This study proposes the supplementation of digestate, fresh organic fraction of municipal solid waste (OFMSW) and a nutrient solution during the anaerobic biostimulation of marine sediments ...contaminated by polycyclic aromatic hydrocarbons (PAHs). The experimental activity was conducted with four PAHs (i.e. phenanthrene, anthracene, fluoranthene and pyrene) under controlled mesophilic conditions (37 ± 1 °C) in 100 mL serum bottles maintained at 130 rpm. After 120 days of incubation, the highest total PAH degradation of 53 and 55% was observed in the experiments with digestate + nutrients and OFMSW + nutrients, respectively. Phenanthrene was the most degraded PAH and the highest removal of 69% was achieved with OFMSW + nutrients. The anaerobic PAH degradation proceeded through the accumulation of volatile fatty acids and the production of hydrogen and methane as biogas constituents. The highest cumulative biohydrogen production of 80 mL H2·g VS−1 was obtained when OFMSW was used as the sole amendment, whereas the highest biomethane yield of 140 mL CH4·g VS−1 was obtained with OFMSW + nutrients. The evolution of PAH removal during anaerobic digestion revealed a higher impact of the methanogenic phase rather than acidogenic phase on PAH degradation.
Display omitted
•The anaerobic biostimulation of PAH-contaminated sediments was investigated.•The addition of digestate, fresh OFMSW and nutrients enhanced PAH degradation.•PAH removal was examined by comparing acidogenic and methanogenic conditions.•The highest PAH removal was achieved with OFMSW and nutrient supplementation.•CH4 and H2 were the main biogas constituents with digestate and OFMSW, respectively.
The demand of iron is increasingly rising nowadays due to the growth of human population. The iron ore reserves are diminishing and this encourages the scientific community to look into the use of ...secondary sources of iron. When iron occurs with nitrate, Fe(II)-mediated autotrophic denitrification is an alternative biotechnology to simultaneously remove nitrate and recover iron through the formation of Fe(III) precipitates. In the last 20 years, a large number of microbial species have been isolated and observed to be capable of coupling Fe(II) oxidation to denitrification under both mixotrophic and strictly lithotrophic conditions. Within mixotrophic metabolism, acetate is the most effective organic electron donor enhancing denitrification rates. The use of mixed cultures results in a more robust process, especially when other contaminants are present. Organic chelating agents allow a higher Fe(II) solubilization at neutral pH but often induce inhibition of microbial activity. The mechanisms that promote the formation of the specific biogenic Fe(III) (hydr)oxides have to be yet elucidated. Further research is crucial in this direction for both environmental and commercial reasons.
Display omitted
•Fe biorecovery and nitrate removal from wastewaters can be simultaneously performed.•Fe(II)-oxidizing denitrifiers grow in both lithothophic and mixotrophic conditions.•Denitrification is generally enhanced in presence of simple organic electron donors.•The use of chelators for Fe at neutral pH can result in microbial inhibition.•Biogenic Fe(III) precipitates have a commercial and environmental relevance.
•High rate, high efficiency autotrophic denitrification was demonstrated in a FBR.•Complete nitrate and nitrite removal was achieved at HRTs as low as 10min.•The nitrate and nitrite loading rates ...reached 600 and 228mgL−1h−1, respectively.•The biofilms were dominated by T. denitrificans and tolerated pHs as low as 5.8.•The optimal temperature for nitrate removal was 26.6°C based on Ratkowsky modeling.
High rate, high efficiency thiosulfate-driven autotrophic denitrification and denitritation with Thiobacillus denitrificans dominated biofilms were achieved in fluidized-bed reactors (FBRs) operated at 20.0±2.0 and 30.0±0.2°C. Complete nitrate removal was obtained even at nitrate loading rate and hydraulic retention time (HRT) of 600mgL−1h−1 and 10min, respectively. Further decrease of HRT to 5min resulted in 50% of nitrate removal efficiency. Nitrite did not accumulate when nitrate was used as electron acceptor unless HRT was decreased to 5min. Effluent pH remained at 5.8 during denitrification. When nitrite was supplemented as the electron acceptor, denitritation effectively proceeded with the highest nitrite loading rate of 228mgL−1h−1. Similar denitrification and denitritation performances were obtained at 20.0±2.0 and 30.0±0.2°C. Batch assays conducted at temperature range from 1 to 46°C, however, showed a significant impact of temperature on autotrophic denitrification. Ratkowsky model was used to estimate the minimum, optimal and maximum growth temperatures of T. denitrificans dominated culture that were below 1, 26.6 and 50.8°C, respectively.
