The use of calcium solutions is a cost-limiting factor for bio-cement production from microbially induced carbonate precipitation (MICP). The aim of this article is to analyse the feasibility of using recycled calcium sources to solidify sand, including oyster shells, scallop shells and eggshells, by comparing the physical and mechanical properties and microstructural characteristics of solidified sand with different recycled calcium sources and chemical calcium nitrate. The results show that oyster shells have the optimal effect on MICP, with values of permeability, dry density, unconfined compressive strength and calcium carbonate precipitation of 1.12 × 10⁻⁴ m s⁻¹, 2.09 g cm⁻³, 1454.6 kPa and 15.28%, respectively. Strength values of bio-cemented sands made from different recycled calcium sources in this article range from 845.1 to 1454.6 kPa. According to the SEM and XRD analysis, calcium carbonates originating from the above recycled calcium sources precipitate as globular vaterite, whereas the precipitation from calcium nitrate is a cluster mixture of vaterite and calcite. Oyster shells, scallop shells and eggshells derived from kitchen waste, which is more economical and environmentally friendly than calcium nitrate, can be applied as recycled calcium solutions in MICP.

The adsorption of Fe(III) onto the surface of microplastics (MPs) enhances their toxicity and mobility in aquatic environments, posing a serious threat to human health and ecosystem balance. This study investigated the adsorption mechanism and influencing factors of Fe(III) on three types of MPs with varying particle sizes and aging degrees using batch experiments in freshwater and saltwater. Machine learning (ML) techniques were employed to predict the adsorption capacity and conduct attribution analysis. The results showed that Fe(III) adsorption in both freshwater and saltwater followed Pseudo-First-Order kinetics and Langmuir isotherms, indicating a monolayer homogeneous physical reaction driven by oxygen-containing functional groups, hydrogen bonds and aromatic rings on the MP surface. The adsorption capacity of MPs for Fe(III) was higher in freshwater than in saltwater, and was positively correlated with the aging degree and pH value, but negatively correlated with the particle size. Among the tested ML models, the Random Forest and Gaussian Process Regression models with Bayesian Optimization performed well in predicting adsorption capacity, with pH value and aging degree identified as key factors based on SHAP analysis. This study conducted a comprehensive investigation of the adsorption behavior between MPs and Fe(III) in water, providing valuable insights for the risk assessment and prevention of MP and Fe(III) pollution in aquatic environments.

Microplastic (MP) pollution in aquatic ecosystems poses significant ecological and public health risks. A comprehensive understanding of estuarine MP pollution, influenced by multiple anthropogenic and environmental factors, remains elusive in current research. This study investigated the spatial distribution patterns and dominant factors influencing MP abundance (MPA) and physicochemical diversity in the river water and sediments of the Pearl River Estuary (PRE), while also assessing the associated ecological risks. The dominant MP categories in river water and sediments were fibers, clear in color, <1 mm in length, and composed of polyethylene terephthalate and polypropylene. Whereas inland regions showed higher MPA, nearshore regions exhibited marginally greater physicochemical diversity. Multivariate statistical analysis identified population density as the primary driver of both MPA in river water and MP physicochemical diversity in sediments. MP physicochemical diversity in river water was predominantly governed by the synergistic effect of salinity and the vegetation land. MPA in sediments depended on the synergistic effect of flow rate and watershed area. Ecological risk assessment identified elevated risks in the eastern study area driven by the presence of polymethyl methacrylate. This study establishes a scientific basis for PRE region MP management and provides global comparative data for estuarine MP research.