From anaerobic membrane bioreactors to water resource recovery facility: experimental validation and sustainability assessment

Technical solutions for the transition from ‘wastewater treatment plant’ (WWTP) to the concept of ‘low-carbon water resource recovery facility’ (WRRF) were assessed, addressing i) water reuse, ii) resource recovery and iii) carbon footprint assessment. Specifically, in terms of water reuse, conventional ‘’fit-for-purpose’’ treatments and innovative solutions as anaerobic treatments were analysed and compared. In this context, a pilot scale system, placed in a hotspot of seawater intrusion, composed of an upflow granular anaerobic sludge blanket (UASB) reactor coupled with AnMBR (Anaerobic Membrane Bioreactor) was set-up and operated for more than 2 years. Different operating conditions, organic loading rate and salinity conditions were investigated for evaluating the performances of the process. At an organic loading rate (OLR) of 1 kg COD/m3/d, biogas production was around 0.39 ± 0.2 L/d. The increase of the OLR to 2 kg COD/m3/d resulted in increase of biogas production to 4.11 ± 3.1 L/d with fermented cellulosic sludge addition. The latter affected the membrane operation and significant fouling occurred after long-term filtration, where the trans-membrane pressure (TMP) reached up to 500 mbar. High saline conditions of 1500 mgCl/L adversely affected the biogas production without deteriorating the membrane operation. The final treated effluent met quality standards of CLASS A of the new EU regulation741/2020 for water reuse and resulted suitable for fertigation purposes in agriculture. An additional unit was coupled with the AnMBR treatment for removing contaminants of emerging concern (CECs), using Molecurarly Imprinted Polymers (MIPs) as adsorbent filler. An adsorption column was started-up and diclofenac was used as target compound. Removal efficiency was up to 50% in the final effluent. Additionally, in the context of safe reuse, also microplastics (MPs) occurrence and removals in different wastewater treatment units were investigated. In this scenario also a prototype system for collecting significant wastewater sampling volumes to detect more representative MPs concentrations was designed and realized. From experimental results the full-scale conventional activated sludge scheme removed 86% of MPs, with the main reduction in the primary and secondary settling. In comparison, the pilot-scale UASB+AnMBR configuration achieved 94% MPs removal. The results highlighted an accumulation phenomenon of MPs in the sludge and this affected negatively the methanogenic activity of anaerobic biomass. Up to 58% of decrease was experimentally observed at the exposure of 50 MPs/gTS. On the other hand, water pollution in stormwater and related water bathing issues were addressed assessing combined sewer overflows (CSOs) management strategies and validating advanced compact treatments, composed of dynamic rotating belt filter, adsorption on granular activated carbon and UV disinfection, to minimize their impacts. The results of pilot treatment showed great potential for TSS, COD and E. coli removal efficiencies with more than 90%, 69% and 99%, respectively. Moreover, feasibility studies in full-scale WWTPs, addressing resource recovery solutions, including phosphorous salts, volatile fatty acids and biopolymers recovery were carried out. In particular, real environment eco-innovative and energy-efficient solutions, developed within the H2020 Smart- Plant project to renovate existing WWTPs and close the circular value chain, were assessed using viii Cost-Benefit Analysis (CBA), Social Life Cycle Assessment (S-LCA) and Social Readiness Level (SRL) methods. Overall, the SMARTechs created benefits both from an environmental and social point of view, with a maximum total economic value (TEV) up to +23% compared to baseline scenario (without SMARTech implementation). In terms of social benefits, the S-LCA highlighted a global positive impact and SMARTechs fell in SRL range of 6-7, which implies a good societal acceptance and adaptation potential. Finally, Carbon Footprint Assessment for the wastewater treatment service was deeply investigated, proposing a new methodological evidence-based approach for the overall determination of direct and indirect emissions in the treatment plants. Most of the considered emissions factors for carbon footprint assessment were validated by site-specific measurements campaigns in 12 relevant WWTPs. Specific carbon footprints resulted in the emissions of 0.04–0.20 tonCO2eq/PE/y, varying according to the size of the plant. The most impactful categories were identified for indirect emissions associated with dissolved GHGs discharged in the surface water body and due to energy consumption, which accounted for 13–70% and 10–40%, respectively.