This study compares the biogas potential of solid common reed residues after undergoing vapothermal and hydrothermal pre-treatment, accompanied by a compositional and structural biomass characterization. In a pre-test series, a design of experiments approach was used to determine the influence of the initial biomass water content during vapothermal pre-treatment on the biogas yield. In the main test series, common reed was pre-treated hydrothermally (i.e., in liquid water) and vapothermally (i.e., in saturated steam) while varying temperature and residence time. The initial biomass water content significantly impacted the biogas potential, with an optimum at a value of 32 to 46 wt-%FM. In the main test series, unlike the residence time, temperature significantly impacted the subsequent anaerobic digestion. Vapothermal pre-treatment had a narrow temperature optimum while hydrothermal pre-treatment led to a biogas increase in a broader temperature range. The optimum temperature of both methods was 170 °C, where methane potentials increased by 28 % (vapothermal) and 36 % (hydrothermal) compared to the untreated sample. Considering the mass loss occurring during the pre-treatment, this increase was still 18 % for vapothermal pre-treatment, while it diminished the increase to 6 % for hydrothermal pre-treatment. Overall, vapothermal pre-treatment produced a similar amount of biogas under comparable conditions, but was less susceptible to carbon loss, and, according to an estimation of the required process energy, may offer energy savings compared to hydrothermal pre-treatment.
This study investigated how the biodegradation rate constant (kbio) of 11 micropollutants (MPs) responded to changes in the concentrations of growth substrates and microbial activities while considering the predominant microbial degraders of MPs. Metformin, losartan, valsartan, and cimetidine (group A) were biodegraded predominantly by nitrifiers. MPs of group A showed a positive correlation with kbio and nitrifying activity, while a negative correlation was observed with the initial concentration of ammonium, possibly due to competitive inhibition. Atenolol, caffeine, and naproxen (group B) were biodegraded predominantly by heterotrophs, with kbio remaining stable despite changes in organic matter concentration or heterotrophic activity. Olmesartan, candesartan, diclofenac, and sulfamethoxazole (group C) showed low kbio regardless of growth substrate concentration and microbial activity, which could be attributed to their chemical structures. These findings suggest that the kbio of MPs in WWTPs could respond differently to growth substrate concentration and microbial activity depending on their principal degraders.
Sugarcane bagasse pith (SBP), a byproduct of sugar production, is often discarded or burned as waste, despite its potential as a biofuel feedstock. This study explores ozone pretreatment as a processing step to enhance the physicochemical and pelletizing properties of SBP for biofuel production. Ozone pretreatment, conducted in a fixed-bed reactor, selectively reduced lignin content and improved the biomass's binding properties, promoting stronger interparticle adhesion during pelletization. Key variables, including moisture content, die temperature, pressure, and ozonation time, were optimized using Response Surface Methodology (RSM) with Central Composite Design (CCD), leading to improved pellet density and mechanical strength. Thermogravimetric analysis revealed enhanced thermal stability and combustion efficiency in ozone-treated SBP pellets. These findings demonstrate that ozone pretreatment is a promising, sustainable approach to valorize SBP and optimize biomass pellet production.