Fixed-film Bioreactor Research Articles

The Valorization of Fruit and Vegetable Wastes Using an Anaerobic Fixed Biofilm Reactor: A Case of Discarded Tomatoes from a Traditional Market

Tomato waste, characterized by high organic matter and moisture content, offers a promising substrate for anaerobic digestion, though rapid acidification can inhibit methanogenic activity. This study investigated the performance of a 10.25 L anaerobic fixed biofilm reactor for biogas production using liquid tomato waste, processed through grinding and filtration, at high organic loading rates, without external pH control or co-digestion. Four scouring pads were vertically installed as a fixed bed within a fiberglass structure. Reactor performance and buffering capacity were assessed over three stages with progressively increasing organic loading rates (3.2, 4.35, and 6.26 gCOD/L·d). Methane yields of 0.419 LCH4/gCOD and 0.563 LCH4/g VS were achieved during the kinetic study following stabilization. Biogas production rates reached 1586 mL/h, 1804 mL/h, and 4117 mL/h across the three stages, with methane contents of 69%, 65%, and 72.3%, respectively. Partial alkalinity fluctuated, starting above 1500 mg CaCO3/L in Stage 1, dropping below 500 mg CaCO3/L in Stage 2, and surpassing 3000 mg CaCO3/L in Stage 3. Despite periods of forced acidification, the system demonstrated significant resilience and high buffering capacity, maintaining stability through hydraulic retention time adjustments without the need for external pH regulation. The key stability indicators identified include partial alkalinity, effluent chemical oxygen demand, pH, and one-day cumulative biogas. This study highlights the effectiveness of anaerobic fixed biofilm reactors in treating tomato waste and similar fruit and vegetable residues for sustainable biogas production.

Removal of nitrogen and phosphorous from blackwater via an integrated nature-based system: hybrid-vertical flow constructed wetland, upflow anaerobic fixed biofilm reactor, and granular activated charcoal column along with in situ electrochlorination disinfection

Abstract The hybrid vertical-flow constructed wetland (H-VFCW) sequenced with an upflow anaerobic fixed biofilm reactor (UAFBR) was developed to treat blackwater for single households. The H-VFCW filter bed layer's redox zonation and hydraulic retention time (HRT) were designed optimally with the potential of simultaneous nitrification, denitrification, and enhanced biological phosphorous removal. The UAFBR optimisation for residual nitrate removal was based on the carbon -nitrogen ratio, HRT, and biofilm growth on carriers. Complete disinfection was achieved by optimised in situ electrochlorination by dosing 0.16% sodium chloride, with 20 min of electrolysis and 44.48 Am−2 of current density. The power consumption was 1.81±0.14 KWhm−3. Ammonia volatilisation was studied on a granular activated charcoal column (GACC) column to remove residual TAN as the final treatment. The integrated treatment system removed 98.63 ± 0.15% chemical oxygen demand (COD), 97.09 ± 0.19% total nitrogen (TN), 93.96 ± 0.34% nitrate (NO3−), 97.92 ± 0.2% TAN, 99.62 ± 1% orthophosphate (PO43−), 87.49 ± 0.36% total suspended solids (TSS), and 100% Coliform, with the final effluent pH of 8.4 ± 0.08. The microbial and functional annotation diversity of the UAFBR biofilm was studied. The treatment systems achieved the Central Pollution Control Board (India) effluent discharge standards.

Enhancing Organic Micropollutants Removal in Wastewater with an Innovative Two-Stage Anaerobic Fixed-Film Bioreactor: Role of Acidogenic and Methanogenic Steps

Enhancing Organic Micropollutants Removal in Wastewater with an Innovative Two-Stage Anaerobic Fixed-Film Bioreactor: Role of Acidogenic and Methanogenic Steps

Assembling fixed-biofilm reactor with modified basalt fiber and modified wild jujube seed biochar for concurrent removal of nitrate, tetracycline and cadmium: Performance and microflora response

