The Application Of Excess Sludge In Garden Planting

A composite coagulant was dosed for the chemical conditioning of the excess sludge from municipal sewage plants and the optimal dosages were determined. Through a series of selective experiments, Zoysia matralla, Agrostis stolonifera, Cosmos bipinnatus, Helianthus annus, Hedera nepalensis var.sinensis and Zebrina pendula were chosen as the target plants to be potted by various proportions of sludge in soil. The growth situation and physiological indexes of the plants were observed, and the effect of applying sludge on the plants was studied so as to determine the optimal ratio of the sludge to soil, which provided the basis for the application of urban sludge in garden planting.The excess sludges of four sewage plants were added with the composite coagulant for chemical conditioning, and the specific resistance of the sludge during vacuum filtration and moisture content of the final sludge cake were investigated. The result showed that when the optimal dosage of the composite coagulant was in the range of 1.5%-2.5%(based on the weight of dry sludge), the dewaterability of the sludge was better. The applying dosage of the composite coagulant could be varied slightly depending on the original sludge sources.The pot experiments indicated that, when the ratio of sludge to soil was small, the sludge promoted the growth of the plants. The height, biomass, content of chlorophyll, soluble sugar and catalase activity (CAT) were all higher than those of the control group. And the content of malonaldehyde (MDA) was slightly higher than the control group, but the increment was small. However, when the ratio of sludge to soil was incresed gradully to some extent, the growth of the plants was inhibitated and some even died. When the ratio of sludge to soil was 10%-15%, it could promote the growth of Zoysia matralla and Agrostis stolonifera. When the ratio was 3%-7%, it could enhance the growth of Cosmos bipinnatus and Helianthus annus. And when the ratio was 3%-5%, the growth of Hedera nepalensis var.sinensis and zebrina pendula behaved better or maintained the same situation as the control.