Conditions Of Hydraulic Retention Time Research Articles

Continuous operation of nano-catalytic ozonation using membrane separation coupling system: Influence factors and mechanism

The application of nano-catalysts in improving the ozonation removal efficiency for refractory organic compounds has been extensively investigated. However, cost-effective nano-catalysts separation remains a challenge. In this study, membrane separation processes were employed to separate nano-MgO catalysts from an ozonation system. A continuous nano-catalytic ozonation membrane separation (nCOMS) coupling system was successfully constructed for treating quinoline. The results showed that long hydraulic retention time (HRT) and high nano-MgO dosage could improve the quinolone removal efficiency but shorten operation cycles. At the optimal operation conditions of HRT = 4 h and nano-MgO dosage = 0.2 g/L, the nCOMS system achieved a stable quinoline removal efficiency of 85.2% for 240 min running with a transmembrane pressure lower than 10 kPa. The quinoline removal efficiency contribution for ozonation, catalysis and membrane separation was 57.1%, 24.9% and 18.0%, respectively. Compared to ozonation membrane separation system, the fouling rate index of the nCOMS system increased by 60% under optimal conditions, but the irreversible fouling was reduced to 28%. In addition, the nCOMS system exhibited reduced adverse effects of coexisting natural organic matter (NOM) on quinoline removal and membrane fouling. In conclusion, the nCOMS system demonstrated higher quinoline removal efficiency, lower irreversible fouling, and reduced adverse effect of coexisting NOM, thereby signifying its potential for practical applications in advanced treatment of industrial wastewater.

Comprehensive comparison of integrated fixed-film activated sludge (IFAS) and AAO activated sludge methods: Influence of different operational parameters

Due to limited land availability in municipal wastewater treatment plants, integrated fixed-film activated sludge (IFAS) technology offers significant advantages in improving nitrogen removal performance and treatment capacity. In this study, two systems, IFAS and Anaerobic-Anoxic-Oxic Activated sludge process (AAO), were compared by adjusting parameters such as hydraulic retention time (HRT), nitrifying solution recycle ratio, sludge recycle ratio, and dissolved oxygen (DO). The objective was to investigate pollutant removal capacity and differences in microbial community composition between the two systems. The study showed that, at an HRT of 12 h, the IFAS system exhibited an average increase of 5.76%, 8.85%, and 12.79% in COD, NH4+-N, and TN removal efficiency respectively, compared to the AAO system at an HRT of 16 h. The TP concentration in the IFAS system reached 0.82 mg/L without the use of additives. The IFAS system demonstrated superior effluent results under lower operating conditions of HRT, nitrification solution recycle ratio, and DO. The 16S rDNA analysis revealed higher abundance of denitrification-related associated flora, including Proteobacteria, Bacteroidetes, and Planctomycetota, in the IFAS system compared to the AAO system. Similarities were observed between microorganisms attached to the media and activated sludge in the anaerobic, anoxic, and oxic tanks. q-PCR analysis indicated that the incorporation of filler material in the IFAS system resulted in similar abundance of nitrifying bacteria genes on the biofilm as in the oxic tank. Additionally, denitrifying genes showed higher levels due to aeration scouring and the presence of alternating aerobic-anaerobic environments on the biofilm surface, enhancing nitrogen removal efficiency.

Energy Recovery Efficiency of Integrating Anaerobic Co-Digestion of Pig Slurry and Feedlot Cattle Manure and Hydrothermal Carbonization of Anaerobic Sludge Cake

