炭化生活污水污泥对酸化红壤的改良效果

Amelioration of Acidified Red Soil by Pyrolyzed Wastewater Sludges

从南京市、马鞍山市和丹阳市的3个污水处理厂采集污泥,在500℃下热解制备炭化污泥,测定了污泥和炭化污泥的性质和重金属含量,研究了污泥和炭化污泥对酸性红壤改良效果,并探讨了炭化污泥中重金属的环境风险。结果表明,污泥和炭化污泥中含有一定量的碱,添加炭化污泥可提高红壤的p H和交换性钙、镁和钾含量,降低土壤交换性铝和交换性H+含量。但污泥中大量铵态氮的硝化作用释放质子,抵消了污泥对红壤酸度的改良作用。添加污泥和炭化污泥提高了土壤有机碳、有效磷和速效钾的含量,提高了土壤肥力。污泥炭化后重金属含量有所增加,但大部分重金属的有效态含量下降,说明热解过程可以降低部分有毒重金属的活性。与对照相比,添加炭化污泥会增加土壤中部分重金属有效态含量,特别是有效态锌含量显著增加,因此炭化污泥农业利用存在一定的环境风险。建议将炭化污泥用于酸化的森林红壤的改良。

The sewage sludges were collected from three municipal sewage treatment plants in Nanjing, Danyang, and Ma Anshan and then the pyrolyzed wastewater sludges were prepared at 500℃. The properties of the wastewater sludges and pyrolyzed wastewater sludges were measured, and their ameliorating effects on the acidity of a red soil and the environmental risk of application of the pyrolyzed wastewater sludges were investigated. The results indicated that incorporation of pyrolyzed wastewater sludges increased soil pH and soil exchangeable Ca2＋, Mg2＋ and K＋ and decreased soil exchangeable acidity due to the alkalinity of the pyrolyzed sludges. However, the strong nitrification occurred due to large amount of ammonium presented in the sludges when the sludges were incorporated into the soil, which produced the large numbers of protons and offset the ameliorating effects of the sludges on the acidified red soil. The incorporation of the sluges and pyrolyzed sluges increased the contents of soil organic carbon, available phosphorus and readily available potassium and thus improved soil fertility. The pyrolyzation of the sluges led to the increase of the total amount of heavy metals in the sluges, while the contents of the available species of most heavy metals in the sluges were decreased, which suggested that the pyrolyzation of the sluges decreased the activity of most heavy metals in the sluges. Compared with control, the incorporation of the pyrolyzed sludges increased the available species of some heavy metals in the soil, and the content of the available Zn increased obviously. Therefore, there is the potential environmental risk for the pyrolyzed wastewater sludges used in agricultural soils. It is a better choice to use the pyrolyzed wastewater sludges to correct the acidity of the forest soils.