H Hydraulic Retention Time Research Articles

Evaluating the scale-up of a reactor for the treatment of textile effluents using Bjerkandera sp

Effluents from the textile industry have a negative environmental impact due to their high load of dyes and hard-to-remove compounds: additives, detergents, and surfactants; these must be treated before effluents can be discharged into water. White-rot fungi show great potential for the bioremediation of water and soil matrices contaminated with recalcitrant pollutants (these are generally toxic). In this work, we designed a 5 L fixed bed reactor and evaluated its performance on the degradation of pollutants in effluents from the textile industry in continuous-operation mode under non-sterile conditions, using ligninolytic fungus Bjerkandera sp. (anamorphic state R1). This setup was based on a previous design of a 0.25 L fixed-bed model bioreactor. The system was designed by taking into account the geometric and hydrodynamic similarities of both setups. In continuous-mode color-removal assays, the bioreactor was operated at a 36 h Hydraulic retention time (HRT), a 1 L/min air flux at 33 °C, and a dye concentration of 75 g/L (sulfur black 1) and 6.5 g/L (indigo Vat blue 1). 69% of the dye was removed, and changes in the chemical structures of the dyes confirmed the ligninolytic activity of the microorganism as the main dye removal mechanism.

A combined activated sludge-filtration-ozonation process for abattoir wastewater treatment

Current industrial livestock production has one of the highest consumptions of water, producing up to ten times more polluted (biological oxygen demand, BOD) wastewaters compared to domestic sewage. Additionally, livestock production grows yearly leading to an increase in the generation of wastewater that varies considerably in terms of organic content and microbial population. Therefore, suitable wastewater treatment methods are required to ensure the wastewater quality meets EU regulations before discharge. In the present study, a combined lab scale activated sludge-filtration-ozonation system was used to treat a pre-treated abattoir wastewater. A 24-h hydraulic retention time and a 13-day solid retention time were used for the activated sludge process, followed by filtration (4–7 μm) and using ozone as tertiary treatment. Average reductions of 93% and 98% were achieved for chemical oxygen demand (COD) and BOD, respectively, obtaining final values of 128 mg/L COD and 12 mg/L BOD. The total suspended solids (TSS) average reduction reached 99% in the same system, reducing the final value down to 3 mg/L. Furthermore, 98% reduction in phosphorus (P) and a complete inactivation of total coliforms (TC) was obtained after 17 min of ozonation. For total viable counts (TVC), a drastic reduction was observed after 30 min of ozonation (6 log inactivation) at an injected ozone dose of 71 mg/L. The reduction percentages reported in this study are higher than those previously reported in the literature. Overall, the combined process was sufficient to meet discharge requirements without further treatment for the measured parameters (COD, BOD, TSS, P, TC and TVC).

Membrane Bioreactor Technology for Wastewater Reclamation

Responding to the water shortage in Egypt, the use of submerged membrane bioreactor (SMBR) for wastewater reclamation has been studied. The impact of hydraulic retention time (HRT), as the most influential operational parameter has been investigated. A bench-scale module was operated at three HRT: 6, 10 &15hs. The results demonstrated that total COD and BOD removal rates were not affected by changing the HRT or by variations in raw wastewater strength. Average residual COD values in the membrane permeate ranged from 14 to 20.3 mg O2 L-1. Corresponding residual BOD was below 3.0 mgL-1. Nitrification capacity of the SMBR was high. HRT was found to be a key parameter for fouling. Decreasing the HRT enhances membrane fouling. At HRT of 6h, fouling happened after 6 days. Corresponding values for HRTs 10 and 15 were 13 day and more than 42 days, respectively. Total coliform bacteria counts in most of the MBR permeate samples were below the detection limit of 10 CFU/100 mL. All protozoan parasitic stages detected in raw wastewater were removed by the SMBR. At HRT of 15h, both human rotaviruses and adenoviruses genome copies were reduced by 2 to 3 log10. This ratio was reduced by decreasing the HRT.

