Development of an integrated fixed-film activated sludge (IFAS) reactor treating landfill leachate for the biological nitrogen removal through nitritation-denitritation.

The current work investigated the performance of an Integrated Fixed-Film Activated Sludge Sequencing Batch Reactor (IFAS-SBR) for Biological Nitrogen Removal (BNR) from mature landfill leachate through the nitritation-denitritation process. During the experimental period two IFAS-SBR configurations were examined using two different biocarrier types with the same filling ratio (50%). The dissolved oxygen (DO) concentration ranged between 2 and 3 mg/L and 4-6 mg/L in the first (baseline-IFAS) and the second (S8-IFAS) setup, respectively. Baseline-IFAS operated for 542 days and demonstrated a high and stable BNR performance maintaining a removal efficiency above 90% under a Nitrogen Loading Rate (NLR) up to 0.45 kg N/m3-d, while S8-IFAS, which operated for 230 days, was characterized by a limited and unstable BNR performance being unable to operate sufficiently under an NLR higher than 0.20 kg N/m3-d. It also experienced a severe inhibition period, when the BNR process was fully deteriorated. Moreover, S8-IFAS suffered from extensive biocarrier stagnant zones and a particularly poor sludge settleability. The attached biomass cultivated in both IFAS configurations had a negligible content of nitrifying bacteria, probably attributed to the insufficient DO diffusion through the biofilm, caused by the low DO concentration in the liquid in the baseline case and the extensive stagnant zones in the S8-IFAS case. As a result of the high biocarrier filling ratio, the S8-IFAS was unstable and low. This was probably attributed to the mass transfer limitations caused by the biocarrier stagnant zones, which hinder substrate and oxygen diffusion, thus reducing the biomass activity and increasing its vulnerability to inhibitory and toxic factors. Hence, the biocarrier filling fraction is a crucial parameter for the efficient operation of the IFAS-SBR and should be carefully selected taking into consideration both the media type and the overall reactor configuration.

Fate of Emerging Contaminants in High-Rate Activated Sludge Systems.

High-rate activated sludge (HRAS) systems are designed to shift the energy-intensive processes to energy-saving and sustainable technologies for wastewater treatment. The high food-to-microorganism (F/M) ratios and low solid retention times (SRTs) and hydraulic retention times (HRTs) applied in HRAS systems result in the maximization of organic matter diversion to the sludge which can produce large amounts of biogas during anaerobic digestion, thus moving toward energy-neutral (or positive) treatment processes. However, in addition to the energy optimization, the removal of emerging contaminants (ECs) is the new challenge in wastewater treatment. In the context of this study, the removal efficiencies and the fates of selected ECs (three endocrine disruptors (endocrine disrupting chemicals (EDCs))-nonylphenol, bisphenol A and triclosan, and four pharmaceuticals (PhACs)-ibuprofen, naproxen, diclofenac and ketoprofen) in HRAS systems have been studied. According to the results, EDCs occurred in raw wastewater and secondary sludge at higher concentrations compared to PhACs. In HRAS operating schemes, all compounds were poorly (<40%) to moderately (<60%) removed. Regarding removal mechanisms, biotransformation was found to be the dominant process for PhACs, while for EDCs sorption onto sludge is the most significant removal mechanism affecting their fates and their presence in excess sludge.

Analytical and mathematical assessment of emerging pollutants fate in a river system.