Hydrothermal carbonization (HTC) is a technology designed to improve the efficiency of bioenergy recovery by subjecting biomass to high-temperature and high-pressure conditions. By integrating this technical feature with anaerobic digestion (AD), enhanced energy recovery efficiency is achieved in treating anaerobic digestate (AD-T). The study investigates enhancing bioenergy recovery efficiency through an integrated process, combining AD of livestock manure and HTC. The primary objective is to improve the energy conversion efficiency of biomass characterized by varying solid contents and chemical compositions. Shortening the hydraulic retention time (HRT) in AD of livestock manure resulted in decreased degradation rate efficiency within the AD-T. This led to increased solid material accumulation, which was crucial for the subsequent HTC reaction. The HTC reaction exhibited its maximum bioenergy recovery at 160 °C. The input energy of the livestock manure, obtained by mixing pig slurry and feedlot cattle manure in a 1:1 (w/w) ratio, was 171,167 MJ/day. Under different HRT conditions (40, 30, and 20 days), recoverable energy from AD of livestock manure ranged from 60,336 to 68,517 MJ/ton. Integration of HTC increased net bioenergy recovery to 106,493 to 130,491 MJ/day under corresponding HRT conditions, highlighting the potential of integrating HTC with AD from livestock manure for enhanced bioenergy recovery efficiency.

Efficient reactivation of anammox sludge after prolonged storage using a combination of batch and continuous reactors.

Due to the slow growth rate of anammox bacteria, enriched sludge is required for the rapid start-up of anammox-based reactors. However, it is still unclear if long-term stored anammox sludge (SAS) is an effective source of inoculum to accelerate reactor start-up. This study explored the reactivation of long-term SAS and developed an efficient protocol to reduce the start-up period of an anammox reactor. Although stored for 13months, a low level of the specific anammox activity of 28mg N/g VSS/d was still detected. Experimental Phase 1 involved the direct application of SAS to an upflow sludge bed reactor (USB) operated for 90 d under varying conditions of hydraulic retention time and nitrogen concentrations. In Phase 2, batch runs were executed prior to the continuous operation of the USB reactor. The biomass reactivation in the continuous flow reactor was unsuccessful. However, the SAS was effectively reactivated through a combination of batch runs and continuous flow feed. Within 75days, the anammox process achieved a stable rate of nitrogen removal of 1.3g N/L/day and a high nitrogen removal efficiency of 84.1 ± 0.2%. Anammox bacteria (Ca. Brocadia) abundance was 37.8% after reactivation. These overall results indicate that SAS is a feasible seed sludge for faster start-up of high-rate mainstream anammox reactors.

Application of full-scale aerobic granular sludge technology for removing nitrate from groundwater intended for human consumption

The dependence on groundwater for human consumption has increased worldwide in the last decades. Nitrate (NO3−) often reaches groundwater and causes significant degradation in groundwater quality. In an effort to address this issue, a full-scale water treatment plant using aerobic granular sludge (AGS) technology was built to remove NO3− from nitrate-polluted groundwater intended for human consumption in a rural village. The impact of changes in the operational conditions of hydraulic retention time (HRT) and organic matter loading (OML) rate on NO3− removal, overall system performance, and the granule microbiome were studied. Regardless of the HRT, the AGS technology was successful in removing NO3− with removal rates >50 % with an optimal OML rate of 75 mg L−1. No significant variations in the total abundance of any of the denitrification genes were observed. The composition of prokaryotic and eukaryotic communities was affected by changes in the HRT and OML rate. Specific prokaryotic taxa were identified as responsive to changes in operational parameters and their abundances were linked to the removal of NO3−, confirming that the microbes are critical to the NO3− removal process. This study demonstrates that the AGS technology can be successfully implemented to treat nitrate-polluted groundwater in rural villages to produce water of drinking quality. In addition, the reported hydraulic retention times and organic matter loading rate can be used to further improve the system performance to remove nitrate from groundwater.

Effect of HRT on nitrogen removal from low carbon source wastewater enhanced by slurry and its mechanism

