Fate of polycyclic aromatic hydrocarbons during composting of activated sewage sludge with green waste

The occurrence characteristics, removal efficiency, and risk assessment of polycyclic aromatic hydrocarbons in sewage sludges from across China

Sewage sludge is considered to be an important sink for polycyclic aromatic hydrocarbons (PAHs) in wastewater treatment plants and the potential risks from sludge contaminated with PAHs during land application has attracted attention. To identify the priority PAHs for control and enhance their removal from sludge, the occurrence characteristics, removal efficiency, and risk assessment of PAHs in sewage sludges from across China were analyzed. Data collection was from 2001 to 2023. Results showed that 16 PAHs were widely detected in Chinese sewage sludge with total amounts (∑16PAHs) between 0.06 and 34.93 mg kg dw-1. Fossil fuel, coal, and biomass combustion are main anthropogenic sources of PAHs in China. In general, phenanthrene (PHE), anthracene (ANT), fluorescein (FL), chrysene (CHR), pyrene (PYR), and benzo[b]fluoranthene (BbF) are regarded as the main components and PAHs with 3-5 rings dominate (84.01%-91.53%) sewage sludge in China. Although aerobic composting and anaerobic treatment significantly improve ∑16PAHs removal, sludge stabilization treatment only reduced the risk by a small amount, especially for high-molecular-weight (HMW) PAHs. The benzo[a]anthracene (BaA), benzo[a]pyrene (BaP), and dibenzo[a,h]anthracene (DahA) are proposed as the priority control contaminants for sewage sludge in China because they have consistently high-risk quotient (RQ) values of 2.42-7.47, 1.28-3.16, 1.06-1.83 before and after sludge stabilization, respectively. More attention should be paid to BaA, BbF, benzo[k]fluoranthene (BkF), BaP, DahA, and indeno[1,2,3-cd]pyrene (IcdP) in Beijing; ANT, BaA, and BaP in Shanghai; and BaA and BaP in Guanghzou. Although the toxic equivalent quotient (TEQ) for PAHs met the limit concentration requirements of the national standard, the potential health risks due to long-term exposure to HMW PAHs cannot be ignored because the incremental lifetime cancer risk (ILCR) was consistently in the risk threshold range (>1 × 10-6). Some suggestions on enhanced treatment approaches and land use standards are proposed to further alleviate the risk from HMW PAHs.

Polycyclic aromatic hydrocarbon (PAH) remediation during vermicomposting and composting: Mechanistic insights through PAH-budgeting

Knowledge on the mechanism of earthworm-induced removal of polycyclic aromatic hydrocarbons (PAH) in vermicomposting systems and interaction with nutrient mineralization and microbial growth is scarce in literature. Moreover, the PAH accumulation capacity of Eudrilus eugeniae has not been studied. This research, therefore, investigates the apportionment dynamics of 13 PAH compounds in aerobic composting and vermicomposting (Eisenia fetida and E. eugeniae) systems using novel budget equations. The PAH removal efficiency of vermicomposting was significantly higher (2-threefold) than composting with concurrent microbial augmentation (p < 0.01). However, the 4-6 ring compounds reduced more significantly (30-50%) than the 3-ring PAHs (p < 0.01), and E. eugeniae was an equally competitive PAH-accumulator compared to E. fetida. The budget equations revealed that although the bioaccumulation capabilities of earthworms were retarded due to PAH exposure, earthworms facilitated PAH-immobilization in decomposed feedstock. A marked increase in bacterial, fungal, and actinomycetes proliferation in PAH-spiked vermibeds with parallel removal of the PAHs indicated that earthworm-induced microbial enrichment plays a vital role in PAH detoxification during vermicomposting. Correlation analyses strongly implied that earthworm-driven mineralization-humification balancing and microbial enrichment could be the critical mechanism of PAH remediation under vermicomposting.

