Methodological approach for trace elements supplementation in anaerobic digestion: Experience from full-scale agricultural biogas plants. (1st October 2018)

• Record Type: Journal Article
• Authors: Garuti, Mirco; Langone, Michela; Fabbri, Claudio; Piccinini, Sergio
• Is Part Of: Journal of environmental management. Volume 223(2018)
• Page Start: 348
• Page End: 357
• Publication Date: 2018-10-01
• Subjects: Agricultural feedstock -- Anaerobic digestion -- Biogas plant -- Process monitoring -- Trace elements -- Volatile organic acids; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2018.06.015
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: Trace metals play a very important role on the performance and stability of agricultural biogas digesters. The purpose of this study was to develop a methodological approach to quickly detect limiting conditions due to Trace Elements (TE) concentration in full-scale biogas plants. The work was based on long-term process monitoring in two full-scale agricultural biogas plants and on the correlation between their performance and TE concentration in the digesters. Monitoring and analysis of data from two different case studies allowed to understand the effect of the TE added on biogas plant performance. Furthermore, over-dosage has been avoided, minimizing the risk of biological inhibition and excess of heavy metal concentration in the effluent digestate according to regulation for land fertilization. TE supplementation has been successfully applied to optimize the biogas production, when a slight volatile organic acid accumulation has been detected (from about 3515 mg CH3 COOHeq L −1 to 4530 mg CH3 COOHeq L −1 ), and to recover the biogas production after a strong organic acid accumulation (up to 7779 mgCH3 COOHeq L −1 ). Molybdenum, nickel, cobalt, and selenium concentrations above the stimulatory level identified in this study showed similar effects in both case studies: a temporary increase of the methane content in the biogas by 15 – 20% and a provisional improvement of the specific methane production. This allowed to decrease the organic loading rate by 10 – 20%, due to rapid degradation of accumulated volatile organic acids. Further, the residual methane potential of the biogas plant in TE limiting conditions reached values up to 4.8% in comparison to the 1.3% residual methane potential achieved when TE concentration was not a limiting factor, proving that a proper use of TE could help in reducing greenhouse gases emission. Graphical abstract: Highlights: A methodological approach to detect limiting trace element conditions has been discussed. Volatile organic acid degradation occurred immediately after trace element supplementation. Trace element supplementation increased the specific methane production and methane content. Anaerobic degradability was improved by additional trace element.