Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Structural optimization of biohydrogen production: Impact of
  pretreatments on volatile fatty acids and biogas parameters   The present study aims to describe an innovative approach that enables the
system to achieve high yielding for biohydrogen (bio-H$_2$) production using
xylose as a by-product of lignocellulosic biomass processing. A hybrid
optimization technique, structural modelling, desirability analysis, and
genetic algorithm could determine the optimum input factors to maximize useful
biogas parameters, especially bio-H$_2$ and CH$_4$. As found, the input factors
(pretreatment, digestion time and biogas relative pressure) and volatile fatty
acids (acetic acid, propionic acid and butyric acid) had indirectly and
significantly impacted the bio-H$_2$ and desirability score. The pretreatment
factor had the most effect on bio-H$_2$ and CH$_4$ production among the
factors, and after that, were propionic acid and digestion time. The
optimization method showed that the best pretreatment was acidic pretreatment,
digestion time > 20 h, relative pressure in a range of 300-800 mbar, acetic
acid in a range of 90-200 mg/L, propionic acid in a range of 20-150 mg/L, and
butyric acid in a range of 250-420 mg/L. These values caused to produce H$_2$ >
10.2 mmol/L, CH$_4$ > 3.9 mmol/L, N$_2$ < 15.3 mmol/L, CO$_2$ < 19.5 mmol/L,
total biogas > 0.31 L, produced biogas > 0.10 L, and accumulated biogas > 0.41
L.

30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol