Studies On The Effects Of Fgdg On The Nitrogen Transformation And Humic Characteristics During Composting

With the sustainable and rapid development of agriculture in China, the agricultural production creates enormous economic and social benefits, but it also leads to large quantities of organic solid waste i.e. livestock manure and crop residues. An inappropriate treatment of organic solid waste will not only waste abundant bioresource, which is rich in protein and coarse fiber, but leads to serious environment problems. Composting represents an effectively strategy of organic solid waste utilization that is expected to convert organic solid waste into fertilizer rich in organic carbon and nitrogen nutrients. However, the inappropriate composting technology will emit large quantities of CO₂ and NH₃, causing loss of carbon and nitrogen nutrients. Therefore, in order to enhance the conservation of carbon and nitrogen nutrients, and accelerate the humification of composts during composting, the studies were conducted as follows:The objective of this study was to investigate the effect of adding flue gas desulphurization gypsum （FGDG） on the transformation of nitrogen during co-composting of dairy manure and pressmud of sugar refinery. The ammonia absorption of FGDG was investigated. The changes in compost temperature, pH, electrical conductivity （EC）, moisture, organic matter, the C/N ratio, Kjeldahl N, NH⁴⁺-N, NO^2--N, NO^3--N were assessed. FGDG addition did not significantly affect compost temperature, pH, EC, moisture, and organic matter degradation. However, the addition of FGDG significantly increased the NH⁴⁺-N content in the compost during the thermophilic phase, and the NH⁴⁺-N maximal content in the compost with FGDG （CPG） was 59.90% more than that in the compost without FGDG （CP）. FGDG was thought to create the formation of （NH₄）₂SO₄ and the cation exchange between NH⁴⁺and Ca²⁺. The NO^2--N content in the CPG peaked on day 15, and no NO^2--N peak was observed in the CP. In the final compost products, the NO^3--N concentration in the CP was more than that in the CPG, which was 1.45 （CP） and 1.11 g·kg^-1 （CPG） dry material. This might be due to the NO^2- accumulation in the CPG, which accelerated N loss in the form of N₂O. There is a strong correlation between N₂O emission and NO^2--N accumulation in the composting process. Compared with the original N content in the compost mixture, the N loss in CP and CPG were 15.00% and 10.80%, respectively. These results revealed that NH⁴⁺-N conservation effect was improved during the thermophilic phase and the total N loss was mitigated by adding FGDG into composting materials. FGDG could be utilized as a potential amendment to conserve nitrogen during composting.To investigate the impacts of flue gas desulphurization gypsum （FGDG） amendment on the nitrification and denitrification during composting, composting with FGDG amendment （CPG） and composting without amendment （CP） were conducted in this work. The physico-chemical parameters and the abundance of nitrification and denitrification functional genes with real-time quantitative polymerase chain reaction （qPCR） during composting were carried out. The correlation between physico-chemical parameters and abundance of these genes were statistically analyzed. A perusal results showed that FGDG amendment had an adverse effect on the abundance of 16S rDNA during composting. FGDG amendment delayed the occurrence of highest abundance of amoA, resulting in an accumulation of NO^2--N in CPG. The nxrA gene abundance in CP was significantly higher than that in CPG during the mature phase, responding to the higher NO^3--N concentration in CP. The narG gene abundance in CPG was higher than that in CP, which would enhance the NO^2--N reduced from NO^3--N. The addition of FGDG increased the relative abundance of narG and nirS during composting. Spearman rank correlations matrix revealed that the amoA showed significant negative correlation with organic matter （OM） and NH⁴⁺-N, and showed positive correlation with NO^3-N. The nxrA displayed negative correlation with temperature. These results demonstrated FGDG amendment significantly affected the copies of nitrification and denitrification functional genes, which changed the nitrogen flux of composting. Our study shed an insight into FGDG amendment affecting the nitrogen transformation during composting on a molecular level.For the purpose of evaluating the effect of FGDG amendment on the humic characteristics during dairy manure and pressmud of sugar refinery co-composting, the characteristics of humic substance （HS） from CP and CPG were assessed with respect to their particle size, elemental analysis, FTIR and UV-Vis spectroscopy, and the molecular composition of HS was characterized via Pyrolysis-GC/MS as well. The particle size of HS ranged between 300 and 600 nm, representing a bimodal distribution, which might result from the different particle size in HA and FA. As composting proceeded, The decrease of H content and C/N, and increase of C/H revealed that the unsaturated degree of HS was elevated, and more nitrogen was condensed in the core of HS. The FTIR and UV-vis spectroscopy indicated that the aromatization of HS was promoted after composting. Adding FGDG increased the unsaturated degree and aromatization of HS. Pyrolysis-GC/MS showed a decrease in the content of alkane and increase in the benzene and nitrogen compounds. The nitrogen compounds of HS in CPG was significantly higher than that in CP on 50 d, which due to the more conserved organic nitrogen in CPG with the addition of FGDG.