Evaluation of fluorene-caused ecotoxicological responses and the mechanism underlying its toxicity in Eisenia fetida: Multi-level analysis of biological organization

Fluorene is an important toxic chemical that exists ubiquitously in the environment, and it has also been suggested to exert potential deleterious effects on soil invertebrates. However, knowledge about the toxic effects of fluorene and its underlying mechanisms of the effects on key soil organism earthworms remains limited. From this view point, this study was undertaken to explore the potential effects of fluorene and its underlying mechanisms in Eisenia fetida at the level of experimental animals, tissue, cell, and molecule. It was concluded that fluorene exerted lethal activity to adult E. fetida on day 14 with the LC₅₀ determined to be 88.61 mg/kg. Fluorene-induced ROS caused oxidative stress in E. fetida, resulting in DNA damage, protein carbonylation, and lipid peroxidation. Moreover, changed antioxidative enzymatic activities, non-enzymatic antioxidative activities, and total antioxidative capacity in E. fetida by fluorene stress are associated with antioxidative and protective effects. High-dose fluorene (> 2.5 mg/kg) exposure significantly caused histopathological lesions including the microstructure of body wall, intestine, and seminal vesicle of earthworms. Also, the reproductive system of E. fetida was clearly disrupted by fluorene stress, leading to poor reproduction ability (decreased cocoon and juvenile production) in earthworms. It is found that E. fetida growth was significantly inhibited when treated with high-dose fluorene, thereby causing normal growth disorders. Additionally, fluorene stress triggered the abnormal mRNA expression related to oxidative stress (e.g., metallothionein and heat shock protein 70), growth (translationally controlled tumour protein), reproduction (annetocin precursor) in E. fetida. Together, both high-dose and long-term exposure elicited more severe poisoning effects on earthworms using the Integrated Biological Response (IBR) index, and E. fetida coelomocyte DNA was the most negatively affected by fluorene stress. This study comprehensively evaluated fluorene-induced toxicity in E. fetida, and its underlying molecular mechanisms mediating the toxic responses have been elucidated. These findings provide valuable data for assessing potential ecological risks posed by fluorene-contaminated soil.

Occurrence, analysis of microplastics in sewage sludge and their fate during composting: A literature review

Microplastics (MP) are ubiquitous contaminants and their presence in sewage sludge has recently received attention as they may enter agro-ecosystems if sludge is used as organic soil amendment. Indeed, plastic particles (<5 mm) can be transported from wastewater and sewage sludge to the soil environment either directly within the plastic matrix or indirectly as adsorbed substances. In this paper, articles from 18 countries reporting the MP quantity and their characteristics in sewage sludge from wastewater treatment plants were reviewed and the MP concentration size and type were compared. The data show that MP abundance in sewage sludge ranged globally from 7.91 to 495 × 10³ particles kg^-1 with highest abundance of fiber shape and MP size of less than 500 μm. In this review, we summarized and discussed the methods most frequently used for extraction and characterization of MP in sewage sludge including organic matter removal, MP extraction; physical and morphological MP characterization and its chemical characterization for polymer identification. We also described the major factors potentially controlling the fate of MP during disposal strategies with particular focus on composting. We show that physical and microbiological factors are important for MP degradation during composting and suggest two remediation practices: (i) inoculation of the initial sludge with microbial plastic decomposers to remove MP from contaminated sewage sludge, and (ii) development of high temperature composting processes.

Combining sequential extraction and 3D fluorescence to investigate the behavior of antibiotic and polycyclic aromatic hydrocarbons during solar drying of sewage sludge

Solar drying and liming are commonly used for sludge treatment, but little is known about their efficiency on antibiotics and Polycyclic Aromatic Hydrocarbons (PAHs) removal. This study aimed to investigate the removal of antibiotics and PAHs during solar drying of Limed Sludge (LS) and Non-Limed Sludge (NLS). Thus, organic matter fractionation and 3D fluorescence were used to assess the accessibility and the complexity of organic matter. 2 experiments have been conducted using LS and NLS for 45 days of drying in a pilot scale tunnel. Physicochemical results indicated significant decrease of water content (90%) for both sludge samples within 15 days of drying. For both treatments, the removal of total organic carbon and total nitrogen was low and similar for both treatments. Through this study, it has been confirmed that liming and drying contributed to a strong modification of the organic matter quality with an increase of its accessibility. On the other hand, drying alone increased the less accessible compartments, while the presence of lime affected the interconnexion between the organic matter pools. 3D fluorescence confirmed the obtained results and indicated that LS leads to obtaining more simple molecules in the most accessible compartments, while NLS leads to obtaining more complex molecules in the less accessible compartments. In addition, solar radiations and leaching may contribute to the significant removal (p < 0.01) of roxithromycin, benzo(a)anthracene, chrysene, benzo[k]fluoranthene, benzo[a]pyrene, and benzo(g, h, i) perylene in the presence of lime. Furthermore, the evolution of organic matter pools in terms of accessibility and complexity may drive the bioavailability of these pollutants, leading to their significant removal.

