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Constructed wetlands (CWs) are a widely used technology for the treatment of wastewater, with Free Water Surface Constructed Wetlands (FWS CWs) being the simplest configuration. However, there is currently no consensus on the Hydraulic Retention Time (HRT) that optimizes P removal efficiency. To address this issue, this study conducted a bibliometric review of 85 scientific articles published between 1997 and 2021 that investigated the relationship between P removal and the HRT in FWS CWs. Scientometric maps were constructed to identify key topics, and bibliometric surveys were used to refine and explore the relationship between P removal and HRT. The analysis found a high correlation between P removal and HRT across all scales of the FWS CW systems, ranging from moderate to very strong. Specifically, the regressions between P removal efficiency and HRT were 73%, 70%, and 67% for lab-scale, pilot-scale, and real-scale systems, respectively. Overall, the FWS CWs demonstrated strong P removal efficiency, with removal rates reaching 95%, making them a promising technology for the tertiary treatment of effluents with a focus on nutrient removal and recovery. Future studies that focus on the many parameters of CW, especially on how macrophytes management affects the nutrient removal performance of these systems, are necessary to enrich our knowledge of CWs and optimize the application of this technology to wastewater treatment. [ABSTRACT FROM AUTHOR]

The Anaerobic Baffled Reactor (ABR) is an effective solution for landfill leachate treatment using an anaerobic fermentation process, which helps to reduce operating costs and sludge volume. To better understand the biological, chemical, and physical processes involved, especially when combining the ABR with an aerobic component, the study aimed to investigate the performance of an Anaerobic–Aerobic Hybrid Baffled Reactor (AABR) that includes an Anaerobic Filter (AF) for treating landfill leachate. This research utilized two glass reactors. The first reactor, designated as AABR-AF, consisted of six independent rectangular glass chambers arranged side by side. The third and sixth chamber designed for aerobic treatment and AF, respectively. The second reactor was used as a control reactor and did not include any aerobic chamber. The highest Removal Efficiencies (REs) for turbidity, COD, BOD, TP, TKN, nitrate, TOC, and TSS in the AABR-AF and ABR-AF were found to be (65.4% and 56.3%), (98.3% and 94.1%), (98.1% and 93.2%), (86.4% and 65%), (89.2% and 76.7%), (81.2% and 64.4%), (88.2% and 79.4%), and (72.4% and 68.5%), respectively. These optimal REs were achieved at an HRT of 48 h and an OLR of 10 kg/m3.d. Also, the highest and the lowest REs in Heavy Metals (HMs) were 89.57% for manganese in AABR-AF and 6.59% for nickel in ABR-AF, in an OLR of 10 kg/m3.d, respectively. The effective removal of Organic Matters (OMs) from landfill leachate using the AABR-AF and ABR-AF was found to be strongly influenced by HRT and OLR. The AABR-AF configuration, featuring a single aerobic chamber in the reactor, exhibited a higher efficiency in removing OMs compared to the ABR-AF configuration. [ABSTRACT FROM AUTHOR]

Photosynthetic microorganisms have a wide range of biotechnical applications, through the application of their versatile metabolisms. However, their use in industry has been extremely limited to date, partially because of the additional complexities associated with their cultivation in comparison to other organisms. Strategies and developments in photobioreactors (PBRs) designed for their culture and applications are needed to drive the field forward. One particular area which bears examination is the use of strategies to separate solid- and hydraulic-residence times (SRT and HRT), to facilitate flow-through systems and continuous processing. The aim of this review is to discuss the various types of PBRs and methods which are currently demonstrated in the literature and industry, with a focus on the separation of HRT and SRT. The use of an efficient method of biomass retention in a PBR may be advantageous as it unlocks the option for continuous operation, which may improve efficiency, and improve economic feasibility of large-scale implementation of photosynthetic biocatalysts, especially where biomass is not the primary product. Due to the underexplored nature of the separation of HRT and SRT in reactors using photosynthetic microorganisms, limited literature is available regarding their performance, efficiencies, and potential issues. This review first introduces an overview into photosynthetic microorganisms cultivated and commonly exploited for use in biotechnological applications, with reference to bioreactor considerations specific to each organism. Following this, the existing technologies used for the separation of HRT and SRT in PBRs are explored. The respective advantages and disadvantages are discussed for each PBR design, which may inform an interested bioprocess engineer. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the biogas production performance of an integrated microbial electrolysis cell and anaerobic reactor system (MEC-AR) treating cattle manure at different applied voltages and hydraulic retention times (HRT) ranging from 6 days to 1 day. The MEC-AR system was operated in semi-continuous mode under various voltage applications of 0.3, 0.6, and 1.0 V and organic loading rates (OLR) ranging from 5 g VS/L/d to 30 g VS/L/d. The MEC-AR system presented 25 to 62% higher biogas production and 10 to 21% higher organic removal rates compared to the control reactor, until the control reactor deteriorated at the HRT of 3 days. As the HRT was decreased further, biogas production of the MEC-AR system increased depending on the applied OLR and voltage. Maximum biogas productions, 4.88 L/L/d (CH4: 76%) and 5.10 L/L/d (CH4: 77%), were observed at HRT of 2 days and OLR of 30 g VS/L/d in MEC-AR0.6 V and MEC-AR1.0 V, respectively. Higher applied voltages (MEC-AR0.6 V and MEC-AR1.0 V) resulted in higher biogas production (16 to 21%) and organic removal rates (9 to 21%) compared to lower applied voltage (MEC-AR0.3 V) especially at high OLRs (22.5 and 30 g VS/L/d). As a result, MEC-AR system can be operated efficiently at challenging operational conditions (as low as 1 and 2 days; OLR of 15–30 g VS/L.d.) that conventional anaerobic reactors cannot withstand. [ABSTRACT FROM AUTHOR]

Hydrolysis at changing hydraulic retention time, recirculation, bedding straw content in the feed, bioaugmentation and the impact of those changes on gradient formation in the liquid phase in plug-flow reactors (PFRs) was examined. The pH-value, conductivity and oxidation–reduction potential (ORP) were monitored at three spots along the PFRs to study potential correlations to process performance during a total process time of 123 weeks. The on-line monitoring showed good correlations to acidogenesis: namely, the pH and ORP to the acidification, to butyric (and lactic) acid concentration and to the acid yield. The ORP (measured at the inlet) showed the most stable correlation to acidogenesis under dynamic operation, while the conductivity (at the outlet) correlated to the acid concentration in dependence on the feedstock. Multiple measurement spots as used in this study allow to gain more information about acidogenic fermentation than a single spot, simplifying process control and automation attempts with recalcitrant feedstock. [ABSTRACT FROM AUTHOR]

At present, eutrophication is increasingly serious, so it is necessary to effectively reduce nitrogen and phosphorus in water bodies. In this study, a pyrite/polycaprolactone-based mixotrophic denitrification (PPMD) system using pyrite and polycaprolactone (PCL) as electron donors was developed and compared with pyrite-based autotrophic denitrification (PAD) system and PCL-based heterotrophic denitrification (PHD) system through continuous flow experiment. The removal efficiency of NO3−–N (NRE) and PO43−–P (PRE) and the contribution proportion of PAD in the PPMD system were significantly increased by prolonging hydraulic retention time (HRT, from 1 to 48 h). When HRT was equal to 24 h, the PPMD system conformed to the zero-order kinetic model, so NRE and PRE were mainly limited by the PAD process. When HRT was equal to 48 h, the PPMD system met the first-order kinetic model with NRE and PRE reaching 98.9 ± 1.1% and 91.8 ± 4.5%, respectively. When HRT = 48 h, the NRE and PRE by PAD system were 82.7 ± 9.1% and 88.5 ± 4.7%, respectively, but the effluent SO42− concentration was as high as 152.1 ± 13.7 mg/L (the influent SO42− concentration was 49.2 ± 3.3 mg/L); the NRE by PHD system was 98.5 ± 1.7%, but the PO43−–P could not be removed ideally. The concentrations of NO3−–N, total nitrogen, PO43−–P, and SO42− in the PPMD system also showed distinct changes along the reactor column. In addition, the microbial diversity analysis showed that prolonging HRT (from 24 to 48 h) increased the abundance of autotrophic denitrifying microorganisms in the PPMD system, ultimately increasing the contribution proportion of PAD. [ABSTRACT FROM AUTHOR]

