High-rate Anaerobic Reactors Research Articles

Full-scale study on high-rate low-temperature anaerobic digestion of agro-food wastewater: process performances and microbial community.

The fast-growing global population has led to a substantial increase in food production, which generates large volumes of wastewater during the process. Despite most industrial wastewater being discharged at lower ambient temperatures (<20 °C), majority of the high-rate anaerobic reactors are operated at mesophilic temperatures (>30 °C). High-rate low-temperature anaerobic digestion (LtAD) has proven successful in treating industrial wastewater both at laboratory and pilot scales, boasting efficient organic removal and biogas production. In this study, we demonstrated the feasibility of two full-scale high-rate LtAD bioreactors treating meat processing and dairy wastewater, and the microbial communities in both reactors were examined. Both reactors exhibited rapid start-up, achieving considerable chemical oxygen demand (COD) removal efficiencies (total COD removal >80%) and generating high-quality biogas (CH4% in biogas >75%). Long-term operations (6-12 months) underscored the robustness of LtAD bioreactors even during winter periods (average temperature <12 °C), as evidenced by sustained high COD removal rates (total COD removal >80%). The stable performance was underpinned by a resilient microbial community comprising active acetoclastic methanogens, hydrolytic, and fermentative bacteria. These findings underscore the feasibility of high-rate low-temperature anaerobic wastewater treatment, offering promising solutions to the zero-emission wastewater treatment challenge.

Hydrolytic enzyme activity in high-rate anaerobic reactors treating municipal wastewater in temperate climates

Particulate matter hydrolysis is the bottleneck in anaerobic treatment of municipal wastewater in temperate climates. Low temperatures theoretically slow enzyme-substrate interactions, hindering utilization kinetics, but this remains poorly understood. β-glucosidase, protease, and lipase activities were evaluated in two pilot-scale upflow anaerobic sludge blanket (UASB) reactors, inoculated with different sludges and later converted to anaerobic membrane bioreactors (AnMBRs). Despite similar methane production and solids hydrolysis rates, significant differences emerged. Specific activity peaked at 37 °C, excluding the predominance of psychrophilic enzymes. Nevertheless, the Michaelis-Menten constant (Km) indicated high enzyme-substrate affinity at the operational temperature of 15–20 °C, notably greater in AnMBRs. It is shown, for the first time, that different seed sludges can equally adapt, as hydrolytic enzymatic affinity to the substrate reached similar values in the two reactors at the operational temperature and identified that membrane ultrafiltration impacted hydrolysis by a favourable enzyme Michaelis-Menten constant.

A Cost Analysis of Two-Stage Thermophilic-Mesophilic Anaerobic Wastewater Treatment Systems

Anaerobic bacteria have displayed great potential as a wastewater treatment method because of their efficiency, high methane yield, and low input requirements. In the past, studies have investigated various aspects of these systems, including their chemical oxygen demand (COD) removal efficiency, methane yield, and retention times. However, they have mostly focused on single stage high rate anaerobic (HRAA) reactors such as the upflow anaerobic sludge blanket (UASB) reactor. In this paper, we aim to synthesize the results of these studies to investigate the advantages of building upon the UASB via a two-stage thermophilic-mesophilic (T-M) reactor system with an anaerobic filter (AF) as the acidification tank. The key constraint for adopting two-stage anaerobic systems is primarily related to construction and O&amp;M costs. Therefore, we propose adjusting pH levels and influent flow rates to enhance energy generation and cost-efficiency. This approach aims to encourage greater utilization of two-stage anaerobic systems for wastewater treatment by lowering costs and increasing profits.