Insufficient carbon sources in low-carbon wastewater have consistently hindered nitrogen removal performance. This work utilized slurry after anaerobic digestion as an additional carbon source, and the optimal hydraulic retention time (HRT) parameters were obtained through adjustment. The findings revealed that, under HRT conditions of 24–12 h, the discharge standards of wastewater treatment plants (WWTPs) could be met. It had been proven that HRT 12 h was the more cost-effective parameter for application in WWTPs, and the removal efficiencies for COD, NH4+-N, NO3–-N, and TN reached impressive levels of 82.43%, 95.24%, 77.49%, and 86.70%, respectively. However, the HRT 6 h struggled to achieve efficient wastewater treatment. Mechanistic analysis demonstrated that shortening the HRT resulted in considerably higher microbial richness, diversity, and evenness, causing notable shifts in microbial community structure. Additionally, a shortened HRT reduced the enrichment abundance of key bacterial phyla (Proteobacteria, Bacteroidetes) and genera (Hydrogenophaga, Filimonas, Meganema) that played an important role in nitrogen and organic matter removal. Furthermore, a shortened HRT increased hydraulic shear forces, impeding the enrichment of carbon and nitrogen metabolism pathways, and reducing the abundance of essential genes associated with glycolysis (HK, pfkA, FBA, GAPDH) and nitrogen metabolism processes (narG, narH, narI, norB, nirS, nosZ). It was noteworthy that the microbial community under the HRT 6 h condition carried the highest risk of microbial pathogenicity. This work revealed the optimal parameters, and carbon and nitrogen metabolism mechanism of wastewater treatment systems with slurry as a carbon source for the first time, and provided novel ideas and insights for low-carbon wastewater treatment.

Feasibility of thermal hydrolysis pretreatment to reduce hydraulic retention time of anaerobic digestion of cattle manure

In this study, we investigated the potential of thermal hydrolysis pretreatment (THP) to reduce the hydraulic retention times (HRTs) in the anaerobic digestion (AD) of cattle manure (CM). The AD with THP (THP AD) outperformed the control AD by over 1.4 times in terms of methane yield and volatile solid removal, even under the same HRT conditions. Remarkably, even when the THP AD was operated with an HRT of 13.2 d, it performed better than the control AD operated with an HRT of 36.0 d. In THP AD, there was a shift in the dominant archaeal genus responsible for methane generation from Methanogranum (at HRT of 36.0 – 13.2 d) to Methanosaeta (at HRT of 8.0 d). However, decreasing HRT, and applying THP resulted in reduced stability, accompanied by increased inhibitory compounds, and changes in the microbial community. Further confirmation is required to assess the long-term stability of THP AD.

Improved integrated anaerobic–anoxic–oxic system for landfill leachate treatment using domestic wastewater as carbon source: Performance study and optimization

Landfill leachate has been treated by using an anaerobic–anoxic–oxic (A2/O) system at Datansha Wastewater Treatment Plant in Guangzhou, South China for nearly five years. Through the pilot-scale testing and engineering experiments, the impulse loads of the wastewater treatment systems were successfully reduced. The results showed that the highest removal efficiencies of chemical oxygen demand (COD), ammonium-nitrogen (NH4+-N), and total nitrogen (TN) for the combined treatment of domestic wastewater and landfill leachate were achieved under the operating conditions of hydraulic retention time = 11 h, dissolved oxygen = 3 mg/L, mixed liquid return ratio = 200%, and sludge return ratio = 80%. Compared with the data obtained from the previous operating A2/O system, the removal efficiencies of COD, NH4+-N, and TN increased by 5.6%, 9.8%, and 5.3%, respectively, under the optimal operating conditions for one year. The average effluent concentrations of BOD5, COD, NH4+-N, TN, and total phosphorus were 12.4, 29.9, 2.5, 18.0, and 0.5 mg/L, respectively, and these values could be kept below standard discharge limits in China.

Hydrogel microbial reactor based on microbially induced calcium precipitation for the removal of calcium, cadmium and nitrate from groundwater

