Demonstration of Anaerobic Digestion of Black Water for Methane Capture and Use in an Office Building

Abstract

Waste source separation including separate treatment of graywater and black water (BW) is gaining popularity as a sustainable integrated water management practice. Along that line, feasibility of anaerobic digestion of BW (toilet water only) from a building occupied with laboratory and office space was investigated using a pilot scale (114 L) upflow anaerobic sludge blanket (UASB) operated at an average temperature of 28 o C. The goal of the reactor was to achieve removal of organics while also generating methane gas for use as a source of energy. Reactor operational OLR varied between 0.21-0.39 kg COD m -3 d -1 and HRT varied from 2.6-4.0 days. Substantial removal of COD (72%), TSS and VSS (95%), and indicator organisms (1.4 log E. coli & 1.1 log fecal coliforms) was achieved over the study period. Methane biogas (61% CH4) produced during digestion provided potential as a source of renewable energy generated through processing the BW.Mounting pressure to conserve water resources has prompted the notion that separation of graywater from wastewater through the use of dual-plumbed systems may enable graywater to be reused to meet nonpotable demands including toilet flushing or irrigation. Graywater reuse has the potential to reduce potable household demand by as much as 20-50% (City of Los Angeles, 1992) and energy requirements for wastewater treatment are greatly reduced. Such water and energy savings have prompted adoption of graywater reuse practices in the United States. In an integrated water management approach where graywater reuse is widely adopted, traditional wastewater treatment practices may not be most appropriate for BW processing. Instead, a more sustainable approach would include anaerobic digestion of BW. This approach not only reduces energy requirements associated with aeration of wastewater, but also has the potential to provide a source of locally available renewable energy through capture of methane biogas.Several research groups have evaluated anaerobic treatment of BW when graywater was treated separately or reused (Masi et al., 2010;Abdel-Shafy, 2009;Zeeman et al., 2008;Elmitwalli et al., 2006;Kujawa-Roeleveld et al., 2006; Luostarinen and Rintala, 2006). For all of these studies, the source of toilet water was from vacuum toilets, except for the study by Luostarinen and Rintala (2006) where synthetic BW was composed, and the systems were operated at ambient temperatures, 10 o C-25 o C, rather than mesophilic temperatures, which are optimal for methane generation. The goal of the studied systems was primarily to achieve acceptable treatment of BW under anaerobic conditions, thus minimizing energy input. Zeeman et al. (2008) demonstrated energy savings by employing this approach compared to traditional methods of wastewater treatment including aeration. Other researchers have operated anaerobic digesters under mesophilic conditions to increase methane generation (van Voorithuizen et al., 2008;Wendland et al., 2007). These researchers demonstrated successful methane generation from BW, with...

A high‐rate anaerobic biofilm reactor for biomethane recovery from source‐separated blackwater at ambient temperature

“…As shown in Figure 2a, biogas production rate in the anaerobic biofilm reactor increased consistently with the increase in OLRs from 0.77 to 3.01 g COD/L‐d in four stages. The specific methane production rate at OLR of 0.77 g COD/L‐d was 105.3 ml/L‐d, which was considerably higher than that observed from some conventional anaerobic bioreactors investigated for blackwater treatment (31–73 ml/L‐d) (Gallagher & Sharvelle, 2010, 2011; Kujawa‐Roeleveld et al., 2005, 2006; Zamalloa et al., 2013). Due to the increase in OLRs, the steady‐state specific methane production rates increased to 162.5, 211.0, and 304.6 ml/L‐d at OLR of 1.03, 1.68, and 3.01 g COD/L‐d, respectively.…”

“…The methane content in biogas was ranged from 75.5% to 83.0%, which was higher than that reported for conventional blackwater digestion systems, such as 61% for a continuously stirred tank reactor (CSTR) (Wendland et al., 2007), 72% for up‐flow anaerobic sludge blankets (UASBs) (Gallagher & Sharvelle, 2010, 2011), and 70% for UASB‐septic tank (UASB‐ST) (Luostarinen & Rintala, 2007). The utilization of CO 2 through DIET‐based methanogenesis could provide high‐quality biogas (Liu, Sun, Zhao, Dang, & Holmes, 2019).…”

“…As shown in Figure 2c, the average methane content in biogas during the entire operation was > 75%. The highest methane content of 83.0% was achieved at OLR of 0.77 g COD/L‐d (Stage 1), which was remarkably higher than that of conventional anaerobic bioreactors for blackwater (62%–78%) (De Graaff et al., 2010; Gallagher & Sharvelle, 2010, 2011; Kujawa‐Roeleveld et al., 2005, 2006; Zamalloa et al., 2013). At OLR of 1.03 g COD/L‐d (Stage 2), methane content slightly decreased to 79.6%.…”

“…The performance comparison of this study with previous studies was shown in Table 2. In previous studies, the OLRs were mostly ranged from 0.3 to 1.0 g COD/L‐d (De Graaff et al., 2010; Gallagher & Sharvelle, 2010, 2011; Kujawa‐Roeleveld et al., 2006; Luostarinen & Rintala, 2005, 2007; Luostarinen et al., 2007; Meulman et al., 2008; Wendland et al., 2007; Zamalloa et al., 2013), including some studies performed under mesophilic conditions (Gallagher & Sharvelle, 2010, 2011; Gao, Guo, et al, 2019; Wendland et al., 2007; Zamalloa et al., 2013). However, in this study, high OLR of 3.01 g COD/L‐d was achieved with a stable performance at 20℃.…”