Short Hydraulic Retention Time Research Articles

Ecofriendly removing microplastics from rivers: A novel air flotation approach crafted with positively charged carrier

Until targeted techniques are developed and implemented, microplastic (MP) particles in freshwater will always exist and remain under consistent growth. In this study, a novel mechanism based on electrostatic -force–-induced aggregation and flotation is proposed to mitigate MP pollution in rivers. First, the air employed as a flotation carrier is first ionized, then. Then, it is dispersed into a circumfluent reactor after the electrons are offset. The four most detected polymers, namely, polyethylene (PE), polystyrene, polyvinyl chloride, and fiber mixture from the cloth washing machine, are pulverized and injected as contaminants into river water and tap water samples to explore the removal characteristics of the configured bench-scale facility. Experimental results suggest that the scheme takes effect rapidly and obtains a maximum removal efficiency (particle number based) of more than 90% for all four polymer samples in 2 min. The removal behaviors of the MP particles vary with the physical properties of the particles and the operational parameters of the system. The easiest MP particle to separate from the river water matrix is PE. Particles with a diameter of more than 200 µm have high removal efficiency. An in-depth analysis of variance is conducted to determine how the five selected operational parameters affect the system’s removal characteristics for the four polymers in the river water sample. Results imply that the proposed process is a promising alternative in tackling the MP problem in rivers because of its short hydraulic retention time, high removal efficiency, no chemical addition requirement, and robustness to polymer types.

Woodchip-sulfur based mixotrophic biotechnology for hexavalent chromium detoxification in the groundwater

This study investigated groundwater hexavalent chromium (Cr(VI)) decontamination by a biological permeable reactive barrier (bio-PRB), where a woodchip-elemental sulfur [S(0)] based mixotrophic process was established. 89.0 ± 0.27% of Cr(VI) was removed from the synthetic groundwater after 72 h at a concentration of 50 mg/L during the preliminary batch experiment. The impact of geochemical and hydrodynamic conditions Cr(VI) removal was investigated in the bio-PRB over 225 days. Although elevated Cr(VI) (i.e., 75 mg/L), addition of nitrate and short hydraulic retention time reduced the Cr(VI) removal, 87.2 ± 2.09% of Cr(VI) removal was accomplished. Characterization of the solids indicated that the soluble Cr(VI) was converted and immobilized as the insoluble trivalent chromium [Cr(III)]. 16S rRNA gene based sequencing results suggested that micromolecules produced by woodchip cellulose hydrolyzing- and sulfur oxidizing bacteria were further used by functional Cr(VI) removal bacteria (e.g., Geobacteraceae and Pseudomonas). The extracellular protein and humic-like substances in extracellular polymeric substances (EPS) can bind toxic Cr(VI) through carboxyl and hydroxyl groups, and reduce Cr(VI) in an enzymatic manner. The preliminary finding of this study provided a potential way to utilize agricultural waste for in-situ Cr(VI) contaminated-groundwater remediation.

Two-stage anaerobic membrane bioreactor for co-treatment of food waste and kitchen wastewater for biogas production and nutrients recovery

Co-digestion of organic waste and wastewater is receiving increased attention as a plausible waste management approach toward energy recovery. However, traditional anaerobic processes for co-digestion are particularly susceptible to severe organic loading rates (OLRs) under long-term treatment. To enhance technological feasibility, this work presented a two-stage Anaerobic Membrane Bioreactor (2 S-AnMBR) composed of a hydrolysis reactor (HR) followed by an anaerobic membrane bioreactor (AnMBR) for long-term co-digestion of food waste and kitchen wastewater. The OLRs were expanded from 4.5, 5.6, and 6.9 kg COD m−3 d−1 to optimize biogas yield, nitrogen recovery, and membrane fouling at ambient temperatures of 25–32 °C. Results showed that specific methane production of UASB was 249 ± 7 L CH4 kg−1 CODremoved at the OLR of 6.9 kg TCOD m−3 d−1. Total Chemical Oxygen Demand (TCOD) loss by hydrolysis was 21.6% of the input TCOD load at the hydraulic retention time (HRT) of 2 days. However, low total volatile fatty acid concentrations were found in the AnMBR, indicating that a sufficiently high hydrolysis efficiency could be accomplished with a short HRT. Furthermore, using AnMBR structure consisting of an Upflow Anaerobic Sludge Blanket Reactor (UASB) followed by a side-stream ultrafiltration membrane alleviated cake membrane fouling. The wasted digestate from the AnMBR comprised 42–47% Total Kjeldahl Nitrogen (TKN) and 57–68% total phosphorous loading, making it suitable for use in soil amendments or fertilizers. Finally, the predominance of fine particles (D10 = 0.8 μm) in the ultrafiltration membrane housing (UFMH) could lead to a faster increase in trans-membrane pressure during the filtration process.