Mixed pollution of nitrate, tetracycline (TC) and cadmium (Cd2+) induced by improper discharge of various wastewater from industry and agriculture has attracted extensive attention. A novel biocarrier (MBF@FMJSB) assembled with modified basalt fiber and modified wild jujube seed biochar (FMJSB) was used to construct fixed-biofilm reactor (FBR) for concurrent removal of nitrate, TC, and Cd2+. The removal efficiencies of nitrate, TC, and Cd2+ of the bioreactor were 79.34%, 85.45%, and 88.02%, respectively, when HRT was 6.0 h, C/N ratio was 1.5, influent nitrate concentration was 25 mg L−1, pH was 6.5, and TC and Cd2+ concentrations was 0.6 and 1 mg L−1. The addition of FMJSB was not only beneficial for bacteria to resist the stress of TC and Cd2+, but also contributed to the removal of TC and Cd2+ pollutants. In addition, microbial metabolism was a key pathway for pollutant removal in FBR. Microflora with Zoogloea as a core genus can dynamically regulate the community structure and expression of microbial metabolism related genes to adapt to TC and Cd2+ stresses. This study was valuable for the treatment of wastewater containing mixed pollutants.

Improving bioenergy recovery from municipal wastewater with a novel cloth-filter anaerobic membrane bioreactor

Anaerobic membrane bioreactors (AnMBR) have been used for treating high-strength industrial wastewater at full-scale and the potential to use them for mainstream municipal wastewater treatment presents an important opportunity to turn energy-intensive plants into net-energy producers. However, several limitations of the AnMBR technology have prevented their adoption in the municipal wastewater industry, namely, high membrane cleaning energy demand and low membrane flux. This study demonstrated a novel AnMBR configuration that uses a commercially available cloth filter technology to address the key limitations of cleaning energy and membrane flux. The cloth filter anaerobic membrane bioreactor (CFAnMBR) is comprised of an anaerobic fixed-film bioreactor coupled with a cloth filter membrane with nominal pore size of 5 µm. The pilot CFAnMBR was operated for 150 days through the winter at a municipal wastewater plant in central Illinois (minimum/average influent temperature 5/13°C). The CFAnMBR increased membrane flux by more than 2 orders of magnitude (3,649 ± 1,246 L per meter squared per hour) and reduced cleaning energy demand by 78%—92% (0.0085 kWh/m3) relative to previously reported AnMBR configurations. With the CFAnMBR, average chemical oxygen demand and total suspended solids removal were 66% and 91%, respectively, and were shown to be increased up to 88% and 96% by in-line coagulant dosing with ferric chloride. Average headspace methane yield was 154 mL CH4/g CODremoved by the end of the study period with influent temperatures of 11°C± 4°C. The CFAnMBR resolves major limitations of AnMBR technology by employing a commercially-available technology already used for other municipal wastewater treatment applications.

Metagenomic analysis of a bioreactor biofilm treating raw textile effluent and biochemical characterization of a novel azoreductase gene

Azo dyes are potent synthetic carcinogens that are widely used in the textile industries and their discharge into the surface water has detrimental consequences for human and ecosystem health. Oxidoreductases have been found to be involved in the metabolism of various xenobiotic compounds including azo dyes. Therefore, in this study shotgun metagenomic sequencing (SGMS) was used to bioprospect novel oxidoreductase genes in the biofilm of a fixed-film bioreactor treating raw textile effluent. According to the SGMS taxonomic and functional annotation, the bacteria found to be dominant in the bioreactor biofilm exhibited versatility and possessed genes that are capable of degrading azo dyes as well as other xenobiotics. A novel azoreductase gene (BM-AzoR) derived from the bioreactor biofilm metagenome was found to encode a previously uncharacterized FMN-dependent NADH azoreductase. In silico analysis of BM-AzoR gene encoded enzyme suggests that it is a thermostable and hydrophilic monomeric protein. The purified BM-AzoR is a flavin protein showing an optimal enzyme activity at pH 5 and 55 °C, respectively. The purified enzyme showed a specific azoreductase activity of 1.348 ± 0.12 U mg−1 in the presence of flavin mononucleotide (FMN) and preferred nicotinamide adenine dinucleotide (NADH) over nicotinamide adenine dinucleotide phosphate (NADPH) as an electron donor. A molecular docking analysis validated the in vitro results by identifying Methyl Red as the best substrate for the BM-AzoR. The purified enzyme retained its activity in a variety of metal ions and solvents, indicating its potential application in azo dye bioremediation.