Occurrence and dissipation mechanism of organic pollutants during the composting of sewage sludge: A critical review

Sewage sludge contains various classes of organic pollutants, limiting its land application. Sludge composting can effectively remove some organic pollutants. This review summarizesrecent researches on concentration changes and dissipation of different organic pollutants including persistent organic pollutants during sludge composting, and discusses their dissipation pathways and the current understanding on dissipation mechanism. Some organic pollutants like PAHs and phthalates were removed mainly through biodegradation or mineralization, and their dissipation percentages were higher than those of PCDD/Fs and PCBs. Nevertheless, some recalcitrant organic pollutants could be sequestrated in organic fractions of sludge mixtures, and their levels and ARG abundance even increased after sludge composting in some studies, posing potential risks for land application. This review demonstrated that microbial community and their corresponding degradation for organic pollutants were influenced by different pollutants, bulking agents, composting methods and processes. Further research perspectives on removing organic pollutants during sludge composting were highlighted.

Formation of non-extractable residues as a potentially dominant process in the fate of PAHs in soil: Insights from a combined field and modeling study on the eastern Tibetan Plateau

Whereas non-extractable residue (NER) formation is recognized as an important process affecting the ecological risk of organic contaminants in soils, it is commonly neglected in regional-scale multi-media models assessing chemical environmental fate and risk. We used a combined field and modeling study to elucidate the relative importance of NER formation to the reduction in available organic contaminants compared with fate processes commonly considered in risk assessment models (volatilization, leaching, and biodegradation). Specifically, four polycyclic aromatic hydrocarbons (PAHs), i.e., phenanthrene (Phe), pyrene (Pyr), benzo[a]pyrene (BaP), and benzo[ghi]perylene (BghiP), were spiked and measured in a one-year field pot experiment at four sites with diverse environmental conditions on the eastern Tibetan Plateau. The rate of NER formation was derived as the difference between the overall rate of decline in total-extractable PAH concentrations, obtained by fitting a biphasic first-order model to the measured concentrations, and the sum of the calculated rates of volatilization, leaching, and biodegradation. Our work shows that the total-extractable PAH concentration undergoes a rapid decline and a slow decline, with shorter overall half-lives (especially for BaP and BghiP) than those observed in earlier studies. Generally, NER formation was assessed to be the dominant contributor (64 ± 33%) to the overall decline of PAHs, followed by biodegradation (35 ± 32%); volatilization and leaching were the smallest contributors. In particular, heavier PAHs (i.e. BaP and BghiP) tend to have shorter half-lives in the rapid and the overall decline phase, indicating that the erroneous estimation of environmental fate and risks might be more pronounced for organic contaminants with a large molecular size. The trend of overall decline rates of PAHs displayed a combined effect of NER formation and biodegradation. This work indicates the need to consider NER formation as a process in multi-media models of chemical fate and risk.

