The fate of di-n-butyl phthalate in a laboratory-scale anaerobic/anoxic/oxic wastewater treatment process

Synthetic microbial community maintains the functional stability of aerobic denitrification under environmental disturbances: Insight into the mechanism of interspecific division of labor

Understanding how synthetic microbial community (SMC) respond to environmental disturbances is the key to realizing SMC engineering applications. Here, dibutyl phthalate (DBP) and levofloxacin (LOFX) were used as environmental disturbances to study their effects on the aerobic denitrification functional stability of SMC composed of Pseudomonas aeruginosa N2 (PA), Acinetobacter baumannii N1(AC) and Aeromonas hydrophila (AH). The results showed that aerobic denitrification efficiency could be maintained at about 93 % under DBP or LOFX disturbance, and interspecific communication was mainly carried out through N-butyryl-L-homoserine lactone (C4-HSL) and N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL), correspondingly. DBP and LOFX induced the acceleration of tricarboxylic acid (TCA) cycle, which facilitated the energy flux and extracellular polymeric substances (EPS) production, thereby allowing SMC to adapt to disturbances. Under DBP disturbance, DBP stimulated phenazine-1-carboxylic acid production to accelerate electron transfer from the quinone pool to complex III, resulting in an increase in electron transfer activity. Up-regulation of complex I, complex III and heme synthesis genes under LOFX disturbance led to enhanced denitrification enzymes expression and electron transfer efficiency. SMC re-regulated different metabolic pathways to build metabolic networks to maintain normal metabolic activity under different disturbances. Overall, SMC maintained functional stability through the labor division in modulation of interspecific communication, formation of defensive barriers, promotion of energy flux, directional transfer of electron flux, and reconstruction of metabolic networks. DBP stimulated AH and PA to occupy functional dominance, while LOFX induced AC and PA to play a major role. The understanding of the stability mechanism under different environmental disturbances provides valuable guidance for stability maintenance and engineering applications of SMC.

Detection of trace chlorine pollutants in recycled pulp using gas chromatography-tandem mass spectrometry with response surface-optimized carbon structure online catalysis

RATIONALE

Chlorinated aromatics and alkanes are widely used for their flame retardancy, but they need to be monitored when used in recycled pulp. This paper reports the use of palladium acetate/activated carbon (Pa/Ac) activated by nitric acid as an online catalyst to determine chlorinated aromatics and chlorinated alkanes in recycled paper products using gas chromatography-tandem mass spectrometry (GC-MS/MS), which significantly improves the sensitivity of the method and remarkably lowers the detection limits.

METHODS

The Pa/Ac catalyst was prepared using a self-made catalytic device and used as key to the online catalytic conversion of target chlorinated aromatic hydrocarbons and chlorinated alkanes for GC-MS/MS analysis. The response surface model was used to optimize catalytic conditions. Then GC-MS/MS in the multireaction monitoring mode with online catalysis was applied for the analysis of polychlorinated biphenyls, polychlorinated terphenyls, polychlorinated naphthalene, and chlorinated paraffins (CP) in recycled paper products.

RESULTS

Compared with traditional methods, the Pa/Ac catalyst can transform chlorinated aromatic hydrocarbons into aromatic hydrocarbons through dechlorination hydrogenation, thus lowering the detection limit of the GC-MS/MS method significantly. It can transform paraffin chloride into the corresponding alkane to better distinguish short-chain, medium-chain, or long-chain CPs. Online catalytic conversion significantly improved the sensitivity and reproducibility (88.7%-113.1%) of the method. Tissue samples with various concentration levels of chlorinated aromatics and chlorinated alkanes were tested. The linearity range of the reduced target compounds in the reduction product solution was 0.02-1.00 μg/ml (R2  > 0.995). The quantitative detection limit was 0.03-0.05 μg/kg, and relative standard deviation was less than 6.9%.

CONCLUSION

This study was the first to introduce the Pa/Ac catalytic device as an online catalytic unit in the determination of chlorinated aromatics and chlorinated alkanes using the GC-MS/MS method. The target compounds were converted into alkanes and aromatic hydrocarbons with unchanged carbon structures, and the method could achieve a low detection limit with no need for high-end methods such as GC-chemical ionization ion source (CI)-MS or high-resolution mass spectrometry. These methods are suitable for the determination of chlorine pollutants in recycled paper and its raw materials.

Effect of hydraulic parameters of leachate treatment process on di(2-ethylhexyl) phthalate removal from aged leachate

The effect of hydraulic parameters of an anaerobic/anoxic/oxic leachate treatment reactor on the removal of di(2-ethylhexyl) phthalate (DEHP) from aged landfill leachate was studied. The mean DEHP removal efficiencies were 79.5%, 87.1%, 89.7% and 87.8% at hydraulic retention times of 6, 4.5, 3 and 2 d, respectively. The removal efficiency of DEHP was significantly higher when the internal reflux ratio was 200% than others. There was no significant difference among the DEHP removal efficiencies at different external reflux ratios of the reactor. Due to the overall efficiency of the reactor, hydraulic retention time 3 d, internal reflux ratio 200% and external reflux ratio 60%, were considered the optimal hydraulic parameters for DEHP removal from aged leachate. The removal efficiency of DEHP was significantly improved (from 75.7% to 89.1%) after the optimization of hydraulic parameters of the reactor. The removal percentages of DEHP in the anaerobic, anoxic, and oxic units of the reactor were 42.8%, 17.6%, and 15.3%, respectively. The oxic microcosms in the reactor had little effect on DEHP removal. The correlation between DEHP and leachate pollutants indicated that DEHP removal was strongly correlated with leachate COD and NH₄⁺-N.

