Effects of Composted Sewage Sludge on Soil Properties and Vegetable Quality from Abandoned Quarries

Abstract

The effects of composted sewage sludge on soil properties and vegetable quality were investigated in a field experiment for two years. The soil was amended with 3, 15 or 30 t/ha of compost. The results indicated that the vegetable net production increased with the amendment dosage of 3 and 15 t/ha, while the net production decreased in the application amount of 30 t/ha. However, the Vitamin C (Vc) content of the three vegetables was reverse. The heavy metals concentrations in vegetables and soils could meet the national food and soil environmental quality standards of China (II). The accumulation concentrations of Cd, As and Hg in the three vegetables increased with the increasing amendment dosage, while the concentrations of Cr and Pb changed significantly with different types of vegetable. Heavy metal accumulation ability was in the order of celery > lettuce > cabbage, except for Cr. The accumulation of different heavy metals in soil was related to the migration characteristic of heavy metals, plant absorption capacities and the amendment dosage. The concentration of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in the soils increased with addition of 15 t/ha and 30 t/ha, while the change was not statistically significant between the amendment of 3 t/ha and the control. The concentration of PCBs and PAHs in vegetables was positively correlated with compost addition amounts. The dissipation rate of PCBs and PAHs followed the principle of first-order kinetics, and vegetables could improve the dissipation rate. Therefore, the application of compost as soil amendment to abandoned quarries is a feasible strategy for sludge disposal because appropriate amount of compost could enhance the soil fertility, while the long-term application should be considered seriously.