Effects of thermal hydrolysis process-generated melanoidins on partial nitritation/anammox in full-scale installations treating waste activated sludge

Journal article (2023)

Authors

J.A. Pavez Jara Sanitary Engineering - CEG
J.B. van Lier Sanitary Engineering - CEG
M.K. de Kreuk Water Management
Research Group
Sanitary Engineering (CEG) (TU Delft)
Copyright: © 2023 J.A. Pavez Jara, J.B. van Lier, M.K. de Kreuk
DOI: https://doi.org/10.1016/j.jclepro.2023.139767
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Published Date

2023

Language

English

Faculty

Civil Engineering & Geosciences

Department

Water Management

Research Group

Sanitary Engineering

Abstract

Thermal hydrolysis process (THP) is a well-established anaerobic digestion (AD) pre-treatment technology. Despite the THP benefits the pre-treatment increases the concentrations of nutrients and melanoidins in the digestate reject water after dewatering. The increased concentrations of nutrients and melanoidins formed during THP-AD can impact downstream processes, such as struvite precipitation and partial nitritation/anammox (PN/A). In our present work, six full-scale PN/A influents and effluents were sampled in The Netherlands (4 with THP and 2 without THP). Full-scale samples were characterised and the stoichiometric O2 consumption and melanoidins chelated to trace elements were analysed. The results showed that THP increased the concentration of total ammoniacal nitrogen (TAN), chemical oxygen demand (COD), total organic carbon (TOC), UVA 254 and colour, which are indicators of melanoidins occurrence. THP furthermore decreased the stoichiometric NO3−-N production from the PN/A reaction in effluents. The disparity between stoichiometric and measured NO3− -N in the THP-using plants was explained by the proliferation of denitrifiers. Moreover, denitrification improved the N removal efficiency due to the consumption of the stoichiometrically-produced NO3− -N. Also, the stoichiometric O2 consumption increased in the plants using THP, reaching up to 56% of the O2 used for partial oxidation of TAN. Trace elements analysis revealed that the plants with elevated concentrations of melanoidins in the effluent showed a high percentage of chelated multivalent cations, particularly transition metals such as Fe. Kendall correlation coefficient analysis showed that the chelation of multivalent cations was correlated mainly with colour occurrence in the reject waters. Overall, the results indicated that in PN/A systems using THP-AD increased O2 consumption and trace elements availability should be considered during the process design.