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PAHs are largely spread in the aquatic environment, and the drawbacks of conventional remediation techniques as well as the expenditures for alternative disposal of polluted sediments lead to seek more effective, environmentally-friendly and sustainable approaches. Therefore, the present review shows a critical overview of the literature evaluated with VOSviewer, focusing on the problem of PAH-contaminated marine sediments and the knowledge of available remediation processes to shed light on what research and technology lack. This review supplies specific information about the key factors affecting biological, physical-chemical and thermal remediation techniques, and carefully examines the drawbacks associated with their employment for remediating PAH-polluted marine sediments by showing adequate alternatives. The technologies thoroughly discussed here are biostimulation, bioaugmentation, sediment washing, carbonaceous adsorbent addition and thermal desorption. The environmental and economic impacts associated with the application of the mentioned remediation technologies have been also taken into account. Finally, this review examines new research directions by showing future recommendations.

This study proposes the phytoremediation of a pyrene (PYR)-contaminated soil by Cannabis sativa L. The experimental campaign was conducted along a 60 days period using three different initial PYR concentrations (i.e., 50, 100 and 150 mg·kg TS−1 of soil) in 300 mL volume pots under greenhouse conditions (18–25 °C and 45–55% humidity). After 60 days of hemp growth and flourishing, the highest PYR removal reached approximately 95% in planted soil, 35% higher than in the unplanted control. PYR accumulation was observed in both roots and aerial parts of the plant, with a higher PYR uptake at increasing initial PYR concentrations in soil. The initial PYR concentration affected the growth and, thus, the phytoremediation potential of C. sativa L., which was the result of different removal mechanisms. Overall, the lowest initial PYR concentration was the one that resulted in the highest PYR removal. The interaction between the plant roots and microorganisms in rhizosphere was likely associated with PYR removal in this study. The highest DHO activity of 66.26 μg INTF g−1 TS−1 was observed in the soil spiked with 50 mg PYR·kg TS−1.

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.

The environmental impact of the dairy industry is heavily influenced by the overproduction of nitrogen- and carbon-rich effluents. The present study proposes an innovative process to recover waste contaminated nitrogen from anaerobic digestate while treating excess cheese whey (CW) and producing high-quality, clean single cell protein (SCP). By relying on direct aeration stripping techniques, employing an airflow subsequently used in the aerobic cheese whey fermentation step, the investigated process was able to strip 41-80% of the total ammonium nitrogen (N-NH4+) from liquid digestate. The stripped ammonia gas (NH3) was completely recovered as N-NH4+ in the acidic CW, and further upcycled into SCP having a total protein content of 74.7% and a balanced amino acids profile. A preliminary techno-economic analysis revealed the potential to directly recover and upcycle nitrogen into SCP at costs (4.1-8.2 €·kgN-1) and energetic inputs (90-132 MJ·kgN-1) matching those of conventional feed and nitrogen management processes.

This study focused on the effect of feed glucose and acetic acid on biohydrogen production by Thermotoga neapolitana under continuous-flow conditions. Increasing the feed glucose concentration from 11.1 to 41.6 mM decreased the hydrogen yield from 3.6 (±0.1) to 1.4 (±0.1) mol H2/mol glucose. The hydrogen production rate concomitantly increased until 27.8 mM of feed glucose but remained unaffected when feed glucose was further raised to 41.6 mM. Increasing the acetic acid concentration from 0 to 240 mM hampered dark fermentation in batch bioassays, diminishing the cumulative hydrogen production by 45% and the hydrogen production rate by 57%, but induced no negative effect during continuous operation. Indeed, throughout the continuous flow operation the process performance improved considerably, as indicated by the 47% increase of hydrogen yield up to 3.1 (±0.1) mol H2/mol glucose on day 110 at 27.8 mM feed glucose.