Biodegradation of polyaromatic hydrocarbons and the influence of environmental factors during the co-composting of sewage sludge and green forest waste

The main aim of this research was to study the biodegradation of polycyclic aromatic hydrocarbons (PAHs) and the influence of environmental factors during composting in order to realize the utilization of PAHs contaminated sewage sludge. A production scale compost experiment was conducted with three mixtures of sewage sludge (SS): green forest waste (GFW) at quality ratios of 3:1 (T1), 3:2 (T2) and 3:3 (T3). The residual concentration of PAHs in the three treatments met the permissible limit prescribed by the Agricultural Sludge Pollutant Control Standard (GB 4284-2018). The biodegradation rates of PAHs were 0.0280, 0.0281 and 0.0218 mg/d, and removal efficiencies were 70.7%, 75.2% and 62.4% in T1, T2, T3, respectively, which followed the first-order rate kinetics. The residual concentration of PAHs in T2 was the lowest (1.81 mg/kg), while the germination index (GI) of Tall Fescues (~0.9) was the highest during 50 days of co-composting. The bacterial diversity negatively correlated with the residual PAHs content. The main genus, Bacillus, Pseudomonas and Methylotenera, with cellulose-degrading and PAHs co-metabolizing functions contributed significantly to sludge maturation and PAHs degradation. The dominant microorganisms, Pseudomonas, Sphingobacterium and Chitinophagaceae_uncultured, could support the high removal rate of PAHs in T2. Temperature, pH, total organic carbon (TOC), total nitrogen (TN) and carbon/nitrogen (C/N) ratio had significant positive effect on the compost maturity and quality, and these parameters correlated with the PAHs biodegradation efficiency during composting, especially in T2.

Assessment of the genotoxicity of antibiotics and chromium in primary sludge and compost using Vicia faba micronucleus test

The objective of this study was to investigate chemical, biological and eco-toxicological parameters of a compost produced through the co-composting of dewatered primary sludge (DPS) and date palm waste to evaluate in which extent it can exploited as a bio-fertilizer. DPS and date palm waste were co-composted in aerobic conditions for 210 days. Physico-chemical parameters were evaluated during composting (total organic carbon, total nitrogen, pH, available forms of phosphorus). Furthermore, heavy metals (Cd, Cu, Cr, Pb, Ni, Zn) and antibiotics (fluoroquinolones, macrolides and tetracyclines) content were analyzed in the DPS. To evaluate the genotoxicity of substrates, Vicia faba micronucleus test was carried out. Single and combined toxicities of a mixture of antibiotics (ciprofloxacin, enroflxacin, nalidixic acid, roxithromycin and sulfapyridin) and chromium (Cr₂ (SO₄)₃ and K₂Cr₂O₇) were examined. Although the final compost product showed a significant decrease of the genotoxicity, almost 50% of the micronucleus frequency still remained, which could be explained by the persistence of several recalcitrant compounds such as chromium and some antibiotics. Overall, the presence of antibiotics and chromium showed that some specific combination of contaminants represent an ecological risk for soil health and ecosystems even at environmentally negligible concentrations.

Organic micropollutants' distribution within sludge organic matter fractions explains their dynamic during sewage sludge anaerobic digestion followed by composting

The simultaneous fate of organic matter and 4 endocrine disruptors (3 polycyclic aromatic hydrocarbons (PAHs) (fluoranthene, benzo(b)fluoranthene, and benzo(a)pyrene) and nonylphenols (NP)) was studied during the anaerobic digestion followed by composting of sludge at lab-scale. Sludge organic matter was characterized, thanks to chemical fractionation and 3D fluorescence deciphering its accessibility and biodegradability. Total chemical oxygen demand (COD) removal was 41% and 56% during anaerobic digestion and composting, respectively. 3D fluorescence highlighted the quality changes of organic matter. During continuous anaerobic digestion, organic micropollutants' removal was 22 ± 14%, 6 ± 5%, 18 ± 9%, and 0% for fluoranthene, benzo(b)fluoranthene, benzo(a)pyrene, and nonylphenols, respectively. Discontinuous composting allowed to go further on the organic micropollutants' removal as 34 ± 8%, 31 ± 20%, 38 ± 10%, and 52 ± 6% of fluoranthene, benzo(b)fluoranthene, benzo(a)pyrene, and nonylphenols were dissipated, respectively. Moreover, the accessibility of PAH and NP expressed by their presence in the various sludge organic matter fractions and its evolution during both treatments was linked to both the quality evolution of the organic matter and the physicochemical properties of the PAH and NP; the presence in most accessible fractions explained the amount of PAH and NP dissipated.