Impacts of dibutyl phthalate on bacterial community composition and carbon and nitrogen metabolic pathways in a municipal wastewater treatment system

Dibutyl phthalate (DBP) is a typical toxic and hazardous pollutant in pharmaceutical wastewater, affecting the metabolism of microbial flora, leading to decreased treatment efficiency, and deteriorated effluent quality in municipal wastewater treatment plants (WWTPs). This study conducted a long-term experiment with 6 operational stages in a pilot-scale A²O-MBR system, analyzing the effect of DBP on the bacterial community and their carbon and nitrogen metabolic pathways. 16S rRNA gene amplicon sequencing analysis and principal components analysis (PCA) showed that DBP at 8 mg/L significantly influenced the structure of bacterial community (P < 0.05), resulting in reduced bacterial community diversity. Metagenomic analysis was used to explore the embedded carbon and nitrogen metabolic pathways. At the presence of DBP, the metabolism of saccharides, lipids, and aromatic compounds were blocked owing to the vanishment of key enzyme (such as acetylaminohexosyltransferase (EC 2.4.1.92) and UDP-sugar pyro phosphorylase (EC 2.7.7.64)) encoding genes, resulting in weakened carbon metabolism, and thus reduced COD removal performance. The resultant deficiency of the genes such as those encoding hydroxyproline dehydrogenase (EC 1.5.5.3) gave rise to interrupted metabolic pathways of amino acid (arginine, proline, tyrosine, and tryptophan), resulting in declined function of nitrogen metabolism and thus reduced TN removal efficiency. The uncovery of the mechanisms by which DBP affects wastewater treatment system efficiency and microbial metabolism is of theoretical importance for the efficient operation of municipal and pharmaceutical wastewater treatment systems.

Impacts of dibutyl phthalate on biological municipal wastewater treatment in a pilot-scale A2/O-MBR system

Dibutyl phthalate (DBP) is a typical contaminant in pharmaceutical wastewater with strong bio-depressive properties which potentially affects the operation of municipal wastewater treatment systems. Based on a year-round monitoring of the quality of influent and effluent of a full-scale pharmaceutical wastewater treatment plant in Northeast China, the DBP was found to be the representative pollutant and its concentration in the effluent ranged 4.28 ± 0.93 mg/L. In this study, the negative effects of DBP on a pilot-scale A²/O-MBR system was investigated. When the influent DBP concentration reached 8.0 mg/L, the removals of chemical oxygen demand (COD) and total nitrogen (TN) were significantly inhabited (P < 0.01), with the effluent concentration of 54.7 ± 2.6 mg/L and 22.8 ± 3.7 mg/L, respectively. The analysis of pollutant removal characteristics of each process unit showed that DBP had the most significant effects on the removals of COD and TN in the anoxic tank. The α- and β-diversity in the system decreased significantly when the influent DBP concentration reached 8.0 mg/L. The impacts of DBP on known nitrifying bacteria, such as Nitrospira, and phosphorus accumulating organisms (PAOs), such as Cadidatus Accumulibacter, were not remarkable. Whereas, DBP negatively affected the proliferation of key denitrifying bacteria, represented by Simplicispira, Dechloromonas and Acinetobacter. This study systematically revealed the impacts of DBP on the pollutants removal performance and the bacterial community structure of the biological municipal wastewater treatment process, which would provide insights for understanding the potential impacts of residues in treated pharmaceutical wastewater on biological municipal wastewater treatment.

Propionate-cultured sludge bioaugmentation to enhance methane production and micropollutant degradation in landfill leachate treatment

This research investigates the use of propionate-cultured sludge to enhance methane (CH₄) production and micropollutant biodegradation in biochemical methane potential (BMP) experiment treating landfill leachate. The experiments were carried out using non-acclimatized and acclimatized seed sludge with variable food to microorganism ratios of 1:1 and 1:2. Under the propionate-cultured sludge bioaugmentation, the concentrations of propionate-cultured sludge were varied between 10, 20, and 30 % (v/v). The acclimatized seed sludge exhibited high microbial abundance and diversity which promoted the CH₄ production and micropollutant biodegradation. The modified Gompertz model indicated that the optimal condition was the acclimatized seed sludge with 30% (v/v) propionate-cultured sludge, achieving the lag time (λ), maximum CH₄ production rate (R_max), and maximum CH₄ potential yield (P_max) of 0.57 day, 17.35 NmL/h, and 140.58 NmL/g COD. The research novelty lies in the use of propionate-cultured sludge bioaugmentation in landfill leachate treatment to enhance CH₄ production and micropollutant biodegradation.

Phthalate Esters Metabolic Strain Gordonia sp. GZ-YC7, a Potential Soil Degrader for High Concentration Di-(2-ethylhexyl) Phthalate

As commonly used chemical plasticizers in plastic products, phthalate esters have become a serious ubiquitous environmental pollutant, such as in soil of plastic film mulch culture. Microbial degradation or transformation was regarded as a suitable strategy to solve the phthalate esters pollution. Thus, a new phthalate esters degrading strain Gordonia sp. GZ-YC7 was isolated in this study, which exhibited the highest di-(2-ethylhexyl) phthalate degradation efficiency under 1000 mg/L and the strongest tolerance to 4000 mg/L. The comparative genomic analysis results showed that there exist diverse esterases for various phthalate esters such as di-(2-ethylhexyl) phthalate and dibutyl phthalate in Gordonia sp. GZ-YC7. This genome characteristic possibly contributes to its broad substrate spectrum, high degrading efficiency, and high tolerance to phthalate esters. Gordonia sp. GZ-YC7 has potential for the bioremediation of phthalate esters in polluted soil environments.

Spatiotemporal Evaluation of Water Quality and Hazardous Substances in Small Coastal Streams According to Watershed Characteristics

In this study, spatial and temporal changes of eight water quality indicators and 30 types of hazardous substances including volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), pesticides, and inorganic matters for the small coastal streams along the West Coast of South Korea were investigated. In coastal streams with clear seasonal changes in water quality, larger watershed areas led to greater contamination by particulate matter (i.e., suspended solids, r = 0.89), and smaller watershed areas led to greater contamination by organic matter (i.e., BOD, r = −0.78). The concentration of VOCs and pesticides was higher in agricultural areas, and those of SVOCs and metals were often higher in urban areas. According to the principal component analysis (PCA), during the wet season, the fluctuation in the water quality of coastal streams was higher in urban areas than in agricultural areas. Furthermore, coastal streams in residential areas exhibited higher levels of SVOCs, and those in industrial areas exhibited higher levels of metallic substances. Based on these results, the spatial and temporal trends of water quality and hazardous substances were obtained according to watershed characteristics, thereby clarifying the pollution characteristics of small-scale coastal streams and the major influencing factors.