Stable enhanced nitrogen removal from low COD/N municipal wastewater via partial nitrification-anammox in the traditional continuous anoxic/oxic process through bio-augmentation of partial nitrification sludge under decreasing temperatures

The application of partial nitrification-anammox (PNA) in continuous flow processes for treating low COD/N (C/N) sewage remains a critical challenge. Here, a traditional continuous anoxic/oxic (A/O) process was operated to investigate nitrogen removal from municipal wastewater by the bio-augmentation of partial nitrification sludge combined with the inoculation of biocarriers under decreasing temperatures. Stable enhanced nitrogen removal via PNA was achieved. The average total inorganic nitrogen in influent and effluent was 44.3 and 7.1 mg N/L under a low C/N ratio (3.4) and a short hydraulic retention time (8.2 h). The bio-augmentation of partial nitrification sludge enhanced the PNA process under low temperatures (16.9 ± 0.6 °C). The nitrogen removal efficiency remained stable at 83.3 ± 5.7 % as the temperature decreased from 29.1 to 16.3 °C, and the relative abundance of Ca. Brocadia in carrier biofilms increased from 2.22 % to 4.31 % and 3.27 % in two aerobic chambers after 70 days of operation.

MABR process development downstream of a carbon redirection unit: opportunities and challenges in nitrogen removal processes

ABSTRACT Carbon redirection has become the desired option for sustainable and energy-efficient wastewater treatment due to its contribution to a circular economy. However, its impact on downstream processes such as nitrification and denitrification requires further investigation. This research characterizes the nitrogen removal performance, footprint, aeration mode, and microbial composition of a flow-through membrane aerated biofilm reactor (MABR) downstream of a chemically enhanced primary treatment (CEPT) carbon redirection unit. The batch and long-term studies demonstrated relatively higher nitrification rates than those reported using conventional primary treated wastewaters. The results indicated that reducing carbon in the liquid train positively impacted nitrification by achieving 87 ± 12% (1.4 ± 0.4 g/m2.d) ammonia removal with an effluent 2.5 ± 2.8 mg/L ammonia concentration at a short hydraulic retention time (HRT) of 2.5 h. Despite the lower (1.9 ± 1) soluble COD:N, up to 75 ± 25% (0.6 ± 0.4 g/m2.d) total nitrogen removal was achieved at 4 h HRT by implementing intermittent aeration. The batch tests using the developed biofilms showed nitrification (denitrification) capacity up to 11 ± 1.7 gNH4-N/m2.d (8.5 ± 0.5 gNO3-N/m2.d) and 2.7 ± 0.6 gNH4-N/m2.d (2 ± 0.3 gNO3-N/m2.d) corresponding to ammonia and nitrate concentrations ranging from 10–30 mg/L and 2–10 mg/L, respectively. Microbial analysis indicated that the nitrifiers such as Nitrosomonas and Nitrospira were the dominant species. The ammonia-oxidizing, nitrite-oxidizing, and denitrifying bacteria relative abundances were 10.3 ± 1.5%, 20.7 ± 1.7%, and 20.0 ± 2.8% under continuous aeration and 1.3 ± 0.07%, 1.8 ± 0.09%, and 40.5 ± 3.1% under intermittent aeration, supporting the observed ammonia and total nitrogen removal processes, respectively. Overall, the results demonstrated that MABR downstream of the CEPT behave differently; thus, design guides should be updated accordingly.

