Selective Removal of Nitrosamines from a Model Amine Carbon-Capture Waterwash Using Low-Cost Activated-Carbon Sorbents

Occurrence and Ecological Risk Assessment of Highly Toxic Halogenated Byproducts during Chlorination Decolorization of Textile Printing and Dyeing Wastewater

Textile printing and dyeing wastewater is a substantial source of highly toxic halogenated pollutants because of the chlorination decolorization. However, information on the occurrence and fate of the highly toxic halogenated byproducts, which are produced by chlorination decolorization of the textile printing and dyeing wastewater, is very limited. In this study, the occurrence of six categories of halogenated byproducts (haloacetic acids (HAAs), haloacetonitriles (HANs), N-nitrosamines (NAs), trihalomethanes, halogenated ketones, and halonitromethanes) was investigated along the full-scale treatment processes of textile printing and dyeing wastewater treatment plants. Furthermore, the ecological risk of the halogenated byproducts was evaluated. The results showed that the total concentration of halogenated byproducts increased significantly after chlorination. Large amounts of HAAs (average 122.1 μg/L), HANs (average 80.9 μg/L), THMs (average 48.3 μg/L), and NAs (average 2314.3 ng/L) were found in the chlorinated textile wastewater, and the results showed that the generations of HANs and NAs were positively correlated with the BIX and β/α index, indicating that the HANs and NAs might form from the microbial metabolites. In addition, HAAs and HANs exhibited high ecological risk quotients (>1), suggesting their high potential ecological risk. The results also demonstrated that most halogenated byproducts could be effectively removed by reverse osmosis treatment processes except NAs, with a lower removal rate of 18%. This study is believed to provide an important theoretical basis for controlling and reducing the ecological risks of halogenated byproducts in textile printing and dyeing wastewater effluents.

Targeted electrochemical reduction of carcinogenic N-nitrosamines from emission control systems within CO2 capture plants

N-Nitrosamines are one of the environmentally significant byproducts from aqueous amine-based post-combustion carbon capture systems (CCS) due to their potential risk to human health. Safely mitigating nitrosamines before they are emitted from these CO₂ capture systems is therefore a key concern before widescale deployment of CCS can be used to address worldwide decarbonization goals. Electrochemical decomposition is one viable route to neutralize these harmful compounds. The circulating emission control waterwash system, commonly installed at the end of the flue gas treatment trains to minimize amine solvent emissions, plays an important role to capture N-nitrosamines and control their emission into the environment. The waterwash solution is the last point where these compounds can be properly neutralized before becoming an environmental hazard. In this study, the decomposition mechanisms of N-nitrosamines in a simulated CCS waterwash with residual alkanolamines was investigated using several laboratory-scale electrolyzers utilizing carbon xerogel (CX) electrodes. H-cell experiments revealed that N-nitrosamines were decomposed through a reduction reaction and are converted into their corresponding secondary amines thereby neutralizing their environmental impact. Batch-cell experiments statistically examined the kinetic models of N-nitrosamine removal by a combined adsorption and decomposition processes. The cathodic reduction of the N-nitrosamines statistically obeyed the first-order reaction model. Finally, a prototype flow-through reactor using an authentic waterwash was used to successfully target and decompose N-nitrosamines to below the detectable level without degrading the amine solvent compounds allowing them to be return to the CCS and lower the system operating costs. The developed electrolyzer was able to efficiently remove greater than 98% of N-nitrosamines from the waterwash solution without producing any additional environmentally harmful compounds and offers an effective and safe route to mitigate these compounds from CO₂ capture systems.