Low carbon-to-nitrogen ratio digestate from high-rate anaerobic baffled reactor facilitates heterotrophic/autotrophic nitrifiers involved in nitrogen removal

In this study, baffled anaerobic–aerobic reactors (AOBRs) with modified basalt fiber (MBF) carriers and felt were used to treat domestic wastewater (DWW). The influent was first treated in anaerobic compartments, with the NH4+-N containing digestate refluxed into aerobic compartment for nitrification. The nitrified liquid was channeled to the anaerobic compartments for further denitrification. Under optimal conditions, AOBR with MBF carriers could remove 91% chemical oxygen demand (COD) and 81% total nitrogen (TN), with biomass production increased by 7.6%, 4.5% and 8.7% in three successive anaerobic compartments compared to the control. Biological viability analysis showed that live cells outnumbered dead cells in bio-nests. Metagenomics analysis showed that multiple metabolic pathways accounted for nitrogen conversion in anaerobic and aerobic compartments. More importantly, low COD/TN ratio digestate facilitated heterotrophic nitrification-aerobic denitrification (HN-AD) species growth in aerobic compartment. This study provides a promising strategy to source treatment of DWW from urban communities.

Modeling and optimization of process parametric interaction during high-rate anaerobic digestion of recycled paper mill wastewater using the response surface methodology

Abstract This study carried out the anaerobic digestion of recycled paper mill wastewater (RPMW) in a high-rate novel anaerobic baffled reactor. The parametric interaction between influent chemical oxygen demand (CODin) and hydraulic retention time (HRT) was modeled, and process responses were optimized by the response surface methodology (RSM) using a three-level factorial design. The results showed that the optimal condition was determined at CODin of 4,000 mg/L and HRT of 2 days and predicted values for COD removal, biochemical oxygen demand (BOD) removal, lignin removal, CH4 content, and CH4 production were found to be 94%, 98%, 68%, 85%, and 20.8 L CH4/d, respectively. According to the statistical analysis of the RSM, all models were significant with very low probability values (from 0.0045 to &amp;lt;0.0001). The parametric interaction showed that increasing the CODin positively influenced the COD, BOD, and lignin removal efficiencies, effluent alkalinity, and methane content and production but was unfavorable for pH and effluent volatile fatty acid (VFA). Shortening the HRT negatively affected the COD, BOD, and lignin removal efficiencies, pH level, alkalinity, and methane content and production, and increased the VFA effluent concentration. The optimal conditions were established at 4,000 mg/L COD and HRT of 2 days, corresponding to the predicted COD, BOD, and lignin removal efficiencies of 91, 98, and 71%, respectively, whereas 28 mg/L of VFA and 0.125 L of CH4/g CODremoved were generated.

Comparative performance of high-rate anaerobic reactors for biodegradation of soybean molasses

Soybean molasses is a residue obtained at the industrial processing of soybean to produce the soy protein concentrate. This residue is the result of the extraction of sugars from de-oiled soybean meal, which viable alternative to its disposal might be the degradation by anaerobic digestion (AD). Thus, a comparative study was performed in two high-rate technologies (UASB and ABR reactors) to evaluate the start-up time and optimum HRT required for the AD of soybean molasses under similar loading operations. The lab-scale reactors were fed with soybean molasses for 134 and 103 days under ambient conditions, respectively. Initially, the UASB reactor was operated at an organic loading rate (OLR) of 0.28 kgCOD m−3 d−1 (HRT = 48 h), while ABR reactor of 0.43 kgCOD m−3 d−1 (HRT = 36 h). OLRs were improved by reducing HRT 48 to 12 h and increasing substrate concentration (COD of 500 to 6000 mg L−1) for six different OLR in both reactors. After the fast start-up period, the UASB reactor attained values of CODTotal and CODFiltered removal efficiencies of 80% and 88%, respectively at an HRT of 24 h (3.91 kgCOD m−3 d−1) whereas ABR reactor presented 95% (CODTotal) and 97% (CODFiltered) at HRT of 36 h (3.86 kgCOD m−3 d−1) for similar OLR. By reducing HRT, both reactors have shown granular sludge flotation (sludge washout) and lower COD removal efficiencies (<80%). The experimental results revealed that high-rate anaerobic configurations (UASB and ABR reactors) can be used for the anaerobic biodegradation of soybean molasses with removal efficiency and a short start-up period.

