Biological denitrification potential as an indicator for measuring digestate stability

Biological stability is an essential parameter for assessing the environmental impact from the land application of digestate as organic amendment. In this paper, a newindicator, biological denitrification potential (BDP), was developed for evaluating the biological stability of digestate. Digestate samples collected along the digestion process from a mesophilic anaerobic batch digester fed with food waste were investigated under different solid retention time. The value of BDP based on nitrate removal ranged from176.3 to 48.3mg-N/g-VSdigestate, corresponding well to the digestion time, and strongly correlated with total organic carbon content. Evolution trends similar to respiration index (RI) and biochemical methane potential (BMP) can be also observed for BDP, indicating that values presented of these stability indices decreased with the degree of digestate stabilization. The mass balance of the BDP process indicated that nitrate was mainly converted into N-2 gas with mineralizing organic carbon from digestate, implying that biostability evaluated by BDP depends on carbon source and denitrification activity in digestate. The denitrifying bacteria Thiopseudomonas and Pseudomonas accounted for the majority of microorganisms. These findings of this study concluded that BDP can be an efficient indicator to assess the bio-stability of digestate planned for agricultural or land use. Compared with the existing biostability index, BDP has the additional advantage of no exogenous inoculum addition, homogenous test condition and possibility of shortening incubation time. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Biological stability of digestate was evaluated using a new indicator called biological denitrification potential (BDP) in this study. Results showed that BDP values correlated well with digestion time and total organic carbon content. Furthermore, BDP was found to depend on the carbon source and denitrification activity in the digestate.