Phosphorus in wastewater sludge is a valuable resource although coagulated sludge reported to give only 10% of plant availability of phosphates. Since all Al and Fe added as coagulants end up in sludge, the potential ...Phosphorus in wastewater sludge is a valuable resource although coagulated sludge reported to give only 10% of plant availability of phosphates. Since all Al and Fe added as coagulants end up in sludge, the potential to substitute them with cationic coagulants was studied. During combined coagulation, substitution possibilities up to 44% were observed with low coagulant-to-particle ratio where the adsorption-charge neutralisation (ACN) anticipated being the predominant mechanism. Comparatively high coagulant-to-particle ratio preferred Sweep-floc mechanism giving <20% substitution possibilities, though even lower values anticipated at higher phosphate removals. The cationic polymers’ ability to compete with positively charged Al- and Fe-hydrolysis products was argued as the explanation for higher substitution possibilities during ACN mechanism. Sub-stitutions can be enhanced with dual coagulation with intermediate sludge separation by avoiding competition between two coagulants.展开更多
Paddy fields in the southeastern basin of Dianchi Lake have rapidly changed to greenhouses since 1999. A total of 61 surface soil samples, including 43 greenhouse soils, 12 upland soils, and 6 paddy soils, were collec...Paddy fields in the southeastern basin of Dianchi Lake have rapidly changed to greenhouses since 1999. A total of 61 surface soil samples, including 43 greenhouse soils, 12 upland soils, and 6 paddy soils, were collected from a flat lowland area mainly used for agricultural production fields in the southeastern basin of Dianchi Lake. Analyses of the soil samples indicated that the greenhouse soils were characterized by a lower organic matter content, lower pH, and higher soluble nutrients than the paddy soils in the area. The lower organic matter content of the greenhouse soils was ascribed to environmental or management factors rather than the clay content of the soil. Accumulation of soluble nutrients, especially inorganic N, was due to over-application of fertilizers, which also caused soil acidification. The average amount of readily available N, P, and K accumulated in the greenhouse soils was estimated to be equal to or higher than the annual input of these nutrients as a fertilizer, indicating that a reduction in fertilizer application was possible and recommended. In contrast, a very low available Si content was observed in the paddy soils, suggesting the need for Si application for rice production.展开更多
文摘Phosphorus in wastewater sludge is a valuable resource although coagulated sludge reported to give only 10% of plant availability of phosphates. Since all Al and Fe added as coagulants end up in sludge, the potential to substitute them with cationic coagulants was studied. During combined coagulation, substitution possibilities up to 44% were observed with low coagulant-to-particle ratio where the adsorption-charge neutralisation (ACN) anticipated being the predominant mechanism. Comparatively high coagulant-to-particle ratio preferred Sweep-floc mechanism giving <20% substitution possibilities, though even lower values anticipated at higher phosphate removals. The cationic polymers’ ability to compete with positively charged Al- and Fe-hydrolysis products was argued as the explanation for higher substitution possibilities during ACN mechanism. Sub-stitutions can be enhanced with dual coagulation with intermediate sludge separation by avoiding competition between two coagulants.
基金Supported by the JSPS KAKENHI,Japan(No.21255007)
文摘Paddy fields in the southeastern basin of Dianchi Lake have rapidly changed to greenhouses since 1999. A total of 61 surface soil samples, including 43 greenhouse soils, 12 upland soils, and 6 paddy soils, were collected from a flat lowland area mainly used for agricultural production fields in the southeastern basin of Dianchi Lake. Analyses of the soil samples indicated that the greenhouse soils were characterized by a lower organic matter content, lower pH, and higher soluble nutrients than the paddy soils in the area. The lower organic matter content of the greenhouse soils was ascribed to environmental or management factors rather than the clay content of the soil. Accumulation of soluble nutrients, especially inorganic N, was due to over-application of fertilizers, which also caused soil acidification. The average amount of readily available N, P, and K accumulated in the greenhouse soils was estimated to be equal to or higher than the annual input of these nutrients as a fertilizer, indicating that a reduction in fertilizer application was possible and recommended. In contrast, a very low available Si content was observed in the paddy soils, suggesting the need for Si application for rice production.
