Computational fluid dynamics study on first reaction chamber of internal circulation anaerobic reactor.

This study aims to investigate the characteristics of gas-liquid-solid three-phase flow in an Internal Circulation (IC) anaerobic reactor during the treatment of wastewater. Through computational fluid dynamics (CFD) simulations of the gas-liquid-solid three-phase in the first reaction chamber and based on the anaerobic granule swarms drag coefficient model, the study investigates the effects of superficial liquid velocity and superficial gas velocity on granules distribution, uniformity index, gas holdup, flow velocities of each phase, and the dimensionless variance of residence time distribution. In addition, the relationship between the fully mixed superficial velocities of gas and liquid in the first reaction chamber is also determined.

Performance evaluation and chemical oxygen demand removal of tannery wastewater through the aerobic-anaerobic route.

With characterized for complex and maximum substance (suspended solids, broke up oil, a mixture of inorganic and chromium sulfides), tannery wastewater was subjected to a treatment process on removal of chemical oxygen demand (COD) via upstream anaerobic sludge blanket reactor where we found reduced departure efficiencies and that process limits were affected by the assortments in regular stacking rates, closeness of chromium, and sulfides. Hence, a combination of the aerobic-anaerobic hybrid reactor was set up for sequential treatment to determine possible COD reduction. This study investigated the biological degradation of tannery wastewater in a laboratory-scale sequential up-flow aerobic-anaerobic reactor. The aerobic zone at the top was packed with spherical ball-shaped polyhedral polypropylene, and the anaerobic zone at the bottom was packed medium with granular media. The aeration flow rate varied by 2 L/min, 4 L/min, and 6 L/min in the aerobic zone, and the reactor maintained an organic loading rate (OLR) of 5 kg COD/m3/d. Parameters like COD and gas yield assess the performance of the reactor. The maximum COD of 86% is removed in the anaerobic zone with an aeration rate of 6 L/min, and the 1800-mL methane gas yield is measured by the 29th day.

Study of two approaches for the process water management from hydrothermal carbonization of swine manure: Anaerobic treatment and nutrient recovery.

Hydrothermal carbonization (HTC) is a promising alternative to transform biomass waste into a solid carbonaceous material (hydrochar) and a process water with potential for material and energy recovery. In this study, two alternatives for process water treatment by conventional and acid-assisted HTC of swine manure are discussed. Process water from conventional HTC at 180 °C showed high biodegradability (55% COD removal) and methane production (∼290 mL STP CH4 g-1 CODadded) and the treatment in an upflow anaerobic sludge blanket reactor allowed obtaining a high methane production yield (1.3 L CH4 L-1 d-1) and COD removal (∼70%). The analysis of the microbiota showed a high concentration of Synergistota and Firmicutes phyla, with high degradation of organic nitrogen-containing organic compounds. Acid-assisted HTC proved to be a viable option for nutrient recovery (migration of 83% of the P to the process water), which allowed obtaining a solid salt by chemical precipitation with Mg(OH)2 (NPK of 4/4/0.4) and MgCl2 (NPK 8/17/0.5), with a negligible content of heavy metals. The characteristics of the precipitated solid complied with the requirements of European Regulation (2019)/1009 for fertilizers and amendments in agricultural soils, being a suitable alternative for the recycling of nutrients from wastes.

The culprit for the declining performance of anaerobic reactors caused by calcification: Bioavailability deterioration.

Calcification is a critical challenge for achieving anaerobic reactors' high-efficiency. However, the aggregation caused by calcification at both granular sludge and reactor levels remain to be fully understood. Herein, this study investigated the characteristics of calcification in an anaerobic reactor (RH) operated with high calcium-containing wastewater for over 200-day. It was found that the COD removal efficiency in RH dropped from 98.00 ± 2.06% to 41.29 ± 3.79%, which was much lower than that of 95.50 ± 1.55% in the control reactor. Morphological analysis revealed that the high influent calcium caused granular sludge aggregation, which would further led to the rapid deterioration in bioavailability, as confirmed by both mass transfer tests and theoretical simulations. Moving forward, statistical analysis showed that the proportion of bioavailability deterioration zones in RH system (61.68%) was similar to the decreased COD removal efficiency (57.87%), proving that bioavailability deterioration was the culprit for the performance decline of anaerobic reactor.