Removal of Di-n-butyl phthalate from aged leachate under optimal hydraulic condition of leachate treatment process and in the presence of its dominant bacterial strains

The effects of hydraulic condition of reactor and the dominant degrading bacteria on the removal of di-n-butyl phthalate (DBP) from aged landfill leachate by anaerobic/anoxic/oxic (A/A/O) leachate treatment process were investigated. The optimal DBP removal (96.0%) was obtained from aged leachate when the hydraulic retention time (HRT) of the reactor was 3 d, internal reflux ratio of the reactor was 200%, and external reflux ratio of the reactor was 60%, respectively. The removal efficiency of DBP was significantly improved after the inoculation of the dominant DBP-degrading bacteria (Pseudomonas sp. W1) in the reactor. The mean removal efficiencies of DBP before and after inoculation were 94.1% and 97.7%, respectively. Furthermore, the inoculation of dominant DBP-degrading bacteria changed the original sludge structure and characteristics, which was more conducive to the removal of DBP. These results provide theoretical basis for the effective removal of DBP from aged leachate by the biological treatment process.

Effect of leachate effluent from activated sludge and membrane bioreactor systems with acclimatized sludge on plant seed germination

This research comparatively investigates the effect of landfill leachate effluent of two biological treatment schemes on germination of Lactuca sativa and Vigna radiata. The treatment schemes are two-stage activated sludge (AS) and two-stage membrane bioreactor (MBR) systems with acclimatized seed sludge. The AS and MBR are operated under two concentrations of landfill leachate influent: moderate (condition 1) and elevated (condition 2). The results show that, under condition 1, the AS and MBR efficiently remove 80-96% of organic compounds and nutrients and 81-100% of harmful micropollutants. Under condition 2 with elevated influent concentration, MBR is more effective in biodegrading micropollutants than the AS system. The germination rate (GR) and germination seed index (GSI) of L. sativa and V. radiata germinated with AS and MBR effluent from condition 1 are 100% and 1.29-1.56. Under condition 2, the GR and GSI with AS effluent are reduced to 80% and 0.65-0.77, while those with MBR effluent are 100% and 1.27-1.38. Quantitative real-time polymerase chain reaction (qPCR) analysis indicates that the bacterial community in the MBR is more abundant than in the AS, especially ammonia oxidizing bacteria, Nitrobacter, and Nitrospira, which aid heterotrophic bacteria in biodegradation of micropollutants and promote the growth of heterotrophs. The bacterial abundance and community composition render the MBR scheme more operationally suitable for elevated landfill-leachate influent concentrations. By comparison, the MBR system is more effective in removal of micropollutants than the AS, as evidenced by higher GR and GSI. The technology also could potentially be applied to water reclamation. A lack of technological and financial resources in many developing countries nevertheless precludes the adoption of MBR despite higher pollutant removal efficiency. An alternative solution is the use of acclimatized seed sludge in AS system to enhance treatment efficiency, especially in influent with low concentrations of micropollutants. In addition, the seed germination results suggest the possibility of water reuse in agriculture.

Role of treatment configuration in simultaneous removal of priority phthalic acid esters and nitrogen in a post anoxic integrated biofilm activated sludge system

To develop future wastewater treatment systems, focus is to improve/investigate existing biological wastewater treatment processes for the concurrent treatment of conventional pollution parameters (essentially nitrogen) and micro pollutants. Majority of the existing biological wastewater treatment systems were not designed for the removal of micro pollutants. This study focuses on understanding the role of treatment configuration for efficient removal of nitrogen and priority phthalic acid esters (PAEs) from real municipal wastewater in an integrated biofilm activated sludge (IBAS) system. The reactor was operated in two phases: Run I, without external carbon source in anoxic reactor and Run II, a nitrogen removal process, with partial diversion of untreated wastewater in anoxic reactor. Nitrogen removal was 70 ± 12% in both operational phases, however, during Run I, removal of PAEs fluctuated with an average removal of 60-78%. Comparatively, removal of PAEs in Run II varied over a smaller range with average removal increased to 89-95%. In both operational scenarios, secondary oxic tank contributed maximum to the overall removal of PAEs in treatment system. Mass balance calculations showed significant contribution of biodegradation towards overall removal of PAEs which was enhanced by the supply of external carbon source. Kinetics and model output supported the PAEs removal performance observed in different reaction environments of IBAS process. A correlation between food to microorganism (F/M) ratio and PAEs removal showed increase in PAEs removal with decrease in F/M ratio. The study showed that treatment configuration and F/M ratio may be one of the guiding parameters for efficient removal of PAEs in biological wastewater treatment.

Personal exposure to PM2.5-bound organic species from domestic solid fuel combustion in rural Guanzhong Basin, China: Characteristics and health implication

Domestic solid fuels combustion produces a mass of fine particulate matter (PM_2.5). PM_2.5-bound organics, including polycyclic aromatic hydrocarbons (PAHs), oxygenated-PAHs (OPAHs), phthalate esters (PAEs) and hopanes, were quantified in indoor, outdoor and personal exposure samples collected in rural Guanzhong Basin, China. The average concentration of total quantified PAHs in personal exposure samples was 310 ± 443 ng m^-3, 1.5 times of those of indoor (211 ± 120 ng m^-3) and outdoor (189 ± 115 ng m^-3). Similar observations were found for the OPAHs and PAEs, i.e., much higher concentrations were seen in personal exposure samples. Hopanes average personal exposure concentration (13 ± 9.7 ng m^-3) was comparable to indoors (15 ± 9.7 ng m^-3) and outdoors (13 ± 9.6 ng m^-3). Among four common heating ways applied in Chinese dwelling, the highest exposure levels to PAHs, OPAHs and PAEs were found for indoor coal chunks stoves. Concentration under electric power was 1.2-4.5 folds lower than those with solid fuels in this study, proved to be the cleanest energy for the household heating. The exposures to PM_2.5 on cell viabilities were also investigated. The largest reduction of 70% on cell viabilities was seen for indoor coal chunks stove housewives, indicating that the emissions from coal combustion had the greatest cytotoxic effects. The results evidenced that the heating ways in rural area could greatly impact on the housewife health in northwestern China. Advanced heating technology and protection should be conducted to reduce the personal exposures to PM_2.5 from domestic solid fuel combustions.

