Responses of soil fertility and microbiomes of atrazine contaminated soil to remediation by hydrochar and persulfate

Applying sludge hydrolysate as a carbon source for biological denitrification after composition optimization via red soil filtration

Sludge hydrolysate, the byproduct generated during sludge hydrothermal treatment (HT), is a potential carbon source for biological denitrification. However, the refractory organic matters and the nutrient substances are unfavorable to the nitrogen removal. In this study, effects of HT conditions on the hydrolysate properties, and the hydrolysate compositions optimization via red soil (RS) filtration were investigated. At HT temperature of 160-220 °C and reaction time of 1-4 h, the highest dissolution rate of organics from sludge to hydrolysate achieved 70.1 %, while the acetic acid dominated volatile fatty acids (VFAs) was no more than 5.0 % of the total organic matter content. The NH4+-N and dissolved organic nitrogen (DON) were the main nitrogen species in hydrolysate. When the hydrolysate was filtered by RS, the high molecular weight organic matters, DON, NH4+ and PO43- were effectively retained by RS, while VFAs and polysaccharide favorable for denitrification were kept in the filtrate. When providing same COD as the carbon source, the filtrate group (Fi-Group) introduced lower concentrations of TN and humic substances but higher content of VFAs. This resulted in TN removal rate (57.0 %) and denitrification efficiency (93.6 %) in Fi-Group higher than those in hydrolysate group (Hy-Group), 39.4 % and 83.7 %, respectively. It is noticeable that both Hy- and Fi- Groups up-regulated most of denitrification functional genes, and increased the richness and diversity of denitrifying bacteria. Also, more denitrifying bacteria genera appeared, and their relative abundance increased significantly from 3.31 % in Control to 21.15 % in Hy- Group and 31.31 % in Fi-Group. This indicates that the filtrate is a more suitable carbon source for denitrification than hydrolysate. Moreover, the pH rose from 4.6 ± 0.14 to 6.5 ± 0.05, and the organic carbon, TN, TP and cation exchange capacity (CEC) of RS increased as well after being filtered, implying that the trapped compounds may have the potential to improve soil quality. This study provides a new insight for hydrolysate application according to its composition characteristics, and helps make the most use of wasted sludge.

Hydrochar reduces oxytetracycline in soil and Chinese cabbage by altering soil properties, shifting microbial community structure and promoting microbial metabolism

The efficient remediation of antibiotic-contaminated soil is critical for agroecosystem and human health. Using the cost-effective and feedstock-independent hydrochar with rich oxygen-containing functional groups as a soil remediation material has become a hot concern nowadays. However, the feasibility and effectiveness of hydrochar amendment in antibiotic-contaminated soil still remain unknown. Therefore, this study investigated the remediation effect and potential mechanisms of different hydrochars from cow manure (H-CM), corn stalk (H-CS) and Myriophyllum aquaticum (H-MA) at two levels (0.5% and 1.0%) in oxytetracycline (OTC)-contaminated soil using a pot experiment. Results showed that compared with CK, OTC content in the soils amended with H-CM and H-MA was decreased by 14.02-15.43% and 9.23-24.98%, respectively, whereas it was increased by 37.03-42.64% in the soils amended with H-CS. Additionally, all hydrochar amendments effectively reduced the OTC uptake in root and shoot of Chinese cabbage by 10.41-57.99% and 31.92-65.99%, respectively. The response of soil microbial community to hydrochar amendment heavily depended on feedstock type rather than hydrochar level. The soil microbial metabolism (e.g., carbohydrate metabolism, amino acid metabolism) was enhanced by hydrochar amendment. The redundancy analysis suggested that TCA cycle was positively related to the abundances of OTC-degrading bacteria (Proteobacteria, Arthrobacter and Sphingomonas) in all hydrochar-amended soils. The hydrochar amendment accelerated the soil OTC removal and reduced plant uptake in soil-Chinese cabbage system by altering soil properties, enhancing OTC-degrading bacteria and promoting microbial metabolism. These findings demonstrated that the cost-effective and sustainable hydrochar was a promising remediation material for antibiotic-contaminated soil.

Wheat straw pyrochar more efficiently decreased enantioselective uptake of dinotefuran by lettuce and dissemination of antibiotic resistance genes than hydrochar in an agricultural soil

Remediation of soils pollution caused by dinotefuran, a chiral pesticide, is indispensable for ensuring human food security. In comparison with pyrochar, the effect of hydrochar on enantioselective fate of dinotefuran, and antibiotic resistance genes (ARGs) profiles in the contaminated soils remain poorly understood. Therefore, wheat straw hydrochar (SHC) and pyrochar (SPC) were prepared at 220 and 500 °C, respectively, to investigate their effects and underlying mechanisms on enantioselective fate of dinotefuran enantiomers and metabolites, and soil ARG abundance in soil-plant ecosystems using a 30-day pot experiment planted with lettuce. SPC showed a greater reduction effect on the accumulation of R- and S-dinotefuran and metabolites in lettuce shoots than SHC. This was mainly resulted from the lowered soil bioavailability of R- and S-dinotefuran due to adsorption/immobilization by chars, together with the char-enhanced pesticide-degrading bacteria resulted from increased soil pH and organic matter content. Both SPC and SHC efficiently reduced ARG levels in soils, owing to lowered abundance of ARG-carrying bacteria and declined horizontal gene transfer induced by decreased dinotefuran bioavailability. The above results provide new insights for optimizing char-based sustainable technologies to mitigate pollution of dinotefuran and spread of ARGs in agroecosystems.

Efficiency and mechanism of the degradation of ciprofloxacin by the oxidation of peroxymonosulfate under the catalysis of a Fe3O4/N co-doped sludge biochar

A novel and recyclable composite material, Fe₃O₄/N co-doped sludge biochar (FNBC), was developed from original sludge biochar (BC) and found to have excellent stability and superior catalytic capacity during the ciprofloxacin (CIP) degradation under the action of peroxymonosulfate (PMS). In the FNBC/PMS system, an approximately complete removal of CIP was achieved within 60 min under the condition of 1.0 g/L FNBC, 3.0 mM PMS, and 20 mg/L CIP, which was about 2.08 times of that in BC/PMS system (48.01%). Besides, FNBC/PMS system could effectively remove CIP under the influence of wide pH (2.0-10.0) or inorganic ions compared with BC/PMS system. Moreover, it was found that there were radical produced under the effect of Fe element, defects, functional groups, pyridinic N and pyrrolic N and non-radical caused by graphitic N, carbon atoms next to the iron atoms and better adsorption capacity in the FNBC/PMS system. It was observed that the contribution of hydroxyl radical (•OH), sulfate radical (SO₄^•-) and singlet oxygen (¹O₂), which were the main reactive oxygen species, during the CIP degradation, were 75.80%, 11.49% and 10.26%, respectively. Furthermore, total organic carbon (TOC) variation was analyzed and the degradation pathway of CIP was speculated. The application of this material could combine the recycling of sludge with the effective degradation of refractory organic pollutant, providing an environmentally friendly and economic method.

Tomato microbiome under long-term organic and conventional farming

The compartment niche is the main reason behind the shifts in endophytic bacterial communities. Long-term organic greenhouse exerted limited influence on the variations of endophytic bacterial communities. Organic greenhouse and root had more complex co-occurrence networks than conventional greenhouse and stem, respectively. Cultivable method results found that Protecbacteria, Bacteriodes, and Actinobacteria are the dominant phyla in the endophytes.