The removal of Polycyclic Aromatic Hydrocarbons in the wastewater treatment process: experimental calculations and model predictions

Modeling and simulation for the sustainable recovery of aromatics (BTX) from petrochemical industrial wastewater

Petrochemical wastewater is a major industrial source of pollution that produces a variety of toxic organic and inorganic pollutants, naturally present or added during the process. These pollutants are a serious threat to the soil, water, environment, and human being due to their complex and hazardous nature. Glycols such as monoethylene glycol (MEG), diethylene glycol (DEG), triethylene glycol (TEG), and aromatics (BTX-benzene, toluene, and xylene) are the most common organic impurities present in petrochemical wastewater. The objective of this paper is to recover aromatics and water from petrochemical industrial wastewater. The reclamation process is used to remove inorganic impurities such as heavy metals Fe, Zn, Pb, Mn, Al, Ni, As, Cr, Cu, Cd, and K and salts. In the present work, 1% sodium bi-carbonate (NaHCO3) is used to precipitate the inorganic impurities present in the wastewater at 40 °C atmospherically. Aspen Hysys simulation software is used for modeling and simulation for the treatment process using NRTL (non-random-two-liquid) thermodynamic model. The process generated from Aspen Hysys is validated with lab experiments. To support global sustainable development, this study is focused on reducing, reusing, and recycling separation techniques such as centrifuge separation and vacuum distillation have been used. The characterization of regenerated water was performed using ICP-OES (inductively coupled plasma-optical emission spectroscopy) to determine the reduction in heavy metals. It was found that > 99.5% of heavy metals were removed. The regeneration of these aromatics is necessary for economic and environmental reasons so that it can be reused to avoid its disposal in and contamination of natural environments.

Occurrence, removal, and risk assessment of polycyclic aromatic hydrocarbons and their derivatives in typical wastewater treatment plants

Wastewater treatment plants (WWTPs) have a certain removal capacity for polycyclic aromatic hydrocarbons (PAHs) and their derivatives, but some of them are discharged with effluent into the environment, which can affect the environment. Therefore, to understand the presence, sources, and potential risks of PAHs and their derivatives in WWTPs. Sixteen PAHs, three chlorinated polycyclic aromatic hydrocarbons (ClPAHs), three oxidized polycyclic aromatic hydrocarbons (OPAHs), and three methylated polycyclic aromatic hydrocarbons (MPAHs) were detected in the influent and effluent water of three WWTPs in China. The average concentrations of their influent ∑PAHs, ∑ClPAHs, ∑OPAHs, and ∑MPAHs ranged from 2682.50 to 2774.53 ng/L, 553.26-906.28 ng/L, 415.40-731.56 ng/L, and 534.04-969.83 ng/L, respectively, and the effluent concentrations ranged from 823.28 to 993.37 ng/L, 269.43-489.94 ng/L, 285.93-463.55 ng/L, and 376.25-512.34 ng/L, respectively. The growth of heat transport and industrial energy consumption in the region has a significant impact on the level of PAHs in WWTPs. According to the calculated removal efficiencies of PAHs and their derivatives in the three WWTPs (A, B, and C), the removal rates of PAHs and their derivatives were 69-72%, 62-71%, and 68-73%, respectively, and for the substituted polycyclic aromatic hydrocarbons (SPAHs), the removal rates were 41-49%, 31-40%, and 33-39%, respectively; moreover, the removal rates of PAHs were greater than those of SPAHs in the WWTPs. The results obtained via the ratio method indicated that the main sources of PAHs in the influent of WWTPs were the combustion of coal and biomass, and petroleum contamination was the secondary source. In risk evaluation, there were 5 compounds for which the risk quotient was considered high ecological risk. During chronic disease evaluation, there were 11 compounds with a risk quotient considered to indicate high risk. PAHs and SPAHs with high relative molecular masses in the effluent of WWTPs pose more serious environmental hazards than their PAHs counterparts.

Efficient performance of InP and InP/ZnS quantum dots for photocatalytic degradation of toxic aquatic pollutants

In recent years, the growing concern over the presence of toxic aquatic pollutants has prompted intensive research into effective and environmentally friendly remediation methods. Photocatalysis using semiconductor quantum dots (QDs) has developed as a promising technology for pollutant degradation. Among various QD materials, indium phosphide (InP) and its hybrid with zinc sulfide (ZnS) have gained considerable attention due to their unique optical and photocatalytic properties. Herein, InP and InP/ZnS QDs were employed for the removal of dyes (crystal violet, and congo red), polyaromatic hydrocarbons (pyrene, naphthalene, and phenanthrene), and pesticides (deltamethrin) in the presence of visible light. The degradation efficiencies of crystal violet (CV) and congo red (CR) were 74.54% and 88.12% with InP, and 84.53% and 91.78% with InP/ZnS, respectively, within 50 min of reaction. The InP/ZnS showed efficient performance for the removal of polyaromatic hydrocarbons (PAHs). For example, the removal percentage for naphthalene, phenanthrene, and pyrene was 99.8%, 99.6%, and 88.97% after the photocatalytic reaction. However, the removal percentage of InP/ZnS for pesticide deltamethrin was 90.2% after 90 min light irradiation. Additionally, advanced characterization techniques including UV-visible spectrophotometer (UV-Vis), photoluminescence (PL), X-ray diffractometer (XRD), energy-dispersive spectrometer (EDS) elemental mapping, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) were used to analyze the crystal structure, morphology, and purity of the fabricated materials in detail. The particle size results obtained from TEM are in the range of 2.28-4.60 nm. Both materials (InP and InP/ZnS) exhibited a spherical morphology, displaying distinct lattice fringes. XRD results of InP depicted lattice planes (111), (220), and (311) in good agreement with cubic geometry. Furthermore, the addition of dopants was discovered to enhance the thermal stability of the fabricated material. In addition, QDs exhibited efficacy in the breakdown of PAHs. The analysis of their fragmentation suggests that the primary mechanism for PAHs degradation is the phthalic acid pathway.

Nano-composite rGO-Ag-Cu-Ni mediated photocatalytic degradation of anthracene and benzene

Polycyclic aromatic hydrocarbons (PAHs) are omnipresent, persistent, and carcinogenic pollutants continuously released in the atmosphere due to the rapid increase in population and industrialization worldwide. Hence, there is an ultimate rise in concern about eliminating the toxic PAHs and their related aromatic hydrocarbons from the air, water, and soil environment by employing efficient removal technologies using nanoparticles as a catalyst. Here, the degradation of selective PAHs viz., anthracene and benzene using laboratory synthesized rGO-Ag-Cu-Ni nanocomposite (catalyst) was studied. Characterization studies revealed the nanocomposites exhibited surface plasma resonance at 350 - 450 nm, confirming the presence of Ag, Cu, and Ni metal ions embedded on the reduced graphene substrate. It was found that the nanocomposites synthesized were spherical, amorphous in nature, and aggregated together with measurements ranging from 423 to 477 nm. An SEM-EDX analysis of the nanocomposite demonstrated that it contained 25.13% O, 14.24% Ni, 27.79% Cu, and 32.84% Ag, which confirms the synthesis of the nanocomposite. Crystalline, sharp nanocomposites of average size 17-41 nm with an average diameter of 118.5 nm (X-ray diffraction and DLS) were observed. FTIR spectra showed that the nanocomposites had the functional groups alkanes, alkenes, alkynes, carboxylic acids, and halogen derivatives. Batch adsorption studies revealed that the maximum degradation achieved at optimum nano-composite concentration of 10 μg/mL, pH value of 5, PAHs concentration of 2 μg/mL and effective irradiation source being UV radiations in the case of both benzene and anthracene pollutants. The degradation of benzene and anthracene followed Freundlich & Langmuir isotherm with the highest R2 value of 0.9894 & 0.9885, respectively. Adsorption kinetic studies under optimum conditions revealed that the adsorption of both benzene and anthracene followed Pseudo-second order kinetics. Antimicrobial studies revealed that the synthesized nano-composite exhibited potential antimicrobial activity against Gram positive bacterium (Bacillus subtilis, Staphylococcus aureus), Gram negative bacterium (Klebsiella pneumonia, Escherichia coli) and fungal strain (Aspergillus niger) respectively. Thus, the synthesized rGO-Ag-Cu-Ni nano-composite acts as an effective antimicrobial agent as well as a PAHs degrading agent, helping to overcome antibiotics resistance and to mitigate the overgrowing PAHs pollution in the environment.

