Effect of Zn on physicochemical characteristics and hydrolase activities during composting of agricultural waste in high temperature and static state

An experiment was conducted using mixed materials of pig excrement, wheat straw and waste auricularia-bran to study the effect of the heavy metal zinc (Zn) on physicochemical characteristics and hydrolase activities during composting at high temperature and static state. The CK treatment (without added Zn) achieved the requirement for harmlessness; the harmless degree of the low Zn treatment (L;Zn concentration 400 mg/kg) was not perfect, as the high-temperature phase (50C) only lasted 3 d. The high Zn treatment (H;Zn concentration 1000 mg/kg) did not achieve the requirement for harmlessness. The effect of Zn on electrical conductivity was mainly in anaphase of the calefactive phase, high-temperature phase, and the initial stage of the hypothermic phase. The effect of Zn on pH was mainly in the high-temperature phase, and only CK was in the optimal pH range (7.5~8.5). Analyses of hydrolase activities indicated that the low Zn treatment showed an activation effect on cellulase activity, while the high Zn treatment had a depressive effect on the high-temperature phase. Addition of Zn (both L and H) showed a negative effect on the hypothermic phase. Addition of Zn (both L and H) showed an activating effect on protease activity in the initial phase of composting (0?4 d). Protease activity in the high Zn treatment was significantly higher than that of the CK treatment. Both L and H treatments showed a negative effect on protease activity in the high-temperature and hypothermic phases. Addition of Zn (both L and H) showed an activating effect on urease activity in the initial phase of composting,but produced a negative effect and hampered the acidamide conversion process in anaphase of composting.