Effect of thermal shock and sustained heat treatment on mainstream partial nitrification and microbial community in sequencing batch reactors.

In order to develop a promising means of achieving mainstream short-cut nitrification, this study evaluated the effect of thermal shock on nitrite accumulation using intermittent offline and continuous inline heat treatment of biomass in sequencing batch reactors (SBRs). The SBRs fed with municipal wastewater were operated at a solid retention time of 7 days and nitrogen loading rate of 0.04 gN/L·d to 0.08 gN/L·d without the application of pre-treatment. Contrary to literature studies that showed suppression of nitrite-oxidizing bacteria at temperature 60 to 80 °C, nitrite accumulation was achieved temporarily when 20% of the biomass was heated for 2 h at 47 °C, as well as in continuously heated SBRs at 37 °C and 42 °C. The continuously heated reactors at 37 °C and 42 °C produced a maximum nitrite accumulation ratio (NAR) of 0.59 and 0.79, respectively, whereas the intermittent offline heating at 47 °C-2 h produced a NAR of 0.37. Although nitrite accumulation was stable only for 10-12 days in all heated reactors, this study demonstrates the achievement of mainstream partial nitrification (PN) at lower temperature (42 °C) than that reported in literature and also highlights the potential for achieving PN by implementing heat treatment of a portion of the return activated sludge (RAS) in biological nitrogen removal (BNR) systems. During the time when full nitrification was achieved, Nitrospira was more dominant than Nitrosomonas in all reactors at ratios of 1.4:1, 2.4:1, 2.4:1, and 3.7:1 for the control SBR (22 °C), 47 °C -2 h offline heating SBR, 37 °C SBR, and 42 °C SBR, respectively, suggesting that it may have played a role as a comammox bacteria capable of degrading ammonia to nitrates at elevated temperature.

Effects of trace elements on digester performance and microbial community response in anaerobic digestion systems.

Trace elements (TE), as micronutrients for microorganisms, have a significant impact on the stability of anaerobic digestion (AD). Studies have been conducted on process stability and performance of the AD of food waste (FW) by supplementing TEs. In this study, mesophilic batch biomethane potential (BMP) tests using FW were conducted to investigate the effect of TEs (Fe, Ni, Co, Se, and Mo) as single and mixed ions. In view of their scarcity, correlations between the microbial community and digester performance such as first-order hydrolysis coefficient (Kh), volatile fatty acids (VFA), methane yield, and methane production rate (MPR) have been developed. Ni2+ at 1 and 1.5 mg/L increased the methane yield by 27% and 23% respectively. Similarly, Co2+ at 0.1 and 0.5 mg/L increased the yield by 21% and 23% respectively, compared to control. Although Se4+ at all concentrations enhanced the methane yield, Fe2+ at only 50 mg/L increased methane yield by 22%. For mixed TEs, the combination of Ni2+ [1 mg/L] +Co2+ was the best and increased methane for all Co2+ concentrations (0.1, 0.4 and 0.5 mg/L) by 16%, 14% and 12% respectively. Firmicutes and Methanosaeta were the most abundant phyla among hydrolytic and methanogenic microbial groups, respectively, constituting 42%-61% and 60-80% of their respective microbial groups. The most significant positive correlations were observed between aceto/acidogenic microorganisms and final VFA concentrations with Pearson correlation factors of 0.91.

Vacuum-enhanced anaerobic fermentation: Achieving process intensification, thickening and improved hydrolysis and VFA yields in a single treatment step.

