Water treatment and reclamation by implementing electrochemical systems with constructed wetlands.

Seasonal or permanent water scarcity in off-grid communities can be alleviated by recycling water in decentralized wastewater treatment systems. Nature-based solutions, such as constructed wetlands (CWs), have become popular solutions for sanitation in remote locations. Although typical CWs can efficiently remove solids and organics to meet water reuse standards, polishing remains necessary for other parameters, such as pathogens, nutrients, and recalcitrant pollutants. Different CW designs and CWs coupled with electrochemical technologies have been proposed to improve treatment efficiency. Electrochemical systems (ECs) have been either implemented within the CW bed (ECin-CW) or as a stage in a sequential treatment (CW + EC). A large body of literature has focused on ECin-CW, and multiple scaled-up systems have recently been successfully implemented, primarily to remove recalcitrant organics. Conversely, only a few reports have explored the opportunity to polish CW effluents in a downstream electrochemical module for the electro-oxidation of micropollutants or electro-disinfection of pathogens to meet more stringent water reuse standards. This paper aims to critically review the opportunities, challenges, and future research directions of the different couplings of CW with EC as a decentralized technology for water treatment and recovery.

Comparison of MBR and MBBR followed by UV or electrochemical disinfection for decentralized greywater treatment.

Greywater is an attractive source for water reuse at the household or building level, particularly for non-potable applications. Two greywater treatment approaches are membrane bioreactors (MBR) and moving bed biofilm reactors (MBBR), yet, their performance has not been compared so far within their respective treatment flowsheets, including post-disinfection. Two lab-scale treatment trains were operated on synthetic greywater: a) MBR with either polymeric (chlorinated polyethylene, C-PE, 165 days) or ceramic (silicon carbide, SiC, 199 days) membranes coupled with UV disinfection; and b) single-stage (66 days) or two-stage (124 days) MBBR coupled with an electrochemical cell (EC) for in-situ disinfectant generation. Water quality was constantly monitored, and Escherichia coli log removals were assessed through spike tests. Under low-flux operation of the MBR (<8 L·m - 2·h - 1), the SiC membranes delayed the onset of membrane fouling and needed less frequent cleaning compared to C-PE membranes. Both treatment systems met most water quality requirements for unrestricted greywater reuse, at a 10-fold lower reactor volume for the MBR than the MBBR. However, neither the MBR nor the two-staged MBBR allowed adequate nitrogen removal, and the MBBR did not consistently meet effluent chemical oxygen demand and turbidity requirements. Both EC and UV provided non-detectable E. coli concentrations in the effluent. Although the EC provided residual disinfection, scaling and fouling decreased its energetic and disinfection performance over time, making it less efficient than UV disinfection. Several outlines to improve the performance of both treatment trains and disinfection processes are proposed, thus, allowing a fit-for-use approach that leverages the advantages of the respective treatment trains. Results from this investigation will assist in elucidating the most efficient, robust, and low-maintenance technology and configurations for small-scale greywater treatment for reuse.

Combined Gold Recovery and Nanoparticle Synthesis in Microbial Systems Using Fractional Factorial Design.

Green synthesis of gold nanoparticles (AuNPs) using microorganisms has been generally studied aiming for high-yield production and morphologies appropriated for various applications, such as bioremediation, (bio)sensors, and (bio)catalysis. Numerous approaches showed the individual effect of factors influencing the synthesis of AuNPs with limited analysis of the governing factors enhancing the production and desired quality of the precipitates. This study proposes a fractional-factorial design to investigate the simultaneous influence of seven environmental factors (cell concentration, temperature, anoxic/oxic conditions, pH, gold concentration, electron donor type, and bacterial species) on the recovery yield and synthesis of targeted AuNPs. Various sizes and morphologies of the AuNPs were obtained by varying the environmental factors studied. The factors with significant effects (i.e., 0.2 mM Au and pH 5) were selected according to statistical analysis for optimal removal of 88.2 ± 3.5% of gold and with the production of valuable 50 nm AuNPs, which are known for their enhanced sensitivity. Implications of the cytochrome-C on the bacterial mechanisms and the provision of electron donors via an electrochemical system are further discussed. This study helps develop gold recovery and nanoparticle synthesis methods, focusing on the determining factor(s) for efficient, low-cost, green synthesis of valuable materials.