In this study, hydrogel biocarriers filled with chia seeds gum biochar encapsulated with Pseudomonas sp. LYF26 were prepared using polyvinyl alcohol and sodium alginate. Simultaneous removal of NO3−, Ca2+ and Cd2+ from low carbon wastewater was achieved by microbially induced carbonate precipitation and denitrification. In order to investigate the performance of the bioreactor, different conditions of hydraulic retention time, pH, and concentration of Cd2+ were studied, and the optimal operating conditions of the bioreactor were finally determined as HRT of 8 h, pH of 6.5 and initial Cd2+ concentration of 3 mg L−1. The results showed that the optimum removal of NO3−-N, Ca2+ and Cd2+ by the reactor was 100%, 54.02% and 100%, respectively. Three-dimensional excitation-emission matrix (3D-EEM) showed that the microorganisms produced extracellular polymers during the operation of the bioreactor, which promoted the removal of Cd2+. Fourier transform infrared spectroscopy (FTIR) detected the presence of -OH, CO, C-O-C and C-O-H, indicating the production of CaCO3 and extracellular polymers. Scanning electron microscope (SEM) observed that the filler surface had a rough and porous character with a large amount of biodeposits attached to its surface. X-ray diffraction (XRD) indicated that the sediments contained CaCO3, CdCO3 and Ca5(PO4)3OH. High-throughput sequencing showed that Pseudomonas was the dominant bacterium.

Gravity-Driven Membrane as seawater desalination pretreatment: Understanding the role of membrane biofilm on water production and AOC removal

Gravity-Driven Membrane (GDM) is considered an emerging seawater reverse osmosis desalination pretreatment. The objective of this study was to assess the GDM process performance under different operating conditions and to evaluate the impact of membrane biofilm on the produced water quantity and quality. Three lab-scale submerged GDM systems (UF12h, UF24h and MF24h) were tested under different conditions of Hydraulic Retention Time (HRT) (12 h/24 h) and membrane pore size (Microfiltration/Ultrafiltration). The best water quality in terms of Assimilable Organic Carbon (AOC) was achieved with the longer HRT (24 h), where significant AOC was removed by the biofilm developed on the membrane. The next generation sequencing indicated that a longer HRT increased the abundance of Proteobacteria and Planctomycetes in the biofilm, which due to their biodegradation capability yielded to the highest AOC removal (~50–55 %). Furthermore, the use of microfiltration led to the highest water production (9.1 L/m2/h) due to larger membrane pore size, and a less dense biofilm. These findings indicate that employing a microfiltration membrane and 24 h HRT provides the best performance in terms of water quantity and AOC-removal. This study demonstrates that controlling GDM design and operation enabled manipulation of the biofilm proprieties yielding to high water production and high AOC-removal.

Study on community structure and nitrogen metabolism mechanism in A2O process under different hydraulic retention time conditions at high altitude region

<p>The unique high-altitude environmental factors in the Linzhi region of Tibet have not been fully investigated in terms of their impact on the microbial mechanisms of water ecology, for which we explored the response of activated sludge microorganisms to different hydraulic retention times (HRT) based on 16S rRNA gene sequencing and PICRUST2 functional prediction. The results showed that different HRT had significant effects on Phylum, Class, Genus, Species and OTU levels, as well as on diversity, richness and evenness (P < 0.05). The relative abundance of Bacteroidetes, Chloroflexi, Firmicutes and AAP99 in the dominant bacterial phylum and genus was significantly influenced by different HRT. In addition, we identified the denitrification reaction as the major pathway in nitrogen metabolism in this study, as well as most of the significantly enriched genera were denitrifying genera as determined by LEfSe analysis. The overall low relative abundance of the nitrifying bacteria genera AOB and NOB may also be an important reason for the poor nitrogen removal. The effect of HRT on the expression of genes of the five functional modules of nitrogen metabolism was inconsistent. In conclusion, the above studies further complement the studies on the effects of plateau-specific environments on the microbial mechanisms of water ecology under different HRT conditions.</p>

A pilot-scale study of a down-flow hanging sponge reactor as a post-treatment for domestic wastewater treatment system at short hydraulic retention times

This study proposes a down-flow hanging sponge (DHS) reactor as a post-treatment process for sewage treatment systems. A pilot-scale DHS reactor was operated over 1000 days under relatively short hydraulic retention times (HRT) of 1–3 h to evaluate its effectiveness as a post-treatment technology. The DHS reactor consistently achieved superior effluent water quality with total suspended solid <10 mg/L, biochemical oxygen demand < 10 mg/L, and ammonium nitrogen < 5 mg/L. The effective removals (> 2-log10 reduction) of Escherichia coli, a fecal contaminant indicator, and Arcobacter spp., a potentially pathogenic bacterial group, were achieved. The treatment performance was compared with the previous operation treating raw domestic wastewater under long HRTs of 4 and 5 h. As a result, the DHS reactor under short HRT conditions showed advantages for biological oxidation and fecal contaminant removal. These results indicate that the DHS reactor could be a compact post-treatment technology.