This study assessed the feasibility of a novel vacuum-enhanced anaerobic digestion technology, referred to as IntensiCarbTM (IC), under mild vacuum pressure (110 mbar), compared to a control (conventional fermenter), and evaluated the impact of the vacuum on the activities of various microbial groups. Both fermenters (test and control) were operated with mixed (50% v/v) municipal sludge at solids concentrations of 2-2.5%, pH of 7.8-8.1, 40-45 °C, a theoretical solids retention time (SRT) of 3 days with different hydraulic retention times (HRT). The intensification factor (IF) of the IC, defined as SRT/HRT, was controlled at 1.3 and 2.0. Simultaneous thickening and fermentation intensification were achieved. Compared with the control, the IC, despite the shorter HRTs, achieved 29.5 to 90.2% increase in the VFA yield (79 to 116 mg ΔVFA/ g VSS vs 61 mg ΔVFA/ g VSS), and 16.2% to 56.4% increase (280 to 377 mg ΔsCOD/ g VSS vs 241 mg ΔsCOD/ g VSS), in the hydrolysis yield. Fermentate from the IC exhibited comparable specific denitrification rates to acetate. Further, the solids-free condensate contained low nutrient concentrations, and thus was far superior to a typical centrates from dewatering as a carbon source. No adverse effects of vacuum on the activity of fermentative bacteria and methanogens were observed. This study demonstrated that the IC can be deployed as an intensification technology for both fermentation and anaerobic digestion of biosolids with the additional significant advantage, i.e. elimination of sidestream ammonia treatment requirements.

A proof-of-concept experimental study for vacuum-driven anaerobic biosolids fermentation using the IntensiCarb technology.

This study demonstrates the potential of an innovative anaerobic treatment technology for municipal biosolids (IntensiCarb), which relies on vacuum evaporation to decouple solids and hydraulic retention times (SRT and HRT). We present proof-of-concept experiments using primary sludge and thickened waste activated sludge (50-50 v/v mixture) as feed for fermentation and carbon upgrading with the IntensiCarb unit. IntensiCarb fully decoupled the HRT and SRT in continuously stirred anaerobic reactors (CSAR) to achieve two intensification factors, that is, 1.3 and 2, while keeping the SRT constant at 3 days (including in the control fermenter). The intensified CSARs were compared to a conventional control system to determine the yields of particulate hydrolysis, VFA production, and nitrogen partitioning between fermentate and condensate. The intensified CSAR operating at an intensification factor 2 achieved a 65% improvement in particulate solubilization. Almost 50% of total ammonia was extracted without pH adjustment, while carbon was retained in the fermentate. Based on these results, the IntensiCarb technology allows water resource recovery facilities to achieve a high degree of plant-wide intensification while partitioning nutrients into different streams and thickening solids. PRACTITIONER POINTS: The IntensiCarb reactor can decouple hydraulic (HRT) and solids (SRT) retention times in anaerobic systems while also increasing particulate hydrolysis and overall plant capacity. Using vacuum as driving force of the IntensiCarb technology, the system could achieve thickening, digestion, and partial dewatering in the same unit-thus eliminating the complexity of multi-stage biosolids treatment lines. The ability to partition nutrients between particulate, fermentate, and condensate assigns to the IntensiCarb unit a key role in recovery strategies for value-added products such as nitrogen, phosphorus, and carbon, which can be recovered separately and independently.

Kinetics of aerobic cellulose degradation in raw municipal wastewater.

Cellulose contributes approximately one third of the influent suspended solids to wastewater treatment plants and is a key target for resource recovery. This study investigated the temperature impact on biological aerobic degradation of cellulose in laboratory-scale sequencing batch reactors (SBR) at four different temperatures (10-33 °C) and two different solids retention times (SRT) of 15 days and 3 days. The degradation efficiency of cellulose was observed to increase with temperature and was slightly dependent on SRT (80%-90% at an SRT of 15 days, and 78%-85% at an SRT of 3 days). Hydrolysis followed 1st order kinetics, rather than the biomass dependent Contois kinetics (default in the activated sludge models), with a hydrolysis coefficient at 20 °C of 1.14 ± 0.01 day-1.

Comparison of carrier particles in the gas-liquid-solid inverse fluidised bed bioreactor.

