Microplastics pollution in freshwater sediments: The pollution status assessment and sustainable management measures.

Microplastics (MPs) pollution in freshwater sediments has brought hidden dangers to food and drinking water supply. Implementing sustainable management measures for MPs pollution in freshwater sediments has become an inevitable trend for sustainable development of society. Existing studies still lacked sufficient discussion in sustainable management of MPs pollution in freshwater sediments. This makes it difficult to formulate sustainable management measures for MPs pollution in freshwater sediments. This study analyzed the pollution status of MPs in freshwater sediments from 84 study areas. The results showed that current studies on MPs pollution in freshwater sediments were mainly concentrated in densely populated and economically developed areas. The average abundance of MPs in freshwater sediments from collected study areas was 1290.88 items/kg, this brought a potential threat to sustainable development in surrounding areas. The pollution load level and potential ecological risk level of MPs in freshwater sediments from these study areas were low. Reducing MPs discharge and restricting the use of high-risk polymers are effective ways to prevent the deterioration of MPs pollution status in freshwater sediments. The abundance and types of MPs in freshwater sediments from these study areas were affected by human activities. Sustainable management of MPs pollution in freshwater sediments from collected study areas requires establishing a lifecycle management system for plastic products, and the industrial structures should be optimized. In addition, legislation and market regulation are effective ways to restrict the discharge of plastic wastes. Sustainable management of MPs in freshwater sediments requires the synergy of legislation and market regulation.

The sustainable management of microplastics pollution in sediments from China: Promulgating relevant laws and implementing targeted management.

Microplastics (MPs) pollution in sediments brings a huge challenge to the sustainable development of society. China is one of the countries with the largest production and application of plastic products in the world. The sustainable management of MPs pollution in sediments from China has important implications for achieving the United Nations Sustainable Development Goals. There is a lack of targeted management measures for the sustainable management of MPs pollution in sediments from China. In this study, 74 study areas were collected to analyze the pollution status of MPs in sediments from China. The results showed that the study on MPs pollution in sediments from China was concentrated in the Bohai Rim Economic Circle (n = 12), the Yangtze River Delta Economic Circle (n = 16) and the Pearl River Delta Economic Circle (n = 13). And the average abundance of MPs in sediments from China showed a decreasing trend from coastal to inland. Fiber had the highest centrality degree in the correlation network of MPs types. The reduction of fiber in sediments can reduce the diversity of MPs in sediments from China. Population density, economic level, urbanization level and industrial structure were significantly correlated with MPs types in sediments from China. The targeted management measures can be formulated based on the contribution of different human activities to MPs types. Managing pollution sources and cutting off transmission pathways are effective means for the targeted management of MPs in sediments. In addition, legislation can effectively restrict the application of plastic products. Promulgating relevant laws and implementing targeted management are conducive to the sustainable management of MPs pollution in sediments from China. In future studies, a big data platform for MPs pollution should be established to obtain a comprehensive understanding in the pollution status of MPs in sediments from China.

The pollution of microplastics in sediments: The ecological risk assessment and pollution source analysis.

The occurrence of microplastics (MPs) pollution in sediments has brought huge challenges to the development of society. Pollution control of MPs in sediments has become an inevitable requirement for current society. This requires implementing targeted pollution control measures in high MPs ecological risk areas and controls MPs discharge in pollution source. Existing studies lack in-depth understanding in MPs ecological risk assessment and MPs pollution source analysis, this limits the pollution control of MPs in sediments. In this study, the studies of MPs pollution in sediments from 2013 to 2022 were reviewed. The results showed that the environmental problems caused by MPs pollution in marine sediments have been widely discussed over the past decade. And the occurrence of MPs pollution in sediments brought potential threat to marine ecology and human food supply. Furthermore, pollution load index, polymer risk index and potential ecological risk index of MPs were frequently used in the existing ecological risk assessment of MPs in sediments. A large amount of monitoring data and simulation data is conducive to improving these MPs ecological risk assessment indicators. This can provide a useful reference for managers to formulate MPs pollution control measures. And MPs types and land-use types can provide basis to analyze the pollution source of MPs in sediments. Developing more accurate MPs detection and analysis technologies can further improve current MPs pollution source analysis system. This is conducive to control the discharge of MPs in the pollution source. In future studies, more complete MPs ecological risk assessment system and MPs pollution source analysis system should be established to control the pollution of MPs in sediments.

Dewatering municipal wastewater sludge using electro-coagulation combined with added free nitrous acid.

An electro-coagulation (EC) process combined with added free nitrous acid (FNA) improves sludge dewaterability. Under optimal conditions(EC voltage of 25 V, EC process time of 60 min, FNA dosage of 1.13 mg/L, pH value of 4.5), specific resistance to filtration (SRF) and water content (WC) was decreased by 89.57%, and 18.90%respectively. The EC process disrupted the sludge structure, reducing sludge particles' size (D50) from 59.5 to 50.5 µm. After adding FNA, the sludge cells lysed, and the DNA concentrations and soluble chemical oxygen demand (SCOD) increased from 6.07 µg/ml and 29 mg/L to 364 µg/ml and 588 mg/L, respectively. The conversion of Fe(II) to Fe(III) was enhanced. The addition of FNA after EC further improved the sludge dewaterability. Combined conditioning using EC and FNA can effectively destroy tightly bound extracellular polymeric substances (TB-EPS) and release bound water. In addition, the pH value is kept low, which benefits sludge dewaterability and the removal of heavy metals. The concentrations of Zn and Mn in the sludge cake were reduced by 92.3% and 69.0%, respectively. The Bureau of Reference (BCR) sequential extraction method showed increases in the percentages of the residual fractions of Zn and Mn, showing that EC combined with FNA is an efficient and versatile means of sludge conditioning.