Upgrading the biogas production from raw landfill leachate using O3/H2O2 pretreatment process: Modeling, optimization and anaerobic digestion performance.

Here, a combined pretreatment oxidation process (O3/H2O2) was investigated to enhance the biodegradability of raw landfill leachate (RLL) and biomethane potential (BMP) in anaerobic reactors. The central composite design (CCD) and response surface methodology (RSM) were employed to optimize the operational parameters influencing on RLL bioavailability in O3/H2O2 process: pH, Oxygen Flow rate, Reaction Time, and H2O2 concentration. The findings revealed that the O3/H2O2 increased biodegradability index (BOD5/COD) of RLL from 0.41 to 0.68 under optimized condition (pH=8, Oxygen flow= 0.25 L.min-1, Reaction Time= 25 min, H2O2 concentration= 2.5 g.L-1). Furthermore, the effects of O3/H2O2 process on BMP of RLL were surveyed under mesophilic anaerobic reactors (Temperature: 37 ± 1 °C) in viewpoints of operational performance and methane yield in a batch mode for incubation period of 24 days. The results showed that O3/H2O2 process simultaneously improve the BMP by 2.99 times higher in a shorter lag-phase period (5 days) compared with control. The pretreatment O3/H2O2 and mesophilic anaerobic digestion process revealed a feasible and efficient method for enhance BMP of RLL.

Performance of an Innovative Low-Cost Recycled Filling (LCRF) in Anaerobic Treatment of Dairy Effluent-A Pilot-Scale Study.

The rapid growth in dairy production leads to increasing outputs of high-load effluent, necessitating new methods of treating such waste. Anaerobic processes have been increasingly popular but are hamstrung by limited nutrient removal efficiency. The aim of the present study was to investigate whether low-cost recycled filling (LCRF) improves the anaerobic treatment of dairy effluent. The addition of LCRF was found to increase both COD removal (86.1 ± 2.6%-92.8 ± 1.6%) and Ptot. removal (22.1 ± 3.5% to 36.9 ± 4.6%) from the wastewater. The LCRF ensured near-neutral pH and stabilized the structure of the anaerobic microbe community (including Archaea) across all pollutant loads tested. This translated to efficient biogas production and high methane content in the LCRF reactors, peaking at 0.35 ± 0.01 m3/kg CODremoved and 68.2 ± 0.6% (respectively) in the best-performing variant.

Development of a post-treatment system using a downflow hanging sponge reactor - an upflow anaerobic reactor for natural rubber processing wastewater treatment.

This study aimed to evaluate the nitrogen removal of a post-treatment system for natural rubber processing wastewater (NRPW) under low chemical oxygen demand to total nitrogen (COD/TN) ratios without any supplemental external carbon source. The system including a downflow hanging sponge (DHS) reactor and an upflow anaerobic reactor (UAR) was operated in two phases. In phase 1 (day 0-102), under a nitrogen loading rate (NLR) of 0.23 ± 0.06 kgN m-3 d-1 and COD/TN ratio of 0.63 ± 0.47, the DHS-UAR system removed 82.5 ± 11.8% and 83.9 ± 7.6% of TN and ammonium concentrations, respectively. In phase 2 (day 103-229), higher COD/TN ratio of 1.96 ± 0.28 was applied to remove increasing NLRs. At the highest NLR of 0.51 kgN m-3 d-1, the system achieved TN and ammonium removal efficiencies of 93.2% and 93.7%, respectively. Nitrogen profiles and the 16S rRNA high-throughput sequencing data suggested that ammonium, a major nitrogen compound in NRPW, was utilized by nitrifying and ammonium assimilation bacteria in DHS, then removed by heterotrophic denitrifying and anammox bacteria in the UAR. The predominance of Acinetobacter detected in both reactors suggested its essential role for the nitrogen conversion.

Microbial dynamics and methanogenic potential of co-digestion of sugarcane vinasse and dairy secondary effluent in an upflow anaerobic sludge blanket reactor.