Drinking water treatment and associated toxic byproducts: Concurrence and urgence

Reclaimed water is highly required for environmental sustainability and to meet sustainable development goals (SDGs). Chemical processes are frequently associated with highly hazardous and toxic by-products, like nitrosamines, trihalomethanes, haloaldehydes, haloketones, and haloacetic acids. In this context, we aim to summarize the formation of various commonly produced disinfection by-products (DBPs) during wastewater treatment and their treatment approaches. Owing to DBPs formation, we discussed permissible limits, concentrations in various water systems reported globally, and their consequences on humans. While most reviews focus on DBPs detection methods, this review discusses factors affecting DBPs formation and critically reviews various remediation approaches, such as adsorption, reverse osmosis, nano/micro-filtration, UV treatment, ozonation, and advanced oxidation process. However, research in the detection of hazardous DBPs and their removal is quite at an early and initial stage, and therefore, numerous advancements are required prior to scale-up at commercial level. DBPs abatement in wastewater treatment approach should be considered. This review provides the baseline for optimizing DBPs formation and advancements in the remediation process, efficiently reducing their production and providing safe, clean drinking water. Future studies should focus on a more efficient and rigorous understanding of DBPs properties and degradation of hazardous pollutants using low-cost techniques in wastewater treatment.

NDMA adsorption and degradation by a new-type of Ag-MONT material carrying nanoscale zero-valent iron

Nitrosamines, which are emerging nitrogenous disinfection by-products, have raised great concern owing to their carcinogenicity and genotoxicity. Thus, exploring efficient materials to remove nitrosamines from the environment is of vital importance. In this work, NaBH₄ was taken as a reducing agent and Ag-based metal organic nanotubes (Ag-MONTs) were impregnated in FeSO₄·7H₂O to prepare nanoscale zero-valent iron (nZVI) supported on the nanotubes (nZVI@Ag-MONTs). The new material was then characterized and applied to N-dimethylnitrosamine (NDMA) adsorption and degradation in water. The material had excellent ability to adsorb and degrade NDMA, and the total concentrations of iron and silver remaining in water did not exceed standard limits after 120 min of adsorption. Coexisting substances, such as NO₃^-, Cl^-, CO₃^2-, humic acid, trichloromethane, and trichloronitromethane, did not affect the NDMA removal efficiency of the adsorbent. The NDMA removal efficiency of the new material exceeded 88% even in the presence of SO₄^2- and PO₄^3-. The NDMA degradation mechanism of nZVI@Ag-MONTs included a catalytic hydrogenation reaction and resulted in dimethylamine as the final degradation product. The nZVI@Ag-MONTs showed favorable stability and reusability. Taking the results together, the nZVI@Ag-MONTs proposed in this work are applicable to NDMA adsorption and degradation in water.

Occurrence of N-nitrosamines and their precursors in the middle and lower reaches of Yangtze River water

The presence of some types of N-nitrosamines in water bodies is of great concern worldwide due to their carcinogenic risks and harmful mutagenic effects on human health. In the present study, eight N-nitrosamines and their formation potentials (FPs) were primarily investigated in Yangtze River surface water to evaluate their spatial distribution, mass loads, and ecological risks. The results showed that of the eight N-nitrosamines investigated, NDMA (<1.5-17 ng/L), NDEA (<1.4-9.5 ng/L), NDPA (1.0 ng/L), NMOR (<1.0-1.3 ng/L), NPIP (<2.1-3.7 ng/L), and NDBA (<3.6-30 ng/L) were detected. The FPs of NDMA (<27-130 ng/L), NDEA (<0.9-2.3 ng/L), NDPA (<1.2-1.9 ng/L), NPYR (<1.4-2.9 ng/L), NMOR (<1.0 ng/L), and NDBA (<1.1-14 ng/L) were significantly identified. NDBA was predominantly observed in surface water, while NDMA was noticeably detected in chloraminated water samples. It was estimated that approximately 5.4 t/y of N-nitrosamines were carried by the Yangtze River to the East China Sea, whereas the input flux of N-nitrosamine precursors was estimated to be approximately 69.5 t/y. Spatial variations were observed due to the input of N-nitrosamines from the upstream dams and lakes. The origin of N-nitrosamine precursors was not associated with the presence of sediment in river water. NDEA could be introduced into river water by the discharge of wastewater. NDBA and its precursors could originate from industrial and aquaculture activities. NDMA and its precursors could result from both of the aforementioned sources. Moreover, the wastewater discharge from small cities, pH value, wastewater treatment ratio, and dilution could be the key factors that influence the occurrence of N-nitrosamines along the Yangtze River. More attention should be paid to the cancer risks posed by N-nitrosamines. The ecological risks posed by N-nitrosamines in the Yangtze River can be ignored.

