Performance of commercially available soil amendments for enhanced Cu attenuation in bioretention media

Replacement depth and lifespan prediction of enhanced bioretention media under TSS impact conditions

The enhanced bioretention system provides a new way to solve the problems of stormwater management brought by urbanization. The knowledge on effects of media modification and long-term operation is scattered, so clogging interaction function, clogging time and depth are analysed to uncover the underneath. River sand, loess, and compost were used as basic fillers, and air-dried water treatment residual (WTR) and recycled aggregate from construction waste (RACW) were used as modifiers to formulate mixed fillers, and synchronized observation of the change rule of hydraulic conductivity and porosity of vertical layering. The study found that the infiltration coefficient of each system tended to decay gradually from top to bottom as the influent TSS accumulated. A set of improved media clogging process prediction framework has been proposed, using rainfall conditions in Northwest China as input conditions, the system clogging time is about 5.5∼7.1 years and the depth of replacement is about 35 cm based on the principles of cake filtration and deep filtration. The results can further understand the function variation of bioretention system under TSS impact conditions, which is helpful to the prediction of the operating life of the system and the evaluation of media replacement depth.

In situ monitoring of internal water storage reveals nitrogen first flush phenomena, intermittent denitrification, and seasonal ammonium flushing

Internal water storage (IWS) can be included in bioretention practices to increase storage capacity or promote denitrification-the microbial reduction of nitrate to nitrogen gas. IWS and nitrate dynamics are well studied in laboratory systems. However, the investigation of field environments, consideration of multiple nitrogen species, and determination between mixing versus denitrification is lacking. This study employs in situ monitoring (∼24 h duration) of water level, dissolved oxygen (DO), conductivity, nitrogen species, and dual isotopes of a field bioretention IWS system for nine storms events over a year period. Rapid peaks in IWS conductivity, DO, and total nitrogen (TN) concentrations occurred along the rising limb of the IWS water level and indicated a first flush effect. TN concentrations generally peaked during the first ∼0.33 h of sampling and the average peak IWS TN concentration (C_max = 4.82 ± 2.46 mg-N/L) was 38% and 64% greater than the average TN along the IWS rising and falling limb, respectively. Dissolved organic nitrogen (DON) and nitrate plus nitrite (NO_x) were the dominant nitrogen species of IWS samples. However, average IWS peak ammonium (NH₄⁺) concentrations August through November (0.28 ± 0.47 mg-N/L) demonstrated statistically significant shifts compared to February through May (2.72 ± 0.95 mg-N/L). Average lysimeter conductivity measurements were more than ten times higher February through May. The sustained presence of sodium observed in lysimeters, from road salt application, contributed to NH₄⁺ flushing from the unsaturated media layer. Dual isotope analysis showed denitrification occurred for discrete time intervals along the tail of the NO_x concentration profile and the hydrologic falling limb. Longer antecedent dry periods (17 days) did not correlate to enhanced denitrification but did correspond to more leaching of soil organic nitrogen. Results from field monitoring highlight the complexities of nitrogen management in bioretention systems. First flush behavior into the IWS suggests management to prevent TN export is most critical during the onset of a storm.

Adaptability of enhanced bioretention cell for nitrogen and phosphorus removal under two antibiotics stress

The overuse of antibiotics in the medical and aquaculture industries has led to the frequent detection of antibiotics in wastewater. Considering antibiotics would have an unknown impact on wastewater treatment in the future, the long-term effects of sulfamethoxazole (SMX) and tetracycline (TC) stress on the performance, functional genes and microbial community in three bioretention cells were investigated. The results showed that during the experiment, 0.8-1.2 mg/L of SMX would not destroy the water treatment capacity of the bioretention cells, and had a promoting effect on total nitrogen and ammonia nitrogen. 1.6 mg/L of SMX would cause the reduction of nitrogen removal efficiency and the phenomenon of phosphorus release, but it could be restored after a period of operation. TC of 0.8-1.2 mg/L did not have a significant impact on the removal of nutrients in AC-BRC (activated carbon-bioretention cell) and ACI-BRC (activated carbon and iron-bioretention cell), but TC of 1.2 mg/L caused the phenomenon of phosphorus release in BRC and the decrease of total nitrogen removal rate, 1.6 mg/L TC could make the bioretention cell lose its water treatment capacity. qPCR analysis of denitrification genes showed that the abundance of nirS, nirK, nosZ, and hzo had varying degrees of decrease before and after antibiotic stress, which meant the two antibiotics significantly inhibited the reduction of nitrite and nitrous oxide. But for the total number of bacteria, the relative abundance of the four genes has increased. The results of microbial community analysis also found that Proteobacteria, Bacteroidetes, Chloroflexi, and BIrii41, Denitratisoma, Ferritrophicum, Thiobacillus occupied the dominant species at the phylum level and the genus level respectively, which included most of the denitrifying bacteria. During the experiment, the nitrogen and phosphorus removal efficiency of AC-BRC and ACI-BRC were enhanced obviously, but ammonia nitrogen accumulated in ACI-BRC in the early stage of the reaction.