Effects of anthracene, pyrene and benzo[a]pyrene spiking and sewage sludge compost amendment on soil ecotoxicity during a bioremediation process

The fate of spiked anthracene, pyrene and benzo[a]pyrene in soil with or without sewage sludge compost was assessed during a 6-month bioremediation process simulating landfarming. Bioassays and physico-chemical analyses were employed to monitor toxicity change in soil samples and elutriates through ten sampling campaigns. Pearson product-moment correlation coefficient was determined to measure the strength of relationship between bioassays and physico-chemical analyses. The PAH dissipation in soil was enhanced after the first water addition, and the remaining amounts at the end of the experiment were positively correlated to the number of benzene rings and the presence of sewage sludge compost. Toxicity of soil elutriates to Daphnia magna was evident at early stages, originating exclusively from sewage sludge compost amendment. The lettuce root elongation was continuously inhibited by elutriates for all the treatments including control soil, probably due to high salinity or to unaddressed leachable phytotoxic compounds that were present in the experimental soil. The newly developed direct solid-phase chronic toxicity test using ostracod (Heterocypris incongruens) succeeded in evaluating the soil-bound PAH toxicity, as PAHs could not be detected in elutriates.     

Changes of polycyclic aromatic hydrocarbons during composting of sewage sludges with chosen physico-chemical properties and PAHs content

The aim of the experiment was to determine changes in the PAH content during sewage sludge composting. The extent was evaluated to which sewage sludge properties influences on PAHs losses during composting. Five municipal sewage sludges were studied from sewage treatment plants located in the south-east of Poland, i.e. in Stalowa Wola, Kra?nik, Lublin, Zamo?? and Bi?goraj. The treatment plants selected were characterised by their differentiation with catchments area as well as the industrial character of the areas. Sludge composting was carried out in aerobic conditions in plastic containers for a period of 76 days. The content of 14 polycyclic aromatic hydrocarbons (PAHs) and some physical-chemical (TOC, Nt, TOC/Nt, CEC, BS, TEB, pH, available potassium and phosphorus, total forms of cations) sewage sludge properties were monitored. In the present study correlations between PAHs losses (during various phases of composting) and physical-chemical properties of sewage sludges and composts were also evaluated. The sewage sludges were characterised both by differentiated properties and by PAH content. The total PAH content (the sum of 14 PAHs from the EPA List with exception of naphthalene and acenaphthene) in the sludges ranged from 3674 to 11236 microg kg(-1). Four- and three-ring compounds were predominant in the sewage sludges. Almost all of the sludges were characterised by differentiated content levels of both individual PAHs groups and PAHs sum. After 76 days of composting, a significant lowering of the PAH content was observed in all sludges as compared to the beginning of the experiment. The range of total observed PAH losses was from 15.8% to 48.6%, depending on the sewage sludge. The largest lowering of the PAH content was observed in the sludge with the lowest concentration of the xenobiotics studied. The largest losses in individual PAHs were observed in the case of five- and six-rings compounds, and were probably related to strong pollutant binding by other components of the sewage sludge. The few significant relationships showed that PAH losses during composting were only slightly determined by the analysed physical-chemical properties.     

PCDD/F, PAH and heavy metals in the sewage sludge from six wastewater treatment plants in Beijing, China