Plasma jet assisted carbonization and activation of coffee ground waste

Activated carbon has been extensively utilized to adsorb pollutants generated by industrial activities. There have been many attempts to efficiently produce activated carbon from spent coffee grounds in the field of environmental technology. In this study, the feasibility of the novel production of activated carbon from coffee ground waste using a plasma jet was evaluated. A rotating gliding arc generator was designed that used an N₂ plasma jet for the carbonization process and a CO₂ plasma jet for the activation process. It was confirmed that the coffee ground waste could be carbonized and activated by the two plasma jets in the same reactor. The characteristics of the surface morphologies of the activated carbon samples varied depending on the plasma treatment conditions, such as the electric power of the plasma jet and the treatment time. The results implied that the adsorption capacity of the activated carbon could be optimized by regulating the pore size and distribution based on the plasma treatment conditions with regard to the molecular size of the target adsorbate.

Role of various factors affecting the photochemical treatment of N-nitrosamines related to CO2 capture

Post-combustion CO₂ capture using amine solvents is the most feasible method of reducing anthropogenic CO₂ emissions, which are the largest contributor to global warming. The formation of carcinogenic N-nitrosamines (i.e. by-products) can hinder the industrial application of this technology. In this study, the effects of direct UV photolysis (N-nitrosamine concentration and amines) and advanced oxidation processes (UV/H₂O₂ and UV/O₃) on the three specific N-nitrosamines that are commonplace in amine-based CO₂ capture (i.e. N-nitrosodiethylamine (NDEA), N-nitrosodiethanolamine (NDELA), and N-nitrosomorpholine (NMOR)) were examined. A significant decrease in the photodegradation rate constants was observed for NDEA (1.02 × 10⁰ to 2.94 × 10^-1 min^-1), NDELA (1.52 × 10⁰ to 3.32 × 10^-1 min^-1), and NMOR (1.93 × 10⁰ to 2.20 × 10^-1 min^-1) as their concentrations increased within 1-50 mg/L. This is the first report of a significant increase in the degradation rate constants of N-nitrosamine with an increase in amine concentrations (i.e. monoethanolamine, diethanolamine, and morpholine) within 10-200 mM. The photodegradation rate constants increased as the molar ratio of H₂O₂ to N-nitrosamine increased to 20, but then decreased at molar ratios beyond this. O₃ had a negligible effect on the photodegradation of N-nitrosamines.

An all-in-one strategy for the adsorption of heavy metal ions and photodegradation of organic pollutants using steel slag-derived calcium silicate hydrate

Low-cost and high-performance materials or techniques that could synergistically remove inorganic heavy metals and organic pollutants in a simple manner are highly desired. Herein, we report a simple and facile strategy by converting poisonous heavy metals into photocatalyst for the in-situ photodegradation of organic pollutants employing steel slag-derived calcium silicate hydrate (CSH). The CSH was synthesized by alkali activation method and showed hierarchical structure and amorphous phase. And, the material exhibited excellent adsorption performance towards all selected heavy metals. After adsorption, the heavy metals were converted into the corresponding amorphous metal hydroxides on the surface of CSH. The resulting CSH-supported amorphous metal hydroxides can act as visible-light photocatalysts for the photodegradation of organic pollutants. The optimal results for the whole water purification route using CSH are > 100 mg/g adsorption capacity for Cu²⁺ and ˜63% / 8 h photodegradation efficiency for methylene blue under visible light. The total cost for the whole route is < 0.1 $/g pollutants, much lower than traditional technologies. The strategy using steel slag derived-CSH not only meets the requirements for high-performance and low-cost materials, but also resolves the challenging issues of developing an all-in-one treatment for heavy metal ions and organic pollutants, which will be of great significance to wastewater purification.

