**3. Results**

*New Advances on Fermentation Processes*

**2.6 Analytical methods**

**Reactor set**

**Table 3.**

the miniature reactors.


(NH4 +

(FAN; g∙kg<sup>−</sup><sup>1</sup>

temperature (K).

conducted using Microsoft Excel.

Total solid (TS) and volatile solid (VS) contents were determined according to the standard method 1684 (EPA) [25]. The total volatile fatty acids (TVFA) were measured using the test kit LCK 365 (Hach Lange GmbH). The samples were centrifuged (10 min, 6000 rpm), and the supernatant was filtered. The time from the sampling up to the execution of the analytical procedure was identical for each sample to ensure the best possible quality of the results. A pH meter (HI991001, Hanna Instruments) was used to measure the pH in commercial reactors, and a mini pH meter (VWR, USA) was used to measure the pH in

**Time (d) HRT (d) Temperature (°C) Organic load rate** 

MR1 95 20 35 0.5 MR2 95 20 35 0.5 CR1 95 20 35 0.5 CR2 95 20 35 0.5

The volume of biogas that was produced from the 3D-printed microreactors and the 300-mL reactors was estimated by the water displacement method, and the measuring devices were standard serum bottles with a volume of 10 and

GmbH, Germany) according to the manufacturer's instructions and were quantified by a spectrophotometer (DR3900, Hach, USA). Free ammonia nitrogen

displacement method and was standardized according to DIN 1343 (standard conditions: temperature (T) = 0°C and pressure (P) = 1.013 bar) [27]. The biogas

where VN is the volume of the dry biogas at standard temperature and pressure (mLN), V is the recorded volume of the biogas (mL), pw is the water vapor pressure as a function of ambient temperature (mmHg), and T is the ambient

All the experiments were carried out in duplicate (two bioreactors for the commercial reactor and two micro-bioreactors, and the experimental data from each reactor was plotted in the corresponding graphs), and the data analysis was

) were determined using commercial assay kits (Hach Lange

\_ 6344

∙day<sup>−</sup><sup>1</sup>

) and ammonium

**(g ∙ VS ∙ (L reactor)<sup>−</sup><sup>1</sup>**

 **∙ d<sup>−</sup><sup>1</sup> )**

273.15+*T*) + 10*pH* (1)

*VN* = *<sup>V</sup>* <sup>×</sup> <sup>273</sup> × (760 <sup>−</sup>*pw*) \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ *<sup>T</sup>* <sup>×</sup> <sup>760</sup> (2)

) was measured with the water

100 mL, respectively. Chemical oxygen demand (COD; g∙kg<sup>−</sup><sup>1</sup>

*Process conditions and masses of organic materials in experimental tests.*

*<sup>N</sup>* <sup>−</sup>*NH*3 = *tan*× 10*pH* \_\_\_\_\_\_\_\_\_\_\_\_ *<sup>e</sup>* (

The biogas volume (mL∙g VSsubstrate<sup>−</sup><sup>1</sup>

volume was normalized according to equation 2 [28]:

) was calculated based on equation 1 [26]:

**182**
