooperation and Development 218 guidelines and three derived artificial sediments prepared by supplementing the SS sediment with various levels of black carbon (lamp black soot) and/or montmorillonite clay. The desorption kinetics exhibited biphasic behavior, i.e., a fast desorbing fraction followed by a slow desorbing fraction. The addition of either lamp black soot or montmorillonite clay resulted in the reduction of the fast desorbing fraction (Ffast) of HCB in three derived sediments compared with SS sediment. Both black carbon and montmorillonite clay treatment effects on the fast desorbing fraction were statistically significant for the four artificial sediments. The black carbon treatment (i.e., addition of 0.5% wt/wt lamp black soot) effect was an average reduction of Ffast by approximately 11%, whereas the montmorillonite treatment (i.e., addition of 15% wt/wt montmorillonite clay) effect was an average reduction of Ffast by approximately 17%. The presence of soot black carbon particles reduced the desorption rate of HCB in sediments since black carbon exhibits very high sorption capacity and extremely slow diffusion rate compared with those of the natural organic matter in sediment.     

PACT工艺处理PAM生产废水的实验研究

采用粉末活性炭活性污泥工艺(PACT)处理经凹凸棒土预处理后的聚丙烯酰胺(PAM)生产废水。实验考察了粉末活性炭(PAC)的投加对活性污泥处理系统的影响,并探讨了PAC投加量、曝气时间、水力停留时间等参数对降解反应的影响。结果表明:PAC的投加能提高水中溶解氧的利用率,改善污泥沉降性能,增强活性污泥系统对有机物的去除效果;在PAC投加量500 mg/L、曝气10 h的条件下,PACT工艺对PAM生产废水的处理效果良好,COD的去除率为80.8%,BOD5去除率为83.8%,丙烯酰胺(AM)去除率为84.2%。     

A2/O工艺缺氧池中反硝化聚磷菌的比例、特性研究及菌株鉴定

用释磷/聚磷装置和微生物筛选、分离方法研究A2/O工艺缺氧池污泥,确定缺氧池中反硝化聚磷菌(DPB)的比例,筛选、分离得反硝化聚磷单菌株且对单菌株聚磷特性进行研究.结果表明,缺氧池中DPB占聚磷菌(PAO)的比例约为21.5%.从缺氧池分离得到的肠杆菌科、气单胞菌属和假单胞菌属都是DPB,而不动杆菌属仅是好氧PAO,葡萄球菌属和微球菌属仅是一种专职的反硝化菌.反应过程中同时存在O2和NO3时,肠杆菌科优先利用水中的O2进行聚磷;在缺氧环境中,肠杆菌科在COD为30mg/L时的聚磷效果优于COD为180 mg/L时的聚磷效果.可见DPB的反硝化和聚磷的特性与电子受体的存在形式和COD有密切关系.因此,改良传统A2/O工艺和研发同步反硝化聚磷装置时,必须控制缺氧反硝化聚磷单元中混合液的DO和COD.     

Characteristics of electrolysis, ozonation, and their combination process on treatment of municipal wastewater.

The characteristics of municipal wastewater treatment by electrolysis, ozonation, and combination processes of electrolysis and aeration using three gaseous species (nitrogen [N2], oxygen [O2], and ozone [O3]) were discussed in this research using ruthenium oxide (RuO2)-coated titanium anodes and stainless-steel (SUS304) cathodes. Electrolysis and electrolysis with nitrogen aeration were characterized by a rapid decrease in 5-day biochemical oxygen demand (BODs) and total nitrogen and a slow decrease in chemical oxygen demand (COD). In contrast, ozonation, electrolysis with oxygen aeration, and electrolysis with ozone aeration were characterized by transformation of persistent organic matter to biodegradable matter and preservation of total nitrogen. The best energy efficiency in removing BOD5 and total nitrogen was demonstrated by electrolysis, as a result of direct anodic oxidation and indirect oxidation with free chlorine produced from the chloride ion (Cl-) at the anodes. However, electrolysis with ozone aeration was found to be superior to the other processes, in terms of its energy efficiency in removing COD and its ability to remove COD completely, as a result of hydroxyl radical (*OH) production via cathodic reduction of ozone.     

Electrochemical treatment of domestic wastewater using boron-doped diamond and nanostructured amorphous carbon electrodes

The performance of the electrochemical oxidation process for efficient treatment of domestic wastewater loaded with organic matter was studied. The process was firstly evaluated in terms of its capability of producing an oxidant agent (H₂O₂) using amorphous carbon (or carbon felt) as cathode, whereas Ti/BDD electrode was used as anode. Relatively high concentrations of H₂O₂ (0.064 mM) was produced after 90 min of electrolysis time, at 4.0 A of current intensity and using amorphous carbon at the cathode. Factorial design and central composite design methodologies were successively used to define the optimal operating conditions to reach maximum removal of chemical oxygen demand (COD) and color. Current intensity and electrolysis time were found to influence the removal of COD and color. The contribution of current intensity on the removal of COD and color was around 59.1 and 58.8 %, respectively, whereas the contribution of treatment time on the removal of COD and color was around 23.2 and 22.9 %, respectively. The electrochemical treatment applied under 3.0 A of current intensity, during 120 min of electrolysis time and using Ti/BDD as anode, was found to be the optimal operating condition in terms of cost/effectiveness. Under these optimal conditions, the average removal rates of COD and color were 78.9?±?2 and 85.5?±?2 %, whereas 70 % of total organic carbon removal was achieved.     