An overview of phthalate acid ester pollution in China over the last decade: Environmental occurrence and human exposure

The toxicity and bioaccumulation potential of phthalate acid esters (PAEs) make their impact on the environment a matter of considerable concern. Due to China's recent economic development and population growth, it has become one of the largest manufacturers and consumers of PAEs, with an associated contamination threat to several environmental compartments. The aim of this overview is to present a systematic account of PAE occurrence in various environmental media in China in the last decade, including the air, surface water, sediments, soil, sewage, and sludge; human exposure to PAEs is also evaluated. This reveals a location-dependence that can be attributed to regional differences in economic and industrial development as well as specific geographic location. A need for further study into the transportation and transformation behavior of PAEs in different environmental media and into PAE control technologies is identified, as a means of effectively assessing potential ecological and health risks.

The efficiency and mechanism of dibutyl phthalate removal by copper-based metal organic frameworks coupled with persulfate

Copper-based metal organic framework (Cu-BTC) was prepared and used to remove dibutyl phthalate (DBP) in the presence of persulfate (PS). The surface characteristics, textural properties, and stability of activated Cu-BTC (denoted as Cu-BTC-A) were evaluated by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, N2 physical adsorption-desorption, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The effects of parameters such as initial pH, PS concentration, catalyst dosage, and free-radical quenchers have been investigated. The results showed that DBP could be removed in a wide pH range by Cu-BTC-A via mechanisms of adsorption and heterogeneous catalytic reaction. Unfortunately, the DBP removal was not completed because of radical scavenging reactions in Cu-BTC-A cages where PS can enter freely but DBP is blocked outside. Another explanation was that Cu-BTC-A showed a low adsorption capacity for DBP because the molecular size of DBP (15.84 × 11.00 × 7.56 Å) is larger than microporous cages (approximately 9 × 9 Å in diameter) of Cu-BTC-A.

Use of aged sludge bioaugmentation in two-stage activated sludge system to enhance the biodegradation of toxic organic compounds in high strength wastewater

This research investigates the toxic organic compounds biodegradation efficiency of two-stage activated sludge systems with (bioaugmented) and without aged sludge bioaugmentation (non-bioaugmented). The influent was a mixture of leachate and agriculture wastewater (1:1, v/v), used as the representative high strength wastewater. The bioaugmented and non-bioaugmented systems were operated in parallel, with three levels (low, moderate, and high) of concentrations of organics, nitrogen, and toxic organic compounds in the influent (conditions 1, 2, and 3). The results showed that both systems could efficiently degrade the organic compounds. Nevertheless, the toxic organic compounds biodegradation efficiency of the bioaugmented system was higher than that of the non-bioaugmented one. The bioaugmentation enhanced the overall removal efficiency under conditions 1 and 2. However, the bioaugmented system became less effective under condition 3. Further analysis indicated that the bacterial groups essential to the toxic organic compounds biodegradation were abundant in the aged sludge, including heterotrophic bacteria, heterotrophic nitrifying bacteria, and nitrifying bacteria. The abundance of the effective bacteria improved the biodegradation and wastewater treatment performance of the bioaugmented system. In essence, the aged sludge bioaugmentation is a viable and eco-friendly solution to improving the treatment efficiency of the biological activated sludge system, despite limited biodegradation efficiency in an elevated compounds-concentration environment.

Toxic compounds biodegradation and toxicity of high strength wastewater treated under elevated nitrogen concentration in the activated sludge and membrane bioreactor systems

This research has assessed the removal efficiencies of toxic compounds in the high strength wastewater (the leachate and agriculture wastewater mixture) using the activated sludge (AS) and membrane bioreactor (MBR) technologies under two carbon to nitrogen (C/N) ratios (C/N 14 and 6) and two toxic compounds concentrations (8-396μg/L and 1000μg/L). In addition, the toxicity evaluations of the AS and MBR effluents to the aquatic environment were undertaken at five effluent dilution ratios (10, 20, 30, 50 and 70% v/v). The findings indicate that the AS treatment performance could be enhanced by the elevation of the nitrogen concentration. Specifically, the C/N 6 environment helps promote the bacterial growth, particularly heterotrophic nitrifying bacteria (HNB) and nitrifying bacteria (NB), which produce the enzymes crucial to the toxic compounds degradation. The improved biodegradation makes the effluents less toxic to the aquatic environment, as evidenced by the lower mortality rates of both experimental fish species raised in the nitrogen-elevated diluted AS effluents. On the other hand, the elevated nitrogen concentration minimally enhances the MBR treatment performance, given the fact that the MBR technology is in itself a biological treatment scheme with very high compounds removal capability. Despite its lower toxic compounds removal efficiency, the AS technology is simple, inexpensive and operationally-friendly, rendering the system more applicable to the treatment operation constrained by the financial, manpower and technological considerations.

Occurrence of phthalates in aquatic environment and their removal during wastewater treatment processes: a review

Phthalates are plasticizers and are concerned environmental endocrine-disrupting compounds. Due to their extensive usage in plastic manufacturing and personal care products as well as the potential to leach out from these products, phthalates have been detected in various aquatic environments including drinking water, groundwater, surface water, and wastewater. The primary source of their environmental occurrence is the discharge of phthalate-laden wastewater and sludge. This review focuses on recent knowledge on the occurrence of phthalate in different aquatic environments and their fate in conventional and advanced wastewater treatment processes. This review also summarizes recent advances in biological removal and degradation mechanisms of phthalates, identifies knowledge gaps, and suggests future research directions.