Co-digestion is a strategy that may prevent microbial inhibition during the anaerobic treatment of sugarcane vinasse, a substrate with highly biodegradable organic load, acidity, and toxic compound levels (e.g., sulfates, phenols). In this context, this study evaluated the microbial dynamics and methanogenic potential throughout the co-digestion of sugarcane vinasse and secondary effluent from the dairy industry in a mesophilic lab-scale upflow anaerobic sludge blanket (UASB) reactor. Periodic next-generation sequencing (NGS) analyses revealed an increase in the relative abundance of the phylum Euryarchaeota (+8.6 % after inoculation), predominating hydrogenotrophic methanogens (Methanobacterium and Methanobrevibacter) at the end of the operation. Moreover, the average methane yield was 221 mLCH4 gCODrem-1, with 69 % of organic matter removal. These results evidenced a progressive acclimation of the anaerobic microbial community to the substrate and a stable operation. Therefore, the proposed experiment demonstrates energy advantages for the agro-industrial sector by implementing a similar but full-scale treatment plant.

Effect of Phase Change Materials and Phase Change Temperature on Optimization of Design Parameters of Anaerobic Reactor Thermal Insulation Structure.

Direct-absorption anaerobic reactors can maintain the fermentation process of microorganisms by utilizing solar absorption and scattering media in the biogas reactor to improve the slurry temperature. Direct-absorption heating alone can save the corresponding electric energy and ensure the normal fermentation process of the biogas slurry in the reactor, but there is still the problem of temperature fluctuation. In order to improve the stability of the fermentation process, it is proposed to optimize the design of this kind of reactor by adding paraffin phase change material. This article mainly studies the influence of paraffin phase change material added on the top and side of the reactor in the fermentation process and gives the corresponding design parameters for different climatic conditions, which lays a theoretical reference for the design process of this kind of reactor.

Modified fractional-order model for biomass degradation in an up-flow anaerobic sludge blanket reactor at Zenein Wastewater Treatment Plant.

This paper presents a modified fractional-order model (FOM) for microorganism stimulation in an up-flow anaerobic sludge blanket (UASB) reactor treating low-strength wastewater. This study aimed to examine the famine period of methanogens due to biomass accumulation in the UASB reactor over long time periods at a constant organic loading rate (OLR). This modified model can investigate the substrate biodegradation in a UASB reactor while considering substrate diffusion into biological granules during the feast and famine periods of methanogens. The Grünwald-Letnikov numerical technique was used to indicate the effect of biomass degradation on the biogas production rate and substrate biodegradation in a UASB reactor installed at Zenein Wastewater Treatment Plant (WWTP) in Giza, Egypt. Several fractional orders were applied in the dynamic model at biomass concentrations of [Formula: see text] and [Formula: see text] in the reactor bed and blanket zones, respectively. An OLR of [Formula: see text] using the calibrated kinetic parameters at [Formula: see text] was applied to comply with the experimental outcomes. The simulation results indicate that the removal efficiency of chemical oxygen demand (COD) was maintained at approximately [Formula: see text], whereas the biogas production rate declined from [Formula: see text] in the reactor bed zone due to a decline in food to microorganism (F/M) ratio from [Formula: see text] during the sludge retention time (SRT) in the UASB reactor.

Modeling the Performance of Full-Scale Anaerobic Biochemical System Treating Deinking Pulp Wastewater Based on Modified Anaerobic Digestion Model No. 1.

The deinking pulp (DIP) is a main resource for paper making, and the wastewater from DIP process needs to be treated. Anaerobic biochemical technique has been widely applied in DIP wastewater treatment, due to the remarkable capability in reducing high chemical oxygen demand (COD). In this study, a mathematical simulation model was established to investigate the performance of a full-scale anaerobic biochemical system for treating DIP wastewater. The model was based on Anaerobic Digestion Model No. 1 (ADM1), which was modified according to the specific anaerobic digestion process for DIP wastewater treatment. The hydrodynamic behavior of a full-scale anaerobic biochemical system was considered in this model. The characteristics of the influent DIP wastewater were assessed, and then, the substrate COD proportion was divided successfully for the necessity of ADM1 applying. The Monte Carlo technique was implemented to distinguish the most sensitive parameters that influenced the model output indicators comprising effluent COD and biogas production. The sensitive parameters were estimated and optimized. The optimized value of k _m_pro is 12.02, K _S_pro is 0.35, k _m_ac is 4.26, K _S_ac is 0.26, k _m_h2 is 16.62, and K _S_h2 is 3.21 × 10-5. The model was calibrated with 150 days operation values measured in the field. The subsequent 100 days on-site values were used to validate the model, and the results obtained by the simulations were in good agreement. This study provides a meaningful and theoretical model guidance for full-scale wastewater anaerobic biochemical treatment simulation.

