| The large amount of liquid digestate is usually used for field application. Anaerobic digestate is typically applied as a liquid fertilizer and soil amendment because it contains relatively high concentrations of plant nutrients. For many years, macronutrient such as nitrogen and phosphorus in liquid digestate has been widely studied, whereas little attention has been paid to plant hormones. The dynamic changes in plant hormone of liquid digestate from lab-scale batch experiments and biogas plant were compared. Results from the lab-scale batch experiment revealed that the liquid digestate contained higher concentrations of plant hormones than the original animal manures. Subsequently, gibberellic acid （GA3） decreased due to instability, whereas indoleacetic acid （IAA） and abscisic acid （ABA） were accumulated during anaerobic digestion. After 30 days of anaerobic digestion, the liquid digestate contained 3.06-5.21 mg·L-1 GA3, unchanged from that in animal manures(1.45-4.25 mg·L-1). However, the concentrations of ABA and IAA increased by 276.8%-348.1% and 201.4%-435.7%, respectively, after 30 days of anaerobic digestion. The liquid digestate from biogas plant contained higher concentration of GA3 （16.37-44.83 mg-L-1） attributed to continuously feeding. Quantitative analysis of samples from large-scale continuously fed biogas plants verified the high contents of plant hormones in liquid digestate including GA3 (16.37-44.83 mg·L-1), IAA (17.38-36.84 mg·L-1) and ABA （13.23-35.59 mg-L"1）.However, the storage experiment demonstrated a significant loss of plant nutritions in liquid digestate prior to land application because of decomposition and transformation. In this study, the effects of storage temperatures （4℃,20℃, and 37℃） on plant nutritions in liquid digestate during the period of 90 days were investigated. The results showed NH4+-N concentration almost kept unchanged under 4℃, and decreased by 50% and 85.9% due to NH3 emissions under 20℃ and 37℃. No significant difference was observed among storage at different temperatures for the losses of plant-available P （40%-53.1%）, which caused by precipitation. The results showed the concentration of GA3 decreased by 80.2% and 80.7%, respectively, under 20℃ and 37℃. The concentration of IAA decreased by 26.2%,48.1% and 70.5% under 4℃,20℃ and 37℃. However, the ABA was unchanged under 4℃ and 20℃, just slightly decreasing by 22.14% under 37℃. Therefore, the GA3 was the most sensitive for temperature and the ABA was more stable.In this study, ammonia stripping and vacuum evaporation were tested to compare their technical feasibilities and the effects on the plant nutrients availability in the liquid fraction of digestate. Batch experiments showed that the nutrients characteristics of liquid digestate including total ammonia nitrogen （TAN）, soluble P, gibberellic acid （GA）, indoleacetic acid （IAA） and abscisic acid （ABA） were strongly dependent on initial pH in both ammonia stripping and vacuum evaporation process. Lower plant nutrient concentration (TAN 136.76 mg·L-1, soluble P 1.49 mg·L-1, IAA 21.12 mg·L-1, GA315.63 mg·L-1, ABA 34.83 mg·L-1) in the liquid digestate was achieved in the ammonia stripping process with Ca（OH）2 addition of 12 g·L-1, while higher nutrient concentration (TAN 2998.07 mg·L-1, soluble P 178.26 mg·L-1, IAA 60.87 mg·L-1 GA3 44.46 mg·L-1, ABA 110.90 mg·L-1) was achieved in vacuum evaporation at pH of 6. According to the results, both ammonia stripping and vacuum evaporation can be used as an alternative of nutrient recovery technics, which, however, should be chosen according to the potential different applications of liquid digestate （soaking seed, increase plant tolerance, nutrients transportation et al.）.Results of indolic derivative analysis in anaerobic reactors treating animal manure and those of investigative experiments using single indolic component as substrate revealed that IAA was produced from L-tryptophan. L-tryptophan metabolism under alkalescent anaerobic condition follows two pathways. i) IAA and Skatole Production （ISP）. L-tryptophan can be converted into skatole via IAA, and exogenous carbon can completely inhibit this process, in which IAA production is enhanced （53.2%）. ii) Indole Production and Mineralization （IPM）. Simultaneously, L-tryptophan can also be directly converted into indole. Exogenous amino acids can significantly improve indole degradation decreasing by 88.1% in this process. Based on these findings, carbon source and amino acids can theoretically regulate IAA production and indole mineralization, respectively. These findings provide some new perspectives on IAA regulation and indole decontamination in liquid digestate. |
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