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Due to enormous quantities with hazards and complexity in nature is a big challenge for effective treatment of wastewater from pharmaceutical processes including herbal extraction through conventional methods of distillation. The situation is further aggravated in countries facing high rising population, urbanization, and industrialization resulting in the generation of industrial wastes. The study has been carried out in the herbal extraction industry by conducting stage-wise sampling of ETP based on the conventional method and further coupled with ozonation as an advanced treatment to comply with regulatory standards. Additionally, the same process was studied that implementing the best available technology (BAT) by providing ETP with advanced technology modules such as MBR (membrane bioreactor) + RO + O3 has not only resulted in compliance with standards but also reuse of treated wastewater into the process and utilities has been proved to be techno-economically a viable and sustainable option. Modifying existing aeration tanks and advanced oxidation through ozone injection post-biological treatment has resulted in COD and BOD reduction of 96.42% and 99.0% respectively. Whereas in the case of MBR + RO + O3, the values of pH, BOD, COD, TSS, and sulfide have been observed as 8.32, 2.0 mg.L-1, 14.0 mg.L-1, 1.0 mg.L-1 and 0.0 mg.L-1 respectively and 98% recovery of treated effluent, thus saving 44 KL.day-1 of freshwater resulting into significant financial benefits of Rupees 12.59 lacs annually, which otherwise was outsourced through tankers. [ABSTRACT FROM AUTHOR]

Copyright of China Pulp & Paper is the property of China Pulp & Paper Magazines Publisher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

This study evaluated the treatment efficiency of two selected fillers and their combination for improving the water quality of aquaculture wastewater using a packed bed biofilm reactor (PBBR) under various process conditions. The fillers used were nanosheet (NS), activated carbon (AC), and a combination of both. The results indicated that the use of combined fillers and the hydraulic retention time (HRT) of 4 h significantly enhanced water quality in the PBBR. The removal rates of chemical oxygen demand, NO2−─N, total suspended solids（TSS）, and chlorophyll a were 63.55%, 74.25%, 62.75%, and 92.85%, respectively. The microbiota analysis revealed that the presence of NS increased the abundance of microbial phyla associated with nitrogen removal, such as Nitrospirae and Proteobacteria. The difference between the M1 and M2 communities was minimal. Additionally, the microbiota in different PBBR samples displayed similar preferences for carbon sources, and carbohydrates and amino acids were the most commonly utilized carbon sources by microbiota. These results indicated that the combination of NS and AC fillers in a PBBR effectively enhanced the treatment efficiency of aquaculture wastewater when operated at an HRT of 4 h. The findings provide valuable insights into optimizing the design of aquaculture wastewater treatment systems. [ABSTRACT FROM AUTHOR]

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract 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.

The escalating demand for water and the increasing pollution of natural water bodies necessitate innovative solutions for wastewater treatment and reuse. This study investigated the potential of a horizontal subsurface flow (HSSF) constructed wetland to treat aquaculture wastewater for reuse. The system, planted with Taro (Colocasia esculenta) and sugarcane (Saccharum officinarum L.), received effluent from a recirculating aquaculture system (RAS) producing African Catfish (Clarias gariepinus). The study assessed the impact of varying hydraulic retention times (1-3 days) and flow rates (11-108 L/min) on water quality parameters, including dissolved oxygen, electrical conductivity, salinity, total dissolved solids, temperature, and pH. Results showed significant increase in dissolved oxygen (4.25-5.52 mg/L), while electrical conductivity (491-677 µS/cm), salinity (0.23-0.32 ppt), and total dissolved solids (237-332 mg/L) decreased considerably. Temperature (29.28-31.07 °C) and pH (7.57-7.59) remained stable and within acceptable ranges for reuse in African Catfish production. However, retention time and flow rate did not significantly affect treatment efficiency within the tested parameters. Further research is recommended to explore the impact of longer retention times, wider flow rate ranges, different plant species and substrate types, and microbial community analysis to optimize the system's performance and promote sustainable aquaculture practices.

There exists a significant risk of water blooms during the utilization of recycled water in landscape environments. The nitrogen and phosphorus discharge standards of sewage treatment plants are very low. Controlling hydraulic retention time (HRT) is currently the most effective means to control water bloom. This article proposes a new method for determining the HRT threshold based on water transparency as a control indicator. The following results were obtained: (1) with the nitrogen and phosphorus concentrations of 15 and 0.5 mg/L, respectively, the threshold for HRT under high temperature and strong light is 4.6 days, while the threshold under low temperature and low light is 11.5 days. (2) With the nitrogen and phosphorus concentrations of 10 and 0.3 mg/L, respectively, the threshold for HRT under high temperature and strong light is 5 days, while the threshold under low temperature and low light conditions is 12.3 days. (3) The HRT threshold obtained under high temperature and strong light is lower than that obtained under low temperature and low light conditions. (4) The higher the concentrations of nitrogen and phosphorus, the smaller the HRT threshold obtained. (5) Blue algae have stronger adaptability than green algae and diatoms. HIGHLIGHTS A new method for determining the hydraulic retention time (HRT) threshold based on water transparency was proposed.; Cyanobacteria have stronger adaptability than green algae and diatoms.; Light and temperature have a significant impact on the determination of the HRT threshold.; The higher the concentrations of nitrogen and phosphorus, the smaller the threshold value of HRT obtained.;

Bioplastics have garnered substantial interest as alternatives to conventional petroleum-based plastics. However, their management and conversion to biogas continues to be significantly challenging. In this study, we evaluated the suitability of various plastics for hydrolysis at 160 °C for 12 h using different solvents. The biogas yield (BGY) of the monomers constituting these plastics and the obtained plastic hydrolyzates was comprehensively evaluated. When water was used as a solvent, 100 % hydrolysis of polylactic acid (PLA) and polybutylene succinate (PBS) was observed. When polybutylene adipate co-terephthalate (PBAT) and polyhydroxybutyrate (PHB) were hydrolyzed with water, the degradation ratio was approximately 30 %; however, using an aqueous lactic acid solution as a solvent improved the degradation ratio to 78 % and 100 %, respectively. In the BGY test of the plastic hydrolyzates, the biogas volumes derived from the hydrolyzates were 563, 461, 337, and 573 mL/g COD-added for PLA, PBS, PBAT, and PHB, respectively. With 1,160 gCOD/L waste PLA hydrolyzate, continuous co-digestion of sewage sludge and the hydrolyzate was conducted. Organic loading rates of sewage sludge and the hydrolyzate were 2.3 and 2.4 gCOD/L/d, respectively. The operation was stable and the methane production volume from the PLA hydrolyzate was 414 L/kgCOD-added. Using highly concentrated PLA hydrolyzate, the hydraulic retention time was 19.3 days, which was only 0.7 days shorter than that of anaerobic digestion of sewage sludge only (20 days). Therefore, highly concentrated PLA hydrolyzate maintains the retention time of normal sewage sludge digestion. Conclusively, the present study has crucial practical implications for plastic waste management.