The performance and energy consumption of a gas-liquid-solid inverse fluidised bed bioreactor (GLS-IFBBR) using polyethylene (PE) particles with different surface coatings (zeolite, lava rock, activated carbon and multi-plastic) as media for synthetic wastewater treatment were investigated at loading rates of 1.64-3.38 kg COD/(m3·d) and 0.17-0.34 kg N/(m3·d) to determine the optimum carrier media. The results showed that PE coated with other inorganic materials could increase the nutrient removal efficiency at the same influent conditions. Compared with other media, PE coated with zeolite (PEZ) was the optimal carrier particles in this study as reflected by the highest COD and nitrogen removal, stable effluent, low biomass yield at different hydraulic retention times (HRT). In addition, the energy consumption of lavarock-coated PE (PEL) with a highest density was the lowest.

Enhanced mainstream nitrogen removal from synthetic wastewater using gel-immobilized anammox in fluidized bed bioreactors: Process performance and disintegration mechanisms.

Anammox retention, which is crucial for successful nitrogen removal because of slow growth, is still a major challenge. Fixed film processes or gel-immobilization techniques can minimize biomass washout. However, the detachment mechanisms from gel-immobilized beads are still unclear. Despite the widely known advantages of fluidized bed reactor (FBR) with respect to biomass retention, the technology has not been investigated for anammox processes, and thus, the current study evaluated the feasibility of using immobilized anammox gel beads as a carrier media in anammox fluidized bed reactor (AFBR), with a particular focus on understanding detachment mechanisms. The study optimized the packing ratio in AFBR and compared holed and non-holed beads. The optimum packing ratio (on a volumetric basis) was 30% (v/v) with a nitrogen removal rate (NRR) of 0.40 kg N/m3-d at a volumetric nitrogen loading rate (NLR) of 0.51 kg N/m3-d. Biomass detachment rates increased linearly with specific anammox activity (SAA). The fluidized bed reactor employing holed (more porous) anammox gel beads (HFBR) exhibited 20% lower biomass detachment rates than the non-holed fluidized bed reactor (NHFBR). Moreover, the HFBR achieved a maximum NRR of 0.81 kg N/m3-d at NLR of 1.01 kg N/m3-d after 35 days without operational problems, whereas the NHFBR with non-holed anammox gel beads failed after 30 days. The hindrance to diffusion of the generated nitrogen gas was the main mechanism of beads breakup and biomass washout, and thus, the sustainability of the beads hinges on increased external porosity. Therefore, developing microporous gel beads is critical for achieving a high rate stable anammox process that overcomes the limitations of the current technologies.

The circulating fluidized bed bioreactor as a biological nutrient removal process for municipal wastewater treatment: Process modelling and costing analysis.

Emerging technologies for wastewater treatment face an uphill battle to be adopted in practice because no large-scale costing data exists to prove their cost competitiveness. Similar technologies and their costing data offer some insight to the approximate cost, but more detailed estimates are required for a final decision on process selection. The circulating fluidized bed bioreactor (CFBBR) is one such technology, proven at the lab and pilot and scale, but is yet to be used on a large scale. In order to demonstrate the potential economic competitiveness of the CFBBR, a method of modifying the CapdetWorks costing software by first modeling the CFBBR in the GPS-X process simulation software was employed. The modelling was used to determine the necessary changes to a moving bed bioreactor (MBBR) process (media size, density, surface area, and bed fill fraction) in CapdetWorks to simulate the CFBBR and then generate costing estimates for both capital cost (CapEx) and operation and maintenance cost (OpEx). Benchmarking the cost estimates against simulations of conventional suspended and attached growth processes and external costing data from the US EPA was performed to both validate the costing method and analyze the CFBBR's economic competitiveness. The calculation of the net present value from the CapEx and OpEx showed that the CFBBR is predicted to have 10%-30% lower costs at low flows of 1.5 and 4.6 MGD and comparative costs to conventional processes at higher flows from 10 to 30 MGD. Furthermore, the smaller land footprint of the CFBBR-based plants and lower landfilled biosolids implies that the CFBBR's environmental footprint is superior to its competitors and offers advantages for both small-sized plants and large urban plants.

