Influence Of Hydraulic Retention Time Research Articles

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.

Influence of hydraulic retention time on the psychrophilic hydrolysis/acidogenesis of proteins.

The influence of the hydraulic retention time (HRT) on the anaerobic hydrolysis of complex substrates has been studied under psychrophilic conditions. For this purpose, a continuous stirred tank reactor was operated at 15 °C and neutral pH and gelatin was considered as a model protein. Three HRTs have been tested: 12, 21 and 36 h. Gelatin hydrolysis was greatly dependent on HRT, increasing from 40% at 12 h-HRT to a maximum of 65% at 36 h-HRT. Molecular size distribution analyses of the effluent showed that hydrolysation of compounds larger than 10 kDa was poor at 12 h-HRT, whereas the fraction of 1-10 kDa was completely transformed into compounds smaller than 1 kDa. Higher HRT (36 h) improved the degradation of the recalcitrant fraction (>10 kDa), obtaining an effluent with around 95% of soluble molecules (<1 kDa). In that way, the use of membrane bioreactors for the treatment of this type of macromolecules could improve the degradation efficiencies by enabling to increase the residence time of the non-hydrolyzed molecules, with what would be possible to achieve higher organic loading rate operation.

Influence of Hydraulic Retention Time and Reactor Configuration During Fermentation of Diluted Chicken Manure.

In this study, single-stage and two-phase semi-continuous thermophilic anaerobic reactors fed with diluted (3% total solids (TS) and 1.8% volatile solids (VS)) chicken manure at three different hydraulic retention times (HRTs) were compared interms of biogas production rate, methane content of the produced biogas, and VS and TS removal. Along the study, HRTs of 16, 12, and 8days were implemented to the single-stage and the two-phase systems. It was observed that the single-stage anaerobic system was superior to the two-phase anaerobic system according to their biogas production rates (517 vs. 356, 551 vs. 359, 459 vs. 386 (mL/g VSfeed)) at all HRTs. On the other hand, methane content of the biogas produced was higher in the two-phase system compared to the single-stage system.

Influence of hydraulic retention time on indigenous microalgae and activated sludge process

Integration of the microalgae and activated sludge (MAAS) process in municipal wastewater treatment and biogas production from recovered MAAS was investigated by studying the hydraulic retention time (HRT) of semi-continuous photo-bioreactors. An average total nitrogen (TN) removal efficiency (RE) of maximum 81.5 ± 5.1 and 64.6 ± 16.2% was achieved at 6 and 4 days HRT. RE of total phosphorous (TP) increased slightly at 6 days (80 ± 12%) HRT and stabilized at 4 days (56 ± 5%) and 2 days (55.5 ± 5.5%) HRT due to the fluctuations in COD and N/P mass ratio of the periodic wastewater. COD and organic carbon were removed efficiently and a rapidly settleable MAAS with a sludge volume index (SVI_10) of less than 117 mL g−1 was observed at all HRTs. The anaerobic digestion of the untreated MAAS showed a higher biogas yield of 349 ± 10 mL g VS−1 with 2 days HRT due to a low solids retention time (SRT). Thermal pretreatment of the MAAS (120 °C, 120 min) did not show any improvement with biogas production at 6 days (269 ± 3 (untreated) and 266 ± 16 (treated) mL gVS−1), 4 days (258 ± 11(untreated) and 263 ± 10 (treated) mL gVS−1) and 2 days (308 ± 19 mL (treated) gVS−1) HRT. Hence, the biogas potential tests showed that the untreated MAAS was a feasible substrate for biogas production. Results from this proof of concept support the application of MAAS in wastewater treatment for Swedish conditions to reduce aeration, precipitation chemicals and CO2 emissions.