Heavy metal removal from aqueous solution using sodium alginate immobilized sulfate reducing bacteria: Mechanism and process optimization

Heavy metal removal was evaluated using sodium alginate immobilized sulfate reducing bacteria (SRB) under batch and continuous mode. Under batch conditions, more than 95% metal removal was achieved due to formation of insoluble metal sulfides exterior to the bead surface. Best heavy metal removal results were obtained at 48 h hydraulic retention time (HRT). Metal loading rate values upto 2.20 mg/L∙h for Fe(III), Zn(II), Cd(II), Pb(II) and Ni(II) and upto 4.29 mg/L∙h for Cu(II) were proved to be favorable for their removal using the continuous downflow column reactor packed with the immobilized SRB beads. Continuous metal removal from a mixture of the heavy metals showed that Cu(II) removal was maximum (99%), followed by Zn(II) (95.8%) and other metals at their respective low inlet concentrations. However, the removal values were reduced at a high inlet concentration of these metals, which matched well with low COD and sulfate reduction values.

Valorization of the Crude Glycerol for Propionic Acid Production Using an Anaerobic Fluidized Bed Reactor with Grounded Tires as Support Material.

This study evaluated the propionic acid (HPr) production from crude glycerol (CG) (5000mgL-1) in an anaerobic fluidized bed reactor (AFBR). Grounded tire particles (2.8-3.35mm) were used as support material for microbial adhesion. The reactor was operated with hydraulic retention times (HRT) varying from 8 to 0.5h under mesophilic (30°C) conditions. The HPr was the main metabolite produced, increasing in composition from 66.5 to 99.6% by decreasing the HRT from 8 to 0.5h. Other metabolic products were 1,3-propanediol, with a maximum of 29.4% with an HRT of 6h, ethanol, acetic, and butyric acids. The decrease in HRT from 8 to 0.5h decreased the HPr yield, with a maximum of 0.48 ± 0.06g HPr g COD-1 and an HRT of 6h, and favored HPr productivity, with a maximum of 4.09 ± 1.24gL-1h-1 and HRT of 0.5h. In the biogas, the H2 content increased from 12.5 to 81.2% by decreasing the HRT from 8 to 0.5h. These results indicate the potential application of the AFBR for HPr production using an immobilized mixed culture.

Enhanced performance and microbial community analysis of bioelectrochemical system integrated with bio-contact oxidation reactor for treatment of wastewater containing azo dye

Feasibility and superiority of the bioelectrochemical system integrated with biocontact oxidation (BES-BCO) for degradation and/or mineralization of azo dyes have been confirmed. In this study, the effects of hydraulic retention time (HRT), applied voltage, and dissolved oxygen (DO) concentration at the bioanode on the performance of BES-BCO and traditional BES were investigated. Using the response surface methodology, the optimum values of HRT, applied voltage, and DO concentration at the bioanode of BES-BCO were investigated to obtain the maximum decolouration and COD removal efficiency and minimum specific energy consumption (SEC). The microbial community structure in BES-BCO was studied for analyzing the change following the introduction of oxygen. The optimised solution was an applied voltage of 0.59V, HRT of 12h, and DO concentration of 0.96mg/L at the bioanode. Under such conditions, the DE, COD removal efficiency, and SEC values were 94.62±0.63%, 89.12±0. 32%, and 687.57±3.86J/g, respectively. In addition, after changing from BES to BES-BCO, the bacterial community structure of the bioanode underwent significant changes. Several aerobic aniline-degrading bacteria and anode-respiration bacteria (ARB) were found to dominate the community of the anode biofilm. The results showed that the removal of azo dye degradation by-products was closely correlated with the o-bioanode and the BCO bacterial community structure.

Formation of Se(0), Te(0), and Se(0)-Te(0) nanostructures during simultaneous bioreduction of selenite and tellurite in a UASB reactor.