Anammox enrichment: impact of sludge retention time on nitrogen removal.

Enrichment of anammox bacteria has long been considered to be time-consuming because of the slow growth rate. This study evaluated the impact of sludge retention time (SRT) on the enrichment of anammox bacteria with a focus on nitrogen removal and specific anammox activity (SAA) in sequencing batch reactors (SBR). A total of eight different SRTs in the range of 30-1280 days at nitrogen loading rates (NLR) range from 12.1 to 122.1 mg/L-d were used to evaluate the anammox activity. SAA was negligible during the first 105 days due to denitrification and continued to increase thereafter to peak at 0.22 g N/g VSS-d on day 530 as the solids and hydraulic retention times (SRT and HRT) decreased from 120 to 80 days and 10 to 2 days, respectively. The stability of SAA (0.21 ± 0.02 g N/g VSS-d) from day 503 to day 670 indicates that anammox bacteria should be enriched at SRTs ranging from 30 to 80 days and NLR of 122.1 mg N/L-d. Moreover, the SBR achieved a maximum nitrogen removal efficiency of 86.6% at an SRT of 30 days and an NLR of 122 mg/L-d. Microbial analysis indicated that the two most abundant microorganisms accounting for 48% of the bacterial population are Anammoxoglobus followed by the heterotrophic denitrifier Rhizobiales. The maximum specific growth rate (was estimated as 0.062 d-1, consistent with typical of 0.057 d-1. The average first-order decay rate was estimated as 0.008 d-1, and the half-saturation constants (ks) averaged 16.2 mg NH4-N/L.

Biological nutrient removal enhancement using fermented primary and rotating belt filter biosolids.

This research compared the impact of two primary treatment options (i.e. primary clarification and rotating belt filtration (RBF)) on biological nutrients removal (BNR) process, using sludge fermentation liquid (SFL) as a carbon source. The liquid fraction of both fermented primary and RBF sludges comparably enhanced BNR. Despite the significant contribution of the unpurified SFL to the sharp increase in nutrient levels; i.e. 47%-64% (primary effluent; PE), and 45%-53% (RBF) of the soluble nitrogen and phosphorus loads; readily biodegradable COD and volatile fatty acids (VFAs) fractions of the combined feed increased significantly (2.5-6.1 times), compared to the original feed by additional SFL. Removal efficiencies in the reactors reached 57% (total nitrogen) and 92% (total phosphorus) after addition of SFL. Effluent nitrogen and phosphorus of the two reactors were close in the range of 15 ± 6 mg N/L, and 0.5 ± 0.3 mg P/L, respectively. Kinetics studies showed denitrification rates of 1.3, and 1.13 kg NO3-N/m3.d for primary effluent and RBF effluent-fed reactors, respectively. Phosphorus release rates were 11.7 and 9.7 mg PO4-P/g VSS.h, for primary, and RBF effluents, respectively; showing 20%-22% lower rates in the RBF SFL. Incorporating experimental data into a plant-wide model for a 100 MLD facility receiving typical medium strength wastewater, showed that although primary treatment enhanced the biogas production by 96% (primary clarification) and 62% (RBF) trains; combined fermentation and anaerobic digestion was effective to enhance the biogas production by 59% on average, compared to the base scenario without primary treatment. Additionally, if primary clarification exists, then the addition of fermentation results in additional revenue of C$1890/d in the plant, considering additional revenue of C$2230/d due to VFA generation in contrast to only C$340/d loss due to the reduced methane production.

Decentralized wastewater treatment in an urban setting: a pilot study of the circulating fluidized bed bioreactor treating septic tank effluent.

