Before you start

The Mixed-culture electroPioreactor (MEP) is the lower-cost electroPioreactor for mixed cultures. Source documents: MixedElectroPioreactor.

1. Buy the parts each step of this guide lists, plus two SodaStream blue screw-in cylinders, two 250 ml GL45 “Duran” bottles, nutrient solution and inoculum.
2. Check your culture grows well.
3. Gather everything under Tools.

BAEP

The Budget aseptic electroPioreactor (BAEP) is an MEP with five 0.2 μm vent filtersA 0.2 µm hydrophobic membrane on luer fittings. Gas passes; microbes and liquid do not, so each gas path stays sterile. on its gas and bottle vents. Its guide has the same steps, plus Add the vent filters after Admit CO₂.

Tool notes

• The computer needs a microSD reader, or an SD reader with a microSD adapter, and Raspberry Pi ImagerThe free Raspberry Pi app that writes the Pioreactor operating system image onto the microSD card. to flash the card.
• The 2.5 mm hex key fits the ElectrodeTopStopThe printed block that sits on top of the MEP's O-ring vial cap. It holds both electrodes parallel and clamps each cable's ring terminal to its electrode with an M3 bolt through a captive nut.’s M3 bolts; the 5 mm hex key fits the blanking plugA 1/8" threaded plug that seals the solenoid's unused right port. It seals on its own o-ring, so it needs no sealant..
• The gas cylinder wrench is 28 mm.
• The analytical balance needs only 0.1 g accuracy, for pump calibration: a jewellery scale will do.
• The vernier callipers set the electrode depth.
• Cryogenic gloves must be safe to at least -80 °C.
• Add any other PPE your supervisor, department, employer or H&S advisor requires, and gloves for handling media.
• Recommended, not required: needle-nose pliers, for assembly and tubing; a multimeter, for checking electrolysisSplitting water with an electric current: hydrogen at the cathode, oxygen at the anode. It supplies the hydrogen the HOB grow on..

Spares

Keep spares: at least one vial and one magnetic stir bar per few units. Vials break.

How the MEP differs from the AEP0.2

Area	AEP0.2	MEP
Culture	Single strain, aseptic	Mixed culture; the BAEP adds vent filters
Vessel	Pioreactor 40 ml v1.5 + XR upgrade kitPioreactor's extended-range optics. Extra eye-spys read light scattered at 45° and 135° as well as 90°, for a lower OD detection limit., ~30 ml working volume	Pioreactor 20 ml v1.1, 14 ml working volume
Computer	RPi 5 1GB, 27 W USB-C supply	RPi Zero 2 W (or 4B), its own 5 V supply
Vial cap	One-piece cap and electrode holder, single silicone septumThe 2 mm silicone disc in the vial cap. It seals the vial mouth, both electrodes and every needle port, and self-heals needle holes.	O-ring vial cap + ElectrodeTopStop, cap O-ring + 2 electrode O-rings
Electrodes	MMO tube anodeThe positive electrode: a titanium tube coated with mixed metal oxide (IrO₂-Ta₂O₅). Oxygen forms on it, and CO₂ flows down its bore into the vial. and stainless steel cathodeThe negative electrode: a stainless steel rod. Hydrogen forms on it, so it shows about twice the bubbles of the anode. It must never be wired as the anode., 100 mm	Platinum-plated titanium anode and stainless steel cathode, 60 mm
Electrode fixing	Ring terminal + thumb screw, M3 nut and spring washer	M3 bolt through a captive nutA nut held in a pocket in the printed part, so a bolt can be tightened into it with one tool. in the ElectrodeTopStop
Ports	Stainless steel needles through the septum	Tubes through the cap’s five 3.2 mm ports
CO₂ regulatorDrops the cylinder's pressure (about 60 bar when full) to a working pressure, about 1 bar here. Its flathead screw fully anti-clockwise is closed.	Adjustable, set to about 1 bar	FZoneThe MEP's budget CO₂ regulator. Its outlet pressure is fixed, so the needle valve alone sets the CO₂ flow. Left gauge: cylinder pressure; right gauge: pressure reaching the solenoid., fixed outlet pressure: the needle valveA fine-adjustment valve on the solenoid's front port. It sets how fast CO₂ flows; turn clockwise to close. alone sets the flow
Pumps	PWMOne of the HAT's five switched power outputs. In this build: 1 stirring, 2 media pump, 3 waste (product) pump, 4 CO₂ solenoid (relay), 5 heating. 2 media, PWM 3 waste	PWM 2 waste, PWM 3 media
Card bundleA zip from the electroPioreactor releases page. Copied onto the card's bootfs drive, it installs the plugins and sets the model on first boot.	AEP bundle: sets the model, adds the precision temperature pluginThe Pioreactor software plugin that runs the Precision Temperature Upgrade Kit's sensor. The AEP card bundle installs it; the MEP bundle has none.	MEP bundle: electroPioreactor plugin only
Not in the MEP	Precision Temperature Upgrade KitAn optional Pioreactor kit. Its MLX90632 far-infrared sensor reads the vial's temperature without contact, replacing the thermistor.; vent filters (see the BAEP)

Tools

• 1×Computer with microSD card readertool
• 1×Phillips PH0 screwdrivertool
• 1×2.5 mm hex keytool
• 1×5 mm hex keytool
• 1×28 mm gas cylinder wrenchtool
• 1×Vernier calliperstool
• 1×Analytical balancetool
• 1×Cryogenic glovestool
• 1×Eye/face protectiontool
• 1×Lab coattool
• 1×Multitool and/or needle nose plierstool
• 1×Multimetertool

Check your work

1. Checking the parts each step of this guide lists, what is still missing?

   • Nothing: every listed part is here
   • One or more parts from a step's list
   • Only the SodaStream cylinders or GL45 bottles
   Show the answer

   Answer: Nothing: every listed part is here

   • If you see One or more parts from a step's list: Each step lists its parts. Components/README.md links suppliers for most of them.
   • If you see Only the SodaStream cylinders or GL45 bottles: Buy them locally: links in item 1.

2. Which items under Tools are not yet to hand?

   • The cryogenic gloves or eye protection
   • None: every tool and all the PPE
   • Another tool on the list
   Show the answer

   Answer: None: every tool and all the PPE

   • If you see The cryogenic gloves or eye protection: Do not fit the CO₂ cylinder without them. Everything before Admit CO₂ can go ahead.
   • If you see Another tool on the list: Get it before the step that lists it.

≈ 0.02 g CO₂e per view