Autotrophic denitrification with biosulfur (ADBIOS) provides a sustainable technological solution for biological nitrogen removal from wastewater driven by biogenic S0, derived from biogas desulfurization. In this study, the effect of different biofilm carriers (conventional AnoxK™ 1 and Z-200 with a pre-defined maximum biofilm thickness) on ADBIOS performance and microbiomics was investigated in duplicate moving bed-biofilm reactors (MBBRs). The MBBRs were operated parallelly in continuous mode for 309 days, whilst gradually decreasing the hydraulic retention time (HRT) from 72 to 21 h, and biosulfur was either pumped in suspension (days 92–223) or supplied in powder form. Highest nitrate removal rates were approximately 225 (±11) mg/L·d and 180 (±7) mg NO3−-N/L·d in the MBBRs operated with K1 and Z-200 carriers, respectively. Despite having the same protected surface area for biofilm development in each MBBR, the biomass attached onto the K1 carrier was 4.8-fold more than that on the Z-200 carrier, with part of the biogenic S0 kept in the biofilm. The microbial communities of K1 and Z-200 biofilms could also be considered similar at cDNA level in terms of abundance (R = 0.953 with p = 0.042). A relatively stable microbial community was formed on K1 carriers, while the active portion of the microbial community varied significantly over time in the MBBRs using Z-200 carriers.

In line with the emerging circular bioeconomy paradigm, the present study investigated the valorisation of abundant hemp biomass residues (HBRs) such as hurds (HH) and a mix of leaves and inflorescences (Mix), and other organic wastes (i.e., cheese whey and grape pomace) through the volatile fatty acid (VFA) production in mono- and co-acidogenic fermentation. The highest VFA yields, measured as acetic acid (HAc) per unit of volatile solids (VS), were obtained with the untreated Mix in mono-fermentation (185 ± 57 mg HAc/g VS) and with the combination of Mix and CW in co-fermentation (651 ± 65 mg HAc/g VS), while the highest HAc percentage reached up to 94% of total VFAs. Finally, a preliminary techno-economic evaluation revealed that the mono-fermentation of alkali pretreated HH could lead to the highest revenues among HBRs, reaching up to 710-1810, 618-1577 and 766-3722 €/ha∙year for the production of HAc, single cell protein and polyhydroxybutyrates, respectively.

Soil contamination by pyrene has increased over the years due to human-related activities, urgently demanding for remediation approaches to ensure human and environment safety. Within this frame, phytoremediation has been successfully applied over the years due to its green and cost-effectiveness features. The scope of this review includes the main phytoremediation mechanisms correlated with the removal of pyrene from contaminated soils and sediments to highlight the impact of different parameters and the supplement of additives on the efficiency of the treatment. Soil organic matter (SOM), plant species, aging time, environmental parameters (pH, soil oxygenation, and temperature) and bioavailability are among the main parameters affecting pyrene removal through phytoremediation. Phytoextraction only accounts for a small part of the entire phytoremediation process, but the addition of surfactants and chelating agents in planted soils could increase pyrene accumulation in plant tissues by 20% as a consequence of the increased pyrene bioavailability. Rhizodegradation is the main phytoremediation mechanism involved due to the activity of bacteria capable of degrading pyrene in the root area. Inoculated-planted soil treatments have the potential to decrease pyrene accumulation in shoots and roots by approximately 30 and 40%, respectively, further stimulating the proliferation of pyrene-degrading bacteria in the rhizosphere. Plant-fungi symbiotic association results in an enhanced accumulation of pyrene in shoots and roots of plants as well as a higher biodegradation. Finally, pyrene removal from soil can be improved in the presence of amendments, such as natural non-ionic surfactants, biochar, and bacterial mixtures.

This study proposes new perspectives for the management and biorefinery of wastes deriving from the agri–food sector such as chestnut shell (CS), which was here used as an organic feedstock for biomethane production through anaerobic digestion (AD). 1–5% alkaline (i.e. NaOH and KOH), hydrothermal (i.e. at 100 °C) and combined hydrothermal–alkaline pretreatments were employed to enhance the CS biodegradability prior to biochemical methane potential (BMP) tests conducted under mesophilic conditions. The hydrothermally–pretreated CS with 3% NaOH achieved the highest biomethane yield of 253 (±9) mL CH4·g VS−1 coupled to a volatile solid reduction of 48%. The hydrothermal–alkaline pretreatment positively affected both delignification and hemicellulose polymerization, promoting an approximately 2.4–fold higher substrate biodegradability compared to the untreated CS, which only reached a CH4 production of 104 (±5) mL CH4·g VS−1. AD proceeded via volatile fatty acid accumulation, subsequently followed by methane production that was effectively simulated via the modified Gompertz kinetic having a R2 of 0.974–0.999. Among the physical–chemical parameters characterizing the CS, the soluble chemical oxygen demand (sCOD) was highly correlated with the BMP showing a Pearson coefficient of 0.952. The cumulative biomethane yield, the sCOD and the cellulose, hemicellulose and lignin amount of CS were also processed through the least square method, obtaining a useful regression equation to predict the BMP. The economic assessment indicated that the hydrothermal–alkaline pretreatment is a cost–effective method to improve the BMP of CS, also for future full–scale applications.