Kinetic assessment of the anaerobic treatment of piggery wastewaters using an EGSB reactor with Cuban natural zeolite

Large pig farms generate enormous volumes of wastewater without proper treatment before discharge. High-rate anaerobic reactors as the expanded granular sludge bed (EGSB) are rarely reported for that purpose. In this study, an EGSB reactor with Cuban natural zeolite addition was evaluated for treating piggery wastewaters at lab scale. This study was conducted at different organic loading rate (OLR) ranging from 0.32 to 6.13 gCOD/Ld with a constant hydraulic retention time (HRT) of 12 h. The evolution of several control and operational parameters as the soluble chemical oxygen demand (COD) demonstrated a proper bioreactor performance to treat piggery wastewater. The results showed that the addition of natural zeolite at 40 gzeo/Lreactor in EGSB reactor results in COD efficiencies over 70%, despite of the fluctuations of fed wastewater characteristics. The kinetic study demonstrates that, the modified Stover-Kincannon model was found to be appropriate for EGSB reactor. The effluent soluble COD was predicted with high determination coefficient. The maximum removal rate constant (Umax) and saturation value constant (KB) were reported for a first time for the EGSB reactor with values of 10.2 and 11.8 gCOD/Ld, respectively. Methane yield for both, batch and continues experiments, were in the range from 214.5 to 299.8 mLCH4/gCOD.

Multi-Integrated Systems for Treatment of Abattoir Wastewater: A Review

Biological wastewater treatment processes such as activated sludge and anaerobic digestion remain the most favorable when compared to processes such as chemical precipitation and ion exchange due to their cost-effectiveness, eco-friendliness, ease of operation, and low maintenance. Since Abattoir Wastewater (AWW) is characterized as having high organic content, anaerobic digestion is slow and inadequate for complete removal of all nutrients and organic matter when required to produce a high-quality effluent that satisfies discharge standards. Multi-integrated systems can be designed in which additional stages are added before the anaerobic digester (pre-treatment), as well as after the digester (post-treatment) for nutrient recovery and pathogen removal. This can aid the water treatment plant effluent to meet the discharge regulations imposed by the legislator and allow the possibility for reuse on-site. This review aims to provide information on the principles of anaerobic digestion, aeration pre-treatment technology using enzymes and a hybrid membrane bioreactor, describing their various roles in AWW treatment. Simultaneous nitrification and denitrification are essential to add after anaerobic digestion for nutrient recovery utilizing a single step process. Nutrient recovery has become more favorable than nutrient removal in wastewater treatment because it consumes less energy, making the process cost-effective. In addition, recovered nutrients can be used to make nutrient-based fertilizers, reducing the effects of eutrophication and land degradation. The downflow expanded granular bed reactor is also compared to other high-rate anaerobic reactors, such as the up-flow anaerobic sludge blanket (UASB) and the expanded granular sludge bed reactor (EGSB).

A new non-steady-state mass balance model for quantifying microbiome responses to disturbances in wastewater bioreactors

Herein we proposed an ecology model, based on a non-steady-state mass balance (16S rRNA MiSeq reads normalized by volatile suspended solids), to quantify microbiome responses to disturbances in wastewater bioreactors. Rather than focusing on the most abundant microbial groups commonly used in the literature, the goal of the model was to identify active species within the community. The model incorporated the temporal changes of operational taxonomic units following a disturbance, through considering the density and type of genotypes in the influent entering the bioreactor, in the effluent leaving the bioreactor, growing in the bioreactor, and in the waste sludge discharged from the bioreactor continuously or instantaneously, as well as the prior microbial community and the sludge characteristics. One application of this model demonstrated that significant differences existed between the key populations responding to an increasing organic loading rate and the dominant species in a high-rate thermophilic upflow anaerobic sludge blanket reactor.