Advanced oxidation of a pulp mill bleaching wastewater.

The degradation, by several advanced oxidation reactions, of a pulp mill ECF bleaching effluent, was studied. The initial biodegradability of the organic matter present in the effluent, estimated as the BOD5/COD, was low (0.3). When the effluent was submitted to ozonation and to five different advanced oxidation systems (O3/UV, O3/UV/ZnO, O3/UV/TiO2, O2/UV/ZnO, O2/UV/TiO2), the biodegradability increase significantly. After five minutes of reaction, the O3/UV system appears as the most efficient in to transform the organic matter to more biodegradable forms. A similar effect was observed when the effluent was submitted to an activated sludge treatment. The COD, TOC and toxicity reduction correlated well with the biodegradability enhancement after AOPs treatments.     

Assessing in situ mineralization of recalcitrant organic compounds in vadose zone sediments using delta13C and 14C measurements

Few techniques exist to measure the biodegradation of recalcitrant organic compounds such as chlorinated hydrocarbons (CHC) in situ, yet predictions of biodegradation rates are needed for assessing monitored natural attenuation. Traditional techniques measuring O2, CO2, or chemical concentrations (in situ respiration, metabolite and soil air monitoring) may not be sufficiently sensitive to estimate biodegradation rates for these compounds. This study combined isotopic measurements (14C and delta13C of CO2 and delta13C of CHCs) in conjunction with traditional methods to assess in situ biodegradation of perchloroethylene (PCE) and its metabolites in PCE-contaminated vadose zone sediments. CHC, ethene, ethane, methane, O2, and CO2 concentrations were measured over 56 days using gas chromatography (GC). delta13C of PCE, trichloroethylene (TCE) and cis-1,2-dichloroethylene (DCE), delta13C and 14C of vadose zone CO2 and sediment organic matter, and delta13C, 14C, and deltaD of methane were measured using a GC-isotope ratio mass spectrometer or accelerator mass spectrometer. PCE metabolites accounted for 0.2% to 18% of CHC concentration suggesting limited reductive dechlorination. Metabolites TCE and DCE were significantly enriched in (13)C with respect to PCE indicating metabolite biodegradation. Average delta13C-CO2 in source area wells (-23.5 per thousand) was significantly lower compared to background wells (-18.4 per thousand) indicating CHC mineralization. Calculated CHC mineralization rates were 0.003 to 0.01 mg DCE/kg soil/day based on lower 14C values of CO2 in the contaminated wells (63% to 107% modern carbon (pMC)) relative to the control well (117 pMC). Approximately 74% of the methane was calculated to be derived from in situ CHC biodegradation based on the 14C measurement of methane (29 pMC). 14C-CO2 analyses was a sensitive measurement for quantifying in situ recalcitrant organic compound mineralization in vadose zone sediments for which limited methodological tools exist.     

Evaluation of the thermal/optical reflectance method for discrimination between char- and soot-EC

Many optical, thermal and chemical methods exist for the measurement of elemental carbon (EC) but are unable or neglect to differentiate between the different forms of EC such as char- or soot-EC. The thermal/optical reflectance (TOR) method applies different temperatures for measuring EC and organic carbon (OC) contents through programmed, progressive heating in a controlled atmosphere, making available eight separate carbon fractions - four OC, one pyrolyzed organic carbon, and three EC. These fractions were defined by temperature protocol, oxidation atmosphere, and laser-light reflectance/transmittance. Stepwise thermal evolutional oxidation of the TOR method makes it possible to distinguish char- from soot-EC. In this study, different EC reference materials, including char and soot, were used for testing it. The thermograms of EC reference materials showed that activation energy is lower for char- than soot-EC. Low-temperature EC1 (550 degrees C in a 98% He/2% O2 atmosphere) is more abundant for char samples. Diesel and n-hexane soot samples exhibit similar EC2 (700 degrees C in a 98% He/2% O2 atmosphere) peaks, while carbon black samples peaks at both EC2 and EC3 (800 degrees C in a 98% He/2% O2 atmosphere). These results supported the use of the TOR method to discriminate between char- and soot-EC.     

Anaerobic treatment of slaughterhouse wastewater: a review

This article presents a review of anaerobic treatment technologies to treat slaughterhouse wastewater including its advantages and disadvantages. Physico-chemical characteristics and biochemical methane potential (BMP) of slaughterhouse wastewater are addressed. Various anaerobic treatment technologies are presented with the related operating parameters, viz., hydraulic retention time (HRT), organic loading rate (OLR), upflow velocity (V_up), and biogas yield vis-a-vis treatment efficiency in terms of chemical oxygen demand (COD). In addition, various factors that affect the anaerobic treatment of slaughterhouse wastewater such as high oil & grease (O & G) concentration in influent, inhibitors, volatile fatty acids (VFAs), and the loading rate are also addressed. The literature review indicated that the slaughterhouse wastewater can be treated effectively by employing any anaerobic treatment technologies at OLRs up to 5 kg COD/m³.d with more than 80% COD removal efficiency without experiencing operational problems. Anaerobic hybrid reactors (AHRs) were found the most effective among various reviewed technologies because of their ability to operate at higher OLRs (8 to 20 kg COD/m³.d) and lower HRTs (8 to 12 hrs).

