Effects of capping on contaminants mobilization and microbial community in a closed municipal solid waste landfill

Author(s)

Alice Kimie Martins Morita

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 2020-11-30

Examining board members

Edson Cezar Wendland; Armando Borges de Castilhos Junior; Ricardo Cesar Aoki Hirata; César Augusto Moreira; Maria Bernadete Amancio Varesche Silva

• Advisor: Edson Cezar Wendland

Abstract

This research aimed to evaluate the effectiveness of capping in mitigating the impacts generated by a closed municipal solid waste landfill (dumpsite) in the city of São Carlos-SP. For that, physicochemical and microbiological analyses (sequencing of the RNAr 16S) of leachate and waste samples were carried out, in stages before and after capping. Electric Resistivity Tomographies (ERT) were carried out complementarily, aiming to assist in the evaluation of the mobilization of contaminants in both stages. In parallel, a study of the area of influence was carried out, with the conduction of ERT in the surrounding area, physico-chemical analysis of groundwater samples and ecotoxicological tests, allowing the construction of conceptual models and the verification of the effectiveness of natural attenuation in the contaminant plume remediation. The diagnosis of the study area allowed to verify the existence of high concentrations of contaminants inside the waste landfill, but a considerable decrease downstream to it, either in the monitoring wells, or at about 500m at the surface water collection points. In this regard, the concentrations of pollutants in the monitoring wells remained stable over 20 years, showing no evidence of depletion, and the metals Pb and Co could be found at distances of 200m from the landfill, showing their mobility in the acidic conditions found in the Guarani Aquifer outcrop zones. Additionally, the ERT showed evolution of the contaminant plume after 20 years of the deposit\'s closure, reaching about 200m from the deposit and 60m deep. The capping was not effective in reducing the volume of produced leachate, but enabled the creation of reducing conditions in the region just below the cover, contributing to the precipitation of metals such as Pb, Cd, Ni, Co, As and Zn as sulfide minerals, favoring their immobilization. The microbial populations adapted to the anaerobic conditions, with the verification of representatives of the phyla Firmicutes, Chloroflexi and Euryarchaeota and the genera Methanosaeta, Hydrogenispora, Smithella and Gelria. The occurrence of anaerobic respiration with the use of NO3, Fe (III) and Mn (IV) as electron acceptors could be verified by the increase in the concentrations of NH4, Fe (II) and Mn (II) below the capping. In this way, it is possible to conclude that the capping of old landfills brings benefits for reducing the contaminants mobility. (AU)

• FAPESP's process: 18/24615-8 - Effects of partial capping in the contaminants mobilization and microbial degradation in a closed waste deposit
• Grantee: Alice Kimie Martins Morita
• Support Opportunities: Scholarships in Brazil - Doctorate