In this study, a laboratory-scale partial nitrification reactor (PN reactor) was used to treat high-ammonia–nitrogen wastewater, by changing the influent NH4+-N conversion rate as the main operating strategy, to investigate the upper limit of its NH4+-N conversion rate (ACR) and explore its feasibility as an anammox pre-process. During the experiment, PN reactor was successfully activated in only 10 days. The PN reactor reached the highest ACR value of approximately 10.24 kg N/(m3 · day) when the influent ACR was 16.57 kg N/(m3 · day), and the ammonia conversion efficiency (ACE) was 61.78% at this time. The ratio of [NO2−-N]Eff/[NH4+-N]Eff was approximately 1.37 which was close to the theoretical ratio of 1.32. And feasibility exploration experiment proved that it was feasible to use this PN reactor as a pre-process of anammox. The PCR-DGGE results showed that the dominant phylum and genus in the reactor during the ACR experiment were Proteobacteria and Nitrosomonas, respectively. With the increase in the ACR, the relative concentration of Nitrosomonas sp. G1 increased from 15 to 40%. This indicates that its abundance is directly correlated with the increase in the ACR. High-throughput sequencing showed that increasing the ACR of the PN reactor greatly reduced the diversity and abundance of the system microbial community structure and changed the dominant phylum and genus; however, the stability of the system was not disrupted. High-throughput sequencing experiments showed that the abundance value of nitrosation enzymes accounted for 91.62%, which was positively correlated with the expression of nitrification genes in the genus Nitrosomonas. [ABSTRACT FROM AUTHOR]

The enhancement of up-flow constructed wetland-microbial fuel cell (UFCW-MFC) performance in energy retrieval from caffeine containing wastewater has been explored via various operating conditions (hydraulic retention time (HRT), multianode (MA), multicathode current collector (MC), external resistance). The anaerobic decaffeination and COD removal improved by 37 and 12% as the HRT extended from 1 to 5 d. The increment in contact time between the microbes and organic substrates promoted the degradation and contributed to higher power output (3.4-fold), CE (eightfold), and NER (14–16-fold). The MA and MC connections facilitated the electron transfer rate and the degradation rate of organic substrates in the multiple anodic zones, which enhanced the removal efficiency in the anaerobic compartment (Caffeine: 4.2%; COD: 7.4%) and led to higher electricity generation (Power: 4.7-fold) and energy recovery (CE: 1.4-fold; NER: 2.3–2.5-fold) compared to SA. The lower external resistance favored the growth of electrogens and induced higher electron flux, where the best treatment performance and electricity production was obtained when the external resistance approached the internal resistance. Overall, it was noteworthy that the optimum operating conditions were achieved with 5 d HRT, MA, and MC connection along with external resistance of 200 Ω, which significantly outperformed the initial conditions (1 d HRT, SA connection, and 1000 Ω) by 43.7 and 29.8% of caffeine and COD removal in the anaerobic compartment, respectively as well as 14-fold of power generation. [ABSTRACT FROM AUTHOR]

Food waste (FW) contains high amounts of organic substances and moisture like lipids, starches, and proteins. Dark fermentation (DF) has the ability to produce from FW high-value by-products, like lactic acid (LA), hydrogen (H2), alcohols (EtOH), short-chain fatty acids, and methane which produced in the oxidative stage of anaerobic digestion. Moreover, it has been proved that hydrogen is one of the promising energy sources which is vital for shrinking dependency on fossil fuels. Otherwise, volatile fatty acids (VFAs) have a wide-ranging of applications such as the utilization of an alternative carbon source. The comparison between the trial PHP (pretreatment, HRT, and pH) and the control system at the same hydraulic retention time (HRT) levels was studied. The paired-samples t-test showed that the trial system has a highly significant difference compared to the control system (P < 0.0001(for both H2 and VFAs production, where H2 production rate was 0.19 mL/L at the control system, and 263.82 mL/L at the trial system. On the other hand, the trial was 1.8 times higher than the control system for VFAs production. Based on the obtained results, the trial system is recommended for producing H2 and VFAs from waste food. [ABSTRACT FROM AUTHOR]

Water scarcity is a worldwide problem. Recycled municipal wastewater is considered a useful alternative to the conventional types of water resources. In this study, a shallow constructed wetland (SCW) with porous filter material and Rotala rotundifolia was used for advanced municipal sewage treatment. The wetland without plant was set as the control (SCW-C). The pollutant removal performance of the system at different hydraulic retention times (HRTs) was investigated. The diversity of the microbial community was analyzed, and the fate of nutrients, mainly N and P, in the system was discussed. Results showed that SCW was efficient in pollutant removal. Effluent concentrations of chemical oxygen demand (COD), total phosphorus (TP), and ammonium nitrogen (NH4+-N) were 15.0–23.6, 0.19–0.28, and 0.83–1.16 mg/L, separately, with average removal efficiencies of 61.2%, 46.3%, and 88.1% at HRT 18 h, which met the requirements of type IV water set by the environmental quality standards for surface water in China. The richness and evenness of the bacterial community were significantly higher in the plant-rooted SCW. They increased along with the system. The dominant genera in the system were phosphate-solubilizing bacteria, nitrifying bacteria, and denitrifying bacteria. The P in the influent mainly flowed to the substrate and plant. At the same time, most N was removed by nitrification and denitrification. These findings suggested that the SCW could remove pollutants from the municipal sewage effluent and meet the standard requirement at low HRT. [ABSTRACT FROM AUTHOR]

This article aims to examine the performance of an aerobic sequential batch reactor in treating real textile wastewater under various hydraulic retention times. The proposed system was operated under various hydraulic retention times, and their effects on the removal efficiency of chemical oxygen demand, color, aromatic amines, and organic compounds from the woolen textile wastewater industry were investigated. The initial concentration of chemical oxygen demand and color was 1000 mg/L and 1000 American Dye Manufacturer's Institute, respectively. Aerobic sequential batch reactor application showed that chemical oxygen demand removal was almost between 86.6 and 90.1% with a slight increase of 4% when the hydraulic retention times were increased from 12 to 48 h, while the color removal was ranged from 62.44 to 77.78% when the hydraulic retention time varied between 12 and 48 h. Chromatographic analysis indicated that aromatic amines are biodegradable under aerobic conditions; simultaneously, the accumulation of aromatic amines on sludge increased by decreasing hydraulic retention times. Moreover, the GC–MS/MS analyses indicated that most of the organic compounds were removed after treating the textile wastewater with the aerobic sequential batch reactor. [ABSTRACT FROM AUTHOR]

Currently, the disposal of sugarcane vinasse is one of the greatest issues of sugarcane biorefineries in Brazil because of the large volumes produced. To contribute with an alternative energy recovery process from this by-product, this study proposed a physicochemical pretreatment and adjustment of operating conditions to improve the performance of the acidogenic stage of the anaerobic digestion of sugarcane vinasse. Therefore, this study evaluated the influence of hydraulic retention time (decreasing from 8 to 6, 4, 2, and 1 h) on the bioconversion of pretreated sugarcane vinasse (5000 mg COD L−1) to hydrogen and value-added products. Two anaerobic fluidized bed reactors were operated under mesophilic (AFBR-M, 30 °C) and thermophilic (AFBR-T, 55 °C) conditions. Despite the low similarity between the bacterial populations of AFBR-M and AFBR-T (40% similarity), the maximum hydrogen production rates (0.27 ± 0.07 and 6.42 ± 1.46 L H2 day−1 L−1) and hydrogen yields (0.27 ± 0.07 and 1.06 ± 0.15 mmol H2 g COD−1) occurred at the hydraulic retention time of 2 h by reducing the values from 8 to 2 h. The highest COD/SO42− ratios of 17.4 and 25.1 were also observed in the effluents of the AFBR-M and AFBR-T, respectively, at the hydraulic retention time of 2 h. Under both mesophilic and thermophilic conditions, a similar metabolic distribution was observed at the HRT of 2 h (acetic, propionic, and butyric acids, for AFBR-M and acetic, propionic, butyric acids, and ethanol for AFBR-T). This finding indicates the functional similarity between bacterial populations in both reactors. [ABSTRACT FROM AUTHOR]

