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

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.

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.

Occurrence, behavior and fate of liquid crystal monomers in municipal wastewater

Liquid crystal monomers (LCMs), the essential substances used in the display screen of electronic devices, have been proposed as a class of emerging chemicals of concern. Despite their detection in various environmental matrices, little is known about the presence of LCMs in municipal sewage systems. This study aimed to investigate the occurrence, distribution, and fate of 64 LCMs released into the aqueous environment from a municipal wastewater treatment plant (WWTP) in Hong Kong, China. In total 14 LCMs were detected in WWTP samples. Specifically, the Σ14LCMs concentrations in crude influent, final effluent, and final sludge were found to be 16.8 ± 0.3 ng/L, 2.71 ± 0.05 ng/L, and 19.2 ± 1.0 ng/g dry weight, respectively. Among them, 10 fluorinated LCMs (F-LCMs) were determined to be present at concentrations of 8.90 ± 0.10 ng/L, 1.69 ± 0.05 ng/L, and 9.94 ± 1.00 ng/g dry weight, respectively. The predominant non-fluorinated LCMs (NF-LCMs) detected in all samples were 3OCB and EPhEMOB, while 2OdF3B was the dominant F-LCM. The overall removal rate of total LCMs was 83.8 ± 0.3 %, with 25.4 ± 4.8 % being removed by biodegradation and UV treatment. Compared to NF-LCMs, F-LCMs were more resistant to biodegradation. Despite the significant removal of LCMs through WWTP, the remaining LCMs in final effluent could result in an annual emission of 3.04 kg of total LCMs from the population of Hong Kong. This study provides the first evidence of LCMs contamination in municipal wastewater, possibly arising from routine electronic devices usage. Further investigation is needed to elucidate the potential impact of LCMs emission via WWTP effluent on the aquatic receiving ecosystem.

Concentration of the main persistent organic pollutants in sewage sludge in relation to wastewater treatment plant parameters and sludge stabilisation

Concentration of 16 polycyclic aromatic hydrocarbons (PAHs), 7 polychlorinated biphenyls (PCBs), and 11 organochlorine pesticides (OCPs) in sewage sludge from 40 wastewater treatment plants (WWTPs) was investigated. Relationship between pollutant sludge contents, main WWTP parameters and type of sludge stabilisation was carefully evaluated. Average load of PAHs, PCBs, and OCPs in different sludges from Czech Republic was 3096, 95.7 and 76.1 μg/kg dry weight, respectively. There were moderate/strong correlations among the individual tested pollutants in sludge (r = 0.40-0.76). Relationship between total pollutant contents in sludge, common WWTP parameters and sludge stabilisation was not evident. Only individual pollutants such anthracene and PCB 52 correlated significantly (P < 0.05) with biochemical oxygen demand (r = -0.35) and chemical oxygen demand removal efficiencies (r = -0.35), suggesting recalcitrance to degradation during wastewater treatment. When sorted according to the design capacity, a linear correlation between WWTP size and pollutant contents in sludge was evident with growing WWTP capacity. Our study indicated that WWTPs with anaerobic digestion are prone to accumulate a statistically higher content of PAHs and PCBs (P < 0.05) in digested sludges compared to aerobically digested ones. The influence of anaerobic digestion temperature of treated sludge on tested pollutants was not evident.

Enhanced waste activated sludge dewaterability by the ozone-peroxymonosulfate oxidation process: Performance, sludge characteristics, and implication

Dewatering treatment is an essential step to diminish sludge volume, cut down transportation costs, and improve subsequent disposal efficiency. In this study, ozone-peroxymonosulfate (O₃/PMS) oxidation process was employed to ameliorate sludge dewaterability. Sludge capillary suction time (CST) and water content (Wc) of dewatered sludge cake could reduce from 70.5 s and 81.93% to 26.7 s and 65.65%, respectively, under the optimal dosage of 30 mg/g TS O₃ and 0.4 mmol/g TS PMS. The increased sludge zeta potential, particle size, and fluidity promoted sludge dewatering performance apparently. The decreased hydrophilic, fluorescent EPS components and proteins/peptides-like + Lipids percentage in EPS as well as the ratio of α-helix/(β-sheet + random coil) of treated EPS protein secondary structure was greatly responsible for the enhanced sludge dewaterability. SO₄^- and OH were detected in ozone-peroxymonosulfate process to crack sludge flocs, eliminate hydrophilic substances and liberate bound water. Moreover, the concentrations of both heavy metals and polycyclic aromatic hydrocarbons (PAHs) of sludge after O₃/PMS conditioning were decreased, and the stability and toxicity of heavy metals were also reduced, except Zn. In conclusion, this work offered a comprehensive insight based on ozone-peroxymonosulfate (O₃/PMS) advanced oxidation for improving the sludge dewaterability and environmental implication.