Antimicrobial Effect of Phytochemicals from Edible Plants

Current strategies of combating bacterial infections are limited and involve the use of antibiotics and preservatives. Each of these agents has generally inadequate efficacy and a number of serious adverse effects. Thus, there is an urgent need for new antimicrobial drugs and food preservatives with higher efficacy and lower toxicity. Edible plants have been used in medicine since ancient times and are well known for their successful antimicrobial activity. Often photosensitizers are present in many edible plants; they could be a promising source for a new generation of drugs and food preservatives. The use of photodynamic therapy allows enhancement of antimicrobial properties in plant photosensitizers. The purpose of this review is to present the verified data on the antimicrobial activities of photodynamic phytochemicals in edible species of the world’s flora, including the various mechanisms of their actions.

Integration of coagulation and ozonation with flat-sheet ceramic membrane filtration for shale gas hydraulic fracturing wastewater treatment: A laboratory study

The performance of the integrated process of coagulation and ozonation with ceramic membrane filtration was evaluated for the treatment of shale gas hydraulic fracturing flowback wastewater (HFFW). The removal efficiencies of carbon oxygen demand (COD_Cr ), dissolved organic carbon (DOC), petroleum oils, and turbidity in effluent by the combined process were 87.1%, 72.2%, 94.3%, and 99.6%, respectively. Compared with sole membrane filtration, the transmembrane pressure (TMP) of ceramic membrane filtration was reduced by >99% with the integrated process. The coagulation and ozonation can effectively remove the organics with high molecular weights in the cake layer of ceramic membrane. To the best of our knowledge, this work proposed the combined process of coagulation, ozonation, and flat-sheet ceramic membrane filtration for the treatment of HFFW for the first time. The water quality of the effluent met the discharge standard (Comprehensive Wastewater Discharge Standard GB8978-1996). The findings can provide an important technical foundation for the innovation of integrated equipment for HFFW treatment. PRACTITIONER POINTS: An integrated process combining coagulation and ozonation with flat-sheet ceramic membrane ultrafiltration for the treatment of shale gas wastewater. The water quality of this integrated process met the discharge standard. Coagulation and ozonation effectively alleviated the membrane fouling related to organics with high molecular weights. A new avenue for on-site treatment of shale gas wastewater and an alternative of the current centralized wastewater management.

Occurrence, distribution and ecological risk assessment of polycyclic aromatic hydrocarbons and their derivatives in the effluents of wastewater treatment plants

In this study, we investigated the concentration distribution of parent polycyclic aromatic hydrocarbons (PAHs) and their derivatives in the effluents of 5 municipal wastewater treatment plants (WWTPs) in Beijing, China for eight months. We first identified the coexistence of PAHs, chlorinated PAHs (Cl-PAHs), brominated PAHs (Br-PAHs) and oxygenated PAHs (OPAHs) in the effluents of WWTPs. Three Cl-PAHs and 7 Br-PAHs were first found. The total concentrations of PAHs, Cl-PAHs, Br-PAHs and OPAHs ranged from 8.99-88.38, n.d.-5.70, n.d.-13.11 ng L^-1 and 15.47-106.92 ng L^-1, respectively. In terms of temporal distributions, the total concentrations of PAHs and OPAHs presented a decreasing trend from April to November and the total concentrations of Cl-PAHs and Br-PAHs fluctuated at lower levels. These results indicated that these compounds will be long-term discharged into the receiving river. In addition, Cl-PAHs, Br-PAHs and OPAHs were likely generated by transformations occurring during chlorination disinfection. For ecological risk assessment, risk quotients of 6 compounds, indeno[1,2,3-cd] pyrene, benzo[g,h,i]perylene, dibenz[a,h]anthracene, 6-bromobenzo[a]pyrene, 1,8-dibromopyrene and 1,6-dibromopyrene, were thought to indicate high ecological risk (fish). Furthermore, Cl-PAHs, Br-PAHs and OPAHs in the effluents of WWTPs can cause more serious environmental hazards than the corresponding PAHs.

A Mechanistic Model to Assess the Fate of Naphthalene and Benzo(a)pyrene in a Chilean WWTP

Polycyclic aromatic hydrocarbons (PAHs) are a family of organic compounds of widespread presence in the environment. They are recalcitrant, ubiquitous, prone to bioaccumulation, and potentially carcinogenic. Effluent from wastewater treatment plants (WWTPs) constitutes a major source of PAHs into water bodies, and their presence should be closely monitored, especially considering the increasing applications of potable and non-potable reuse of treated wastewater worldwide. Modeling the fate and distribution of PAHs in WWTPs is a valuable tool to overcome the complexity and cost of monitoring and quantifying PAHs. A mechanistic model was built to evaluate the fate of PAHs in both water and sludge lines of a Chilean WWTP. Naphthalene and benzo(a)pyrene were used as models of low-MW and high-MW PAHs. As there were no reported experimental data available for the case study, the influent load was determined through a statistical approach based on reported values worldwide. For both naphthalene and benzo(a)pyrene, the predominant mechanism in the water line was sorption to sludge, while that in the sludge line was desorption. Compared to other studies in the literature, the model satisfactorily describes the mechanisms involved in the fate and distribution of PAHs in a conventional activated sludge WWTP. Even though there is evidence of the presence of PAHs in urban centers in Chile, local regulatory standards do not consider PAHs in the disposal of WWTP effluents. Monitoring of PAHs in both treated effluents and biosolids is imperative, especially when considering de facto reuse and soil amendment in agricultural activities are currently practiced downstream of the studied WWTP.

Metal-Based Nanocomposite Materials for Efficient Photocatalytic Degradation of Phenanthrene from Aqueous Solutions

Polycyclic aromatic hydrocarbons (PAHs) are a class of naturally occurring chemicals resulting from the insufficient combustion of fossil fuels. Among the PAHs, phenanthrene is one of the most studied compounds in the marine ecosystems. The damaging effects of phenanthrene on the environment are increasing day by day globally. To lessen its effect on the environment, it is essential to remove phenanthrene from the water resources in particular and the environment in general through advanced treatment methods such as photocatalytic degradation with high-performance characteristics and low cost. Therefore, the combination of metals or amalgamation of bimetallic oxides as an efficient photocatalyst demonstrated its propitiousness for the degradation of phenanthrene from aqueous solutions. Here, we reviewed the different nanocomposite materials as a photocatalyst, the mechanism and reactions to the treatment of phenanthrene, as well as the influence of other variables on the rate of phenanthrene degradation.

Occurrence and removal of micropollutants in full-scale aerobic, anaerobic and facultative wastewater treatment plants in Brazil

This study aims to evaluate micropollutant occurrence and removal in a low-middle income country (LMIC) by investigating the occurrence of 28 chemicals from different classes (triclosan, 15 polycyclic aromatic hydrocarbons (PAHs), 4 estrogens and 8 polybrominated diphenyl ether (PBDE) congeners) in three technologically diverse full-scale Brazilian wastewater treatment plants (WWTPs). These chemicals were detected at concentrations similar to those reported in other low-middle income countries (LMICs) and high-income countries (HICs) (0.1-49 μg/L) indicating their widespread use globally and the need for more studies in LMICs that are typically characterized by relatively inadequate wastewater treatment barriers. Among the three different WWTPs investigated for removal of these chemicals, the least energy intensive system, waste stabilization ponds (WSPs), was the most effective (95-99%) compared to the activated sludge (79-94%), and Up-flow sludge blanket reactor (UASB) with trickling filters system (89-95%). These results highlight the potential of WSPs for micropollutant removal-especially in warm climates. However, the effluent from all three WWTP could pose a risk to aquatic organisms when discharged into the receiving waters as the effluent concentrations of triclosan, some estrogens, PAHs and BDE 209 were above European environmental quality standards (EQS) or predicted no effect concentration (PNEC values), indicating that receiving water bodies could benefit from further treatment. In combination, these results help to further understand prevailing concentrations of micropollutants globally and fate in current wastewater treatment systems.