In order to better understand land application of sewage sludge, the characterization of heavy metals, PCDD/F and PAHs in sewage sludge was investigated from six different wastewater treatment plants (WWTP) in Beijing City, China. It was found that the total concentrations of Zn in Wujiacun (WJC) sewage sludge, and Cd and Hg in sewage sludge generated from all of the six different places are higher than Chinese regulation limit of pollutants for sludge to be used for agriculture (GB18918-2002). The levels of 16 PAHs that have been categorized as priority pollutants by US EPA in the sewage sludge samples varied from 2467 to 25923 microg/kg (dry weight), the highest values of 25923 microg/kg being found in WJC WWTP. The concentrations of Benzo[a]pyrene were as high as 6.1mg/kg dry weight in WJC sewage sludge, exceeding the maximum permitted content by GB18918-2002. Individual PAH content varies considerably with sewage samples. The ratios of anthracene to anthracene plus phenanthrene (An/178), benz[a]anthracene to benz[a]anthracene plus chrysene (BaA/228), indene[1,2,3-cd]pyrene to indene[1,2,3-cd]pyrene plus benzo[g,h,i]perylene (In/In+BP), and fluoranthene to fluoranthene plus pyrene (Fl/Fl+Py) suggest that petroleum and combustion of fossil fuel were the dominant contributions for the PAHs in sewage sludge. The concentrations of total PCDD/F in the sewage sludge ranged from 330 to 4245 pg/g d.w. The toxicity equivalent concentrations is between 3.47-88.24 pg I-TEQ according to NATO/CCMS, which is below Chinese legislation limit value proposed for land application. The PCDD/F congener/homologue profiles found in the Beijing samples indicated that the high chlorinated PCDD/F contamination might originate mainly from PCP-related source and depositional sources while the low chlorinated PCDD/F homologues could be originating from incineration or coal combustion. The major source of PCDD/Fs in Beijing sludge is still unclear.     

Occurrence of organic contaminants in sewage sludges from eleven wastewater treatment plants, China

This study presents the occurrence of 43 semi-volatile organic compounds (SVOCs) listed as priority pollutants by both China and the United States Environmental Protection Agency, in sewage sludges collected from eleven wastewater treatment plants (WWTPs) of mainland and Hong Kong, China. Thirty-six SVOCs were detected by gas chromatography coupled with mass spectrometer (GC-MS) and at least 14 in each sample. The most abundant compounds were phthalic acid esters (PAEs) and polycyclic aromatic hydrocarbons (PAHs) with total concentrations ranging from 10 to 114mgkg(-1) dry weight (d.w.) (with a mean of 30mgkg(-1) d.w.) and from 1.4 to 33mgkg(-1)d.w. (with a mean of 16mgkg(-1) d.w.), respectively, followed by chlorobenzenes, nitroaromatics, haloethers and halogenated hydrocarbons which occurred generally at concentrations lower than 10mgkg(-1) d.w. Large variations were observed between the concentrations of individual compounds as well as their total concentrations in sludge samples from different WWTPs. The highest values of sum concentration of 16 PAHs and of 6 PAEs were found in sewage sludge from Beijing. The mean total concentration of each class of SVOCs in sewage sludge from mainland was remarkably higher than that from Hong Kong. The concentrations of di(2-ethylhexyl) phthalate in 91% sludge samples met the limit (100mgkg(-1)d.w.) proposed by the Europe Union for land application, whereas the PAH concentrations of 64% sludge samples exceeded the maximum permissible concentration (6.0mgkg(-1)d.w.). The occurrence of SVOCs in this study are compared with other studies and their sources are discussed.     

PAH removal from spiked municipal wastewater sewage sludge using biological, chemical and electrochemical treatments

Polycyclic aromatic hydrocarbons (PAHs) have been widely studied due to their presence in all the environmental media and toxicity to life. These molecules are strongly adsorbed on the particulate matters of soils, sludges or sediments because of their strong hydrophobicity which makes them less bioavailability, thus limiting their bioremediation. Different sludge treatment processes were tested to evaluate their performances for PAH removal from sludge prealably doped with 11 PAHs (5.5mg each PAH kg(-1) of dry matter (DM)): two biological processes (mesophilic aerobic digestion (MAD) and simultaneous sewage sludge digestion and metal leaching (METIX-BS)) were tested to evaluate PAH biodegradation in sewage sludge. In parallel, two chemical processes (quite similar Fenton processes: chemical metal leaching (METIX-AC) and chemical stabilization (STABIOX)) and one electrochemical process (electrochemical stabilization (ELECSTAB)) were tested to measure PAH removal by these oxidative processes. Moreover, PAH solubilisation from sludge by addition of a nonionic surfactant Tween 80 (Tw80) was also tested. The best yields of PAH removal were obtained by MAD and METIX-BS with more than 95% 3-ring PAH removal after a 21-day treatment period. Tw80 addition during MAD treatment increased 4-ring PAHs removal rate. In addition, more than 45% of 3-ring PAHs were removed from sludge by METIX-AC and during ELECSTAB process were quiet good with approximately 62% of 3-ring PAHs removal. However, little weaker removal of 3-ring PAHs (<35%) by STABIOX. None of the tested processes were efficient for the elimination of high molecular weight (> or = 5-ring) PAHs from sludge.     