Full-Scale Application of Up-flow High Rate Anaerobic Reactor with Substrate Modification and Effluent Recirculation for Sugarcane Vinasse Degradation and Biogas Generation

Full-Scale Application of Up-flow High Rate Anaerobic Reactor with Substrate Modification and Effluent Recirculation for Sugarcane Vinasse Degradation and Biogas Generation

Soybean molasses as feedstock for sustainable generation of biomethane using high-rate anaerobic reactor

Anaerobic digestion of agro-industrial wastes is an environmentally friendly green biotechnology of significant interest in order to facilitate sustainable development of bioenergy production. Thus, it becomes important to invest in management processes for agro-industrial wastes, particularly low-cost ones. In this paper, the main purposes were to investigate the performance of a high-rate reactor and biogas generation potential by anaerobic digestion of soybean molasses, which is a viscous liquid of brown color obtained as a byproduct from processing of the soy protein industry concentrate. A lab-scale up-flow anaerobic sludge blanket reactor (UASB reactor), with a total volume of 12 L, was operated at six different organic loading rates (OLR) ranging from 0.28 to 6.98kgCODm−3d−1 (COD of 500–4000 mg L−1). The reactor was fed with soybean molasses for 134 days and maintained under mesophilic conditions. Different values were tested for the hydraulic retention time (HRT of 48, 24 and 12 h). After the fast startup period (52 days), the mean values of removal efficiencies (CODTotal) ranged from 70% to 83% in all experimental periods. In a UASB reactor, a higher organic loading rate of 6.98kgCODm−3d−1 could be tolerated, but it resulted in a lower biomethane yield of 356.1mLCH4gCOD−1. In addition, for all the tested COD concentrations and HRT, high concentrations of methane in the biogas were obtained from 72.5% to 82.1%. Based on the experimental results, it can be verified that this high-rate anaerobic configuration can be used for the biomethane generation of soybean molasses and the produced effluent can be reutilized in the dilution of soybean molasses for reactor feed.

A REVIEW ON ORGANIC REMOVAL OF MUNICIPAL AND INDUSTRIAL WASTEWATER USING UP-FLOW ANAEROBIC SLUDGE BLANKET (UASB) AND ITS APPLICATION IN ANAMMOX PROCESS

Anaerobic treatment processes are widely recognized as a sustainable wastewater management system for their encouraging results in treating highly concentrated wastewater (bCOD &gt; 4000 mg/L) with low energy requirement, which is more economical than aerobic processes. High rate anaerobic reactors, particularly up-flow anaerobic sludge blanket (UASB) reactors, have been extensively employed worldwide due to their high volumetric organic capacity and less sludge yield. However, some limiting factors need to be resolved for large-scale applications. This review aims to emphasize the organic removal of municipal and industrial wastewater using UASB technology and its application in the anammox process in treating ammonia-rich wastewater.Keywords: Anaerobic, anammox, granulation, Up-flow Anaerobic Sludge Blanket (UASB)

A review on the prospective use of chicken manure leachate in high-rate anaerobic reactors

The global production of chicken arises over the world, which leads to increasing manure generation and environmental problems. Anaerobic digestion (AD) is a well-known process to produce biogas from biomass. Chicken manure (CM) is considered as a feedstock for biogas production due to its high organic load, but there are some challenges to be considered, such as the heterogeneity and the high solid content. To overcome these issues, pretreatments techniques that enhance biogas production could be used. In this context, the use of the leachate process for CM pretreatment could be a novel alternative producing an easily biodegradable liquid substrate for AD. High-rate anaerobic reactors (HRAR), as mature technologies in the market, represent an opportunity for its technological simplicity and economy. Improvements of AD with leaching pretreatment were studied considering the use of HRAR as recent achievements to produce biogas and perspectives in the world. For mathematical modeling, the leaching process with CM as substrate, Computational Fluid Dynamics (CFD) methods are presented as a numerical simulation tool for a better understanding of the process. The integration of the leaching-efficient AD process in a biorefinery approach in a developing country using CM as a substrate could diversify its productions, in addition to reducing emissions to the environment. The results obtained became a tool for decision-makers and researchers about the implementation of leaching pretreatment prior to high-efficiency technologies for CM management in Poultry Farms to obtain the highest benefits, not only in Cuba but also in other developing countries with a similar situation. Production of biogas from CM is a technical solution that contributes to substitute fossil fuels by renewable energy.