The algal–bacterial shortcut nitrogen removal (ABSNR) process can be used to treat high ammonia strength wastewaters without external aeration. However, prior algal–bacterial SNR studies have been conducted under fixed light/dark periods that were not representative of natural light conditions. In this study, laboratory-scale photo-sequencing batch reactors (PSBRs) were used to treat anaerobic digester sidestream under varying light intensities that mimicked summer and winter conditions in Tampa, FL, USA. A dynamic mathematical model was developed for the ABSNR process, which was calibrated and validated using data sets from the laboratory PSBRs. The model elucidated the dynamics of algal and bacterial biomass growth under natural illumination conditions as well as transformation processes for nitrogen species, oxygen, organic and inorganic carbon. A full-scale PSBR with a 1.2 m depth, a 6-day hydraulic retention time (HRT) and a 10-day solids retention time (SRT) was simulated for treatment of anaerobic digester sidestream. The full-scale PSBR could achieve >90% ammonia removal, significantly reducing the nitrogen load to the mainstream wastewater treatment plant (WWTP). The dynamic simulation showed that ABSNR process can help wastewater treatment facilities meet stringent nitrogen removal standards with low energy inputs. HIGHLIGHTS Sidestream wastewater treatment by algal–bacterial shortcut nitrogen removal.; Varying illumination simulated summer/winter outdoor conditions.; Model developed for dynamic PSBR simulation under varying illumination.; Long-term simulation employed for TN removal in a full-scale WWTP.;

The biological aeration unit (BAU) is essential for removing organic and inorganic matter in the wastewater. Microorganisms present in the wastewater are able to remove organic and inorganic matter. The challenge is that the BAU consumes large quantities of energy during the process, due to the constant supply of air for the respiration of microorganisms. The standard hydraulic retention time (HRT) in the BAU is between 4 and 12 h per treatment cycle which is extensive, hence the high levels of energy consumption. The purpose of this study is to optimize the HRT in the BAU, by reducing the operation time of the air pumps/blowers, resulting in less energy consumption per treatment cycle. Particle swarm optimization (PSO) algorithm optimizes the HRT in the BAU. Variables in the optimization model are verified using the sensitivity analysis method. The results of the study show a reduction in HRT from 4 to 2.4954 h, which is a 37.6 % energy saving in the BAU. The biggest drivers in the HRT optimization model are energy consumption (61.3 %), airflow rate (36.8 %), and temperature (1.2 %). Therefore, decreasing airflow rate and increasing wastewater temperature reduces HRT in BAU.

Converting corn grains into bioethanol is an expanding practice for sustainable fuel production, but this is accompanied by the production of large quantities of by-products such as whole stillage. In the present study, the influence of advanced wet oxidation and steam explosion (AWOEx) pretreatment on biogas production and lignocellulose decomposition of corn whole stillage (CWS) was evaluated using semi-continuous thermophilic reactors. The digestion of the CWS was shown to be feasible with an organic loading rate (OLR) of 1.12 ± 0.03 kg VS/m3 day and a hydraulic retention time (HRT) of 30 days, achieving a methane yield of 0.75 ± 0.05 L CH4/g VSfed for untreated stillage and 0.86 ± 0.04 L CH4/g VSfed for pretreated stillage, corresponding with an increase in methane yield of about 15%. However, the reactors showed unstable performance with the highest investigated OLRs and shortest HRTs. Under optimal conditions, the conversion efficiencies of COD, cellulose, hemicellulose, and lignin were 88, 95, 97, and 59% for pretreated CWS, and 86, 94, 95, and 51% for untreated CWS, respectively. Microbial community analysis showed that Proteiniphilum, MBA03, and Acetomicrobium were the dominant genera in the digestate and were likely responsible for the conversion of proteins and volatile fatty acids in CWS. [ABSTRACT FROM AUTHOR]

BACKGROUND: Carbon (C) source consumption in industrial bioreactors removing soluble selenium (Se) contributes to the operating cost and can influence the rate of removal. This study used a laboratory chemostat to investigate the dependency of the rate of dissolved Se removal on the concentration of acetate and methanol, two C sources used in treatment of Se containing mine‐influenced water. It was hypothesized that the rate of dissolved Se removal follows a Monod kinetic model with C source as the limiting substrate. RESULTS: A chemostat fed with 25 mg‐selenate‐Se L−1 and acetate as C source at different concentrations operated over a range of hydraulic retention times (HRTs) achieved maximal removal of 99.7% dissolved Se at an HRT of 1.5 days [rate 16.7 mg‐Se (L day)−1]. When methanol was fed into the chemostat as the C source instead of acetate, the extent and rate of removal were much less [65% at an HRT of 6 days, rate 2.7 mg‐Se (L day)−1]. Carbon source consumption per mole of dissolved Se removed was not constant and exceeded stoichiometric estimates. Monod kinetic parameters for the Dechloromonas/Ralstonia consortium growing on acetate were estimated as KC= 3.36 mg‐C L−1 and YX/Cqmax,C= 0.70 L day−1. The Methylophilaceae consortium growing on methanol did not exhibit Monod kinetic growth. CONCLUSIONS: Using acetate as a C source achieved greater efficiency of dissolved Se removal than when methanol was used. Total dissolved Se removal rate was dependent on acetate only at low concentrations and when the HRT was close to washout. However, total dissolved Se removal rate was strongly dependent on HRT when methanol was used. © 2024 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Background: Spoiled milk from the dairy industry was subjected to anaerobic treatment to produce biogas at 37℃ in this experiment. Parameters such as inoculum dosage, pH, Chemical Oxygen Demand (COD), and retention time were optimized in a laboratory-scale batch reactor for 90 days. Methods: The anaerobic digestion of spoilt milk was carried out in a laboratory setting using a batch reactor. Then, using the recognized protocols of the APHA, the characteristics of the spoilt milk were assessed. In order to enhance the accuracy of predicting the reactor's performance, the research adopted two different models for kinetic analysis: the Stover-Kincannon model and the Grau second-order multi-component model. The reactor's improved performance, as indicated by evaluated kinetic parameters, was shown by the superior results from both of these models. Results: The results attained from the reactor's performance were then used as a reference to improve biogas production in a 100 L Anaerobic Sequential Batch Reactor (ASBR) for 45 days. The ASBR achieved a high COD removal efficiency of 92.4% and produced a maximum of 70.4 L of biogas per liter of spoiled milk, equivalent to 69.6% methane content. Conclusion: The Stover-Kincannon model yielded kinetic parameters of Umax = 0.295 gCOD/L and KB = 12.87 gCOD/L, whereas the Grau second-order model presented kinetic coefficients a = 6.744 and b = 2.578. The results obtained from the two models suggest that the investigated kinetic coefficients could be improved upon to increase the reactor's capability for handling different substrates during the AD process. [ABSTRACT FROM AUTHOR]