Persistence of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge-amended soil

The application of sewage sludge as a fertilizer is a common method used to improve soil properties. However, sewage sludge may contain various organic pollutants including polycyclic aromatic hydrocarbons. In the present study, the persistence of PAHs in soils fertilized with different sewage sludge doses was compared in relation to the sewage sludge dose applied (30, 75, 150, 300 and 600 Mgha(-1)) and the content of the polycyclic aromatic hydrocarbons in them. The experiment was carried out in two blocks of experimental plots divided according to the type of plants grown: field plants and perennial-willow. Sewage sludge addition to soils resulted in an increase in the content of polycyclic aromatic hydrocarbons in these soils. This increase was proportional to the quantity of sewage sludge applied. The results obtained showed that during a 42/54-month period, more than half of the individual PAHs introduced into the soil with sewage sludge were degraded. The scope of dissipation depended on the sewage sludge dose and the use to which the area was put. In the experiment with the willow only in the case of the highest sludge dose was a decrease in the PAH content above 50% noted; whereas in the case of the experiment with the field plants, it was higher by 50% for all sewage sludge doses. In experiment with field plants the highest scope of individual PAH disappearance was observed in the soil with the sewage sludge dose amounting to 300 Mgha(-1). In experiment with willow a relatively high dissipation of individual PAHs (>50%) was found in the treatment with the highest sludge dose (600 Mgha(-1)). A wider PAH dissipation range in the experiment with field plants was conditioned by the more favourable conditions created as a result of the breeding treatments applied. Agrotechnical treatments clearly increased the disappearance of the PAHs in those soils fertilized with the lowest sewage sludge doses (30 and 75 Mgha(-1)). The results obtained showed that the preferred method of treating a light soil fertilised with sewage sludges should be a one-year system, with a sludge application of 75 Mgha(-1).     

Di-(2-ethylhexyl)phthalate in sewage sludge and post-treated sludge: quantitative determination by HRGC-MS and mass spectral characterization

DEHP was quantified into sewage sludge, thermally dried sludge and compost samples from different areas of Catalonia (North East Spain) using high-resolution gas chromatography (HRGC) coupled to a mass spectrometry (MS). The aim of the work was to determine the evolution of this ubiquitous environmental contaminant along some post-treatment sludge processes, such as composting and thermally drying. DEHP concentration detected in some sludges are above the maximum limit suggested by the EC (100 ppm d.m.) for agricultural use. However, the composting and thermally drying reduce the amount of DEHP in sewage sludge to acceptable level for safe land application. The study was completed with the characterization and long-term observation of DEHP in sewage sludge, composted sludge and thermally dried sludge mixed with two types of soils. In all cases, the percentage of DEHP degraded was higher than 50% after 9 months of incubation.     

Migration of polycyclic aromatic hydrocarbons (PAHs) in urban treatment sludge to the air during PAH removal applications