Simultaneous removal of selenite and tellurite from synthetic wastewater was achieved through microbial reduction in a lab-scale upflow anaerobic sludge blanket reactor operated with 12h hydraulic retention time at 30°C and pH7 for 120days. Lactate was supplied as electron donor at an organic loading rate of 528 or 880mg COD L-1day-1. The reactor was initially fed with a synthetic influent containing 0.05mM selenite and tellurite each (phase I, day 1-60) and subsequently with 0.1mM selenite and tellurite each (phase II, day 61-120). At the end of phase I, selenite and tellurite removal efficiencies were 93 and 96%, respectively. The removal percentage dropped to 87 and 81% for selenite and tellurite, respectively, at the beginning of phase II because of the increased influent concentrations. The removal efficiencies of both selenite and tellurite were gradually restored within 20days and stabilized at ≥ 97% towards the end of the experiment. Powder X-ray diffraction and Raman spectroscopy confirmed the formation of biogenic Se(0), Te(0), and Se(0)-Te(0) nanostructures. Scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy showed aggregates comprising of Se(0), Te(0), and Se-Te nanostructures embedded in a layer of extracellular polymeric substances (EPS). Infrared spectroscopy confirmed the presence of chemical signatures of the EPS which capped the nanoparticle aggregates that had been formed and immobilized in the granular sludge. This study suggests a model for technologies for remediation of effluents containing Se and Te oxyanions coupled with biorecovery of bimetal(loid) nanostructures.

Biohydrogen fermentation of galactose at various substrate concentrations in an immobilized system and its microbial correspondence

The effects of substrate concentration on fermentative hydrogen production from galactose at a fixed hydraulic retention time of 12h were investigated in an immobilized continuously stirred tank reactor. Peak hydrogen production rate and hydrogen yield of 9.57L/L-d and 1.10mol/mol galactoseadded, respectively, were obtained at a feed substrate concentration of 30g/L and an organic loading rate of 60L/L-d. Quantitative polymerase chain reaction analysis showed that the variations in the performance resulted primarily from metabolic alterations within the metabolism of the established microbial community rather than modifications in the population. The results obtained showed that optimal substrate concentration is essential for the efficient, continuous production of hydrogen from galactose.

Effect of organic loading rates on biogas production and anaerobic biodegradation of composting leachate in the anaerobic series bioreactors

This study investigated the biodegradability of composting leachate and biogas production in different Organic Loading Rates (OLRs) in lab-scale series AMBR-ASBR bioreactors, Anaerobic Migrating Blanket Reactor (AMBR) and Anaerobic Sequencing Batch Reactor (ASBR). The raw Leachate with OLRs of 1.04–19.65gCOD/L.d went into the AMBR reactor and then into the ASBR reactor with hydraulic retention time of 24h. The produced methane and biogas were measured by GC-TCD and gas meter. The results showed that the best removal efficiency for BOD5, COD and readily biodegradable COD (rbCOD) in AMBR-ASBR hybrid reactor were 99.43%, 97.35% and 99.79%, respectively. The maximum amounts of biogas and methane production were 16.37 and 9.99L in OLR of 10.08gCOD/L.d. With the increase in OLRs, biogas production also increased, but in higher OLRs (18.52gCOD/L.d) with a sudden increase in OLR, methane and biogas production decreased. Moreover, the ratio of the biogas production to inlet COD was 1.35L (R2=0.994), that is equal to the ratio of produced biogas (L) to inlet Volatile Suspended Solids (VSS) (g) (R2=0.972). Thus, considering OLRs effects, it was observed that the AMBR-ASBR hybrid reactor as a novel series system could be remarkably efficient in compost leachate treatment and increasing biogas production.

Continuous fermentation and kinetic experiments for the conversion of crude glycerol derived from second-generation biodiesel into 1,3 propanediol and butyric acid

This study investigated the performance of different mixed microbial cultures (MMC) able to ferment crude glycerol generated from animal fat-based biodiesel to produce 1,3 propanediol (1,3 PDO) and butyric acid, under non-sterile conditions. Eight different continuous flow stirred-tank reactors (CSTR) were set up with different inoculum types and growth media. The distribution of metabolic products under variable operating conditions was determined. All MMC were characterized from a kinetic point of view and overall stoichiometric reactions were constructed. Changes in the microbial communities were monitored by means of Next Generation Sequencing (NGS). Maximum substrate degradation rate reached approximately 110g/L/d of glycerol (with a productivity of 38g/L/d and 11g/L/d for 1,3 PDO and butyric acid, respectively), obtained with an hydraulic retention time of 12h and 60g/L feed. The maximum feed concentration reached almost 90g/L, leading though to an incomplete substrate degradation.

