Abstract
Activated sludge is now one of the most widely used biological processes for the treatment of wastewaters from medium to large populations. It produces high amounts of sewage sludge that can be managed and perceived in two main ways: as a waste it is discharged in landfill, as a fertilizer it is disposed in agriculture with direct application to soil or subjected to anaerobic digestion and composting. Other solutions, such as incineration or production of concrete, bricks and asphalt play a secondary role in terms of their degree of diffusion. The agronomical value of domestic sewage sludge is a proved question, which may be hidden by the presence of several pollutants such as heavy metals, organic compounds and pathogens. In this way, the sustainability of sewage sludge agricultural disposal requires a value judgment based on knowledge and evaluation of the level of pollution of both sewage sludge and soil. The article analyzed a typical Italian case study, a water management system of small communities, applying the criteria of evaluation of the last official document of European Union about sewage sludge land application, the “Working Document on Sludge (3rd draft, 2000)”. The report brought out good sewage sludge from small wastewater treatment plants and soils quality suggesting a sustainable application.
Highlights
IntroductionLarge-scale cropland application of municipal wastewater was first practiced about 150 years ago after flush toilets and sewer systems were introduced into cities in Western Europe and North America
Large-scale cropland application of municipal wastewater was first practiced about 150 years ago after flush toilets and sewer systems were introduced into cities in Western Europe and North America.Wastewater was discharged without any treatment and receiving watercourses became heavily polluted [1].Many “sewage farms” were designated as a preferred alternative to the direct discharge of raw sewage into waterways [2]; in 1875, this “land treatment” served England and major cities in Europe and with the new century it has started in the United States
In the study several soils interested by application of these three types of sewage sludge were considered: on the base of sludge quantities applied to each single plot in a time lapse of ten years and annual chemical analyses of sewage sludge applied, average annual quantities of heavy metals introduced into each sample was calculated; data were related to limits for soil application suggested by the working document on sludge
Summary
Large-scale cropland application of municipal wastewater was first practiced about 150 years ago after flush toilets and sewer systems were introduced into cities in Western Europe and North America. In Europe the most pragmatic and environmentally sustainable approach to manage sludge from wastewater treatment plants is recycling it on agricultural land [7] This strategy is supported by many scientific and regulatory authorities even if it is not adopted by all European countries. The last official document from the European Union about sewage sludge should be a useful instrument to get a sense about the level of pollution of sewage sludge and soils: about twenty years passed from the first and the last European regulation on sludge in agricultural use (86/278/EEC) [9] In this final directive, only heavy metals as potential pollutants in sewage sludge were considered, even if many studies have evidenced potential health hazards associated with sludge-borne toxic organic [10,11]. Analysis were performed on three typical and different sludge from wastewater treatment plants of small Italian municipalities; soils receiving continuous applications of sewage sludge produced by these plants were investigated
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