Effect of heavy metal Cu on compost materials property and oxidoreductase activity during pig waste composting

Changes in polyphenoloxidase and dehydrogenase activities, temperatures, pH and E4/E6 ratio of humic acids during aerobic fermentation and thermophilic aerobic state of compost materials during pig waste composting were determined in this study. The aim of the study was to lay the fundamental groundwork for learning biological behaviors during composting of heavy metal Cu-treated compost. Pig manure and straw were used as experimental compost materials in three treatments — low content (100 mg·kg^-1) heavy metal Cu treatment (A1), high content (500 mg·kg^-1) heavy metal Cu treatment (A2) and non-heavy metal Cu treatment (CK). The results showed that temperature was higher in CK than in A1 and A2 treatments during compost cooling phase. The lowest pH and average E4/E6 of CK were 5.94 and 3.88. The highest pH and average E4/E6 were 8.85 and 3.68 for A2 in the study. Temperature rise was fastest in A1, with higher temperatures and longer high temperature duration than in the other treatments. This effectively destroyed pathogens and reached harmless conditions at the end of the composting experiment. Under A1 treatment, pH was 7~8 and E4/E6 was for most of the time lower than in CK and A2. Polyphenoloxidase and dehydrogenase activities in A1 were the highest. However, dehydrogenase activity occurred concurrently with other processes that resisted enzyme activity.