Electrochemically and Bioelectrochemically Induced Ammonium Recovery

Summary

We demonstrate the extraction of ammonium from an ammonium-rich stream using an electrochemical and a bioelectrochemical system. The reactor setup, operation and data analysis are discussed.

Abstract

Streams such as urine and manure can contain high levels of ammonium, which could be recovered for reuse in agriculture or chemistry. The extraction of ammonium from an ammonium-rich stream is demonstrated using an electrochemical and a bioelectrochemical system. Both systems are controlled by a potentiostat to either fix the current (for the electrochemical cell) or fix the potential of the working electrode (for the bioelectrochemical cell). In the bioelectrochemical cell, electroactive bacteria catalyze the anodic reaction, whereas in the electrochemical cell the potentiostat applies a higher voltage to produce a current. The current and consequent restoration of the charge balance across the cell allow the transport of cations, such as ammonium, across a cation exchange membrane from the anolyte to the catholyte. The high pH of the catholyte leads to formation of ammonia, which can be stripped from the medium and captured in an acid solution, thus enabling the recovery of a valuable nutrient. The flux of ammonium across the membrane is characterized at different anolyte ammonium concentrations and currents for both the abiotic and biotic reactor systems. Both systems are compared based on current and removal efficiencies for ammonium, as well as the energy input required to drive ammonium transfer across the cation exchange membrane. Finally, a comparative analysis considering key aspects such as reliability, electrode cost, and rate is made.

This video article and protocol provide the necessary information to conduct electrochemical and bioelectrochemical ammonia recovery experiments. The reactor setup for the two cases is explained, as well as the reactor operation. We elaborate on data analysis for both reactor types and on the advantages and disadvantages of bioelectrochemical and electrochemical systems.

Introduction

Recovery of valuable products from wastewater gains importance as valuable resources become scarce and treatment without recovery represents only a cost. Wastewater contains both energy and nutrients that can be recovered, and nutrient recovery can help to close the production loop¹. Recovery of energy through anaerobic digestion is a well-established process, while recovery of nutrients is less common. Recovery of nutrients from liquid waste streams such as urine and manure has been widely investigated, e.g., through the production of struvite and direct stripping of ammonia^2,3. However, the need for chemical addition is a downside of t....

Protocol

1. Assembling the Reactor and Connecting the Stripping and Absorption Units

1. Collect all necessary material to build the reactor: electrodes, frames and rubbers (See List of Materials). Carefully cut all parts to the same dimensions to avoid leaks while assembling the reactor.
2. Drill holes in the reactor compartments to fit a male to male connector. Drill one additional hole in the middle of the side of one of the reactor compartments to fit the reference electrode.
3. Prepare a stock of 1 M H₂SO₄ for the absorption column. Increase this concentration as necessary to accommodate higher loads of ammonia.
4. Ensure....

Results

Chronoamperometry results from the bioreactor

The chronoamperometry results, calculated according to Equation 1, show a typical graph for a continuous reactor (Figure 4). At the start of the experiment, the anode and cathode were operated in recirculation mode. This allows a biofilm to develop and the onset of the current production. After 5 days of operation, the current density reached a maximum, followed by a decrease in current production. This is an indic.......

Discussion

This manuscript provides the necessary tools to set up a bioelectrochemical and an electrochemical cell for ammonium recovery. The calculations presented in the results section provide the parameters for evaluation of the system performance. The biological and electrochemical systems are similar in setup and function. The main difference between the two systems is the choice of a fixed current for the electrochemical cell versus a fixed anode potential for the bioelectrochemical setup. The fixed current for the abiotic s.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Carbon Felt 3.18 mm Thick	Alfa Aesar	ALFA43199	Used as bioanode, 110 mm x 110 mm
Ti electrode coated with Ir MMO	Magneto Special Anodes (The Netherlands)		Used as stable anode for electrochemical tests
Stainless steel mesh	Solana (Belgium)	RVS 554/64: material AISI 316L, mesh width: 564 micron, wire thickness: 140 micron, mesh number: 36,6	Used as cathode, 110 mm x 110 mm
Stainless steel plate	Solana (Belgium)	inox 304 sheet, thickness: 0.5 mm	Used as current collector for the bioanode
Ag/AgCl Reference Electrode	Bio-Logic (France)	A-012167 RE-1B
Potentiostat (VSP Multipotentiostat)	Bio-Logic (France)
EC Lab	Bio-Logic (France)		software for performing electrochemistry measurements
Cation Exchange Membrane	Membranes International (USA)	Ultrex CMI-7000	Pretreated according to the manufacturers' instructions
Turbulence Promotor mesh	ElectroCell Europe A/S (Tarm, Denmark)	EPC20432-PP-2	spacer material, 110 mm x 110 mm
Connectors	Serto	1,281,161,120	Other sizes possible, dependant on tubing type and size of holes in frames
Strip and absorption column			In house design
Tubing	Masterflex	HV-06404-16
Gas bag	Keika Ventures		Kynar gas bag with Roberts valve
Rashig Rings	Glasatelier Saillart (Belgium)	Raschig rings 4 x 4 mm	Put inside the strip and absorption column to improve the air/liquid contact. Available with many suppliers
Rubber sheet			Cut to fit on the perspex frames
Perspex reactor frames	Vlaeminck, Beernem		In-house design, see tab "reactor frames" in this file