Enhanced degradation of benzo[a]pyrene and toxicity reduction by microbubble ozonation

The microbubble technique has drawn great attention for efficient utilization of ozone for advance oxidation processes. Therefore, in this study, microbubble ozonation was investigated to evaluate the removal efficiency and toxicity reduction of benzo[a]pyrene. Compared with conventional macrobubble ozonation, microbubble ozonation produced higher concentrations of hydroxyl radicals and ozone in aqueous solutions, resulting in more efficient and persistent degradation of benzo[a]pyrene. Moreover, microbubble ozonation completely removed the acute toxicity of benzo[a]pyrene to Daphnia magna, whereas the toxicity reduction by macrobubble ozonation was not consistent owing possibly to toxic degradation products. These findings suggest that microbubble ozonation is a promising technique in terms of both chemical degradation and toxicity reduction of organic pollutants.

Occurrence, Removal, and Mass Balance of Polycyclic Aromatic Hydrocarbons and Their Derivatives in Wastewater Treatment Plants in Northeast China

Polycyclic aromatic hydrocarbons (PAHs), 33 methylated PAHs (Me-PAHs), and 14 nitrated PAHs (NPAHs) were measured in wastewater treatment plants (WWTPs) to study the removal efficiency of these compounds through the WWTPs, as well as their source appointment and potential risk in the effluent. The concentrations of ∑PAHs, ∑Me-PAHs, and ∑NPAHs were 2.01–8.91, 23.0–102, and 6.21–171 µg/L in the influent, and 0.17–1.37, 0.06–0.41 and 0.01–2.41 µg/L in the effluent, respectively. Simple Treat 4.0 and meta-regression methods were applied to calculate the removal efficiencies (REs) for the 63 PAHs and their derivatives in 10 WWTPs and the results were compared with the monitoring data. Overall, the ranges of REs were 55.3–95.4% predicated by the Simple Treat and 47.5–97.7% by the meta-regression. The results by diagnostic ratios and principal component analysis PCA showed that “mixed source” biomass, coal composition, and petroleum could be recognized to either petrogenic or pyrogenic sources. The risk assessment of the effluent was also evaluated, indicating that seven carcinogenic PAHs, Benzo[a]pyrene, Dibenz[a,h]anthracene, and Benzo(a)anthracene were major contributors to the toxics equivalency concentrations (TEQs) in the effluent of WWTPs, to which attention should be paid.

Quantifying the electron-donating and -accepting capacities of wastewater for evaluating and optimizing biological wastewater treatment processes

Biological processes have been widely used for the treatment of both domestic and industrial wastewaters. In such biological processes, pollutants are converted into pollution-free substances by microorganisms through oxidation-reduction reactions. Thus, how to quantify the internal oxidation-reduction properties wastewaters and seek out targeted countermeasures is essential to understand, operate, and optimize biological wastewater treatment systems. So far, no such approach is available yet. In this work, a novel concept of electron neutralization-based evaluation is proposed to describe the internal oxidation-reduction properties of wastewater. Pollutants in wastewater are defined as electron donor substances (EDSs) or electron acceptor substances (EASs), which could give or accept electrons, respectively. With such an electron neutralization concept, several parameters, i.e., electron residual concentration (R), economy-related index (E and E_r), and economical evaluation index (Y and Y_r), are defined. Then, these parameters are used to evaluate the performance and economic aspects of currently applied wastewater treatment processes and even optimize systems. Three case studies demonstrate that the proposed concept could be effectively used to reduce wastewater treatment costs, assess energy recovery, and evaluate process performance. Therefore, a new, simple, and reliable methodology is established to describe the oxidation-reduction properties of wastewater and assess the biological wastewater treatment processes.

Review on polycyclic aromatic hydrocarbons (PAHs) migration from wastewater

Rapidly increasing global population and increased civilization has increased burden on potable water resources and results in larger volumes of wastewater. Physical wastewater management techniques has advanced for domestic usage and commercial effluent new conceptions about imminent wastewater treatment have been acclaimed for highly carcinogenic polycyclic aromatic hydrocarbon (PAH) compounds. The present review study emphasis on the assessment of several accessible PAHs treatment methods used in wastewater management. The elementary principles, contextual remediation mechanisms and recent development in PAHs removal practices have also been precisely explained. The comprehensive information regarding sources, dispersal, classification, physicochemical properties, PAHs toxicity for humans and aquatics life, conventional treatment procedures, and advanced oxidation processes specified can assist us to identify the PAHs problem and their intensity. The performance evaluation of different removal techniques are discussed in details and found that highest PAHs' reduction for 5-or 6-ring (99%,) while 3-ring (79% reduction) with oxidant dose of 1.64 mL/L using titanium catalyst. In case of MWTPs, with secondary techniques, the average removal efficiency found in the range of 81.1-92.9% while for AOPs are 32-99.3%. Here, overall yield through AOPs most suitable if process used with some catalyst enhanced the yield as well and suitable for high ring as well as low ring PAHs. Among various processes, advanced oxidation and catalytic oxidation processes are the most valuable and promising techniques for PAHs removal. Based on the given evidences, the AOPs coupled with catalysts have been decided as the most competent design for wastewater PAHs treatment.

Investigation of micropollutants removal from landfill leachate in a full-scale advanced treatment plant in Istanbul city, Turkey

Although the levels of micropollutants in landfill leachate and municipal wastewater are well-established, the individual removal mechanisms and the fate of micropollutants throughout a landfill leachate treatment plant (LTP) were seldom investigated. Therefore, the determination of the removal efficiencies and the fates of micropollutants in a full-scale leachate treatment plant located in the largest city of Turkey were aimed in this study. Some important processes, such as equalization pond, bioreactor, ultrafiltration (UF) and nanofiltration (NF), are being operated in the treatment plant. Landfill leachate was characterized as an intense pollution source of macro and micropollutants compared to other water types. Chemical oxygen demand (COD), NH₃, suspended solids (SS) and electrical conductivity (EC) values of the landfill leachate (and their removal efficiencies in the treatment plant) were determined as 18,656 ± 12,098 mg/L (98%), 3090 ± 845 mg/L (99%), 4175 ± 1832 mg/L (95%) and 31 ± 2 mS/cm (51%), respectively. Within the scope of the study, the most frequently and abundantly detected micropollutants in the treatment plant were found as heavy metals (8 ± 1.7 mg/L), VOCs (38 ± 2 μg/L), alkylphenols (9 ± 3 μg/L) and phthalates (8 ± 3 μg/L) and the overall removal efficiencies of these micropollutants ranged from -11% to 100% in the treatment processes. The main removal mechanism of VOCs in the aerobic treatment process has been found as the volatilization due to Henry constants greater than 100 Pa·m³/mol. However, the molecular weight cut off restriction of UF membrane has caused to less or negative removal efficiencies for some VOCs. The biological treatment unit which consists of sequential anoxic and oxic units (A/O) was found effective on the removal of PAHs (62%) and alkylphenols (87%). It was inferred that both NO₃ accumulation in anoxic reactor, high hydraulic retention time (HRT) and sludge retention time (SRT) in aerobic reactor provide higher biodegradation and volatilization efficiencies as compared to the literature. Membrane processes were more effective on the removal of alkylphenols (60-80%) and pesticides (59-74%) in terms of influent and effluent loads of each unit. Removal efficiencies for Cu, Ni and Cr, which were the dominant heavy metals, were determined as 92, 91 and 51%, respectively and the main removal mechanism for heavy metals has thought to be coprecipitation of suspended solids by microbial biopolymers in the bioreactor and the separation of colloids during membrane filtration. Total effluent loads of the LTP for VOCs, semi volatiles and heavy metals were 1.0 g/day, 5.2 g/day and 1.5 kg/day, respectively. It has been concluded that the LTP was effectively removing both conventional pollutants and micropollutants with the specific operation costs of 0.27 $/(kg of removed COD), 0.13 $/(g of removed VOCs), 0.35 $/(g of removed SVOCs) and 2.6 $/(kg of removed metals).