     

Measurement of biologically available organic material in intertidal sediments subject to inputs of sea coal or colliery wastes

A method for the measurement of biologically available organic matter in intertidal or subtidal marine sediments subject to an input of sea coal or colliery wastes is described. The method involves boiling sediment in hydrogen peroxide (H2O2) for 4 h at 160 degrees C to dissolve non-colliery waste organic matter which is then recorded as weight lost after rinsing and drying. Samples are then ashed at 495 degrees C to determine the weight of coal or colliery wastes present. Although H2O2 shows a slight reaction with colliery wastes (overall mean of 0.86% weight loss), it is appropriate to use this technique for the determination of organic matter available to sediment-dwelling biota. We show that shore organic content should not be determined merely by ashing sediment, even on shores which do not appear to contain wastes, since even visibly 'clean' shores in north-east England generally contain some coal fragments in their sediment. Our method is suitable anywhere where biologically available organic matter needs to be measured independently of waste content, e.g. in terrestrial systems close to centres of mining activity.     

Effects of untreated hospital effluents on the accumulation of toxic metals in sediments of receiving system under tropical conditions: Case of South India and Democratic Republic of Congo

Physicochemical and ecotoxicological analyses have been performed to assess the quality of sediments receiving untreated hospital effluents from Indian and Democratic Republic of Congo (DRC) hospitals. The sediments were collected monthly and characterized for grain size, organic matter, total organic carbon, total carbon, nitrogen, phosphorus, toxic metals and ecotoxicity. The results highlight the high concentration of toxic metals from the Indian hospital effluent receiving systems, especially for Cr, Cu, As, Zn and Hg. On the other hand, the metal concentrations in the sediment receiving system from DRC are low (e.g. maximum Hg and Zn concentration were 0.46 and 48.84 mg kg⁻¹ respectively). Ostracods exposed to sediment samples H2 (September month sample) and H3 (June and September month samples) were found dead after 6 d of exposure whereas the higher mortality rate for Congo sediments was 23% but was accompanied with 33 ± 7% of growth inhibition. The results of this study show the variation of sediment composition on toxic metal levels as well as toxicity related to both, the type of hospitals and the sampling period. Additionally, hospital effluent disposal practices at the study sites can lead to the pollution of water resources and may generate risks for aquatic organisms and human health.     

Slurry-phase ozonation for remediation of sediments contaminated by polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic, persistent, bioaccumulating organic compounds containing two or more fused aromatic rings. They are listed by the U.S. Environmental Protection Agency as priority pollutants because of their carcinogenicity and toxicity. Employing ozonation as a remediation technique, this work investigated the treatability of a sediment sample from a freshwater boat slip subjected to coal tar contamination over a long period. The contaminated sediment sample contained high levels of PAHs in the forms of naphthalene, phenanthrene, pyrene, and benzo[a]pyrene, among other byproducts present in the humic and solid phases of the sediment. The objectives of this work were to examine (1) the degradation of PAHs in the contaminated sediment as treated by ozonation in the slurry form, (2) the effects of ozonation upon the soil matrix and the biodegradability of the resultant PAH intermediates, and (3) the feasibility of a combined technique using O3 as a pretreatment followed by biological degradation. The sediment was made into 3% w/w soil slurries and ozonated in a 1.7-L semi-batch, well-stirred reactor equipped with pH control and a cold trap for the gaseous effluent. Samples were collected after different ozonation durations and tested for biochemical oxygen demand (BOD), chemical oxygen demand (COD), UV absorbance, and toxicity, along with quantitative and qualitative determinations of the parent and daughter intermediates using gas chromatography/flame ionization detection (GC/FID), GC/mass spectrometry (MS), and ion chromatography (IC) techniques. The GC/MS technique identified 16 compounds associated with the humic and solid phases of the sediment. Intermediates identified at different ozonation times suggested that the degradation of PAHs was initiated by an O3 attack resulting in ring cleavage, followed by the intermediates' oxidation reactions with O3 and the concomitant OH radical toward their mineralization. Results suggested that ozonation for 2 hr removed 50-100% of various PAHs in the solid and liquid phases (as well as the aqueous and gaseous media resulting from the treatment process) of the sediment sample and that organic and inorganic constituents of the sediment were also altered by ozonation. Measurements and comparisons of BOD, COD, UV absorbance, and toxicity of the samples further suggested that ozonation improved the bioavailability and biodegradability of the contaminants, despite the increased toxicity of the treatment effluent. An integrated chemical-biological system appeared to be feasible for treating recalcitrant compounds.