The risks posed by algal blooms caused by nitrogen and phosphorus in reclaimed water used in urban water landscapes need to be carefully controlled. In this study, the combined effects of the nitrogen and phosphorus concentrations and the light intensity and temperature on the specific growth rates of algae were determined using Monod, Steele, and Arrhenius models, then an integrated algal growth model was developed. The algae biomass, nitrogen concentration, and phosphorus concentration mass balance equations were used to establish a new control model describing the nitrogen and phosphorus concentration and hydraulic retention time thresholds for algal blooms. The model parameters were determined by fitting the models to data acquired experimentally. Finally, the control model and numerical simulations for six typical algae and mixed algae under standard conditions were used to determine nitrogen/phosphorus concentration and hydraulic retention time thresholds for landscape water to which reclaimed water is supplied (i.e., for a reclaimed water landscape). [ABSTRACT FROM AUTHOR]

The construction of artificial reservoirs with various regulation types on river is currently an important form of comprehensive utilization of water energy and water resources in river basins. The type of regulation is important in controlling the residence time, which in turn affects the photosynthesis-respiration balance in the water. This process has a significant impact on carbon dioxide (CO2) emissions from reservoirs. In this study, seasonal observations were carried out from September 2020 to July 2021 at five artificial reservoirs in the Qiantang River Basin, eastern China, to reveal the characteristics of CO2 emission from the water–air interface of reservoirs with different regulating types. The results showed that the annual average CO2 emission flux of the studied reservoirs varied significantly, ranging from 4.2 to 155.3 mmol m−2 day−1 with an average of 48.4 mmol m−2 day−1, which also had a significant negative correlation with the hydraulic retention time. While downstream of the dam, the annual average CO2 emission flux was quite high with a range of 105.8 to 543.0 mmol m−2 day−1, averaging 381.6 mmol m−2 day−1. This is mainly due to the release of water with high-concentration CO2 from the bottom of the reservoir. Additionally, using related data of reservoirs around the world, a CO2 emission model with hydraulic retention time, air temperature, and reservoir age as the primary parameters was developed, which was conducive to evaluate reservoir CO2 emissions on a larger scale and provided theoretical support for effective reservoir management. [ABSTRACT FROM AUTHOR]

This paper presents the removal of nine potential endocrine disruptors including pesticides, pharmaceuticals and industrial chemicals using a submerged membrane bioreactor (MBR) system. Two lab-scale submerged MBRs having ceramic membranes were operated at three different sludge retention times (SRT: 15, 45, 90 days) and two hydraulic retention times (HRT: 12, 6 h) and the effects of SRT and HRT on both micropollutant removal and membrane fouling were investigated. While the effect of SRT and HRT change was observed on the removal of atrazine, fluoxetine, penconazole, no significant change was detected for the other micropollutants studied. It was determined that physicochemical properties such as distribution coefficient (LogD) and hydrophobicity of micropollutants are also effective on the removal efficiency of micropollutants. High removal efficiencies (≥ 97.5%) were observed for hydrophobic pollutants (logD > 3.2) except for penconazole (72.1%) and for hydrophilic pollutants (logD < 3.2) except for atrazine (42.5%). Membrane fouling was significantly affected by different operational parameters applied, with the slowest fouling occurring at 45 days of SRT and 12 h of HRT. However, micropollutant addition did not have a significant effect on membrane fouling. It has been shown that the simultaneous and effective treatment performance for micropollutants makes the membrane bioreactor system a promising wastewater treatment process. [ABSTRACT FROM AUTHOR]

Presence of organic compounds from cosmetics, detergents or pharmaceuticals found in wastewater is mainly a consequence of human activity. In wastewater treatment plants (WWTPs) removal of these pollutants takes place as secondary treatment in the aeration tank. An important parameter in this treatment is hydraulic retention time, which represents the treatment period in the aeration tank, recommended for most systems of 4 to 8 h. Also, several mathematical models were developed to determine the fate and removal efficiency of organic compounds in WWTPs. One of the most used is the SimpleTreat model ("9-box" model) which was created by the National Institute of Public Health and Environment in Netherlands (RIVM). The model considers 9 compartments or boxes in which the primary settler, aeration tank and secondary clarifier of a WWTP are contained separately. Each basin has a liquid (water) and a solid phase (suspended solids) in which the pollutant may be dissolved and/or adsorbed, respectively. Estimations of the organic compound concentration values may be determined in each WWTP basin and also discharged via effluent. All values are expressed in percentage from compound nominal concentration in influent representing the removal efficiency. This study presents estimations with the SimpleTreat model of the removal efficiency of six organic compounds found in products as: cosmetics—Tonalide (AHTN), decamethylcyclopentasiloxane (D5) and edetic acid (EDTA); detergents—benzalkonium chloride (BAC) and pharmaceuticals—Permethrin (PMT) and Atenolol (A). Depending on their chemical properties, these compounds may be found in influent mostly dissolved in the liquid phase or mostly adsorbed on the surface of the suspended solids. The removal efficiency is evaluated after 2, 5, and 10 h of retention in the aeration tank. [ABSTRACT FROM AUTHOR]

The domestic wastewater collection and treatment rate of Nairobi, Kenya are not high. The wastewater in the Kibera slum on the outskirts of the city that is directly discharged to the environment and pollution of the surrounding water body is a serious problem. This paper takes the domestic wastewater in the slum area as the research objective and researches on the wastewater characteristics, collection, and treatment, therefore providing the reference for the wastewater collection and treatment technology in the region. In this paper, domestic wastewater in the Kibera slum of Nairobi was sampled and investigated to find out the characteristics of wastewater discharged, the way of discharge of the household wastewater, and the management in this area. The study shows that there are differences in the concentration of main pollutants such as nutrients and organic matter in the wastewater from the household discharged to the residential river in the slum area. The domestic wastewater in this slum area contained a high concentration of nutrients such as nitrogen and phosphorus and other organics, total suspended solids (TSS), total coliforms and color, and with no treatment methods. Therefore, economic and feasible treatment technology needs to be developed. A pilot study was conducted on the treatment of domestic wastewater in the slum area by combining the seed extract of the natural plant Moringa oleifera as a coagulant and vertical flow constructed wetland (VFCW) at Tongji University, Shanghai, China. The VFCW system was efficient in chemical oxygen demand (COD), TSS, turbidity, total phosphorus (TP), and phosphates (PO4-P) removal, but the removal efficiency of nitrogen (total nitrogen (TN), ammonium nitrogen (NH4-N), and nitrate (NO3-N)) was poor, and the effluent pH reached the required discharge country's standard of the water. The average removal efficiencies for COD (79.99%), TSS (86.84%), turbidity (87.35%), TP (61.29%), PO4-P (65.66%), TN (14.11%), NH4-N (18.17%), and NO3-N (93%) were achieved by the treatment system. Furthermore, the removal efficiencies of pollutants such as TP, PO4-P, TN, and NH4-N were carried out by using the fruit extract of Moringa oleifera as raw material and zeolite as an auxiliary agent. The comprehensive effect of zeolite combined with VFCW and natural coagulant in the treatment of domestic wastewater was investigated. The COD removal efficiency was increased by (9%). TN by (46%), NH4-N by (67%), TP by (19%), and turbidity improved by (9%). In short, the domestic wastewater in the Kibera slum was collected and pretreated with natural plant coagulant, and then purified by vertical flow constructed wetland, which can not only significantly reduce the pollutant concentration but also basically meet the discharge standards. It is a low-cost sewage treatment technology suitable for poor areas. [ABSTRACT FROM AUTHOR]

