The reuse of biosolids on agricultural land: Critical issues and perspective

Abstract

The sludge management represents a considerable amount of operational costs for wastewater treatment plants (WWTPs). Issues concerning the treatment and the recovery/disposal of biosolids are gaining importance especially in Lombardy region, where the biosolid landspreading on agricultural soils is a very common practice. The aim of this work was to evaluate the results obtained from a survey carried out on the biosolids/sludge, derived from WWTPs, ingoing to and outgoing from the STPs (sludge treatment plants—authorized for the treatment on behalf of third parties) located in Pavia Province. Moreover, the characterization of agricultural soils that receive the biosolids is carried out. Furthermore, the whole biosolid management chain, from production to landspreading on agricultural soils, was studied, highlighting the critical issues based on the survey results. The results obtained suggested the following actions: (a) the reduction of sludge production in WWTPs; (b) a more “controlled” production in terms of biosolid qualitative characteristics; (c) better “selection” of the sludge ingoing to STPs; and (d) more effective actions to control the “response” of the agricultural soils. Furthermore, full compliance with the best spreading practices on the soils is required, as well as a better use of agronomic skills to obtain a higher resource valorization. Practitioner points In this work, the characteristics of biosolid spread in agricultural soils in Pavia Province were analyzed. The minimization of sludge production in WWTPs is encouraged in order to reduce critical issues related to biosolid management. The stabilization process in WWTPs should improve in order to obtain a better quality sludge. A better “selection” of the sludge ingoing to STPs and a more effective monitoring of the agricultural soils are encouraged.

Legislation for the Reuse of Biosolids on Agricultural Land in Europe: Overview

“…They found that heavy metal average concentrations were largely below the national and regional normative limits in the whole period of the survey [53]. Only sporadic overruns of the Zn, Ni, and Cd have been reported [53]. However, in a study conducted in the USA, Islam et al [33] studied the effects of the application of biosolids on well-drained silt soil, and they found that the heavy metal concentration increased significantly.…”

“…The presence of heavy metals in the biosolids is an important parameter to check before its spreading on land. Their presence in biosolids can be due to the presence of industrial wastewater treated by WWTPs [52,53]. Some heavy metals are considered essential micronutrients for plant growth, but elevated concentrations of these compounds are toxic to food crops, domestic animals, and humans [54,55].…”

“…Moreover, some countries (Austria, Hungary, and the UK) introduce limit values for additional heavy metals in the soil-Styria (Austria Lander) provides limits for molybdenum ( Studies on the heavy metals content in the soils due to the application of biosolids were carried out, but in some cases, the results are conflicting. For instance, Collivignarelli et al [53] analyzed the heavy metal presence in the soils where the spreading of biosolids occurs during 2012 to 2016 in Lombardy (Italy). In the analyzed area, the soils presented mainly silty-sandy components [95].…”

“…In the analyzed area, the soils presented mainly silty-sandy components [95]. They found that heavy metal average concentrations were largely below the national and regional normative limits in the whole period of the survey [53]. Only sporadic overruns of the Zn, Ni, and Cd have been reported [53].…”

“…In Italy, the reuse of biosolids in agriculture in 2012 was about 30% [53]. Agricultural reuse is the most prevalent route in the regions of northern Italy.…”