New insights into microbial interactions and putative competitive mechanisms during the hydrogen production from tequila vinasses.

This study aimed to characterize the prokaryotic community and putative microbial interactions involved in hydrogen (H2) production during the dark fermentation (DF) process, applying principal components analysis (PCA) to correlate changes in operational, physicochemical, and biological variables. For this purpose, a continuous stirred-tank reactor-type digester fed with tequila vinasses was operated at 24, 18, and 12h of hydraulic retention times (HRTs) to apply organic loading rates of 20, 36, and 54g-COD L-1 d-1, corresponding to stages I, II, and III, respectively. Results indicated high population dynamics for Archaea during the DF process toward a decrease in total sequences from 6299 to 99. Concerning the Bacteria community, lactic acid bacteria (LAB) were dominant reaching a relative abundance of 57.67%, while dominant H2-producing bacteria (HPB) decreased from 25.76% to 21.06% during stage III. Putative competitive exclusion mechanisms such as competition for substrates, bacteriocins production, and micronutrient depletion carried out by Archaea and non-H2-producing bacteria (non-HPB), especially LAB, could negatively impact the dominance of HPB such as Ethanoligenens harbinense and Clostridium tyrobutyricum. As a consequence, low maximal volumetric H2 production rate (672mL-H2 L-1 d-1) and yield (3.88mol-H2 assimilated sugars-1) were obtained. The global scenario obtained by PCA correlations suggested that C. tyrobutyricum positively impacted H2 molar yield through butyrate fermentation using the butyryl-CoA:acetate CoA transferase pathway, while the most abundant HPB E. harbinense decreased its relative abundance at the shortest HRT toward the dominance of non-HPB. This study provides new insights into the microbial interactions and helps to better understand the DF performance for H2 production using tequila vinasses as substrate. KEY POINTS: • E. harbinense and C. tyrobutyricum were responsible for H2 production. • Clostridiales used acetate and butyrate fermentations for H2 production. • LAB won the competition for sugars against Clostridiales during DF. • Putative bacteriocins production and micronutrients depletion could favor LAB.

Performance evaluation of vertical constructed wetland units with hydraulic retention time as a variable operating factor

The current research intends to assess the impact of shorter hydraulic retention time (HRTs) and different sized filter material on the pollutant removal performance of two pilot-scale vertical sub-surface flow constructed wetlands (VSSF CW) to treat dairy wastewater. Two CWs (CW-1 & CW-2) were filled with 10 and 20 mm gravels, respectively, planted with Arundo donax, and operated at three different HRTs for treating dairy farm wastewater viz. 6, 12, and 24 h. Over three months, the effluent was tested for TSS, BOD5, TP, and NH4–N removal using standard procedures at regular intervals. Average concentrations of TSS, BOD5, TP, and NH4–N at the final outlets CW-1 and CW-2 were recorded in the range of; TSS: 44.7–118.7 mg L−1, BOD5: 8.1–33.9 mg L−1, TP: 13.7–22.2 mg L−1and NH4–N: 9.1–11.4 mg L−1, respectively. The highest removal of TSS (81.2%), BOD5 (90.2%), TP (65.1%), and NH4–N (82.5%) from wastewater was seen after a 12 h HRT, whereas maximum DO rise (579.0%) was reported after a 6 h HRT in 20 mm gravel-filled CW units. Short HRTs of 6, 12, and 24 h were found to be effective in removing all pollutants from wastewater and maintaining a constant treatment throughout the evaluation period. Results suggest that VSSF CW systems can be operated efficiently under short HRTs while still effectively removing contaminants from dairy wastewater.