Fate of antibiotics present in a primary sludge of WWTP during their co-composting with palm wastes

Antibiotics persistence in the primary sludge can contribute to the emergence of these molecules in the environment and limit the agricultural recycling of sludge without any preliminary treatment. Composting is a widely used process for recycling sludges and then can contribute to the antibiotics removal. However, little interest is actually given to the evaluation of the persistence of some antibiotics families after the sludge co-composting and more particularly to the final compost valorization. In this work, antibiotics concentrations of βeta-lactams, Macrolides, Lincosamide, Tetracyclines, Sulfonamides and Fluoroquinolones were checked in the primary sludge of the wastewater treatment plants (WWTP) of Marrakesh (Morocco) before its co-composting. The results showed a final high amount of the fluoroquinolones family (4.21 and 2.92 μg/kg DM for Ciprofloxacin and Ofloxacin respectively) compared to the other studied families. To assess the fate of antibiotics, the primary sludge and palm waste were windrowed and composted during 120 days. The final compost showed a high level of organic matter decomposition (52%) and a C/N ratio of 12 which insure the compost quality. The assessment of antibiotics concentrations during co-composting showed that clarithromycin is more degraded particularly during the stabilization stage (43%), the degradation of lincomycin and tetracyclines is more significant during the maturation stage (36 and 75% respectively). Ampicillin and trimethoprim were degraded all along the process of co-composting (46 and 35% respectively). By the way, the persistence of the fluoroquinolones family was observed. This persistence could be a limiting key factor for the composted sludge valorization. So, more knowledge is needed to understand fluoroquinolones behavior and, then, to optimize their composting conditions.

Loading and removal of PAHs, fragrance compounds, triclosan and toxicity by composting process from sewage sludge

Although the production of compost from sewage sludge is well established in developed countries, the use of sludge-based compost may represent a source of pollutants. The present study assessed the levels of potentially harmful compounds in compost as well as their rates of decrease during composting. The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs), three fragrance compounds (OTNE, HHCB and AHTN) and triclosan were determined in the initial sewage sludge and in compost over the span of 1year. Simultaneously, the toxicity to luminescent bacteria (Aliivibrio fischeri) and aryl hydrocarbon receptor reactivity of organic solvent extracts of sludge and compost samples were assessed. Higher PAH, fragrance compounds, and triclosan concentrations were found in sewage sludge from urban areas compared with rural regions, and the urban sludge was also more toxic than the rural sludge. The high pollutant concentrations in urban sludge raised the concentrations of these compounds in the raw materials for composting and in the resulting composts. The organic matter was decomposed by 65% during the composting process, and the measured toxic substances were decreased by a similar amount, with the exception of triclosan, which decreased by only 35%. The toxicity to A. fischeri decreased to a greater extent (90%) than did the organic matter, while the aryl hydrocarbon receptor reactivity decreased by only 35%. This lower decrease coincided with that of the aryl hydrocarbon receptor-reactive PAHs (37%).

Microbial communities in pyrene amended soil-compost mixture and fertilized soil

Polycyclic aromatic hydrocarbons are distributed ubiquitously in the environment and form metabolites toxic to most organisms. Organic amendment of PAH contaminated soil with compost and farmyard manure has proven to be efficient for PAH bioremediation mediated by native microorganisms, even though information on the identity of PAH degraders in organic-amended soil is still scarce. Here we provide molecular insight into the bacterial communities in soil amended with compost or farmyard manure for which the degradation mass balances of ¹³C-labeled pyrene have been recently published and assess the relevant bacterial genera capable of degrading pyrene as a model PAH. We performed statistical analyses of bacterial genera abundance data based on total DNA and RNA (for comparison) extracted from the soil samples. The results revealed complex pyrene degrading communities with low abundance of individual degraders instead of a limited number of abundant key players. The bacterial degrader communities of the soil-compost mixture and soil fertilized with farmyard manure differed considerably in composition albeit showing similar degradation kinetics. Additional analyses were carried out on enrichment cultures and enabled the reconstruction of several nearly complete genomes, thus allowing to link microcosm and enrichment experiments. However, pyrene mineralizing bacteria enriched from the compost or unfertilized soil-compost samples did not dominate pyrene degradation in the soils. Based on the present findings, evaluations of PAH degrading microorganisms in complex soil mixtures with high organic matter content should not target abundant key degrading species, since the specific degraders may be highly diverse, of low abundance, and masked by high bacterial background.

