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

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 < 0.40) with Fe chemical dynamics while other parameters showed stronger correlations (coefficients ≥ 0.60). Under acidification, VFAs initiated the conversion of exchangeable Fe into water soluble fraction. Residual fraction might play important role in regulating Fe shifting to more bioavailable states.

[Effects of sulfur on chemical properties of calcareous soil].

A pot trial with two continuous crops of rape was conducted to study the effects of sulfur on the chemical properties of calcareous soil. The results indicated that sulfur could decrease soil pH, while increase the electrical conductivity of soil solution markedly. Applying sulfur could enhance the contents of soil exchangeable Na+ and K+ and the accumulation of soil water-soluble anions, but had less effect on soil exchangeable Ca2+ and Mg2+, CEC, and alkalization degree. Comparing with urea, sulfur-coated urea (SCU) had less effect on soil pH and electrical conductivity, but markedly affected soil exchangeable cations and water-soluble anions. Sulfur application had no obvious yield-increasing effect, and higher application rate of sulfur could decrease the rape yield significantly.