Science Inventory

A proof of concept study for wastewater reuse using bioelectrochemical processes combined with complementary post-treatment technologies

Citation:

Khan, W., J. Nam, H. Woo, H. Ryu, S. Kim, S. Maeng, AND H. Kim. A proof of concept study for wastewater reuse using bioelectrochemical processes combined with complementary post-treatment technologies. Environmental Science: Water Research & Technology. Royal Society of Chemistry, Cambridge, Uk, 5:1489-1498, (2019). https://doi.org/10.1039/C9EW00358D

Impact/Purpose:

Wastewater reclamation is of the utmost concern today to overcome the current water shortage that is aggravated by climate change and increasing population. Biological processing for domestic wastewater treatment generally focuses on removing biodegradable organic carbon and inorganic nutrients. This can lead to accumulation of non- or slowly biodegradable compounds and their persistent metabolites in the effluent, which constitutes a major concern for wastewater reuse, associated with the possible ecological impact on biota within the environment. Moreover, conventional biological processes involve the production of an activated mass of microorganisms capable of aerobic stabilization of organic substrates in wastewater. These processes require a robust aeration to sustain the microorganisms actively in the system, typically accounting for 45‒75% of total energy consumption. Various integrated treatment strategies combined with complementary technologies for removing the compounds of emerging concern should be considered and investigated to minimize the adverse effects on the environment that are associated with wastewater reuse. Therefore, the objective of this research was to investigate a novel process configuration for wastewater reuse to achieve the following goals during treatment of synthetic domestic wastewater: (1) consistent bioelectrosynthesis of H2O2 and concurrent removal of carbonaceous organic matter; (2) photochemical oxidation of recalcitrant organic carbons using UVC/H2O2; (3) increased biodegradability of effluent organic matter prior to artificial aquifer recharge; (4) robust removal of inorganic nutrients (N and P) when required to comply with the discharge permits. For those purposes, this study integrated microbial electrochemical cells (MECs), photolytic oxidation, and algal treatment. To the best of our knowledge, the process configuration investigated in this study has not been proposed for wastewater reuse, which typically requires membrane-based tertiary treatment. One could say that extensive studies have already been carried out with each of the elements of this treatment processes. However, this work connects them with one another systematically to complement each other and maximize system performance. This is significant, as our strategy produces a useful chemical for the purpose of on-site use (e.g., advanced oxidation and disinfection), employs living components that are capable of reproduction and substrate uptake, and is designed to be operated with high flexibility to meet diverse desires of the end user.

Description:

This article describes a proof-of-concept study designed for the reuse of wastewater using microbial electrochemical cells (MECs) combined with complementary post-treatment technologies. This study mainly focused on how the integrated approach works effectively for wastewater reuse. In this study, microalgae and ultraviolet C (UVC) light were used for advanced wastewater treatment to achieve site-specific treatment goals such as agricultural reuse and aquifer recharge. The bio-electrosynthesis of H2O2 in MECs was carried out based on a novel concept to integrate with UVC, especially for a roust removal of trace organic compounds (TOrCs) resistant to biodegradation, and the algal treatment was configured for nutrient removal from MEC effluent. UVC irradiation has also proven to be an effective disinfectant for bacteria, protozoa, and viruses in water. The average energy consumption rate for MECs fed acetate-based synthetic wastewater was 0.28±0.01 kWh per kg of H2O2, which was significantly more efficient than are conventional electrochemical processes. MECs achieved 89±2% removal of carbonaceous organic matter (measured as chemical oxygen demand) in the wastewater (anolyte) and concurrent production of H2O2 up to 222±11 mg L−1 in the tapwater (catholyte). The nutrients (N and P) remaining after MECs were successfully removed by subsequent phycoremediation with microalgae when aerated (5% CO2, v/v) in the light. This complied with discharge permits that limit N to 20 mg L−1 and P to 0.5 mg L−1 in the effluent. H2O2 produced on site was used to mediate photolytic oxidation with UVC light for degradation of recalcitrant TOrCs in the algal-treated wastewater. Carbamazepine was used as a model compound and was almost completely removed with an added 10 mg L−1 of H2O2 at a UVC dose of 1000 mJ cm−2. These results should not be generalized, but critically discussed, because of the limitations of using synthetic wastewater.