To solve both the problems of P deficiency in arable soil and excessive waste sludge disposal, we evaluated hydrothermal carbonization of sludge with the aim of recycling sludge P resources for soil amendment. In contrast with pyrochars obtained through pyrolysis, hydrochars generated from hydrothermal carbonization often feature variable properties and therefore require detailed characterization. In this study, sludge-derived hydrochars were evaluated to determine their P content and fractionation, release and availability of P, and P adsorption and desorption behavior. We also assessed changes in P availability after soil was amended with the hydrochars. Our results showed that the chars were rich in total P (up to 25,175 mg kg −1 ), but most of the free fractions were transformed to bound fractions, thereby reducing the available P concentrations. However, available P content was >417 mg kg −1 , which was far higher than soil demand. The hydrochars shifted from releasing to adsorbing P adsorbent when the environmental P concentration increased above 20 mg L −1 . The hydrochars showed a high phosphate adsorption capacity (up to 23,815 mg kg −1 ) and the adsorbed P could be readily released. The addition of 1% P-laden hydrochar significantly enhanced the soil available P content by 8.93 mg kg −1 . These findings have important implications for further development of hydrochar-based P carriers as a slow-releasing fertilizer. Core Ideas Charring transformed P from readily available fractions to moderately available ones. Sludge-derived hydrochars showed the best performance in long-term P release. Sludge-derived hydrochars had better P retention capacity than their feedstock. Applying the sludge-derived hydrochar improved the available P content of soil.
Development of an efficient and green adsorbent is of great significance for phosphorus removal and recovery from eutrophic water. This work prepared an eggshell modified biochar (ESBC) by co-pyrolysis of eggshells and corn stalk. ESBC exhibited an excellent performance for phosphorus adsorption over a wide pH range (5–13), and achieved a maximum adsorption of 557.0 mg P/g. The adsorption process was well fitted by pseudo-second-order model (R 2 > 0.962) and Sips model (R 2 > 0.965), and it was endothermic (ΔH 0 > 0) and spontaneous (ΔG 0 < 0) according to thermodynamic analysis. The column experiment confirmed the feasibility of ESBC as a filter media for phosphorus removal in flow condition, and obtained a P removal of 460.0 mg/g. Soil burial tests indicated P-laden ESBC has a good P slow-release performance (maintained for up to 25 days). Overall, ESBC has a promising application potential as an efficient adsorbent for phosphorus recovery and subsequently as a slow-release fertilizer.
Mulch film and slow-release fertilizers are widely used in agriculture and horticulture, and it has become a trend to use degradable materials for the preparation of mulch films using slow-release materials. However, most degradable materials have poor performance or relatively high cost. In this study, three types of degradable materials, namely, poly(vinyl alcohol) (PVA), corn starch (CS), and alkali lignin (AL), were used as degradable materials to obtain a mulch film with a slow-release fertilizer function (MSRF). MSRF had excellent performance when 10% AL was added. The properties consisted of elongation at break (180.14%), water vapor permeability (203.8 g m–2 day–1), water resistance (its morphology remained good for 50 days), water absorption (300%), and urea release efficiency (cumulative release of 70.63% in 30 days). Rapid plant growth trials demonstrated that the MSRF had excellent functionality and that the MSRF could reduce the amount of fertilizer applied by about 70%. These excellent performances were due to the combination of chemical cross-linking (chemical bonding) between AL and PVA/CS molecular chains, the hydrogen bonding between the AL, PVA, and CS molecules, and the aggregation properties of AL. This provided a green and efficient strategy for the preparation and application of dual functions of mulching and the slow release of fertilizer.
危险品化学品经营许可证（带存储）