Influence of sludge organic matter on elimination of polycyclic aromatic hydrocarbons (PAHs) from waste activated sludge by ozonation: Controversy over aromatic compounds

Ozonation has been widely used as a viable advanced oxidation process (AOP) for elimination of PAHs in waste activated sludge through effective sludge disintegration and abatement of organic pollutants. However, sludge organic matter (SOM) influences PAHs degradation during ozone treatment is still rarely understood. In this study, we investigated such an influence with the aid of solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy and the corresponding two-dimensional correlation analysis (2D-COS) strategy. The results showed that the degradation of SOM macromolecules in the order of aromatic substances > aliphatic carbon > α carbon > amides groups > O-alkyl upon ozone treatment. Moreover, the PAHs removal efficiency was positively correlated with the aromaticity of sludge (R² = 0.84-0.98), while negative associated with its aliphaticity (R² = 0.81-0.95). Lastly, humic acid (HA) was used as a proxy of aromatic SOM to further explore their interaction with PAHs in sludge matrix. The results revealed that freely dissolved (HA-D) and suspended particulates (HA-S) imposed distinctively different influence on ozone-based PAHs degradation. The HA-S facilitated the elimination of PAHs by 7.95 ± 0.11%, while those HA-D reduced the removal efficiency by 16.70 ± 0.13%.

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.

Determination of Polycyclic Aromatic Hydrocarbons and Their Methylated Derivatives in Sewage Sludge from Northeastern China: Occurrence, Profiles and Toxicity Evaluation

This paper assesses the occurrence, distribution, source, and toxicity of polycyclic aromatic hydrocarbons (PAHs), and their methylated form (Me-PAHs) in sewage sludge from 10 WWTPs in Northeastern China was noted. The concentrations of ∑PAHs, ∑Me-PAHs ranged from 567 to 5040 and 48.1 to 479 ng.g−1dw, which is greater than the safety limit for sludge in agriculture in China. High and low molecular weight 4 and 2-ring PAHs and Me-PAHs in sludge were prevalent. The flux of sludge PAHs and Me-PAHs released from ten WWTPs, in Heilongjiang province, was calculated to be over 100 kg/year. Principal component analysis (PCA), diagnostic ratios and positive matrix factorization (PMF) determined a similar mixed pyrogenic and petrogenic source of sewage sludge. The average values of Benzo[a]pyrene was below the safe value of 600 ng.g−1 dependent on an incremental lifetime cancer risk ILCR of 10⁻⁶. Sludge is an important source for the transfer of pollutants into the environment, such as PAHs and Me-PAHs. Consequently, greater consideration should be given to its widespread occurrence.

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.

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.

Ecological risks of heavy metals/metalloid discharged from two sewage treatment works to Mai Po Ramsar site, South China

The concentrations of six heavy metal/metalloids (HMs) cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), zinc (Zn), and arsenic (As) were determined in the influent, effluent, and dewatered sludge of two sewage treatment works (Yuen Long Sewage Treatment Work (YLSTW) and Shek Wu Hui Sewage Treatment Work (SWHSTW)) and river waters and sediment (Shan Pui River and Ng Tung River) within the Mai Po Ramsar site in Hong Kong SAR, China. In both STWs, Pb had the highest removal efficiencies (YLSTW 86.5 ± 19.0% to 97.3 ± 3.04%; SWHSTW 87.4 ± 12.8% to 100 ± 0.0800%). In the whole effluent toxicity test, both STWs were effective in lowering the toxicity of the effluent to zebrafish and cherry shrimp. The environmental risk assessments of these HMs on three local aquatic organisms, three species of fish, two species of crustaceans, and three species of algae, were calculated based on measured HMs concentrations in river water and sewage samples, and the predicted no-effect concentrations. Results showed that Zn concentrations in all collected samples posed potential risks to all studied aquatic organisms (average risk quotient = 445). The concentrations of Cu in the rivers posed potential risks (average risk quotient = 5.42) to all fish species. It was concluded that Zn and Hg derived from the STWs might pose potential risks to the living organisms inhabiting the Ramsar site, and Cu, Cd, Pb, and As in the rivers were originated from the two rivers and possibly other tributaries.