Nitrogen removal from mature landfill leachate through enhanced Partial Nitrification-Anammox process in an innovative multi-stage fixed biofilm reactor

In the current integrated PN/A method/process for mature landfill leachate treatment, microbial inhibition and low nitrogen removal capacity are the big barriers due to high ammonia concentration and low C/N. This study aimed to evaluate the performance of a high-rate nitrogen removal lab-scale reactor, which combines pre-denitrification and Partial Nitrification-Anammox (PN/A) in a multi-stage fixed biofilm reactor (MFBR), for mature landfill leachate treatment. A nitrogen removal efficiency (NRE) of 90.43 % and an average nitrogen removal rate (NRR) of 0.94 kg/m3·d were observed at an influent NH+ 4-N concentration of 2274.39 mg/L during the last operational phase. The nitrogen mass balance showed that the nitrogen concentration gradually decreases along the course, and nitrogen was mainly removed in the aerobic chambers, in which Anammox contributed to 86.4 % of the removed nitrogen, while the front anoxic chamber is mainly used to remove NO- 3-N from the recirculation. Redundancy analysis showed that the variation in NH+ 4-N concentration along the course was the main factor affecting microbial community succession, which shows that the reactor configuration enables efficient cooperation and distribution of different microorganisms. Moreover, economic analysis of MFBR process showed that the energy consumption and carbon addition were reduced by 58.9 % and 100 %, respectively. Therefore, the MFBR established in this study, with its new configuration, achieves efficient treatment of landfill leachate in a single reactor and is environmentally friendly, and could be considered as a reference for full-scale landfill leachate treatment.

The application of post-denitrification fixed biofilm reactor for polishing secondary effluent: Nitrate removal, soluble microbial products and micropollutants biotransformation

This study was conducted to comprehensively evaluate the role of hydraulic retention time (HRT) on simultaneous removal of nitrate and micropollutants (MPs) in secondary effluent from wastewater treatment plants in post-denitrification fixed biofilm reactor (PDFBR). Results showed that PDFBR was favorable for nitrate removal (above 94%). Prolonged HRT promoted the bio-utilization of nonaromatic soluble microbial products with low molecular weight and reduced biomass production. MPs was partially removed in PDFBRs (below 48%). Microbial diversity increased along the extending of HRT and thus partially enhanced MPs removal. Batch experiments showed that changing HRT had no direct impact on the biodegradation rates of the selected MPs. Correlation analysis revealed that Dechloromonas, Terrimonas, and Phreatobacter were reasonable for simultaneous removal of MPs and nitrate. The abundance of nosZ gene had a rapid decrease under extreme HRT. This study provides insights into polishing nitrate and MPs from secondary effluent in a denitrifying biofilm system.

Effect of temperature and hydraulic retention time on hydrogen production from palm oil mill effluent (POME) in an integrated up-flow anaerobic sludge fixed-film (UASFF) bioreactor

The current state of palm oil mill wastewater treatment focuses solely on open ponding or closed lagoon systems for biogas production. However, efforts to convert this wastewater into biohydrogen are limited. Therefore, this research investigates the feasibility of converting palm oil mill effluent (POME) for biohydrogen production via dark fermentation. Temperature and hydraulic retention time (HRT) effects on biohydrogen production and COD removal efficiency in an up-flow anaerobic sludge fixed-film (UASFF) bioreactor were investigated. The experiment was carried out and analysed using a central composite design (CCD) and the Response Surface Methodology (RSM). The hydrogen (H 2 ) yield, H 2 production rate (HPR), and COD removal efficiency were investigated as responses. HPR increased significantly by 28.8 folds as temperature increased from 37 °C to 53.5 °C (transition from mesophilic to thermophilic) at HRT of 3 h. Meanwhile, the COD removal efficiency significantly increased from 24.76% to 33.33% between 4 to 9 h of HRT. Maximum H 2 yield of 0.95 L H 2 g −1 COD removed , HPR of 10.39 L H 2 d −1 , and 35.9% COD removal were reported at the optimum HRT and temperature of 7 h and 57 °C, respectively. This study indicates that under the thermophilic condition and short HRT, POME could be treated while producing biohydrogen using the UASFF bioreactor. • The temperature has a significant impact on hydrogen yield and hydrogen production rate. • Low HRT significantly impacted the COD removal efficiency of POME. • Optimum temperature and HRT were 57 °C and 7 h, respectively. • Acetobacter spp. is found to be dominant under a thermophilic condition in the H 2 -UASFF unit.

Facilitation of interspecies electron transfer in anaerobic processes through pine needle biochar.