Influence of hydraulic retention time and plant species on performance of mesocosm subsurface constructed wetlands during municipal wastewater treatment in super-arid areas

ABSTRACTA constructed wetland (CW) in arid areas requires special knowledge given the particular climatic conditions. Among other aspects, the Hydraulic Retention Time (HRT) and plant species may be two important design parameters in hyper- and super-arid areas. Therefore, the study aimed to evaluate the influence of both variables in the application of CW in super-arid areas. Two HRT, 3.5 d and 7 d, and plant species classified by their origin: (a) native, Festuca Orthopylla, Cortaderia atacamensis and Schoenoplectus americanus, and (b) foreign, Cyperus papyrus, were evaluated in four Mesocosm Constructed Wetlands (MCW) operated in a super-arid area. The results showed that the HRT significantly increased (α < 0.05) in more than 10% the removal efficiency of nitrogen and phosphorus forms (TN, NH4+-N, TP, PO4−3-P). These results were the same for the two groups of plants assessed. Moreover, Cyperus papyrus significantly increased (α < 0.05) above 30% the removal efficiency, but only for nitrogen and phosphorus forms. MCW with this plant species showed a water loss above 25% and significantly increased (α < 0.05) the Electrical Conductivity (EC) of effluents. MCW planted with Schoenoplectus americanus showed water losses of around 25% for the both HRT evaluated, and its influence was not significant (α > 0.05) on the EC of the effluents. These results suggest that Schoenoplectus americanus would be an ideal candidate species for use in CW with subsurface flow in super-arid areas, with HRT varying between 3.5 d and 7 d.

Optimization denitrifying phosphorus removal at different hydraulic retention times in a novel anaerobic anoxic oxic-biological contact oxidation process

A modified two-sludge system consisting of AAO and BCO (Anaerobic anoxic oxic-biological contact oxidation) was developed. The unique advantage was the high efficient utilization of influent carbon sources in AAO reactor with NO3−-N produced in BCO reactor, which achieved the simultaneous removal of both nitrogen and phosphorus. With real municipal wastewater at low carbon/nitrogen ratio (COD/TN=3.50), the influence of hydraulic retention time (HRT=6 –12h) in the AAO reactor on denitrifying phosphorus removal was observed. The mass balance analysis demonstrated that the system saved about 30–35% carbon sources compared with traditional biological nutrient removal (BNR) systems. HRT of 10h was found to be optimal for denitrifying phosphorous removal due to the limitation of poly-β-hydroxyalkanoates (PHA) utilization and denitrification capacity (NO3−-N/PO43−-P ratio). It was also determined that the NO3−-N concentration of the middle settler should be kept around 1.50–2.50mg/L to prevent secondary phosphorus release. Finally, anoxic duration and NO3−-N loading were the major limiting factors for denitrifying phosphorus accumulation organisms (DNPAOs) growth.

Influence of Hydraulic Retention Time, Sludge Retention Time, and Ozonation on the Removal of Free and Conjugated Estrogens in Japanese Activated Sludge Treatment Plants

This study describes the occurrence, fate,and removal of free estrogens (estrone (E1), 17β‐estradiol (E2), estriol (E3), 17α‐ethynylestradiol (EE2)) and their glucuronide and sulfate conjugates (estrone‐3‐sulphate (E1‐3S), 17β‐estradiol‐3‐sulfate (E2‐3S), estriol‐3‐sulfate (E3‐3S), estrone‐3‐glucuronide (E1‐3G), 17β‐estradiol‐3‐glucuronide (E2‐3G), and estriol‐3‐glucuronide (E3‐3G)) in 12 sewage treatment plants in Japan. Glucuronide conjugates were only rarely detected in sewage influents and entirely eliminated within the treatment plants. E1 was found at 69 ng/L, E2 at 108 ng/L, E1‐3S at 18 ng/L, and E2‐3S at 78 ng/L in the sewage influents. The average removal efficiency for E1, E2, and sulfate conjugates was 88, 92, and 93%, respectively, following activated sludge treatment. The removal of E1 and E2 was improved with increasing the sludge retention time (SRT), with the highest removal typically found from 12 days SRT onward. The removal of sulfate conjugates was also related to SRT with highest removals found from eight days SRT onward. No correlation was found between the hydraulic retention time and the removal of any of the estrogens. The ozone dosage of 4–7 mg/L reduced E3 and E2‐3S and E3‐3S to below detection levels. Overall ozonation reduced the estrogenicity of the effluents as expressed as estradiol equivalents from 8.4 to 0.7 ng/L. The results suggest adequate river basin management of estrogens in Japan could be accomplished by a mixture of activated sludge plants with long SRT and where necessary, the addition of tertiary ozonation.

