Effects of bentonite and humic acid on Zn and Cu passivation and microbial communities in pig manure composting
This study aimed to improve the utilization of compost resources and reduce agricultural non-point source pollution.An experiment was conducted a study on the effects of adding 10%bentonite(BT)and 10%humic acid(HA)separately,as well as a mixture of 2.5%bentonite+7.5%humic acid(BH1),5.0%bentonite+5.0%humic acid(BH2),and 7.5%bentonite+2.5%humic acid(BH3)on the passivation effect of heavy metals Zn and Cu and microbial community composition in pig manure composting.The results showed that the addition of bentonite and humic acid prolonged the high-temperature period of composting,and the degradation rate of dissolved organic carbon in the BH3 treatment reached 40.52%,significantly increasing by 12.46 percentage points compared to that of the control treatment(CK)(P<0.05).In the composting process,the percentage of bioavailable Cu in the BH3 treatment decreased by 12.17 percentage points compared with that before composting,while the percentage of Zn in the oxidized state increased by 29.74 percentage points compared with that before composting,and the decrease and increase were significantly higher than those in the other composting treatments(P<0.05).Compared to CK and the individual addition treatments,the mixed addition of additives significantly improved the passivation efficiency of heavy metals Cu and Zn.The passivation rates of Cu and Zn treated with BH3 reached 79.84%and 36.97%,respectively,significantly increasing by 47.80 percentage points and 23.09 percentage points compared to that of CK(P<0.05).The mixed addition of bentonite and humic acid promoted a higher relative abundance of beneficial species involved in fiber degradation,such as Firmicutes and Clostridia,to varying degrees.The relative abundance of Bacteroidota and Bacteroidia in the BH3 treatment was significantly higher than that in other treatments at the same time.The co-composting of bentonite and humic acid with pig manure was more conducive to composting maturity and heavy metal passivation.The best recommended ratio is to add 7.5%bentonite and 2.5%humic acid together.
pig manure compostingbentonitehumic acidheavy metal passivationmicroorganism
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