Emerging concerns of VOCs and SVOCs in coking wastewater treatment processes: Distribution profile, emission characteristics, and health risk assessment

In this study, the distribution profiles, emission characteristics, and health risks associated with 43 volatile and semi-volatile organic compounds, including 15 phenols, 18 polycyclic aromatic hydrocarbons (PAHs), 6 BTEX, and 4 other compounds, were determined in the wastewater treatment plant (WWTP) of a coking factory (plant C) and the succeeding final WWTP (central WWTP). Total phenols with a concentration of 361,000 μg L^-1 were the predominant compounds in the influent wastewater of plant C, whereas PAHs were the major compounds in the final effluents of both coking WWTPs (84.4 μg L^-1 and 30.7 μg L^-1, respectively). The biological treatment process in plant C removed the majority of volatile organic pollutants (94.1%-99.9%). A mass balance analysis for plant C showed that biodegradation was the main removal pathway for all the target compounds (56.6%-99.9%) except BTEX, chlorinated phenols, and high molecular weight (MW) PAHs. Chlorinated phenols and high MW PAHs were mainly removed via sorption to activated sludge (51.8%-73.2% and 60.2%-75.9%, respectively). Air stripping and volatilization were the dominant mechanisms for removing the BTEX compounds (59.8%-73.8%). The total emission rates of the detected volatile pollutants from plant C and the central WWTP were 1,640 g d^-1 and 784 g d^-1, respectively. Benzene from the equalization basins of plant C and the central WWTP corresponded to the highest inhalation carcinogenic risks (1.4 × 10^-3 and 3.2 × 10^-4, respectively), which exceeded the acceptable level for human health (1 × 10^-6) recommended by the United States Environmental Protection Agency. The results showed that BaP exhibited the highest inhalation non-cancer risk, with a hazard index ratio of 70 and 30 for plant C and the central WWTP, respectively. Moreover, the excess sludge generated during wastewater treatment should also be carefully handled because it adsorbed abundant PAHs and chlorinated phenols at coking plant C (58,000 μg g^-1 and 3,500 μg g^-1) and the central WWTP (622 μg g^-1 and 54 μg g^-1).

Occurrence, loadings and removal of EU-priority polycyclic aromatic hydrocarbons (PAHs) in wastewater and sludge by advanced biological treatment, stabilization pond and constructed wetland

Eight polycyclic aromatic hydrocarbon (PAH) compounds which have been accepted as priority micropollutants by European Union (EU) were analyzed both in wastewater and sludge lines throughout three full scale (located in city, sub-province and village) WWTPs during 12-month sampling period. Investigated WWTPs have different treatment types including advanced biological treatment, stabilization pond (SP) and constructed wetland (CW). Removal efficiencies for total PAH compounds varied from 48% in CW to 85% in advanced biological treatment plant. The maximum concentrations of 360-2282 ng/L observed for naphthalene in raw wastewater were decreased to 103-370 ng/L by treatment processes. Minimum concentration were detected for benzo(k)fluoranthene (B[k]F) and benzo(g,h,i)perylene (B[g,h,i]P) ranged between 8 and 12 ng/L and 19-33 ng/L, respectively. While minimum removal efficiencies were obtained for B[k]F and B[g,h,i]P maximum removal efficiencies were obtained for naphthalene in all WWTPs. PAHs present in minimum and maximum levels in the sludge samples were detected as 54 and 6826 ng/g for the B[g,h,I]P and naphthalene, respectively. Considering the removal mechanisms, PAHs have been determined to be removed by biodegradation or vaporization up to 84% and by settling (adsorption onto sludge) up to 2%. The greatest portion (99%) of naphthalene and anthracene were determined to be biodegraded or vaporized in biological treatment due to their low molecular weights. On the other hand, mechanism of adsorption onto sludge was determined as negligible for these two compounds. In addition, approximately 14% of PAHs were discharged to the receiving environment. Among the different WWTP types investigated, advanced biological treatment was found to be the most efficient plant for the removal of PAH compounds.

Modelling PAHs removal in activated sludge process: effect of disintegration

The removal of polycyclic aromatic hydrocarbons (PAHs) in activated sludge was evaluated using two laboratory-scale bioreactors, coupled or not with a disintegration system (sonication). Mass balances performed on each system underlined that PAHs removal was significantly improved after sludge disintegration, especially for the higher molecular weight PAHs studied, which tended to adsorb to suspended matter. A model was developed in order to study the effect of sludge disintegration on the content of dissolved and colloidal matter (DCM), and to predict the potential impacts on PAHs availability and degradation. Results showed that this new model was efficient for capturing apparent degradation improvement trends and for discriminating between the involved mechanisms. This study showed that DCM content increased after sludge disintegration, and proved to be the main driver for improving PAHs apparent degradation.

Removal efficiency and mass balance of polycyclic aromatic hydrocarbons, phthalates, ethoxylated alkylphenols and alkylphenols in a mixed textile-domestic wastewater treatment plant

In this work the occurrence and fate of polycyclic aromatic hydrocarbons (PAHs), phthalic acid esters (PAEs), mono and diethoxylate alkylphenols (AP_1-2EOs) and alkylphenols (APs) have been investigated during a two-weeks period in a facility treating mixed textile-domestic wastewater (Prato, Italy). The wastewater treatment plant (WWTP) consists of primary sedimentation, activated sludge biological oxidation, secondary sedimentation, clariflocculation and ozonation. The sludge is treated within the facility by thickening, dewatering and final incineration, thus providing the almost quantitative removal of the adsorbed micropollutants. Naphthalene (50%), di(2-ethylhexyl) phthalate (74%) and branched 4-nonylphenols (59%) were the individual main representative compounds of each class in the influent wastewater, which showed concentration ranges of 5.6-66, 85-290 and 21-133μg/L for PAHs, PAEs and APs+AP_1-2EOs, respectively. The WWTP efficiently removed PAHs, PAEs and APs+AP_1-2EOs, providing effluent concentrations of 0.075-0.16ng/L 0.38-9.9μg/L and 0.53-1.4μg/L. All targeted priority and priority-hazardous micropollutants showed effluent concentrations in line with the European environmental quality standards (EQS), even though for di(2-ethylhexyl) phthalate and benzo(a)pyrene after correction for the dilution factor of the recipient. The WWTP performance was evaluated by mass balance, verifying its accuracy by monitoring Pb and Cd as conservative species. The biological treatment sections provided mass losses of 85.5%, 74.5% and 56.8% for APs+AP_1-2EOs, PAEs and PAHs, highlighting efficient biotransformation performances of the activated sludge process. However, for the more volatile PAHs (e.g. naphthalene), a significant contribution of stripping cannot be excluded. A remarkable mass loss was also determined in the ozonation stage for PAEs (72.9%) and especially PAHs (97.0%), whereas a lower efficiency was observed for APs+AP_1-2EOs (41.3%). The whole plant allowed for obtaining an almost quantitative removal (96.7-98.4%) for all targeted compounds.

Existence, removal and transformation of parent and nitrated polycyclic aromatic hydrocarbons in two biological wastewater treatment processes

Polycyclic aromatic hydrocarbons (PAHs) and nitrated polycyclic aromatic hydrocarbons (NPAHs) are pollutants commonly present in the environment. Some NPAHs are considered to have more severe toxic effects than their parent PAHs. The existence of 16 PAHs (678.5-3817.8 ng/L in wastewater, 499.9 ng/g-1239.6 ng/g in sludge) and 5 NPAHs (175.8-1392.4 ng/L in wastewater, 483.5 ng/g-2763.1 ng/g in sludge) was determined in a biological wastewater treatment plant (WWTP) in Qingdao, China. Anthracene and naphthalene were the predominant PAHs, and 2-nitrofluorene and 9-nitroanthracene were the predominant NPAHs. Petroleum, liquid fossil fuel combustion and exhaust emissions were the main sources of PAHs and NPAHs in this study. In both the sequencing batch reactor/moving-bed biofilm (SBR/MBBR) and the anaerobic-anoxic-aerobic (A²O) process, low-molecular-weight PAHs were mainly removed through volatilization and biodegradation/biotransformation. Meanwhile, the removal of high-molecular-weight PAHs and NPAHs depended on adsorption and sedimentation. The transformation from PAHs to NPAHs mainly occurred in the aqueous-phase, especially in summer and that was confirmed by mass flow and ratios variation. Overall, the removal capacity of the A²O process for PAHs and NPAHs was better than that of the SBR/MBBR process. Tertiary treatment processes had little effect or even a negative effect on the removal of PAHs and NPAHs.

Solid fuel combustion as a major contributor of polycyclic aromatic hydrocarbons in rural China: Evidence from emission inventory and congener profiles in tree bark

Polycyclic aromatic hydrocarbons (PAHs) remain a focal concern of the air pollution in China. To discriminate the sources of airborne PAHs in Chinese rural regions, a national-scale tree bark sampling campaign and emission inventory estimation were conducted. The concentrations of the sum of 16 U.S. EPA priority PAHs in rural bark ranged from 6.30 to 3803 ng/g, with the dominance of 3- and 4-ring PAHs. Bark residual PAH concentration correlated significantly with emission flux rate, bark lipid content, ambient PM_2.5, precipitation and sampling location. Based on the information of emission data, bark PAH congener profiles, principal component analysis, diagnostic ratios and compound-specific isotope analysis, solid fuel combustion was identified as the major source and could explain 40.3%-46.4% of bark PAH residues in rural China. The δ¹³C values of most individual PAHs were more negative at sites with lower longitude and latitude, suggesting a greater contribution of biomass combustion to PAH residues. Our results suggest the importance of regulating solid fuel combustion to significantly improve the air quality in China, and bark samples can provide a wealth of information on effectively monitoring and controlling the sources of PAH emission in rural China.

