Insight into the pathways of biochar/smectite-induced humification during chicken manure composting

As representative organic and inorganic additives, both biochar and smectite exhibit an excellent capacity to improve humification efficiency during composting. Nevertheless, the mechanisms underlying biochar/smectite-induced compost humification have still not been fully explored from the perspective of overall organic substances. In this study, three composting treatments were performed as follows: 10 % biochar-amended composting, 10 % smectite-amended composting and natural composting without any additive. UV-visible parameters and synchronous hetero two-dimensional correlation spectra showed that biochar accelerated dissolved organic matter (DOM) complications, unsaturation and aromatization. For example, biochar promoted the C2 and simple C3 peaks to convert into a sophisticated C3/360 peak. However, the effect of smectite was negligible in complicating the DOM structure. Both biochar and smectite displayed an invigorating role in promoting humic substance (HS) formation. The strengthened relations between bacterial richness and physicochemical indicators and HS fractions might contribute to the positive action of biochar/smectite on HS synthesis. Network analysis showed that both bacterial functional omnipotence and specialization in response to the addition of catalysts may contribute to compost humification. The chemical pathway involved in DOM humification was intensified by enhancing the role of pH in biochar composting and weakening the degradation of unsaturated aromatic compounds of DOM with smectite addition. These findings benefit the practical application of biochar/smectite in promoting composting efficiency.

Insight into complexation of Cu(II) to hyperthermophilic compost-derived humic acids by EEM-PARAFAC combined with heterospectral two dimensional correlation analyses

Hyperthermophilic composting has been demonstrated to overcome the disadvantages of conventional composting in products with better quality. However, the complexation of heavy metals to hyperthermophilic compost (HTC)-derived HA remains unclear. In the present work, using Cu(II) as the representative heavy metal, we investigated the binding process of Cu(II) to HAs derived from HTC, thermophilic compost (TC), and sewage sludge (SS). The complexation ability of three HAs was analyzed by the method of parallel factor (PARAFAC) coupled with hetero two-dimensional correlation spectroscopy (hetero-2DCOS) analyses. Results showed that HTC-derived HA has the greater complexation ability (log K_M = 5.68, CC_M = 1.21) than both TC-derived HA (log K_M = 5.27, CC_M = 0.94) and SS-derived HA (log K_M = 5.19, CC_M = 0.586), likely due to the higher humification degree, as well as the faster response of carboxyl and phenols to Cu(II) binding with HTC-derived HA. This study demonstrated that the utilization of HTC might provide an effective approach for remediation of Cu(II)-polluted soils. Moreover, PARAFAC analysis integrated with hetero-2DCOS offers a unique insight into understanding the correlation between HAs fractions and functional groups during the Cu(II) binding process.