An original Arduino-controlled anaerobic bioreactor packed with biochar as a porous filter media

Abstract

Bioreactors are commonly used apparatuses generally equipped with several built-in specifications for the investigation of biological treatment studies. Each bioreactor test may require different types of specialty such as heating, agitation, re-circulation and some further technologies like online sensoring. Even thought, there are many ready-to-use fabricated bioreactors available in the market with a cost usually over than 1000 €, it is often not possible to access those advanced (but inflexible) systems for many students, young-researchers or small-scale private R&D companies. In this work, a new low cost (≈100€) packed-bed anaerobic bioreactor was developed, and all methodological details including open-source coding and 3D design files are shared with informative descriptions. Some preliminary tests were conducted to verify the developed bioreactor system's credibility in terms of leak-tightness, accurate gas monitoring, temperature controlling, and mass balance (COD-eq) coverage, which all have shown a very promising performance.•A consistent model bioreactor that will be called as "tetrapod" was developed for anaerobic treatment of challenging substrates such as pyrolytic liquids.•Coarse biochar grains were used as an organic packing material to stimulate the microbial bioconversion by increasing the active surface area for the attached-growth anaerobic mixed microbial culture (MMC).•An open-source Arduino based digital gasometer was developed for online monitoring of biogas change in the lab-scale system. Arduino was also used as a digital controller for maintaining pulse-mode liquid recirculation of the bioreactor.

Keywords: 3D printing; Anaerobic fermentation; Arduino digital controller; Biochar filter; COD, Chemical Oxygen Demand; Custom-made reactor; Digital gasometer; GC, Gas Chromatography; H2, Hydrogen Gas; ID, Inner Diameter; Inexpensive bioreactor system; LOD, Limit of Detection; Lab-scale fermenter; M:M, Mass to Mass ratio; MMC, Mixed microbial culture; MS, Mass Spectrometer; Mixed microbial culture; O2, Oxygen Gas; OD, Outer Diameter; PA12, Polyamide; Single-board microcontroller; TCD, Thermal Capture Detector; V:V, Volume to Volume ratio.

Graphical abstract

Fig. 1

Schematic diagram of the experimental equipment: (a) Biochar-packed tetrapod, (b) Inert-bed tetrapod.

Fig. 2

A cross-section drawing of the modified pneumatic hoses of the ‘tetrapod’ bioreactor.

Fig. 3

(a) 3D-Printed PLA structure assembled with HC-SR04™ Ultrasonic sensor. (b) Final structure of the Digital Gasometer with a Supel™ 30,226-U gasbag and a rectangular plastic piece (yellow) to homogenize the surface (right).

Fig. 4

(a) Packing materials; wetted coarse biochar grains (top), small glassbeads with Ø4.0 mm (middle), large glassbeads with Ø7.8 mm (bottom). (b) Biochar amended tetrapod supported with small beads and large beads. (c) Inert-bed tetrapod filled only with large glassbeads as packing material.

Fig. 5

Operational start-up steps of the ‘Tetrapod’ bioreactor system: (a) Assembled tetrapods before operation; biochar packed bioreactor on the left, inert-bed bioreactor on the right. (b) Freshly inoculated tetrapod with anaerobic MMC. (c) An on-going experiment of one tetrapod covered with a thermal jacket.

Fig. 6

(a) Calibration graph of the Digital Gasometer. (b) Accuracy test of the Digital Gasometer.

Fig. 7

Biogas production from MMC fermentation of glucose.

Fig. 8

Temperature variation of the bioreactor during a long-test.

Fig. 9

Hydrogen (H₂) leaking test.

Fig. 10

Gas leaking and monitoring test under simulated operational conditions (Italy, December 2020).

Fig. 11

Overall COD balance of a 10-day anaerobic test which was conducted in tetrapod system.