Paired denitrifying bioreactors with wide orientation for increased drainage flow capacity

Denitrifying bioreactors are a conservation drainage practice for reducing nitrate loads in subsurface agricultural drainage. Bioreactor hydraulic capacity is limited by cross-sectional area perpendicular to flow through the woodchip bed, with excess bypass flow untreated. Paired bioreactors with wide orientations were built in 2017 in Illinois, USA, to treat drainage from a relatively large 29 ha field. The paired design consisted of: a larger, Main bioreactor (LWD: 6.1 × 18.3 × 0.9 m) for treating base flow, and 2) a smaller, Booster bioreactor (7.8 × 13.1 × 0.9 m) receiving bypass flow from the Main bioreactor during periods of high flow. Over three years of monitoring, the paired bioreactor captured 84–92% of the annual drainage discharge which demonstrated an expanded cross-sectional area could improve bioreactor flow capture, even for a large drainage area. However, the paired bioreactors removed 6–28% of the annual N load leaving the field (1.8–5.6 kg N ha−1 removed; 52–161 kg N), which was not a notable improvement compared to bioreactors treating smaller drainage areas. The design operated as intended at low annual flow-weighted hydraulic retention times (HRTs) of usually ≤2 h, but these short HRTs ultimately limited bioreactor nitrate removal efficiency. Daily HRTs of <2 h often resulted in nitrate flushing. The Main bioreactor had higher hydraulic loading as intended and was responsible for the majority of flow captured in each year although not always the most nitrate mass removal. The Booster bioreactor provided better nitrate removal than the Main at HRTs of 3.0–11.9 h, possibly due to its drying cycles which may have liberated more available carbon. This new design approach tested at the field-scale illustrated tradeoffs between greater flow capacity (via increased bioreactor width) and longer HRT (via increased length), given a consistent bioreactor surface footprint.

Enhanced Biodegradation of Formaldehyde Using Aerobic Sequencing Batch Rotating Bed Bioreactor With and Without Stimulation by Hydrogen Peroxide

The removal of formaldehyde as a toxic substance from aqueous solutions is of particular importance. In this research, a sequencing batch rotating-bed bioreactor (SBRB) was used on a laboratory scale for biodegradation of formaldehyde from synthetic wastewater. The reactor was made of plexiglas with a cylindrical shape. Kaldnes media were placed in a rotating cylindrical basket in the reactor. The effects of formaldehyde concentration (500–1500 mg/L), hydraulic retention time (HRT) (8, 15, 24 hours), and injection of hydrogen peroxide (0.1-0.5 mM) on the performance of the reactor were investigated. The results showed that in the SBRB, at an HRT of 24 hours and an inlet formaldehyde concentration of 1000 mg/L, the removal efficiencies of formaldehyde and chemical oxygen demand (COD) were 99.2% and 92%, respectively, while without rotating the bed, the removal efficiency of formaldehyde and COD was found to be 95% and 83%, respectively. By adding hydrogen peroxide at a concentration of 0.3 mM and operation of the SBRB with an HRT of 8 hours and an inlet formaldehyde concentration of 1000 mg/L, an improvement in the removal efficiency of formaldehyde and COD (4% and 22%, respectively) was observed. Accordingly, SBRB stimulation with hydrogen peroxide could be considered as a high-performance process for the removal of formaldehyde and corresponding COD at a short HRT.

Anaerobic Digestion of Pig Slurry in Fixed-Bed and Expanded Granular Sludge Bed Reactors

Anaerobic digestion of animal manure is a potential bioenergy resource that avoids greenhouse gas emissions. However, the conventional approach is to use continuously stirred tank reactors (CSTRs) with hydraulic retention times (HRTs) of greater than 30 d. Reactors with biomass retention were investigated in this study in order to increase the efficiency of the digestion process. Filtered pig slurry was used as a substrate in an expanded granular sludge bed (EGSB) reactor and fixed-bed (FB) reactor. The highest degradation efficiency (ηCOD) and methane yield (MY) relative to the chemical oxygen demand (COD) were observed at the minimum loading rates, with MY = 262 L/kgCOD and ηCOD = 73% for the FB reactor and MY = 292 L/kgCOD and ηCOD = 76% for the EGSB reactor. The highest daily methane production rate (MPR) was observed at the maximum loading rate, with MPR = 3.00 m3/m3/d at HRT = 2 d for the FB reactor and MPR = 2.16 m3/m3/d at HRT = 3 d for the EGSB reactor. For both reactors, a reduction in HRT was possible compared to conventionally driven CSTRs, with the EGSB reactor offering a higher methane yield and production rate at a shorter HRT.