Worldwide, the transfer from the level of knowledge to operation at full scale is often difficult due to the expectation of some problems associated with new technologies that usually cannot be identified and solved on a full scale. Therefore, aspects of start-up times and methodologies become even more relevant when starting to implement any (or any project) processing system in wastewater treatment. Thus, this work aimed to develop and validate a concept for starting up a laboratory-scale lagoon system. This system typically contains a series of three continuous-flow lagoons to treat 50 Liters in the day from a municipal sewage facility in Al Rumaitha City, located north of Al Muthanaa Province in Iraq. Further, the influence of hydraulic detention time (HRT) on the hydraulic lagoon performance depending on site-specific conditions and determining factors influencing actual hydraulic residence time was evaluated by investigating the start-up of three different HRTs: 7 days, 14 days, and 21 days, as changing it altered the depth and, thus, the effective volume. The start-up experiment involved two different phases of experiments, and they were conducted for four months, distributed in two different periods: the first period of start-up experiments was characterized to develop a proper microbial floc as quickly as possible and also to select the appropriate HRT of the lagoon. The results from these experiments led to the selection of the best three-cell lagoons design, which had an HRT of 7 days because it remained more stable concerning COD removal. After that, the second period of the experiments began, devoted to helping performance assessment of these facilities in continuous mode via providing basic information about the treatment processes occurring in a lagoon and summarizing performance expectations until a steady state was reached. Throughout the period of this experiment, average removal efficiencies were found to be 73.34% for COD, 76.54% for NH4+-N, 36.06% for TN, and 38.30% for TP. [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]

Abstract The objective of the study was to evaluate the performance of Pistia stratiotes for treatment of domestic wastewater in a free surface water flow constructed wetland. The objective of the study was to evaluate contaminants removal efficiency of the constructed wetland vegetated with P. stratiotes in treatment of domestic wastewater against Hydraulic retention time (HRT) of 10, 20 and 30 days was investigated. This asks for newer and efficient low-cost nature-based water treatment system which along with cost takes into consideration the sustainability of the ecosystem. Five constructed wetland setups improved the wastewater quality and purify it significantly by reducing the TDS by 83%, TSS by 82%, BOD by 82%, COD by 81%, Chloride by 80%, Sulfate by 77%, NH3 by 84% and Total Oil and Grease by 74%. There was an increase in pH of about 11.9%. Color and odor of wastewater was also improved significantly and effectively. It was observed that 30 days’ HRT was optimum for the treatment of domestic wastewater. The final effluent was found to be suitable as per national environmental quality standards and recycled for watering plants and crop irrigation but not for drinking purposes. The treatment in constructed wetland system was found to be economical, as the cost of construction only was involved and operational and maintenance cost very minimal. Even this research was conducted on the sole purpose of commuting the efficiency of pollutant removal in short span time.

Abstract 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. Graphical Abstract

Due to the natural energy sources used in constructed wetlands, minimal energy and chemicals are required for wastewater treatment. For the successful wastewater treatment via constructed wetlands, adequate pretreatment and a sufficient amount of oxygen are crucial. Constructed wetlands can be used to treat industrial wastewater, such as wastewater from the dairy industry, with prior degreasing. This study was conducted on a horizontal flow pilot constructed wetland located on a plot of land used by the Biotechnical Faculty in Bihać. The constructed wetland consisted of two fields planted with rushes (Typha latifolia) and reeds (Phragmites australis). The substrate and plants were not changed during the experimental period. We monitored the efficiency of industrial wastewater treatment (wastewater from the dairy industry) by season, varying the flow rate as well as the hydraulic retention time of the water in the device. The quality of the influent and effluent was monitored by determining analytical parameters. The constructed wetland showed the highest efficiency in the summer period, with a hydraulic retention time of 6 days, with removal efficiencies of 98.03% for ammonia, 98.19% for total nitrogen, 95.27% for total phosphorous, 94.50% for COD and 97.73% for BOD5. The organic substance removal efficiency across all four seasons was 94.68%.

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]

Wastewater treatment faces a growing challenge in removing nutrients and organic matter. This study aimed to evaluate the effectiveness of the moving bed biofilm reactor (MBBR) system in removing nutrients and organic from municipal wastewater. The impact of different carrier filling ratios and hydraulic retention times (HRT) on the removal efficiency was systematically investigated. Moreover, the addition of nanoparticle additives to enhance system performance was evaluated. The optimal conditions for the MBBR system were 30-45% filling ratios and a 10-hour HRT, resulting in maximum removal efficiencies for biological oxygen demand (BOD5), chemical oxygen demand (COD) and ammonia (NH4 +-N) with a percentage of 85.23%, 81.69%, and 54.45% respectively. Furthermore, adding nanoparticles improved the BOD5 and COD removal efficiencies by 6.6% and 8.0% respectively, compared to the MBBR system without nanoparticles. [ABSTRACT FROM AUTHOR]

Biohythane production through anaerobic digestion of organic waste in a single reactor is a potentially more cost-effective process compared to the traditional two-stage scheme. In this work, the production and composition of biohythane obtained from complex organic waste in a semi-continuous thermophilic anaerobic bioreactor was studied with a gradual increase in hydraulic retention time (HRT) from 2 to 5 days and a corresponding decrease in the organic loading rate from 12.27 to 4.8 g VS/(L·d). At low HRT, a significant predominance of hydrogen content in biogas was observed. However, with an increase in HRT to 5 days, the volumetric and specific yield of methane increased. The modified Gompertz model and the first order model showed a high coefficient of determination (R2 = 0.97–1) for the calculated kinetic parameters of hydrogen and methane formation. At all values of HRT, the predominance of the hydrogen-producing genus Thermoanaerobacterium was observed in the microbial community. When HRT was increased to 5 days, representatives of methanogenic archaea of the genera Methanosarcina and Methanosaeta actively developed. The hydrogen and methane content in the final biogas mixture was approximately 37 % and 30 %, respectively. Potential research avenues for improving biohythane production in a single reactor have been considered. [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]