In the present study, the amounts of polycylic aromatic hydrocarbons (PAHs) penetrating into air during PAH removal applications from the urban treatment sludge were investigated. The effects of the temperature, photocatalyst type, and dose on the PAH removal efficiencies and PAH evaporation were explained. The sludge samples were taken from an urban wastewater treatment plant located in the city of Bursa, with 585,000 equivalent population. The ultraviolet C (UV-C) light of 254 nm wavelength was used within the UV applications performed on a specially designed setup. Internal air of the setup was vacuumed through polyurethane foam (PUF) columns in order to collect the evaporated PAHs from the sludge during the PAH removal applications. All experiments were performed with three repetitions. The PAH concentrations were measured by gas chromatography–mass spectrometry (GC-MS). It was observed that the amounts of PAHs penetrating into the air were increased with increase of temperature, and more than 80% of PAHs migrated to the air consisted of 3-ring compounds during the UV and UV-diethylamine (DEA) experiments at 38 and 53 °C. It was determined that 40% decrease was ensured in Σ₁₂ (total of 12) PAH amounts with UV application and 13% of PAHs in sludge penetrated into the air. In the UV-TiO₂ applications, a maximum 80% of Σ₁₂ PAH removal was obtained by adding 0.5% TiO₂ of dry weight of sludge. The quantity of PAH penetrating into air did not exceed 15%. UV-TiO₂ applications ensured high levels of PAH removal in the sludge and also reduced the quantity of PAH penetrating into the air. Within the scope of the samples added with DEA, there was no increase in PAH removal efficiencies and the penetration of PAHs into air was not decreased. In light of these data, it was concluded that UV-TiO₂ application is the most suitable PAH removal alternative that restricts the convection of PAH pollution.

Implications: Polycyclic aromatic hydrocarbon (PAH) evaporation rates from sludge samples obtained from an urban wastewater treatment plant were investigated here for the first time by employing removal applications. TiO₂ and diethylamine were used as photocatalysts in this study. A special device was designed and successfully used in this study. Treatment sludge can be a significant source of PAHs for the atmosphere. The data highlight the need for removal of PAHs in treatment sludge via methods limiting their evaporation to the air. It was observed that UV-TiO₂ application was the most suitable PAH removal alternative that restricts the convection of PAH pollution.     

Effect of humification processes on polyaromatic hydrocarbons concentration during wastewater treatment.

The aim of the present work was to compare the concentration changes of polyaromatic hydrocarbons (PAH) and the course of humification processes during wastewater treatment. Studies of samples from a biological-mechanical wastewater treatment plant in Sosnowiec-Zagórze (Poland) were carried out. Determination of PAH was performed both for wastewater sludge and sludge water. Observations of the course of humification processes for humic acid fractions isolated from sludges were conducted. Analysis of PAH extracted from wastewaters and from sludge was performed by means of high-performance liquid chromatography. Investigations of humification processes were conducted by electron paramagnetic resonance and nuclear magnetic resonance methods. The elementary composition changes in the structure of the extracted humic acids were determined. It was found that polyaromatic hydrocarbons appear during the processes of humification. Their content in water decreased only after the process of sludge aeration; however, sludge water leaving the settlers was PAH-enriched.     

Investigation of potentially bioavailable and sequestrated forms of polycyclic aromatic hydrocarbons during sewage sludge composting

The present study focuses on the influence of the composting process on the formation of potentially bioavailable and sequestrated PAH fractions. The potentially bioavailable fraction was determined by means of a mild-solvent extraction (with n-butanol). The total and potentially bioavailable PAH content was evaluated in the consecutive composting stages, i.e. at the onset of the experiment, after the stabilization phase (on the 35th day), and after the maturation phase (on the 76th day). Four municipal sewage sludges with differentiated PAH content were selected for the present experiment. Eleven PAHs from the US EPA list (with exception of naphthalene, acenaphthylene, acenaphtene, fluorene and benz[ah]anthracene) were determined for the purpose of this experiment. The content of the total PAHs ranged from 3052 to 10352microg kg(-1). The share of the potentially bioavailable fraction was at a similar level in the sludge samples tested and ranged from 75% to 81%. Greater differences were noted in the share of the bioavailable fraction in the case of individual PAH groups. The influence of the composting process on the contribution of the potentially bioavailable fraction of the PAH clearly depended on the stage of the experiment and sewage sludge type. However, in the case of all sludges, a lowering of the bioavailable fraction by 19-52% as compared to the level at the outset of the experiment was observed. During the first phase (stabilization) of the sewage sludge composting process, a reduction of the PAH content took place mainly at the expense of potentially bioavailable fraction, whereas in the second phase (maturation), sequestration processes predominated. The above phenomenon was most clearly visible for the 6-rings PAHs.     

