DOI: 10.13140/RG.2.2.10734.98888
Growing urban populations and rising demands on water infrastructure make decentralized wastewater treatment an urgent research priority. Conventional centralized plants are often energy intensive and limited in their ability to recover valuable resources.
Exploring integrated bioelectric systems offers a pathway to not only improve nutrient removal but also generate useful byproducts such as biogas and hydrogen. Pilot-scale studies are required to demonstrate feasibility, optimize reactor design, and assess performance under realistic operating conditions.
Researchers at the Mexican Institute of Water Technology (IMTA) in Jiutepec , Mexico, addressed the pressing need for sustainable, modular solutions. They recently published their pilot in the journal Bioprocess and Biosystems Engineering. Their system could possibly serve households, hotels, and other facilities where both wastewater volumes and energy demands converge.
An integrated, decentralized treatment system consisting of an electrolysis reactor, an anaerobic biofilm reactor, and an aerobic moving-bed reactor was tested at pilot scale. The total volume was 50 liters, with 10.4 liters allocated to the electrolysis chamber. Domestic wastewater was treated while simultaneously producing hydrogen.
The system comprised the following individual reactors
- An electrolysis chamber with graphite felt anode and cathode and a cation exchange membrane (CMI‑7000S),
- A fixed-bed reactor with polyurethane foam as carrier material,
- An aerobic moving-bed reactor with modified LDPE carrier elements (≈1,500 m²/m³ specific surface area) and targeted aeration,
- A high-performance sedimentation unit.
The system was installed in a tank and operated under continuous flow at two different rates. The hydraulic retention time was 0.75 or 1.5 days. Applied voltages ranged from 0.7 to 1.0 V. Various organic loads (chemical oxygen demand, COD) of 0.2–0.44 kg/m³/d were also investigated.
| Contamination | Removal |
|---|---|
| COD | 81–84% |
| BOD₅₀ | 84–85% |
| TSS | 76–88% |
| TN | 53–68% |
| NH₄⁺ | 88–98% |
| TP | 11–30% |
With increasing load, the treatment rated tended to decrease. Current densities reached up to 0.41 A/m² with a maximum hydrogen production rate of 0.007 L/L/d (absolute: 0.072 L/d). The higher voltage of 1.0 V promoted hydrogen formation as well as nitrogen and phosphorus conversions. A control phase without applied voltage was used to isolate the contribution of voltage to treatment performance.
This voltage-free control quantified the actual contribution of the electrochemical field. No current flow or hydrogen production occurred. Organic load removal continued, but only through conventional steps. Nitrogen and phosphorus conversions were significantly reduced, especially ammonium removal. Overall, the system showed lower treatment performance without applied voltage.
Microbial electrolysis in the combined system did not merely add passive biofilm volume. Under applied voltage it provided an independent functional contribution to nitrogen and phosphorus conversion and energy recovery. Without voltage, the microbial electrolysis cell behaved hydraulically like an additional reactor space but lost its added value as a bioelectric unit.
The study demonstrated that integrated bioelectrolysis combinations at small pilot scale can achieve high organic degradation rates and relevant nitrogen conversions, while simultaneously producing hydrogen or biogas. This makes the approach suitable as a low-energy, modular pre- and main treatment for domestic wastewater with potential for useful gas recovery. The hotel industry is particularly interesting as a market, given the necessary flow volumes and corresponding gas demand.
Phosphate removal was too low (11–30%) to meet regulatory requirements. Post-treatment in municipal wastewater plants remained necessary. Higher organic loads worsened nutrient and solids removal, making the system only partially suitable for industrial wastewater with higher loads. For discharge and reuse standards, additional post-treatment steps were also required in industrial applications.
The pilot-scale integration of bioelectric reactors into domestic wastewater treatment marks an exciting step toward industrialization of sustainable water management. By coupling high organic removal efficiencies with simultaneous hydrogen generation, this approach demonstrated how treatment systems can evolve from purely consumptive infrastructure into resource-recovering platforms.
At Frontis Energy we believe that, while challenges remain, particularly in phosphorus removal and scaling to higher organic loads, the promise of modular, low-energy systems that deliver both clean water and usable energy is compelling. The next phase will involve refining nutrient conversion, optimizing reactor design for larger volumes, and exploring real-world applications in sectors such as hospitality and decentralized communities. This trajectory points toward a future where wastewater treatment is not just a necessity but a driver of circular economy innovation.
Estrada-Arriaga, et al. 2024, Performance of a pilot-scale microbial electrolysis cell coupled with biofilm-based reactor for household wastewater treatment: simultaneous pollutant removal and hydrogen production. Bioprocess and Biosystems Engineering, 47, 1929–1950, DOI: 10.1007/s00449-024-03079-0
