Electrochemically and Bioelectrochemically Induced Ammonium Recovery

The overall goal of the following experiment is to investigate the recovery of nutrients from nitrogen rich streams using either an electrochemical or bio electrochemical approach. The former approach is achieved by passing the stream through an electrochemical system, which after oxidation of water creates a driving force that can be used to flux charge ammonium from the anode side across an ion exchange membrane to the cathode side. As a second step, the high pH at the cathode side results in the conversion of ammonium to volatile ammonia.

The high level of selectivity of the ion exchange membrane enables the creation of a pure ammonia hydrogen stream. Next, the catho is circulated through a stripping and absorption column in order to trap the ammonia in an acidic medium. The electrochemical extraction can also be driven by bio electrochemical processes, where the development of a biofilm on the anode allows the conversion of organics present in the waste stream into carbon dioxide, protons, and electrons.

This will, again, drive a flux of ammonium from the anode to the cathode. The results show that both approaches can recover nutrients from nitrogen rich streams such as urine. The conventional nitrification denitrification approach on wastewater treatment takes the ammonia from the wastewater and turns it into nitrogen gas, which goes back in the atmosphere, so we lose the nitrogen.

The advantage of our approach is that we take the ammonia and we recover it in a clean form so we can do something with it. We can reuse it or convert it to another product. A second advantage of our approach is that we use electricity as a driver.

It's essentially a clean and cheap source of energy, and it avoids the use of chemicals. Demonstrating the procedure will be Sylvia Hilde Bain and Steven Anderson. Both PhD students from my lab Prior to starting this procedure collect all necessary material to build the reactor, including the electrodes, frames, and rubbers.

After ensuring that the membrane is pretreated according to the manufacturer's instructions, pretreat the carbon felt electrode by soaking it in two millimolar acetyl trimethyl ammonium bromide, or A-C-T-A-B for three minutes. Then rinse the carbon felt electrode with demineralized water. Following this, stack the different reactor parts in order according to the reactor type.

Then stack the reactor parts for the electrochemical cell. Use nuts and bolts to close the reactor and hand tighten the bolts on opposite sides to equalize the pressure. Seal the connection ports of the reactor using Teflon.

Make sure the port is properly tightened. Place the reference electrode in the same compartment as the working electrode. Next, fill the reactor with water to test if it is leak free.

If leaks are observed, check if the bolts are tightened enough or if one of the reactor parts moved while assembling the reactor. If no leaks are detected, empty the water from the reactor. Connect the feed and recirculation pumps to the reactor and the air pump to the stripping and absorption units.

Fill the absorption column with 250 milliliters of one molar sulfuric acid to cover the che rings. Ensure that the Airstream mixes the acid well when the pump is switched on. After preparing analyte and catalyte solutions, flush the analyte by purging with nitrogen gas for at least 30 minutes to remove oxygen.

For the inoculum, prepare a 30 milliliter mixture of effluence from active anaerobic bioreactors, including a bio anode. Collect the mixture in a syringe. Next, connect a gas bag filled with nitrogen to the analyte bottle.

In order to keep the pressure stable while not allowing oxygen to enter. Mix the inoculum source with the volume of analyte by emptying the syringe with inoculum into the medium bottle using a syringe filled the anode and cathode compartments simultaneously with their respective solutions. When both reactor compartments are filled, turn on the recirculation pump at a recirculation rate of approximately six liters per hour.

Following this, connect the potential stat cable with three electrodes using the anode as the working electrode. Switch on the potential stat in chrono aberrometry mode. Using the potentials stat software, select a fixed anode potential of negative 200 millivolts versus the silver, silver chloride reference electrode to change to continuous feeding.

Switch on the feed pump for the anode and cathode at a hydraulic residence. Time of six hours switch on the air pump of the strip and absorption unit. Then recirculate the air in a closed loop.

Refresh the medium three times per week with fresh analyte and catalyte as described in the text. Attach a gas bag filled with nitrogen to the closed feed bottle. Stop the feed pump and put a clamp on the effluent line.

Then switch the old and new bottles. Remove the clamps and restart the pump each time the feed is refreshed. Remove five milliliter liquid samples of the effluent and effluent of the analyte and catalyte for measurement of conductivity, pH acetate content and ammonium concentration.

In addition, remove a three milliliter sample of the absorption column to monitor the pH and for total ammonium nitrogen or tan analysis. When the pH approaches four, replace the AB absorbent with fresh one molar sulfuric acid solution to ensure high absorption efficiency. If the current stabilization is not caused by acetate limitations, increase the ammonium concentration in the feed and wait for stabilization of the current.

In order to assess extraction efficiencies for electrochemical extraction, prepare a synthetic wastewater stream as analyte according to the following table. Add ammonium sulfate to reach a final concentration of five grams of nitrogen per liter. Following this switch on the feed pump to fill the reactor compartments, reduce the pump speed to obtain a hydraulic residence time of six hours.

Once the reactor is filled, as before, switch on the recirculation pump at a rate of six liters per hour. Then remove a five milliliter sample of the in fluent after starting the strip and absorption unit. Switch on the potential stat in chronometry mode using the potential stat software.

First, apply a low current density of about 0.5 NPIs per meter squared for 24 hours to polarize the membrane and to determine nitrogen flux due to diffusion alone. When the system has been polarized for 24 hours, apply the current density necessary for the experiment, usually ranging from 10 amp piers per meter squared to 50 amp piers per meter squared. Once the reactor has reached steady state, take at least three five milliliter samples over a time course from the anode and cathode effluence as well as the absorption column.

The chrono porometer results show a typical graph for a continuous reactor. The change to continuous operation on day six resulted in a continuous increase in current production until a plateau was reached at 3.5 ampers per meter squared between day 12 and 16. The influence of day and night temperature on the current production is clearly visible.

For example, from day 42 to 46, the ammonium concentration in the feed was increased in several steps. The current increase was linked to an increased conductivity of the anode feed in which the addition of ammonium bicarbonate increased the ion concentration and thus the conductivity. The cell voltage for the electrochemical system is higher than for the bioreactor.

This is mainly due to the higher anode potential required for electrochemical oxidation of water to oxygen. The nitrogen flux for the bioreactor is higher than the electrochemical system. This can be explained by the lower alkalinity of the feed of the electrochemical system, resulting in a lower analy pH h.

This resulted in a higher competition between ammonium and protons to restore the charge balance over the membrane. This technique now paves the way for environmental engineers to explore biological and non-biological electrochemical recovery of charged species from waste streams such as anaerobic digest state. More specifically here, we've shown that a biological approach comes at a lower energy input, but may suffer from somewhat lower robustness and a longer startup time.

The purely electrochemical approach may just deliver that robustness, but it will come at a somewhat higher cost. After watching this video, you should have a good understanding of how to set up a biochemical system for the recovery of ammonium from wastewater. You should be able to construct a robust and leak-free biochemical cell, and they strip an absorption unit to recover the ammonia.