Nitrogen (N) and phosphorus (P) play pivotal roles in water eutrophication. Effective removal of N and P from water is a crucial approach to mitigating eutrophication. In the present study, pyrolyzed shell powder (PSP) and its silicon composite (CPSP-Si) were used for the simultaneous removal of N and P. Sodium silicate was added to PSP, which solidified PSP and thus reduced the loss of metal oxides contained in PSP during sintering, and enhanced the adsorption capacity for N and P. Kinetic test results revealed that simultaneous removal of N and P by PSP was 12.424 and 2.0 times higher than the removal of only N and only P systems, respectively. Adsorption isotherms showed that the maximum adsorption capacities of PSP for N and P in the N and P system were 433.15 mg N/g and 623.77 mg P/g, respectively. X-ray diffraction (XRD) analysis indicated that the products included conventional compounds such as calcium phosphate and magnesium phosphate, as well as struvite, swaknoite, and dittmarite. The fixed-bed column experiments revealed the breakthrough bed volume (BV) points for PSP at 259 BV and 778 BV, and for CPSP-Si at 1,156 BV and 1,203 BV, corresponding to N and P, respectively. Furthermore, the N and P adsorption efficiencies of CPSP-Si were significantly higher than those of PSP. Our results also showed that breeding wastewater treated with CPSP-Si significantly inhibited the growth of Chlorella vulgaris. Additionally, the maize pot experiment indicated that CPSP-Si enriching N and P has promising potential as a soil amendment in agricultural fields.
Li et al. (Mon,) studied this question.