Variability of release rate of flame retardants in wastewater treatment plants

Information on variability is important in the assessment of the releases and potential risks of brominated flame retardants (BRFs) in the environment, but related data are limited. In this study, two release-characterizing parameters, release fraction to final effluent and influent-biosolids transfer coefficient, were used to quantify releases of five BFRs from eight secondary wastewater treatment plants (WWTPs). The five BFRs are recalcitrant, hydrophobic, and low in volatility. The two parameters for these BFRs were found to vary from day to day and season to season within individual WWTPs as well as from one WWTP to another. These temporal and spatial variations were, however, comparable to each other and both within a factor of 3 above or below the parameter averages. Averages for release fraction were in the range of 0.02-0.29 and those for influent-biosolids transfer coefficient in the range of 3-26 L/g, depending upon a given BFR at a given WWTP. These ranges and the observed factor-3 variability are not only useful for estimating releases of the five BFRs, but more importantly provide read-across data for the assessment of substances with similar physical-chemical properties.

Fluorene oxidation by solar-driven photo-Fenton process: toward mild pH conditions

Polycyclic aromatic hydrocarbons (PAHs) are on the list of priority pollutants to be eliminated from the environment due to their carcinogenic and mutagenic action, chemical stability, and resistance to biodegradation. The aim of this study was to evaluate the degradation of fluorene, a well-known PAH, in aqueous solutions (0.03 and 0.08 mg L^-1), by means of a solar-driven conventional (PF) and modified photo-Fenton mediated by ferrioxalate complexes (PFF). Photolysis was also employed for comparison purposes. PF reaction was evaluated at different pH values (2.8, 3.5, and 4.0) and iron concentrations (2, 5, 10, and 20 mg L^-1). On the other hand, PFF studies were conducted at mild pH conditions (4.0, 5.0, and 6.0) and iron content of 2 mg L^-1, keeping initial iron/oxalate molar ratio at 1:3. In both PF and PFF, the initial hydrogen peroxide/iron molar ratio was maintained at 5. In the presence of methanol as cosolvent for fluorene dissolution, the PF reaction was hampered and no consumption of H₂O₂ was observed during the reaction carried out at constant pH (2.8). This led to low degradation rates, similar to those achieved by photolysis. Under the same pH but using acetonitrile as cosolvent for fluorene dissolution, fluorene degradation was found to be proportional to the iron content used in the PF experiments. On the other hand, at an invariable iron concentration of 5 mg Fe²⁺ L^-1, the increase in pH was accompanied by a decrease in the molar fraction of the most photoactive iron complex (FeOH²⁺) and ferric hydroxides precipitation, leading to a reduction in the fluorene degradation rate. With regard to the PFF tests, similar fluorene degradation performance was achieved at pH 4 and 5, while at pH 6 iron precipitation became relevant and the degradation rate was slightly slower. PFF has shown to be more efficient than the PF under the same pH (4) and iron concentration (2 mg L^-1). Moreover, even at near neutral pH (6), fluorine degradation was shown to be feasible by using ferrioxalate complexes.

Modelling PAH partitioning during sludge disintegration: The key role of dissolved and colloidal matter

The partitioning between solids and the aqueous phase largely controls the fate of PAH compounds in biological treatment. The prediction of PAH sorption behaviour into activated sludge was investigated here. The suitability of a three-compartment model to describe partitioning in such a complex matrix was first evaluated by adding increasing quantities of dissolved and colloidal matter (DCM) (from 0 to 34.9% of the total matter). In a range of DCM concentrations varying from 0 to 1.4 g L^-1, the PAH aqueous fraction, including both freely dissolved and sorbed to DCM molecules, increased from 9.9% to 33% for naphthalene (the most soluble PAH) and from 0.29% to 13.3% for indeno(1,2,3,c,d)pyrene (the least soluble PAH tested). The sorption of PAHs on dissolved and colloidal matter (DCM) was assessed by determining two partitioning constants (K_PART and K_DCM) for the 16 PAHs listed by the US EPA. New experiments were carried out for model validation and show that the model properly predicts the PAH partitioning following sludge disintegration by sonication.

Removal and fate of polycyclic aromatic hydrocarbons in a hybrid anaerobic-anoxic-oxic process for highly toxic coke wastewater treatment

Elimination of polycyclic aromatic hydrocarbons (PAHs) from coke wastewater is crucial to minimize the PAHs contamination levels to the environment. Knowledge about the characteristics of PAHs removal in biological treatment processes, especially hybrid systems, for real coke wastewater treatment has been very scarce. In this study, a lab-scale hybrid anaerobic-anoxic-oxic (A₁/A₂/O) process was used to treat highly toxic coke wastewater and operated more than 600 d at total hydraulic retention time (HRT) of 50 h, 40 h, 30 h, 20 h and internal mixed liquor recirculation ratio (R) of 3, 6, 9. Removal performance and behaviors of priority PAHs in the hybrid A₁/A₂/O system were investigated. The results showed that the appropriate total HRT and R from oxic reactor to anoxic reactor for organics and nitrogen removal was 40 h and 3, respectively. The concentrations of total PAHs were very high (254-488 μg/L) in the raw coke wastewater, and effectively reduced to 4.1-4.5 μg/L in the final effluent by the present system under the optimized operational conditions. Among the three treatment units, anoxic reactor made the largest contribution to the total PAHs removal. Large amounts of PAHs (415-1310 μg/g) were adsorbed to the activated sludge in the anoxic and oxic reactor, leading to a much higher load of PAHs (2535 μg/d) in the excess sludge than that in the treated coke wastewater (93 μg/d) at SRT 60 d. Therefore, the excess sludge was identified as the major emission source of PAHs in coke wastewater during the hybrid A₁/A₂/O process, and might pose an environmental risk if the excess sludge was not properly treated and disposed.

Appraisement, source apportionment and health risk of polycyclic aromatic hydrocarbons (PAHs) in vehicle-wash wastewater, Pakistan

Vehicle-wash wastewater (VWW) contains elevated concentrations of different petrochemicals including polycyclic aromatic hydrocarbons (PAHs), a carcinogenic group of organic compounds. This study investigates the discharge of PAHs present in the untreated wastewater of vehicle-wash stations (VWS) located in district Peshawar, Pakistan. The data obtained was being novel with the detection of 16 USEPA PAHs (both individuals and total) and compared with earlier studies and international standards. The ∑16PAHs in wastewater from light vehicle-wash stations (LVWS) and heavy vehicle-wash stations (HVWS) ranged from 245-429μg/l and 957-1582μg/l, respectively. A significant difference (p<0.01) was observed in PAHs discharged from LVWS and HVWS. The projected ∑16PAHs discharge from both HVWS (92% of total generated PAHs) and LVWS (8%) was about 5109.9 g per annum. According to PAH diagnostic ratios, PAHs were both petrogenic (chrysene/benz(a)anthracene, low molecular weight/high molecular weight) and pyrogenic (phenanthrene/anthracene, fluoranthene/pyrene, fluoranthene/fluoranthene+pyrene) in origin. The highest toxic equivalent quotient (TEQ) value was shown by benzo(a)pyrene (21.6μg/l) followed by dibenz(ah)anthracene (9.81μg/l) in wastewater from HVWS. However, in LVWS the case was reversed with highest value (7.54μg/l) for dibenz(ah)anthracene followed by benzo(a)pyrene (3.54μg/l). The lowest TEQ value was indicated for phenanthrene (0.007μg/l) in wastewater of LVWS, while pyrene showed the lowest value (0.007μg/l) in wastewater of HVWS. The results indicated that VWS contribute significant amount of PAHs each year, which is of great concern regarding water quality, ecological and human health risk. This is the first systematic and comprehensive research related with generation of PAHs load per day, week, month and annum from VWS, their source apportionment and health effects in Pakistan.

