Biochar-derived dissolved organic carbon (BDOC) may influence the environmental fate and behavior of tetracycline antibiotics in subsurface environments. In this study, BDOC derived from the pyrolysis of wheat straw at three distinct temperatures (300 °C, 450 °C, and 600 °C) was used to investigate its influence on the transport of oxytetracycline (OTC) through saturated quartz sand. The findings demonstrated that BDOC enhanced OTC mobility due to steric hindrance caused by organic matter accumulation, competition for retention sites between OTC and BDOC, and increased electrostatic repulsion between anionic species, including OTC⁻ ions and quartz sand. Notably, the mobility-enhancing effects of BDOC became significantly more pronounced at higher pyrolysis temperatures, likely resulting from increased organic matter deposition on sand surfaces and intensified electrostatic interactions. However, the promoting effect of BDOC on OTC transport was attenuated as pH increased from 5.0 to 9.0, which was attributed to reduced competitive deposition and steric effects caused by BDOC retention. Furthermore, cation-bridging, particularly with Cu²⁺ in the background solution, amplified BDOC's promotion effects. These results highlight that dissolved organic carbon released from biochar exerts a notable influence on the antibiotics' mobility within the aquifers.

Low impact development (LID) devices or green infrastructures have been advocated for urban stormwater management worldwide. Currently, the design and evaluation of LID devices adopt the Intensity-Duration-Frequency (IDF) method, which employs the average rainfall intensity. However, due to variations of rainfall intensity during a storm event, using average rainfall intensity may generate certain errors when designing a LID device. This paper presents an analytical study to calculate the magnitude of such errors with respect to LID device design and associated device performance evaluation. The normal distribution rainfall (NDR) with different standard deviations was employed to represent realistic rainfall processes. Compared with NDR method, the error in sizing the LID device was determined using the IDF method. Moreover, the overflow difference calculated using the IDF method was evaluated. We employed a programmed hydrological model to simulate different design scenarios. Using storm data from 31 regions with different climatic conditions in continental China, the results showed that different rainfall distributions (as represented by standard deviations (σ) of 5, 3, and 2) have little influence on the design depth of LID devices in most regions. The relative difference in design depth using IDF method was less than 1.00% in humid areas, −0.61% to 3.97% in semi-humid areas, and the significant error was 46.13% in arid areas. The maximum absolute difference in design depth resulting from the IDF method was 2.8 cm. For a LID device designed for storms with a 2-year recurrence interval, when meeting for the 5-year storm, the relative differences in calculated overflow volume using IDF method ranged from 19.8% to 95.3%, while those for the 20-year storm ranged from 7.4% to 40.5%. The average relative difference of the estimated overflow volume was 29.9% under a 5-year storm, and 12.0% under a 20-year storm. The relative difference in calculated overflow volumes using IDF method showed a decreasing tendency from northwest to southeast. Findings from this study suggest that the existing IDF method is adequate for use in sizing LID devices when the design storm is not usually very intense. However, accurate rainfall process data are required to estimate the overflow volume under large storms.