Thermophilic and hyper-thermophilic anaerobic digestion (AD) are promising techniques for the treatment of concentrated black water. It was shown that thermophilic AD of concentrated BW reaches the same methanisation and COD removal as mesophilic anaerobic treatment of BW (conventional vacuum toilets) and kitchen waste while applying a higher loading rate (OLR) (2.5–4.0 kgCOD/m3/day) [1]. The retention time was 8.7 days with an organic loading rate of >3 kgCOD/m3/day. This resulted in a COD removal of 70% and a methanisation of 62% (based on CODt) during thermophilic AD. Hyper-thermophilic (70 ◦C) reached lower levels of methanisation (38%).
During both TAD and HTAD pathogen indicator organisms were removed to a high extent. Compared to mesophilic anaerobic digestion there is a significant increase in the removal of Escherichia coli and extended-spectrum β-lactamases producing E. coli. Both were almost fully eliminated during TAD and HTAD. Since there was no significant difference between TAD and HTAD in terms of pathogen removal, there is no additional benefit for hyper-thermophilic AD over thermophilic AD. Additionally, TAD has better COD removal and methanisation performance than HTAD. Therefore, TAD is suggested as novel treatment technology for concentrated BW with simultaneous pathogen removal. Next challenge is the development of efficient nutrient recovery strategies during TAD, preferably with separate product streams for nitrogen, phosphorous and potassium.
Source: Moerland, M. J. 2021. Thermophilic and hyper-thermophilic anaerobic digestion as novel treatment technologies for safe nutrient recovery from concentrated black water. Resource recovery and wastewater treatment technologies, Clean Water & Ecosystem Restoration. AIWW 2021
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