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.

Influence of low operating temperature on biomass yield during anaerobic treatment of chocolate confectionery wastewater in a pilot-scale UASB reactor

It has been found that biomass yield (Yobs) increases as operating temperature decreases in batch reactors fed with synthetic substrate; nevertheless, there is a gap in literature about this phenomenon in pilot-scale reactors treating real industrial wastewaters, such as from the chocolate confectionery industry. Therefore, the effect of low operating temperature on the Yobs during the anaerobic treatment of chocolate confectionery wastewater (CCWW) was studied. In this research, the CCWW was treated in a 244-L pilot-scale upflow anaerobic sludge blanket reactor, which was operated for 275 days at short hydraulic retention time (6 h), medium total applied organic loading rates (OLRTappl) (6.7–11.6 kg-total chemical oxygen demand (CODT/m3/d)), and low operating temperature (14–20 °C). The COD removal efficiency ranged from 70 to 90 % and the methane production rate varied between 230 and 393 L-CH4/d at standard temperature and pressure (84 % of methane in biogas). The results showed that Yobs was higher at 14 °C [0.20 g-volatile suspended solids/g-removed COD (g-VSS/g-CODrem)] than at 20 °C (0.15 g-VSS/g-COD). Also, high Yobs values lead to a larger anaerobic biomass washout in the reactor effluent. The anaerobic biomass washout was also influenced by the presence of sodium in CCWW, the high OLRTappl and the low operating temperature, which made difficult the solids-liquid separation.

Mutual boost of granulation and enrichment of anammox bacteria in an anaerobic/oxic/anoxic system as the temperature decreases when treating municipal wastewater

Low temperature is an important factor affecting the municipal wastewater treatment systems. The aim of this study was tracking the variations in the abundance of anammox bacteria (AnAOB) and the sludge form as the temperature decreased. Mutual boost of granulation and enrichment of AnAOB was achieved even though the temperature dropped from 20.4 °C to 12.9 °C. The average particle size of the sludge increased from 128.5 μm to 245.6 μm. With low dissolved oxygen (DO) aeration (0.2–0.5 mg/L) and short oxic hydraulic retention time (HRT) (5 h), nitritation in the anaerobic/oxic/anoxic (AOA) system was stable enough to provide NO2– for AnAOB. Ca. Brocadia, a type of typical AnAOB, was enriched from 0.03% to 0.24% in the suspended sludge and reached 16.09% in the granular sludge. Overall, this study presents the prospects of anammox and granule technologies when treating municipal wastewater at a low temperature.

Purification of polluted surface water by sponge moving bed membrane bioreactor with short hydraulic retention time operation

AbstractA sponge moving bed membrane bioreactor (SMB‐MBR) was developed for high‐rate biological purification of polluted surface water for nonpotable utilization purposes. The SMB‐MBR contains polyurethane sponge cubes (10% v/v) and submerged hollow fibre membranes in a solid separation compartment and operated under a short hydraulic retention time of 1 h. High organic (96% biochemical oxygen demand [BOD], 85% soluble chemical oxygen demand [COD] and 84% COD) and nitrogen (99% ammonium nitrogen [NH4+], 98% total Kjeldahl nitrogen [TKN] and 87% total nitrogen [TN]) removals were achieved. In the SMB‐MBR, the suspended and attached biomass were allowed to develop under no sludge wastage operation. The co‐existence of heterotrophs, nitrifiers and denitrifiers in the biomass was confirmed under a high oxygen environment. Sustainable operation of SMB‐MBR could be achieved by maintaining stable membrane flux without chemical cleaning for 60 days. This research demonstrates the technical feasibility of applying the SMB‐MBR for clean water production when the polluted surface is the only raw water source.