Synthesis and characterization of a molecularly imprinted polymer for the isolation of the 16 US-EPA priority polycyclic aromatic hydrocarbons (PAHs) in solution

A smart sorbent consisting of benzo[k]fluoranthene-imprinted and indeno[1 2 3-cd]pyrene-imprinted polymers mixed at 1:1 (w/w) was successfully screened from several cavity-tuning experiments and used in the isolation of polycyclic aromatic hydrocarbons from spiked solution. The polymer mixture showed high cross selectivity and affinity towards all the 16 US-EPA priority polycyclic aromatic hydrocarbons. The average extraction efficiency from a cyclohexane solution was 65 ± 13.3% (n = 16, SD). Batch adsorption and kinetic studies confirmed that the binding of polycyclic aromatic hydrocarbons onto the polymer particles resulted in formation of a monolayer and that the binding process was the rate limiting step. The imprinted polymer performance studies confirmed that the synthesized polymer had an imprinting efficiency of 103.9 ± 3.91% (n = 3, SD). A comparison of the theoretical number of cavities and the experimental binding capacity showed that the overall extent of occupation of the imprinted cavities in the presence of excess polycyclic aromatic hydrocarbons was 128 ± 6.45% (n = 3, SD). The loss of selectivity was estimated at 2.9% with every elution cycle indicating that the polymer can be re-used several times with limited loss of selectivity and sensitivity. The polymer combination has shown to be an effective adsorbent that can be used to isolate all the 16 US-EPA priority polycyclic aromatic hydrocarbons in solution.

Review and prospect of emerging contaminants in waste--key issues and challenges linked to their presence in waste treatment schemes: general aspects and focus on nanoparticles

The presence in waste of emerging pollutants (EPs), whose behaviours and effects are not well understood, may present unexpected health and environmental risks and risks for the treatment processes themselves. EP may include substances that are newly detected in the environment, substances already identified as risky and whose use in items is prohibited (but which may be present in old or imported product waste) or substances already known but whose recent use in products can cause problems during their future treatment as waste. Several scientific studies have been conducted to assess the presence of EP in waste, but they are mostly dedicated to a single category of substance or one particular waste treatment. In the absence of a comprehensive review focused on the impact of the presence of EP on waste treatment schemes, the authors present a review of the key issues associated with the treatment of waste containing emerging pollutants. This review presents the typologies of emerging pollutants that are potentially present in waste along with the major challenges for each treatment scheme (recycling, composting, digestion, incineration, landfilling and wastewater treatment). All conventional treatment processes are affected by these new pollutants, and they were almost never originally designed to consider these substances. In addition to these general aspects, a comprehensive review of available data, projects and future R&D needs related to the impact of nanoparticles on waste treatment is presented as a case study.

Acute effect of benzo[a]anthracene on the biodegradation of peptone under aerobic conditions

BACKGROUND

This study investigated the acute effect of benzo[a]anthracene, a significant compound among polycyclic aromatic hydrocarbons, on the biodegradation of a synthetic organic substrate-a peptone/meat extract mixture-under aerobic conditions.

METHODS

A laboratory-scale sequencing batch reactor was sustained at steady state at a sludge age of 10 days with substrate feeding. Inhibition tests involved running a series of batch reactors initially seeded with the biomass obtained from the parent reactor. After the biomass seeding, the reactors were started with the peptone mixture and a range of initial benzo[a]anthracene concentrations between 0.5 and 88 mg/L. Experimental profiles of oxygen uptake rates and polyhydroxyalkanoates were evaluated by calibration of a selected model.