Potential effects of low molecular weight phthalate esters (C16H22O4 and C12H14O4) on the freshwater fish Cyprinus carpio

The aim of the present study is to assess the toxic effect of dibutyl phthalate (DBP) and diethyl phthalate (DEP) on the freshwater fish Cyprinus carpio. The median lethal concentrations of DBP and DEP for 96 h are found to be 35 and 53 mg L-1, respectively. Fish were exposed to 3.5 mg L-1 (Treatment I) and 1.75 mg L-1 (Treatment II) of DBP and 5.3 mg L-1 (Treatment I) and 2.65 mg L-1 (Treatment II) of DEP for a period of 35 days. The DBP and DEP exposed fish show a concentration based toxic effect on the selected parameters of this study. The hematological parameters, such as hemoglobin (Hb), hematocrit (Hct) and erythrocyte (RBC), were found to decrease in the DBP and DEP treated fish, whereas their leucocyte (WBC) count increased compared to that of the control groups. A biphasic response is noted in the erythrocyte indices, such as mean cellular volume (MCV), mean cellular hemoglobin (MCH) and mean cellular hemoglobin concentration (MCHC), throughout the study period. Exposure to DBP and DEP caused a significant (p < 0.05) decrease in sodium (Na+), potassium (K+), and chloride (Cl-) levels in the gill and brain of the fish throughout the study period when compared to that of their respective controls. The plasma protein level decreased in all the treatments, whereas the plasma glucose level significantly increased in the DBP and DEP exposed fish. Maximum inhibition of Na+/K+-ATPase activity was noticed in the gill and brain of the fish exposed to DBP and DEP. The cholinesterase (ChE) activity in the brain of the fish significantly decreased throughout the study period. A significant (p < 0.05) increase in glutamate oxaloacetate transaminase (GOT) and glutamic pyruvate transaminase (GPT) activity was noted in the fish exposed to both toxicants. The antioxidant enzymatic parameters such as superoxide dismutase (SOD) and catalase (CAT) activities were found to decrease in the gill and liver of the DBP and DEP treated fish, whereas a significant (p < 0.05) increase in lipid peroxidation (LPO) was observed. The above mentioned parameters could be used as potential biomarkers in clinical trials for the assessment of plasticizers. This study provides indispensable information towards future research on the effect of plasticizers on non-target organisms including humans.

A comparative study of anaerobic fixed film baffled reactor and up-flow anaerobic fixed film fixed bed reactor for biological removal of diethyl phthalate from wastewater: a performance, kinetic, biogas, and metabolic pathway study

BACKGROUND

Phthalic acid esters, including diethyl phthalate (DEP), which are considered as top-priority and hazardous pollutants, have received significant attention over the last decades. It is vital for industries to select the best treatment technology, especially when the DEP concentration in wastewater is high. Meanwhile, anaerobic biofilm-based reactors are considered as a promising option. Therefore, in the present study, for the biological removal of DEP from synthetic wastewater, two different anaerobic biofilm-based reactors, including anaerobic fixed film baffled reactor (AnFFBR) and up-flow anaerobic fixed film fixed bed reactor (UAnFFFBR), were compared from kinetic and performance standpoints. As in the previous studies, only the kinetic coefficients have been calculated and the relationship between kinetic coefficients and their interpretation has not been evaluated, the other aim of the present study was to fill this research gap.

RESULTS

In optimum conditions, 90.31 and 86.91% of COD as well as 91.11 and 88.72% of DEP removal were achieved for the AnFFBR and UAnFFFBR, respectively. According to kinetic coefficients (except biomass yield), the AnFFBR had better performance as it provided a more favorable condition for microbial growth. The Grau model was selected as the best mathematical model for designing and predicting the bioreactors' performance due to its high coefficients of determination (0.97 < R²). With regard to the insignificant variations of the calculated Grau kinetic coefficients (K_G) when the organic loading rate (with constant HRT) increased, it can be concluded that both of the bioreactors can tolerate high organic loading rate and their performance is not affected by the applied DEP concentrations.

CONCLUSIONS

Both the bioreactors were capable of treating low-to-high strength DEP wastewater; however, according to the experimental results and obtained kinetic coefficients, the AnFFBR indicated higher performance. Although the AnFFBR can be considered as a safer treatment option than the UAnFFFBR due to its lower DEP concentrations in sludge, the UAnFFFBR had lower VSS/TSS ratio and sludge yield, which could make it more practical for digestion. Finally, both the bioreactors showed considerable methane yield; however, compared to the UAnFFFBR, the AnFFBR had more potential for bioenergy production. Although both the selected bioreactors achieved nearly 90% of DEP removal, they can only be considered as pre-treatment methods according to the standard regulations and should be coupled with further technology.

Improving the efficiency of dissolved oxygen control using an on-line control system based on a genetic algorithm evolving FWNN software sensor

This work proposes an on-line hybrid intelligent control system based on a genetic algorithm (GA) evolving fuzzy wavelet neural network software sensor to control dissolved oxygen (DO) in an anaerobic/anoxic/oxic process for treating papermaking wastewater. With the self-learning and memory abilities of neural network, handling the uncertainty capacity of fuzzy logic, analyzing local detail superiority of wavelet transform and global search of GA, this proposed control system can extract the dynamic behavior and complex interrelationships between various operation variables. The results indicate that the reasonable forecasting and control performances were achieved with optimal DO, and the effluent quality was stable at and below the desired values in real time. Our proposed hybrid approach proved to be a robust and effective DO control tool, attaining not only adequate effluent quality but also minimizing the demand for energy, and is easily integrated into a global monitoring system for purposes of cost management.

