Feasibility Study On Sewage Sludge Landscaping Application In Xi’an

Productivity of municipal sewage sludge increased with the increasing sewagetreatment rate, which brings about the high pressure on its final disposal. Application ofmunicipal sewage sludge to landscaping is considered to be one of the promising sludgedisposal options. In this study, dewatered sewage sludge from four wastewater treatmentplants in Xi’an city were collected and analyzed. Experiments of aerobic compost inhigh temperature were conducted for dewatering sludge to investigate the change ofnutrients and heavy metal forms. Thereafter, the compost prepared was used as manurefor the growth of plants to investigate its effect on the growth. As such, feasibility ofmunicipal sewage sludge landscaping application in Xi’an was discussed and proposed.Main conclusions of the study are as follows：(1) Basic physical and chemical properties of sewage sludge in Xi’an were prettysimilar. They were all rich in manurial composition with highly comparable with pigand cattle manures. However, high moisture content and EC are adverse to directlandscaping use although their pH and CEC are suitable for plant growth. The contentsof heavy metals differed greatly in the sludges investigated. All the concentrations ofheavy metals determined met the threshold value on alkaline soils（pH<6.5）except Cd.In general, it is feasible for sewage sludge in Xi’an to be used in landscaping.(2) Aerobic composting is one of the most cost-effective methods of sludgedisposal. After composting， physico-chemical characteristics，contents of availablenutrients and heavy metal forms were all changed to some extent. Increase ofgermination index (GI) indicated decreased phytotoxicity.(3) Response of plants growth to sludge compost varied with different plants. Littlenegative effects on the growth of ptropurpurea with larger plants were observed while the negative growth effects on hibiscus syriacus and festuca arundinace were obviouslyidentified. In addition, it has been found that the uptake capacity of plants to heavymetals was varied. More interestingly, different parts of the same plant exhibiteddifferent ability for heavy metal uptake. It has been demonstrated that apricot hasrelatively strong capability of adsorbing Cr，which demands for cautious attitude tofruiter utilization.(4) Risks from the leaching of nitrogen and phosphorus could be caused byexcessive sludge dosing. The amounts of nitrate nitrogen and total phosphorus leachedfrom soil with sludge application were much more than that from the soil withoutsludge application. It showed that massive use of sludge without effective control couldlead to potential pollution of surface water. Therefore，long-term follow-up study on theleaching behaviour of the pollutant in the soil fertilized by sludge compost should beconducted.