Estimation of Total Soluble Solids in MSW Incineration Bottom Ash by Higher Dilution Method: Assessment for Geotechnical Reuse

Abstract

The unavailability of new space and brimming of the existing ones to dump municipal solid waste (MSW) in cities like Delhi has caused the government to switch to MSW incineration (MSWI) in waste-to-energy (WtE) plants. Attempts are being made worldwide to utilize the residues from WtE plants as a substitute for natural soil in civil engineering applications. Though adequate from the strength perspective, MSWI bottom ash (BA) has significantly high total soluble solids (SS) which need to be addressed before being put to reuse. The present study assesses whether the existing Indian Standards IS-2720 Part-XXI for estimating SS in soil can be used for soil-like fraction of MSWI BA or if certain modifications are required. The study identifies that the dilution ratio (DR) or liquid-to-solid ratio of 10 l/kg used in the standard method to dissolve all the soluble solids is inadequate for estimation of SS in the soil-like fraction from MSWI BA. SS was measured in MSWI BA collected from three WtE plants in Delhi, and the results were compared with coal BA from a thermal power plant and two locally available soils. The procedure as mentioned in IS-2720 Part-XXI was adopted but with minor modifications and with varying DR ranging from 10 to 200 l/kg. DR of 10 l/kg, though adequate for SS determination in coal BA and local soils, underestimated SS levels in MSWI BA substantially. It is recommended that IS-code method be used with caution for estimating SS in materials which are soil-like but not exactly soil.