Effect of temperature and solids retention time on the removal of antibiotic resistance genes during anaerobic digestion of sludge

Influence upon Biogas Production of the C/N Ratio and the Heavy Metal Incidence in the Manure Composition

“…Table 1 shows the content of carbon (C) and nitrogen (N), as well as the C/N ratio for each of the nine analyzed samples. Although the vast majority of researchers concludes that the optimal C/N ratio must be between 20 and 30, there are researchers who demonstrated that good results can be obtained with a lower C/N ratio (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) [27, 29, and 39]. Following a sequence of 3 repeated analyses on the same species (for which the arithmetic mean is representative), one found; the C/N ratio for pig manure ranges between 6.8 and 16.7, for cow manure between 16.5 and 30.2, for chicken manure it is 6.7, for ostrich manure 15.3, and for horse manure 22.…”

“…Temperature is one of the primary operating parameters [19] (p. 101377), having the ability to influence the rate of microbial growth and degradation of organic matter [20] (p. e11174). Low temperature reduces the performance of the anaerobic digestion process [21] (p. 135808), whereas variable temperature can affect the metabolic activity of methanogens, affecting methane production [22] (p. 128054).…”

“…Likewise, the quality of the compost is influenced by the C/N ratio [38] (p. 37). The recommended C/N ratio for anaerobic degradation is considered 20-30 [27,29], but some researchers think that lower C/N ratios (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) can produce good results [39] (p. 121-181). Since a ratio lower than 20 can inhibit the process, and a ratio greater than 30 leads to a decrease in the amount of biogas [3,40].…”

An overview of the occurrence, impact of process parameters, and the fate of antibiotic resistance genes during anaerobic digestion processes

“…sulI and tetM enriched in mesophilic AD Zhang et al ( 2015 ) Pig manure Thermophilic AD at 55 °C and mesophilic AD at 35 °C for 25 days. Then, H 2 was added to reactors 5 drug classes Addition of H 2 did not affect mesophilic AD, but in thermophilic AD, increased number of macrolides, glycopeptide, lincosamide, and fluoroquinolone genes Zhu et al ( 2021b ) Sludge Psychrophilic AD at 15 °C and mesophilic AD at 35 °C for 35 days 14 ARG types Psychrophilic AD performed better in the absence of oxytetracycline Yun et al ( 2021 ) Cattle manure Solid-state thermophilic AD at 55 °C, mesophilic AD at 35 °C and liquid AD at 35 °C 20 ARG types Mesophilic solid-state achieved most reduction than other treatments Sun et al ( 2019c ) Sewage sludge Mesophilic AD for 60 and 109 days 11 ARG types Shorter SRT improved ARGs reduction in single-stage and two-stage digestion Zhang et al ( 2019b ) Sewage sludge Mesophilic and thermophilic AD at different SRTs of 20, 30, and 40 days Sul1 , sul2 , tetW , tetX , tetA , ermF , aac(6′)-lb , intl1 , intl2 , tnpA Higher removal of ARGs was achieved in long SRTs in mesophilic AD while thermophilic AD removed more ARGs in short SRTs Mortezaei et al ( 2023 ) …”

“…According to the results, macrolide resistance genes could be eliminated in shorter SRT, but longer SRT was required to eliminate sulfonamides and tetracycline resistance genes. Recently, Mortezaei et al ( 2023 ) studied the effect of temperature and SRT on the attenuation of ARGs and MGEs. The results showed that thermophilic AD outperformed (75.8% removal efficiency) mesophilic AD in short SRTs (20 days) whereas in longer SRTs (30 and 40 days) mesophilic AD performed better than thermophilic AD.…”