The fate of several emerging pollutants in a Greek river system was assessed through analytical measurements and mathematical modelling. Target compounds selected in this study consist of five endocrine disrupting chemicals and four non-steroidal anti-inflammatory drugs. Two sampling campaigns were implemented to assess target compounds concentrations along the river system during dry period. Furthermore a mathematical model was developed in order to simulate the spatial distribution of target compounds concentration. The mathematical model describes several abiotic and biotic processes (sorption, photodegradation, biodegradation, biotransformation) in order to account for the removal of target compounds. Following sensitivity analysis, the model was calibrated and validated against measured values. Environmental risk assessment was performed based on both analytical measurements and simulation results. Uncertainty analysis was also conducted by applying Monte Carlo technique. According to the results the simulation data matched very satisfactorily with the analytical measurements, thus confirming the main experimental observations showing that the primary removal mechanism for the photo-sensitive chemicals is photodegradation, the latter being mostly influenced by weather conditions and river general quality characteristics (e.g. chlorophyll, turbidity). Model results demonstrate a gradual increase of uncertainty from the upstream to the downstream of the river system for all target compounds.

Assessment of the environmental fate of endocrine disrupting chemicals in rivers.

Laboratory tests were conducted with five endocrine disruptors (bishenol A, triclosan. nonylphenol, nonylphenol monoethoxylate and nonylphenol diethoxylate) under different redox conditions (aerobic, anoxic, anaerobic and sulfate-reducing conditions) to assess abiotic and biotic degradation in a river water/sediment system. The river water sample was collected from Spercheios River while the sediment was collected from the banks of a tributary of the river at the point where the discharge point of a wastewater treatment plant is located. To describe quantitatively elimination kinetics of the target compounds, pseudo first-order kinetics were adopted. According to the results from the microcosms studies, it can be stated that the substances are eliminated from the aqueous phase with relatively high rates under aerobic conditions due to both sorption and biotransformation processes. However, when reduced oxygen conditions were established in the microcosms incubations, biotransformation decreased, indicating the almost complete cease of the EDCs microbial degradation, while substances' sorption onto sediments showed no significant differences. All compounds were found to be biodegradable under aerobic conditions, and the low to high order of the calculated dissipation rate constants was 0.064±0.004d-1 (TCS)→0.067±0.006d-1 (NP)→0.076±0.009d-1 (NP2EO)→0.081±0.007d-1 (NP1EO)→0.103±0.011d-1 (BPA). Finally, regarding the biotransformation experiments, the elimination of the compounds limited in the absence of oxygen as compared to aerobic.

Environmental fate of non-steroidal anti-inflammatory drugs in river water/sediment systems.

Laboratory tests were conducted with four non-steroidal anti-inflammatory drugs (naproxen, ibuprofen, diclofenac and ketoprofen) under different redox conditions (aerobic, anoxic, anaerobic and sulfate-reducing conditions) in order to assess abiotic and biotic degradation in a river water/sediment system. The river water was sampled from Sperchios River and the sediment was collected from the banks of a rural stream where the discharge point of a wastewater treatment plant is located. To quantitatively describe degradation kinetics of the selected compounds, pseudo first-order kinetics were adopted. According to the results, it can be stated that the concentration of the substances remained constant or decreased only marginally (p≥0.05) in the sterile experiments and this excludes abiotic processes such as hydrolysis or sorption as major removal mechanisms of the target compounds from the water phase and assign their removal to microbial action. Results showed that the removal rate of the compounds decreases as dissolved oxygen concentration in the river water/sediment system decreases. All compounds were found to be biodegradable under aerobic conditions at dissipation half-lives between 1.6 and 20.1days, while dissipation half-lives for naproxen and ketoprofen increase by a factor of 2 under all tested conditions in the absence of oxygen.

Chlorination of benzothiazoles and benzotriazoles and transformation products identification by LC-HR-MS/MS.