Role of biochar in promoting methanogenesis during anaerobic processes was investigated in this research. Biochar produced from Himalayan pine needles was used as medium for conductive material mediated interspecies electron transfer (CM-IET) amongst the electron producing microorganisms and electron consuming methanogenic archaea. Three anaerobic continuous stirrer tank reactors (CSTRs) with 0, 5 and 10 g/L pine needle biochar (PNB) were operated at steady state organic loading rate (OLR) of 2.0-2.5 kgCOD/(m3.d). R0 (0 g/L PNB), representing indirect interspecies electron transfer (IIET), failed at an OLR of 2.0 kgCOD/(m3.d) due to the highest volatile fatty acid (VFA) concentration of 6,300 mg/L among the three CSTRs. On the other hand, at an OLR of 2.5 kgCOD/(m3.d), R2 (10 g/L PNB) showed the most superior performance with chemical oxygen demand (COD) removal of 55% and volatile fatty acid (VFA) concentration of 3,500 mg/L, while R1 (5 g/L PNB) recorded COD removal of 45% and VFA concentration of 4,400 mg/L. In comparison, fixed biofilm reactor (FBR) with 80 g/L of PNB as support material operated satisfactorily at OLR of 13.8 kgCOD/(m3.d) with 70% COD removal and VFA concentration of 1,400 mg/L. These investigations confirmed the beneficial role of biochar in anaerobic processes by promoting CM-IET amongst VFA degrading bacteria and methane producing archaea.

Dynamics of methanogenic archaean populations in a FBR digester during the transition from mesophilic to thermophilic conditions applying control schemes

The purpose of this study was the molecular characterization of the methanogenic Archaea community in a fixed biofilm reactor (FBR) fed with tequila vinasses. This characterization was realized during the transition from mesophilic (37 °C) to thermophilic (55 °C) conditions applying cascade control schemes. Initially, the FBR was started-up and operated under mesophilic conditions applying a change from 5 to 6.6 g-COD L-1 d-1 in the organic loading rate to evaluate a control scheme where the reference variable was the alkalinity (alpha factor) and the controlled variable was the tequila vinasses (substrate) flow rates. Subsequently, the FBR was operated under thermophilic conditions increasing the temperature in a direct manner and after, in a stepwise manner by applying a control scheme which used the alkalinity (alpha factor) as a reference factor to regulate the temperature of the bioprocess, keeping the tequila vinasses flow rate constant. The Archaea community was characterized by mass sequencing and further phylogenetic analysis of the variable regions 4 and 5 of the 16S ribosomal RNA gene. The results on the characterization of the Archaea community indicated that the populations of methane-producing Archaea by the acetotrophic pathway (Methanosaeta harundinaceae, M. thermoacetophila, Methanosaeta sp., Methanosarcina thermophila and Methanometylovorans uponensis) showed a reduction in their relative abundances during the disturbances applied under mesophilic conditions. Whereas, the populations of methane-producing Archaea by the hydrogenotrophic pathway (Methanobacterium beijingense, M. subterraneum, Methanofollis liminatans, Methanoculleus marisnigri, Methanolinea tarda, and Methanomassiliicoccus sp.) increased their relative abundances, indicating a phenomenon of physiological adaptation to the environmental disturbances under mesophilic conditions, obtaining a hydrogenotrophic:acetotrophic Archaea ratio of 87:8. However, the population dynamics during the thermophilic stage indicated that the methanogenic acetotrophic archaea doubled their relative abundance reaching a hydrogenotrophic:acetotrophic Archaea ratio of 81:16, indicating a phenomenon of physiological adaptation to thermophilic conditions when the control scheme applied the increase of the temperature in a stepwise manner, since the direct increase to 55 °C destabilized the Archaea community and the alpha factor.

Microbial induced calcium precipitation based anaerobic immobilized biofilm reactor for fluoride, calcium, and nitrate removal from groundwater