Comparative study of Rushton and paddle turbines performance for biohydrogen production from palm oil mill effluent in a continuous stirred tank reactor under thermophilic condition

Biohydrogen production from palm oil mill effluent (POME) using Thermoanaerobacterium thermosaccharolyticum PSU-2-rich sludge was conducted in a 5L continuous stirred tank reactor (CSTR). Mixing of effluent is crucial factor for hydrogen yield and net energy gain. Two types of turbines, namely the Rushton turbine and paddle turbine at 10, 50, 100, and 150rpm were the comparative factors in this study. The operating parameters were 60°C, 24-h hydraulic retention time (HRT), and 55gCOD Linfluent−1 d−1 organic loading rate (OLR). Computational fluid dynamics (CFD) was employed to understand the flow pattern, including dead zones and swirls of effluent in the CSTR. Mixing by Rushton turbine developed lesser dead zone and better mixing swirl than those of paddle turbine. At all mixing speeds, higher hydrogen yield was obtained when a Rushton turbine was applied. The highest hydrogen yield was 6826mL H2 LPOME−1 (350mL H2 gCOD−1) at 150rpm. However, the operating speed to achieve the maximum net energy gain (of 29.95kJ) was 100rpm.

Effect of 5-hydroxymethylfurfural (5-HMF) on high-rate continuous biohydrogen production from galactose

This study investigated the effect of 5-hydroxymethylfurfural (5-HMF) on high-rate continuous fermentative H2 production in a lab-scale fixed bed reactor (FBR) inoculated with mixed culture granules and fed with 15g/L galactose at a hydraulic retention time of 6h and at 37°C. During the 83days of operation, 5-HMF up to 2.4g/L was spiked into the feedstock. The maximum hydrogen production performance of 26.6L/L-d and 2.9mol H2/mol galactoseadded were achieved at 5-HMF concentration of 0.6g/L. 5-HMF concentration exceeding 0.9g/L not only inhibited hydrogen production but also affected the biofilm structure and microbial community population. However, when 5-HMF was eliminated from the feedstock, the performance and microbial community population were rapidly recovered.

Municipal wastewater treatment via co-immobilized microalgal-bacterial symbiosis: Microorganism growth and nutrients removal

A symbiotic microalgal-bacterial system may be an optional technology for wastewater treatment. In this study, co-immobilized of a bacterium isolated from a municipal wastewater treatment plant (Pseudomonas putida) and a microalgae Chlorella vulgaris was used in the study of cell growth and nutrient removal during wastewater treatment under batch and continuous culture conditions. Under batch culture conditions, co-immobilization treatment significantly increased the cell density of C. vulgaris and P. putida compared with other treatments. The co-immobilized treatment also showed higher removal of ammonium, phosphate and COD than any single treatment, indicating that the nutrient uptake capability of C. vulgaris and P. Putida was mutually enhanced mutually. When tested in continuous mode, the treatment with a hydraulic retention time of 24h at the organic load rate of 1159.2mgCODL−1d−1 was most appropriate for wastewater treatment.

Applicability of upflow anaerobic sludge blanket and dynamic membrane-coupled process for the treatment of municipal wastewater.

This study investigated the applicability of dynamic membrane filter (DMF) technology in an upflow anaerobic sludge blanket (UASB) and DMF-coupled process for the treatment of municipal wastewater. The overall treatment performance and effects of hydraulic retention time (HRT), operating flux, and mesh pore size on the UASB + DMF were assessed. The UASB + DMF-coupled process demonstrated removal efficiencies of over 64 and 86% for TCOD and TSS, respectively. The effects of filtration flux and support mesh pore size were investigated and it was found that while there was little impact on the treatment performance, a 67% increase in operating flux resulted in a 25% increase in fouling rate. Similarly, with smaller mesh pore size (Mesh 500 with pore size of 28μm) the fouling rate increased by fourfold as compared to Mesh 300 (pore size of 46μm). In consideration of the operation duration and contaminant removal, the DMF with Mesh 300 support layer and operating at 100L/m2-h was the most efficient configuration for treating the effluent of the UASB operated with a HRT of 6h. Microbial analyses of the foulant layer revealed changes in relative abundance as compared to the bulk sludge, particularly with the hydrogenotrophic methanogens completely outcompeting the acetoclastic methanogens. Overall, the coupled process improved the system robustness and reduced variability of the treated effluent.

