Effect Of Hydraulic Residence Time Research Articles

Dark fermentative hydrogen gas production from waste peach pulp by intermittent feeding: Effects of hydraulic residence time and substrate loading rate

Peach has a big share of the world fruit market, with significant annual waste production. This study reports dark fermentative hydrogen gas production from waste peach pulp using intermittent feeding. In this context, the effects of hydraulic residence time (HRT) and substrate loading rate (SLR) on hydrogen production were determined in two sets of experiments. All experiments were performed in 310 mL serum bottles. During the first set of experiments, HRT was varied between 1 and 6 days and hydrogen production was more favorable at short HRTs. In the second set of experiments, SLR was varied between 9 and 90 gTOC/L.d, and more efficient hydrogen formation was observed by increasing the SLR. The most convenient HRT and SLR resulting in maximum hydrogen formation rate (931.8 mLH2/L.d) was obtained at 1 day and 90 gTOC/L.d, respectively.

Effect of Hydraulic Residence Time on Removal Efficiency of Pollutants in Subsurface Flow Constructed Wetlands and Analysis of Denitrification Mechanism

This study used vertical and horizontal subsurface constructed wetlands with continuous inflow, to compare and analyze the effects of four hydraulic residence times on the removal efficiency of conventional pollutants. Using the optimal hydraulic retention time, the two types of wetlands were examined in terms of the stromal layer nitrification, denitrification, and ammonia oxidation abundance of functional genes, as well as the intensity of nitrification and denitrification. In addition, redundancy analysis and variance decomposition analysis were used to determine the main factors affecting nitrogen removal in the two kinds of wetlands, so that targeted improvement measures can be suggested. The best removal efficiency of conventional pollutants (COD, TP, TN, and NH4+-N) was achieved with a hydraulic retention time of 24 h, resulting in a removal rate of more than 70%. With a 24 h retention time, the removal rate of NH4+-N and TN and the intensity of nitrification and denitrification exhibited a gradually decreasing trend along the flow direction. Among the three functional genes, the abundance of denitrification functional genes (nirS) was much higher than that of nitrification functional genes (nxrA) and ammonia oxidation functional genes (AOB-amoA). In this study, the nitrogen removal ability of the two subsurface flow constructed wetlands was jointly affected by environmental factors and microbial factors, among which microbial factors contributed the most to nitrogen removal (55% and 48%). In addition, the removal rates of TN and NH4+-N were proportional to DO, specific surface area of substrate, COD concentration, as well as nitrification and denitrification functional genes, but inversely proportional to pH. Therefore, in order to improve the nitrogen removal efficiency of both systems, the amount of dissolved oxygen and carbon sources in the substrate layer should be increased, while the pH value should be appropriately reduced. Moreover, the horizontal subsurface constructed wetland significantly improves the nitrogen removal efficiency of the system, as the substrate layer has a larger specific surface area. This study provides a theoretical basis for the design of constructed wetlands and the selection of an optimal hydraulic residence time. Quantitative analysis of nitrogen removal pathways is of great significance for understanding the nitrogen removal mechanism and improving the nitrogen removal rate in constructed wetlands.

Relationship between microbial community structures and degradation efficiencies in biological contact process on domestic sewage

In order to ascertain the characteristics of two different biofilm reactors and its efficiency, the influence of pH, DO and HRT in the clean-up of COD, NH3-N and TP as well as determining the relationship between microbial community structures and its performance of the two biofilm reactors. This study made use of a biological contact oxidation process system in a small-scale experiment to treat domestic sewage. This contemporary study examined the performance of two different fillers thus, BCF and MBBF in removal of organic pollutants from domestic wastewater as a novel technique of BCOP for sewage treatment. Two self-made biological contact biofilm reactors were used for the experiment: BCR (mounted with BCF) and MBBR (mounted with MBBF). After the biological treatment, the COD concentration of effluent could stay below 350 mg/L. The study analyzed the effects of hydraulic residence time (HRT) on COD, ammonia nitrogen (NH3-N), and total phosphorus (TP) as well as the characteristics of each biofilm filler. The optimal HRT was 12 h; at that time, the experimental results indicated that BCF had higher removal efficiency of chemical oxygen demand, ammonia-nitrogen and total phosphorus at 50%, 96%, and 86%, respectively. Great contribution was made by the process by means of improving the biodegradability of domestic sewage and reducing sludge emergence via fermentation in the biological reactor.