Optimization Removal of COD and Nitrogen at Different Hydraulic Retention Times in Biocord-Integrated Fixed-Film Activated Sludge Syste

Although conventional activated sludge has been demonstrated to be a feasible approach for extracting nitrogenous chemicals and organic pollutants from wastewater, it still has a number of drawbacks. In this research, a pilot-scale biocord-integrated fixed-film activated sludge (Biocord-IFAS) reactor fed with actual domestic wastewater was operated to examine the effect of varying hydraulic retention time (HRT) on the COD and nitrogen removal. The type of material employed in this study is fibrous polypropylene (biocord), which is a major difference. The contribution of the Biocord-IFAS to COD removal efficiency reached 94.2% at HRT of 8 h and gradually decreased to 82.9% when HRT was reduced to 4 h. During the investigation period, a slight decrease in nitrification was found at a shorter HRT. The NH4+-N removal efficiencies at HRTs of 10, 8, 6, and 4 h were 97.8%, 98.7%, 97.1%, and 96.3%, respectively. The average effluent nitrate concentration was 5.3 mg/L with HRTs from 10 to 6 h, but over 30 mg/L with an HRT of 4 h. The SEM analysis results show that microorganisms have formed on the biocord surface. The results of this research have demonstrated the potential application of IFAS reactors in bioremediation procedures employing biocord material with great processing efficiency.

Beyond an Applicable Rate in Low-Strength Wastewater Treatment by Anammox: Motivated Labor at an Extremely Short Hydraulic Retention Time.

The application of anammox technology in low-strength wastewater treatment is still challenging due to unstable nitrite (NO2--N) generation. Partial denitrification (PD) of nitrate (NO3--N) reduction ending with NO2--N provides a promising solution. However, little is known about the feasibility of accelerating nitrogen removal toward the practical application of anammox combined with heterotrophic denitrification. In this work, an ultrafast, highly stable, and impressive nitrogen removal performance was demonstrated in the PD coupling with an anammox (PD/A) system. With a low-strength influent [50 mg/L each of ammonia (NH4+-N) and NO3--N] at a low chemical oxygen demand/NO3--N ratio of 2.2, the hydraulic retention time could be shortened from 16.0 to 1.0 h. Remarkable nitrogen removal rates of 1.28 kg N/(m3 d) and excellent total nitrogen removal efficiency of 94.1% were achieved, far exceeding the applicable capacity for mainstream treatment. Stimulated enzymatic reaction activity of anammox was obtained due to the fast NO2--N jump followed by a famine condition with limited organic carbon utilization. This high-rate PD/A system exhibited efficient renewal of bacteria with a short sludge retention time. The 16S rRNA sequencing unraveled the rapid growth of the genus Thauera, possibly responsible for the incomplete reduction of NO3--N to NO2--N and a decreasing abundance of anammox bacteria. This provides new insights into the practical application of the PD/A process in the energy-efficient treatment of low-strength wastewater with less land occupancy and desirable effluent quality.

Enhancement of biohydrogen production by employing a packed-filter bioreactor (PFBR) utilizing sulfite-rich organic effluent obtained from a washing process of beverage manufactures

Escalating necessity over exhausting fossil fuels needs an alternative source of energy. In this investigation, a packed-filter bioreactor was employed to generate hydrogen using sulfite wastewater as a substrate. The seed sludge was obtained from the sewage treatment plant. The results discovered that the substrate concentration was 10 g total sugar/L, the hydrogen content ranged from 36.3 to 29.18%, the hydrogen production rate (HPR) ranged from 20.8 to 6.50 L/L/d the sulfite concentration ranged from 20 to 80 mg. The wastewater's biohydrogen production rate declined when the sulfite concentration exceeded 40 mg/L. The hydrogen production rate in the packed-filter bioreactor (PFBR) using sulfite wastewater can stretch to 15.2 ± 0.41 L/L/d, Yield of 0.82 ± 0.01 mol H2/mol hexose, cell concentration of 6.57 ± 0.21 g VSS/L when operating under 2.5 g total sugar/L, hydraulic retention time 0.25 h, despite the unfavorable sulfite. The PFBR can degrade organic matter in sulfite wastewater with a short hydraulic retention time and a high organic loading rate. In a nutshell, the findings of this research can be utilized to broaden the usage of gaseous bioenergy in the practical implementation of government sewerage.