The contamination of sediments by polycyclic aromatic hydrocarbons (PAHs) has been widely spread for years due to human activities, imposing the research and development of effective remediation technologies for achieving efficient treatment and reuse of sediments. In this context, the amendment of biochar in PAH–contaminated sediments has been lately proposed as an innovative and sustainable technology. This review provides detailed information about the mechanisms and impacts associated with the supplementation of biochar to sediments polluted by PAHs. The properties of biochar employed in these applications have been thoroughly examined. Sorption onto biochar is the main mechanism involved in PAH removal from sediments. Sorption efficiency can be significantly improved even in the presence of a low remediation time (i.e. 30 d) when a multi–PAH system is used and biochar is provided with a high dosage (i.e. by 5% in a mass ratio with the sediment) and a specific surface area of approximately 360 m2 g−1. The use of biochar results in a decrease (i.e. up to 20%) of the PAH degradation during bioaugmentation and phytoremediation of sediments, as a consequence of the reduction of PAH bioavailability and an increase of water and nutrient retention. In contrast, PAH degradation has been reported to increase up to 54% when nitrate is used as electron acceptor in low–temperature biochar–amended sediments. Finally, biochar is effective in co–application with Fe2+ for the persulfate degradation of PAHs (i.e. up to 80%), mainly when a high catalyst dose and an acidic pH are used.

The continuous dredging of sediments contaminated by polycyclic aromatic hydrocarbons such as phenanthrene (PHE) has required the employment of high–efficiency technologies, including sediment washing (SW). However, the large amount of generated spent SW effluents requires the development of effective, eco–friendly and cost–saving approaches, which can tackle the waste formation in favor of the recovery of chemicals. This study proposes the treatment of a spent SW solution containing ethanol (EtOH) as extracting agent, by testing different initial PHE concentrations (i.e. 20–140 mg L−1) within six consecutive cycles in a fed–batch bioreactor under aerobic conditions. The biological process achieved a PHE removal of 63–91% after the enrichment of PHE–degrading bacteria and the proper supplementation of nutrients, and was mainly affected by the initial PHE concentration value and the excessive decrease of pH and dissolved oxygen. Achromobacter, Sphingobacterium and Dysgonomonas genera were mainly involved in PHE degradation, which followed a first–order kinetic model (R2 = 0.652–0.928) with a degradation rate and half–life time of 0.127–1.177 d−1 and 0.589–2.912 d, respectively. A techno–economic assessment revealed that a virtuous operation of SW, EtOH recovery and biodegradation of the SW solution can allow the recovery of up to 1.35 tons of EtOH per ton of remediated sediment and the decrease of the overall costs by 50%.

International audience; Nowadays, nitrate represents one of the major contaminants of the hydrosphere, mainly affecting the quality of groundwater intended to the production of drinking water. This study proposes the use of Fe(II)-driven autotrophic denitrification as a high-potential, innovative bioprocess to couple microbially-catalyzed nitrate reduction to Fe(II) oxidation. Two identical up-flow packed bed reactors (PBRs), i.e. PBR1 and PBR2, with granular activated carbon as biofilm carrier were seeded with a Thiobacillus-mixed culture and operated for 153 days at different feed nitrate concentrations and hydraulic retention times (HRTs). The results show enhanced nitrate removal rates and efficiencies at increasing nitrate loading rates. In particular, nitrate removal and Fe(II) oxidation up to 85 and 95 %, respectively, were achieved in PBR1 at nitrate loading rates as high as 12.5 mg NO3−/L/h. Besides not undermining the denitrification efficiency, increasing the nitrate loading rate from 8.1 to 12.5 mg NO3−/L/h led to specific nitrate removal rates as high as 14.3 mg NO3−/g VS/h. In PBR2, Fe(II)-driven denitrification was investigated at a constant nitrate loading rate by concomitantly decreasing the feed nitrate concentration and HRT. Despite the less severe operational conditions, the use of lower nitrate loading rates resulted in a lower nitrate removal efficiency than that obtained in PBR1.