To meet the increasing wastewater treatment demand while minimizing the land footprint of the treatment systems and plants, more efficient and compact processes are needed. The circulating fluidized bed bioreactor (CFBBR) has been proven to achieve high levels of biological nutrient removal. Past studies at the lab and pilot scale achieved 94% COD removal and 80% nitrogen removal at HRT's of 2-4 h. A collaborative project between Western University and the Guangzhou Institute of Energy Conversion (GIEC), in Guangzhou, China, further explored the treatment of municipal wastewater with the CFBBR. A pilot CFBBR, with aerobic and anoxic columns for nitrification and denitrification, was constructed at the GIEC for in-situ treatment of septic tank effluent from a residential building. Due to high concentrations of ammonia (NH4-N), the wastewater had a COD/N ratio of 2-3. Thus, operating at a longer HRT and supplementing COD, in the form of glucose, was necessary to achieve a high nitrogen removal efficiency. The system was run both with and without supplemental COD at HRT's between 16 and 21 h, treating approximately 1000-1270 L/d. Overall, a COD removal efficiency of at least 92%, ammonia removal of 97%, and nitrogen removal of 82% was achieved. The CFBBR system achieved an effluent with BOD and NH4-N concentrations both below 5 mg/L, a NO3-N concentration below 15 mg/L, and a total nitrogen concentration below 25 mg/L. The compact design of this pilot-CFBBR, coupled with its high BNR performance make it an excellent option for decentralized treatment of urban wastewaters.

Oxygen transfer and plant-wide energy assessment of primary screening in WRRFs.

Primary screening is gaining interest as a method to achieve removal performances comparable to primary clarification while reducing the footprint and increasing operational elasticity. Aeration efficiency indicators in a pilot sequential batch reactor (SBR) and a full scale water resource recovery facility (WRRF) were investigated after the implementation of rotating belt filters/screens (RBF). To compare the impact between screened (350 µm) and nonscreened primary influent, two identical treatment lines were monitored using off-gas and respirometric measurements. The study provides the first result on improved oxygen transfer efficiency due to primary screening. Consistent aeration efficiency improvements of 27% and 20% between screened and nonscreened were obtained at pilot and full scale, respectively. Changes in aeration efficiency and carbon redirection were integrated into a set of models to investigate the primary screening impact on the WRRF energy balance. While the plant-wide assessment for different scenarios improved the energy balance up to 15%, a detailed comparative analysis between various treatment schemes gained insight into the advantages and limitations of the energetic sustainability of primary screening. PRACTITIONER POINTS: Aeration efficiency improved 27% at pilot scale Aeration efficiency improved 20% at full scale. Use of primary screening can improve the energy balance up to 15 Assessment of advantages and limitations of primary screening.

Dynamic impact of cellulose and readily biodegradable substrate on oxygen transfer efficiency in sequencing batch reactors.

Aeration is a major contributor to the high energy demand in municipal wastewater treatment plants. Thus, it is important to understand the dynamic impact of wastewater characteristics on oxygen transfer efficiency to develop suitable control strategies for minimizing energy consumption since aeration efficiency is influenced by the biodegradation of pollutants in the influent. The real-time impact of acetate as a readily biodegradable substrate and cellulose as a slowly biodegradable substrate were studied at different operational conditions. Cellulose in the influent wastewater can be removed efficiently using primary treatment technologies, such as the rotating belt filter (RBF). At an ambient DO of 2 mg l-1 and air flow of 1.02 m3h-1 (0.6 SCFM), the α-factor was more sensitive to readily biodegradable substrates than to cellulose. On average, α-factor decreased by 48% and 19% due to the addition of acetate and cellulose, respectively. At a DO of 4 mg l-1 and air flow of 1.7 m3h-1 (1 SCFM), α-factor remained constant irrespective of cellulose and acetate concentrations. Without active biomass, α-factor decreased by 47% and 43% at a DO of 2 mg l-1 (air flow of 1.02 m3h-1) and high DO of 5 mg l-1 (air flow of 1.7 m3h-1), respectively. An inverse correlation between α-factor and sCOD was defined and incorporated into a dynamic model to estimate the real-time airflow rates associated with the improvement of the oxygen transfer efficiency due to biodegradation. Finally, the RBF operated with a 158-µm mesh selectively removed cellulose, thus reducing air requirements, and energy by 25%.