Statistical optimization of operating parameters of microbial electrolysis cell treating dairy industry wastewater using quadratic model to enhance energy generation

The performance of Microbial electrolysis cell (MEC) is affected by several operating conditions. Therefore, in the present study, an optimization study was done to determine the working efficiency of MEC in terms of COD (chemical oxygen demand) removal, hydrogen and current generation. Optimization was carried out using a quadratic mathematical model of response surface methodology (RSM). Thirteen sets of experimental runs were performed to optimize the applied voltage and hydraulic retention time (HRT) of single chambered batch fed MEC operated with dairy industry wastewater. The operating conditions (i.e) an applied voltage of 0.8 V and HRT of 2 days that showed a maximum COD removal response was chosen for further studies. The MEC operated at optimized condition (HRT- 2 days and applied voltage- 0.8 V) showed a COD removal efficiency of 95 ± 2%, hydrogen generation of 32 ± 5 mL/L/d, Power density of 152 mW/cm2 and current generation of 19 mA. The results of the study implied that RSM, with its high degree of accuracy can be a reliable tool for optimizing the process of wastewater treatment. Also, dairy industry wastewater can be considered to be a potential source to generate hydrogen and energy through MEC at short HRT.

Efficient biodegradation of phenol at high concentrations by Acinetobacter biofilm at extremely short hydraulic retention times

Efficient biofilm-forming bacteria are crucial for biofilm wastewater treatment reactors. Nevertheless, finding a suitable bacterial culture with high biodegradation capabilities and ability to grow a stable and effective biofilm that can survive the reactor environment poses a challenge. Here, we present a newly isolated bacterium Acinetobacter EMY that exhibits excellent growth rate, biofilm formation capability, and ability to biodegrade phenol at high concentrations. The phenol degradation rate of Acinetobacter EMY immobilized on polyethylene biocarriers in batch and continuous moving bed bioreactors (MBBRs) treated with phenol as the sole carbon source was significantly higher than that of a bacterial suspension. The continuous MBBR demonstrated impressive phenol removal rates (8.11 and 10.95 kg/m3/d at extremely short hydraulic retention times of 0.5 and 0.25 h, respectively). The phenol removal efficacy was 100% for hydraulic retention times of ≥0.5 h and 67.25% at 0.25 h. The Acinetobacter EMY biofilm batch bioreactor loaded with 165, 330, 665, 1150, and 2100 mg/L phenol achieved the maximum biodegradation rates of 7.65, 7.03, 9.15, 4.48, and 4.16 kg/m3/d, respectively. The new Acinetobacter EMY isolate showed enhanced phenol biodegradation capabilities compared with other isolates in similar studies. Chemical oxygen demand measurements proved that Acinetobacter EMY also consumed the intermediates of phenol degradation. In summary, Acinetobacter EMY is a promising bacterium for use in MBBR systems that treat water containing phenols.

Submerged anaerobic membrane bioreactor applied for mainstream municipal wastewater treatment at a low temperature: Sludge yield, energy balance and membrane filtration behaviors

The anaerobic membrane bioreactor (AnMBR) has potential as a low-cost wastewater treatment process with the benefit of energy production. However, to ensure satisfactory treatment performance, an AnMBR is operated at a relatively high temperature currently. Research focused on the operation of the AnMBR at low temperature is significant since the energy required for heating is an impediment to the application of AnMBRs for municipal wastewater treatment. Hence, in this study, a constant low-temperature (15 °C) AnMBR was evaluated for the treatment of real municipal wastewater with hydraulic retention times (HRTs) in the range of 6–24 h. During the long-term experiment, a chemical oxygen demand (COD) removal efficiency of approximately 90.5% was obtained with a sludge yield below 0.13 g-VSS/g-CODrem at HRTs of 16 and 24 h. The amount of energy generated was theoretically calculated based on biogas production, with a high of 0.62 kWh/t. The energy balance analysis showed that the AnMBR process can be energy positive under the optimal operational conditions investigated. Membrane filtration performed well during operation at 15 °C with HRTs ranging between 12 and 24 h, while it was compromised at the extremely short HRT of 6 h. In this study, the effectiveness of optimizing the conditions on the performance of the AnMBR operating at low temperature was confirmed, along with the potential for energy recoverability under those conditions.