The effectiveness and feasibility of ball-milled powdered activated carbon (BPAC) for removal of organic pesticides in conventional drinking water treatment process.

In the conventional drinking water treatment process (CDWTP), powdered activated carbon (PAC) is commonly used for removing organic pesticides, or other organic contaminants. However, the hydraulic retention time (HRT) in CDWTP is insufficient for fulfilling PAC adsorption equilibrium to realize its full capacity. This study examined the adsorption kinetics, adsorption thermal dynamics, and removal efficiency for six organic pesticides using the ball-milled PAC (BPAC) with varying particle sizes in CDWTP. Based on the experiments with the pesticides of atrazine, diazinon, dimethoate, fenitrothion, isoproturon and thiometon, the results indicated that as the particle size reduced from around 38 µm for the commercial PAC to 1 µm for the BPAC, the adsorption rates for hydrophobic pesticides increased up to twentyfold. Diffusional adsorption from the bulk solution to the external PAC surface is the most likely predominant mechanism. This could allow a sufficient pesticides' adsorption within the limited HRT and to achieve a great depth removal of these toxic compounds. However, the addition of BPAC with a diameter of 1 µm was observed to significantly increase residual particles in treated water after the conventional treatment process. With a further systematic evaluation of both adsorption rate and particle penetration, a particle size of around 6 µm BPAC was considered a practical compromise between the adsorption rate and particle penetration for real application. Results from five surface waters of different water quality indicated that, compared to commercial PAC, application of 6 µm BPAC could achieve up to a 75% reduction in adsorbent dosage while maintaining around the same pesticide removal efficiencies. Additionally, thermodynamic analyses suggest that adsorption of these pesticides could be enthalpically or entropically driven depending on the degree of pesticide hydrophobicity.

Distribution Characteristic and Migration Mechanism of Toxic Gases in Goafs during Close-Distance Coal Seam Mining: a Case Study of Shaping Coal Mine.

It is imperative to have an in-depth understanding of the gas migration mechanism during close-distance coal seam mining, not only to prevent fires in the coal industry but also to propose safety strategies for controlling toxic gases. The 1818 working face of the Shaping Coal Mine was used as an exemplary close-distance coal seam mine. Through the construction of boreholes and the arrangement of bundle pipes in the two parallel grooves of the working face and the upper goaf at the corresponding positions in the working face, the gases in the upper and lower goafs were monitored online timely. The firsthand information about the gas distribution was obtained through on-site tests, which provided the robust data for studying the migration mechanism of toxic gases during close-distance coal seam mining. By studying the spatial distribution of harmful gases in the upper goaf without mining the overlying coal, the static distribution law of gas was obtained. By discussing the spatial distribution and migration of harmful gases in the goaf of the overlying coal seam during mining, the dynamic distribution law of the gas was obtained. By studying the spatial distribution and migration of toxic gases in the mined-out area of the lower coal seam during mining, the dynamic distribution of gases in the mined-out area of the lower coal seam was obtained. Moreover, the migration mechanism of gas emission from the goafs in the close-distance coal seam was explored. By analyzing the factors responsible for the accumulation of toxic gases in the return air corner, feasible safety measures were also proposed to prevent this hazard during close-distance coal seam mining.