Treatment of polyvinyl alcohol containing wastewater in two stage spiral symmetrical stream anaerobic bioreactors coupled a sequencing batch reactor.

This work aimed to study the treatment of polyvinyl alcohol containing wastewater (PVA-containing wastewater) discharged from textile industry. The batch experiment verified the feasibility of anaerobic treatment and determined that the optimal substrate COD was around 3000 mg/L. The single spiral symmetrical stream anaerobic bioreactor (SSSAB) was used for treating PVA-containing wastewater, which shows the stability of SSSAB and the improvement of biodegradability of wastewater. Finally, two stage SSSABs coupled SBR was proposed. By this scheme, under the influent COD of 3014 mg/L and PVA of 413 mg/L, the COD and PVA removal reached 89.4% and 90.7%, respectively, which were higher than the values obtained by other schemes. Contribution rates of reactors show that each reactor plays an essential role, and SEM images show the unique of microbial flora in each SSSAB. The SSSAB-SSSAB-SBR process can provide an alternative to the chemical methods for treating PVA-containing wastewater.

Substrate competition and microbial function in sulfate-reducing internal circulation anaerobic reactor in the presence of nitrate.

Nitrate and sulfate often coexist in organic wastewater. In this study, an internal circulation anaerobic reactor was conducted to investigate the impact of nitrate on sulfate reduction. The results showed that sulfate reduction rate dropped from 78.4% to 41.4% at NO3- /SO42- ratios ranging from 0 to 1.03, largely attributed to the inactivity of acetate-utilizing sulfate-reducing bacteria (SRB) and preferential usage of nitrate of propionate-utilizing SRB. Meanwhile, high nitrate removal efficiency was maintained and COD removal efficiency increased with nitrate addition. Enhancement of propionate and butyrate degradation based on Modified Gompertz model and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2) analysis. Moreover, nitrate triggered the shift of microbial community and function. Twelve genera affiliated to Firmicutes, Bacteroidetes and Proteobacteria were identified as keystone genera via network analysis, which kept functional stability of the bacterial community responding to nitrate stress. Increased nitrate inhibited Desulfovibrio, but promoted the growth of Desulforhabdus. Both the predicted functional genes associated with assimilatory sulfate reduction pathway (cysC and cysNC) and dissimilatory sulfate reduction pathway (aprA, aprB, dsrA and dsrB) exhibited negative relationship with nitrate addition.

Roles of modified biochar in the performance, sludge characteristics, and microbial community features of anaerobic reactor for treatment food waste.

Anaerobic digestion (AD) is a green technology widely applied to food waste treatment. Although the AD has high efficiency, instability often occurs. The main purpose of the study is to understand the mechanism of modified biochar improving AD performance. The effects of different modified biochar on the efficiency and microecology of an anaerobic reactor treating food waste were investigated. Bagasse biochar was used as the substrate to explore the effects of iron-modified (A), chitosan-modified (B), iron-chitosan-modified (C) and iron­magnesium-chitosan-modified (D) biochar on the anaerobic digestion process, sludge characteristics and microbial community. The results show that the average COD removal efficiency of the four reactors during the last five days of the experimentation period was 86.95%, 85.90%, 92.22% and 93.29%, respectively. Adding iron­magnesium-chitosan-modified biochar could improve the efficiency of COD removal in the anaerobic reactor under ammonia nitrogen stress. On day 10 of operation, the content of coenzyme F420 in the sludge of anaerobic reactors C and D reached to 0.44 and 0.57 mmol/g, respectively, indicating that the metal-chitosan complex biochar could promote the production of coenzyme F420 in the early stage of the experiment. Within the four anaerobic reactors, Firmicutes, Bacteroidetes, Proteobacteria and Chloroflexi were the dominant bacteria, and the abundance of Chloroflexi reached a maximum of 26.24% in the reactor C. As for archaea, Methanobacterium and Methanothrix were the most dominant accounting for 44.03%, 49.88%, 31.29%, 52.01% and 38.34%, 34.52%, 50.9%, 35.72% respectively in the four reactors. KEGG functional analysis showed that the energy metabolism of bacteria and archaea in the reactor D was the largest among the four reactors. Meanwhile, the gene abundance associated with carbohydrate metabolism and membrane transport of microorganisms in the reactor D was greater than that of other groups.