Combination of polycyclic aromatic hydrocarbons and temperature exposure: In vitro effects on immune response of European clam (Ruditapes decussatus)

Marine organisms are subjected to various biotic and abiotic factors such as changes of temperature and pollutants [e.g. polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and heavy metals, which may affect their defense mechanisms. In this context, the aim was to evaluate the combined effects of temperature (20 and 30 °C) and PAHs (fluorene, phenanthrene and pyrene) at two concentrations (10^-5 and 10^-3 mg mL^-1) on the immune responses of the European clam Ruditapes decussatus were after 24 h of in vitro exposure. Total haemocyte count, cell viability, phenoloxidase, lysozyme, alkaline phosphatase, esterase, antibacterial and agglutinating activities were measured. Exposure to high temperatures resulted in lower phosphatase alkaline activity and higher haemocyte viability and antibacterial and haemagglutinating activities, compared with the values recorded for clams maintained at low temperature. Only pyrene induced a significant decrease in haemocyte lysozyme (at 20 and 30 °C) and esterase (at 30 °C) activities. The total haemocyte count was increased by phenanthrene and pyrene at 20 °C and at 30 °C, respectively. Alkaline phosphatase activity increased when haemocytes were exposed to pyrene at 30 °C but decreased in the presence of fluorene at 20 °C. Furthermore, haemocyte viability was low in the presence of pyrene and fluorene at 20 °C and 30 °C, respectively, but was unaffected by phenanthrene. Antibacterial activity was significantly increased and no-significantly affected by the presence of pyrene and fluorene at 20 °C and 30 °C, respectively. The present study demonstrates the strong effect of PAHs and high temperature on haemocyte viability and other important immune functions, including phosphatase alkaline and antibacterial activities. Furthermore, changes in the immune parameters of European clam resulting from high temperatures may modulate the effects of PAHs and vice versa.

Removal Efficiency and Risk Assessment of Polycyclic Aromatic Hydrocarbons in a Typical Municipal Wastewater Treatment Facility in Guangzhou, China

The loading and removal efficiency of 16 US EPA polycyclic aromatic hydrocarbons (PAHs) were examined in an inverted A²/O wastewater treatment plant (WWTP) located in an urban area in China. The total PAH concentrations were 554.3 to 723.2 ng/L in the influent and 189.6 to 262.7 ng/L in the effluent. The removal efficiencies of ∑PAHs in the dissolved phase ranged from 63 to 69%, with the highest observed in naphthalene (80% removal). Concentration and distribution of PAHs revealed that the higher molecular weight PAHs became more concentrated with treatment in both the dissolved phase and the dewatered sludge. The sharpest reduction was observed during the pretreatment and the biological phase. Noncarcinogenic risk, carcinogenic risk, and total health risk of PAHs found in the effluent and sewage sludge were also assessed. The effluent BaP toxic equivalent quantities (TEQ_BaP) were above, or far above, standards in countries. The potential toxicities of PAHs in sewage effluent were approximately 10 to 15 times higher than the acceptable risk level in China. The health risk associated with the sewage sludge also exceeded international recommended levels and was mainly contributed from seven carcinogenic PAHs. Given that WWTP effluent is a major PAH contributor to surface water bodies in China and better reduction efficiencies are achievable, the present study highlights the possibility of utilizing WWTPs for restoring water quality in riverine and coastal regions heavily impacted by PAHs contamination.

Single-Cell Real-Time Visualization and Quantification of Perylene Bioaccumulation in Microorganisms

Bioaccumulation of perylene in Escherichia coli and Staphylococcus aureus was visualized and quantified in real time with high sensitivity at high temporal resolution. For the first time, single-molecule fluorescence microscopy (SMFM) with a microfluidic flow chamber and temperature control has enabled us to record the dynamic process of perylene bioaccumulation in single bacterial cells and examine the cell-to-cell heterogeneity. Although with identical genomes, individual E. coli cells exhibited a high degree of heterogeneity in perylene accumulation dynamics, as shown by the high coefficient of variation (C.V = 1.40). This remarkable heterogeneity was exhibited only in live E. coli cells. However, the bioaccumulation of perylene in live and dead S. aureus cells showed similar patterns with a low degree of heterogeneity (C.V = 0.36). We found that the efflux systems associated with Tol C played an essential role in perylene bioaccumulation in E. coli, which caused a significantly lower accumulation and a high cell-to-cell heterogeneity. In comparison with E. coli, the Gram-positive bacteria S. aureus lacked an efficient efflux system against perylene. Therefore, perylene bioaccumulation in S. aureus was simply a passive diffusion process across the cell membrane.

Organic Pollutants in Shale Gas Flowback and Produced Waters: Identification, Potential Ecological Impact, and Implications for Treatment Strategies

Organic contaminants in shale gas flowback and produced water (FPW) are traditionally expressed as total organic carbon (TOC) or chemical oxygen demand (COD), though these parameters do not provide information on the toxicity and environmental fate of individual components. This review addresses identification of individual organic contaminants in FPW, and stresses the gaps in the knowledge on FPW composition that exist so far. Furthermore, the risk quotient approach was applied to predict the toxicity of the quantified organic compounds for fresh water organisms in recipient surface waters. This resulted in an identification of a number of FPW related organic compounds that are potentially harmful namely those compounds originating from shale formations (e.g., polycyclic aromatic hydrocarbons, phthalates), fracturing fluids (e.g., quaternary ammonium biocides, 2-butoxyethanol) and downhole transformations of organic compounds (e.g., carbon disulfide, halogenated organic compounds). Removal of these compounds by FPW treatment processes is reviewed and potential and efficient abatement strategies are defined.

Profiles and removal efficiency of polycyclic aromatic hydrocarbons by two different types of sewage treatment plants in Hong Kong

Sewage discharge could be a major source of polycyclic aromatic hydrocarbons (PAHs) in the coastal waters. Stonecutters Island and Shatin Sewage Treatment Works (SCISTW and STSTW) in Hong Kong, adopted chemically enhanced primary treatment and biological treatment, respectively. This study aimed at (1) determining the removal efficiencies of PAHs, (2) comparing the capabilities in removing PAHs, and (3) characterizing the profile of each individual PAHs, in the two sewage treatment plants (STPs). Quantification of 16 PAHs was conducted by a Gas Chromatography. The concentrations of total PAHs decreased gradually along the treatment processes (from 301±255 and 307±217ng/L to 14.9±12.1 and 63.3±54.1ng/L in STSTW and SCISTW, respectively). It was noted that STSTW was more capable in removing total PAHs than SCISTW with average total removal efficiency 94.4%±4.12% vs. 79.2%±7.48% (p<0.05). The removal of PAHs was probably due to sorption in particular matter, confirmed by the higher distribution coefficient of individual and total PAHs in solid samples (dewatered sludge contained 92.5% and 74.7% of total PAHs in SCISTW and STSTW, respectively) than liquid samples (final effluent-total contained 7.53% and 25.3% of total PAHs in STSTW and SCISTW, respectively). Despite the impressive capability of STSTW and SCISTW in removing PAHs, there was still a considerable amount of total PAHs (1.85 and 39.3kg/year, respectively for the two STPs) being discharged into Hong Kong coastal waters, which would be an environmental concern.

Fate and mass balance of triclosan and its degradation products: Comparison of three different types of wastewater treatments and aerobic/anaerobic sludge digestion

Triclosan (TCS) as an antimicrobial agent has been ubiquitously found in wastewater and sewage sludge. TCS may undergo transformation/degradation during wastewater treatment. Some of the resulted products such as 2,4-dichlorophenol (2,4-DCP), 2,8-dichlorodibenzoparadioxin (2,8-DCDD) and methyl triclosan (MTCS) are presumed toxic/persistent compounds. In this study, fate of TCS and the probability of formation of important degradation products were investigated in three susceptible wastewater/sludge treatment practices. 24.1% and 27.2% of the loading TCS was adsorbed to the generated sludge, whereas up to 60% of the loading TCS was biotransformed. Up to 9.9% and 13.0% of TCS loss was attributed to the formation of 2,4-DCP and 2,8-DCDD in chlorination and UV disinfection, respectively. Anaerobic and aerobic sludge digestion processes eliminated up to 23.0% and 56.0% of TCS, respectively. About 7.4% of TCS in aerobic digestion was transformed to methyl triclosan (MTCS). Significant temporal variation of TCS was observed in primary sedimentations, except for chemically enhanced primary treatment that was suggested to be governed by chemical-forced sedimentation. Distribution coefficient (K_d) of TCS was directly correlated to the total organic carbon of the sludge (TOC). Moreover, strong correlation was observed between elimination efficiency in primary sedimentation and loading concentration.