Alternated biodegradation of naphthalene (NAP), acenaphthylene (ACY) and acenaphthene (ACE) in an aerobic granular sludge reactor (GSBR)

The paper presents quantitative changes of selected 2- and 3-ring PAHs after process phases of GSBR reactor. The studies have been carried out for 264 cycles of GSBR reactor, during which concentration of naphthalene was increased in the range of 3.00-710.00 μg/L, acenaphthylene 1.00-160.00 μg/L, acenaphthene 3.00-440.00 μg/L. GSBR operating cycle consisted of filling (30 min), mixing (90 min), aeration (540 min), sedimentation (10 min), decanting (30 min) and downtime (20 min) phases. Activated sludge dry mass concentration was 4.00 kg/m³. Conducted studies showed that in GSBR reactor naphthalene was degraded with the highest intensity. Results of the statistical analysis confirmed that naphthalene concentrations were statistically significantly different (α = 0.05) after each individual GSBR process phase, while in case of acenaphthene and acenaphthylene, the differences were observed only between mixing and aeration phases. Additionally, equations estimating concentrations of PAHs in treated wastewater were developed. Selected activated sludge technological parameters (sludge volume index, sludge and hydraulic retention time) and concentration of PAHs were used for equations. The R² coefficients of equations were above 0.99, which indicates a good adjustment of estimation to observed values.

Size distribution of particulate polycyclic aromatic hydrocarbons in fresh combustion smoke and ambient air: A review

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the atmosphere and they mostly stem from the imperfect combustion of fossil fuels and biofuels. PAHs are inherently associated with homogenous fine particles or distributed to different-sized particles during the aging of air masses. PAHs carried by fine particles undergo a long-range transport to remote areas while those adsorbed on coarse particles have a shorter lifetime in ambient air. More importantly, PAHs with higher molecular weights tend to be bound with finer particles and can deeply enter the lungs, posing severe health risks to humans. Thus, the environmental fate and health effects of particulate PAHs are strongly size-dependent. This review summarizes the size distributions of particulate PAHs freshly emitted from combustion sources as well as the distribution patterns of PAHs in ambient particles. It was found that PAHs from stationary sources are primarily bound to fine particles, which are slightly larger than particles to which PAHs from mobile sources are bound. In ambient air, particulate PAHs are distributed in larger size modes than those in the combustion fume, and the particle size decreases with PAH molecular weight increasing. The relevant mechanisms and influencing factors of particle size distribution changes are illustrated in this article, which are essentially attributed to combustion and ambient temperature as well as the physical and chemical properties of PAHs. Overall, the study on the particle size distribution of PAHs will contribute for a full understanding of the origin, atmospheric behaviors and health effects of particulate PAHs.

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.

Spatial distribution and source identification of hydrophobic organic compounds (HOCs) on sedimentary microplastic in Hong Kong

The spatial distribution, composition and source of hydrophobic organic compounds (HOCs) including polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorinated pesticides (OCPs) of the sedimentary microplastics (0.25-5 mm) in Hong Kong were investigated. The concentration of ΣPAHs ranged between 70.8 and 1509 ng g^-1 with inter-site differences although the regional difference was insignificant, indicating localised pyrolytic and petrogenic input of PAHs. The concentration of ΣPCBs (13-1083 ng g^-1) varied with both study sites and regions with higher concentrations obtained in the western waters, possibly due to the input from Pearl River. Significantly higher concentrations of OCPs on eastern shores highlighted fishing and aquaculture activities in South China Sea a potential major source of OCPs. DDT and its metabolites (DDX, ranged from 1.96 to 626 ng g^-1) were the dominant forms of OCPs (45%-80%). Since most of the DDX existed as DDT, this suggested that there was a fresh input of DDT into the microplastics. As microplastics and HOCs cannot be removed effectively from the environment, reduction of potential ecotoxicological risks should rely on minimizing the use of plastics and HOCs.