Performance evaluation of horizontal flow constructed wetlands as primary and secondary treatment for university campus wastewater

Horizontal flow constructed wetland (HFCW) is an attractive green technology for wastewater treatment. In the present study, four laboratory-scale HFCWs were constructed to serve as the primary and secondary treatment of university campus wastewater. The effect of hydraulic residence time (HRT) and pre-aeration of influent were investigated. The experimental results demonstrated that the wetland vegetation played an important role in the oxygen restoration and the influence of pre-aeration was minor. In the primary treatment, effective removals of TSS and NH4-N were observed. However, the treatment of BOD and NO3-N were insignificant due to the low influent concentrations. As for secondary treatment, the HFCWs effectively reduced the concentrations of BOD, NH4-N, and NO3-N in the effluent from the Intermittent Decanted Extended Aeration (IDEA) plant. The effluent quality of all HFCWs complied with the Standard A sewage discharge. Longer HRTs brought a positive effect to the removals of organic matter and nitrogen.

Effect of hydraulic residence time on biological sulphate reduction and elemental sulphur recovery in a single-stage hybrid linear flow channel reactor

Biological sulphate reduction and partial sulphide oxidation, occurring simultaneously within the hybrid linear flow channel reactor (LFCR) were evaluated, under controlled conditions at laboratory scale, as a function of hydraulic residence time (HRT) using a synthetic media containing 1 g/L sulphate. The hybrid LFCR comprises a rectangular channel containing carbon microfibers as a support matrix for attachment of sulphate-reducing bacteria and an exposed air-liquid interface to facilitate the formation of a floating sulphur biofilm. Exposure to decreasing HRT, from 3 days to 12 h, resulted in an increase in the volumetric sulphate reduction rate (0.14 to 0.63 mmol/L.h), achieving levels typically associated with active reactors. Sulphate conversion was highest (97 %) at a 3 day HRT, decreasing to 73 % at 12 h. The highest sulphide removal efficiency (82 %) and accompanying sulphur recovery through harvesting of the floating sulphur biofilm (FSB) was observed at a 2 day HRT. The sulphur fraction not recovered through the biofilm was predominantly released within the effluent as colloidal elemental sulphur and fragments of the sulphur-rich biofilm, with minimal re-oxidation to sulphate occurring in the reactor. The hybrid LFCR technology was able to achieve high rates of sulphate reduction and effective sulphide removal within a single, semi-passive reactor unit.

Neutral or acidic pH for the removal of contaminants of emerging concern in wastewater by solar photo-Fenton? A techno-economic assessment of continuous raceway pond reactors

As far as the authors know, no in-depth comparison has been made between the different performances of the solar photo-Fenton process for the removal of contaminants of emerging concern (CECs) as a function of pH. To this end, real WWTP secondary effluents were treated in continuous flow mode at pilot plant scale. The effect of hydraulic residence time (HRT), liquid depth and percentage of CEC removal on treatment capacity was studied. At acidic pH (2.8), the iron source was FeSO4 and at neutral pH (7.0), it was Fe(III)-EDDS. At both pH values, 2250 L m−2 d−1 can be treated in 15-cm deep raceway pond reactors at 30 min HRT with 0.1 mM iron and 0.88 mM H2O2 in order to achieve 80% CEC removal. Treatment costs were 0.25 € m−3 and 0.56 € m−3 at acidic and neutral pH, respectively. This study paves the way for the solar photo-Fenton process to be employed on a commercial scale.

Effect of hydraulic residence time and inlet flow distribution ratio on the pollutant removal of low‐temperature municipal wastewater in multistage AO process

AbstractLow temperature environment was one of the difficulties in sewage treatment. In this study, the removal efficiency of multistage AO process was analysed under different hydraulic residence time (12 h, 8 h and 6 h) and inlet flow distribution ratio(5 : 4 : 4, 3 : 2 : 1 and 25 : 15 : 6), the rules of pollutant migration and transformation were compared and analysed under different control parameters. The results show that enhanced nitrogen removal and optimised organics utilisation were obtained simultaneously in the feeding process with hydraulic retention time of 8 h as well as influent distribution ratio of 3 : 2 : 1. HRT and inlet flow distribution ratio affect nitrogen load and organic matter distribution in each stage of the multistage AO system, the removal efficiency of ammonia nitrogen in each stage of the system was more than 80% under optimal conditions, the total nitrogen removal rate was more than 80%, among which the synchronous nitrification and denitrification account for 29.50%.