Treatment effects and genotoxicity relevance of the toxic organic pollutants in semi-coking wastewater by combined treatment process

The removal effects of main toxic organic pollutants in semi-coking wastewater by combined treatment process were investigated, while the genotoxicity relevance of wastewater from different treatment units were monitored by using Vicia faba bioassays. Results showed that 37 kinds of toxic organic pollutants were detected in the crude sewage, most of them were removed by physicochemical pretreatment, and the total concentration of organic pollutants decreased from 4826 mg L^-1 to 546 mg L^-1. After pretreatment, benzenes, phenols, quinolines and indoles in the wastewater were mainly removed by anaerobic/aerobic biodegradation, but the polycyclic aromatic hydrocarbons (PAHs) were removed mainly by advanced treatment, total concentration of toxic organic pollutants was lower than 0.5 mg L^-1 in the effluent. Genotoxicity evaluation results showed that the wastewater from coagulating sedimentation unit or foregoing had significant mutagenic properties. However, the micronuclei (MN) frequency (‰, which was calculated by observing 1000 cells) induced by wastewater after adsorption with modified coke was only 8.06‰, it was no significant difference compared with negative control (7.43‰). It could be concluded that the adsorption treatment was required for the safety of effluent, and the physicochemical-biochemical combined process in this study was suitable for high concentration semi-coking wastewater treatment.

Enhanced adsorbability and photocatalytic activity of TiO2-graphene composite for polycyclic aromatic hydrocarbons removal in aqueous phase

Photodegradation via titanium dioxide (TiO₂) has been used to remove polycyclic aromatic hydrocarbons (PAHs) from environmental media broadly. In this study, a series of TiO₂-graphene composites (P25-GR) with different GR weight ratios were synthesized via hydrothermal reaction of graphene oxide (GO) and P25. Their structures were characterized and the proprieties were tested in aqueous phase. Phenanthrene (PHE), fluoranthene (FLAN), and benzo[a]pyrene (BaP) were selected as models of PAHs. The experiment indicated that P25-2.5%GR exhibited enhancement in both adsorption and photodegradation, ∼80% of PAHs were removed after 2h photocatalysis. The influence of photodegradation rate was studied, including PAHs initial concentration and pH. Aromatic intermediates were identified during the reaction process and the degradation pathways were portrayed. This work explored the enhanced photocatalysis performance was attributed to the PAH-selective adsorbability and the strong electron transfer ability of the composite. The analysis of the degradation intermediates confirmed that the reaction proceeded with the formation of free radicals, leading to the gradual PAH mineralization.

Distribution, Fate, Inhalation Exposure and Lung Cancer Risk of Atmospheric Polycyclic Aromatic Hydrocarbons in Some Asian Countries

A large-scale monitoring program, the Asia Soil and Air Monitoring Program (Asia-SAMP), was conducted in five Asian countries, including China, Japan, South Korea, Vietnam, and India. Air samples were collected using passive air samplers with polyurethane foam disks over four consecutive 3-month periods from September 2012 to August 2013 to measure the seasonal concentrations of 47 polycyclic aromatic hydrocarbons (PAHs), including 21 parent and 26 alkylated PAHs, at 176 sites (11 background, 83 rural, and 82 urban). The annual concentrations of total 47 PAHs (∑47PAHs) at all sites ranged from 6.29 to 688 ng/m(3) with median of 82.2 ng/m(3). Air concentrations of PAHs in China, Vietnam, and India were greater than those in Japan and South Korea. As expected, the air concentrations (ng/m(3)) were highest at urban sites (143 ± 117) followed by rural (126 ± 147) and background sites (22.4 ± 11.4). Significant positive correlations were found between PAH concentrations and atmosphere aerosol optical depth. The average benzo(a)pyrene equivalent concentration (BaPeq) was 5.61 ng/m(3). It was estimated that the annual BaPeq concentrations at 78.8% of the sampling sites exceeded the WHO guideline level. The mean population attributable fraction (PAF) for lung cancer due to inhalation exposure to outdoor PAHs was on the order 8.8‰ (0.056-52‰) for China, 0.38‰ (0.007-3.2‰) for Japan, 0.85‰ (0.042-4.5‰) for South Korea, 7.5‰ (0.26-27‰) for Vietnam, and 3.2‰ (0.047-20‰) for India. We estimated a number of lifetime excess lung cancer cases caused by exposure to PAHs, which the concentrations ranging from 27.8 to 2200, 1.36 to 108, 2.45 to 194, 21.8 to 1730, and 9.10 to 720 per million people for China, Japan, South Korea, Vietnam, and India, respectively. Overall, the lung cancer risk in China and Vietnam were higher than that in Japan, South Korea, and India.

Distribution, partition and removal of polycyclic aromatic hydrocarbons (PAHs) during coking wastewater treatment processes

In this study, we report the performance of a full-scale conventional activated sludge (A-O1-O2) treatment in eliminating polycyclic aromatic hydrocarbons (PAHs). Both aqueous and solid phases along with the coking wastewater treatment processes were analyzed for the presence of 18 PAHs. It was found that the target compounds occurred widely in raw coking wastewater, treated effluent and sludge samples. In the coking wastewater treatment system, 4-5 ring PAHs were the dominant compounds, while 4 rings PAHs predominated in the sludge samples. Over 98% of the PAH removal was achieved in the coking wastewater treatment plant (WWTP), with the total concentration of PAHs being 21.3 ± 1.9 μg L(-1) in the final effluent. During the coking wastewater treatment processes, the association of the lower molecular weight PAH with suspended solids was generally less than 60%, while the association of higher molecular weight PAHs was greater than 90%. High distribution efficiencies (Kdp and Kds) were found, suggesting that adsorption was the potential removal pathway of PAHs. Finally, the mass balances of PAHs in various stages of the coking WWTP were obtained, and the results indicated that adsorption to sludge was the main removal pathway for PAHs in the coking wastewater treatment processes.

Removal of polycyclic aromatic hydrocarbons in aqueous environment by chemical treatments: a review

Due to their carcinogenic, mutagenic and teratogenic potential, the removal of polycyclic aromatic hydrocarbons (PAHs) from aqueous environment using physical, biological and chemical processes has been studied by several researchers. This paper reviews the current state of knowledge concerning PAHs including their physico-chemical properties, input sources, occurrence, adverse effects and conventional and alternative chemical processes applied for their removal from water. The mechanisms and reactions involved in each treatment method are reported, and the effects of various variables on the PAH degradation rate as well as the extent of degradation are also discussed. Extensive literature analysis has shown that an effective way to perform the conversion and mineralization of this type of substances is the application of advanced oxidation processes (AOPs). Furthermore, combined processes, particularly AOPs coupled with biological treatments, seem to be one of the best solutions for the treatment of effluents containing PAHs.

Biofiltration vs conventional activated sludge plants: what about priority and emerging pollutants removal?

This paper compares the removal performances of two complete wastewater treatment plants (WWTPs) for all priority substances listed in the Water Framework Directive and additional compounds of interest including flame retardants, surfactants, pesticides, and personal care products (PCPs) (n = 104). First, primary treatments such as physicochemical lamellar settling (PCLS) and primary settling (PS) are compared. Similarly, biofiltration (BF) and conventional activated sludge (CAS) are then examined. Finally, the removal efficiency per unit of nitrogen removed of both WWTPs for micropollutants is discussed, as nitrogenous pollution treatment results in a special design of processes and operational conditions. For primary treatments, hydrophobic pollutants (log K ow > 4) are well removed (>70 %) for both systems despite high variations of removal. PCLS allows an obvious gain of about 20 % regarding pollutant removals, as a result of better suspended solids elimination and possible coagulant impact on soluble compounds. For biological treatments, variations of removal are much weaker, and the majority of pollutants are comparably removed within both systems. Hydrophobic and volatile compounds are well (>60 %) or very well removed (>80 %) by sorption and volatilization. Some readily biodegradable molecules are better removed by CAS, indicating a better biodegradation. A better sorption of pollutants on activated sludge could be also expected considering the differences of characteristics between a biofilm and flocs. Finally, comparison of global processes efficiency using removals of micropollutants load normalized to nitrogen shows that PCLS + BF is as efficient as PS + CAS despite a higher compactness and a shorter hydraulic retention time (HRT). Only some groups of pollutants seem better removed by PS + CAS like alkylphenols, flame retardants, or di-2-ethylhexyl phthalate (DEHP), thanks to better biodegradation and sorption resulting from HRT and biomass characteristics. For both processes, and out of the 68 molecules found in raw water, only half of them are still detected in the water discharged, most of the time close to their detection limit. However, some of them are detected at higher concentrations (>1 μg/L and/or lower than environmental quality standards), which is problematic as they represent a threat for aquatic environment.