Isolation and Characterization of an Erythromycin-Degrading Strain and Application for Bioaugmentation in a Biological Aerated Filter

An erythromycin-degrading bacterium was isolated from the activated sludge of a sewage treatment plant (STP). Based on the morphological and physiological characteristics, the isolated strain was identified and named as Pseudomonas sp. ERY-E. In an inorganic salt medium inoculated at 1 % (v/v) of ERY-E strain containing 50 mg/L of erythromycin (ERY), the removal efficiency of ERY as high as 83.7 % was obtained under the optimum conditions with temperature of 30 °C, pH of 7.0, and 10 mg/L of yeast as the external carbon source. Subsequently, the ERY-E strain was used for bioaugmenting a biological aerated filter (BAF) to treat surface water containing low-concentration ERY. The influence of hydraulic retention time (HRT) and air-liquid ratio (A/L) on the performance of BAF was investigated. The average removal efficiencies of ERY and permanganate index (CODMn) were about 60.6 and 26.1 % in bioaugmented system (BAF2) and 26.9 and 26.0 % in unbioaugmented system (BAF1), respectively, under the optimum conditions with HRT of 4.0 h and A/L of 4:1 at steady state. Due to the stable removal of CODMn in BAF2 as compared with BAF1, it can be concluded that the introduction of ERY-E strain could collaborate with the indigenous microorganisms to attain a better ERY removal efficiency. As a result, the bioaugmented BAF method can be considered as an alternative technology for the treatment of surface water containing low-concentration emerging pollutants.

Comparative research on phosphorus removal by pilot-scale vertical flow constructed wetlands using steel slag and modified steel slag as substrates.

This research mainly focused on the phosphorus removal performance of pilot-scale vertical flow constructed wetlands with steel slag (SS) and modified steel slag (MSS). First, bench-scale experiments were conducted to evaluate the phosphorus adsorption capacity. Results showed that the Langmuir model could better describe the adsorption characteristics of the two materials; the maximum adsorption of MSS reached 12.7 mg/g, increasing by 34% compared to SS (9.5 mg/g). Moreover, pilot-scale constructed wetlands with SS and MSS were set up outdoors. Then, the influence of hydraulic retention time (HRT) and phosphorus concentration in phosphorus removal for two wetlands were investigated. Results revealed that better performance of the two systems could be achieved with an HRT of 2 d and phosphorus concentration in the range of 3-4.5 mg/L; the system with MSS had a better removal efficiency than the one with SS in the same control operation. Finally, the study implied that MSS could be used as a promising substrate for wetlands to treat wastewater with a high phosphorus concentration. However, considering energy consumption, SS could be regarded as a better alternative for substrate when treating sewage with a low phosphorus concentration.

Denitrification in biofilm configured horizontal flow woodchip bioreactor: effect of hydraulic retention time and biomass growth

Removal of nitrates and nitrogen (NO3−-N) from surface and groundwater was a matter of special importance, and there was a need for sustaining the public health problems and aquatic life related to the presence of NO3−-N in drinking water supplies. The influence of hydraulic retention time (HRT), volumetric loading rates (VLRs) and temperature on denitrification were investigated in a biofilm configured woodchip bioreactor (WBR) from synthetic tile water. Three HRTs were examined, ranging from 4 to 12h. The denitrification removal efficiency (RE) >99% was obtained in WBR operated at 8-h HRT. The WBR was operated with VLR ranging from 49 to 198g NO3−-N/L/day for denitrification study. The maximum load reduction of the WBR showed 99% in second level of reactor operation with biomass concentration of 12.3g/L. The pH (6.5–7.2) and temperature (17–20°C) under the unique study profoundly impact on denitrification. The coefficient factors of 0.8 and 1.05 have been reported in studies with a temperature change from 4 to 20°C. Scanning electron microscope (SEM) analysis documented formation of biofilm on woodchips in each level of reactor operation study. Therefore we recommend from this study, that the horizontal flow based WBR to enhance denitrification while minimizing higher operating conditions in denitrification beds.