RESULTS

Lower doses of benzo[a]anthracene had no effect on process kinetics. The noticeable acute impact was only observed with the addition of 88 mg/L of benzo[a]anthracene, but it was limited with the storage mechanism: the amount of organic substrate diverted to polyhydroxyalkanoates was significantly reduced with a corresponding decrease in the maximum storage rate, k (STO), from 2.7 down to 0.6 day(-1). Similarly, the maximum growth rate from internally stored polyhydroxyalkanoates was lowered from 2.3 to 1.0 day(-1).

CONCLUSION

Among the mechanisms for direct substrate utilization, only the hydrolysis rate was slightly reduced, but otherwise, the overall COD removal efficiency was not affected.

Dissipation pathways of organic pollutants during the composting of organic wastes

The organic pollutants (OPs) present in compostable organic residues can be recovered in the final composts leading to environmental impacts related to their use in agriculture. However, the composting process may contribute to their partial dissipation that is classically evaluated through the concentration decrease in extractable OPs, without identification of the responsible mechanisms as mineralization or stabilization of OP as non-extractable residues (NER) or bound residues. The dissipation of four (14)C-labeled OPs (fluoranthene; 4-n-nonylphenol, NP; sodium linear dodecylbenzene sulfonate, LAS; glyphosate) was assessed during composting of sewage sludge and green waste. The dissipation of LAS largely resulted from its mineralization (51% of initial LAS), whereas mineralization was intermediate for NP (29%) and glyphosate (24%), and negligible for fluoranthene. The NER pathway mostly concerned NP and glyphosate, with 45% and 37% of the recovered (14)C being found as NER at the end of composting, respectively. In the final composts, the proportions of water soluble residues of OPs considered as readily available were <11% of recovered (14)C-OPs. However, most fluoranthene remained solvent extractable (72%) and potentially available, whereas only 18% of glyphosate and less than 7% of both NP and LAS remained solvent extractable in the final compost.

Combined effects of bacterial-feeding nematodes and prometryne on the soil microbial activity

Microcosm experiments were carried out to study the effects of bacterial-feeding nematodes and indigenous microbes and their interactions on the degradation of prometryne and soil microbial activity in contaminated soil. The results showed that soil indigenous microbes could degrade prometryne up to 59.6-67.9%; bacterial-feeding nematodes accelerated the degradation of prometryne in contaminated soil, and prometryne degradation was raised by 8.36-10.69%. Soil microbial biomass C (C(mic)), basal soil respiration (BSR), and respiratory quotient (qCO(2)) increased in the beginning of the experiment and decreased in the later stage of the experiment. Nematodes grew and reproduced quite fast, and did increase the growth of soil microbes and enhance soil microbial activity in prometryne contaminated soil during the incubation period.

Chemometrics-assisted fluorimetry for the rapid and selective determination of heavy polycyclic aromatic hydrocarbons in contaminated river waters and activated sludges

The most concerned polycyclic aromatic hydrocarbons (PAHs) benzo[a]pyrene, dibenz[a,h]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene and benz[a]anthracene were simultaneously determined in the presence of other 10 interfering PAHs, applying second-order multivariate calibration to the data obtained with a flow-through optosensor interfaced to a fast-scanning spectrofluorimeter. Using a sample volume of 2.5 mL, detection limits in the range 5-115 ng L(-1) were obtained in interfering samples, with a sample frequency of ca. 15 samples per hour, and with a minimum use of organic solvents, competing very favorably with chromatographic methods. The significance of this study lies in the solution of the quantitative analysis problem of six PAHs in real matrices of unknown composition. The unfolded partial least-squares/residual bilinearization (U-PLS/RBL) algorithm showed the best performance in resolving the complex studied system.

Environmental impacts of post-consumer material managements: recycling, biological treatments, incineration

The environmental impacts of recycling, mechanical biological treatments (MBT) and waste-to-energy incineration, the main management strategies to respond to the increasing production of post-consumer materials are reviewed and compared. Several studies carried out according to life-cycle assessment (LCA) confirm that the lowest environmental impact, on a global scale, is obtained by recycling and by biological treatments (composting and anaerobic fermentations) if compost is used in agriculture. The available air emission factors suggest that, on a local scale, mechanical biological treatments with energy recovery of biogas, may be intrinsically safer than waste-to-energy incinerators. Several studies confirm the capability of biological treatments to degrade many toxic xenobiotic contaminating urban wastes such as dioxins and polycyclic aromatic hydrocarbons, an important property to be improved, for safe agricultural use of compost. Further LCA studies to compare the environmental impact of MBTs and of waste-to-energy incinerators are recommended.