Anaerobic Treatment of Diluted Decanted Palm Oil Mill Effluent in a High-Rate Thermophilic Upflow Anaerobic Sludge Blanket Reactor: Microbial Selection and Enhanced Population of Hydrogenotrophic Methanogen

This paper presents a study of the startup and operation of a high-rate upflow anaerobic sludge blanket (UASB) treating diluted decanted palm oil mill effluent (POME) under thermophilic conditions. The operating temperature was increased in one-step from 25 to 55 °C. The organic loading rate (OLR) of POME was increased stepwise from 2 g/L day of COD to 23.8 g/L day. High-rate anaerobic digestion with methane (CH4) productivity of 8 L/L day was achieved. The development of microbial populations in the sludge involved an increase in both H2 producers, specifically the genus Clostridium, and H2 consumers, specifically the order Methanobacteriales. A gene quantification based on real-time polymerase chain reaction (PCR) showed that the archaeal rRNA gene concentration increased from 3.48 × 107 copies/mL in the original digested sludge to 1.89 × 109 copies/mL in the acclimated sludge. The increase in archaeal rRNA gene concentration was accompanied by a 3700 times increase in Methanobacteriales gene concentration. However, the Methanobacteriales was found to be vulnerable to substrate over-loading with its gene concentration decreasing 35 fold from that in the original digested sludge at an OLR of 23.8 g/L day.

Biopaq®ICX: The next generation high rate anaerobic reactor proves itself at full scale

Abstract The ICX (Internal Circulation eXperience) is the next generation high rate anaerobic reactor. The unique design with a two-stage phase separation device enables excellent biomass retention. The novel biomass retention device allows for high volumetric loading rates to be applied compared to IC (internal circulation) and UASB (Upflow Anaerobic Sludge Bed) reactors. Since the first demonstration test in 2013, more than 70 full scale ICX reactors have been built, ranging in size from 85 to 5,000 m3. This paper presents the results of the first ICX demonstration reactor (85 m3) and from a full scale ICX reference (350 m3). These results confirm that very high volumetric loading rates can be achieved with the ICX, whilst maintaining a stable and high COD removal efficiency. Biomass growth is clearly demonstrated in both the demonstration reactor and in the full scale reference, proving that efficient biomass retention is achieved in the ICX.

Reduction of scum accumulation through the addition of low-cost enzymatic extract in the feeding of high-rate anaerobic reactor.

This work evaluates the reduction of scum accumulation on the top surface of upflow anaerobic sludge blanket (UASB) reactors by the addition of hydrolytic enzymes in their feed. For over 1 year, two UASB reactors of 1.4 L were maintained at 30 °C and continuously fed with synthetic domestic wastewater (containing 150 mg/L of soybean oil) under a hydraulic retention time of 10 h. The Control reactor was only fed with synthetic wastewater. Beginning at the 226th day of operation, low-cost hydrolytic enzymes (obtained by solid-state fermentation of Aspergillus terreus, a fungus isolated from a primary sewage sludge) were added into the feed of the other reactor (Test) for a lipase activity of 24 U/L, considerably reducing the formation of scum. In the Test reactor, the scum showed oil and grease (O&G) concentration between 0.8 and 1.3 g/L and an accumulation rate of 20 to 27 mg O&G/d. In the Control reactor, the scum had values twice as high (1.5-2.5 g/L and 34-51 mg O&G/d, respectively) and there were more operational problems. During the entire period of operation, both reactors presented high chemical oxygen demand removal (>80%), with no loss of effluent quality due to the addition of the enzymes.

