Recovery phosphorus (P) from P-contaminated wastewater is an efficient and environmentally friendly mean to prevent water pollution and alleviate the P shortage crisis. In this study, oyster shell as calcium sources and peanut shells as carbon sources (mass ratio 1:1) were used to prepare a novel Ca-modified biochar (OBC) via co-pyrolysis, and its potential application after P adsorption as a P biofertilizer for soil was also investigated. The results shown that OBC had a remarkable P adsorption capacity from wastewater in a wide range of pH 4–12. The maximum P adsorption capacity of OBC was about 168.2 mg/g with adsorbent dosage 1 g/L, which was about 27.6 times that of the unmodified biochar. The adsorption isotherm and kinetic data were better described by Langmuir isotherm model (R² > 0.986) and the pseudo second-order model (R² > 0.975), respectively. Characterization analysis of OBC before and after P adsorption by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and specific surface area and porosity analyzer (BET) indicated that the remarkable P adsorption capacity of OBC was mainly ascribed to chemical precipitation, electrostatic adsorption, and hydrogen bonding. Pot experiment results showed that OBC after P adsorption could significantly promote the germination and growth of Spinacia, which manifested that OBC after P adsorption exhibited a good ability to be reused as P fertilizer for soil.

Sewage sludge ash (SSA) was created by burning municipal sludge. The potential of clay containing 1 or 3 or 5% SSA was assessed for use as a landfill liner-soil material. Batch adsorption, low temperature N₂adsorption, and TG-DTA tests were performed to evaluate the adsorption capacity, micropore structure, thermostability, and components of soils under Cr(VI) and Pb(II) chemical solutions. With the increasing amount of SSA in modified clay, the adsorption capacity of Cr(VI) and Pb(II) to the modified clay increases gradually. After absorption, the pore size of modified clay ranges from 2 nm to 8 nm. With the increasing amount of absorption, the pore volume decreases and the specific surface area increases. With the increasing of adsorption concentration of Cr(VI) and Pb(II), the mass loss percentage of modified clay increases to 23.4% and 12.6%, respectively. The modified clay containing SSA may be used as a good barrier material to attenuate contamination of Cr(VI) and Pb(II) in landfills.