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]

The effects of hydraulic retention time (HRT) on the performance of two-phase anaerobic fermentation for caproic acid production from Chinese cabbage waste (CCW) were investigated. In the electron donor phase, yeast was inoculated to achieve efficient autopoietic ethanol, providing electron donors for the chain elongation process. Shorter HRT led to drastic fluctuations in microorganisms, thus resulting in lower acid yields at HRT of 6 days. At HRT of 10 days, the balanced collaboration of various key bacteria avoided the accumulation of intermediate by-products, and the caproic acid production reached 4660 mg COD/L, which was 119.5% and 154.8% higher than that at HRTs of 6 and 14 days, respectively. At HRT of 14 days, the low ethanol loading rate resulted in ethanol excessive-oxidation to acetic acid. Acetic acid accounted for 41.5% of the total product, while the selectivity of caproic acid was only 15.3%. The main contributor to the production process of caproic acid was Caproiciproducens , while the Ruminalococcaceae also played a role in the process. This study provided a theoretical basis for the efficient production of caproic acid through continuous fermentation with autopoietic electron donors. • Efficient autopoietic electron donors were achieved by inoculating yeast. • The highest caproic acid yield of 4660 mg COD/L was obtained at HRT of 10 days. • Low ethanol loading rate tended to produce acetic acid. • HRT has a selection effect on microorganisms. [ABSTRACT FROM AUTHOR]

Effects of total vermibed depth, as well as the ratio of aerobic (the unsubmerged) to anaerobic (the submerged) zone on the performance of the horizontal subsurface flow macrophyte‐assisted vermifilters (HSSF‐MAVFs) treating synthetic brewery wastewater at a higher hydraulic loading rate (HLR), were investigated for the first time. Results showed that the HSSF‐MAVF with a 50 cm total and 18 cm submerged vermibed depth yielded the optimum removal of the pollutants, ensuring a (91.2 ± 1.7)%, (81.8 ± 1.9)%, (67.4 ± 3.9)%, and (63.1 ± 2.3)% removal of chemical oxygen demand (COD), ammonium N (NH4+–N), total N (TN), and organic N, respectively, whereas there was an increase of (142 ± 6.3)% in the effluent nitrate–N (NO3−–N) than that in the influent. At the optimum condition, the effluent concentrations of all the pollutants including COD, NH4+–N, NO3−–N, TN, and organic N were well below the surface water discharge standards specified by the Central Pollution Control Board (CPCB), and thus, the effluent of the HSSF‐MAVF could be safely discharged into the surface water bodies. Practitioner Points: Total vermibed depth of HSSF‐MAVFs was optimized for organic and nitrogen removal.HSSF‐MAVFs were subjected to the higher HLR of synthetic brewery wastewater.Removal of COD and NH4+–N was decreased with the increase in submerged bed depth.Removal of organic N and TN was increased with the increase in submerged bed depth.Total/unsubmerged bed depth had a positive impact on the organic and N removal. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) are a viable source of clean and renewable energy from wastewater and gaining attention on a global scale. Thus, this research work focuses on the energy production from high-strength palm oil mill wastewater using MFCs. A state-of-the-art technique for improving the performance of MFCs by covering a carbon fibre anode with various sized powdered activated carbon (PAC) particles was investigated. In addition, the MFCs were tested at various hydraulic retention times (HRT) to assess the performance displayed by modified MFCs. Results showed that a relatively smaller amount of PAC with a diameter of 13 μm coated at the anode during the cultivation stage at a shorter hydraulic retention time (4 days) would produce 504.1 ± 8.7 mW m−3 of power, 39.9 ± 2.9% of chemical oxygen demand removal efficiency, and 299 ± 63 mL of biogas. While, MFC running at a longer hydraulic retention time (12 days) was able to produce more power and had better effluent quality than those operating at a shorter hydraulic retention period. [Display omitted] • Ability of MFC to produce energy and treat palm oil wastewater simultaneously. • MFC-carbon cloth anode coated PAC produced almost doubled energy than control. • About 10% higher COD removal with MFC-carbon cloth anode coated PAC than control. • Inverse relationship between biogas production and power generation was identified. [ABSTRACT FROM AUTHOR]

Denitrifying woodchip bioreactors successfully remove nitrates from reverse osmosis desalinization brine. On-farm desalination plants only operate for several hours per day in batch mode, meaning bioreactors should also operate in batch cycles, although this type of bioreactor operation is relatively unstudied. This study compared two tests of three cycles of 24 h per week with two treatments each (Test 1 8 vs. 24 h, and Test 2 8 vs. 12 h). Cylindrical pilot-scale bioreactors were filled with 130 kg of citrus woodchips and an average of 322 L of brine. The results show that the treatments with longer saturation periods of 24 and 12 h exhibited higher removal rates under operational conditions (i.e., 8 h flooding based on a 24 h cycle) than the 8 h treatment. However, the nitrate removal rates of the 8 h treatment were higher under fill cycle conditions (i.e., 8 h flooding based on an 8 h cycle). Dissolved organic carbon liberated from the woodchips was greater in treatments with longer drying periods (i.e., treatments with shorter saturation periods). Batch bioreactors should be considered under applicable conditions to increase nitrate removal rates. [ABSTRACT FROM AUTHOR]

