@phdthesis{01HABRGCGF69ZPJ598NPWQY2JD,
  abstract     = {{Water is essential for all living beings and critical for meeting societal, agricultural, and industrial development. Access to freshwater to satisfy all current needs is threatened due to the decline in clean water sources and the increasing demand. The former is mainly due to changes in the hydrological cycle by climate change, pollution, and techno-economical limitations impeding treatment in place, and the latter is due to urban migration and population growth. Therefore, there is an urgent need for wiser water management to cope with the ongoing water stress and to meet the sustainable development goal (SDG) 6 on Clean Water & Sanitation by 2030. Multiple solutions have been proposed as alternative water sources, including water desalination, rainwater harvesting, and water reclamation. Reclaiming water in centralised domestic wastewater treatment plants has been a preferred solution in urban locations for countries facing water scarcity, such as China, the USA, Singapore, and Mexico. Conversely, decentralised treatment strategies are proposed as a potential solution for dispersed settlements. In this study, we selected the coupling of a nature-based solution (i.e., constructed wetlands) with an innovative disinfection unit (i.e., electrochemical systems) for safe water discharge or reclamation.
Constructed wetlands (CWs) are considered a mature technology that can be implemented to treat domestic wastewater in diverse scales from a single household to a metropolis level. The effluents of biologically treated wastewater, such as in CWs, usually require disinfection to meet effluent discharge or water reclamation standards consistently. Electrochemical systems can disinfect (non-)treated effluents by producing oxidants such as hydrogen peroxide and chlorine in a process denominated electrochemical disinfection (ECD). ECD systems are considered innovative and versatile to accomplish the desired treatment target, but applied research is still required to reach a higher technology readiness level before encompassing widespread implementation. In this thesis, three experimental chapters were organised based on the current gaps in the available literature, explored in Chapter 1, with a particular focus on the ECD of CW effluents.
Hydrogen peroxide is a disinfectant that can be produced at the cathode of an electrochemical cell. By using a microbial anode harvesting high-energy electrons from the oxidation of organics, H2O2 can be generated at low energy cost in the so-called bioelectrochemical system (BES). While a proof of concept has previously been established, a longer-term operation than most reported literature (e.g., ≤24 h) and the putative impact of H2O2 on the anodic electroactive biofilm (EAB) have not been extensively studied. In Chapter 2, three membrane-divided BES were analysed to determine their robustness when challenged to two H2O2 concentrations (1 and 5 g L−1 H2O2) recirculating in a chamber contiguous to the one containing the EAB. A key finding was the workability of BES operating with 1 g L−1 H2O2 in the chamber next to the anodic one, as it did not show any significant (p> 0.05) deterioration in the catalytic activity of the EAB for 28 days. The latter H2O2 concentration can be sufficient to disinfect CW effluents. However, the overall feasibility of BES will also depend on the biodegradable organics in the wastewater fed in the anodic compartment to maintain adequate microbial current generation. Other interesting results include chronic deterioration of BES materials exposed to H2O2, including stainless steel corrosion during downtimes of BES containing H2O2, and the decrease in relative abundance of putative electroactive microorganisms when exposed to ≥ 5 g L−1 H2O2 in the adjacent chamber. Even though carbon electrodes can produce H2O2 in electrochemical systems at concentrations that allow disinfection, the production rates are slow (up to 0.78 g L−1h−1), which thwarts the practical implementation of this technology for a decentralised treatment coupled to CWs.
In Chapter 3, the electrochemical chlorine production for disinfection of CW effluent in decentralised settings was explored. Chlorine can be generated anodically from the oxidation of naturally present Cl−. Chlorine is a more efficient disinfectant, stable, and easily generated than H2O2. Thus, a two-chamber electrochemical cell was designed to produce chlorine at a Ti/IrO2RuO2 anode with a synthetic electrolyte containing 650 mg Cl− L−1 and subsequently tested with real CW effluents from two locations (Ecuador and Belgium). Interestingly, ECD systems built with an anion exchange membrane produced about twice as much free chlorine than those built with a cation exchange membrane because of chloride recovery by electromigration from the catholyte to the anolyte. During the disinfection experiments, up to 5-log removal of total coliforms was inactivated during the ECD of CW effluents, and residual chlorine remained in the disinfected water, which was crucial to avoid pathogen regrowth. Lower residence times (15 s) and current densities (50 A m−2) induced the most energy-efficient operation with a charge density of 37.5 C L−1 and energy consumption of 0.1 kWh.m−3 when disinfecting the effluent of a CW in Guayaquil-Ecuador. The results of this chapter encouraged the practical implementation of the coupling of CW+ECD as a treatment train.
In Chapter 4, an assessment of ECD of CW effluents was designed in real field conditions. A pilot-scale CW was operated for 28 weeks on a calcium-rich wastewater stream (130 ± 42 mg L−1) from a building that recirculated its treated effluent. Five membranes separated ECD systems were tested varying in the water route, membrane type and the nature of the catholyte. All five ECD systems effectively disinfected pathogens, but four faced large issues with fouling, especially scaling, within a week. Only the fifth configuration allowed a continuous operation for at least 21 weeks by implementing a precipitation tank at pH 11.6 upstream of the ECD system. Exceptionally low flow rates (1.8 L h−1) and high energy consumption (5.9 kWh m−3) were attained as the alkaline stream from the precipitation step must be neutralized by water oxidation before an efficient chlorine evolution takes place at the anode. This chapter illustrates the hurdles faced during the implementation of ECD systems treating natural wastewater and proposes solutions to deal with the impact of scaling.
Overall, decentralised wastewater systems implementing CW+ECD can be a potential solution for providing proper sanitation and allowing an alternative water source. ECD systems producing chlorine provide water disinfection during continuous treatment and are advisable when water reclamation is desired. However, fouling issues should be overcome, as well as diminishing capex and energy consumption. The strategies discussed in this thesis are alternative solutions to decrease the chances of reactor failure and pave the way for future full-scale applications.}},
  author       = {{Mosquera Romero, Suanny Sophia}},
  isbn         = {{9789463576550}},
  keywords     = {{BES performance,EAB sequencing,H2O2 diffusion,,on site application,Electrochemical disinfection,nature-based solutions,low-income countries,non-potable water reuse,ion-exchange membranes,chlorine electrogeneration,cathode scaling,decentralised treatment,membrane fouling,pathogen inactivation}},
  language     = {{eng}},
  pages        = {{XI, 220}},
  publisher    = {{Ghent University. Faculty of Bioscience Engineering}},
  school       = {{Ghent University}},
  title        = {{(Bio)electrochemical disinfection of constructed wetland effluents for safe water discharge or reclamation for non-potable application}},
  year         = {{2023}},
}