Cascade dam has important effects on the magnitude and dynamics of sediment particles, heavy metals, and biogenic elements in reservoirs. However, systematic studies on the interception effect of cascade dam on the various elements that occur in rivers at the watershed scale are lacking. The aims of this study were to (1) assess the interception effect of a cascade dam on heavy metals and biogenic elements and (2) investigate the key factors of these effects of the cascade dam. Surface sediments were collected from 29 sites distributed in the Wujiang River Basin (WRB, a watershed scale in Southwest China), including from tributaries (7 sites), the main stream (13 sites), and cascade reservoirs (9 sites). In addition, the particle sizes, heavy metals (Fe, Mn, Zn, Cr, Cu, As, Pb, and Cd), and biogenic elements (TOC, TN, and TP) of sediments were analyzed. Compared with the tributaries, D50 (median particle size) was significantly reduced by 56.8% of cascade reservoirs. The proportion of 63–2,000 μm decreased from 13.78 to 1.34%, indicating that more coarse particles were intercepted in the cascade reservoirs. The contents of heavy metals (Fe, Zn, Cu, As, and Cd) declined significantly along the way. On the whole, the contents of TOC, TN, and TP were highest in the midstream and lower in the upstream and downstream. The hydrological condition (reservoir age, HRT, and flow) and the basin area and internal and external inputs of cascade reservoirs are important factors. The findings deepen the current understanding of the mechanisms by which cascade dam affects the river transport of heavy metals and biogenic elements at the watershed scale and provide an important reference for establishing hydropower developments along rivers and developing aquatic environment management strategies. [ABSTRACT FROM AUTHOR]

Ichthyoplankton drift is threatened by hydropower dams elsewhere. Here we evaluated whether eggs and larvae of fish can perform downstream movements along a large reservoir in a white-water river on the Amazon. Samplings were performed in the reservoir and downstream from Santo Antônio dam. Generalized linear models with negative binomial distribution and logarithmic link function were fitted to model the ichthyoplankton drift throughout the reservoir. Six different models were fitted having the abundances of ichthyoplankton as the response variable. The linear predictor differed as to the inclusion of the predictor variables larval development stage, sampling sites and dam distance (linear and quadratic effect). All ichthyoplankton and the most representative taxonomic orders were analyzed. The results indicate that fish reproductive activity occurred both upstream Jirau Dam and within the Santo Antônio Reservoir. Some part of the ichthyoplankton transposed the Santo Antônio Dam, reaching downstream. However, all of the taxonomic orders presented both reproductive activity and disappearance of at least some of their larval development stages along the reservoir. The most critical section was in the last 10 km of the reservoir, possibly as result of the drifting characteristics or of mortality rates. [ABSTRACT FROM AUTHOR]

Recycling waste and converting municipal solid waste (MSW) to useful materials, especially energy sources, is one of the most useful environmental effort, which prevent biological pollution and minimizes the stress on natural resources. This study investigates the improvement of biogas gained from MSW. Anaerobic digestion (AD) MSW and sewage sludge (SS) were studied at different mixing ratios at mesophilic condition. Higher methane yield but longer hydraulic retention time (HRT) was observed by increasing the percentage of MSW. The optimal mixing ratio for biogas production was determined. After 20 days, approximately 90% (376.84 mL/g VS) of the cumulative methane was produced. The same ratio was used for further study on the effect of total solids (TS) (5–25%) on biogas yield. It was found that lower TS levels (5–10%) yield more methane. Biogas production at 5% TS was 64% higher than that of 25% TS. The amounts of methane produced at 5, 10, 15, 20, and 25% TS were 230.3, 196.8, 159.5, 129.4, and 83.3 mL/g VS, respectively. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the impact of biochar addition on the mesophilic semi-continuous anaerobic digestion of swine waste with a focus on the effects of the organic loading rate (OLR) on biogas production, methane yield, total volatile fatty acids (TVFA), alkalinity, ammonium, volatile solids (VS) removal efficiency and process stability. Four reactors, two with amended biochar (R1 and R2) and two without biochar addition as controls (R3 and R4), were operated at OLRs in the range of 2–7 g VS/(L d), which corresponded to hydraulic retention times (HRTs) in the range of 7–2 days, respectively. The addition of biochar initially caused an increase in the generation of biogas and methane when compared to the control reactors when the process operated at OLRs of 2 and 3 g VS/(L d). This behaviour could be attributed to the presence of several trace elements (such as Fe, Co, Ni and Mn) in the biochar, which are involved in the action of acetyl-CoA synthase and methyl coenzyme M reductase to catalyse key metabolic steps, especially the methanogenic stage. The pH, alkalinity, TVFA and TVFA/Alkalinity ratio values for the effluents remained within the optimal ranges for the anaerobic digestion process. It was also found that the increase in OLR in the range of 2–5 g VS/(L d) determined a proportional increase in the VS removal rate. However, when the OLR increased up to 7 g VS/(L d), a drastic decrease in the VS removal rate was found for the control reactors. Biochar amendment contributed to a more balanced state of the anaerobic process, preventing biomass washout. [ABSTRACT FROM AUTHOR]

Purpose: This work aimed to (i) investigate the effect of hydraulic retention time (HRT) on controlling the release of phosphorus from sediment and (ii) interpret the phosphorus migration and transformation mechanism in the Al-PHOSLOCK thin-layer capping system. Methods: A 35-day laboratory dynamic simulation experiment was conducted by applying the Al-PHOSLOCK thin-layer capping to evaluate the effect of HRT on interrupting the release of phosphorus from contaminated sediments. The total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP), non-apatite inorganic phosphorus (NAIP), and apatite phosphorus (AP) were identified as different phosphorus species and analyzed during the experiment to further elucidate the migration and transformation of phosphorus. Results and discussion: The release of phosphorus from contaminated sediment was successfully suppressed by the Al-PHOSLOCK capping layer with an efficiency of higher than 90%. The HRT exerted a dual role on phosphorus controlling: at low HRT, slight water flow facilitated phosphorus migrating out from sediment and diffusing to the overlying water; at high HRT, the migration of phosphorus from overlying water back to sediment was strengthened. It was demonstrated that the phosphorus release was effectively controlled by the Al-PHOSLOCK thin-layer capping under different HRT conditions (static, 0.5 d, 1.0 d, and 3.0 d). The mechanism of phosphorus migration and transformation in the Al-PHOSLOCK thin-layer capping system was elucidated, including three significant stages of physical interception, adsorption, and capture/hold/transform process. Conclusion: This study verified the good capacity of the Al-PHOSLOCK capping system for controlling the release of sediment phosphorus under different HRT. Therefore, it was expected to be a promising approach in the handling of water eutrophication. [ABSTRACT FROM AUTHOR]

Though having an economic and ecological impact on Marriott Lake management in Egypt, water hyacinth (Eichhornia crassipes) is an aquatic floating macrophyte with a known phytoremediation potential. In order to assess its remediation potential, pilot floating treatment wetlands (FTWs) with E. crassipes were built in duplicates to evaluate the removal of nutrients and heavy metals from the polluted lake water. The experimental design included units with different water depths (15, 25, and 35 cm; D15, D25, and D35, respectively) and plant coverage (90, 70, 50, and 0%; P90, P70, P50, and P0, respectively). The pilot FTWs were monitored over a 7-day operation cycle to identify the optimum combination of design (plant coverage, water depth) and operation (hydraulic retention time; HRT) parameters needed for maximum BOD5, TN, NH4-N, and TP removal. NH4-N removal reached 97.4% in the D25P50 unit after 3 days, BOD5 75% in the D15P90 after 3 days, TN 82% in the D25P70 after 4 days, and TP 84.2% in the D35P70 after 4 days. The open-water evaporation rate was higher than the evapotranspiration rate in the planted units, probably due to the warm climate of the study area. Metals were also sufficiently removed through bioaccumulation in plant tissues in the order of Fe > Pb > Cu > Ni (62.5%, 88.9%, 81.7%, and 80.4% for D25P50, D25P70, D25P50, and D25P90, respectively), while most of the assimilated metal mass was translocated to the plant roots. The biochemical composition of the plant tissue was significantly different between the shoot and root parts. Overall, the FTW with 70% E. crassipes coverage, 25-cm water depth, and an HRT of 3–5 days was identified as the optimum design for effective remediation of the polluted Marriott Lake in Egypt. [ABSTRACT FROM AUTHOR]

