247 Synthesis and discussion ammonium and methane removal from the discharge of these anaerobic systems through the combination of anammox and N-DAMO as a sustainable solution to avoid indirect greenhouse gas emissions (Fan et al., 2023; Lu et al., 2024; van Kessel et al., 2018). These systems have been conceptualized in both one-stage and two-stage configurations. In one-stage systems, two approaches are common. The first utilizes membrane biofilm reactors (MBfRs) that combine nitrifiers and N-DAMO in a single step. The second involves granular sludge, where nitrifiers can reside in the outer layers to oxidize nitrogen compounds (Wang et al., 2017). A key feature of the granular system is its ability to prevent biomass washout with its dense and robust biomass structures (granules), crucial for decoupling the solids retention time from the HRT. This biomass retention in the reactor, crucial for slowgrowing microorganisms, coupled with the granules” ability to have an oxygen gradient across its structure (external to internal), offers a unique biotechnological application. We propose integrating the scaled-up N-DAMO cultures in high-rate activated granular sludge (low retention time, carbon capture and no nitrification) combined with nitritation (nitrification) in a WWTP process (Figure 2). The initial step would involve removing/capturing organic matter and separating it from the ammoniumrich effluent. This carbon would then be directed through an anaerobic process to produce recycle energy in the form of methane. The effluent with saturated dissolved methane (dCH4) would be removed by the N-DAMO reactor. During nitrification, ammonium would be partially oxidized to nitrite and nitrate, creating optimal conditions for the subsequent autotrophic (with most organic matter removed) stage where anammox and N-DAMO processes would facilitate methane and ammonium removal. This could occur either in saline conditions, with sulfideoxidizing denitrifiers as outlined in Chapter 4, or in freshwater, as described in Chapter 5 (Figure 2). N-DAMO and anammox processes have already been detected in various WWTPs (Meng et al., 2021), and the careful inoculation of a pilot plant could represent an exciting next step. Furthermore, saline WWTPs (Hao et al., 2014) could be tested with cultures tolerant to higher salinity and sulfide concentrations, as these systems are capable of detoxifying sulfide as also shown in Chapters 4 and 5. Retention times would need to be carefully managed through granulation to preserve slow-growing microbes, such as “Ca. Methanoperedens”. High-salinity 8
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