Livestock farming wastewater is complex in composition, containing a large number of pathogenic microorganisms and ammonia nitrogen (NH 4 +-N) with high concentration, which makes biological treatment difficult. In this study, tidal flow constructed wetlands were applied to treat piggery biogas slurry. Compared with a continuous flow constructed wetland, two tidal influent modes (hydraulic retention time: idling time for 12 h:12 h and 20 h:4 h, namely TFCW1 and TFCW2) were set up to explore treatment performances on chromaticity, turbidity, chemical oxygen demand (COD), total nitrogen (TN), NH 4 +-N and total phosphorus (TP), and determine the relationship between nitrogen transfer and dissolved oxygen (DO) contents. The fluorescence spectra of dissolved organic matter (DOM) in constructed wetlands were analyzed by excitation-emission matrix spectroscopy-parallel factor analysis to reveal its composition and content of humus. The results showed that tidal flow constructed wetlands obviously improved the removal of chromaticity and turbidity by 44.6% and 10.1%, in comparison to continuous flow constructed wetland. TFCW2 had enhanced reduction on pollutants, with removal efficiencies of COD, NH 4 +-N and TP at 78.6%, 82.1% and 84.0%, respectively. Furthermore, three fluorescent components were detected in TFCW2, and the value of Fmax was increased in the effluent, among which the Fmax of C3 (Humic-like substances) increased obviously from 0.320 to 9.39. The ratio of C2 (Aquatic fulvic acids) to C3 showed a slow increasing trend in the daily outflow of TFCW2, while C1 (dark-incubation substances) remained relatively constant. Fluorescence index (FI), humification index (HIX) and biological index (BIX) increased from 1.35 to 2.09, 0.210–1.51, and 0.240–1.05, respectively, showing that the effluent from the tidal flow constructed wetland had a high microbial activity. This study provided a new insight for the advanced treatment of livestock biogas slurry with a high NH 4 +-N content. [Display omitted] • Actual piggery biogas slurry was treated by tidal flow constructed wetland. • The changes of DO and pollutant concentrations along the system were detected. • 82.1% of NH 4 +-N and 84.0% of TP were removed by tidal flow constructed wetlands. • Dark-incubation substances, aquatic fulvic acids and humic-like substances were three main components in DOM. [ABSTRACT FROM AUTHOR]

Water scarcity is a global issue and finding alternative ways to meet our water needs within available resources is becoming increasingly important. Repurposing greywater for non‐potable uses, such as irrigation and car washing, can help alleviate the demand for drinking water. Greywater recycling and reuse are viable options to combat water scarcity. This study investigated the treatment of greywater using phytoremediation, specifically focusing on the effect of water hyacinth density and hydraulic retention time (HRT). An artificial neural network was used to optimize these parameters in the treatment system. The experiment spanned over 7 weeks and consisted of two phases. In phase I, different water hyacinth densities (ranging from 1.0 to 4.0 kg/m2) were tested, while phase II examined various HRTs (ranging from 12 to 48 h). The results indicated that the optimal conditions for greywater treatment were a water hyacinth density of 2 kg/m2 and an HRT of 48 h. Under these optimal conditions, the treatment system achieved high removal efficiencies for turbidity (98.02 ± 0.75%), chemical oxygen demand (59.42 ± 5.64%), ammonium‐nitrogen (87.45 ± 7.29%), and phosphate (94.50 ± 2.19%). However, the removal of total suspended solids was relatively low at 43.98 ± 9.20%. These findings were confirmed using an artificial neural network, showing a strong correlation (R > 0.99). The study concludes that phytoremediation using water hyacinth can be a viable option for greywater recycling and reuse, effectively addressing water scarcity. The recommended optimal conditions include a water hyacinth density of 2 kg/m2 and an HRT of 48 h. [ABSTRACT FROM AUTHOR]

Due to the natural energy sources used in constructed wetlands, minimal energy and chemicals are required for wastewater treatment. For the successful wastewater treatment via constructed wetlands, adequate pretreatment and a sufficient amount of oxygen are crucial. Constructed wetlands can be used to treat industrial wastewater, such as wastewater from the dairy industry, with prior degreasing. This study was conducted on a horizontal flow pilot constructed wetland located on a plot of land used by the Biotechnical Faculty in Bihać. The constructed wetland consisted of two fields planted with rushes (Typha latifolia) and reeds (Phragmites australis). The substrate and plants were not changed during the experimental period. We monitored the efficiency of industrial wastewater treatment (wastewater from the dairy industry) by season, varying the flow rate as well as the hydraulic retention time of the water in the device. The quality of the influent and effluent was monitored by determining analytical parameters. The constructed wetland showed the highest efficiency in the summer period, with a hydraulic retention time of 6 days, with removal efficiencies of 98.03% for ammonia, 98.19% for total nitrogen, 95.27% for total phosphorous, 94.50% for COD and 97.73% for BOD5. The organic substance removal efficiency across all four seasons was 94.68%. [ABSTRACT FROM AUTHOR]

This study employed a laboratory-scale continuous upflow bio-contact oxidation reactor to treat 50 L/day of municipal wastewater in Al Rumaitha City, located north of Al Muthanaa Province in Iraq. The reactor configuration consisted of two anoxic-aerobic reactors nested inside each other, with a 1:3 volume ratio of anoxic to aerobic zones. Both the anoxic and aerobic reactors were loaded with K1 bio-media, filling them to 50% capacity for fixing and preserving the biomass. The reactors were operated in a mode that achieved full nitrification-denitrification without any sludge return, relying solely on internal recycling from the aerobic to the anoxic reactor. After biofilm formation on the carriers, three distinct hydraulic retention times (HRTs) were investigated - ranging from 24 to 12 hours - to evaluate their impact on removing biological nutrients from municipal sewage. In this operational approach, the preferred internal recycle ratio and gas/water ratio for effective nitrogen removal were a complete feed rate recycle of 100% and a ratio of 1:5, respectively. The experiment results highlighted that a 24-hour hydraulic retention time was most suitable for the simultaneous removal of organic carbon (COD) and nutrients. During this period, average removal efficiencies were found to be 93.51% for COD, 94.50% for ammonium (NH4 +), 60.98% for total nitrogen (TN), and 67.57% for total phosphorus (TP). Furthermore, the aerobic bio-contact oxidation reactors maintained an average dissolved oxygen (DO) concentration of 4.89 mg/L. In contrast, the anoxic biocontact oxidation reactors exhibited a lower average DO concentration of 0.38 mg/L. [ABSTRACT FROM AUTHOR]

The impacts of changes in hydraulic retention time (HRT) on nitrogen elimination, the activity of sludge and the structure of microbial communities in a sequencing batch reactor under the joint stress of ibuprofen (IBP) and ciprofloxacin (CIP) were investigated. Under the combined stress of IBP (belonged to nonsteroidal anti-inflammatory drugs) and CIP (belonged to antibiotics), the elimination level of ammonia nitrogen, chemical oxygen demand, and the rate of specific ammonia oxidation, specific nitrite oxidation, specific nitrate reduction in activated sludge declined with the shortening of HRT. Under the joint stress of IBP and CIP, the content of polysaccharide (PS) and protein (PN) together with the ratio of PN to PS in the extracellular polymeric substances grew with the shortening of HRT, and the content of aromatic proteins increased significantly, which indicated that aromatic proteins were the major protective response substances to the shortening of HRT. Under the joint stress of IBP and CIP, with the reduction of HRT, and the reduction rate of relative abundance of nitrifying bacteria was more evident than that of denitrifying bacteria. This exploration gives novel thoughts for understanding the impacts of HRT on biological nitrogen removal of wastewater under combined stress of IBP and CIP. [ABSTRACT FROM AUTHOR]