Display omitted
•Anaerobic digestion (AD) of hazelnut skin (HS) was investigated in fed-batch mode.•Higher CH4 production was obtained at lower solid retention time and higher HS load.•Maceration and ...organosolv pretreatment removed 82 and 97% of the HS polyphenols.•Methanol-organosolv pretreatment increased the CH4 potential of HS by 21%.•Reactor configuration enabled enriching microorganisms capable of HS degradation.
This study provided important insights on the anaerobic digestion (AD) of hazelnut skin (HS) by operating a fed-batch AD reactor over 240 days and focusing on several factors impacting the process in the long term. An efficient reactor configuration was proposed to increase the substrate load while reducing the solid retention time during the fed-batch AD of HS. Raw HS produced maximally 19.29 mL CH4/g VSadd/d. Polyphenols accumulated in the reactor and the use of NaOH to adjust the pH likely inhibited AD. Maceration and methanol-organosolv pretreatments were, thus, used to remove polyphenols from HS (i.e. 82 and 97%, respectively) and improve HS biodegradation. Additionally, organosolv pretreatment removed 9% of the lignin. The organosolv-pretreated HS showed an increment in methane potential of 21%, while macerated HS produced less methane than the raw substrate, probably due to the loss of non-structural sugars during maceration.
Display omitted
Lignocellulosic materials (LMs) are abundant feedstocks with excellent potential for biofuels and biocommodities production. In particular, nut and coffee wastes are rich in ...biomolecules, e.g. sugars and polyphenols, the valorisation of which still has to be fully disclosed. This study investigated the effectiveness of ultrasounds coupled with hydrothermal (i.e. ambient temperature vs 80 °C) and methanol (MeOH)-based pretreatments for polyphenols and sugar solubilisation from hazelnut skin (HS), almond shell (AS), and spent coffee grounds (SCG). The liquid fraction obtained from the pretreated HS was the most promising in terms of biomolecules solubilisation. The highest polyphenols, i.e. 123.9 (±2.3) mg/g TS, and sugar, i.e. 146.0 (±3.4) mg/g TS, solubilisation was obtained using the MeOH-based medium. However, the MeOH-based media were not suitable for direct anaerobic digestion (AD) due to the MeOH inhibition during AD. The water-based liquors obtained from pretreated AS and SCG exhibited a higher methane potential, i.e. 434.2 (±25.1) and 685.5 (±39.5) mL CH4/g glucosein, respectively, than the HS liquors despite having a lower sugar concentration. The solid residues recovered after ultrasounds pretreatment were used as substrates for AD as well. Regardless the pretreatment condition, the methane potential of the ultrasounds pretreated HS, AS, and SCG was not improved, achieving maximally 255.4 (±7.4), 42.8 (±3.3), and 366.2 (±4.2) mL CH4/g VS, respectively. Hence, the solid and liquid fractions obtained from HS, AS, and SCG showed great potential either as substrates for AD or, in perspective, for biomolecules recovery in a biorefinery context.
•Arsenic effects on nitrification were revealed using FBR enriched cultures.•Nitrification was not affected by 100mg AsTOT/L at neutral pH.•150–200mg AsTOT/L inhibited ammonium oxidation by ...25%.•As(III) oxidation to As(V) decreased arsenic toxicity to nitrification.•FBR enrichment consisted of C. Nitrospira defluvii and other nitrifying species.
Mining and mineral processing of gold-bearing ores often release arsenic to the environment. Ammonium is released when N-based explosives or cyanide are used. Nitrification of simulated As-rich mining waters was investigated in batch bioassays using nitrifying cultures enriched in a fluidized-bed reactor (FBR). Nitrification was maintained at 100mg AsTOT/L. In batch assays, ammonium was totally oxidized by the FBR enrichment in 48h. As(III) oxidation to As(V) occurred during the first 3h attenuating arsenic toxicity to nitrification. At 150 and 200mg AsTOT/L, nitrification was inhibited by 25%. Candidatus Nitrospira defluvii and other nitrifying species mainly colonized the FBR. In conclusion, the FBR enriched cultures of municipal activated sludge origins tolerated high As concentrations making nitrification a potent process for mining water treatment.