Simultaneous nitrification-denitrifying phosphorus removal (SNDPR) at low DO for treating carbon-limited municipal wastewater.

This study investigated simultaneous nitrification-denitrifying phosphorus removal in a sequencing batch reactor (SBR) activated sludge process. The process consisted of an extended anaerobic period (180 min) followed by a low DO (0.3 ± 0.05 mg/L) simultaneous nitrification-denitrifying phosphorus removal. The reactor was operated within a wide range of COD/N ratio (5-10) without any volatile fatty acids (VFA) supplementation. N and P removal efficiencies were as high as 91% and 96%, respectively. The process was efficient even at a very low COD /N ratio of 5, with N and P removal efficiencies of 70% and 90%, respectively. The N and P removal efficiencies improved to more than 90% at a COD/N ratio 8. It was found that the initial filtered flocculated COD (ffCOD)/[total oxidized Kjeldahl Nitrogen (TKNoxidized) + NOx-Nintitial] ratio in the reactor played a significant role in the process efficiency. It was observed that N-removal efficiency decreased with a decrease of [ffCODinitial/ (TKNoxidized + NOx-Ninitial)] ratio even at high COD/N ratio of 10. Simultaneous nitrification denitrification (SND) efficiencies varied between 60%-88% depending on the influent COD/N ratio and [ffCODinitial/ (TKNoxidized + NOx-Ninitial)] ratio in the reactor. Cyclic studies showed a distinct two step phosphorus release in the extended anaerobic period in contrast to the more conventional single step phosphorus release. During the aerobic period, low DO favored denitrifying P-removal without significant accumulation of NO3-N, and NO2-N until all endogenous carbon was consumed. Denitrifying phosphorus accumulating organisms (DPAOs) played a vital role in simultaneous denitrification and phosphorus removal. Aerobic and anoxic P-removal represented about 55% and 45% of the overall phosphorus removal, respectively. Cycle tests showed that DPAOs have a competitive advantage over NOB for nitrite consumption at low DO. The process was found to be carbon efficient as evidenced by the COD/NOx-N ratio of 4.2 for denitrification. Compared to traditional enhanced biological phosphorus removal (EBPR) coupled with exogenous denitrification, this process reduces carbon and oxygen demand for combined N and P removal from municipal wastewater by about 45%, and 35% respectively.

Integrated fermentation and anaerobic digestion of primary sludges for simultaneous resource and energy recovery: Impact of volatile fatty acids recovery.

This research assessed the impact of volatile fatty acids (VFA) recovery and biomethane potential in an integrated fermentation-digestion process with a single stage digestion of primary and rotating belt filtration (RBF) sludges. Implementing semi-continuous fermentation at 1, 2, and 4 days solids retention time (SRT) showed a direct impact on the hydrolysis and VFA recovery which increased as SRT increased, while also improving the dewaterability by reducing the concentrated sludge volume index of the processed sludge. pH-controlled fermentation was effective improving the VFA yields by up to 93% and 72% at pH 9 (relative to no pH control), for RBF and primary sludges, respectively; although fermentation at pH 6 (optimum) showed promise for enhancing VFAs while lowering the required chemicals significantly. Although cellulose constituted only 21.0% and 29.5% of the TSS in primary and RBF sludges, it contributed 38-41% of the methane production for the two sludges, respectively. Experimental results of integrated fermentation-digestion and single stage digestion processes were incorporated in techno-economic analysis. Results confirmed the economic viability of fermentation with payback periods of 2.7 ± 1.1 years (RBF), and 3.6 ± 2.7 years (PS), while also revealed that VFA recovery could save up to 7.2 ± 2.0% (RBF), and 7.6 ± 2.7% (PS) of the respective total sludge handling and disposal costs, despite an average of 12.7% and 8.4% decrease in biogas production due to VFA extraction in the integrated systems of RBF and primary sludges, respectively. Overall, the integrated fermentation-digestion system economically outperformed the single stage digestion for both sludge types under all studied scenarios.