The production of Volatile Fatty Acids (VFAs) from wastewater holds significant importance in the context of biorefinery concepts due to their potential as valuable precursors for various bio-based processes. Therefore, the primary objective of this research is to investigate the fermentation of Winery Wastewater (WW) in an Upflow Anaerobic Sludge Blanket (UASB) reactor to generate VFAs, with particular emphasis on Caproic Acid (HCa) production and the dynamics of the microbiota, under varying Hydraulic Retention Time (HRT) periods (8, 5, and 2.5 h). The change from an 8 h to a 5 h HRT period resulted in an approximately 20% increase in total VFA production. However, when the HRT was further reduced to 2.5 h, total VFA production decreased by approximately 50%. Concerning the specific production of HCa, expressed in grams of Chemical Oxygen Demand (gCOD), the maximum yield was observed at around 0.9 gCOD/L for a 5-h HRT. Microbial population analysis revealed that Eubacteria outnumbered Archaea across all HRTs. Population dynamics analysis indicated that the Firmicutes Phylum was predominant in all cases. Within this phylum, bacteria such as Clostridium kluyveri and Clostridium sp., known for their ability to produce HCa, were identified. Based on the results obtained, the application of the UASB reactor for WW treatment, within the biorefinery framework, has the potential to provide a practical alternative for HCa production when operated with a 5 h HRT. [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]

Understanding the impact of various parameters on the kinetics of dissolved selenium (Se) removal in bioreactors can be a challenging task, primarily due to the mass transfer limitations inherent in bioreactors employing attached growth configurations. This study successfully established a proof-of-concept for the efficient removal of Se from aqueous solutions using a chemostat bioreactor that relies solely on suspended growth. The research investigated the effect of selenate-Se feed concentrations under two distinct Se concentration conditions. One experiment was conducted at a considerably elevated concentration of 25 mg/L to impose stress on the system and evaluate its response. Another experiment replicated an environmentally relevant concentration of 1 mg/L, mirroring the typical Se concentrations in mine water. The bioreactor, featuring a working volume of 0.35 L, was operated as an anaerobic, fully mixed chemostat with hydraulic retention times (HRTs) ranging from 5 to 0.25 days. The outcomes revealed the chemostat's capacity to remove up to 25 mg/L of dissolved Se from water for all HRTs exceeding 1 day, under otherwise optimal conditions encompassing temperature, pH, and salinity. The research's significance lies in the development of a versatile tool designed to examine Se removal kinetics within a system devoid of mass transfer limitations. Furthermore, this study verified the ability of the bacterial consortium, obtained from a mine-influenced environment and enriched in the laboratory, to grow and sustain Se removal activities within a chemostat operating with HRTs as short as 1 day.

The Nakdong River underwent water impoundment after eight weirs were constructed as part of South Korea's Four Major River Restoration Project from 2009 to 2012. In this study, we aimed to confirm whether the assemblage of phytoplankton based on phytoplankton functional groups (PFGs), could indicate environmental changes in the weir section (WS) and non-weir section (NWS) of the lower Nakdong River after the construction of the weir. Thus, we examined the relationships between PFGs and gradients in environmental drivers, such as physicochemical, meteorological, and hydrological variables. Environmental gradients were observed between the WS and NWS in dissolved oxygen (DO), electric conductivity (EC), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), dissolved total nitrogen (DTN), dissolved total phosphorus (DTP), ammonia nitrogen (NH3–N), nitrate nitrogen (NO3–N), and phosphorus (PO4–P), which were relatively higher in the WS. Seventeen PFGs were identified (A, B, C, D, E, F, G, H1, J, LM, LO, MP, P, T, W1, X1, and X2).Additionally, the LM and P groups, preferring an enriched lentic system more than other groups, were found to be the dominant PFGs that led the succession of assemblages. Traditional nutrients (N, P) and organic pollutants (BOD, COD) primarily affected the autochthonous growth of the most dominant PFGs in the WS as HRT (hydraulic retention time) increased. Furthermore, the hydrological variables associated with meteorological conditions have a synergistic effect on the composition of the major PFGs and chemical and physical variables in the WS. In other words, the WS may be a new source of inoculum that primarily determines the occurrence and maintenance of phytoplankton in the immediate downstream region (NWS). In particular, group LM (mainly potentially toxic Microcystis) developing in the upper weir impoundment is transported downstream, resulting in a high inoculation effect on further growth in the NWS during the summer monsoon season.

Abstract Background Two parallel plug-flow reactors were successfully applied as a hydrolysis stage for the anaerobic pre-digestion of maize silage and recalcitrant bedding straw (30% and 66% w/w) under variations of the hydraulic retention time (HRT) and thin-sludge recirculation. Results The study proved that the hydrolysis rate profits from shorter HRTs while the hydrolysis yield remained similar and was limited by a low pH-value with values of 264–310 and 180–200 gO2 kgVS −1 for 30% and 66% of bedding straw correspondingly. Longer HRT led to metabolite accumulation, significantly increased gas production, a higher acid production rate and a 10–18% higher acid yield of 78 gSCCA kgVS −1 for 66% of straw. Thin-sludge recirculation increased the acid yield and stabilized the process, especially at a short HRT. Hydrolysis efficiency can thus be improved by shorter HRT, whereas the acidogenic process performance is increased by longer HRT and thin-sludge recirculation. Two main fermentation patterns of the acidogenic community were found: above a pH-value of 3.8, butyric and acetic acid were the main products, while below a pH-value of 3.5, lactic, acetic and succinic acid were mainly accumulating. During plug-flow digestion with recirculation, at low pH-values, butyric acid remained high compared to all other acids. Both fermentation patterns had virtually equal yields of hydrolysis and acidogenesis and showed good reproducibility among the parallel reactor operation. Conclusions The suitable combination of HRT and thin-sludge recirculation proved to be useful in a plug-flow hydrolysis as primary stage in biorefinery systems with the benefits of a wider feedstock spectrum including feedstock with cellulolytic components at an increased process robustness against changes in the feedstock composition. Graphical Abstract