Acid mine drainage is an important environmental problem related to the release of acidic, sulfate-, and metal-containing wastewater into the environment. Sulfate-reducing bacteria can be used for ...treating mining wastewaters and recovering metals in several bioreactor configurations. The fluidized-bed configuration is an efficient way for acid mine drainage remediation due to the high biomass retention, the great resistance to inhibitors, and the possibility to use high organic, sulfate, and metal loading rates at low hydraulic retention times. Additional research is needed to assess the removal of the organic rest-pollution and the factors that promote a better metal recovery in single-stage processes.
Lignocellulosic residues (LRs) are one of the most abundant wastes produced worldwide. Nevertheless, unlocking the full energy potential from LRs for biofuel production is limited by their complex ...structure. This study investigated the effect of N-methylmorpholine N-oxide (NMMO) pretreatment on almond shell (AS), spent coffee grounds (SCG), and hazelnut skin (HS) to improve their bioconversion to methane. The pretreatment was performed using a 73% NMMO solution heated at 120 °C for 1, 3, and 5 h. The baseline methane productions achieved from raw AS, SCG, and HS were 54.7 (± 5.3), 337.4 (± 16.5), and 265.4 (± 10.4) mL CH
4
/g VS, respectively. The NMMO pretreatment enhanced the methane potential of AS up to 58%, although no changes in chemical composition and external surface were observed after pretreatment. Opposite to this, pretreated SCG showed increased porosity (up to 63%) and a higher sugar percentage (up to 27%) after pretreatment despite failing to increase methane production. All pretreatment conditions were effective on HS, achieving the highest methane production of 400.4 (± 9.5) mL CH
4
/g VS after 5 h pretreatment. The enhanced methane production was due to the increased sugar percentage (up to 112%), lignin removal (up to 29%), and loss of inhibitory compounds during the pretreatment. An energy assessment revealed that the NMMO pretreatment is an attractive technology to be implemented on an industrial scale for energy recovery from HS residues.
► Sulfide concentration governs the location of metal precipitates in sulfate reducing bioreactors. ► High dissolved sulfide induces metal precipitation in the bulk liquid as fines. ► Low dissolved ...sulfide concentrations yield local supersaturation and thus metal precipitation in the biofilm.
The effect of the sulfide concentration on the location of the metal precipitates within sulfate-reducing inversed fluidized bed (IFB) reactors was evaluated. Two mesophilic IFB reactors were operated for over 100 days at the same operational conditions, but with different chemical oxygen demand (COD) to SO
4
2− ratio (5 and 1, respectively). After a start up phase, 10
mg/L of Cu, Pb, Cd and Zn each were added to the influent. The sulfide concentration in one IFB reactor reached 648
mg/L, while it reached only 59
mg/L in the other one. In the high sulfide IFB reactor, the precipitated metals were mainly located in the bulk liquid (as fines), whereas in the low sulfide IFB reactor the metal preciptiates were mainly present in the biofilm. The latter can be explained by local supersaturation due to sulfide production in the biofilm. This paper demonstrates that the sulfide concentration needs to be controlled in sulfate reducing IFB reactors to steer the location of the metal precipitates for recovery.
A local sensitivity analysis was performed for a chemically synthesized elemental sulfur (S
)-based two-step denitrification model, accounting for nitrite (NO
) accumulation, biomass growth and S
...hydrolysis. The sensitivity analysis was aimed at verifying the model stability, understanding the model structure and individuating the model parameters to be further optimized. The mass specific area of the sulfur particles (a*) and hydrolysis kinetic constant (k
) were identified as the dominant parameters on the model outputs, i.e. nitrate (NO
), NO
and sulfate (SO
) concentrations, confirming that the microbially catalyzed S
hydrolysis is the rate-limiting step during S
-driven denitrification. Additionally, the maximum growth rates of the denitrifying biomass on NO
and NO
were detected as the most sensitive kinetic parameters.
PDF