The effectiveness of compost, peat-calcite, and wood ash to remove Ni from a circum-neutral-contaminated mine water was tested in continuous flow experiments. Materials were compared in 4.8-L columns at hydraulic residence times (HRT) of ∼ 16.5 h over the course of 2.5–4 months. During this period, all columns successfully treated over 400 L of synthetic contaminated neutral drainage (4.05 mg/L Ni), mainly through sorption processes. Mid-column results (HRT ∼ 9 h) indicated that wood ash was the most effective material for Ni removal, and chemical extractions revealed that retained Ni was less mobile in this spent material. The pH-increasing properties of wood ash played a major role in this material's performance, but a pH correction would be required in the initial stages of full-scale treatment to maintain the effluent within regulatory limits (6–9.5). Scaled to full-sized, mid-column results indicated that treatment cell sizes, designed for the 1-year treatment of a high discharge (10 m3/h)–contaminated effluent (4.05 mg/L Ni), would be the smallest with wood ash (< 500 m3), followed by compost (600 ± 140 m3) and peat-calcite (720 ± 50 m3). [ABSTRACT FROM AUTHOR]

A laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor was developed and constructed for the treatment of landfill leachate and acid mine drainage (AMD). The removal of chemical oxygen demand (COD), sulfate, and metal ions was studied. The maximum COD and sulfate removal efficiency reached 75% and 69%, respectively, during the start-up phase of the UASB. The hydraulic retention time (HRT) had a significant influence on the system. The maximum removal efficiency for COD and sulfate reached 83% and 78%, respectively, at an HRT of 20 h. The methane production process competed with the sulfate reduction process in the UASB. The fractionation of metals in the sludge was analyzed to facilitate metal recovery in a later processing stage. The most abundant sulfate-reducing bacteria was Desulfobulbus, and the methanogen archaeal community in the reactor was mainly composed of Methanobacterium. [ABSTRACT FROM AUTHOR]

This article presents a review of anaerobic treatment technologies to treat slaughterhouse wastewater including its advantages and disadvantages. Physico-chemical characteristics and biochemical methane potential (BMP) of slaughterhouse wastewater are addressed. Various anaerobic treatment technologies are presented with the related operating parameters, viz., hydraulic retention time (HRT), organic loading rate (OLR), upflow velocity (Vup), and biogas yield vis-a-vis treatment efficiency in terms of chemical oxygen demand (COD). In addition, various factors that affect the anaerobic treatment of slaughterhouse wastewater such as high oil & grease (O & G) concentration in influent, inhibitors, volatile fatty acids (VFAs), and the loading rate are also addressed. The literature review indicated that the slaughterhouse wastewater can be treated effectively by employing any anaerobic treatment technologies at OLRs up to 5 kg COD/m3.d with more than 80% COD removal efficiency without experiencing operational problems. Anaerobic hybrid reactors (AHRs) were found the most effective among various reviewed technologies because of their ability to operate at higher OLRs (8 to 20 kg COD/m3.d) and lower HRTs (8 to 12 hrs). [ABSTRACT FROM AUTHOR]

A cost sensitivity analysis was performed for an industrial membrane bioreactor to quantify the effects of hydraulic retention times and related operational parameters on cost. Different hydraulic retention times (72–24 h) were subjected to a flat-sheet membrane bioreactor updated from an existing 72 h oxidation ditch treating antibiotic production wastewa ter. Field experimental data from the membrane bioreactor, both full-scale (500 m3/d) and pilot (1.0 m3/d), were used to calculate the net present value (NPV), incorporating both capital expenditure (CAPEX) and operating expenditure. The results showed that the tank cost was estimated above membrane cost in the 38.2%, where capital expenditure contributed 24.2% more than operational expenditure. Tank construction cost was decisive in determining the net present value contributed 62.1% to the capital expenditure. The membrane bioreactor has the advantage of a longer lifespan flat-sheet membrane, while flux decline was tolerable. The antibiotics decreased to 1.87±0.33 mg/L in the MBR effluent. The upgrade to the membrane bioreactor also benefited further treatments by 10.1%–44.7% lower direct investment. [ABSTRACT FROM AUTHOR]

This study explored the influence of ferrous iron (Fe2+) addition on ammonium nitrogen (NH4-N) removal and microbial communities in horizontal subsurface flow constructed wetlands (HSSFs) at different carbon/nitrogen (C/N) ratios. Fe2+ addition could improve NH4-N removal under the C/N ratio of 2.1 and alter the microbial community structure. The microbial diversity and functional genes at the C/N ratio of 2.1 were enhanced by the addition of 50 mg/L Fe2+, with the increases observed in NH4-N and total nitrogen (TN) removal. This indicates the enhancement of nitrogen removal by Fe2+ addition with the presence of high organic matter. However, the enhancement of Fe2+ on chemical oxygen demand removal was not obvious overall. The relative abundance of functional genes and those related to energy metabolism, xenobiotic biodegradation, and metabolism decreased significantly in HSSFs with Fe2+ at C/N ratio of 1.1, whereas they increased in HSSFs with the addition of 50 mg/L Fe2+ at C/N ratio of 2.1. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the study was to investigate the role of trace elements (TEs) supplementation in connection with the organic load rate (OLR) and the hydraulic retention time (HRT) on methane (CH4) yields in semi-continuous anaerobic digestion of deinking sludge (DS) in order to judge the possibility to use DS as alternative energy source in wastepaper recycling companies. Methods: After substrate characterization, a semi-continuous anaerobic digestion was performed for 74 days using 2-L stirred tank reactors at a mesophilic (37 °C) condition, whereas one of them was supplemented with a mixture of TEs (cobalt, nickel, molybdenum and selenium). The feeding periods had a duration of 4, 7 or 8 days. Results: The highest cumulative CH4 yield after a feeding period was found to be 151 NmL/g oDM after TE supplementation. The TEs-supplementation has resulted in 42% increase in CH4 yield compared to the non-supplemented variant. The increase took place at the end of the experiment. Earlier feeding periods with similar conditions regarding HRT and OLR, did not show an increase. This can be explained by the fact that TEs supplementation requires a longer adaption time for the microorganism. Conclusions: TEs addition has shown a strongly positive impact on CH4 yields. Our results showed that it is possible to receive the same yields in semi-continuous, more practice-close operation, compared to previous potential determination experiments under batch conditions. A further optimization potential is seen by optimizing TEs supplementation in connection with VOA level in the reactor, optimizing C/N ratio and lowering the duration of the feeding intervals. [ABSTRACT FROM AUTHOR]

The microbial fuel cell coupled constructed wetland (CW-MFC) was used for treatment sewage and simultaneously generating electricity. The main aim of this study was to explore the optimal conditions for the treatment of hexavalent chromium (Cr (VI)) wastewater by the CW-MFC system. The performance of CW-MFC in removing Cr (VI) and chemical oxygen demands (COD) contained in wastewater and its electricity generation were studied. Electrode spacing, Cr (VI) and COD concentration, and hydraulic retention time (HRT) had certain effects on the performance of CW-MFC. For the electrode spacing of 10 cm, the highest power density of 458.2 mW/m3 could be obtained with the influent concentration of Cr (VI) (60 mg/L) and COD (500 mg/L). The highest Cr (VI) and COD removal rate were obtained with the HRT of 3 days. Compared with CW system, the electrical energy generated in CW-MFC was beneficial to improving the removal efficiency of COD and Cr (VI). Thus, the results confirmed that CW-MFC is a promising technology to remove Cr (VI) from wastewater and achieve bioelectricity production simultaneously. [ABSTRACT FROM AUTHOR]