A New Efficient Hybrid Intelligent Model for Biodegradation Process of DMP with Fuzzy Wavelet Neural Networks

A new efficient hybrid intelligent approach based on fuzzy wavelet neural network (FWNN) was proposed for effectively modeling and simulating biodegradation process of Dimethyl phthalate (DMP) in an anaerobic/anoxic/oxic (AAO) wastewater treatment process. With the self learning and memory abilities of neural networks (NN), handling uncertainty capacity of fuzzy logic (FL), analyzing local details superiority of wavelet transform (WT) and global search of genetic algorithm (GA), the proposed hybrid intelligent model can extract the dynamic behavior and complex interrelationships from various water quality variables. For finding the optimal values for parameters of the proposed FWNN, a hybrid learning algorithm integrating an improved genetic optimization and gradient descent algorithm is employed. The results show, compared with NN model (optimized by GA) and kinetic model, the proposed FWNN model have the quicker convergence speed, the higher prediction performance, and smaller RMSE (0.080), MSE (0.0064), MAPE (1.8158) and higher R² (0.9851) values. which illustrates FWNN model simulates effluent DMP more accurately than the mechanism model.

Application of fuzzy neural networks for modeling of biodegradation and biogas production in a full-scale internal circulation anaerobic reactor

This paper presents the development and evaluation of three fuzzy neural network (FNN) models for a full-scale anaerobic digestion system treating paper-mill wastewater. The aim was the investigation of feasibility of the approach-based control system for the prediction of effluent quality and biogas production from an internal circulation (IC) anaerobic reactor system. To improve FNN performance, fuzzy subtractive clustering was used to identify model's architecture and optimize fuzzy rule, and a total of 5 rules were extracted in the IF-THEN format. Findings of this study clearly indicated that, compared to NN models, FNN models had smaller RMSE and MAPE as well as bigger R for the testing datasets than NN models. The proposed FNN model produced smaller deviations and exhibited a superior predictive performance on forecasting of both effluent quality and biogas (methane) production rates with satisfactory determination coefficients greater than 0.90. From the results, it was concluded that FNN modeling could be applied in IC anaerobic reactor for predicting the biodegradation and biogas production using paper-mill wastewater.

Degradation behavior of dimethyl phthalate in an anaerobic/anoxic/oxic system

Dimethyl phthalate (DMP) as one of the most important and extensively used Phthalic acid esters (PAEs) is known to likely cause dysfunctions of the endocrine systems, liver, and nervous systems of animals. In this paper, the degradation and behavior of DMP were investigated in a laboratory scale anaerobic/anoxic/oxic (AAO) treatment system. In addition, a degradation model including biodegradation and sorption was formulated so as to evaluate the fate of DMP in the treatment system, and a mass balance model was designed to determine kinetic parameters of the removal model. The study indicated that the optimal operation condition of HRT and SRT for DMP and nutrients removal were 18 h and 15 d respectively, and the degradation rates of anaerobic, anoxic and aerobic zones for DMP were 13.4%, 13.0% and 67.7%, respectively. Under the optimal conditions, the degraded DMP was 73.8%, the released DMP in the effluent was 5.8%, the accumulated DMP was 19.3%, and the remained DMP in the waste sludge was 1.1%. Moreover, the degradation process of DMP by acclimated activated sludge was in accordance with the first-order kinetics equation. The model can be used for accurately modeling the degradation and behavior of DMP in the AAO system.

A comparative study of occurrence and fate of endocrine disruptors: diethyl phthalate and dibutyl phthalate in ASP- and SBR-based wastewater treatment plants

Phthalates are endocrine-disrupting chemicals which affect endocrine system by bio-accumulation in aquatic organisms and produce adverse health effects in aquatic organisms as well as human beings, when come in contact. Present study focuses on occurrence and removal of two phthalates: diethylphthalate (DEP) and dibutylphthalate (DBP) in two full-scale wastewater treatment plants (WWTPs) i.e. sewage treatment plants (STPs) based on well-adopted technologies, activated sludge process (ASP) and sequencing batch reactor (SBR).Gas chromatography-mass spectrometry (GC-MS) analysis was performed for both wastewater and sludge sample for determination and identification of the concentration of these compounds in both STPs by monitoring the STPs for 9 months. It was observed that the concentration of DEP was less than DBP in the influent of ASP and SBR. Average concentrations of DEP and DBP in sludge sample of ASP were found to be 2.15 and 2.08 ng/g, whereas in SBR plant, these values were observed as 1.71 and 2.01 ng/g, respectively. Concerning the removal efficiency of DEP, SBR and ASP plants were found effective with removal efficiency of 91.51 and 91.03 %, respectively. However, in the case of DBP, SBR showed lower removal efficiency (85.42 %) as compared to ASP (92.67 %). Comparative study of both plants proposed that in ASP plant, DBP reduction was higher than the SBR. Fourier transformation infrared (FTIR) analysis also confirmed the same result of sludge analysis for both STPs. Sludge disposal studied with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and thermo-gravimetric analysis (TGA) techniques confirmed that sludge of both STPs have high calorific value and can be used as fuel to make fuel-briquettes and bottom ash to make firebricks.

Effects of hydraulic retention time and carbon to nitrogen ratio on micro-pollutant biodegradation in membrane bioreactor for leachate treatment

This research investigated the biodegradation of the micro-pollutants in leachate by the membrane bioreactor (MBR) system under six treatment conditions, comprising two C/N ratios (6, 10) and three hydraulic retention time (HRT) durations (6, 12, 24h). The experimental results indicated that the C/N 6 environment was more advantageous to the bacterial growth. The bacterial communities residing in the sludge were those of heterotrophic bacteria (HB), heterotrophic nitrifying bacteria (HNB) and ammonia oxidizing bacteria (AOB). It was found that HB and HNB produced phenol hydroxylase (PH), esterase (EST), phthalate dioxygenase (PDO) and laccase (LAC) and also enhanced the biodegradation rate constants (k) in the system. At the same time, AOB promoted the production of HB and HNB. The findings also revealed that the 12h HRT was the optimal condition with regard to the highest growth of the bacteria responsible for the biodegradation of phenols and phthalates. Meanwhile, the longer HRT duration (i.e. 24h) was required to effectively bio-degrade carbamazepine (CBZ), N,N-diethyl-m-toluamide (DEET) and diclofenac (DCF).

