Dosing of Ethylenediamine-N,N″-disuccinic acid (EDDS) to improve the bioavailability of Fe²⁺ in the presence of sulfide in a submerged anaerobic membrane bioreactor

This study evaluated the effect of 8 mg/L sulfide on the speciation and bioavailability of 10 mg/L iron (Fe²⁺), with and without a biodegradable chelating agent, Ethylenediamine-N,N′-disuccinic acid (EDDS). These tests were carried out in the presence of sulfide, in both batch assays, and in a continuous submerged anaerobic membrane bioreactor (SAMBR). The EDDS was added at 1:1 M ratio to the Fe²⁺ (10 mg/L), either simultaneously, or as Fe-EDDS complex. Results showed that adding 8 mg/L of sulfide limited the bioavailability of Fe²⁺ by shifting its speciation toward less bioavailable fractions based on the Bureau Communautaire de Reference (BCR) extraction analysis, i.e. organic matter/sulfide and residual, resulting in a decrease in methane yields and an increase in VFA levels. An Fe-EDDS complex was found to be more effective controlling the change in sulfide levels in the SAMBR as it helped to reverse the shift in Fe²⁺ speciation, and increased methane yields by 9.46%.