The fixed-film sequencing batch reactor, or F-SBR, was developed to treat high organic compound levels and toxic cyanide concentrations in cassava wastewater. The performance of the F-SBR was compared with that of a conventional sequencing batch reactor, or SBR, that was operated with organic compound contents of 16,266.67–26,666 mg COD/L and 132.92–252.66 mg CN−/L. The cyanide and chemical oxygen demand removal efficiencies of the conventional SBR system were 42.61% and 36.83%, respectively, while those of the F-SBR were 77.95% and 74.43%, respectively; the cyanide removal efficiency reached 95.45% when the hydraulic retention time was increased to 5 days, and the F-SBR was very effective for the complete removal of cyanide when the hydraulic retention time was increased to 10 days. This effectiveness was similar to the effectiveness of chemical oxygen demand removal, which reached 40–78% efficiency with the F-SBR system. These results showed that the immobilization of cyanide-degrading bacteria such as Agrobacterium tumefaciens SUTS 1 and Pseudomonas monteilii SUTS 2 carried out with a polypropylene ring in a fixed-film aerobic system enhanced the performance of the reactor and can be successfully applied for cyanide and chemical oxygen demand removal from industrial wastewater with high cyanide and chemical oxygen demand concentrations. This study may provide a promising alternative technique that reduces economic operation costs in solving wastewater contamination problems. [ABSTRACT FROM AUTHOR]

Storage of greywater is controversial for environmental and health reasons. Artificial greywater was assessed after 2 and 7 days of storage time. Two different greywater pollutant strengths were statistically compared at each storage time. A negative significant (p < 0.05) correlation was evident with increasing storage time for the 5-day biochemical oxygen demand for more than 2 days. However, the concentrations of 5-day biochemical oxygen and chemical oxygen demands reduced significantly at 2 days of storage when compared with freshly prepared greywater. Biodegradability (5-day biochemical oxygen demand/chemical oxygen demand ratio) decreased significantly after storage to between 0.14 and 0.39. The nitrification process was improved significantly with increasing storage time concerning low strength greywater with a significant increase in the removal of ammonia-nitrogen and a non-significant decrease in the removal of nitrate-nitrogen. The correlation was significantly positive between ammonia-nitrogen and 5-day biochemical oxygen demand for stored greywater, while it was significantly negative between total suspended solids and both 5-day biochemical oxygen demand and dissolved oxygen. Significant reductions in colour, total suspended solids and turbidity were correlated positively with storage time. Precipitation of dissolved metals was suspected to occur in storing greywater by binding the inorganic components with the sediment and collide surfaces through adsorption, allowing a significant drop in concentrations of dissolved and undissolved metals with increasing storage time through sedimentation. Synthetic greywater of low mineral pollution had significantly higher removals for almost all concentrations compared with those for high concentrations. More advanced technologies for high trace element removal are required. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of hydraulic retention time (HRT) on the simultaneous hydrogen and ethanol production in two anaerobic fluidized bed reactors (55 °C) from mono-fermentation of cellulosic hydrolysate (AFBR-C) and the fermentation of glucose and xylose as co-substrates (AFBR-GX). In AFBR-C, the HRT was decreased from 24 to 8 h, while in AFBR-GX, the HRT was decreased from 16 to 0.5 h. The carbohydrate concentration was maintained at 4 g/L (AFBR-GX) and 2 g/L (AFBR-C). In AFBR-C, the main results observed by decreasing the HRT from 24 to 8 h were the increase in H2 yield (0.6–1.1 mol H2/mol hexose) and ethanol concentration (0.02–0.48 g/L). However, the H2 yield in AFBR-GX decreased from 0.4 to 0.1 mol H2/mol hexose by decreasing the HRT from 16 to 0.5 h. Additionally, the shortest HRTs applied to the AFBR-C (8 h) and AFBR-GX (0.5 h) resulted in the maximum hydrogen production rates of 115.7 and 279.9 mL H2/h L, the maximum energy yields of 7.4 and 47.7 kJ/h L, and EtOH molar fractions of 58.9 and 50.2%, respectively. [ABSTRACT FROM AUTHOR]

The effect of hydraulic retention time (HRT) and sludge retention time (SRT) on extracellular polymer substrate (EPS) content and resistance of a hybrid membrane bioreactor (HMBR) treating domestic sewage was analyzed by Box-Behnken response surface methodology. The quadratic response surface model demonstrated significant effects of both HRT and SRT on EPS content (both P value < 0.05), SRT on membrane resistance (P value = 0.0119), and their interaction was significant (P value = 0.0273) for EPS but not membrane resistance (P value = 0.0609). Model optimization indicates that the optimal conditions for the HMBR to control membrane fouling were an HRT of 10 h and SRT of 30 days. Under these optimal conditions, both the EPS content and the predicted membrane resistance closely matched the actual average value with the error about 8%. Thus, the feasibility of applying response surface methodology to an HMBR for treating domestic sewage was demonstrated. According to the detection result of the three-dimensional fluorescence (excitation-emission matrix), humic acid-like and fulvic acid-like substances gain much higher levels in the suspended carriers than those in the membrane and sludge, suggesting that these are key components of the membrane pollutants. [ABSTRACT FROM AUTHOR]

Experimental tests on continuous two-stage anaerobic digestion (TSAD) were conducted, to assess its energetic performance, using organic market waste as a substrate. The systems were tested to ascertain the effects of external stressors, which allow the separation into two different microorganism consortia, that is, hydrogen-producing bacteria and hydrogen-consuming bacteria, to be maintained. Two bioreactors were run in series under different operational conditions, including pH, mixing rate, and initial inoculum, and three different decreasing hydraulic retention times were considered, with a fixed ratio of 1:10 in volume between the first bioreactor (hydrogen) and the second one (methane). The performance of the whole system was assessed over > 140 days to monitor the stability of the process, in terms of the reduction of the volatile solids and the energy productivity for each step. Each tested condition was scored using two parameters: efficiency and efficacy. The first corresponds to the fraction of recovered energy of the available (η) and the second (ξ) was used to compare the energy produced by the TSAD with that of one-step anaerobic digestion. The efficiency resulted to be (24–32)%, while the efficacy proved to be around 1.20. The share of energy, under the form of hydrogen, compared to the total energy recovery, was in the (8–12) % range. Finally, the oscillation behaviour of the quasi-steady-state condition was analysed in terms of the Fano factor to establish the most stable conditions. [ABSTRACT FROM AUTHOR]

