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Composting is an effective way to treat agricultural waste, whereas inappropriate initial conditions could cause lower maturity and system instability. In this study, the dissolved organic matter dynamics and microbial community succession of cattle-manure composting were investigated under different initial moisture content (MC) and pH of raw material. The results indicated that the extended duration of thermophilic phase and the highest GI (germination index) value of final product were observed at matrix 60% MC and pH 8.5 (AT2 treatment). Microbial analysis showed that the succession of bacterial and fungal community was significantly influenced by total carbon (TN), pH and MC (P 0.05). The relationship between microbial community and fluorescence regional integration (FRI) parameters demonstrated that Thermobifida (bacterial genus), Mycothermus and Thermomyces (fungal genera) were positively correlated with P

The considerable spatial and temporal variabilities of nitrogen (N) processing introduce large uncertainties for quantifying N cycles on a large scale, particularly in plain river network regions with complicated hydrographic connections and mixed multiple N sources. In this paper, the dual isotopes δ15N and δ18O and dissolved anions in regularly collected samples (n = 10) from the studied river, which is one of the most seriously polluted rivers in the plain river network regions of the Taihu Lake catchment, were analyzed to ascertain the main nitrate (NO3-) sources and watershed N processing in the context of monsoon climate. The seasonal variations in precipitation, temperature, and hydrology play key roles in the regulation of the river NO3- concentration, NO3- sources, and watershed N processing. Nitrification of N-containing materials in the soil was possibly the major source of NO3- all year round, especially in the rainy season, whereas manure and sewage significantly contributed to the NO3- load in the Taige River in the dry season. Nitrification and denitrification processes within the area were closely related. The significant negative relationship between the water temperature and δ18O-NO3- values indicated the occurrence of nitrification in the soil throughout the year. By contrast, seasonal variations of denitrification were apparent from May to July with the high soil temperature and moisture, thereby indicating the occurrence of denitrification (22.9%) within the watershed. After the assessment of temporal variations of NO3- sources and watershed N processing, improved environmental management practices can be implemented to protect water resources and prevent further water quality deterioration in human-impacted watersheds.

Biochar application as a soil amendment has attracted worldwide attention. Nevertheless, polycyclic aromatic hydrocarbons (PAHs) formed during biochar production might enter into ecosystems and threaten human health after application to soil. Continuous pyrolysis systems tend to cause an accumulation of PAHs in biochar owing to short residence time and rapid cooling. This study conducted a comprehensive assessment regarding potential risk of PAHs in biochars produced by a continuous pyrolysis system based on bioavailability, leaching behavior, toxic equivalent quantity, health risk and phytotoxicity of PAHs. Results showed that the concentrations of total PAHs in biochars were in the range of 93.40–172.40 mg/kg, exceeding the European Biochar Certificate standard. 3-rings PAHs were the predominant groups. The percentages of total freely dissolved and leachable PAHs were lower than 1%. RH contained the least bioavailable and leachable PAHs concentration and phytotoxicity compared with CS and PS, which might attribute to the characteristic of three biochars. CS and PS were acidic and exhibited high levels of DOC and VFAs, while RH was strongly alkaline and presented greater aromaticity and higher surface area, which might have resulted in high adsorptive capacity and decreased bioavailability of PAHs. When the biochar application rate was higher than 0.6 t/ha, the incremental lifetime cancer risk value for human exposure to biochar-borne PAHs through the biochar-amended soil was over 10−6, suggesting carcinogenic risks. Germination index values of biochars ranged from 25.66 to 88.95%. Phytotoxicity mainly was caused by bioavailable PAHs and dissolved organic compounds. Overall, these findings highlighted that although the percentage of bioavailable PAHs was low, the potential health risk and phytotoxicity of PAHs in biochars produced by a continuous pyrolysis system was of a great concern. High biochar application rates should be avoided without processing both for soil safety and human health.

In order to explore changes in microbial enzyme activity and bacterial community, a 60-day composting experiment was conducted using cattle manure and straw under aeration rates of 0.45, 0.68, and 0.90 L min−1 kg−1 fresh weight. High aeration rate increased the cellulase, urease, alkaline and acid phosphatase activities, but decreased that of invertase and catalase. Cellulase, alkaline phosphatase and catalase were the main enzymes that affected the composting process. Microbial analysis showed that high aeration rate increased the uniformity of bacterial community in thermophilic phase, but decreased that in mature phase. Different aeration rate affected the bacterial community structure and further influenced the relationship between enzyme and functional bacteria. Regulating the temperature, moisture content and EC in specific phases to affect bacterial community succession could provide guidance for improving maturity of composting.

Intensive and unregulated use of feed additives in China has led to high levels of heavy metals such as copper and zinc in fertilizers, considerable quantities of which find their way into the environment. Studies have shown that composting could significantly decrease the bioavailability of heavy metals. This study was to investigate the effects of addition of biochar and a microbial agent on the morphological changes in copper and zinc during composting. Results show that treatment T8 successfully immobilized 70.36% of copper as a result of biochar addition. Treatment T3 successfully immobilized 40.76% of zinc; transformation of zinc to a higher stable state was found to be closely related to the formation of fulvic and humic acids. Results of fluorescence spectrum analysis also corroborate that the conversion of copper and zinc to forms with higher stability was associated with the formation of fulvic and humic acid-like substances.

Amino acids (AAs) are important functional substances in compost product. The evolution of three groups of AAs was determined during the co-composting of pig manure and maize straw mixture. And the correlations between AAs and other humification indicators such as lignocellulose, phosphatase activity, and humic substances (HSs) were analyzed. Results showed that the total AA content decreased during the primary fermentation but increased to 3.578 g kg−1 after the second fermentation, exhibiting a 1.5-fold increase in the final compost. The neutral phosphatase activity, hemicellulose, and HSs had a promoting effect on AAs. Generally, the compost product quality was significantly improved due to the increment of AAs and additional small molecules during the secondary fermentation. Our study provided a new direction for future research on improving composting products of organic waste.