Removal of 17α-ethinylestradiol and caffeine from wastewater by UASB-Fenton coupled system.

In aquatic systems, some substances considered as endocrine disruptors have been detected, which can be due to their incomplete elimination in wastewater treatment plants (WWTPs) and inadequate disposal of pharmaceuticals. Among these contaminants are 17α-ethinylestradiol (EE2) and caffeine (CAF). Moreover, it has been reported that this kind of contaminants may provoke different adverse effects in many aquatic organisms. Because of that, in the present study, up-flow anaerobic sludge blanket reactors (UASB) coupled with the Fenton process was evaluated for EE2 and CAF removal spiked in wastewater samples. First, the best reaction conditions were established in each process. For UASB reactor, two hydraulic retention times (HRT 8 and 24 h) were evaluated, achieving the highest chemical organic demand (COD) removal (70 %) and drug elimination (84 %-86 %) with HRT 24 h. Subsequently, Fenton process was conducted at pH 3 with different levels of Fe2+ (0.05-0.5 mmol/L) and molar ratios Fe2+:H2O2 (1:1-1:10). Better results were obtained with 0.5 mmol Fe2+/L, and 1:10 ratio molar Fe2+:H2O2. Finally, UASB-Fenton coupled system allowed 80 % of COD decrease, almost complete removal of drugs and the toxicity of samples on Vibrio fischeri was reduced from 73 % to 30 %, demonstrating that this coupled system is a promising and efficient system for pharmaceutical compounds removal from wastewater.

Effects of organic loading rate and temperature fluctuation on the microbial community and performance of anaerobic digestion of food waste.

Semi-continuous anaerobic fermentation of food waste was carried out using a solar-assisted heat reactor to explore effects of temperature fluctuation and organic loading rate (OLR: 2.0, 4.0, 6.0, 7.0 kg/(m3 day)VS on the reactor performance and microbial community structure. The results showed that the best methane production was achieved when OLR was 6.0 kg/(m3 day)VS because the reactors did not operate stably at 7.0 kg/(m3 day)VS. Compared with fluctuation of fermentation temperature, methane production at stable fermentation temperature increased by 21.72%, but higher power consumption occured. The results of high-throughput sequencing showed that OLR played a decisive role in succession of microbial community structure, while temperature fluctuation was more likely to affect microbial activity. When OLR was lower than 4.0 kg/(m3 day)VS, aceticlastic methanogens Methanosaeta were the dominant bacteria, while at 6.0 kg/(m3 day)VS, relative abundance of hydrogenotrophic methanogens Methanoregula and Methanospirillum increased.

Performance evaluation and kinetic modeling of down-flow high-rate anaerobic bioreactors for poultry slaughterhouse wastewater treatment.

In this study, the treatment of poultry slaughterhouse wastewater (PSW) was evaluated using two new down-flow high-rate anaerobic bioreactor systems (HRABS), including the down-flow expanded granular bed reactor (DEGBR) and the static granular bed reactor (SGBR). These two bioreactors have demonstrated a good performance for the treatment of PSW with removal percentages of the biochemical oxygen demand (BOD5), the chemical oxygen demand (COD), and fats, oil, and grease (FOG) exceeding 95% during peak performance days. This performance of down-flow HRABS appears as a breakthrough in the field of anaerobic treatment of medium to high-strength wastewater because down-flow anaerobic bioreactors have been neglected for the high-rate anaerobic treatment of such wastewater due to the success of up-flow anaerobic reactors such as the UASB and the EGSB as a result of the granulation of a consortium of anaerobic bacteria required for efficient anaerobic digestion and biogas production. Hence, to promote the recourse to such technologies and provide further explanation to their performance, this study approached the kinetic analysis of these two down-flow HRABS using the modified Stover-Kincannon and the Grau second-order multi-component substrate models. From a comparison between the two models investigated, the modified Stover-Kincannon model provided the best prediction for the concentration of the substrate in the effluent from the two HRABS. This analysis led to the determination of the kinetic parameters of the two models that can be used for the design of the two HRABS and the prediction of the performance of the SGBR and DEGBR. The kinetic parameters determined using the Modified Stover-Kincannon were Umax = 40.5 gCOD/L.day and KB = 47.3 gCOD/L.day for the DEGBR and Umax = 33.6 gCOD/L.day and KB = 44.9 gCOD/L.day for the SGBR; while, using the Grau second-order model, the kinetic models determined were a = 0.058 and b = 1.112 for the DEGBR and a = 0.135 and b = 1.33 for the SGBR.