Bio-entrapped membrane reactor and salt marsh sediment membrane bioreactor for the treatment of pharmaceutical wastewater: Treatment performance and microbial communities

In this study, a bio-entrapped membrane reactor (BEMR) and a salt marsh sediment membrane bioreactor (SMSMBR) were evaluated to study the organic treatment performance of pharmaceutical wastewater. The influences of hydraulic retention time (HRT) and salinity were also studied. The conventional biomass in the BEMR cannot tolerate well of the hypersaline conditions, resulting in total chemical oxygen demand (TCOD) removal efficiency of 54.2–68.0%. On the other hand, microorganisms in the SMSMBR, which was seeded from coastal shore, strived and was able to degrade the complex organic in the presence of salt effectively, achieving 74.7–90.9% of TCOD removal efficiencies. Marine microorganisms able to degrade recalcitrant compounds and utilize hydrocarbon compounds were found in the SMSMBR, which resulted in higher organic removal efficiency than the BEMR. However, specific nitrifying activity decreased and inhibited due to the saline effect that led to poor ammonia nitrogen removal.

Simultaneous electricity generation and pollutant removal in microbial fuel cell with denitrifying biocathode over nitrite

The influences of hydraulic retention time, temperature and free buffer on the performance of short-cut denitrifying microbial fuel cell were investigated after it was successfully started up using nitrite as the cathodic electron acceptor. The results revealed that a power density of 8.3±0.5Wm−3NC was obtained after 15days operation. The desirable hydraulic retention time was found in this study to be 8h, with a COD removal rate of 2.117±0.006kgm−3NCd−1 and a total nitrogen removal rate of 0.041±0.002kgm−3NCd−1, respectively. It demonstrated that temperature had different effects on the electricity generation and pollutant removal performance of microbial fuel cell. The suitable temperature for power generation and pollutant removal was found to be 20°C and 25°C, respectively. Free buffer led to 50% decrease of both total nitrogen removal rate and power density of microbial fuel cell compared to that with phosphate buffer solution addition. The optimal total nitrogen removal rate obtained in the case with sodium azide addition (0.075±0.008kgm−3NCd−1) increased by 50% as compared to that without sodium azide addition. It suggested that abolishing oxygen or inhibiting nitrite oxidizing bacteria would favor nitrogen removal.

Characteristics and performance of aerobic granular sludge treating rubber wastewater at different hydraulic retention time

The influence of hydraulic retention time (HRT, 24, 12, and 6h) on the physical characteristics of granules and performance of a sequencing batch reactor (SBR) treating rubber wastewater was investigated. Results showed larger granular sludge formation at HRT of 6h with a mean size of 2.0±0.1mm, sludge volume index of 20.1mLg(-1), settling velocity of 61mh(-1), density of 78.2gL(-1) and integrity coefficient of 9.54. Scanning electron microscope analyses revealed different morphology of microorganisms and structural features of granules when operated at various HRT. The results also demonstrated that up to 98.4% COD reduction was achieved when the reactor was operated at low HRT (6h). Around 92.7% and 89.5% removal efficiency was noted for ammonia and total nitrogen in the granular SBR system during the treatment of rubber wastewater.