As a global pollutant, Hg (Hg) since the turn of the last century has received increased attention. Decreasing the emission of Hg into the food chain and the atmosphere is an effective way to reduce the Hg damage. The current study provided information about pilot-scale horizontal subsurface flow (HSSF) constructed wetlands (CWs) to remove different Hg species in polluted water. Synthetic wastewater was fed to two HSSF CWs, one was planted with Acorus calamus L and the other was unplanted as a control. The total Hg (THg), dissolved Hg (DHg), and particulate Hg (PHg) from five sites along the HSSF CWs were analyzed to describe the process of Hg removal. Results show that the CWs have high removal efficiency of Hg which is more than 90%. The removal efficiencies of THg and DHg from the unplanted CW were 92.1 ± 3.6% and 72.4 ± 13.1%, respectively. While, the removal efficiencies of THg and DHg in planted CW were 95.9 ± 7.5% and 94.9 ± 4.9%, which were higher than that in blank CW. The PHg was mainly removed in the first quarter of the CWs, which was also revealed by the partition coefficient Kd. To a certain extent, the effect of plants depends on the hydraulic retention time (HRT). The results in the current study show the potential of the HSSF-CWs for restoration from Hg-contaminated water. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) is among the most serious threats to water and the typical alkali-based treatment costs are high. This study's main objective was the establishment of a highly efficient biological process using an upflow anaerobic sludge blanket (UASB) reactor to treat AMD based on a shorter hydraulic retention time (HRT) and lower organic matter input. The process was evaluated for a long-term operation (739 days) in terms of the influence of HRT (14-24 h), metal addition, sulfate loading rate (0.5-2.6 g SO42− l−1 d−1), and the COD/SO42− ratio (0.67-1.0) using ethanol as the only electron donor at a pH of 4.0. Neutral effluent pH was achieved throughout the time apart from operational modifications. The reduction in HRT from 24 to 16 h and an increase in the sulfate loading rate (SLR) up to 2.25 g SO42− l−1 d−1 improved the sulfate removal to (92.1 ± 1.8)% with 80% chemical oxygen demand (COD) removal. However, the sulfate reduction was less than 80% when the HRT and SLR was changed to 14 h and 2.6 g SO42− l−1 d−1, respectively. The oxidation of organic matter by sulfate reduction was greater than 50% regardless of the conditions imposed but the use of ethanol to treat AMD was more efficient when either the HRT was 16 h (1.5 g SO42− l−1 d−1) in the presence of Fe, Zn, and Cu or the HRT was 14 h (2.6 g SO42− l−1 d−1) but the COD/SO42− ratio was reduced to 0.67. The fully optimized conditions of the UASB reactor were set at an HRT of 16 h, SLR of 1.5 g SO42− l−1 d−1, and a COD/SO42− ratio of 1.0. [ABSTRACT FROM AUTHOR]

Conventional activated sludge (CAS) process is one of the most commonly applied processes for municipal wastewater treatment. However, it requires a high energy input and does not promote energy recovery. Currently, high-rate activated sludge (HRAS) process is gaining importance as a good option to reduce the energy demand of wastewater treatment and to capture organic matter for valorizing through anaerobic digestion (AD). Besides, food waste addition to wastewater can help to increase the organic matter content of wastewater and thus, energy recovery in AD. The objective of this study is to evaluate the applicability of co-treatment of municipal wastewater and food waste in a pilot-scale HRAS system as well as to test the minimal hydraulic retention times (HRTs) such as 60 and 30 min. Food waste addition to the wastewater resulted in a 10% increase in chemical oxygen demand (COD) concentration of influent. In the following stages of the study, the pilot-scale system was operated with wastewater solely under the HRTs of 60 and 30 min. With the decrease of HRT, particulate COD removal increased; however, soluble COD removal decreased. The results demonstrated that if the settling process is optimized, more particulate matter can be diverted to sludge stream. [ABSTRACT FROM AUTHOR]

In most developing countries, stormwater runoff has had significant impacts on aquatic environment by directly causing pollution of receiving water and reduction in treatment performance of wastewater treatment plants. With increasing encroachment on natural wetlands in Uganda, constructed wetlands offer a feasible option for the environment to cope up and buffer the impact of pollutants from the ever-increasing urban masses. This study investigated the performance efficiencies of three configurations (varied by the substrate used) of microcosm wetlands to remove physicochemical parameters from stormwater runoff in Uganda. The parameters monitored included chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP). Hydraulic retention times (HRTs) of 2, 4, 6, and 8 days were studied. The mean concentrations of the physicochemical parameters in the runoff were 219.4 ± 12.8 mg/L COD, 77.4 ± 8.3 mg/L TSS, 9.0 ± 0.4 mg/L TN, and 1.6 ± 0.1 mg/L TP. Configuration A, vegetated with cattail (Typha latifolia) and bulrush (Scirpus lacustris), achieved maximum COD removal of 75.9% (HRT = 6 days), TN removal of 72.8% (HRT = 8 days), and TP removal of 62.8% (HRT = 8 days). Configuration C, the control, with no substrate, achieved the highest TSS removal of 75.6%. The results suggest that vegetated microcosm constructed wetlands can potentially be used to pre-treat stormwater within the catchment. However, an upstream sedimentation process unit is required to enhance their performance and to avoid premature clogging of the wetlands by TSS. The pre-treated stormwater reduces pollutant load into wastewater treatment plants and consequently better raw water quality for water treatment plants. [ABSTRACT FROM AUTHOR]

The production of 1,3-propanediol from crude glycerol and mixed anaerobic sludge was investigated in batch experiments and continuous reactors. Using a 23 complete factorial design, the effects of the concentration of glycerol (22-30 g L−1), KH2PO4 (1.50-2.00 g L−1), and vitamin B12 (7-8 mg L−1) were examined in batch reactors. As an evaluated response, the highest 1,3-PD yields occurred for high concentrations of vitamin B12 and low levels of KH2PO4, reaching 0.57 g g−1 glycerol consumed. The variable glycerol concentration was not significant in the studied range. In addition, the condition that provided the best 1,3-PD yield was applied to an anaerobic fluidized bed reactor fed with crude glycerol (26.0 g L−1), which was monitored as the hydraulic retention time (HRT) decreased from 36 to 12 h. The greatest 1,3-PD yield, of 0.31 g g−1 glycerol, was obtained with an HRT of 28 h. [ABSTRACT FROM AUTHOR]

The effects of hydraulic retention time (HRT) on the performance of algal-bacterial-based aquaponics (AA) were investigated in this study. Both the highest fish growth and algal biomass increase were observed in the AA system at 2-day HRT, resulting in the highest nitrogen utilization efficiency (NUE) (39.28%) in this microcosm. On the contrary, ammonia oxidation bacteria (AOB) abundance at 4-day HRT was approximately ten times higher than that at 2-day HRT, since longer HRT would benefit bacterial growth. The 15N labeling study showed that microalgae assimilation was the main pathway of NH4+ removal in the AA system, and oxygen produced by microalgae could in situ support complete nitrification, thus leading to much lower NH4+ concentrations at 2-day HRT. Accordingly, better water quality was achieved at 2-day HRT. Considering all the factors, HRT of 2-day was considered to be optimal for the AA system. [ABSTRACT FROM AUTHOR]

A sequencing batch conventional membrane bioreactor (SB-CMBR) and sequencing batch hybrid membrane bioreactor (SB-HMBR) were operated in parallel under two different hydraulic retention times (HRTs) (namely 12 h and 6 h), and their chemical oxygen demand (COD) and nutrient removal performance, membrane fouling behavior, and microbial community characteristics were compared. Both systems exhibited high organic matter (> 95%) and ammonium (> 98%) removal performance regardless of the HRT applied. As the HRT was reduced from 12 to 6 h, total nitrogen removal slightly increased in both reactors, being higher in the carrier-based MBR, where anoxic zones may have been established within the biofilm. Conversely, total phosphorus removal improved only in the SB-CMBR at the shorter HRT. Moreover, activity batch assays have shown a faster P uptake rate in the SB-CMBR than in the SB-HMBR, a result likely associated with the lower relative abundance of phosphate-accumulating organisms in both adhered and suspended biomass fractions in the hybrid MBR. The results also revealed that more pronounced increases in the transmembrane pressure and, consequently, in the membrane fouling rate at higher COD loading rates were observed in the SB-CMBR, where the soluble microbial products (proteins, polysaccharides, and especially, transparent exopolymer particles), supernatant turbidity, and filamentous bacteria were more significant. Overall, as compared to the conventional MBR, the plastic media-based SB-HMBR showed a lower fouling propensity at all hydraulic conditions tested. [ABSTRACT FROM AUTHOR]

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

Conventional activated sludge (CAS) technology has been the most commonly applied technology for treatment of municipal wastewater for more than a century; however, a significant portion of energy content of the wastewater cannot be recovered by this technology. Therefore, different modifications can be applied to the CAS technology in order to increase the energy harvesting from wastewaters. In this paper, physically treated wastewater from a municipal preliminary wastewater treatment plant (WWTP) was treated at a pilot-scale high-rate activated sludge (HRAS) system. The HRAS system was operated under three different hydraulic retention times (HRTs) and the treatment performances were evaluated. Within this concept, HRTs of 130, 95, and 60 min were tested. The results revealed that total chemical oxygen demand (tCOD) removal of 59% was achievable and the effluent total suspended solids (TSS) concentration was 90 mg/L at the HRT of 60 min. Effluent COD and TSS concentrations decreased with the decrease in HRT by means of enhanced flocculation and sedimentation. This is confirmed by the improvement of sludge volume index (SVI) values at decreased HRTs. The calculated mass balance showed that more COD was diverted to sludge stream with decrease in HRT. Diversion of more COD to sludge can improve the energy balance of wastewater treatment by the application of anaerobic sludge digestion. By this way, HRAS process would be a promising technology in the concept of energy efficient wastewater treatment systems. [ABSTRACT FROM AUTHOR]