A comparison of TEQ contributions from PCDDs,PCDFs and dioxin-like PCBs in sewage sludges from Catalonia,Spain

Eight sewage sludges from rural, urban and industrial wastewater treatment plants (WWTPs) in Catalonia (Spain) were analysed for polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) to determine the present levels of contamination. A method based on an automated cleanup system followed by an isotope-dilution high-resolution mass spectrometric analysis was employed. Total toxicity equivalent (WHO-TEQ) values were calculated using the toxicity equivalent factors (WHO-TEFs) proposed by WHO for dioxin-like PCBs, PCDDs and PCDFs. The WHO-TEQ(PCDD/F) values for these samples ranged from 4.9 to 20.8 pg/g dry weight (d.w.), with a mean value of 9.3 pg/g d.w., whereas WHO-TEQ(PCB) levels ranged between 1.9 and 6.6 pg/g d.w., with a mean value of 4.2 pg/g d.w. The WHO-TEQ(PCB) contribution varied from 13% to 50%, suggesting that PCB contribution on the toxicity of the samples must be taken into account. Moreover, these contemporary PCDD, PCDF and PCB concentrations were compared with previous data obtained from sewage sludge samples collected during the 80s. Our findings show that contemporary PCDD, PCDF and PCB levels have declined since the 80s.     

Natural attenuation/phytoremediation in the vadose zone of a former industrial sludge basin

The natural attenuation of polyaromatic hydrocarbons (PAHs) in the vadose zone of a naturally revegetated former industrial sludge basin (0.45 ha) was examined. This was accomplished by comparing the concentration of 16 PAH contaminants present in sludge collected below the root zone of plants with contaminants present at 3 shallower depths within the root zone. Chemical analysis of 240 samples from 60 cores showed the average concentration of total and individual PAHs in the 0-30 cm, 30-60 cm, and bottom of the root zone strata were approximately 10, 20, and 50%, respectively, of the 16, 800 ppm average total PAH concentration in deep non-rooted sludge. Statistically significant differences in average PAH concentrations were observed between each strata studied and the non-rooted sludge except for the concentrations of acenaphthene and chrysene present at the bottom of the root zone in comparison to sludge values. The rooting depth of the vegetation growing in the basin was dependent on both vegetation type and plant age. Average rooting depths for trees, forbs (herbaceous non-grasses), and grasses were 90, 60, and 50 cm, respectively. The deepest root systems observed (100-120 cm) were associated with the oldest (12-14 year-old) mulberry trees. Examination of root systems and PAH concentrations at numerous locations and depths within the basin indicated that plant roots and their microbially active rhizospheres fostered PAH disappearance; including water insoluble, low volatility compounds, i.e. benzo(a)pyrene and benzo(ghi)perylene. The reduced concentration of PAHs in the upper strata of this revegetated former sludge basin indicated that natural attenuation had occurred. This observation supports the concept that through appropriate planting and management practices (phytoremediation) it will be possible to accelerate, maximize, and sustain natural processes, whereby even the most recalcitrant PAH contaminants (i.e. benzo(a)pyrene) can be remediated over time.     

PCDDs and PCDFs in sewage sludges from two wastewater treatment plants in Beijing, China

The levels of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analyzed by an isotope-dilution high-resolution mass spectrometric in 16 sewage sludges, sampled from 2004 to 2009, from two municipal wastewater treatment plants (WWTPs) in Beijing. Total toxicity equivalent (TEQ) values were evaluated using the toxicity equivalent factors proposed by International for PCDD/Fs. The I-TEQs for these sewage sludges were from 0.97 to 15.0 pg g⁻¹ dry weight (dw) with a mean value 4.43 pg g⁻¹ dw, indicating that all I-TEQs were below Chinese legislation limit value regulated for agricultural use in soils.The results from limited samples (16 samples) showed that the levels of PCDD/Fs might be correlated with the sludge age. Meanwhile, the temporal trends of PCD/Fs suggested that the I-TEQs may correlate with rainfall in the present study.     

