Armando Oliva

Hydrogenotrophic denitrification (H₂Den) is a promising strategy for NO₃⁻ removal from a supply water with low or negligible organic carbon content. However, its performance may be affected by emerging contaminants (ECs), which pose increasing risks to the environment and human health. This study investigates the acute effect of two widely detected ECs, acetaminophen (ACN) and chloramphenicol (CHP), at a 200 mg/L concentration, on H₂Den using anaerobic granular sludge (AnGS) as inoculum. Acute exposure to ACN enhanced NO₃⁻ removal, likely due to the formation of oxidizable metabolites serving as electron donors through the heterotrophic pathway. On day 3, the residual NO₃⁻ concentration had already dropped below the regulatory limit of 50 mg/L, reaching 4.3 mg NO₃⁻/L. In contrast, CHP initially inhibited the denitrification process, resulting in limited NO₃⁻ removal, i.e., a residual concentration of 145.4 mg NO₃⁻/L on day 3. Nevertheless, short-term microbial adaptation likely enabled performance recovery under CHP exposure. On day 6, both EC exposure tests allowed a NO₃⁻ removal above 97%, although CHP resulted in residual NO₂⁻, i.e., 37 mg NO₂⁻/L. In the presence of ACN, the accumulation of gaseous denitrification intermediates was observed, with NO concentration in the headspace peaking at 9.5% (i.e., 16.2 × 10⁻² µg NO/min/g VS) on day 6. Thus, in terms of either the production of gaseous intermediates or the presence of residual nitrogen in the liquid phase, ACN and CHP significantly influenced the denitrification performance, highlighting the importance of considering their presence in the operation of the denitrification process.

Nitrogen-rich effluents from anaerobic processes present nutrient resource recovery opportunities for fertilizer applications in hydroponic systems, thus facilitating agricultural production in less conventional contexts such as urbanized areas. However, the high ammonia and soluble chemical oxygen demand, which is common in anaerobic digestate, can inhibit crop development in a hydroponic system, requiring conditioning to enable optimal performance of the system. This study examines the use of three nutrient sources to support the growth of lettuce (Lactuca sativa) in vertical hydroponic systems: (i) synthetic permeate (SP) solution, (ii) desorption solution (DS) from an anaerobic membrane bioreactor (AnMBR), and (iii) DS modified with acetic acid addition. Two light conditions were used to observe the effect of photon flux (from 150–200 to 10–15 μmol/[m²·s]) on lettuce crop development and nitrification efficiency of the treated AnMBR permeate. Fresh and dry mass of the harvested lettuce crops as well as chlorophyll content were measured as an indicator of crop quality after a 13-day development period. Crops grown under well-lit conditions in DS had harvested fresh weight (2929.0 ± 454.6 mg/plant) than SP-grown crops (2646.2 ± 908.8 mg/plant). The lighting conditions did not significantly impact the nitrification efficiency; thus nitrate, the preferred form of nitrogen for supporting lettuce crop development, was sufficiently available to support crop growth in the recirculating hydroponic systems.

The need to ensure adequate levels of both human and environmental health protection calls for the identification of efficient wastewater treatment processes that target the removal of conventional pollutants as well as emerging contaminants, including synthetic dyes. This study explores the potential of ozone for use in the decolorization of both pretreated tannery wastewater and urban wastewater effluents. Different ozone contact times (15, 30, and 45 min) were applied to such wastewater samples at an uncontrolled (7.5–8.2) pH as well as at a pH adjusted to 10. The highest color removal efficiencies (REs) (>90%) were obtained with urban wastewater after a 45 min contact time and at pH 10. Under the same conditions, a COD RE from 31 to 51% was achieved. Even without pH adjustment, color and COD REs ranging from 81 to 92% and 39 to 41%, respectively, were obtained. A preliminary evaluation of the costs associated with the implementation of an ozonation stage within the wastewater treatment plant (WWTP) generating the urban wastewater used here was carried out. The energy cost of the ozone treatment would account for a 69% increase in the total energy cost of the WWTP, suggesting the need to identify proper strategies to enhance the cost-competitiveness of this technology.

The request for alternative sources of energy has led to evaluating untapped routes for energy production, such as using abundant and low-cost waste materials, e.g., lignocellulosic wastes, as the substrate for biological processes aimed at biofuel production. This study focused on peanut shells (PS) valorisation via anaerobic digestion (AD). Two emerging pretreatments, i.e., organosolv and ultrasounds, were investigated to unlock the full AD potential of PS. The impact of a substrate-to-solvent ratio in organosolv pretreatment was investigated (i.e., 1:5 vs. 1:10 vs. 1:20). Different exposure times were tested for ultrasound pretreatment, corresponding to applied energy densities of 30,000, 12,000, and 6000 kJ/kg VS, respectively. Organosolv pretreatment achieved the maximal polyphenol solubilisation, i.e., 4.90 mg/g TS, when increasing the substrate-to-solvent ratio, whereas methane production did not benefit from the pretreatment, being comparable with that of raw PS at most (i.e., 55.0 mL CH₄/g VS). On the other hand, ultrasounds mainly affected sugar solubilisation (up to 37.90 mg/g TS), enhancing methane production up to an extra 64%, achieved with the highest energy density. The organosolv route would benefit from further downstream steps to recover the biomolecules released in the liquid fraction, whereas ultrasounds pretreatment provided a slurry suitable for direct AD.

The anaerobic digestion of sewage sludge is highly sensitive to high zinc concentrations. Although sulfate-reducing bacteria (SRB) activity can negatively affect methanogenesis, SRB-mediated metal sulfide precipitation can alleviate zinc toxicity. A series of mesophilic anaerobic batch experiments was performed for the biomethane potential of three different sewage sludge samples for 74 days using the background sludge zinc content, alone or in combination with the external addition of 200, 300 and 400 mg Zn/L. The highest biomethane production was 165 ± 1 mL CH₄/g VS using activated sludge (AS) with a background concentration of 93 mg Zn/L. A slight decrease in the biomethane yield (i.e., 157 ± 1, 158 ± 1 and 159 ± 1 mL CH₄/g VS) was obtained in the presence of 293, 393 and 493 mg Zn/L, respectively. The potential reason for the high methanogenic activity at high inlet Zn concentrations could be that the AS used in this study was already acclimated to those conditions. Zinc was likely removed from the system by sulfide precipitation, and a removal efficiency above 99% was achieved under all zinc concentrations. A sulfate reduction efficiency of 99% was also obtained. Overall, this study details the potential utilization of biogenic sulfide as a metal detoxifying agent without detrimental effects on methane production from sewage sludge.