Air quality in Northern China has become a global hot spot issue due to a series of air pollution events in the recent years. In this study, five representative air pollutants (PM_2.5, SO₂, NO₂, CO, and O₃) were employed to reveal the spatial and temporal distribution of air pollution in Northern China. Periodic decline in PM_2.5, SO₂, CO, and NO₂ from 2016 to 2018 indicated that air pollution control measures have achieved desired results. In addition, PM2.5 was significantly positively correlated with SO₂, CO, and NO₂ (p < 0.001), and O₃ had negative correlations with the other four pollutants. Furthermore, the heavy pollution phenomenon in Shijiazhuang, Anyang, Xingtai, and Handan was attributed to their industrial structures (e.g., steel industry) and geographical location based on clustering analysis. Contrary to above four pollutants, the annual average concentrations of O₃ increased in all the nine cities (1.4–35.9%) from 2016 to 2018. It is necessary to plan mitigation strategy for O₃ based on further investigation of source and formation mechanism of O₃.

Cd(II) ion-imprinted mesoporous (IIM) materials were synthesized using surface imprinting technique. The materials were characterized by TEM, FTIR, XRD and the adsorption behavior of the materials towards Cd(II) in aqueous solution was studied. The results show that the material has a typical mesoporous structure with the average pore size of 6.23 nm. The batch adsorption experiments were performed using the prepared ionic imprinted mesoporous material as absorbent. The effects of adsorption time, temperature and pH on the adsorption capacity were investigated. Additionally, the thermodynamics and kinetics analyses were also carried out. The results demonstrate that the adsorption capacity is 49.6 mg · g^–1 when the adsorption time is 1 h, the temperature is 25 °C and pH is 7.0. The removal efficiency can exceed 80%. The adsorption is a spontaneous, exothermic and entropy decrease process based on the results of adsorption thermodynamics. The obtained ionic imprinted mesoporous material possesses high adsorption capacity towards Cd(II) and can be reused.

Effective nitrogen removal from anaerobic co-digestion is a major challenge to achieving dual-carbon goals. This study explored the acclimatization process of a lab-scale two-stage partial nitritation and anammox process of a stepwise increase in the percentage of raw anaerobic co-digestion liquor from kitchen waste, human feces, and municipal sludge in a venous industrial park in China, which has not been reported yet. Under limited dissolved oxygen (below 0.5 mg/L) and high ammonia levels (200–1500 mg/L), based on adjusting aeration rates, partial nitritation rapidly started up in 50 days. After acclimatization, partial nitritation still performed efficiently and stably, with the final total nitrogen loading rate (TNLR) of 1.24 ± 0.09 gN/L/d, nitrite accumulation rate of 99 ± 4%, and ratio of eff. nitrite/ammonia of 1.32 ± 0.13. In the anammox process, the final total nitrogen removal efficiency, total nitrogen removal rate, and TNLR reached 94 ± 5%, 1.27 ± 0.03 gN/L/d, and 1.36 ± 0.05 gN/L/d, respectively. Chemical oxygen demand (COD) was also reduced in both reactors, with COD removal rates of 0.7 gCOD/L/d in the partial nitritation and 0.4 gCOD/L/d in the anammox process. Overall, the PNA system demonstrated its feasibility in adapting to high ammonia, salinity, and iron levels, when treating anaerobic co-digestion liquor, particularly regarding resource recovery in venous industrial parks.