Freeze-thaw combined with activated carbon improves electrochemical dewaterability of sludge: analysis of sludge floc structure and dewatering mechanism.

Freeze-thaw (F/T) and electrochemistry both are environment-friendly and efficient sludge treatment technologies. In this study, the sludge samples were frozen at - 15 °C, and 20% g/gTss activated carbon (AC) was added to the dissolved sludge. Finally, the uniformly mixed sludge was treated at a voltage of 15 V for 25 min. During the experiment, the effect of F/T on the floc structure was analyzed by a laser particle analyzer and scanning electron microscope. F/T treatment improved the dewatering performance of the sludge and promoted the aggregation of sludge flocs into larger particles either. At the same time, the median diameter (D50) increased from 45.27 to 128.94 µm. AC was added to the thawed sludge solution before electrochemical treatment (EP). The conductivity of AC enhanced the effect of EP, thereby cracking the sludge flocs. Therefore, the three-dimensional excitation-emission matrix (3D-EEM) intensity of tightly bound extracellular polymeric substances (TB-EPS) decreased significantly. The protein in TB-EPS decreased from 54 to 33%, and the D50 was also reduced to 105.3 µm. The final specific resistance of filtration and water content were reduced by 96.39% and 32.17%, respectively. The dehydrated cake elemental analysis showed that increased AC improved the sludge cake's combustion efficiency significantly. Moreover, the preliminary economic analysis indicated that the cost of this research was low, which implied the potential application value of combined treatment.

Granular activated carbon-supported titanium dioxide nanoparticles as an amendment for amending copper-contaminated sediments: Effect on the pH in sediments and enzymatic activities.

The problem of heavy metal pollution in sediments attracts increasing attention with the process of industrialization. In this study, a novel sediments amendment granular activated carbon (GAC)-supported titanium dioxide nanoparticles (GATN) was synthesized to amend copper (Cu)-contaminated sediments. The effect of the amendments on the potential mobility and bioavailability of Cu was evaluated by the concentration of Cu in the overlying water and the chemical speciations of Cu in sediments. After 35 days of incubation, GATN and GAC were separated from the GATN-amended sediments and the GAC-amended sediments. The European Community Bureau of Reference (BCR) sequence extraction procedure was performed on the separated sediments. Compared with the control group, the addition of 20% GATN amended sediments for 35 days, the Cu concentration in the overlying water decreased by 90.75%. Compared with original sediments, the exchangeable fraction and reducible fraction of Cu decreased from 42.30% to 17.36%-3.63% and 6.57%, respectively, and the oxidizable fraction and residual fraction of Cu increased from 13.57% to 26.77%-33.21% and 56.58%, respectively. The potential mobility and bioavailability of Cu were significantly reduced. According to the BCR sequence extraction results of the remaining sediments after the separation of the GATN, the Cu adsorbed on the GATN surface is mainly an oxidizable fraction, which is generated by the complexation reaction of hydroxyl (-OH) and Cu2+. Meanwhile, the present of GATN also can enhance the remediation capacity of sediments, which plays an important role during the amendment process. The pH was measured after GATN-amended sediments adding. Results showed that GATN improved their remediation capacity of sediments by optimizing the pH in sediments. The enzyme activity-experiment indicated that GATN effectively reduces the biological toxicity of Cu in Cu-contaminated sediments. Results verified that GATN, as a sediments amendment, has good application potential.

Remediation of copper contaminated sediments by granular activated carbon-supported titanium dioxide nanoparticles: Mechanism study and effect on enzyme activities.

After much effort, the remediation of heavy metal contaminated sediments still remains physically hard and technically challenging issue to resolve. In this study, granular activated carbon-supported titanium dioxide nanoparticles (GAC-TiO2 NPs) are synthesized to remedy heavy metal copper (Cu) contaminated sediments. The concentration and chemical speciation of Cu in overlying water, interstitial water and contaminated sediments are fully assessed to examine the remediation effect of GAC-TiO2 NPs. The GAC-TiO2 NPs are separated from GAC-TiO2 NPs-remedied sediments and characterized by X-ray photoelectron spectra (XPS), which reveals the mechanism of GAC-TiO2 NPs remedy Cu Contaminated sediments. The results show that after 35 days adding 20% GAC-TiO2 NPs to contaminated sediments, the Cu concentration in the overlying water and interstitial water decreases 89.47% and 83.52%, respectively, and the exchangeable fraction (F-1) of Cu in sediments decreases from 43.91% to 7.49%. The percentage of residual fraction (F-4) increases sharply from 42.79% to 80.30%. XPS results show that hydroxyl (-OH) plays an important role in the remediation process. The synergistic effects of pH, phosphorus concentration and organic matter (OM) content on the remediation effect are explored. When the pH value is 8, phosphorus concentration is 0.32 mg/L and OM content is 151.2 g/kg, adding 20% GAC-TiO2 NPs achieves the best remediation effect on Cu contaminated sediment. Biological enzyme-activity experiments prove that GAC-TiO2 NPs not only reduce the bioavailability and biotoxicity of Cu, but also effectively suppress the negative effects of granular activated carbon (GAC) on enzyme activities. All these results indicate that GAC-TiO2 NPs is an environmentally friendly remediation material for Cu contaminated sediments with high-potential applications.