A novel in-situ enhancement strategy of denitrification biofilter for simultaneous removal of steroid estrogens and total nitrogen from low C/N wastewater

Widely-used denitrification biofilter (DNBF) is facing the challenge towards the simultaneous removal of steroid estrogens (SEs) and total nitrogen (TN) from secondary effluent. Herein, slow-release calcium peroxide (SR-nCP) was firstly introduced into DNBF to construct SR-nCP/biofilter to in-situ enhance the removal of SEs and TN from low carbon to nitrogen (C/N) ratio wastewater. Results showed that the SEs removal rate could reach >95 % and the effluent TN maintained <15 mg/L. Under hydraulic retention time (HRT) = 3 h, 17α-ethinyl estradiol (EE2) removal increased by 22.0 %–27.0 %, and the denitrification load increased by 123.5 % to reach (60.8 ± 4.8) g·N (m3·d)−1. Moreover, SR-nCP/biofilter improved the reduction of both endocrine disrupting and acute toxicity, and the enhancement effect was more prominent under the low HRT condition. Furthermore, Sediminibacterium and Steroidobacter were identified as core aerobic bacterium that acted on SEs degradation and anaerobic bacterium that was responsible for simultaneous removal of SEs and TN, respectively. The presented strategy exhibited a synergistic effect of oxygen and organic carbon from SR-nCP and confirmed the feasibility of the SR-nCP/biofilter for the removal of SEs and TN from low C/N wastewater, highlighting a promising in-situ enhancement method for upgrading the function of current DNBF in advanced wastewater purification.

Sulfur cycle contributes to stable autotrophic denitrification and lower N2O accumulation in electrochemically integrated constructed wetlands: Electron transfers patterns and metagenome insights

Excessive discharge of nutrients from wastewater treatment plants (WWTPs) is an important pollutant source of eutrophic water bodies. In this work, three electrochemically integrated horizontal flow constructed wetlands (E-HFCWs) were developed for advanced nutrients removal from WWTPs effluent with different S/N ratios. In E-HFCWs, PO43−-P, NO3−-N and TN removal percentages at current of 0.2 A and hydraulic retention time (HRT) of 24 h did not differ significantly as S/N ratios altered. When fed with low, middle and high concentrations of SO42−-S wastewater during this period, PO43−-P removal percentages respectively reached 99.3 %±0.9 %, 99.2 %±1.1 % and 99.0 %±1.4 %, NO3−-N removal percentages respectively reached 99.5 %±0.5 %, 99.6 %±0.4 % and 99.4 %±0.8 %, and TN removal percentages respectively reached 92.0 %±2.5 %, 90.8 %±3.4 % and 91.2 %±2.7 %. This work highlighted that sulfur cycle played crucial roles in improving nitrogen removal stability as current or HRT decreased in higher S/N ratio groups. The formed sulfur ferrites under higher current or HRT condition served as “electron reservoir”, and would resupply electron for denitrification when electron supplied by electrolysis was deficient. In addition, the higher S/N ratio groups allowed significantly lower N2O accumulation, which was accordance with the concept of carbon neutral. Based on metagenome results, the occurrence of more abundant sulfur-oxidizing denitrifying genes and bacteria (e.g., Thiobacillus) in higher S/N ratio groups under lower current or HRT further demonstrated the significant roles of sulfur cycle in stable autotrophic denitrification performance in E-HFCWs. Overall, this work provides perspective on the future practical application for the regulation of nitrogen removal stability enhancement and N2O emission reduction in electrochemically integrated bioreactors.