Exploration of sulfate reducing sludge granulation with real domestic sulfate-laden wastewater.

Extending sulfate reducing sludge granulation to real sulfate-laden wastewater was trialed in this study. Two types of reactors, namely sulfate reducing upflow sludge blanket (SRUSB) reactor and continuous stirred tank reactor (CSTR), were used for granulation. Sulfate-reducing granules were observed after 5 months' operation of stepwise hydraulic retention time (HRT) shortening, recirculation cycle adjustment, and air scouring in the SRUSB reactor. Comparatively, granular sludge was achieved in the CSTR after 6 months of cultivation with an average size of 220 µm. With the process of granulation, the HRTs of the two types of reactors were reduced to 2.2 and 2.8 h, respectively for the SRUSB and CSTR reactors. The abundance of sulfate-reducing bacteria (SRB) related genera reached 29.3 and 45% in the SRUSB and CSTR reactors, respectively. Incomplete organic oxidizing SRB were dominant in the CSTR and SRUSB is predominated by complete organic oxidizing SRB, which facilitated a higher organic loading rate. Considering the operating merits, the CSTR is preferable as a pretreatment unit (e.g., for acidification), while the SRUSB reactor can be used for maximum organics removal or sulfide production. Due to the high suspended solids in the influent, full granulation was not achieved by using real sulfate-laden wastewater, and fine particles accumulation in the reactor was also a concern particularly for the long-term operation.

Evaluating the performance of inorganic draw solution concentrations in an anaerobic forward osmosis membrane bioreactor for real municipal sewage treatment.

Sewage can become a valuable source if its treatment is re-oriented for recovery. An anaerobic forward osmosis membrane bioreactor (AnOMBR) was developed for real municipal sewage treatment to investigate performance, biogas production, flux change and mixed liquor characteristics. The AnOMBR had a good treatment capacity with removal ratio of chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus more than 96%, 88%, 89% and almost 100%. Although high DS concentration increased the initial flux, it caused rapid decline and poor recoverability of FO membrane flux. Low DS concentration led to too long hydraulic retention time, thus resulting in a low reactor efficiency. Additionally, it was observed that salt, protein, polysaccharide and humic acid were all accumulated in the reactor, which was not conducive to stable long-term operation. Based on the characteristics of membrane fouling, salt accumulation and AnOMBR performance, the optimal DS of 1 M NaCl solution was selected.

An integrated anaerobic system for on-site treatment of wastewater from food waste disposer.

In this study, an integrated system of siphon-driven self-agitated anaerobic reactor (SDSAR) and anaerobic fixed bed reactor (AFBR) was conducted for the treatment of wastewater from food waste disposer (FWD), and the effect of influent total solids (TS) concentration on the process performance was evaluated. When the influent TS concentration increased from 7.04 to 15.5 g/L, the methane gas production rate increased from 0.45 to 0.92 L-CH4/L/day. However, with the influent TS concentration of food waste (FW) further increased to 23.5 g/L, a large amount of scum formed and accumulated in the SDSAR. According to the result of chemical oxygen demand (COD) recovery, the proportion of COD remained in the effluent at different TS concentrations was only around 2%. On the other hand, with an increase in TS concentration, the proportion of COD remained in the reactors increased significantly. Our results demonstrated that effluent from the integrated system can meet the water quality requirements recommended by Japan Sewage Works Association (JSWA) for wastewater from FWD. In addition, to enhance the process stability, the influent TS concentration should be maintained below 15.5 g/L.