Biological indicators capable of assessing thermal treatment efficiency of hydrocarbon mixture-contaminated soil

In China, there are many special sites for recycling and washing the used drums, which release a variety of C5-C40 hydrocarbon mixture into the soil around the site. The remediation of these contaminated sites by thermal treatment is adopted ubiquitously and needs to be assessed. Here we report the feasibility of biological indicators applied to assess thermal treatment efficiency in such contaminated soil. A series of biological indicators, including seed germination index (SGI), root elongation index (REI), plant growth height, biomass, carbon dioxide evolved (CDE), soil respiration inhibition (SRI) and soil enzymatic activities, were employed to monitor or assess hydrocarbon mixture removal in thermal treated soil. The results showed that residual hydrocarbon mixture content correlated strongly negatively with SGI for sesamum (Sesamum indicum L.), plant height, and biomass for ryegrass (Lolium perenne L.) in the concentration ranges of 0-3990, 0-3170 and 0-2910 mg kg(-1), respectively. In contrast, REI for sesamum was positively correlated with residual hydrocarbon mixture content from 0 to 1860 mg kg(-1). In addition, both CDE and SRI demonstrated that 600 mg kg(-1) of residual hydrocarbon mixture content caused the highest amount of soil carbon dioxide emission and inhabitation of soil respiration. The results of soil enzymes indicated that 1000 mg kg(-1) of residual hydrocarbon mixture content was the threshold value of stimulating or inhibiting the activities of phosphatase and catalase, or completely destroying the activities of dehydrogenase, invertase, and urease. In conclusion, these biological indicators can be used as a meaningful complementation for traditional chemical content measurement in evaluating the environmental risk of the contaminated sites before and after thermal treatment.

In-vessel treatment of urban primary sludge by aerobic composting

The aim of this work is the study of recycling urban primary sludge by in-vessel aerobic composting way. Two series of composting trials were carried out in an automated accelerated bioreactor in mixture with agricultural wastes: sugar beet leaves (C1); straw, sheep manure and sugar beet leaves (C2). Treatments were monitored with regard to physicochemical characteristics, heavy metal amounts and microbiological parameters of the final compost product. The general pattern of the temperature curve was typical for composts of organic waste. The different physicochemical characteristics of the final composts after a retention time in the bioreactor of 30 and 23 days, respectively for C1 and C2 were: pH: 7.3-7.2; C/N: 10.2-12; organic matter: 49.7-58.3%; NH(4)(+)/NO(3)(-): 0.24-0.2. Final compost showed low amounts of heavy metals, relatively high contents of nutrients and significant reduction of pathogens, suggesting the agricultural purposes of urban primary sludge.

Fate and effect of linuron and metribuzin on the co-composting of green waste and sewage sludge

The fate and effect of the herbicides linuron and metribuzin on the co-composting of sewage sludge and green waste were addressed in this work. The experiments were conducted in metal cubic containers of 1.0m(3) volume simulating a windrow composting system. A mixture of sludge and green waste was prepared at a ratio of 1:5 v/v. The mixture was split in four equal parts and the two herbicides were added, using a pressure sprayer, as sole or mixed pollutant in each of the three mixtures. The forth mixture was composted without any addition of herbicide, to serve as control. Temperature, physicochemical characteristics, herbicide concentration, carbon dioxide emission, methane emission and microbiological parameters were measured either daily or every time the mixtures were turned, for a period of 80 days. Both herbicides' concentration decreased significantly resulting in removal efficiencies of 99.1-99.7% and 95.8-96.0% for linuron and metribuzin, respectively. Incubation of microbiologically inactive mixtures at a temperature schedule following the spontaneous temperature evolution in the composters resulted in very little (1-11%) decomposition for both herbicides. Comparison of the variation of physicochemical parameters and microbial populations during composting indicated that both herbicides did not affect the composting process.