Influence of hydraulic retention time on partial nitrification of continuous-flow aerobic granular-sludge reactor

This study investigated the effects of hydraulic retention time (HRT) at 12 h, 7.2 h and 2.4 h on partial nitrification efficiency of continuous-flow aerobic granular reactors (CFAGRs) with mature aerobic granules (500±20 mg l−1). At HRT 12 h and 7.2 h, the removal efficiency of both ammonia–nitrogen (NH 4+−N) and nitrite accumulation rate were exceeding 90%. At HRT 2.4 h, NH 4+−N removal efficiency was reduced but most of the conversion efficiency to nitrite was only slightly reduced. At HRT<2.4 h, washout of aerobic granules occurred. In all tests conducted herein, the chemical oxygen demand removal efficiencies exceeded 90%. The clone library results noted the presence of ammonia-oxidizing bacteria belonged to β -Proteobacteria subclass, including 94% of Nitrosomonas europaea and 6% of Nitrosomonas sp. The polymerase chain reaction and denaturing gradient gel electrophoresis results suggested that Alpha proteobacterium, Pseudoxanthomonas mexicana strain, Sphaerotilus natans and Uncultured gamma proteobacterium were responsible for the aerobic granular stability and processing performance. The present CFAGR successfully implemented continuous partial nitrification using aerobic granules at low HRT.

Study on Hydraulic Characteristics of Opposite Folded Plate Reactor

By using Chlorides (Cl-) as the tracer, the residence time distribution (RTD) method was applied to study the hydraulic characteristic influences of hydraulic retention time (HRT) on the opposite folded plate reactor and the plate baffle reactor under the condition of steady operation of both clear and sludge water. Under the condition of the same HRT, dead zone of opposite folded plate reactor was less than the one of flat plate reactor.

Influence of hydraulic retention time on heterotrophic biomass in a wastewater moving bed membrane bioreactor treatment plant

Wastewater treatment using moving bed membrane bioreactor technology was tested with real urban wastewater at a pilot plant, combining moving bed treatment as a biological process with hybrid biomass (suspended and fixed) and the advantages of a membrane separation system. The evolution of the kinetic constants of the hybrid biomass and organic matter removal were studied in a pilot plant under different operational conditions, by varying hydraulic retention time (HRT), mixed liquor suspended solids (MLSS) and temperature, and considering the attached biomass of the carrier and the dispersed biomass of the flocs to reproduce real treatment conditions. The rates of organic matter removal were 97.73 ± 0.81 % of biochemical oxygen demand (BOD5), 93.44 ± 2.13 % of chemical oxygen demand (COD), 94.41 ± 2.26 % of BOD5 and 87.62 ± 2.47 % of COD using 24.00 ± 0.39 and 10.00 ± 0.07 h of HRT, respectively. The influence of the environmental variables and operational conditions on kinetic constants was studied; it was determined that the most influential variable for the decay coefficient for heterotrophic biomass was HRT (0.34 ± 0.14 and 0.31 ± 0.10 days−1 with 10.00 ± 0.07 and 24.00 ± 0.39 h of HRT, respectively), while for heterotrophic biomass yield, this was temperature (0.61 ± 0.04 and 0.52 ± 0.06 with 10.00 ± 0.07 and 24.00 ± 0.39 h of HRT, respectively). The results show that introducing carriers in an MBR system provides similar results for organic matter removal, but with a lower concentration of MLSS.

Effect of cultivated species and retention time on the performance of constructed wetlands

This study aimed to evaluate the influence of hydraulic retention time (HRT) and cultivated species in vertical-flow constructed wetlands (CW) on the removal of pollutants found in swine wastewater. The applied organic loading per unit area was 20 g m−2 d−1 of COD in nine cylindrical CW planted with Cyperus sp., Heliconia rostrata and Hedychium coronarium, and three controls containing only gravel. The HRT tested were 24, 48, 72 and 96 h. The following parameters of the CW influent and effluent were analysed: pH, ORP, turbidity, alkalinity, COD, TN, TKN, NHx, , TP, K and Na. Statistical analysis was performed at a 1% level of probability according to the Tukey test. It was noted that the greatest reductions were observed when CW were operated at higher HRT. TKN removals were 1.3 times greater than in unplanted CW. The best combination was CW planted with Cyperus sp. operating with a 72 h HRT, presenting the highest average mass removals with values of 69.1% (COD), 56.5% (TKN), 61.7% (NHx), 64.3% (TP) and 55.0% (K).

