Peng Li

Livestock and poultry farming effluents (LPFE) have become a significant source of pollution in the agricultural water environment, with nitrogen (N) and phosphorus (P) being the major pollutants. The use of inexpensive Mg2⁺ -modified materials as crystallization carriers can enhance the struvite crystallization and precipitation reaction, enabling efficient recovery of N and P nutrients from LPFE. In this study, Mg2⁺ -modified corncob biochar (CCBC-Mg) and Mg2⁺ -modified natural zeolite (NZ-Mg) were assessed for their simultaneous recovery of N and P from LPFE. BET, SEM-EDS, FTIR, XRD and adsorption isotherm and adsorption kinetics modelling were used to study the N and P adsorption properties and mechanisms. The results showed that Mg2⁺ modification significantly enhanced the simultaneous ammonia nitrogen (AN) and total phosphorus (TP) recovery of the two materials. After modification, corncob biochar (CCBC-Mg) showed the best P recovery performance, while natural zeolite (NZ-Mg) showed the best AN recovery, with adsorption quantities reaching 116.99 mg/g and 47.50 mg/g, respectively. The findings demonstrated that the adsorption processes for both AN and phosphate across all materials adhered to the pseudo-second-order kinetic model and Langmuir isotherm, collectively indicating that monolayer adsorption governed by chemical interactions was the predominant mechanism. CCBC and NZ mainly adsorbed AN and TP by electrostatic attraction and ion exchange, whereas CCBC-Mg and NZ-Mg, mainly relied on struvite precipitation on the material surface. The Mg2⁺ - modification increased the solution pH and formed Mg-P precipitates on the material surface, providing a favourable alkaline environment and nucleation conditions for the struvite reaction, thereby promoting the simultaneous recovery of AN and TP by the materials. This study could provide a theoretical basis for the design of struvite carrier for the simultaneous recovery of AN and TP from LPFE by the struvite precipitation method, and promote the application of this process in livestock and poultry farming effluent treatments.

Coagulation can effectively recover substances from wastewater; however, there is a lack of efficient coagulants for simultaneous recovery of organic matter, nitrogen, and phosphorus. We prepared a composite polysilicate metal (CSM) flocculant by combining Fe³⁺ and Mg²⁺ ions in polysilicic acid (PSiA). According to the results of scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), the CSM exhibited a larger amorphous phase along with new compounds, including Mg₃Fe₂(SiO₄)₃ and hydroxyl metals. The CSM demonstrated a higher coagulation efficiency than PSiA and polymeric ferric sulfate, particularly for PO₄³⁻-P and NH₄⁺-N removal. The metal/silicate molar ratio substantially influenced the structure and composition of the CSM, along with the coagulation efficiency, with an optimal ratio of 3:1. Additionally, we proposed a novel preparation strategy to achieve an optimum CSM basicity (B*) for coagulation by adjusting the initial pH of PSiA (pH_Initial) without adding an alkali agent. The results demonstrated that the optimum B* can be obtained by adjusting pH_Initial to 0.5 or 1. The overall optimum coagulation performance for the simultaneous removal of organic matter, PO₄³⁻P, and NH₄⁺-N from wastewater was 68.5%, 99%, and 17.5%, respectively. This study provides a feasible approach for synchronous pollutant recovery from wastewater.

The nitrate nitrogen of groundwater samples which sampled 24 times from 2006 to 2017 in the intensive agricultural region of Pinggu district in Beijing were analyzed in this study, in order to investigate its dynamic change and important influence factors of this region. The results indicated that the mean value of nitrate nitrogen in groundwater of this region was 6.23 mg/L, which had reached the third level of the national groundwater quality standard, and the annual nitrate nitrogen concentration in groundwater of the region tended to increase. The significant positive correlations between the annual average concentrations of nitrate nitrogen in groundwater and the statistical data of livestock and poultry products from 2006 to 2015 implied that the impact of livestock and poultry industry on the nitrate in groundwater should not be ignored in the region. The increase of precipitation has a trend of increasing the difference of nitrate in groundwater in Pinggu district. The nitrate nitrogen in groundwater sampled from orchard was markedly higher than which from grain field and vegetable field. Samples from deeper well (WD3) always locatd in mountainous area, their nitrate nitrogen was significantly higher than which from spring well (WD1) and well with 30 to 100 m depth (WD2).