Performance and microbial community of a novel combined anaerobic bioreactor integrating anaerobic baffling and anaerobic filtration process for low-strength rural wastewater treatment

A novel combined bioreactor integrating anaerobic baffling and anaerobic filtration process was developed and operated for 210days to treat low-strength rural wastewater. The effects of hydraulic residence time (HRT) and organic loading rate (OLR) on chemical oxygen demand (COD) removal and methane (CH4) production of the combined bioreactor were investigated. The combined bioreactor can start up successfully in 25days and achieve enhanced performance. The COD removal rate and CH4 yield were influenced significantly by HRT and OLR. The influent COD was removed effectively through the synergistic effects of the anaerobic baffling and anaerobic filtration. The baffle zone played the main role in the degradation of the pollutants, and the filter zone mainly contributed to improve the resistance to shock loading. High-throughput sequencing technology was used to analyze the bacterial and archaeal community structure and diversity. Clostridium_sensu_stricto, Longilinea, Acetoanaerobium, Arcobacter, and Acinetobacter were found to be the dominant bacteria. While Methanothrix and Methanoregula were the dominant archaea, which were responsible for methane generation. This study not only highlights the good energy recovery and resource utilization potential of the combined bioreactor but also presents significant guidance for the application of the combined anaerobic process for low-strength rural wastewater treatment.

Performance and microbial community of simultaneous removal of NO3−-N, Cd2+ and Ca2+ in MBBR

A moving-bed biofilm reactor (MBBR) containing immobilized Acinetobacter sp.CN86 was operated to investigate the simultaneous denitrification, bio-mineralization and cadmium removal performance. Effects of hydraulic residence time (HRT) (4 h, 6 h and 8 h), pH (6.0, 7.0 and 8.0) and influent Cd2+ concentrations (10 mg/L, 30 mg/L and 50 mg/L) were assessed on the simultaneous removal of nitrate, Cd2+ and Ca2+. Results indicate that the highest pollutant removal efficiency (98.33% (1.866 mg/L·h) for NO3−-N; 99.36% (1.242 mg/L·h) for Cd2+; 68.80% (15.480 mg/L·h) for Ca2+) was achieved under the conditions of a hydraulic residence time of 8 h, pH of 7.0 and initial Cd2+ concentration of 10 mg/L. Analyses of microbial distribution and community structures showed that Acinetobacter sp.CN86 was the main contributor (occupy 15.3% at the species level) to the effective removal of multiple pollutants in the MBBR. In addition, the main gas and precipitation components in the biofilm reactor were identified by gas chromatography, scanning electron microscope, and X-ray diffraction analyses.

Maximisation of the organic load rate and minimisation of oxygen consumption in aerobic biological wastewater treatment processes by manipulation of the hydraulic and solids residence time

A systematic experimental study of the effect of hydraulic residence time (HRT) and solids residence time (SRT) on conventional suspended-growth biological wastewater treatment processes was carried out. The aim of this study was to identify the conditions that minimise the reactor volume, i.e. maximise the organic load rate (OLR), and minimise the oxygen consumption. Lab-scale sequencing batch reactors (SBRs) were operated with glucose or ethanol as only carbon sources, with HRT in the range 0.25–4 day and SRT in the range 1–71 day. The highest OLR values which gave satisfactory performance were 4.28 and 4.14 gCOD/l.day for glucose and ethanol, respectively, which are among the highest reported for conventional aerobic suspended-growth processes. The highest OLR values were obtained with HRT = 0.25 day, SRT = 3.1 day for glucose and HRT = 0.5 day, SRT = 4.9 day for ethanol. The minimum oxygen consumption was 0.36 and 0.69 kg O2/kg COD removed for glucose and ethanol, respectively. In disagreement with conventional theories, it was found that biomass production also depended on the OLR as well as on the SRT, higher OLRs giving lower biomass production for the same SRT. From the kinetic analysis of the experimental data, this behaviour, which has important consequences for the design of biological wastewater treatment processes, was explained with a higher rate of endogenous metabolism at higher OLRs.