High-rate anaerobic treatment of digestate using fixed film reactors

The effluent stream of the anaerobic digestion processes, the digestate, accommodates high residual organic content that needs to be further treated before discharge. Anaerobic treatment of digestate would not only reduce the residual organic compounds in digestate but also has a potential to capture the associated biogas. High-rate anaerobic reactor configurations can treat the waste streams using lower hydraulic retention times which requires less footprint opposed to the conventional completely stirred tank reactors. This study investigated the high-rate anaerobic treatment performance and the associated biogas capture from the digestate of a manure mixture composed of 90% laying hen and 10% cattle manures in fixed-film reactors. The results indicated that it was possible to reduce total chemical oxygen demand content of the digestate by 57–62% in 1.3–1.4 days of hydraulic retention time. The corresponding biogas yields obtained were in the range of 0.395–0.430 Lbiogas/g VSadded which were found to be comparable to many raw feedstocks. Moreover, significant total phosphorus reduction (36–47%) and greenhouse gas capture (over 14.5–18.1 tCO2e/d per m3 digestate) were also recorded in the anaerobic fixed-film reactors.

Design, installation, operation and experimentation of septic tank – UASB wastewater treatment system

The project intends to design, fabricate and test a highrate anaerobic reactor that can treat the domestic wastewater and produce biogas as a byproduct. The biogas is a combustible mixture of methane, carbon monoxide, hydrogen gases etc. and can be used in the table burner. The target of the biogas reactor is to treat the wastewater generate from domestic wastewater at Kathmandu University. The major outcome of this project is to be a working design of the biogas digester which can be fabricated and can be coupled with domestic septic for the domestic wastewater treatment. The septic tank uses as a primary treatment of the wastewater whereas UASB is taken as a secondary treatment. We design pilot scale UASB wastewater treatment system and test know the proper operation of the reactor. The septic tank-UASB combine system has TSS and CODt removal efficiency of 83% and 88% respectively. This system is one of the appropriate systems for onsite wastewater treatment in the developing country.

Bioaccumulation of metals and granular sludge development in a newly-inoculated high rate anaerobic reactor

For treatment of wastewater from soft drink production, a full scale (546 m3) expanded granular sludge bed (EGSB) reactor was inoculated with granular sludge previously used to treat wastewater from paper and food processing industries. During startup and subsequent phases, there were significant changes observed in granule composition, performance, and population distribution. Microbial, compositional and functional development of granular sludge during a six month time period immediately following inoculation was investigated. Reaction kinetics and fluorescence in situ hybridization (FISH) analysis were used to describe population dynamics and evolution of methanogens and fermentative microbes within the granules. Bioaccumulation of elements was quantified and analyzed statistically with respect to operational parameters; calcium and sulfate deficiencies in the new wastewater likely contributed to granule disintegration and eventual reactor failure. Second generation granules formed from the novel conditions exhibited characteristics from multiple granulation models.

Model-based design of a software sensor for real-time diagnosis of the stability conditions in high-rate anaerobic reactors – Full-scale application to Internal Circulation technology

Internal Circulation (IC) anaerobic systems are especially suitable when plant designs that involve both small footprints and high organic loading rates (>25 kg COD m−3 d−1) are required. However, given that operating anaerobic processes at high organic loads increases their vulnerability to external disturbances, real-time indicators of the stability conditions become particularly pertinent for IC reactors. This paper addresses the design and full-scale validation of a software sensor that uses only feeding flow-rate and biogas flow-rate measurements to classify the operating conditions of the reactor as “strongly”, “moderately” or “weakly” stable. A simulation-based procedure was used to design the software sensor and configure its parameters. Then, the performance of the software sensor was tested under real conditions in a full-scale IC reactor of 1679 m3 installed in a recycled paper mill (RPM).