Influence of matured compost inoculation on sewage sludge composting: Enzyme activity, bacterial and fungal community succession.

The influence of matured compost inoculation during sewage sludge with sawdust composting was assessed. Mature compost reduced the heating rate, thermophilic phase, peak temperature, and volatile solid degradation rate, with no significant effect on pH and germination index. Matured compost addition also increased the cellulase, peroxidase, arylsulfatase, and urease contents during the mesophilic phase, and increased the urease content but decreased the cellulase, peroxidase, protease, and arylsulfatase contents during the cooling phase, with no significant effect on enzyme activities at the thermophilic phase. Matured compost increased the diversity of bacteria during the mesophilic and thermophilic phases, but reduced the fungal diversity throughout composting. Matured compost significantly improved uniformity of the bacterial community and affected the structure of the bacterial and fungal communities, while changing the correlation between some functional microorganisms and enzyme activities. These results provide guidance for optimizing the composting process when matured compost as bulking agent.

Direct evidence of lead contamination in wheat tissues from atmospheric deposition based on atmospheric deposition exposure contrast tests.

A field experiment was conducted to assess the atmospheric deposition effects on lead (Pb) contamination in wheat by two contrasting treatments: wheat exposed or not to atmospheric deposition. Plants were housed in a shed during wheat greening for the non-exposed treatment. The Pb contents of wheat during different growth stages, of soil and of atmospheric deposits were analysed and combined with Pb stable isotope data to quantify the contribution of atmospheric deposition and soil to Pb in wheat tissue. The Pb content in atmospheric deposits was significantly higher than those in soil and wheat tissue, and the Pb content in wheat tissue exposed to atmospheric deposition was significantly higher than the Pb content in non-exposed tissue (p < 0.05). The 206Pb/207Pb of soil was significantly higher than the 206Pb/207Pb of atmospheric deposits (p < 0.05), and soil and atmospheric deposition were the two sources of Pb in wheat tissue. Atmospheric deposition was the main source of wheat tissue Pb in the exposed treatment, and most of the wheat tissue Pb, except for that in the stem, also came from atmospheric deposition in the maturing stage. The proportion of Pb from atmospheric deposition in roots, stems and leaves evidently decreased after the shed was erected, and the contribution of Pb from atmospheric deposition to wheat tissue was significantly higher in the exposed treatment than in the non-exposed treatment (p < 0.05). This contrast test directly confirmed that atmospheric deposition was the main source of Pb in the wheat tissues. Therefore, taking measures to reduce the absorption of Pb by wheat from atmospheric deposition can effectively ensure food safety.