The fate of four benzotriazoles [1-H-benzotriazole (1-H-BTRi), tolyltriazole (TTRi), xylyltriazole (XTRi) and 1-hydroxy-benzotriazole (1-OH-BTRi)] and three benzothiazoles [benzothiazole (BTH), 2-hydroxy-benzothiazole (2-OH-BTH) and 2-amino-benzothiazole (2-amino-BTH)], during chlorination batch experiments was investigated. In the first step, their degradation under different experimental conditions (applied molar ratio of NaOCl and the target contaminant (m.r.), reaction's contact time, pH value of the reaction's solution and the influence of total suspended solids (TSS) presence) was investigated and their removal kinetics parameters (kobs and t1/2) were determined. In the second step, LC-QTOFMS/MS was used for the detection and identification of transformation products (TPs) formed during chlorination, through the application of suspect and non-target screening approaches. Four and five TPs of XTRi and 2-amino-BTH, respectively, were detected and tentatively identified, while 1-H-BTRi was proven to be formed by the chlorination of 1-OH-BTRi. Moreover, since the identified TPs were also detected in spiked wastewater samples, after lab-scale chlorination experiments, toxicity assessment was carried out by ECOSAR calculations for the environmental relevance of their occurrence. The proposed chlorinated TPs were proven to be more toxic than their parent compounds.

Degradation of emerging contaminants from water under natural sunlight: The effect of season, pH, humic acids and nitrate and identification of photodegradation by-products.

Both photodegradation and hydrolysis of non-steroidal anti-inflammatory drugs (NSAIDs) and endocrine disrupting chemicals (EDCs) were investigated in order to evaluate their photochemical fate in aquatic environment and to assess the effect of season and specific characteristics of water (pH, humic acids and nitrate concentration) on the removal of target EDCs and NSAIDs through photodegradation. An additional objective was the identification of the photodegradation by-products of specific NSAIDs and their dependence on irradiation time. Selected compounds' transformation was investigated under natural sunlight radiation while control experiments were conducted in the dark. As expected, most of compounds' degradation rate decreased with decreasing light intensity between two different experimental periods. Most of the tested compounds exhibited different rates of degradation during direct and indirect photolysis. The degradation rate of the selected compounds increased in the presence of NO3(-) and the photodegradation rate was higher for some compounds in alkaline than in acidic solution. The effect of humic acids' presence in the water depends on the absorbance spectrum of the compound and the produced photosensitizers. More specifically, humic acids act as inner filter toward most of the selected NSAIDs and as photosensitizers toward most of the EDCs. The results of the irradiation experiments in the presence of both humic acids and NO3(-), indicate that the direct photolysis is much more efficient than indirect photochemical processes. Finally, several degradation by-products of ketoprofen and diclofenac were identified in the samples, exposed to sunlight. The dependence of these by-products on radiation time is also demonstrated.

Removal of endocrine disruptors and non-steroidal anti-inflammatory drugs through wastewater chlorination: the effect of pH, total suspended solids and humic acids and identification of degradation by-products.

Endocrine disrupting chemicals (EDCs) and non-steroidal anti-inflammatory drugs (NSAIDs) are two groups of emerging pollutants the significance of which rests on their persistent detection in the aquatic environment and their possible adverse effects. Wastewater treatment plants are one of the major ways for transporting such chemicals in the aquatic environment. Chlorination is usually the last stage of treatment before wastewater being disposed to the aquatic environment. This work focuses on the evaluation of the effect of chlorine dose and specific wastewater characteristics (pH, total suspended solids and humic acids) on the removal of target EDCs and NSAIDs through chlorination. Another objective of this study is the identification of chlorination by-products of specific EDCs and NSAIDs and their dependence on contact time. Based on the results it is concluded that the effect of chlorine dose and humic acids concentration on the degradation of target compounds during chlorination is minimal. On the contrary, pH is a critical parameter which highly affects process performance. Moreover, it is concluded that not only the free available chlorine species, but also the properties of EDCs and NSAIDs under different pH conditions can affect chlorination process performance. The effect of TSS on the degradation of the target compounds during chlorination is more profound for chemicals with high Kow values and therefore higher affinity to partition to the particulate phase (i.e. nonylphenols, triclosan). Several degradation by-products were identified through chlorination of nonylphenol, bisphenol A and diclofenac. The dependence of these by-products on chlorination contact time is also demonstrated.