Optimizing the culture conditions of DBP degradation by bacteria and investigating its biodegradation pathways have a great importance to develop effective PAEs pollution control strategies. In this study, we investigated the cultivation condition optimization, degradation kinetics, and degradation pathways of a newly isolated dibutyl phthalate (DBP) degradation strain, which was isolated from activated sludge and identified as Acinetobacter baumannii DP-2 via morphological observation, biochemical identification, and 16S rDNA sequence analysis. The degradation conditions were optimized based on the results of single-factor experiments and response surface optimization experiments. The DBP degradation rate of Acinetobacter baumannii DP-2 reached up to 85.86% when the inoculation amount was 17.14%, the DBP concentration was 9.81 mg·L⁻¹ and the NaCl concentration was 5 g·L⁻¹. The GC-MS analysis results indicated that the intermediate metabolites of Acinetobacter baumannii DP-2 mainly consisted of DMP, MBP, PA, and benzoic acid derivatives, which confirmed the degradation pathway from DBP to PA under aerobic pathway and then to BA under anaerobic pathway. In summary, Acinetobacter baumannii DP-2 shows great potential for the degradation of DBP in contaminated soils.

Application of organic manure on farmland is one of the most important tasks in agricultural recycling. However, few studies have investigated the potential impact of different solid–liquid separation (SLS) technologies on soil porosity and greenhouse gas (GHG) emissions as a result of the application of liquid fractions (LFs). A microcosm experiment was conducted to track the emissions of ammonia (NH₃), nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) from soils (1) without liquid manure application (CK), (2) with a raw dairy slurry (RM), (3) with the liquid fractions of mechanical solid–liquid separation (MS) technologies, and (4) with the LF of an enhanced solid–liquid separation technology including a flocculant (tannic acid, Ta) (MS + Ta). Soil porosities of different treatments were measured using computed tomography (CT). The saturated water conductivities of the RM and MS treatments were 53.38% and 78.63%, respectively, lower than that of the CK. The application of raw slurry and LFs reduced the gas diffusion due to the strong decrease in pore sizes >500 μm and increased gas emissions compared to the CK. Compared with RM, MS had greater N₂O and lower CH₄ emissions, whereas MS + Ta had lower NH₃ and N₂O emissions. MS had the greatest CO₂-e emissions, mainly owing to high N₂O emissions, followed by RM and MS + Ta. The implementation of a simple SLS led to an increase in nitrogen (N) loss and GHG emissions when the resultant LFs were applied to farmlands, whereas high emissions were reduced when a simple SLS was combined with a flocculant, such as Ta. Further research is required to elucidate the reduction mechanism and its effectiveness under field conditions.

Soil labile organic carbon (C) fractions play a key role in agricultural soil fertility. However, the effects of long-term organic substitution regimes on soil organic carbon (SOC), its labile fractions, stability, and vegetable yields as well as the relationships among these factors in the open-field are less well-studied. Hence, the objective of this study was to analyze the effects of long-term organic substitution regimes on SOC sequestration, labile C fractions [particulate organic C (POC), microbial biomass carbon (MBC), dissolved organic C (DOC), and readily oxidizable C (ROC)], SOC stability, the C pool management index (CMI), and vegetable yields in a long-term (13 years) open-field experiment. Five treatments were examined: 100% chemical nitrogen fertilizer (CN), substituting 25% of the chemical N with manure (MN) or straw (SN), and substituting 50% of the chemical N with manure (2MN) or manure plus straw (MSN). Compared to the CN, organic substitution treatments increased the average yields of vegetable, the SOC, the labile C fractions’ contents, and the C pool management index (CMI) to varying degrees, but only MSN reached significant levels for these factors. However, the MSN treatment had a significantly lower C stability index (SI) than the CN. ¹³C-NMR analyses also confirmed that organic substitution treatments increased the proportion of O-alkyl C and the OA/A, but reduced SOC stability. Pearson correlation analysis and the partial least squares path model indicated that labile C fractions were the mainly direct contributors to yield and SOC stability. Overall, substituting 50% of the chemical N with manure plus straw is a relatively ideal fertilization practice to improve vegetable yields and enhance C activity in an open field.