Production of hydrogen from beverage wastewater by dark fermentation in an internal circulation reactor: Effect on pH and hydraulic retention time

• Interaction and the RSM should be performed to determine the optimal zone for H 2 . • Interaction between factors established that the pH was main factor in the operation. • Distribution of VFAs and multivariate statistics allow an integral analysis. Energy demand currently is mostly satisfied by the use of fossil fuels that present not only problems for the environment, but also are not renewable. Dark fermentation (DF) is a biological process that can provide an alternative to meet energy needs. The use of industrial effluents from carbon-rich waters in the production of hydrogen and volatile fatty acids (VFAs) through the DF is a promising strategy. However, determining the optimal operating conditions to increase the production of the sub-products has been not being thoroughly studied. This study aims at determining the optimal condition of hydraulic retention time (HRT) and pH to improve hydrogen production in an internal recirculation (IC) reactor treating beverage wastewater using Response Surface Methodology and interaction between factors. The study also assessed VFAs concentrations when operating at optimal conditions. The results showed that the combination of an 8.0 h HRT and 5.5 produced 30% of hydrogen and the interaction between factors established that the pH was the main factor influencing the results. Also, it was observed that the concentration of lactic acid did not inhibit the production of H 2 for the optimal value of pH. However, it is evident that more studies using HRT of less than 8 h and of VFAs distribution are needed. Future optimization technique considerations are necessary to reduce uncertainties for biological hydrogen production purposes.

Performance optimization and microbial community evaluation for domestic wastewater treatment in a constructed wetland-microbial fuel cell

Constructed wetland-microbial fuel cell system (CW-MFC), an attractive technology still under study, has shown to improve domestic wastewater treatment efficiency and generate bioelectricity. This work investigated the effect of multiple factors on the performance optimization for the pollutants removal and bioelectricity production compared to a traditional CW, including influent chemical oxygen demand (COD) concentration, hydraulic retention time (HRT) and external resistance. The results showed that the optimal operating conditions of COD concentration, HRT and external resistance for CW-MFC were 200 mg/L, 24 h and 1000 Ω, respectively. The average COD, NH4+-N, NO3--N and TP removal efficiencies were 6.06%, 3.85%, 3.68% and 3.68% higher than these in CW system, respectively. Meanwhile, the maximum output voltage and power density of CW-MFC were 388 ± 12 mV and 107.54 mW/m3. In addition, the microbial community analysis indicated that the pollution removal and bioelectricity generation might benefit from the gradual enrichment of electroactive bacteria (Tolumonas) and denitrifying bacteria (Denitratisoma, Methylotenera and Sulfuritales). The findings can provide the optimum operation parameters and mechanism insight for the performance of CW-MFC systems.

Membrane Fouling Controlled by Adjustment of Biological Treatment Parameters in Step-Aerating MBR.

A promising solution for membrane fouling reduction in membrane bioreactors (MBRs) could be the adjustment of operating parameters of the MBR, such as hydraulic retention time (HRT), food/microorganisms (F/M) loading and dissolved oxygen (DO) concentration, aiming to modify the sludge morphology to the direction of improvement of the membrane filtration. In this work, these parameters were investigated in a step-aerating pilot MBR that treated municipal wastewater, in order to control the filamentous population. When F/M loading in the first aeration tank (AT1) was ≤0.65 ± 0.2 g COD/g MLSS/d at 20 ± 3 °C, DO = 2.5 ± 0.1 mg/L and HRT = 1.6 h, the filamentous bacteria were controlled effectively at a moderate filament index of 1.5–3. The moderate population of filamentous bacteria improved the membrane performance, leading to low transmembrane pressure (TMP) at values ≤ 2 kPa for a great period, while at the control MBR the TMP gradually increased reaching 14 kPa. Soluble microbial products (SMP), were also maintained at low concentrations, contributing additionally to the reduction of ΤΜP. Finally, the step-aerating MBR process and the selected imposed operating conditions of HRT, F/M and DO improved the MBR performance in terms of fouling control, facilitating its future wider application.