The comparative performance of an inverse fluidized bed reactor (IFBR) having high density polyethylene beads as carrier materials for biofilm formation and a continuous stirred tank reactor (CSTR), both maintaining autotrophic denitrification using biogenic sulphur (ADBIOS) in the absence and presence of nickel (Ni2+), was studied. The reactors were compared in terms of NO3−-N and NO2−-N removal and SO42--S production throughout the study. A simulated wastewater with an inlet NO3−-N concentration of 225 mg/L and a decreasing concentration of biogenic sulphur (bio-S) from 1.5 to 0.375 g/L was used. Both reactors were operated at a hydraulic retention time (HRT) of 48 h for 140 days and at an HRT of 42 h for the following 68 days. A more efficient ADBIOS was observed in the CSTR than IFBR throughout the study due to a better mixing of the feed wastewater in the bulk liquid and a higher availability of bio-S to the suspended cells. The NO3−-N removal efficiency in the IFBR decreased by approximately 41% when the feed bio-S was reduced to 0.375 g/L, while it remained unaffected in the CSTR. Conversely, the presence of Ni2+ did not significantly affect NO3−-N removal in both reactors even at a feed Ni2+ concentration of 120 mg/L. The highest NO3−-N removal rates achieved were 86 and 108 mg NO3−-N/(L·day) in the IFBR and CSTR, respectively, in the presence of 120 mg/L of feed Ni2+ at an HRT of 42 h. Batch studies conducted with acclimatized biomass showed that the continuous-flow operation mode in both reactors played a major role in helping the autotrophic denitrifiers to tolerate Ni2+ toxicity.

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.

The recovery of iron and other heavy metals by the formation of Fe(III) (hydr)oxides is an important application of microbially-driven processes. The mineral characterization of the precipitates formed during Fe(II)-mediated autotrophic denitrification with and without the addition of Cu, Ni, and Zn by four different microbial cultures was investigated by X-ray fluorescence (XRF), Raman spectroscopy, scanning electron microscopy equipped with energy dispersive X-Ray analyzer (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and X-ray Powder Diffraction (XRD) analyses. Fe(II)-mediated autotrophic denitrification resulted in the formation of a mixture of Fe(III) (hydr)oxides composed of amorphous phase, poorly crystalline (ferrihydrite) and crystalline phases (hematite, akaganeite and maghemite). The use of a Thiobacillus-dominated mixed culture enhanced the formation of akaganeite, while activated sludge enrichment and the two pure cultures of T. denitrificans and Pseudogulbenkiania strain 2002 mainly resulted in the formation of maghemite. The addition of Cu, Ni and Zn led to similar Fe(III) (hydr)oxides precipitates, probably due to the low metal concentrations. However, supplementing Ni and Zn slightly stimulated the formation of maghemite. A thermal post-treatment performed at 650 °C enhanced the crystallinity of the precipitates and favored the formation of hematite and some other crystalline forms of Fe associated with P, Na and Ca.

International audience; High-solids anaerobic digestion (HS-AD) of the organic fraction of municipal solid waste (OFMSW) is operated at a total solid (TS) content ≥ 10% to enhance the waste treatment economy, though it might be associated to free ammonia (NH3) inhibition. This study aimed to calibrate and cross-validate a HS-AD model for homogenized reactors in order to assess the effects of high NH3 levels in HS-AD of OFMSW, but also to evaluate the suitability of the reversible non-competitive inhibition function to reproduce the effect of NH3 on the main acetogenic and methanogenic populations. The practical identifiability of structural/biochemical parameters (i.e. 35) and initial conditions (i.e. 32) was evaluated using batch experiments at different TS and/or inoculum-to-substrate ratios. Variance-based global sensitivity analysis and approximate Bayesian computation were used for parameter optimization. The experimental data in this study permitted to estimate up to 8 biochemical parameters, whereas the rest of parameters and biomass contents were poorly identifiable. The study also showed the relatively high levels of NH3 (i.e. up to 2.3 g N/L) and ionic strength (i.e. up to 0.9 M) when increasing TS in HS-AD of OFMSW. However, the NH3 non-competitive function was unable to capture the acetogenic/methanogenic inhibition. Therefore, the calibration emphasized the need for target-oriented experimental data to enhance the practical identifiability and the predictive capabilities of structured HS-AD models, but also the need for further testing the NH3 inhibition function used in these simulations.

