Economic cost–benefit analysis for the agricultural use of sewage sludge treated with lime and fly ash

Abstract

AbstractA tool for calculating the economic and environmental impacts of the use of byproducts of industrial processes that can substitute for perishable resources was presented. This was exemplified by fly ash (the fine fraction of ash originating from coal burned to generate electricity and collected by filtering exhaust gases leaving the furnace), added to soil as a component of sewage sludge stabilized with fly ash and lime (NVS). Application to soil of NVS has potential agricultural and environmental advantages and disadvantages. The costs and benefits of such application were calculated using both a database and expert opinions. The calculations assumed a representative assemblage of soils and crops, with weights assigned to each crop type and soil characteristic. The annual weighted benefits (additional income for the farmer) and costs per hectare reached 324 $/ha and 131 $/ha respectively. Major potential benefits include: Chemical fertilizer replacement, 159 $/ha; Improvement to the soil's physical properties, 75 $/ha; Supply of vital trace elements, 33 $/ha. Major potential costs were: Regulatory limitations on marketing of crops pending proof of absence of risk of heavy metals or radionuclides accumulation in these crops, (17 $/ha and 36 $/ha respectively); Application and incorporation cost, 50 $/ha. The presented estimates of the costs and benefits refer to the array of soils and conditions typical to Israel. It is possible to maximize potential benefits by applying fly ash only to the most suitable agricultural soils while improper use of fly ash will increase the costs incurred from its use.