Polycyclic aromatic hydrocarbons in sewage,mussels and tap water

Polycyclic aromatic hydrocarbons (PAH) have been determined in sewage discharge, mussels and tap water by glass capillary gas chromatography. Up to 30 PAH compounds have been identified. The concentration levels are low, respectively 0.8 – 7.7μg/1, 0.5–1.1 μg/g and 0.002 – 0.2μg/1 of sum PAH have been determined in sewage discharge, mussels and tap water. The accumulation rate in mussels seems to be rather slow at the ambient water concentrations.     

Polynuclear aromatic hydrocarbons in crops from long-term field experiments amended with sewage sludge

This study reports on the polynuclear aromatic hydrocarbon (PAH) content of crop plants grown at three different field experiments where controlled additions of sewage sludge were made a number of years ago. Archived samples of several crops have been analysed from sludge-amended and unsludged control plots for 15 PAH compounds. Root crops and above ground plant parts were available for several years following the last applications of sludge. Although the soil PAH burden increased substantially due to sewage sludge additions, and residues of these compounds have persisted in the soils for many years, increased PAH concentrations relative to the unsludged controls were not consistently detected in plant tissues. Plant samples were relatively enriched with low molecular weight compounds such as acenaphthene/fluorene nd phenanthrene. Various lines of evidence indicate that PAHs detected in above ground plant parts are chiefly derived from atmospheric inputs, while PAHs detected in root crops probably arise from adsorption to the root surface.     

Levels and distribution patterns of short chain chlorinated paraffins in sewage sludge of wastewater treatment plants in China

Short chain chlorinated paraffins (SCCPs) are listed as persistent organic pollutant candidates in the Stockholm Convention and are receiving more and more attentions worldwide. In general, concentrations of contaminants in sewage sludge can give an important indication on their pollution levels at a local/regional basis. In this study, SCCPs were investigated in sewage sludge samples collected from 52 wastewater treatment plants in China. Concentrations of total SCCPs (ΣSCCPs) in sludge were in the range of 0.80-52.7 μg/g dry weight (dw), with a mean value of 10.7 μg/g dw. Most of SCCPs in the sludge samples showed a similar congener distribution patterns, and C(11) and Cl(7,8) were identified as the dominant carbon and chlorine congener groups. Significant linear relationships were found among different SCCP congener groups (r(2) ≥ 0.9). High concentrations of SCCPs in sewage sludge imply that SCCPs are widely present in China.     

Biodegradation of phthalate esters in polluted soil by using organic amendment

This study investigated the biodegradation of the phthalate esters (PAEs) di-n-butyl phthalate (DBP) and di-(2-ethyl hexyl) phthalate (DEHP) in sludge and sludge-amended soil. DBP (100 mg kg(-1)) and DEHP (100 mg kg(-1)) were added to sewage sludge, which was subsequently added to soil. The results showed that sewage sludge can degrade PAEs and the addition of sewage sludge to soil enhanced PAE degradation. Sludge samples were separated into fractions with various particle size ranges, which spanned 0.1-0.45 μm to 500-2000 μm. The sludge fractions with smaller particle sizes demonstrated higher PAE degradation rates. However, when the different sludge fractions were added to soil, particle size had no significant effect on the rate of PAE degradation. The results from this study showed that microbial strains F4 (Rhodococcus sp.) and F8 (Microbacterium sp.) were constantly dominant in the mixtures of soil and sludge.     