Converting corn grains into bioethanol is an expanding practice for sustainable fuel production, but this is accompanied by the production of large quantities of by-products such as whole stillage. In the present study, the influence of advanced wet oxidation and steam explosion (AWOEx) pretreatment on biogas production and lignocellulose decomposition of corn whole stillage (CWS) was evaluated using semi-continuous thermophilic reactors. The digestion of the CWS was shown to be feasible with an organic loading rate (OLR) of 1.12 ± 0.03 kg VS/m3 day and a hydraulic retention time (HRT) of 30 days, achieving a methane yield of 0.75 ± 0.05 L CH4/g VSfed for untreated stillage and 0.86 ± 0.04 L CH4/g VSfed for pretreated stillage, corresponding with an increase in methane yield of about 15%. However, the reactors showed unstable performance with the highest investigated OLRs and shortest HRTs. Under optimal conditions, the conversion efficiencies of COD, cellulose, hemicellulose, and lignin were 88, 95, 97, and 59% for pretreated CWS, and 86, 94, 95, and 51% for untreated CWS, respectively. Microbial community analysis showed that Proteiniphilum, MBA03, and Acetomicrobium were the dominant genera in the digestate and were likely responsible for the conversion of proteins and volatile fatty acids in CWS.

Interest in wastewater recycling as an alternative source has grown as a result of increased water demand, water shortage due to population increase, low rainfall, and economic and environmental issues. Water recycling from greywater can serve as a sustainable solution for water demands. Nowadays, membrane bioreactor systems have significantly improved treatment performance and have been widely used in water reuse and reclamation. However, optimization of the MBR system in greywater treatment has received less attention. In this context, an experimental investigation of the MBR for greywater reuse was considered to identify the optimal hydraulic retention time of the MBR system. The lab-scale MBR consisted of a bioreactor with a net volume of 10 L, containing one submerged polypropylene hollow fiber membrane module with an area of 0.2 m2. The lab-scale MBR was fed with greywater collected from a dormitory of Shiraz University and operated for 160 days. Four HRTs (3, 5, 7 and 9 h) were tested to investigate the performance of the MBR system on the removal of total ammonia nitrogen, organic matter, turbidity, and total suspended solid. The results showed that the MBR system could remove more than 95% of COD, 99.5% of BOD5, 99% TAN, and 99.2% of TSS from greywater. The COD, BOD5, TSS effluents, and turbidity were below 10.5 mg/L, 0.4 mg/L, 0.6 mg/L, and 0.3 NTU, respectively. The results also showed that the optimal HRT of the MBR system for greywater treatment was 3 h. In conclusion, the MBR system with optimal HRT of 3 h is highly efficient for greywater treatment and it could produce sustainable water for non-potable reuse such as toilet flushing reuse in terms of chemical–physical quality parameters.

In China, aquaculture is the primary source of aquatic products due to the decrease in wild fishery resources. In 2018, the total output of aquatic products in China expanded to 47.6 million tons, accounting for 58% of global aquaculture production. Intensive culture methods generally use significant quantities of feed however, approximately 75% of nitrogen in the feed is retained in aquaculture water, mainly as soluble nitrogen, such as ammonia nitrogen (NH4+-N) and nitrate (NO3–-N), owing to low feed-utilization rates during cultivation. At the same time, fishes generate a substantial amount of excreta, which will cause the increase of nitrogen compounds in water and negatively affects the quality of aquatic products. Serious problems could occur if nitrogen compounds are discharged into the environment, including the eutrophication of rivers, the deterioration of drinking water sources, and hazards to human health. Furthermore, nitrates can form potentially carcinogenic compounds, such as nitrosamines and nitrosamides, and nitrate consumption can cause methemoglobinemia in infants. The Second National Census of Pollution Sources survey showed that the total nitrogen emission from aquaculture was 99 100 tons in 2017. To protect the environment and human health, it is important to remove nitrogen from aquaculture tailwater before discharging it to the surrounding waters. Biological denitrification is considered the most promising approach since nitrate can be reduced to harmless nitrogen gas by bacteria. A sufficient carbon source is necessary during the heterotrophic denitrification process. To solve the problems mentioned above, external liquid carbon sources such as methanol, acetic acid, and glucose are added to the tailwater, but they are costly, require high-energy, and have high operating requirement. In contrast, agricultural wastes as a carbon source have exhibited significant economic advantages and high efficiency. Many aquaculture tailwater treatment systems often face variations in hydraulic retention times (HRT) and influent nitrate concentration (INC), which are caused by acute changes in tailwater characteristics and production, and HRT and INC often exert a profound effect on the treatment performance of biological treatment systems. Extensive research has confirmed that adding agricultural waste (such as corncob, woodchip and rice straw) to municipal sewage and industrial wastewater can effectively improve denitrification efficiency. However, the effect of using agricultural waste as denitrifying carbon source to treat aquaculture tail water remains unclear. Banana stalk (BS), a typical agricultural waste product, is used as a denitrifying carbon source for the first time in this study. The study investigated the effects of HRT and INC on the denitrification performance of BS, and provided a theoretical basis for the application of agricultural waste in aquaculture tailwater treatment. In this study, using BS as a carbon source and a towel as biological carrier, the performance of solid-phase denitrification under dynamic flow conditions was studied by using a 1-D column experiment. In the HRT optimization experiment, INC was maintained at 50 mg/L and operated under four HRTs (16 h, 20 h, 24 h and 28 h) for 14 days. The effluent NO3–-N, nitrite (NO2–-N), NH4+-N, Total nitrogen (TN), Total phosphorus (TP), and chemical oxygen demand (COD) removal efficiency were measured every 2 days. The optimal HRT of BS-DR (banana stalk-denitrification reactor) was optimized by one-way ANOVA analysis. Then, based on the optimization of HRT, the reactor was operated for 14 days under different INC (75 mg/L, 100 mg/L, and 125 mg/L). The sampling time interval and measurement indexes were the same as those of the HRT optimization experiment. The Illumina MiSeq high-throughput sequencing method was used to sequence and analyze the two hyper-variable regions (V3-V4) of the 16S rRNA gene of bacteria in the initial and final stages of the BS-DR. The results indicated that HRT and INC are the key factors affecting the denitrification performance of BS-DR. There was no significant difference in nitrate removal efficiency when the HRT was 20 h (96.71±1.36)%, 24 h (94.57±4.73)%, and 28 h (99.41±0.64)%, but they were significantly higher than that when the HRT was 16 h (87.53±7.95)%. Therefore, the optimal HRT for BS-DR was 20 h, and no nitrite accumulation. The second set of experiments was conducted using the optimal HRT obtained from the first set of experiments. The effluent nitrate concentration (ENC) and nitrate removal rate (NRR) of BS-DR increased significantly with increase in INC (P < 0.05), and the effluent COD decreased with increase in INC, and the proper INC for BS-DR was ≤50 mg/L. It is worth noting that BS-DR could completely remove NH4+-N in both experiments. In addition, HRT significantly affects the removal efficiency of TP, but INC has little effect. According to pyrosequencing analysis, the microbial community structure of BS-DR changed after long-term operation, with the relative abundances of Proteobacteria, Bacteroidetes, Campilobacterota, and Firmicutes increasing to 31.20%, 6.67%, 3.08%, and 4.26%, respectively, ensuring the efficient operation of the reactor. On the contrary, the relative abundances of Halobacterota, Desulfobacterota, Sva0485, Chloroflexi, and Verrucomicrobiota decreased to 10.39%, 5.13%, 2.82%, 2.00%, and 1.17 %, respectively, in the reactor. In addition, at the genus level, most of the dominant bacteria at the end of reactor operation play a role in denitrification and degradation of agricultural waste, which is significantly different from that at the beginning of the reactor operation.