Assessing pollution and risk of polycyclic aromatic hydrocarbons in sewage sludge from wastewater treatment plants in China's top coal-producing region

Managing and disposing of sewage sludge have been a severe environmental challenge around the world. China produces hundreds of million tons of sewage sludge annually, and a better understanding of the extent and risk of the associated pollution is of critical importance for implementing environmentally safe regulations and practices. The present study examined the quantity, composition, source, and risk of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge from 18 wastewater treatment plants (WWTPs) in Shaanxi, one of China's top coal-producing provinces. The total concentrations of 16 PAHs varied from 778 to 3264 ng/g dry weight, which is below the upper safety limit (5000 ng/g dry weight) set for the disposal of sludge from municipal wastewater treatment plants for agricultural use in China. However, the concentration of individual PAH compound exceeded the acceptable level prescribed by the Netherland Soil Standard. Three-ring PAHs were the most abundant constituent (50% of total PAHs on average), followed by four-ring PAHs averaging 25%. Relative to sludge PAHs in the same region a decade ago, the total concentrations decreased by more than 27% and the composition shifted to a more pronounced dominance by low molecular weight compounds. This compositional shift suggests higher contributions of petrogenic sources, which may reflect China's increasing consumption of petroleum products over the past decade. The flux of sludge PAHs from each WWTP was positively correlated with the corresponding city's GDP and population, and the total flux amounted to over 100 kg each year for WWTPs in the Xi'an city. The mean toxicity equivalent quantity (TEQ) value was more than twice higher than the value recommended by the Netherlands Soil Standard, and seven carcinogenic PAHs were the primary contributor (i.e., 89-99%) of the TEQ. Collectively, our findings demonstrate that sewage sludge PAHs in Shaanxi constitute a significant source of environmental pollution and toxicity, which cautions against the direct discharge and reuse of sewage sludge and further highlights challenges in managing and disposing of the vast quantities of sewage sludge in China.

A mobile, modular and rapidly-acting treatment system for optimizing and improving the removal of non-aqueous phase liquids (NAPLs) in groundwater

Non-aqueous phase liquids (NAPLs) in pumped groundwater are highly variable, challenging the selection of above-ground treatment strategies in pump-and-treat system. Adjustable systems with multiple treatment units are urgently required. In the present study, a mobile, modular and rapidly-acting treatment system was developed to treat groundwater contaminated by NAPLs at a chemical industrial site. The system integrated four units of coagulation sedimentation, air flotation, air stripping and chemical oxidation. During a 3-month onsite operation, the composition of groundwater NAPLs had huge fluctuations and different treatment units had unique advantages in eliminating some components. For instance, air stripping exhibited satisfactory removal efficiencies (>80%) for short-chain petroleum hydrocarbons and chloroalkanes, but poor performance for others comparing to other units. A decision-making tool and a central control system were further developed to combine and adjust the four units in proper orders, achieving satisfied removal efficiency (70-90%) for multi-component NAPLs, regardless of composition fluctuation. These findings raise the state-of-the-art modular and rapidly-acting groundwater treatment system to clean up NAPLs contaminated groundwater through pump-and-treat strategy, help in better understanding on the decision and management to improve the treatment performance, and provide guidelines for its implication at other sites contaminated with multi-component NAPLs or undergoing accidental contamination.

Monitoring of 943 organic micropollutants in wastewater from municipal wastewater treatment plants with secondary and advanced treatment processes

To perform a systematic survey on the occurrence and removal of micropollutants during municipal wastewater treatment, 943 semi-volatile organic chemicals in 32 wastewater samples including influents of secondary treatments, secondary effluents and final effluents (effluents of advanced treatments), which were collected from seven full-scale municipal wastewater treatment plants (MWTPs) in China, were examined by gas chromatography-mass spectrometry (GC-MS) coupled with an automated identification and quantification system with a database (AIQS-DB). In total, 196 and 145 chemicals were detected in secondary and final effluents, respectively. The majority of the total concentrations (average removal efficiency, 87.0%±5.9%) of the micropollutants were removed during secondary treatments. However, advanced treatments achieved different micropollutant removal extents from secondary effluents depending on the different treatment processes employed. Highly variable removal efficiencies of total concentrations (32.7%-99.3%) were observed among the different advanced processes. Among them, ozonation-based processes could remove 70.0%-80.9% of the total concentrations of studied micropollutants. The potentially harmful micropollutants, based on their detection frequency and concentration in secondary and final effluents, were polycyclic aromatic hydrocarbons (PAHs) (2-methylnaphthalene, fluoranthene, pyrene, naphthalene and phenanthrene), phosphorus flame retardants (tributyl phosphate (TBP), tris(2-chloroethyl) phosphate (TCEP) and tris(1,3-dichloro-2-propyl) phosphate (TDCP)), phthalates (bis(2-ethylhexyl)phthalate (DEHP)), benzothiazoles (benzothiazole, 2-(methylthio)-benzothiazol, and 2(3H)-benzothiazolone) and phenol. This study indicated that the presence of considerable amounts of micropollutants in secondary effluent creates the need for suitable advanced treatment before their reuse.

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.