Start-up phase of a UASB-septic tank used for high strength municipal wastewater treatment in Mexico

The objective of this work was to assess the performance during the start-up phase of a Upflow anaerobic sludge blanket (UASB)-septic tank for municipal wastewater treatment in Mexico City. A lab scale UASB-septic tank (62 L total volume, acrylic), consisting of three chambers treated high strength municipal wastewater at ambient temperature (16 °C–24 °C), under 72 h Hydraulic retention time (HRT) during three months. Total and soluble chemical oxygen demand (COD), total biological oxygen demand (BOD5), total solids and total suspended solids (TSS) removals were 75.2 ± 6.5%, 54.8 ± 6.7%, 64.2 ± 4.8%, 25.9 ± 5% and 82.9 ± 5%, respectively. These results are comparable with the removals reported in other works with similar arrangements; and are similar even with average removals of COD, BOD and TSS in UASB reactors installed in Latin America. The good performance obtained showed that it is possible to achieve a short start-up period with UASB-septic tank if it is inoculated with anaerobic sludge. These findings also evidenced the feasibility and reliability of the UASB-septic tank system for decentralized wastewater management in Mexico.

Denitrification using excess activated sludge as carbon source: Performance and the microbial community dynamics

In this study, the feasibility of using excess activated sludge as carbon source for denitrification to remove low concentrations of nitrate from wastewater was investigated. With an optimized upflow anaerobic reactor, high denitrification performance for both synthetic wastewater and effluent from municipal wastewater treatment plant was achieved. The results showed that the nitrate nitrogen can be reduced down to <1mgL−1 with a hydraulic retention time of 6h. The total nitrogen removal increased with the amount of sludge added, while, the nitrogen removal per unit of added sludge decreased with the amount of sludge added. 16S rRNA gene high-throughput sequencing showed that the bacterial community changed during the startup period and the subsequent denitrification process. And, it was found that some bacterial species in genus Pseudomonas and Thauera obviously decreased during the reactor operation, suggesting that they were likely digested and released organic matters for the denitrification.

Recovering hydrogen production performance of upflow anaerobic sludge blanket reactor (UASBR) fed with galactose via repeated heat treatment strategy

This study evaluated the effect of repeated heat treatment towards the enhancement of hydrogen fermentation from galactose in an upflow anaerobic sludge blanket reactor with the hydraulic retention time of 6h and the operation temperature of 37°C. The hydrogen production rate (HPR) and hydrogen yield (HY) gradually increased up to 9.1L/L/d and 1.1mol/mol galactose, respectively, until the 33rd day of operation. When heat treatment at 80°C for 30min was applied, hydrogen production performance was enhanced by 37% with the enrichment of hydrogen producing bacteria population. The HPR and HY were achieved at 12.5L/L/d and 1.5mol/mol hexose, respectively, during further 30 cycles of reactor operation. The repeated heat treatment would be a viable strategy to warrant reliable continuous hydrogen production using mixed culture.