Fate of micropollutants in chemically enhanced primary treatment using recovered coagulants.

In this study, the fate of several micropollutants (MPs) in wastewater due to coagulation using both fresh and recovered aluminum and iron coagulants was determined. 18 MPs from different groups such as antibiotics, food additives, and surfactants were selected and spiked into the primary influent collected from a local wastewater plant. The distribution of MPs in the recovered coagulant and treated effluent after coagulation was determined for both fresh and recycled coagulants. The distribution of MPs in wastewater and the removal during coagulation were compound specific; MPs with log Kow < 2.5 were predominantly present in the effluent after coagulation, while MPs with log Kow > 2.5 were sorbed on the coagulated sludge. The distribution ratio (Kd) of all the MPs (diclofenac, clarithromycin, etc.) with log Kow > 2.5 was determined along with their extent of accumulation in sludge due to the recycling of coagulants. Compounds such as sulfamethoxazole, erythromycin and sulfathiazole, showed low removal during coagulation. The tetracycline group of compounds showed possible chelation with iron and aluminum. Only <10% of the initially spiked MPs with log Kow > 2.5 was being recycled with the recovered coagulant, thus alleviating the concern of accumulation of the MPs during recycle of the coagulants.

Enzymatic pre-treatment for enhancement of primary sludge fermentation.

This research showed the interrelated impact of cellulase enzyme, temperature, and SRT on enhancement of primary and rotating belt filter (PS, RBF) sludges fermentation. SRTs of 1, 2, and 4-days were tested at 25 °C and 35 °C. Enzymatic enhancement was examined using three different doses of enzyme (i.e. 0.5%, 1%, and 1.5% of the total solids in the feed). The results showed a positive impact of enzyme dose as well as temperature and SRT on VFA and soluble COD production. For the RBF sludge, enzyme addition enhanced the VFA yield of fermentation at room temperature (25 °C) from 52-103 mgCOD/g VS to 93-188 mgCOD/g VS, as compared with increase from 78-192 to 87-202 mgCOD/gVS in PS. Intensification of the fermentation process, particularly for the cellulose-rich RBF sludge, by enzyme addition confirms process viability as an alternative to the extraneous carbon sources for biological nutrient removal in wastewater treatment plants.

Performance and bacterial community structure of a novel inverse fluidized bed bioreactor (IFBBR) treating synthetic municipal wastewater.

The performance of a lab-scale integrated anoxic and aerobic inverse fluidized bed bioreactors (IFBBR) for biological nutrient removal from synthetic municipal wastewater was studied at chemical oxygen demand (COD) loading rates of 0.34-2.10 kg COD/(m3-d) and nitrogen loading rates of 0.035-0.213 kg N/(m3-d). Total COD removal efficiencies of >84% were achieved, concomitantly with complete nitrification. The overall nitrogen removal efficiencies were >75%. Low biomass yields of 0.030-0.101 g VSS/g COD were achieved. Compared with other FBBR systems, the energy consumption for this IFBBR system was an average 59% less at organic loading rates (OLRs) of 1.02 and 2.10 kg COD/(m3-d). Bacterial community structures of attached and suspended biomass revealed that the dominant phyla were Proteobacteria, Bacteroidetes, and Epsilonbacteraeota, etc. The relative abundance of ammonia-oxidizing bacteria (AOBs) and nitrite-oxidizing bacteria (NOBs) in the aerobic attached biomass were 0.451% and 0.110%, respectively. COD mass balance in the anoxic zone was closed by consideration of sulfate reduction, which was confirmed by the presence of genus Chlorobium (sulfate-reducing bacteria) in the anoxic attached biofilm with a relative abundance of 0.32%.