In this study, the anaerobic quartz sand fixed biofilm reactor containing Cupriavidus sp. W12 was established to simultaneously remove calcium (Ca2+), fluoride (F−) and nitrate (NO3–N) from groundwater. After 84 days of continuous operation, the optimum operating parameters and defluoridation mechanism were explored, and the microbial community structure under different pH environments were compared and analyzed. Under the optimal operation conditions (HRT of 6 h, initial Ca2+ concentration of 180 mg L−1, and pH of 7.0), the removal efficiencies of Ca2+, F−, and NO3–N were 58.97%, 91.93%, and 100%, respectively. Gas chromatography (GC) results indicate that N2 is the main gas produced by the bioreactor. Three−dimension excitation emission matrix fluorescence spectroscopy (3D−EEM) showed that extracellular polymers (EPS) are produced during bacterial growth and metabolism. The results of Scanning electron microscopy−energy dispersive spectrometer (SEM−EDS), X−ray diffraction (XRD), and Fourier transform infrared spectrometer (FTIR) demonstrated that the defluoridation mechanism is attributed to the synergetic effects of ion exchange, co−precipitation, and chemisorption. The comparative analysis of the microbial community structure under different pH conditions show that Cupriavidus is the dominant bacteria in the bioreactor throughout the experiment, and it shows a prominent advantage at pH of 7.0. This research provides an application foundation for anaerobic microbial induced calcium precipitation (MICP) bioremediation of Ca2+, F−, and NO3–N from groundwater.

Evaluating fixed-film nitrification systems in autotrophic mode: enhanced biomass retention does not improve bioreactor performance during alkalinity induced stress

Fixed-film bioreactors with different biomass loads operated in parallel. Similar ammonia removal rates indicated a lack of biomass-concentration dependent mechanisms to overcome alkalinity induced stress.

The anammox coupled partial-denitrification process in an integrated granular sludge and fixed-biofilm reactor developed for mainstream wastewater treatment: Performance and community structure

This study describes an integrated granular sludge and fixed-biofilm (iGB) reactor innovatively designed to carry out the anammox/partial-denitrification (A/PD) process for nitrogen removal with mainstream municipal wastewater. The iGB-A/PD reactor consists of anammox granules inoculated in the lower region of reactor and an acclimated fixed-biofilm positioned in the upper region. Compared to the other reported A/PD systems for mainstream wastewater treatment, this iGB-A/PD reactor is notable due to its higher quality effluent with a total inorganic nitrogen (TIN) of ∼3 mg•L−1 and operation at a high nitrogen removal rate (NRR) of 0.8 ± 0.1 kg-N•m−3•d−1. Reads-based metatranscriptomic analysis found that the expression values of hzsA and hdh, key genes associated with anammox, were much higher than other functional genes on nitrogen conversion, confirming the major roles of the anammox bacteria in nitrogen bio-removal. In both regions of the reactor, the nitrate reduction genes (napA/narG) had expression values of 56–99 RPM, which were similar to that of the nitrite reduction genes (nirS/nirK). The expression reads from genes for dissimilatory nitrate reduction to ammonium (DNRA), nrfA and nirB, were unexpectedly high, and were over the half of the levels of reads from genes required for nitrate reduction. Kinetic assays confirmed that the granules had an anammox activity of 16.2 g-NH4+-N•kg−1-VSS•d−1 and a nitrate reduction activity of 4.1 g-N•kg−1-VSS•d−1. While these values were changed to be 4.9 g- NH4+-N•kg−1-VSS•d−1and 4.3 g-N•kg−1-VSS•d−1 respectively in the fixed-biofilm. Mass flux determination found that PD and DNRA was responsible for ∼50% and ∼25% of nitrate reduction, respectively, in the whole reactor, consistent with high effluent quality and treatment efficiency via a nitrite loop. Metagenomic binning analysis revealed that new and unidentified anammox species, affiliated with Candidatus Brocadia, were the dominant anammox organisms. Myxococcota and Planctomycetota were the principal organisms associated with the PD and DNRA processes, respectively.

A novel bio-physical approach for perchlorate contaminated well water treatment

A novel bio-physical approach for treating well water contaminated with perchlorate (ClO4¯) at 15 mg/L is reported in this study. In this process, the ClO4¯ was initially treated in an anaerobic fixed-film bioreactor (55 L), followed by a ceramic Micro-Filtration (MF) unit (1.5 μm pore size, 0.12 m2 surface area) and a Reverse Osmosis (RO) unit (0.38 m2 surface area) connected in series. The bioreactor inoculated with a ClO4¯ reducing bacterium Serratia marcescens (Gen bank no. JQ807993) removed ~97% of the ClO4¯ using acetate as substrate (acetate/ClO4¯ ratio = 4). Subsequently, the MF and RO units removed ClO4¯ to <10 μg/L, Total Dissolved Solids (TDS) to <25 mg/L and Total Chemical Oxygen Demand (TCOD) to below detection Limit. The fouling associated with membranes was controlled (88–100%) through hourly manual backwashing with 2 L pure water at 25 L/h, and 60 psi, and forward flushing with 1 L pure water at 30 L/h and 3–5 psi for MF and RO units, respectively. The rejects and membrane wash water were also treated in the bioreactor, resulted in complete removal of ClO4¯ through this approach. This is the first report where biotreatment is adopted as a pre- and post-treatment to membrane process for removing ClO4¯, and this will find field application for treating ClO4¯ contaminated ground as well as surface water sources.