Occurrence and ecological risk assessment of disinfection byproducts from chlorination of wastewater effluents in East China

Effluents containing disinfection byproducts (DBPs) from wastewater treatment plants (WWTPs) may be discharged to the receiving water bodies or reused for irrigation, landscaping, and environmental supplies as well as a source to replenish groundwater. Thus the formation and risk of the DBPs in disinfected wastewater effluents should be concerned. In this study, the occurrence of 44 DBPs including 6 trihalomethanes (THMs), 9 haloaceticacids (HAAs), 2 haloketones (HKs), 9 halonitromethanes (HNMs), 9 haloacetonitriles (HANs) and 9 nitrosamines (NAs) was investigated in 12 chlorinated WWTP effluents from five cities of East China. The contribution of each class of DBPs to the total DBPs concentration and additive toxicity was calculated. The average concentrations of the 6 classes of DBPs were ranked as follows: HAAs (47.0 μg/L) > THMs (28.0 μg/L) > HANs (9.9 μg/L) > HNMs (2.9 μg/L) > HKs (0.79 μg/L) > NAs (0.69 μg/L). The significant positive correlations were observed between the formation of THMs and HAAs, THMs and HANs, as well as HAAs and HANs. The results showed that HAAs and THMs were the dominant DBPs on a mass concentration basis and accounted for 54% and 29%, respectively in the total measured DBPs, but they made a minor contribution to the calculated DBP-associated cytotoxicity. HANs and NAs dominated the DBP-associated cytotoxicity, accounting for 50% and 34% on an additive toxicity basis despite the minor contributions to the mass concentration with 10% and 1%, respectively. The risk quotients for three taxonomic groups (fish, daphnid, and green algae) were calculated to assess the ecological risk of DBPs, and the results demonstrated that both HAAs and HANs had high ecological risk for green algae in chlorinated wastewater effluents.

Reducing Energy Penalty of CO2 Capture Using Fe Promoted SO42-/ZrO2/MCM-41 Catalyst

The high energy consumption of CO₂-loaded solvent regeneration is the biggest impediment for the real application of the amine-based CO₂ capture process. To lower the energy requirement, three Fe promoted SO₄^2-/ZrO₂ supported on MCM-41 (SZMF) catalysts with different iron oxide content (5%, 10%, and 15%) were synthesized and applied for the rich monoethanolamine solution regeneration process at 98 °C. Results reveal that the use of SZMF hugely enhanced the CO₂ desorption performances (i.e., desorption factor) by 260-388% and reduced the heat duty by about 28-40%, which is better than most of the reported catalysts for this purpose. The eminent catalytic activities of SZMF are related to their enhanced ratio of Brønsted to Lewis acid sites, weak acid sites, basic sites, and high dispersed Fe³⁺ species. Meanwhile, the addition of SZMF for CO₂ desorption shows a promotional effect on its CO₂ absorption performance, and SZMF presents an excellent cyclic stability. A possible mechanism is suggested for the SZMF catalyzed CO₂ desorption process. Results of this work may provide direction for future research and rational design of more efficient catalysts for this potential catalyst-aided CO₂ desorption technology.

Wastewater treatment in amine-based carbon capture

Amine-based CO₂ capture (ACC) has become one cost-effective method for reducing carbon emissions in order to mitigate climate changes. The amine-rich wastewater (ARWW) generated from ACC may contain a series of degradation products of amine-based solvents (ABSs). These products are harmful for ecological environment and human health. Effective and reliable ARWW treatment methods are highly required for mitigating the harmfulness. However, there is a lack of a comprehensive review of the existing limited methods that can guide ARWW-related technological advancements and treatment practices. To fill this gap, the review is achieved in this study. All available technologies for treating the ARWW from washwater, condenser, and reclaimer units in ACC are examined based on clarification of degradation mechanisms and ARWW compounds. A series of significant findings and recommendations are revealed through this review. For instance, ARWW treatment methods should be selected according to degradation conditions and pollution concentrations. UV light can be only used for treating wastewater from washwater and condenser units in ACC. Biological activated carbon is feasible for removing nitrosamines from washwater and condenser units. Sequence batch reactors, microbial fuel cells, and the other techniques for removing amines and similar degradation products are applicable for treating ARWW. This review provides scientific support for the selection and improvement of ARWW treatment techniques, the mitigation of ACC's consequences in environment, health and other aspects, and the extensive development and applications of ACC systems.