The exponential decay of the amount of new litter on Wadahama Beach, Nii-jima Island, Japan revealed by 20-month mark-recapture experiments demonstrates a linear response of the beach to the input of target items. Here we show the amplitude and phase characteristics of the beach as a time-invariant linear input/output system and discuss the hydrodynamic and geomorphological factors that would determine the characteristics with the aid of a diffusion equation. The characteristics are fully determined by the residence time of the items (τr=209days) and can be described as functions of the ratio of τr to the period of input variability. The decay is reproduced well by the analytical solution of the equation with a constant diffusion coefficient (D), whose order was estimated by τr and the backshore width. Generally, D would depend on hydrodynamical statistics and beach geomorphology as well as the dimensions and density of the items.

Microporous–mesoporous activated carbons from five different types of agro-industrial wastes were produced using chemical activation with ZnCl₂ and carbonization at mild conditions of 600 °C, comprehensively characterized and investigated for removal of methylene blue (MB) in aqueous solution, a model large-molecular-size organic pollutant. The external part of the mango pit (mango seed husk) was used for the production of activated carbon (AC) for the first time. Despite that the raw agro-materials exhibited significantly different porosity, all activated carbons produced possessed well-developed microporous–mesoporous structures showing high surface areas and micropore volumes. Further, it was revealed that the pore size distribution of raw agro-material is a more important property in development of microporous–mesoporous structure of produced ACs than their overall porosity. All activated carbons produced adsorbed MB, reaching in most cases 100 % removal from the aqueous phase. Adsorption data were fitted well to a pseudo-second-order kinetic model. For MB adsorption, the mesoporosity and the ratio of micropores accessible for MB were the key factors since there exists the size-selectivity effect on MB adsorption due to MB molecular dimensions. The molecular dimensions of MB were estimated via DFT calculations to 1.66 × 0.82 × 0.54 nm, and this parameter was correlated with determined micropore size distributions of activated carbons.