In this study, the current situation of five types of toxic organics and endocrine disrupters in the sediments of rivers around Beijing, i.e., polycyclic aromatic hydrocarbons (PAHs), phthalic acid esters (PAEs), organic chlorinated pesticides (OCPs), estrogens (Es), and bisphenol A (BPA), which included 56 contaminants, was analyzed and compared with that registered by the historical literatures. The ecological risks were also assessed. The total concentration of PAHs, PAEs, OCPs, Es, and BPA ranged from 232.5 ng·g–1 to 5429.7 ng·g–1, 2047.2 ng·g–1 to 18051.5 ng·g–1, 4.5 ng·g–1 to 11.7 ng·g–1, 18.1 ng·g–1 to 105.2 ng·g–1, and 36.3 ng·g–1 to 69.6 ng·g–1, respectively. Among these five types of organic compounds, the concentration levels of PAHs and OCPs have decreased significantly in the last ten years, while those of PAEs and Es had an upward trend compared with the previous studies. BPA still remained at a moderately high level, as it was ten years ago. The risks of the PAEs in all of the sample sites, and fluoranthene, benzo[a]anthrene, and benzo[a]pyrene in the Wenyu River sediment, were relatively high. These results supplemented the database of toxic organics’ concentration levels in the sediments of Beijing rivers.
A membrane-aerated biofilm reactor was employed to investigate the nitrogen removal of one typical municipal reverse osmosis(RO) concentrate with a high total nitrogen (TN) concentration and a low C/ N ratio. The effects of operational conditions, including the aeration pressure, the hydraulic retention time and the C/N ratio, on the systematic performance were evaluated. The nitrogen removal mechanism was evaluated by monitoring the effluent concentrations of nitrogen contents. Furthermore, the microbial tolerance with elevated salinity was identified. The results indicated that the optimal TN removal efficiency of 79.2% was achieved of the aeration pressure of 0.02 MPa, hydraulic retention time of 24 h, and the C/N ratio of 5.8, respectively. It is essential to supplement the carbon source for the targeted RO concentrate to promote the denitrification process. The inhibitory effect of salinity on denitrifying bacteria and nitrite oxidizing bacteria was significant, revealing the limited TN removal capacity of the conditions in this work. The TN removal efficiency remained more than 70% with the addition of salt (NaCl) amount below 20 g/L. This work preliminarily demonstrated the MABR feasibility for the nitrogen removal of municipal RO concentrate with low C/N ratio and provided technical guidance for further scale-up application.