Multi-Level Contact Oxidation Process Performance When Treating Automobile Painting Wastewater: Pollutant Removal Efficiency and Microbial Community Structures

This study applied a multi-level contact oxidation process system in a pilot-scale experiment to treat automobile painting wastewater. The experimental wastewater had been pre-treated through a series of physicochemical methods, but the water still contained a high concentration of chemical oxygen demand (COD) and had poor biodegradability. After the biological treatment, the COD concentration of effluent could stay below 300 mg/L. The study analyzed the effects of hydraulic residence time (HRT) on COD, ammonia nitrogen (NH4+-N), and total nitrogen (TN). The optimal HRT was 8 h; at that time, removal efficiencies of COD, ammonia nitrogen, and total nitrogen were 83.8%, 86.3%, and 65%, respectively. The system also greatly reduced excess sludge production; the removal efficiency was 82.8% with a HRT of 8 h. The study applied high-throughput pyrosequencing technology to evaluate the microbial diversity and community structures in distinct stages of the biological reactor. The relevance between process performance and microbial community structure was analyzed at the phylum and class level. The abundant Firmicutes made a large contribution to improving the biodegradability of painting wastewater through hydrolysis acidification and reducing sludge production through fermentation in the biological reactor.

Electricity production from Azo dye wastewater using a microbial fuel cell coupled constructed wetland operating under different operating conditions

Microbial fuel cells (MFCs) have got tremendous attention for their capability to enhance the degradation of some recalcitrant pollutants and simultaneous electricity production. A microbial fuel cell coupled constructed wetland (CW-MFC) is a new device to treat the wastewater and produce energy which has more wastewater treatment volume and more easily to maintenance than others MFCs. The studies on the performance of CW-MFCs are necessary. In this work, the effects of hydraulic residence time (HRT), reactive brilliant red X-3B (ABRX3) proportion and COD concentration on the electricity production of CW-MFC and the degradation characteristics of ABRX3 were investigated. The decolorization rate and the electricity production increased to a peak before slowing down with the elongation of HRT. The highest decolorization rate and electricity production were obtained when HRT was 3 days. The ABRX3 proportion (calculated as COD) in the wastewater played an important role in decolorization and electricity production, which may influence the distribution of electrons in the system. The power density of CW-MFC and the decolorization rate decreased concomitantly with an increasing ABRX3 proportion. The COD concentration influenced the CW-MFC performance slightly. The highest decolorization rate and power density reached 95.6% and 0.852W/m3, respectively, when the COD concentration was 300mg/L while the ABRX3 proportion was 30%. The coulombic efficiency of the CW-MFC depended on glucose and ABRX3 proportions in the wastewater. ABRX3 acquired more electrons than the anode. Further investigations are needed to optimize CW-MFC performance and explain the mechanism of biorefractory compounds degradation and electron motion in CW-MFCs.

Evaluation of a MBR pilot treating industrial wastewater with a high COD/N ratio

BACKGROUND In this study the performance of a membrane bioreactor (MBR) pilot plant treating industrial wastewater at the Heraklion Industrial Park, at three different sludge retention times (SRTs), was investigated. Membrane fouling in the MBR was monitored through the transmembrane pressure build up and by measuring accumulation of extracellular polymeric substances (EPS) and soluble microbial products (SMP). The effect of hydraulic residence time (HRT) on effluent quality and membrane fouling was examined as well. RESULTS The highest removal efficiencies (COD, TN, P) of the order of 99.2%, 94.3% and 89.3%, respectively, as well as moderate formation of EPS and SMPs were observed at a SRT of 20 days. Changes in HRT had a small effect on carbon and ammonium removal, but a strong impact on denitrification and phosphate removal. Total EPS and SMP were higher at higher SRTs in contrast to reported common observations. However, the shorter SRT of 15 days led to a more rapid increase of TMP. CONCLUSION The system's performance regarding COD, TN and P removal was very good despite the high COD/N input ratio and the huge variations in influent quality. The observed membrane fouling behavior reflects the complexity of the biological process. © 2014 Society of Chemical Industry

Bio-hydrogen production from ground wheat starch by continuous combined fermentation using annular-hybrid bioreactor