Comparative assessment of phthalate removal and risk in biological wastewater treatment systems of developing countries and small communities

Phthalates are widely used in plastic and personnel care products. Being non-steroid endocrine disrupting compounds, their exposure have toxic effects on aquatic life and human health. The aim of this study was a comparative assessment of their fate and risk in full scale wastewater treatment along with influence of seasonal variations. Four priority phthalates, Diethylphthalate (DEP), Dibutylphthalate (DBP), Benzylbutyl phthalate (BBP) and Diethylhexyl phthalate (DEHP) were chosen for this study and wastewater treatment plants investigated were designed as nutrient removal based sequencing batch reactor (SBR), conventional activated sludge process (ASP) and up flow anaerobic sludge blanket (UASB) with polishing pond. Results showed that the main removal mechanism of phthalates was biotransformation with removal contribution of 74% in SBR, 65% in conventional ASP and 37% in UASB. Overall removal of phthalates was maximum in the treatment combination of UASB and pond (83%) followed by SBR (80%) and conventional ASP (74%). Seasonal influences on occurrence, removal and risk of these phthalates were also studied. The concentration of DEP, DBP and DEHP in untreated wastewater increased by 2, 7 and 2μg/L, respectively in summer. However in sludge, only large molecular weight phthalates BBP and DEHP increased in winter by 3mg/kg and 12mg/kg, respectively. Seasonal variations in removal of phthalates were discrepant in each process with better removal during summer. Risk assessment of phthalates to aquatic life showed that there is no potential risk of DEP, DBP and BBP from effluents of treatment plants however risk quotient of DEHP was in the range of 27-73 in both seasons which indicate probable risk to aquatic organisms. Phthalate risk to human beings estimated by daily intake of phthalates was in the range of 0.3±0.1 to 20±0.7ng/kg/d and far below their respective reference dosages, demonstrating the potential of these treatment plants to reduce the risk of phthalates.

Contamination level of four priority phthalates in North Indian wastewater treatment plants and their fate in sequencing batch reactor systems

The contamination level of four phthalates in untreated and treated wastewater of fifteen wastewater treatment plants (WWTPs) and their fate in a full scale sequencing batch reactor (SBR) based WWTP was evaluated in this study. The four phthalates were diethyl phthalate (DEP), dibutyl phthalate (DBP), benzylbutyl phthalate (BBP) and diethylhexyl phthalate (DEHP). All compounds were present in untreated wastewater with DEHP being present in the highest mean concentration of 28.4 ± 5.3 μg L(-1). The concentration was in the range of 7.3 μg L(-1) (BBP) to 28.4 μg L(-1) (DEHP) in untreated wastewater and 1.3 μg L(-1) (DBP) to 2.6 μg L(-1) (DEHP) in treated wastewater. The nutrient removal process and advance tertiary treatment based WWTPs showed the highest phthalate removal efficiencies of 87% and 93%, respectively. The correlation between phthalate removal and conventional performance of WWTPs was positive. Fate analysis of these phthalates in a SBR based WWTP showed that total removal of the sum of phthalates in a primary settling tank and SBR was 84% out of which 55% is removed by biodegradation and 29% was removed by sorption to primary and secondary sludge. The percentage removal of four phthalates in primary settling tanks was 18%. Comparison of the diluted effluent DEHP concentration with its environmental quality standards showed that the dilution in an effluent receiving water body can reduce the DEHP emissions to acceptable values.

Phthalate esters in the environment: A critical review of their occurrence, biodegradation, and removal during wastewater treatment processes

Phthalate esters are one of the most frequently detected persistent organic pollutants in the environment. A better understanding of their occurrence and degradation in the environment and during wastewater treatment processes will facilitate the development of strategies to reduce these pollutants and to bioremediate contaminated freshwater and soil. Phthalate esters occur at measurable levels in different environments worldwide. For example, the concentrations of dimethyl phthalate (DMP) in atmospheric particulate matter, fresh water and sediments, soil, and landfills are N.D.-10.4 ng/m(3), N.D.-31.7 μg/L, N.D.-316 μg/kg dry weight, and N.D.-200 μg/kg dry weight, N.D.-43.27 μg/L, respectively. Bis(2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DBP) are primary phthalate ester pollutants. Urbanization has increased the discharge of phthalate esters to atmospheric and aquatic environments, and the use of agricultural plastics has exacerbated soil contamination by phthalate esters in rural areas. Aerobic biodegradation is the primary manner of phthalate ester mineralization in the environment, and this process has been widely studied. Phthalate esters can be removed during wastewater treatment processes. The combination of different wastewater treatment technologies showed greater efficiency in the removal of phthalate esters than individual treatment steps, such as the combination of anaerobic wastewater treatment with a membrane bioreactor would increase the efficiency of phthalate ester removal from 65%-71% to 95%-97%. This review provides a useful framework to identify future research objectives to achieve the mineralization and elimination of phthalate esters in the environment.

Occurrence and fate of endocrine disrupting chemicals in ASP based sewage treatment plant in Hardwar

The occurrence of emerging contaminants such as endocrine disrupting chemicals (EDCs) in our water resources is of prime concern. With this context, fate and seasonal variation of six EDCs (testosterone, T; progesterone, P; diethyl phthalate, DEP; dibutyl phthalate, DBP; propyl-paraben, PP and butyl-paraben, BP) were assessed throughout the year, i.e. in rainy, winter, spring and summer seasons in the raw, treated wastewater and activated sludge in an activated sludge process (ASP) based sewage treatment plant (STP) located in Haridwar, India. Qualitative and quantitative measurements were performed by gas chromatography-mass spectrometry (GC-MS) analysis. Results indicate that in summer, the examined STP could effectively remove 82.9% of T, 86.4% of P, 95.5% of DEP, 92.4% of DBP, 91.5% of PP, and 89.9% of BP from the wastewater. Among the EDCs considered, higher removal efficiencies were achieved for phthalates in the summer season. GC-MS analysis showed that a small fraction of EDCs was sorbed on the solid fraction of activated sludge. Scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transformation infrared spectroscopy analysis were also performed to investigate the occurrence of EDCs in biomass samples. Results of this study also demonstrated that removal efficiency, assessed in terms of physicochemical and microbiological parameters, was maximum in summer and reached minimum in rainy season.