In this study, mono-digestion of the organic fraction of municipal solid waste (OFMSW) and co-digestion of OFMSW with beech sawdust, simulating green waste, were used to investigate the maximum operational total solid (TS) content in semi-continuous high-solids anaerobic digestion (HS-AD). To alleviate substrate overloading in HS-AD, the effluent mass was relatively reduced compared to the influent mass, extending the mass retention time. To this aim, the reactor mass was daily evaluated, permitting to assess the reactor content removal by biogas production. During mono-digestion of OFMSW, the NH3 inhibition and the rapid TS removal prevented to maintain HS-AD conditions (i.e. TS ≥ 10%), without exacerbating the risk of reactor acidification. In contrast, the inclusion of sawdust in OFMSW permitted to operate HS-AD up to 30% TS, before acidification occurred. Therefore, including a lignocellulosic substrate in OFMSW can prevent acidification and stabilize HS-AD at very high TS contents (i.e. 20–30%).

International audience; This study evaluates the main effects of including ‘non-ideal’ bio-physical-chemical corrections in high-solids anaerobic digestion (HS-AD) of the organic fraction of municipal solid waste (OFMSW), at total solid (TS) between 10 and 40%. As a novel approach, a simple ‘non-ideal’ module, accounting for the effects of ionic strength (I) on the main acid-base equilibriums, was coupled to a HS-AD model, to jointly evaluate the effects of ‘non-ideality’ and the TS content dynamics on the HS-AD bio-physical-chemistry. ‘Non-ideality’ influenced the pH, concentration of inhibitors (i.e. NH3), and liquid-gas transfer (i.e. CO2), particularly at higher TS (i.e. ≥ 20%). Meanwhile, fitting the experimental data for batch assays at 15% TS showed that HS-AD of OFMSW might be operated at I ≥ 0.5 M. Therefore, all HS-AD simulations should account for ‘non-ideal’ corrections, when assessing the main inhibitory mechanisms (i.e. NH3 buildup and acidification) potentially occurring in HS-AD of OFMSW.

Chemolithotrophic denitrification is an inexpensive and advantageous process for nitrate removal and represents a promising alternative to classical denitrification with organics. Chemolithotrophic denitrifiers are microorganisms able to reduce nitrate and nitrite using inorganic compounds as source of energy. Ferrous iron, sulfur-reduced compounds (e.g. hydrogen sulfide, elemental sulfur and thiosulfate), hydrogen gas, pyrite and arsenite have been used as inorganic electron donors resulting in diverse outcomes. In the last 40 years, a large number of engineered systems have been used to maintain chemolithotrophic denitrification and improve rate and efficiency of the process. Among them, biofilm reactors proved to be robust and high-performing technologies. Packed bed reactors are particularly suitable for the removal of low nitrate concentrations, since high retention times are required to complete denitrification. Fluidized bed and membrane biofilm reactors result in the highest denitrification rates (>20 kg N-NO 3 − /m 3 d) when hydrogen gas and sulfur reduced compounds are used as electron donors. Hydrogen gas pressure and current intensity rule the performance of membrane biofilm and biofilm electrode reactors, respectively. Biofouling is the most common and detrimental issue in biofilm reactors. Bed fluidization and hydrogen supply limitation are convenient and effective solutions to mitigate biofouling.

This study revealed that fluidized-bed denitrifying cultures tolerated soluble Ni concentrations up to 500 mg/L at 7–8 and 22 C. From 10 to 40 mg/L of feed Ni, denitrification resulted in complete nitrate and nitrite removal. The concomitant reduction of 30 mg/L of sulfate produced 10 mg/L of sulfide that precipitated nickel, resulting in soluble effluent Ni below 22 mg/L. At this stage, Dechloromonas species were the dominant denitrifying bacteria. From 60 to 500 mg/L of feed Ni, nickel remained in solution due to the inhibition of sulfate reduction. At soluble 60 mg/L of Ni, denitrification was partially inhibited prior to recover after 34 days of enrichment by other Ni-tolerant species (including Delftia, Zoogloea and Azospira) that supported Dechloromonas. Subsequently, the FBR cultures completely removed nitrate even at 500 mg/L of Ni. Visual Minteq speciation model predicted the formation of NiS, NiCO3 and Ni3(PO4)2, whilst only Ni3(PO4)2 was detected by XRD.