Municipal wastewater treatment by purple phototropic bacteria at low infrared irradiances using a photo-anaerobic membrane bioreactor.

Light energy is one of the major costs for phototrophic systems. This study evaluated the photoreactor efficiency of purple phototropic bacteria anaerobic membrane bioreactor (PAnMBR) at low irradiance for the treatment of municipal wastewater. Infrared irradiance levels of 3.0 and 1.4 W/m2 produced by an infrared (IR) lamp emitting in the 800-900 nm wavelength range were investigated, with the ultimate goal of optimizing the irradiance energy demand. Experimental and modeling results demonstrated the ability of PPB to grow and treat raw municipal wastewater at the applied low irradiances, with effluent quality below target limits of TCOD˂50 mg/L, TN˂10 mg/L, and TP˂1 mg/L. While Monod kinetic parameters, km and Y, were determined to be lower than previous high-energy studies (1.9 mgCOD/mgVSS-d and 0.38 mgVSS/mgCOD, respectively), the photobioreactor performance were consistently maintained, indicating that energy cost associated with IR illumination can be reduced by up to 97%. To determine whether the treatment process could approach energy neutrality, subsequent anaerobic digestion experiments of the residual PPB biomass proved a potential for biogas recovery of up to 240 NmLCH4/gVSSadded, and a moderate biomass biodegradability of 41%. As a result, the net energy consumption of the process was estimated at 0.5 kWh/m3 of treated municipal wastewater, considering an energy demand for illumination of 0.67 kWh/m3 and an energy recovery attributed to the anaerobic digestion of 0.17 kWh/m3 from the excess PPB biomass wasted from PAnMBR.

Supraglottic Airway Devices for Elective Pediatric Anesthesia: I-gel versus Air-Q, Which is the Best?

OBJECTIVES: The objectives of the study were to compare the insertion facility, the effect on hemodynamic parameters, and effective ventilation using I-gel versus Air-Q supraglottic airway devices (SADs) for pediatric patients undergoing short-duration surgical procedures. PATIENTS AND METHODS: One hundred and fifty children aged 3-10 years were randomly divided into two equal groups: Group I received I-gel and Group Q received Air-Q SAD. All patients were anesthetized by sevoflurane inhalation using a face mask without neuromuscular blockade. Study outcomes included SAD insertion success rate (SR), insertion time, anatomic alignment of the SAD to the larynx as judged using fiberoptic bronchoscope (FOB) inserted through the SAD, and tidal volume leak, and incidence of postoperative complications. RESULTS: Total and first attempt SRs were 97.3% and 85.3% for I-gel and 94.7% and 82.7% respectively, for Air-Q with nonsignificant differences. However, I-gel insertion time (12.3 ± 3.6 s.) was significantly (P = 0.034) shorter than Air-Q (13.7 ± 4.2 s). FOB grading of laryngeal view through SAD was better with I-gel but without significant difference for patients who had view Grades 1-2. Percentage of tidal volume loss was significantly decreased at 5 min after insertion than immediately after insertion, in all patients, with a nonsignificant difference in favor of I-gel. Intraoperative hemodynamic changes and postoperative complications showed a nonsignificant difference between both the groups. CONCLUSION: Both Air-Q and I-gel SAD provided advantages for pediatric anesthesia during short-duration surgical procedure with nonsignificant differences. However, I-gel SAD required a shorter insertion time and provided a high SR which is satisfactory for trainees and during an emergency. I-gel SAD allowed minimization of tidal volume leak and gastric inflation and is associated with infrequent complications.