Micronutrient component changes in the biogas slurry treated by a pilot solar-heated anaerobic reactor

A solar-heated anaerobic reactor system was applied to decompose livestock wastewater, in which cattle manure and chopped straw were mixed (COD_Cr 15,000∼25,000 mg·l^-1), the commercial microorganisms were added to ambient acidification (about 32°C) and the acclimated sludge was inoculated. Then, the experiments were carried out on wastewater anaerobic degradation and biogas production at 40∼42°C, as fed every 10 days till stable running. The results showed that NH₃-N and PO₄^3- of the biogas slurry were 441 mg·l^-1 and 65.0 mg·l^-1 on the 35^th day, respectively. The concentration of K was up to 350 mg·l^-1 in the biogas slurry, rather higher than that of Mg and Fe, which indicated that the available K could contribute more in the agricultural irrigation. Total amino acids were up to 23.7 mg·l^-1 after anaerobic digestion, in which Lys, Thr, Ala and Arg were prominent in the biogas slurry. These amino acids could be beneficial to seed soaking, feed adding and apply as foliar fertilizer. The major volatile organic compounds were detected in the biogas slurry, including toluene, m-cresol (up to 0.036% in the process of ambient acidification) and triethylsilane, which could be reduced to scarcely influence on agricultural application after anaerobic digestion.