Identification and removal of polycyclic aromatic hydrocarbons in wastewater treatment processes from coke production plants

Identification and removal of polycyclic aromatic hydrocarbons (PAHs) were investigated at two coke plants located in Shaoguan, Guangdong Province of China. Samples of raw coking wastewaters and wastewaters from subunits of a coke production plant were analyzed using gas chromatography-mass spectrometry (GC/MS) to provide a detailed chemical characterization of PAHs. The identification and characterization of PAH isomers was based on a positive match of mass spectral data of sample peaks with those for PAH isomers in mass spectra databases with electron impact ionization mass spectra and retention times of internal reference compounds. In total, 270 PAH compounds including numerous nitrogen, oxygen, and sulfur heteroatomic derivatives were positively identified for the first time. Quantitative analysis of target PAHs revealed that total PAH concentrations in coking wastewaters were in the range of 98.5 ± 8.9 to 216 ± 20.2 μg/L, with 3-4-ring PAHs as dominant compounds. Calculation of daily PAH output from four plant subunits indicated that PAHs in the coking wastewater came mainly from ammonia stripping wastewater. Coking wastewater treatment processes played an important role in removing PAHs in coking wastewater, successfully removing 92 % of the target compounds. However, 69 weakly polar compounds, including PAH isomers, were still discharged in the final effluent, producing 8.8 ± 2.7 to 31.9 ± 6.8 g/day of PAHs with potential toxicity to environmental waters. The study of coking wastewater herein proposed can be used to better predict improvement of coke production facilities and treatment conditions according to the identification and removal of PAHs in the coke plant as well as to assess risks associated with continuous discharge of these contaminants to receiving waters.

Sources, fluxes and risk of organic micropollutants to the Cantabrian Sea (Spain)

The sources, distribution and risk of 51 organic micropollutants (OMPs) in the Cantabrian coastal environment (NW Spain) were evaluated. Gas chromatography coupled to tandem mass spectrometry was used to determine polycyclic aromatic hydrocarbons, polychlorinated biphenyls, organochlorinated pesticides, polybrominated diphenyl ethers, phthalates esters, bisphenol A and alkylphenols. 45 OMPs were detected in coastal/estuarine waters. Wastewater treatment plant effluents and emissary discharges were identified as the main sources of contamination. The accumulation of OMPs in sediments and the bioaccumulation in 21 days caged mussels were also assessed. Chemical results were combined with the "Combined Monitoring-based and Modeling-based Priority Setting Scheme" COMMPS procedure for risk assessment analysis. Finally, the chemical status of the different sampling locations was estimated using site risk indexes. Those indexes can be conveniently displayed in quality geographical maps and are considered a valuable tool for the environmental management and risk assessment of the region under study.

Characterization, treatment and releases of PBDEs and PAHs in a typical municipal sewage treatment plant situated beside an urban river, East China

Characterization, treatment and releases of eight polybrominated diphenyl ethers (PBDEs) congeners and sixteen polycyclic aromatic hydrocarbons (PAHs) in wastewater were evaluated along the treatment processes of a typical secondary treatment municipal sewage treatment plant (STP) (in Hefei City) situated the beside Nanfei River, East China. The findings showed that the average concentrations of the total PBDEs in raw wastewater and treated effluent were 188.578 and 36.884 ng/L respectively. Brominated diphenyl ether (BDE) 209 congener, the predominant PBDE in the STP and Nanfei River, could be related to the discharge of car-industry-derived wastes. For PAHs, the average concentrations in raw wastewater and treated effluent were 5758.8 and 2240.4 ng/L respectively, with naphthalene, benzo[a]pyrene and indeno[1,2,3-c,d]pyrene being detected at the highest concentrations. PAHs mainly originate from the combustion of biomass/coal and petroleum. The STP reduced about 80% of the PBDEs and 61% of the PAHs, which were eliminated mainly by sedimentation processes. The removal rates of PBDEs/PAHs increased with the increase of their solid-water partitioning coefficients. Accordingly, the STP's effluent, containing some PBDE congeners (e.g., BDE 47, 99 and 209, etc.) and low-molecular-weight PAHs, could be an important contributor of these contaminants' input to Nanfei River. It resulted in a significant increase of PBDE/PAH concentrations and PAH toxicological risk in the river water downstream. About 4.040 kg/yr of PBDEs and 245.324 kg/yr of PAHs could be released into the Nanfei River. The current conventional wastewater treatment processes should be improved to remove the relatively low-molecular-weight PBDEs/PAHs more effectively.

Adsorption of Polycyclic aromatic hydrocarbons (fluoranthene and anthracenemethanol) by functional graphene oxide and removal by pH and temperature-sensitive coagulation

A new kind of functional graphene oxide with fine stability in water was fabricated by mixing graphene oxide (GO) and brilliant blue (BB) with a certain weight ratio. The adsorption performance of this mixture of BB and GO (BBGO) to polycyclic aromatic hydrocarbons (anthracenemethanol (AC) and fluoranthene (FL)) was investigated, and the results indicated BBGO possessed adsorption capacity of 1.676 mmol/g and removal efficiency of 72.7% as to AC and adsorption capacity of 2.212 mmol/g and removal efficiency of 93.2% as to FL. After adsorption, pH and temperature-sensitive coagulation (PTC) method was used to remove the AC/BBGO or FL/BBGO complex and proved to be an effective approach to flocculate the AC/BBGO or FL/BBGO complex into large flocs, which tended to be removed from the aqueous solution.

Occurrence of polycyclic aromatic hydrocarbons in sludges from different stages of a wastewater treatment plant in Italy

The occurrence of polycyclic aromatic hydrocarbons (PAHs) in various sludge types from a moderate-big wastewater treatment plant in the Lombardy region, Italy, was studied. Pyrene was continuously the most abundant PAH, whereas anthracene was the PAH with the lowest concentrations. Average sigmaPAH concentrations ranged between 2405 ng/g (dry weight) in the secondary sludge and 2645 ng/g (dry weight) in the final sludge. A mass balance estimation between the various sludges showed no evident degradation of PAHs. The final sludge PAH concentrations were constantly at around half of the maximum permissible limit set by the European Union for use of sewage sludge in agriculture (6 mg/kg). The highest PAH concentrations were observed during the summer periods. Finally, two approaches were used to estimate the raw wastewater concentrations based on the sludge PAH concentrations. The values obtained did not differ much from the average concentrations measured at the influent wastewaters.

Using slow-release permanganate candles to remediate PAH-contaminated water

Surface waters impacted by urban runoff in metropolitan areas are becoming increasingly contaminated with polycyclic aromatic hydrocarbons (PAHs). Slow-release oxidant candles (paraffin-KMnO(4)) are a relatively new technology being used to treat contaminated groundwater and could potentially be used to treat urban runoff. Given that these candles only release permanganate when submerged, the ephemeral nature of runoff events would influence when the permanganate is released for treating PAHs. Our objective was to determine if slow-release permanganate candles could be used to degrade and mineralize PAHs. Batch experiments quantified PAH degradation rates in the presence of the oxidant candles. Results showed most of the 16 PAHs tested were degraded within 2-4 h. Using (14)C-labled phenanthrene and benzo(a)pyrene, we demonstrated that the wax matrix of the candle initially adsorbs the PAH, but then releases the PAH back into solution as transformed, more water soluble products. While permanganate was unable to mineralize the PAHs (i.e., convert to CO(2)), we found that the permanganate-treated PAHs were much more biodegradable in soil microcosms. To test the concept of using candles to treat PAHs in multiple runoff events, we used a flow-through system where urban runoff water was pumped over a miniature candle in repetitive wet-dry, 24-h cycles. Results showed that the candle was robust in removing PAHs by repeatedly releasing permanganate and degrading the PAHs. These results provide proof-of-concept that permanganate candles could potentially provide a low-cost, low-maintenance approach to remediating PAH-contaminated water.