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Purpose: Excessive application of nitrogen fertilizers on farmland widely occurs in China, which has been recognized as one of the main sources of non-point pollution. To reduce the nitrogen loss in agricultural soils, some specific biochar can be introduced to increase the water-holding capacity of soils and to reserve soil nutrition. The effects and mechanisms of biochar application on decreasing nutrient losses after fertilization were systematically evaluated and understood through both pot and field experiments. Materials and methods: This study was objected to investigate the effects of neutral biochar (NBC, pH 6.6–7.1) and its combination with urease inhibitor (UI) on nitrogen mitigation and reservation in farmland soil, and the interactions among the mixed soils (biochar, nitrogen fertilizer, and soil) under both pot and field experiments. Results and discussion: The application of straw biochar could reduce the amount of ammonia volatilization in soil. The maximum inhibition of ammonia volatilization loss accounted for 27.67% of fertilizer applications. In field experiments, neutral biochar could reduce the leaching of soil NH4+-N and NO3—-N, and this effect was more evident for NO3—-N (68 mg/kg) compared to no fertilization in the soil layer 20–40 cm. With the addition of neutral biochar and urease inhibitors, the content of soil total nitrogen increased greatly with 1.70 g/kg. Conclusion: Neutral biochar from waste agricultural straw and commercial urease inhibitors were applied for nitrogen reservation in pot and field experiments. The application of neutral biochar played a positive role in lower volatile ammonia loss and higher nitrate content compared to urease inhibitor application only. These findings reveal the potential of neutral biochar for the improvement of agricultural soil. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the biohydrogen production from thermal (T), alkaline (A) or thermal-alkaline (TA) pretreated sludge fermentation liquid (SFL) in a microbial electrolysis cells (MECs) without buffer addition. Highest hydrogen yield of 36.87±4.36 mgH2/gVSS (0.026 m3/kg COD) was achieved in TA pretreated SFL separated by centrifugation, which was 5.12, 2.35 and 43.25 times higher than that of individual alkaline, thermal pretreatment and raw sludge, respectively. Separating SFL from sludge by centrifugation eliminated the negative effects of particulate matters, was more conducive for hydrogen production than filtration. The accumulated short chain fatty acid (SCFAs) after pretreatments were the main substrates for MEC hydrogen production. The maximum utilization ratio of acetic acid, propionic acid and n-butyric acid was 93.69%, 90.72% and 91.85%, respectively. These results revealed that pretreated WAS was highly efficient to stimulate the accumulation of SCFAs. And the characteristics and cascade bioconversion of complex substrates were the main factor that determined the energy efficiency and hydrogen conversion rate of MECs. [ABSTRACT FROM AUTHOR]

A novel pretreatment method combining ultrasonic with thermophilic bacteria ( Geobacillus sp. G1) was employed to pretreat waste-activated sludge (WAS) for enhancing the WAS hydrolysis and subsequent volatile fatty acids (VFAs) production. The soluble protein and carbohydrate were mostly released from intracellular ultrasonic-assisted Geobacillus sp. G1 pretreatment, and accumulated to 917 ± 70 and 772 ± 89 mg COD/L, respectively, which were 2.53- and 2.62-fold higher than that obtained in control test. Excitation emission matrix (EEM) fluorescence spectroscopy revealed the highest fluorescence intensity (FI) of protein-like substances, indicating the synergistic effect of ultrasonic and Geobacillus sp. G1 pretreatments on WAS hydrolysis. The maximum VFAs accumulation was 4437 ± 15 mg COD/L obtained in ultrasonic-assisted Geobacillus sp. G1 pretreatment test. High-throughput pyrosequencing analysis investigated that the microbial communities were substantial determined by the pretreatment used. The hydrolysis enhancement was caused by an increase in extracellular enzymes, which was produced by one of dominant species Caloramator sp. The positive effect was well explained to the enhancement of WAS hydrolysis and final VFAs accumulation. [ABSTRACT FROM AUTHOR]

Most studies on the production of volatile fatty acids (VFAs) from waste activated sludge (WAS) digestion have focused on operating conditions, pretreatments and characteristic adjustments. Conditioning by extra carbon sources (ECS), normally added in a solid form, has been reported to be an efficient approach. However, this has caused considerable waste of monomeric sugars in the hydrolysate. In this study, the effects of two added forms (pretreated straw (S) and hydrolyzed liquid (L)) of cornstover (CS) on WAS acidification were investigated. To obtain different cellulosic compositions of CS, low-thermal or autoclaved assisted alkaline (TA or AA) pretreatments were conducted. The results showed that AA-L test achieved the highest VFAs value (653 mg COD/g VSS), followed by AA-S (613 mg COD/g VSS). These values were 12% and 28% higher, respectively, than that obtained in the TA-L and TA-S tests. Meanwhile, higher percentages of acetic acid were observed after AA pretreatment (~62% versus ~53% in TA). The added forms of CS played an important role in structuring the innate microbial community in the WAS, as shown by high-throughput sequencing and canonical correspondence analysis. The findings obtained in this work may provide a scientific basis for the potential implementation of co-digesting WAS with ECS simultaneously obtaining energy and high value-added products. [ABSTRACT FROM AUTHOR]