Microplastics removal from aquatic environment by coagulation: Selecting the best coagulant based on variables determined from a systematic review

Towards sustainable microplastic cleanup: Al/Fe ionotropic chitosan hydrogels for efficient PET removal

Chitosan (CHI) was modified with iron and aluminum salts to create ionotropic beads, Fe-CHI and Al-CHI, for the removal of polyethylene terephthalate microplastics (PET-MP) from water. Infrared spectroscopy revealed reduced hydrogen bonding associated with N-H vibration of CHI (3500-3100 cm-1) due to the interaction with the metal ions, and absorption peaks between 500 and 916 cm⁻1 predominantly due to metal-oxygen stretching vibrations. The swelling behavior of the beads increased with temperature but decreased as pH and metal doping concentration increased. Conductivity and PET-MP removal efficiency improved with higher metal ion concentrations, with Al-CHI exhibiting greater swelling and conductivity compared to Fe-CHI. The highest efficiency for MP remediation was recorded at low pH levels. MP adsorption decreased with rising temperatures and varied with pH changes due to protonation and deprotonation reactions of CHI, along with the various cationic and anionic species formed by the metals. At pH 7, MP removal by Fe-CHI beads declined as the doping concentration increased, attributed to specific Fe species that emerged at this pH. The zeta potential measurements showed that both the beads and the MP were in an unstable range at low pH but shifted towards stability at higher pH levels. Re-adsorption efficiencies exceeded 70% for both low and high-doped Fe-CHI and Al-CHI beads when tested with ~ 40 MP/mL of MP suspension over three different cycles. Overall, the use of ionotropic CHI beads offers a promising, eco-friendly method for effectively reducing PET-MPs in water.

Potential health, environmental implication of microplastics: A review on its detection

Microplastic contamination of terrestrial and aquatic environment has gained immense research attention due to their potential ecotoxicity and biomagnification property when enterer into food chain. Heterogenous nature of microplastics coupled with their ability to combine with other emerging pollutants have increased the severity of this crisis. Existing detection methods often fails to accurately quantify the amount of microplastic components present in environmental and biological samples. Thus, a great deal of research gap always exists in our current understanding about microplastics including the limitations in screening, detection and mitigation. This review work presents a comprehensive out look on the impact of microplastics on both terrestrial and aquatic environment. Furthermore, an in-depth discussion on various microplastic detection techniques recently used for microplastic quantification along with their significance and limitations is summarised in this review. The review also elaborates various physical, chemical and biological methods used for the mitigation of microplastics from environmental samples.

Innovative solutions for the removal of emerging microplastics from water by utilizing advanced techniques

Microplastic pollution is one of the most pressing global environmental problems due to its harmful effects on living organisms and ecosystems. To address this issue, researchers have explored several techniques to successfully eliminate microplastics from water sources. Chemical coagulation, electrocoagulation, magnetic extraction, adsorption, photocatalytic degradation, and biodegradation are some of the recognized techniques used for the removal of microplastics from water. In addition, membrane-based techniques encompass processes propelled by pressure or potential, along with sophisticated membrane technologies like the dynamic membrane and the membrane bioreactor. Recently, researchers have been developing advanced membranes composed of metal-organic frameworks, MXene, zeolites, carbon nanomaterials, metals, and metal oxides to remove microplastics. This paper aims to analyze the effectiveness, advantages, and drawbacks of each method to provide insights into their application for reducing microplastic pollution.

Emerging isolation and degradation technology of microplastics and nanoplastics in the environment

Microplastics (MPs, less than 5 mm in size) are widely distributed in surroundings in various forms and ways, and threaten ecosystems security and human health. Its environmental behavior as pollutants carrier and the after-effects exposed to MPs has been extensively exploited; whereas, current knowledge on technologies for the separation and degradation of MPs is relatively limited. It is essential to isolate MPs from surroundings and/or degrade to safe levels. This in-depth review details the origin and distribution of MPs. Provides a comprehensive summary of currently available MPs separation and degradation technologies, and discusses the mechanisms, challenges, and application prospects of these technologies. Comparison of the contribution of various separation methods to the separation of NPs and MPs. Furthermore, the latest research trends and direction in bio-degradation technology are outlooked.

Removal of microplastics from water by coagulation of cationic-modified starch: An environmentally friendly solution

Microplastics (MPs) pose a potential risk to aquatic ecosystems, and there is a growing demand to alleviate the contamination of MPs. Here, we introduce cationic-modified starch (CS) as an eco-friendly bio-coagulant for removing MPs from water. CS with varying degrees of substitution was synthesized and characterized, and its performance in removing MPs was evaluated under different MP sizes, types, and aging, as well as various water conditions. The results indicated that CS efficiently removed MPs, achieving an average removal rate of 65.33 % for polystyrene particles, with higher removal rates for larger, high-density, and aged MPs. The efficiency of CS remained consistent across a wide range of water pH values, but was significantly reduced in the presence of kaolin clay or/and humic acid. The removal efficiency of CS for MPs was enhanced by the non-ionic surfactant, Tween 20, but inhibited by the anionic surfactant, cetyltrimethylammonium bromide. In addition, CS could concurrently remove both MPs and phenanthrene, as a typical water contaminant. Moreover, the applicability of CS was demonstrated in natural water samples from the Ecological Demonstration Zone of the Yangtze River Delta, China, with an average removal rate of 60.13 ± 3.15 %. Taken together, this study offers an environmentally friendly and cost-effective approach for the removal of MPs from water, demonstrating CS has significant application potential as a sustainable solution to mitigate microplastic pollution.

Removal of most frequent microplastic types and sizes in secondary effluent using Al2(SO4)3: choosing variables by a fuzzy Delphi method

Microplastics (MPs) as an emerging pollutant can affect aquatic organisms through physical ingestion, chemical problems and possible creation of biological layers on their surfaces in the environment. One of the significant ways for MPs to enter the aquatic environment is through the effluent discharge of wastewater treatment plants (WWTPs). In this study, first, the concentration and characteristics of MPs in secondary wastewater effluent, and the influential variables related to the coagulation process, for MPs removal were identified using systematic reviews of previous studies. Then, the most proper MPs characterization and coagulation variables were chosen by experts' opinions using a fuzzy Delphi method. Therefore, the experiment tested in conditions close to the full-scale wastewater treatments. Finally, in the laboratory removal of MPs by coagulation of polyamide (PA), polystyrene (PS), and polyethylene (PE), < 125 and 300-600 μm in size, was tested by a jar test applying Al2(SO4)3 in doses of 5 to 100 mg/L plus 15 mg/L polyacrylamide as a coagulant aid. Using R and Excel software, the results were analyzed statistically. It was concluded that the maximum and minimum removal efficiency was 74.7 and 1.39% for small PA and large PE, respectively. Smaller MPs were found to have higher removal efficiency. The MPs type PA achieved greater removal efficiency than PS, while PE had the least removal efficiency.