Continuous combined fermentation of ground wheat starch was realized in an annular-hybrid bioreactor (AHB) for hydrogen gas production. A mixture of pure cultures of Clostridium beijerinkii (DSMZ-791) and Rhodobacter sphaeroides-RV were used as seed cultures in combined fermentation. The feed contained 5 g L −1 ground wheat with some nutrient supplementation. Effects of hydraulic residence time (HRT) on the rate and yield of hydrogen gas formation were investigated. Steady-state daily hydrogen production decreased but, hydrogen yield increased with increasing HRT. The highest hydrogen yield was 90 ml g −1 starch at HRT of 6 days. Hydrolysis of starch and fermentation of glucose to volatile fatty acids (VFA) were readily realized at all HRTs. However, slow conversion of VFAs to H 2 and CO 2 by photo-fermentation caused accumulation of VFAs in the medium. Specific and volumetric rates of hydrogen formation also decreased with increasing HRT. High hydrogen yields obtained at high HRTs are due to partial fermentation of VFAs by Rhodobacter sp. The system should be operated at HRTs longer than 5 days for effective hydrogen gas formation by the dark and photo-fermentation bacteria.

Effects of Temperature and Hydraulic Residence Time (HRT) on Treatment of Dilute Wastewater in a Carrier Anaerobic Baffled Reactor

To examine the effect of hydraulic residence time (HRT) on the performance and stability, to treat dilute wastewater at different operational temperatures in a carrier anaerobic baffled reactor (CABR), and hence to gain a deeper insight into microbial responses to hydraulic shocks on the base of the relationships among macroscopic performance, catabolic intermediate, and microcosmic alternation. COD, VFAs, and microbial activity were detected with constant feed strength (300 mg/L) at different HRTs (9-18 h) and temperatures (10 degrees C-28 degrees C) in a CABR. The removal efficiencies declined with the decreases of HRTs and temperatures. However, the COD removal load was still higher at short HRT than at long HRT. Devastating reactor performance happened at temperature of 10 degrees C and at HRT of 9 h. HRTs had effect on the VFAs in the reactor slightly both at high and low temperatures, but the reasons differed from each other. Microbial activity was sensitive to indicate changes of environmental and operational parameters in the reactor. The CABR offers to certain extent an application to treat dilute wastewater under a hydraulic-shock at temperatures from 10 degrees C to 28 degrees C.

Effect of temperature, hydraulic residence time and elevated [formula omitted] on acid neutralization within a pulsed limestone bed reactor

Limestone has potential for reducing reagent costs and sludge volume associated with treatment of acid mine drainage, but its use is restricted by slow dissolution rates and the deposition of Fe, Al and Mn-based hydrolysis products on reactive surfaces. We evaluated a pulsed limestone bed (PLB) reactor (15 L/min capacity) that uses a CO 2 pretreatment step to accelerate dissolution and hydraulic shearing forces provided by intermittent fluidization to abrade and carry away surface scales. We established the effects of hydraulic residence time (HRT, 5.1–15.9 min), temperature ( T, 12–22 °C) and CO 2 tension ( P CO 2 , 34.5–206.8 kPa) on effluent quality when inlet acidity (Acy) was fixed at 440 mg/L (pH=2.48) with H 2SO 4. The PLB reactor neutralized all H + acidity ( N=80) while concurrently providing unusually high levels of effluent alkalinity (247–1028 mg/L as CaCO 3) that allow for side-stream treatment with blending. Alkalinity (Alk) yields rose with increases in P CO 2 , HRT and settled bed height (BH, cm) and decreased with T following the relationship ( R 2=0.926; p<0.001): (Alk) non-filtered=−548.726+33.571·( P CO 2 ) 0.5+33.671·(HRT)+7.734·(BH)−5.197·( T). Numerical modeling showed CO 2 feed requirements for a target Alk yield decrease with increases in HRT, T and the efficiency of off-gas (CO 2) recycling.