Assessment of the aerobic glass beads fixed biofilm reactor (GBs-FBR) for the treatment of simulated methylene blue wastewater

The present research is focused on the application of glass beads (GBs) in fixed biofilm reactor (FBR) for the treatment of simulated methylene blue (MB) wastewater for 9 weeks under aerobic conditions. The COD of MB wastewater showed a reduction of 86.48% from 2000 to 270.4 mg/L, and BOD was declined up to 97.7% from 1095.5 to 25.03 mg/L. A drastic increase in the pH was observed until the 3rd week (8.5 to 8.28), and later, marginal changes between 8.30 ± 0.02 were noticed. A dramatic fluctuation was observed in ammonia concentration which increased (74.25 mg/L) up till the 2nd week, and from the 3rd week it started declining. In the 9th week, the ammonia concentration dropped to 16.5 mg/L. The color intensity increased significantly up till the 2nd week (259,237.46 Pt/Co) of the experiment and started decreasing slowly thereafter. The SEM–EDX analysis has shown the maximum quantity of carbon content in the GBs without biofilm, and then in the GB samples of 1st, and 9th-week old aerobic biofilms. Furthermore, Raman spectroscopy results revealed that the 9th-week GBs has a fine and strong MB peak and matched with that of the MB stock solution. Overall, the results have shown that the GBs filter media were suitable for the development of active biofilm communities for the treatment of dye wastewater. Thus, GBs-FBR system can be used for wastewater treatment to solve the current problem of industrial pollution in many countries and to protect the aquatic environment from dye pollution caused by the textile industry.

Biosurfactant assisted degradation of High Molecular Weight Polycyclic Aromatic Hydrocarbons by mixed cultures from a car service oil dump from Pretoria Central Business District (South Africa)

Abstract Biomineralisation of polycyclic aromatic hydrocarbons (PAHs) and other toxic organic pollutants to CO2 and H2O is one of the most environmentally friendly and economically efficient options for treatment of deleterious organic pollutants in water and soil. Although most intermediate and high molecular weight (I-, HMW) PAHs are biodegradable, the degradability of these PAHs is limited by their low solubility. Experiments were conducted in batch reactors, and later, in continuous flow fixed-film bioreactor systems to take advantage of mass-transport resistance to reduce toxicity exposure within the biofilm. The results from this study showed a tenfold performance improvement in cumulative removal of PAHs in the biofilm reactor system. The active microbial agents were predominated by Pseudomonas aeruginosa MS-1 and Acinetobacter species. 98%, 88%, and 63% degradation of fluoranthene, pyrene and chrysene was achieved in the biofilm process, respectively, at steady doses of 45 kg/d fluoranthene, 12 kg/d pyrene and 7.5 kg/d chrysene, respectively. Product purification was further evaluated in a continuous flow fed-batch and plug-flow reactor system in which a high quality oil product was separated from oily sludge.

Biofuel generation from high-fat effluent in a biofilm reactor with backwash

ABSTRACT The performance of an up-flow 0.5 m high and 0.076 m diameter fixed-film bioreactor treating lipid-rich synthetic wastewater has been investigated under the present study. The initial porosity of the filter bed using immobilised microorganisms were on the support matrices has been measured to be 0.67. Excess biomass accumulation on the support leads to an increase in biofilm thickness with time. The filter bed has been regenerated by backwashing after the stipulated time to regain its efficiency in terms of COD removal through the revival of the contact surface. A mathematical model has been developed to predict the loss of contact area and decrease in the porosity of bed with operation time. The backwashing time has been correlated to the inlet concentration of substrate. Methanogens like Methanococcus sp. and Methanosarcina sp. are detected in the mixed anaerobic consortia and favourable growth condition for methanogens in the reactor leads to a maximum cumulative methane production at the exit of the reactor estimated to be 785 ml CH4 (STP)/(g VSS added). The originality of the present research lies in investigating erucic acid-rich wastewater in a bioreactor with backwash and proposing an integration of this bioconversion with syngas-based 2G-Biorefinery.