Effects of hydraulic retention time, co-substrate and nitrogen source on laundry wastewater anionic surfactant degradation in fluidized bed reactors

The aim of this study was to evaluate the influence of hydraulic retention time (HRT) on linear alkylbenzene sulfonate (LAS) removal in fluidized bed reactors (FBRs). FBR1 (HRT of 8h) and FBR2 (HRT of 12h) were fed laundry wastewater with 18.6±4.1 to 27.1±5.6mg/L of LAS in the following conditions: ethanol and nitrate addition (Phases I, II and III), nitrate (Phase IV), ethanol (Phase V) and laundry wastewater (Phase VI). LAS removal was 93±12% (FBR1) and 99±2% (FBR2). In FBR1, nitrate influenced significantly on LAS removal (99±3% – Phase IV) compared to the phase without nitrate (90±15% – Phase V). In FBR1 the absence of ethanol was more favourable for LAS removal (99±3% – Phase IV) compared to ethanol addition (87±16% – Phase II). In FBR2, 99±2% LAS removal was found up to 436days. By microbial characterization were identified bacteria as Acinetobacter, Dechloromonas, Pseudomonas and Zoogloea.

Effect of low pH start-up on continuous mixed-culture lactic acid fermentation of dairy effluent.

Mixed-culture fermentation that does not require an energy-intensive sterilization process is a viable approach for the economically feasible production of lactic acid (LA) due to the potential use of organic waste as feedstock. This study investigated mixed-culture LA fermentation of whey, a high-strength organic wastewater, in continuous mode. Variations in the hydraulic retention time (HRT) from 120 to 8h under different pH regimes in two thermophilic reactors (55°C) were compared for their fermentation performance. One reactor was maintained at a low pH (pH 3.0) during operation at HRTs of 120 to 24h and then adjusted to pH 5.5 in the later phases of fermentation at HRTs of 24 to 8h (R1), while the second reactor was maintained at pH 5.5 throughout the experiment (R2). Although the LA production in R1 was negligible at low pH, it increased dramatically after the pH was raised to 5.5 and exceeded that in R2 when stabilized at HRTs of 8 and 12h. The maximum yield (0.62g LA/g substrate fed as the chemical oxygen demand (COD) equivalent), the production rate (11.5g/Lday), and the selectivity (95%) of LA were all determined at a 12-h HRT in R1. Additionally, molecular and statistical analyses revealed that changes in the HRT and the pH significantly affected the bacterial community structure and thus the fermentation characteristics of the experimental reactors. Bacillus coagulans was likely the predominant LA producer in both reactors. The overall results suggest that low pH start-up has a positive effect on yield and selectivity in mixed-culture LA fermentation.

The accelerated enzymatic biodegradation and COD removal of petroleum hydrocarbons in the SCR using active bacterial biomass capable of in-situ generating peroxidase and biosurfactants

The enzyme-accelerated biodegradation of total petroleum hydrocarbons (TPH) was investigated in a sequencing continuous-inflow reactor (SCR) at different operational parameters of H2O2/TPH ratio, initial TPH concentration and hydraulic retention time (HRT). The optimum H2O2/TPH mass ratio was determined to be 0.35 at which the complete TPH removal of inlet TPH concentrations up to 4g/L at HRT of 24h, corresponding to the loading rate of 4kgTPH/m3.d, was attained. The average COD removal efficiency at this loading rate was 96.7%. With increasing the inlet TPH concentration from 1 to 2.5g/L, the biomass bacterial activity as dehydrogenase activity (DHA) increased from 7.5 to 27.1μgTF/gbiomass.d and remained almost unchanged with further increase of TPH concentration. The peroxidase activity (PA) remained high between 382 and 410U/gbiomass. In addition, the complete removal of 1g/L TPH (88.7% COD removal) was observed at HRT of as small as 4h (corresponding to the loading rate of 6kgTPH/m3.d) under optimum H2O2/TPH mass ratio. With the decrease of HRT from 24h to 4h at the constant TPH concentration of 1g/L the value of DHA remained between 24.4 and 28.4μgTF/gbiomass.d while the PA value increased from 287.9 to 394.4U/gbiomass. Total production of biosurfactants was 131mg/L (38mg/L rhamnolipid and 93mg/L surfactin) when the SCR was operated at TPH loading rate of 6kg/m3.d.Finally, the enhanced enzymatic biodegradation of TPH by using diverse microbial consortia capable of in-situ production of peroxidase and biosurfactant generation in the SCR is a very efficient and promising technique for accelerated biodegradation and COD removal of petroleum hydrocarbons.