The performance of two tropical plants, Rhynchospora corymbosa L. (RC) and Coix lacryma-jobi, L (CL) in treatment of primary sewage effluent in lab-scale vertical-flow constructed wetlands (VFCW) along with no plant control wetland was investigated. A batch-flow VFCWs were operated under batch fill and drain hydraulic loading system with hydraulic retention times (HRT) of 0.5, 1, and 2 days and fill rate of 8 L/day. Removal of solids, organics, nutrients, and pathogens were monitored. The volumetric contaminant removal rates were best described by 1st order kinetics except for ammonia and phosphate, which was best described by Stover-Kincannon kinetics. Influent TSS, PO43−, COD, BOD5, and total coliform concentration were low but high in NH4+ concentration. CL was better in nutrient removal as HRT increases compared to RC. RC was more efficient at TSS, turbidity, and organics removal. Pathogen removal was independent of plant type but HRT. Solids and organic removal were lower in CL planted CWs due to preferential flow paths created by their bulky root. CL planted CWs removed more nutrients followed by RC planted CWs and then no-plant control CWs. The results of these tests demonstrate that both CL and RC are suitable for the treatment of municipal wastewater in VFCW system. [ABSTRACT FROM AUTHOR]

The carboxylate platform is a sustainable and cost-effective way to valorize wastes into biochemicals that replace those of fossil origin. Short-chain fatty acids (SCFAs) are intermediates generated during anaerobic fermentation (AF) and are considered high-value-added biochemicals among carboxylates. This investigation aimed to produce SCFAs through the AF of sugar beet molasses at 25 °C and semi-continuous feeding mode in completely stirred tank reactors. A particular focus was devoted to the role of hydraulic retention time (HRT) variation in SCFAs production and distribution profile. The highest SCFAs concentration (44.1 ± 2.3 gCOD/L) was reached at the HRT of 30 days. Caproic acid accounted for 32.5–35.5% (COD-concentration basis) at the long HRTs of 20 and 30 days due to the carbon chain elongation of shorter carboxylic acids. The findings of this study proved that HRT could be used to steer the anaerobic process toward the targeted SCFAs for specific uses. Furthermore, the successful operation at low-temperature conditions (i.e., 25 °C) makes the process economically promising. [ABSTRACT FROM AUTHOR]

Municipal and industrial wastewater discharge is a longstanding environmental problem that pollutes water bodies, affecting both the landscape and human health. In the department of Sucre, Colombia, nearby urban sewage is discharged into the Arroyo Grande de la Sabana, and only Sincelejo city has a treatment system in place. Therefore, it is critical to identify effective treatment methods for removing contaminants from water. The objective of this study was to evaluate the efficiency of a constructed wetland (CW) with horizontal subsurface flow (HSSF) planted with Thalia geniculata for treating wastewater from the Arroyo Grande de la Sabana in Sucre, Colombia. The study investigated the effectiveness of a constructed wetland planted with Thalia geniculata for treating wastewater from the Arroyo Grande de la Sabana in Sucre, Colombia. Two different hydraulic retention times (HRTs) of 3 and 5 days were tested, and the plant population density was analyzed to determine the better adaptation of plants to the constructed wetlands. The results showed that on the fifth day of treatment, nitrate concentrations decreased by 33.22%, nitrite by 93.04%, and phosphate by 95.66%. Additionally, the biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) values decreased by 97.27% and 80.27%, respectively. On the third day of retention, turbidity, and total suspended solids (TSS) in the water decreased by 90.13% and 83.08%, respectively. The study concluded that the 5-day HRT was most effective in removing contaminants such as nitrites, nitrates, and phosphates, while the 3-day HRT was more efficient for TSS, turbidity, total coliforms (TCs), and fecal coliforms (FCs). [ABSTRACT FROM AUTHOR]

BACKGROUND: Microalgal biofilm systems are a promising approach for wastewater treatment and for production of biodiesel precursors through simple biomass harvesting. However, the low concentration of nutrients in wastewater limits possible approaches for microalgal growth. The effective decoupling of the solid retention time (SRT) and the hydraulic retention time (HRT) in biofilm reactors as an alternative for increasing microalgae growth and biodiesel performance in low‐strength wastewater has not been investigated. In this study, we tracked how decoupling the SRT and the HRT influences the removal of organics and nutrients, the biomass productivity and the production of fatty acid methyl esters (FAME). RESULTS: Three perturbations of the HRT, SRT and liquid level (LL) with regards to the base case condition (HRT 2.6 h; SRT 21 days, LL 5 mm) performance were analyzed. The base case showed the highest TN and TP removal (>50%) outcomes with high pH values (>10). A decrease of HRT and SRT from 2.6 to 1.3 h and 21 to 10 days, respectively, promoted an increment of microalgal productivity ≤5.8 ± 0.7 g m−2 day−1. A short HRT of 1.3 h enhanced the nitrogen removal rate up to 1.2 g N m−2 day−1, which triggered an increase in the FAME productivity and microalgal density on the biofilms without affecting their productivity. CONCLUSION: Our study demonstrated that the strategy of decoupling HRT and SRT allows operation at shorter HRTs, promoting microalgal growth without affecting FAME production in low‐strength municipal wastewater. © 2023 Society of Chemical Industry (SCI). [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]