Performance study of vertical flow constructed wetlands for phosphorus removal with water quenched slag as a substrate

Two pilot-scale vertical flow constructed wetlands (VFCW) were designed, with one system containing water quenched slag (WQS) from a steel plant as a substrate and the other one as a control without WQS. Each VFCW consisted of a down-flow unit and an up-flow unit. Both of the VFCWs were planted with Canna indica Linn. This study focused on evaluation of the ability to remove phosphorus (P) for both VFCWs. Batch P adsorption and desorption tests were conducted. The influence of hydraulic retention time (HRT) and phosphorus loadings on phosphorus removal were investigated. Results showed that the WQS had much higher P adsorption capacity than gravel. The amounts of phosphorus adsorbed on the WQS were 0.17g/kg and 0.05g/kg for the down-flow and up-flow units, respectively, and were 0.09g/kg and 0.025g/kg on the corresponding gravel, respectively. Dates from the adsorption experiment were fitted to both Freundlich and Langmuir adsorption isotherm equations. Desorption test demonstrated that the adsorption of phosphorus to the WQS was not a reversible process. An HRT of 1d, which favored the VFCW system operation, was proposed. More than 80% of phosphorus removal was achieved for the VFCW with WQS when phosphorus loadings were in the range of 12.2–36.8g/m2d. The down-flow and up-flow units of the wetland system ensured sequential and efficient removal of phosphorus from wastewater, and also easy and flexible replacement of the WQS substrate in case of saturation. The WQS used in this study can be a promising substrate for the VFCW for improving phosphorus removal.

Performance of Granular Media from Blast Furnace Slag on Beer Wastewater Treatment

In order to improve utilization ratio of blast furnace slag (BFS), the study used BFS, cement and building glue to make blast-furnace-slag granular media (BGM) in a non-sintered process. The characterization of BGM was analyzed by physical method, scanning electron microscopy (SEM) and D/max-rA X-ray diffraction (XRD). And the influence of hydraulic retention time (HRT) and air-liquid ratio (A/L) on the removal of average chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) were also investigated. The results indicated that the BGM presented high total porosity, large total surface area and low bulk and apparent density. The BGM reactor showed the good removal efficiency on COD and NH4+-N with HRT of 6 h and A/L of 5:1, which were above 86% and 90%, respectively. Overall, BGM showed good performance as wastewater treatment filter media in biological aerated filters (BAF), whose application is a promising way to use waste blast furnace slag.

Effect of hydraulic retention time on biohydrogen and volatile fatty acids production during acidogenic digestion of dephenolized olive mill wastewaters

The influence of Hydraulic Retention Time (HRT) on the performances of a recently developed biotechnological anaerobic acidogenic process fed with dephenolized Olive Mill Wastewater (OMW) was investigated. The study was carried out under mesophilic conditions in Packed Bed Biofilm Reactors (PBBRs), filled with ceramic cubes and inoculated with a characterized and acclimated acidogenic microbial consortium. The PBBRs were fed with a HRT of 7, 5, 3 or 1 day, which corresponded to Organic Loading Rates (OLRs) of about 5.5, 7.8, 12.9 and 38.8 g L−1 d−1, respectively. A significant production of a H2-rich biogas was observed when shorter HRTs were applied: in particular, H2 relative amount and productivity increased from 3% to 32% and from 0.20 to 6.10 dm3 m−3 h−1, respectively, by decreasing the HRT from 7 to 1 day. On the contrary, shorter HRTs turned into a lower accumulation of Volatile Fatty Acids (VFAs), whose highest amounts were found with HRTs of 7 and 5 days (about 18.4 and 19.7 g L−1 COD equivalents, respectively). The highest conversion yield of COD into VFAs (36%) was obtained with a HRT of 5 days, when VFAs represented about 78% of the effluent COD. HRT also influenced the composition of the VFA mixture: acetic, propionic and butyric acid were the most prominent VFAs, being their relative amounts higher when PBBRs were operated with shorter HRTs (up to 19, 12 and 42% of the whole mixture, respectively, when HRT was 1 day).