Microbial adaptation to biodegrade toxic organic micro-pollutants in membrane bioreactor using different sludge sources

Biodegradation of toxic organic micro-pollutants in municipal solid waste (MSW) leachate by membrane bioreactor (MBR) was investigated. The MBR systems were seeded with different sludge sources, one was from a pilot-scale MBR system treating MSW leachate and the other was from an activated sludge sewage treatment plant. The biodegradation of BPA, 2,6-DTBP, BHT, DEP, DBP and DEHP, DCP and BBzP, by sludge from both reactors were found improved with time. However, enhanced biodegradation of micro-pollutants was observed in MBR operated under long sludge age condition. Bacterial population analyses determined by PCR-DGGE revealed the development of phenol and phthalate degrading bacteria consortium in MBR sludge during its operation.

Occurrence and fate of phthalate esters in full-scale domestic wastewater treatment plants and their impact on receiving waters along the Songhua River in China

The occurrence and fate of six phthalates: dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butyl benzyl phthalate (BBP), bis (2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DOP) were investigated as phthalates passed through three full-scale wastewater treatment plants (WWTPs) with different treatment processes, and ultimately into the recipient Songhua River water in Harbin (China). The six phthalates were detected in the majority of aqueous and solid samples, with DEHP being the most abundant compound. The overall removal efficiency of ΣPAEs in the Cyclic Activated Sludge Technology (CAST) process was over 72%, while both the A/O and A/A/O processes achieved approximately 30% removal. The better performance of the CAST process relative to the Anoxic/Oxic (A/O) and Anaerobic/Anoxic/Oxic (A/A/O) processes was attributed to the indoor-conditions of the CAST plants, which effectively maintained the temperature of the treatment system. The fate of PAEs within two different types of WWTPs (CAST and A/A/O) were assessed qualitatively using mass balances. The results suggested that PAEs removal resulted from both biotransformation and adsorption, of which the former was particularly significant in the CAST process, while the latter was more significant in the A/A/O process. Substantial levels of several PAEs were detected in the Songhua River, especially downstream of the WWTPs, which means that the discharge from WWTPs has a strong impact on the water quality of the Songhua River during cold winter conditions.

Biodegradation of di-n-butyl phthalate by a stable bacterial consortium, HD-1, enriched from activated sludge

HD-1, a stable microbial consortium capable of mineralizing di-n-butyl phthalate (DBP), was developed from activated sludge. The dominant microorganisms in the consortium, Gordonia sp., Burkholderia sp. and Achromobacter sp., were identified by denaturing gradient gel electrophoresis (DGGE). The consortium could mineralize approximately 90% of 1200 mg/L DBP after 48 h of cultivation. The optimal DBP degradation conditions were 25-30 °C and pH 8.0-9.0. The addition of yeast (0.5 g/L), sodium acetate (0.5 g/L, 1.0 g/L), Brij 35 (0.2%, 0.5%, 1.0%), or Triton X-100 (0.2%) enhanced DBP degradation. The DBP degradation rate was influenced by the presence of dimethyl phthalate (DMP) and diethyl phthalate (DEP). Only one main intermediate, phthalic acid, could be monitored by gas chromatography-mass spectrometry (GC-MS) during the degradation process. The HD-1 consortium also utilized phenol, o-dihydroxybenzene as the sole carbon and energy source. The results indicate the consortium may represent a promising application for DBP bioremediation.

Characteristic of Phthalates Adsorption on the Organic Medium

Phthalates were of heath concern in groundwater and drink water. In order to understand how Phthalates were transported at organic medium of the aquatic environment, adsorption experiments were conducted using sludge as organic adsorbents for adsorbing Di-n-butyl phthalate and Bis(2-Ethylhexyl) phthalate. As a result, The adsorption of Phthalates by the sludge displayed Freundlich adsorption characteristics, and the much larger Freundlich affinity coefficient for Bis(2-Ethylhexyl) phthalate than that for Di-n-butyl phthalate is an indication of higher affinity of the sludge particles for Bis(2-Ethylhexyl) phthalate. By Scanning electron microscope analysis of the sludge, in principle very porous structure of the sludge would not be the limit condition and multilayer adsorption would become possible.

A hybrid genetic--neural algorithm for modeling the biodegradation process of DnBP in AAO system

A hybrid artificial neural network - genetic algorithm numerical technique was successfully developed to model, and to simulate the biodegradation process of di-n-butyl phthalate in an anaerobic/anoxic/oxic (AAO) system. The fate of DnBP was investigated, and a removal kinetic model including sorption and biodegradation was formulated. To correlate the experimental data with available models or some modified empirical equations, the steady state model equations describing the biodegradation process have been solved using genetic algorithm (GA) and artificial neural network (ANN) from the water quality characteristic parameters. Compared with the kinetic model, the performance of the GA-ANN for modeling the DnBP was found to be more impressive. The results show that the predicted values well fit measured concentrations, which was also supported by the relatively low RMSE (0.2724), MAPE (3.6137) and MSE (0.0742)and very high R (0.9859) values, and which illustrates the GA-ANN model predicting effluent DnBP more accurately than the mechanism model forecasting.

Prediction model of DnBP degradation based on BP neural network in AAO system

A laboratory-scale anaerobic-anoxic-oxic (AAO) system was established to investigate the fate of DnBP. A removal kinetic model including sorption and biodegradation was formulated, and kinetic parameters were evaluated with batch experiments under anaerobic, anoxic, oxic conditions. However, it is highly complex and is difficult to confirm the kinetic parameters using conventional mathematical modeling. To correlate the experimental data with available models or some modified empirical equations, an artificial neural network model based on multilayered partial recurrent back propagation (BP) algorithm was applied for the biodegradation of DnBP from the water quality characteristic parameters. Compared to the kinetic model, the performance of the network for modeling DnBP is found to be more impressive. The results showed that the biggest relative error of BP network prediction model was 9.95%, while the kinetic model was 14.52%, which illustrates BP model predicting effluent DnBP more accurately than kinetic model forecasting.