Biostimulation versus bioaugmentation for the electro-bioremediation of 2,4-dichlorophenoxyacetic acid polluted soils

The aim of this work is to compare three biological strategies for the in situ remediation of a 2,4-dichlorophenoxyacetic acid (2,4-D) polluted clayey soil by coupling electrokinetics (EK) and bioremediation (technology named as electrobioremediation, EBR). The first option (i) is EK-biostimulation, in which the activity of microorganisms already present in soil is enhanced by EK phenomena. The second and third options are EK-bioaugmentation, which consist of addition of microorganisms to soil through the inclusion of permeable biological barriers: (ii) using a microbial fixed biofilm reactor as biobarrier (BB1), and (iii) using a mixture of clean soil and a microbial suspension as biobarrier (BB2). Thus, three batch experiments at bench scale were conducted under a constant electric field of 1 V cm−1, and electrode polarity was periodically reversed every 12 h (2 d−1). The duration of each test was 10 days. Two additional tests using only biodegradation or only EK were performed as auxiliary reference tests. A microbial consortium acclimated to 2,4-D biodegradation was employed. Results showed that EK-biostimulation strategy offered the best pollutant removal efficiency (reaching up almost 100%) while biobarriers offered pollutant removal rates between 75 and 85%. Permeable biobarriers allowed the introduction of microorganism but caused a decrease in the electro-osmotic flow which, in turn, reduced the mobilization and contact between microorganisms and pollutants. These results can contribute to the knowledge and understanding of electrobioremediation of polluted soil and to the feasibility of delivering microorganism to the soil by using biobarriers. Despite biostimulation was found to be the best option, results show that permeable reactive biobarriers may result in a successful alternative for in-situ EK-bioaugmentation when acclimated microbial population is not already present in soil.

Autotrophic Fixed-Film Systems Treating High Strength Ammonia Wastewater.

The aim of the study was enrichment of nitrifying bacteria and to investigate the potential of autotrophic fixed-film and hybrid bioreactors to treat high strength ammonia wastewater (up to 1,000 mg N/L). Two types of fixed-film systems [moving bed biofilm reactor (MBBR) and BioCordTM] in two different configurations [sequencing batch reactor (SBR) and a continuous stirred tank reactor (CSTR)] were operated for 306 days. The laboratory-scale bioreactors were seeded with activated sludge from a municipal wastewater treatment plant and fed synthetic wastewater with no organics. Strategies for acclimation included biomass reseeding (during bioreactor start-up), and gradual increase in the influent ammonia concentration [from 130 to 1,000 mg N/L (10% every 5 days)]. Stable ammonia removal was observed up to 750 mg N/L from 45 to 145 days in the MBBR SBR (94–100%) and CSTR (72–100%), and BioCordTM SBR (96–100%) and CSTR (92–100%). Ammonia removal declined to 87% ± 6, in all bioreactors treating 1,000 mg N/L (on day 185). Following long-term operation at 1,000 mg N/L (on day 306), ammonia removal was 93–94% in both the MBBR SBR and BioCordTM CSTR; whereas, ammonia removal was relatively lower in MBBR CSTR (20–35%) and BioCordTM SBR (45–54%). Acclimation to increasing concentrations of ammonia led to the enrichment of nitrifying (Nitrosomonas, Nitrospira, and Nitrobacter) and denitrifying (Comamonas, OLB8, and Rhodanobacter) bacteria [16S rRNA gene sequencing (Illumina)] in all bioreactors. In the hybrid bioreactor, the nitrifying and denitrifying bacteria were relatively more abundant in flocs and biofilms, respectively. The presence of dead cells (in biofilms) suggests that in the absence of an organic substrate, endogenous decay is a likely contributor of nutrients for denitrifying bacteria. The nitrite accumulation and abundance of denitrifying bacteria indicate partial denitrification in fixed-film bioreactors operated under limited carbon conditions. Further studies are required to assess the contribution of organic material produced in autotrophic biofilms (by endogenous decay and soluble microbial products) to the overall treatment process. Furthermore, the possibility of sustaining autotrophic nitrogen in high strength waste-streams in the presence of organic substrates warrants further investigation.