The study focused on the feasibility of high NH -N (400-600 mg/L) and COD load at two different hydraulic retention times (HRTs = 36 and 24 h) in two identical aerobic-anoxic sequencing bioreactors which were constructed in series in a single system using a specifically designed single biomass containing autotrophic nitrifying and heterotrophic denitrifying bacteria. Internal recirculation of synthetic wastewater from one tank to other was not carried out like the conventional aerobic-anoxic processes. Cycles of 15 days under sequences of aerated and non-aerated periods of three hour each were repeated during each continuous flow experiment conducted. Sodium bicarbonate and sodium acetate were selected as the appropriate inorganic and organic carbon sources. The results showed that the HRT may not affect the simultaneous nitrification and denitrification processes. Average nitrification ratio was obtained to be above 20 mg/L NH -N/h daily. Results of 90 days' operation also showed high removal efficiencies of ammoniacal nitrogen of about 83% daily. The main advantage of this process includes efficient ammoniacal nitrogen removal without separated aerobic and anoxic tanks, decrease operating costs due to the lesser oxygen concentration requirement in the bioreactors. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate the influence of hydraulic retention time (HRT) and cheese whey (CW) substrate concentration (15 and 25 g lactose l) on the performance of EGSB reactors (R15 and R25, respectively) for H production. Results: A decrease in the HRT from 8 to 4 h favored the H yield and H production rate (HPR) in R15, with maximum values of 0.86 ± 0.11 mmol H g COD and 0.23 ± 0.024 l H h l, respectively. H production in R25 was also favored at a HRT of 4 h, with maximum yield and HPR values of 0.64 ± 0.023 mmol H g COD and 0.31 ± 0.032 l H h l, respectively. The main metabolites produced were butyric, acetic and lactic acids. Conclusions: The EGSB reactor was evaluated as a viable acidogenic step in the two-stage anaerobic treatment of CW for the increase of COD removal efficiency and biomethane production. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effects of hydraulic retention time (HRT) (8 to 0.5 h) and temperature (55 to 75 °C) in two anaerobic fluidized bed reactors (AFBR) using cheese whey (AFBR-CW = 10,000 mg sugars L) and vinasse (AFBR-V = 10,000 mg COD L) as substrates. Decreasing the HRT to 0.5 h increased the hydrogen production rates in both reactors, with maximum values of 5.36 ± 0.81 L H h L in AFBR-CW and 0.71 ± 0.16 L H h L in AFBR-V. The optimal conditions for hydrogen production were the HRT of 4 h and temperature of 65 °C in AFBR-CW, observing maximum hydrogen yield (HY) of 5.51 ± 0.37 mmol H g COD. Still, the maximum HY in AFBR-V was 1.64 ± 0.22 mmol H g COD at 4 h and 55 °C. However, increasing the temperature to 75 °C reduced the hydrogen production in both reactors. Methanol and butyric, acetic, and lactic acids were the main metabolites at temperatures of 55 and 65 °C, favoring the butyric and acetic metabolic pathways of hydrogen production. The increased productions of lactate, propionate, and methanol at 75 °C indicate that the hydrogen-producing bacteria in the thermophilic inoculum were inhibited under hyperthermophilic conditions. [ABSTRACT FROM AUTHOR]

The present study focuses on the exploitation of food industry waste for hydrogen and methane production, via biological processes. Fermentative hydrogen production in an anaerobic up-flow column reactor (AUFCR), using indigenous microbial species and fed with the soluble fraction of the waste coming after an extraction procedure, was investigated at different Hydraulic Retention Times (HRTs) in the range of 12-2 h. The highest hydrogen production rate (2.94 ± 0.37 L H/L/d) was obtained at the HRT of 2 h, while the highest yield of hydrogen produced per mol of consumed carbohydrates, expressed in glucose equivalents was achieved at the HRT of 12 h (0.14 ± 0.01 mol/mol). Methane production via anaerobic digestion (AD) in a CSTR-type reactor was also assessed, using the whole diluted food industry waste (without extraction). The HRTs tested were 20, 15 and 10 days, while when the reactor operated at the HRT of 10 days, the feeding medium was also thermally treated, in order to assess the effect of pretreatment in AD. The maximum methane production rate (0.24 ± 0.02 L CH/L/d) was observed for the HRT of 10 days and thermally treated substrate, while the maximum methane yield was obtained at the HRT of 15 days (247.9 ± 0.15 L CH/kg waste). The IWA ADM1 model was finally used to predict the anaerobic digesters' behavior through the operational period, resulting to a quite satisfactory simulation for a wide range of operational conditions. [ABSTRACT FROM AUTHOR]

A laboratory-scale anoxic-oxic sequential reactor system was seeded with acclimatized mixed microbial consortium for the treatment of common effluent treatment plant (CETP) wastewater having 7000-7400 mg L of COD and 3000-3400 mg L of BOD. Initially, CETP wastewater was treated under anoxic reactor at 5000 mg L of MLSS concentrations, 5.26 ± 0.27 kg COD m day of organic loading rate (OLR) and 36 h of hydraulic retention time (HRT). Further, the effluent of anoxic reactor was treated in oxic reactor with an OLR of 6.6 ± 0.31 kg COD m day and 18 h HRT. Maximum color and COD removal were found to be 72 and 85 % at total HRT of 2.25 days under anoxic-oxic sequential reactor at 37 °C and pH 7.0. The UV-VIS, FTIR, NMR and GCMS studies showed that majority of peaks observed in untreated wastewater were either shifted or disappeared after sequential treatment. Phytotoxicity study with the seeds of Vigna radiata and Triticum aestivum showed more sensitivity toward the CETP wastewater, while the products obtained after sequential treatment does not have any inhibitory effects. The results demonstrated that the anoxic-oxic reactor fed with bacterial consortium VN11 could bring about efficient bioremediation of industrial wastewaters. [ABSTRACT FROM AUTHOR]

Fenton oxidation and ultrasound-based pretreatment have been applied to improve the treatment of real industrial wastewater based on the use of biological oxidation. The effect of operating parameters such as Fe loading, contact time, initial pH, and hydrogen peroxide loading on the extent of chemical oxygen demand (COD) reduction and change in biochemical oxygen demand (BOD)/COD ratio has been investigated. The optimum operating conditions established for the pretreatment were initial pH of 3.0, Fe loading of 2.0, and 2.5 g L for the US/Fenton/stirring and Fenton approach, respectively, and temperature of 25 °C with initial HO loading of 1.5 g L. The use of pretreatment resulted in a significant increase in the BOD/COD ratio confirming the production of easily digestible intermediates. The effect of the type of sludge in the aerobic biodegradation was also investigated based on the use of primary activated sludge (PAS), modified activated sludge (MAS), and activated sludge (AS). Enhanced removal of the pollutants as well as higher biomass yield was observed for MAS as compared to PAS and AS. The use of US/Fenton/stirring pretreatment under the optimized conditions followed by biological oxidation using MAS resulted in maximum COD removal at 97.9 %. The required hydraulic retention time for the combined oxidation system was also significantly lower as compared to only biological oxidation operation. Kinetic studies revealed that the reduction in the COD followed a first-order kinetic model for advanced oxidation and pseudo first-order model for biodegradation. The study clearly established the utility of the combined technology for the effective treatment of real industrial wastewater. [ABSTRACT FROM AUTHOR]