Fe(II)-mediated autotrophic denitrification in the presence of copper (Cu), nickel (Ni) and zinc (Zn) with four different microbial cultures was investigated in batch bioassays. In the absence of metals, complete nitrate removal and Fe(II) oxidation were achieved with a Thiobacillus-dominated mixed culture and Pseudogulbenkiania sp. 2002 after 7 d. A nitrate removal of 96 and 91% was observed with a pure culture of T. denitrificans and an activated sludge enrichment, respectively, after 10 d of incubation. Cu, Ni and Zn were then supplemented at an initial concentration of 5, 10, 20 and 40 mg Me/L. A decrease of approximately 50% of the soluble metal concentrations occurred in the first 4 d of denitrification, due to metal precipitation, co-precipitation, sorption onto iron (hydr)oxides, and probably sorption onto biomass. A higher sensitivity to metal toxicity was observed for the microbial pure cultures. Pseudogulbenkiania sp. 2002 was the least tolerant among the biomasses tested, resulting in only 6, 8 and 6% nitrate removal for the highest Cu, Ni and Zn concentrations, respectively. In contrast, the highest nitrate removal efficiency and specific rates were achieved with the Thiobacillus-dominated mixed culture, which better tolerated the presence of metals. Averagely, Cu resulted in the highest inhibition of nitrate removal, followed by Zn and Ni.

International audience; During high-solids anaerobic digestion (HS-AD) of the organic fraction of municipal solid waste (OFMSW), an important total solid (TS) removal occurs, leading to the modification of the reactor content mass/volume, in contrast to ‘wet’ anaerobic digestion (AD). Therefore, HS-AD mathematical simulations need to be approached differently than ‘wet’ AD simulations. This study aimed to develop a modelling tool based on the anaerobic digestion model 1 (ADM1) capable of simulating the TS and the reactor mass/volume dynamics in the HS-AD of OFMSW. Four hypotheses were used, including the effects of apparent concentrations at high TS. The model simulated adequately HS-AD of OFMSW in batch and continuous mode, particularly the evolution of TS, reactor mass, ammonia and volatile fatty acids. By adequately simulating the reactor content mass/volume and the TS, this model might bring further insight about potentially inhibitory mechanisms (i.e. NH3 buildup and/or acidification) occurring in HS-AD of OFMSW.

The dewaterability of sludge from two conventional activated sludge (CAS) and three membrane bioreactor (MBR)-based wastewater treatment plants is investigated prior to and after anaerobic digestion. The concentration and composition of extracellular polymeric substances (EPS) mostly affect the dewaterability of all raw sludge samples. Better sludge dewaterability is observed when the concentration of proteins, carbohydrates, uronic acids, and humic acids is below approximately 400, 250, 200, and 40 mg/L, respectively. In contrast, the specific resistance to filtration (SRF) increases in the sludge samples with a higher EPS concentration. The MBR results in a lower EPS production and a uronic acid-dominating EPS composition. This especially affects the dewaterability of one MBR sludge, also characterized by high salinity and a smaller particle size. Anaerobic digestion results in a higher SRF for both CAS and MBR sludge, with the particle-size distribution having the preponderant effect on the digested sludge dewaterability.

The effect of trace elements (TEs) addition and NaOH pretreatment on the anaerobic digestion of rice straw was investigated in batch tests. Co, Ni and Se were added to the raw rice straw at different dosages. The NaOH pretreatment was applied to the rice straw both alone and in combination with the addition of TEs, in order to evaluate potential synergistic effects of the pretreatment and the TEs supplementation on the biogas production yields. The results obtained showed that the alkaline pretreatment was more effective than the TEs addition in increasing the cumulative biogas production, causing a 21.4% enhancement of the final biomethane yield, whereas the increase due to TEs dosing was not statistically significant. The analysis of volatile fatty acids (VFAs) confirmed that the NaOH pretreatment resulted in a higher production of VFAs, indicating an increased hydrolysis, while TEs addition did not cause significant changes in the VFA concentrations.

