Essential regulators of iron chemical speciation distributions in anaerobic digestion of pretreated food waste: Organic volatile fatty acids or inorganic acid radicals?

[Display omitted] •Volatile fatty acids dominate Fe speciation rather than inorganic acid radicals.•Residual fraction is a potentially crucial factor of Fe speciation dynamics.•Acidification causes positive correlations of volatile fatty acids and Fe speciation.•Strong alkalinity causes volatile fatty acids negatively correlated to Fe speciation. In this work, a 30-days batched mesophilic assay on pretreated food waste (PFW) under different inoculum/substrate (I/S) ratios (1:5, 1:2, 1:1, 2:1, 4:1 and 1:0) was carried out, to target the most important parameters in AD matrix on regulating iron (Fe) chemical speciation. Correlation coefficients were calculated within four Fe chemical forms and AD parameters of pH, volatile fatty acids (VFAs), inorganic acid radicals (IARs), and alkalinity. Results showed that IARs were not key factors on regulating Fe speciation. Without acidification, IARs showed weak correlations (coefficients