Levels of dioxin-like compounds in sewage sludge determined with a bioassay based on EROD induction in chicken embryo liver cultures

A bioassay for the detection of dioxin-like compounds was used to estimate levels in sewage sludge from Swedish sewage treatment plants (STPs). The sludge extracts were HPLC-separated into three fractions containing a) monoaromatic/aliphatic, b) diaromatic (e.g. polychlorinated biphenyls [PCBs], polychlorinated dibenzodioxins and polychlorinated dibenzofurans [PCDDs/Fs]), and c) polyaromatic compounds (e.g. polycyclic aromatic hydrocarbons [PAHs]). The bioassay, which is based on EROD (7-ethoxyresorufin O-deethylase) induction in cultured chicken embryo livers detected dioxin-like activity in all unfractionated extracts and in the di- and polyaromatic fractions of all sludge extracts, but not in the monoaromatic/aliphatic fractions. The levels ranged between 6 and 109 pg bio-TEQ/g sludge (d.w.). In sediment samples from rural lakes in Sweden, levels of about 5 pg bio-TEQ/g (d.w.) have been found. The polyaromatic fractions of the sludge samples were potent in the bioassay, probably due to various PAHs and other polyaromatics in the sludge. The levels of six PAHs that are screened for in the sludge at Swedish STPs accounted for only 3-10% of the observed EROD-induction by the polyaromatic fractions. Consequently, many other polyaromatic EROD-inducing compounds were present in the sludge. Inclusion of a biological test like the chicken embryo liver bioassay in the screening of sludge would improve the ability to detect the presence of bioactive dioxin-like compounds. A theoretical estimation of bio-TEQ concentrations in farm-soil following long-term application of sludge with bio-TEQ concentrations similar to those observed in this investigation indicated that the bio-TEQ levels in soil would increase very slowly over time. The chicken embryo liver bioassay proved useful in assessing levels of dioxin-like compounds in sewage sludge and it gives valuable complementary information to chemical analysis data.     

Biological and chemical tools in the toxicological risk assessment of Jarama River, Madrid, Spain

Four river water samples (R) and three sewage samples (S) were collected at different points in the Jarama River, Spain. Organic concentrates were tested on the RTG-2 in vitro cytotoxicity test and analyzed by HPLC and GC/MS. The cytotoxicity assessment demonstrated a progressive increase in the toxicity of the river water when moving downstream. A wide range, from slightly harmful to highly toxic, was observed for sewage samples. The most toxic samples produced decreases of 95% to 100% in the ATP content, cell viability and cell detachment (a parameter to estimate mortality). The most toxic organic concentrates (the sewage from an urban + industrial effluent collected in Paracuellos, Madrid, Spain, and the river 100 m downstream from the discharge of this effluent) were fractioned by an HPLC system. Each chromatographic peak was collected as a fraction of the whole concentrate. The cytotoxicity of each fraction was also assessed on RTG-2 cells. A toxic peak with a retention time of 38.3 min was detected in both samples; this time belongs to the PAHs retention time interval under our chromatographic conditions. Analytical procedures identified fluorene (0.62 microg/l) and benz(a)anthracene (0.44 microg/l) in the sewage and anthracene (0.40 microg/l) and benz(a)anthracene (0.14 microg/l) in the river water. However, the observed cytotoxicity could not be explained by the PAH concentrations. Five additional toxic peaks were observed in each sample. Results suggest that the combination of HPLC with cost-effective toxicity tests produces a useful tool to define environmental management decisions when the chemical analysis cannot identify the substances responsible for the environmental risk.     

Aerobic thermophilic treatment of sewage sludge contaminated with 4-nonylphenol

4-Nonylphenol (4-NP) occurs in sewage sludge as a result of the breakdown of detergents which contains nonylphenol ethoxylates (NPEs). 4-NP is of environmental concern because of its toxicity to biological systems. The present paper reports results of aerobic treatment under thermophilic conditions of sewage sludge artificially contaminated with 4-NP. Experiments were carried out using three parallel laboratory-scale batch reactors operating with blank, 50 and 100 mg/l of 4-NP concentration. For the two studied concentrations up to 66% 4-NP reduction was achieved at a specific air flow rate of 16 l/(l.h) and a thermophilic temperature of 60 degrees C, within 10 days of operation. The presence of 4-NP has minor effect on the rate of sludge oxidation and the nitrogen and phosphorous content in the sludge.