This study focused on continuous-flow hydrogen production by Thermotoga neapolitana at a hydraulic retention time (HRT) decreasing from 24 to 5 h. At each HRT reduction, the hydrogen yield (HY) immediately dropped, but recovered during prolonged cultivation at constant HRT. The final HY in each operating period decreased from 3.4 (±0.1) to 2.0 (±0.0) mol H2/mol glucose when reducing the HRT from 24 to 7 h. Simultaneously, the hydrogen production rate (HPR) and the liquid phase hydrogen concentration (H2aq) increased from 82 (±1) to 192 (±4) mL/L/h and from 9.1 (±0.3) to 15.6 (±0.7) mL/L, respectively. Additionally, the effluent glucose concentration increased from 2.1 (±0.1) to above 10 mM. Recirculating H2-rich biogas prevented the supersaturation of H2aq reaching a value of 9.3 (±0.7) mL/L, resulting in complete glucose consumption and the highest HPR of 277 mL/L/h at an HRT of 5 h.

Stormwater runoff is often contaminated by human activities. Stormwater discharge into water bodies significantly contributes to environmental pollution. The choice of suitable treatment technologies is dependent on the pollutant concentrations. Wastewater quality indicators such as biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), and total dissolved solids (TDS) give a measure of the main pollutants. The aim of this study is to provide an indirect methodology for the estimation of the main wastewater quality indicators, based on some characteristics of the drainage basin. The catchment is seen as a black box: the physical processes of accumulation, washing, and transport of pollutants are not mathematically described. Two models deriving from studies on artificial intelligence have been used in this research: Support Vector Regression (SVR) and Regression Trees (RT). Both the models showed robustness, reliability, and high generalization capability. However, with reference to coefficient of determination R2 and root‐mean square error, Support Vector Regression showed a better performance than Regression Tree in predicting TSS, TDS, and COD. As regards BOD5, the two models showed a comparable performance. Therefore, the considered machine learning algorithms may be useful for providing an estimation of the values to be considered for the sizing of the treatment units in absence of direct measures.

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 600 mg L−1 h−1 and 10 min, respectively. Further decrease of HRT to 5 min resulted in 50% of nitrate removal efficiency. Nitrite did not accumulate when nitrate was used as electron acceptor unless HRT was decreased to 5 min. 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 228 mg L−1 h−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.

Treatment of acidic solution containing 5 g/L of Fe(II) and 10 mg/L of As(III) was studied in a system consisting of a biological fluidized-bed reactor (FBR) for iron oxidation, and a gravity settler for iron precipitation and separation of the ferric precipitates. At pH 3.0 and FBR retention time of 5.7 h, 96–98% of the added Fe(II) precipitated (99.1% of which was jarosite). The highest iron oxidation and precipitation rates were 1070 and 28 mg/L/h, respectively, and were achieved at pH 3.0. Subsequently, the effect of pH on arsenic removal through sorption and/or co-precipitation was examined by gradually decreasing solution pH from 3.0 to 1.6 (feed pH). At pH 3.0, 2.4 and 1.6, the highest arsenic removal efficiencies obtained were 99.5%, 80.1% and 7.1%, respectively. As the system had ferric precipitates in excess, decreased arsenic removal was likely due to reduced co-precipitation at pH < 2.4. As(III) was partially oxidized to As(V) in the system. In shake flask experiments, As(V) sorbed onto jarosite better than As(III). Moreover, the sorption capacity of biogenic jarosite was significantly higher than that of synthetic jarosite. The developed bioprocess simultaneously and efficiently removes iron and arsenic from acidic solutions, indicating potential for mining wastewater treatment.

The dispersion of nitrogenous compounds and heavy metals into the environment is frequent during mining activities. The effects of nickel (Ni) and cobalt (Co) on denitrification of simulated mine waters were investigated in batch bioassays and fluidized-bed reactors (FBRs). At pH 7, batch tests revealed that Co did not exhibit inhibition on denitrification even at 86.6 mg/L. Ni showed to be inhibitory at 50 and 100 mg/L by decreasing nitrate removal efficiencies of 18 and 65 %, respectively. In two FBRs, operated at 7-8 and 22 °C, 5.5 mg/L Ni did not affect nitrate and nitrite removals because of FBR potential of diluting soluble Ni feed concentration. On the contrary, the effluent pH clearly decreased in both FBR1 and FBR2 because of nickel sulfide precipitation and Ni inhibition of the last two steps of denitrification. When Ni injection was stopped, the process recovered more slowly at 22 than 7-8 °C. This is the first study reporting the effect of Ni on denitrification in biological FBRs.