Perchlorate bioreduction in UASB reactor: S2--autotrophic granular sludge formation and sulphate generation control

ABSTRACT Perchlorate () industrial wastewater requires efficient removal to prevent adverse environmental impacts, however, high concentration and low biodegradability give rise to poor bioreduction performance. -autotrophic granular sludge (-AuGS) was firstly cultivated for high concentration perchlorate () removal in the upflow anaerobic sludge blanket (UASB) reactor (: 150 mg L−1). Simultaneously, the was utilized to control the generation as electron donor, the effluent concentration (190 mg L−1) was satisfied with drinking water standard (250 mg L−1). Under the optimized condition of hydraulic retention time (HRT) (6 h) and / molar ratio (2.2), more EPS was secreted, which promoted the -AuGS formation and stability. Though acclimation of 146 d, the -AuGS was formed with a large average granular sludge size (612 μm) and an excellent settleability (sludge volume index: SVI5/SVI30 = 1). With the mature -AuGS formation, the highest and loading was increased to 1.06 and 0.75 kg m−3 d−1. Interestingly, Georgfuchsia, Methyloversatilis, Sulfurisoma, and Exiguobacterium were the main microbial community in the -AuGS. This study proposed to form a novel -AuGS for developing the high concentration removal performance and to utilize the as an electron donor for controlling the excessive generation.

Regulatory strategies and microbial response characteristics of single-level biological aerated filter-enhanced nitrogen removal

A single-level biological aerated filter (BAF) was used to treat domestic wastewater. The response surface method (RSM) model was applied to optimize the operating parameters such as hydraulic retention time (HRT), reflux ratio (R), and aeration-stop ratio. The characteristics of the wastewater were analyzed. The results showed the average removal efficiencies for COD, TN, and NH4+-N were 87.77, 75.41, and 87.28%, for a COD/N ratio of 3.44 under the RSM optimized conditions of HRT = 7 h, R = 105%, and aeration-stop ratio of 1:1. The environment was favorable for enhanced denitrification in the 30–70 cm section. The proportion of Proteobacteria showed a valley pattern along the range direction, while Planctomycetes and Nitrospirae were gradually increasing. The microorganisms involved in denitrification were more abundant at the phylum level, notably Proteobacteria (22.87–47.56%), Planctomycetes (6.62–10.68%), Nitrospirae (0.79–3.02%), and denitrifying bacteria were also evident at the genus level, i.e., Flavobacterium (0.21–1.43%). The BAF system with internal reflux-coupled intermittent aeration enhances nitrification and denitrification, thereby facilitating nitrogen removal.

Pilot-Scale Airlift Bioreactor with Function-Enhanced Microbes for the Reduction of Refinery Excess Sludge.

A pilot-scale airlift bioreactor (ALBR) system was built and operated continuously for refinery excess sludge (RES) reduction. Combined ALBR and function-enhanced microbes (composed of photosynthetic bacteria and yeast) were integrated into the system. The pilot-scale ALBR was operated for 62 days, and the start-up time was 7 d. Continuous operation showed that the sludge reduction efficiency was more than 56.22%, and the water quality of the effluent was satisfactory. This study focused on investigating the effects of hydraulic retention time (HRT) on the stability of the system and the effect of sludge reduction. Under different HRT conditions of 40, 26.7, 20, and 16 h, the sludge reduction rates reached 56.22%, 73.24%, 74.09%, and 69.64%, respectively. The removal rates of chemical oxygen demand (COD) and total nitrogen (TN) decreased with decreasing HRT, whereas the removal rate of NH4+-N increased. The removal rate of total phosphorus (TP) was approximately 30%. Results indicate that the ALBR and function-enhanced microbe system can reduce sludge and treat sewage simultaneously, and the effluent is up to the national emission standard. Addition of function-enhanced microbes can promote the degradation of petroleum hydrocarbon substances in the sludge, especially alkanes with low carbon numbers. This study suggests that the optimal HRT for the system is 16 h. The total operation cost of the ALBR combined with the function-enhanced microbe system can be reduced by 50% compared with the cost of direct treatment of the RES system.