Continuous ethanol fermentation of cheese whey powder solution: effects of hydraulic residence time

Continuous ethanol fermentation of cheese whey powder solution was realized using pure culture of Kluyveromyces marxianus (DSMZ 7239) at hydraulic residence times (HRT) between 12.5 and 60 h. Sugar utilization, ethanol and biomass formation were investigated as functions of HRT. Effluent sugar concentration decreased, but percent sugar utilization, ethanol and biomass concentrations increased with HRT. Ethanol productivity was maximum (0.745 gE l(-1)h(-1)) at an HRT of 43.2 h where the biomass productivity was almost minimum (0.18 gX l(-1) h(-1)). The ethanol yield coefficient was almost constant at 0.4 gE g(-1)S up to HRT of 43.2 h and the growth yield coefficient was minimum at HRT of 43.2 h. Kinetic models were developed and the constants were determined by using the experimental data.

Performance of a hybrid-loop bioreactor system in biological treatment of 2,4,6-tri-chlorophenol containing synthetic wastewater: Effects of hydraulic residence time

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with effluent recycle was used for biological treatment of 2,4,6-tri-chlorophenol (TCP) containing synthetic wastewater. Effects of hydraulic residence time (HRT) on COD, TCP and toxicity removal performance of the reactor were investigated for the HRT values between 5 and 30 h, while the feed COD (2700 ± 100 mg l −1), TCP (300 ± 10 mg l −1) and the solids retention time (sludge age, SRT, 20 d) were constant. Percent TCP, COD and toxicity removals increased with increasing HRT resulting in more than 90% COD, TCP and toxicity removals at HRT values above 25 h. Biomass concentrations in the packed column and in the aeration tank increased with increasing HRT resulting in low reactor TCP concentrations and therefore high TCP, COD and toxicity removals at high HRT values. Volumetric and specific rates of TCP and COD removals decreased with increasing HRT due to increased biomass and decreased flow rates at high HRT levels. Volumetric and specific removal rates of COD and TCP were maximum at an HRT of 5 h.

Copper(II) ion toxicity in activated sludge processes as function of operating parameters

Effects of hydraulic residence time (HRT) and the sludge age (solids retention time, SRT) on the performance of an activated sludge unit treating synthetic wastewater containing 14 mg l −1 Cu(II) ion were investigated. Percent COD removal increased with increasing sludge age for both Cu-free and Cu(II)-containing wastewater. However, percent COD removal was lower in the presence of Cu(II) due to Cu(II) ion toxicity on the microorganisms at all sludge ages. Cu(II) ion toxicity was eliminated at high sludge ages (30 days) due to high biomass concentrations. Percent toxicity removals and biomass concentrations increased, but the sludge volume index (SVI) decreased with increasing sludge age. Increases in hydraulic residence time also resulted in increases in percent COD and toxicity removals and also in biomass concentrations, but decreases in the sludge volume index (SVI) for both in the absence and presence of Cu(II) ions. Percent COD removals were much higher in the absence of Cu(II) ions for all HRT levels tested. Copper ion toxicity on COD removal performance of the activated sludge unit was partially eliminated by operation at high sludge ages (30 days) and HRTs (25 h).

Para-chlorophenol containing synthetic wastewater treatment in an activated sludge unit: Effects of hydraulic residence time

Due to the toxic nature of chlorophenol compounds present in some chemical industry effluents, biological treatment of such wastewaters is usually realized with low treatment efficiencies. Para-chlorophenol (4-chlorophenol, 4-CP) containing synthetic wastewater was treated in an activated sludge unit at different hydraulic residence times (HRT) varying between 5 and 30 h while the feed COD (2500 mg l −1), 4-CP (500 mg l −1) and sludge age (SRT, 10 days) were constant. Effects of HRT variations on COD, 4-CP, toxicity removals and on settling characteristics of the sludge were investigated. Percent COD removals increased and the effluent COD concentrations decreased when HRT increased from 5 to 15 h and remained almost constant for larger HRT levels. Nearly, 91% COD and 99% 4-CP removals were obtained at HRT levels above 15 h. Because of the highly concentrated microbial population at HRT levels of above 15 h, low effluent (reactor) 4-CP concentrations and almost complete toxicity removals were obtained. High biomass concentrations obtained at HRT levels above 15 h were due to low 4-CP contents in the aeration tank yielding negligible inhibition effects and low maintenance requirements. The sludge volume index (SVI) decreased with increasing HRT up to 15 h due to high biomass concentrations at high HRT levels resulting in well settling sludge with low SVI values. Hydraulic residence times above 15 h resulted in more than 90% COD and complete 4-CP and toxicity removals along with well settling sludge.