Mining often leads to nitrate and metal contamination of groundwater and water bodies. Denitrification of acidic water was investigated in two up-flow fluidized-bed reactors (FBR) and using batch assays. Bacterial communities were enriched on ethanol plus nitrate in the FBRs. Initially, the effects of temperature, low-pH and ethanol/nitrate on denitrification were revealed. Batch assays showed that pH 4.8 was inhibitory to denitrification, whereas FBR characteristics permitted denitrification even at feed pH of 2.5 and at 7–8 °C. Nitrate and ethanol were removed and the feed pH was neutralized, provided that ethanol was supplied in excess to nitrate. Subsequently, Fe(II) and Cu impact on denitrification was investigated within batch tests at pH 7. Iron supplementation up to 100 mg/L resulted in iron oxidation and soluble concentrations ranging from 0.4 to 1.6 mg/L that stimulated denitrification. On the contrary, 0.7 mg/L of soluble Cu significantly slowed denitrification down resulting in about 45 % of inhibition in the first 8 h. Polymerase chain reaction—denaturant gradient gel electrophoresis demonstrated the co-existence of different denitrifying microbial consortia in FBRs. Dechloromonas denitrificans and Hydrogenophaga caeni were present in both FBRs and mainly responsible for nitrate reduction.

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.

Purity and settling properties determine metal sulfide recovery from bioreactors. The influence of macronutrients commonly present in mineral media and wastewaters on Cu, Pb, Cd and Zn depletion kinetics and characteristics was evaluated in batch experiments with chemically produced sulfide at different concentrations. The metal depletion kinetics showed that metals with slower depletion rates (Zn and Cd) are susceptible to other removal mechanisms such as biosorption onto the sulfate reducing biofilm and precipitation with macronutrients when sulfide is below the stoichiometric metal to sulfide ratio. For Zn, the main mechanism of removal is its sorption onto apatite (Ca(5)(PO(4)))(3)(+)(OH(-)), a compound formed due to the presence of CaCl(2)·2H(2)O and KH(2)PO(4) in the mineral medium. All precipitates were 8.1-10.0μm regardless the sulfide concentration demonstrating that this parameter is less relevant for particle growth and settling, compared to the agglomeration of the precipitates.

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, 10mg/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.

The hydrolysis of elemental sulfur (S0) coupled to S0-based denitrification and denitritation was investigated in batch bioassays by microbiological and modeling approaches. In the denitrification experiments, the highest obtained NO3−-N removal rate was 20.9 mg/l·d. In the experiments with the biomass enriched on NO2−, a NO2−-N removal rate of 10.7 mg/l·d was achieved even at a NO2−-N concentration as high as 240 mg/l. The Helicobacteraceae family was only observed in the biofilm attached onto the chemically-synthesized S0 particles with a relative abundance up to 37.1%, suggesting it was the hydrolytic biomass capable of S0 solubilization in the novel surface-based model. S0-driven denitrification was modeled as a two-step process in order to explicitly account for the sequential reduction of NO3− to NO2− and then to N2 by denitrifying bacteria.

In this study, the biokinetics of autotrophic denitrification with biogenic S0 (ADBIOS) for the treatment of nitrogen pollution in wastewaters were investigated. The used biogenic S0, a by-product of gas desulfurization, was an elemental microcrystalline orthorhombic sulfur with a median size of 4.69 µm and a specific surface area of 3.38 m2/g, which made S0 particularly reactive and bioavailable. During denitritation, the biomass enriched on nitrite (NO2–) was capable of degrading up to 240 mg/l NO2–-N with a denitritation activity of 339.5 mg NO2–-N/g VSS·d. The use of biogenic S0 induced a low NO2–-N accumulation, hindering the NO2–-N negative impact on the denitrifying consortia and resulting in a specific denitrification activity of 223.0 mg NO3–-N/g VSS·d. Besides Thiobacillus being the most abundant genus, Moheibacter and Thermomonas were predominantly selected for denitrification and denitritation, respectively.