High-rate Anaerobic Digestion 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.

Upflow Anaerobic Sludge Blanket (UASB) reactors for Bio-methane production from limed tannery fleshings: Lab and pilot scale reactors

The Upflow Anaerobic Sludge Blanket reactor is a viable high-rate anaerobic digestion design for the treatment of different wastewater with low to high solubility. This can also be used for the treatment of solid wastes with less HRT. In this study, the performance evaluation of a lab-scale UASB reactor was carried out for different hydraulic retention times of 24, 21, 18, 15 and 12 h for obtaining the best HRT for tannery fleshings. The gas production varied between 3.7 – 4.5 L with a methane content of 64.31 – 67.72%. It was observed that the maximum gas production was at 18 h HRT and this optimized condition was applied to the pilot-scale UASB reactor. The performance evaluation of the pilot-scale UASB reactor was carried out with an HRT of 18 h. The gas production of 450 ± 50 L, the maximum specific gas production of 0.274 m3/kg of VS destroyed and 0.239 m3/kg of TS destroyed was obtained and the maximum biogas productivity of 0.495 L was observed at 18 h HRT with the highest methane content of 67.86%. The payback period of the pilot scale reactor is 3.2 years.

Performance and microbial community composition of full-scale high-rate cascade sludge digestion system via pie-shaped reactor configuration

A full-scale high-rate cascade anaerobic digestion (CAD) system was evaluated for its ability to enhance enzymatic sludge hydrolysis. The system included a newly built digester, innovatively divided into three pie-shaped compartments (500 m3 each), followed by an existing, larger digester (1500 m3). The system treated a mixture of waste activated sludge and primary sludge, achieving a stable total chemical oxygen demand reduction efficiency (56.1 ± 6.8 %), and enhanced sludge hydrolytic enzyme activities at a 14.5-day total solids retention time (SRT). High-throughput sequencing data revealed a consistent microbial community across reactors, dominated by consortia that govern hydrolysis and acidogenesis. Despite relatively short SRTs in the initial reactors of the CAD system, acetoclastic methanogens belonging to Methanosaeta became the most abundant archaea. ‬‬‬‬‬‬‬‬‬‬‬‬‬ This study proves that the CAD system achieves stable sludge reduction, accelerates enzymatic hydrolysis at full-scale, and paves the way for its industrialization in municipal waste sewage sludge treatment.

Balancing acidogenesis and methanogenesis metabolism in thermophilic anaerobic digestion of food waste under a high loading rate

Achieving a metabolic balance between volatile fatty acid (VFA) production and conversion is a standing challenge in high temperature and organic loading rate anaerobic digestion. A thermophilic anaerobic digestion reactor fed with food waste was therefore operated for 230 days to investigate metabolic performance in acidogenesis and methanogenesis. Results showed a methane yield of 310 mL/g·COD under an organic loading rate (OLR) of 10.0 kg·COD/(m3·d). The VFA concentration of 110 mg/L was low, indicating well-balanced VFA production and conversion metabolism. Highly specific acetic acid and propionic acid methanogenic activity showed satisfactory metabolic capability. Methanosarcina (95.2%) predominated in the high OLR state and increased abundance of Methanothermobactger (4.2%) was also observed. Syntrophic acetic acid oxidation bacterial was not found in different HRT conditions. It is therefore reasonable to speculate cleavage of acetic acid by mixotrophic Methanosarcina. Good acidogenesis and methanogenesis balance promote stable thermophilic AD of food waste under a high OLR.

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.

High-rate anaerobic digestion of sewage sludge by membrane separation solubilization coupled with UASB process

High-rate anaerobic digestion of sewage sludge by membrane separation solubilization coupled with UASB process

Development of a high-rate anaerobic thermophilic upflow packed bed reactor for efficient bioconversion of diluted three-phase olive mill wastewater into methane

Olive mill wastewater is the main by-product derived from olive mills using the three-phase extraction process, displaying a serious environmental risk due to its notable content in organics and phenolics. This work focused on a high-rate thermophilic anaerobic digester development, able to remove high organic load amounts, by converting it to biogas. The proposed system is an upflow packed bed reactor with recycling stream and biomass carriers appropriate for inoculum colonization. An anaerobic inoculum was acclimatized under thermophilic conditions and subsequently added into the reactor. Its performance examination against twice-centrifuged olive mill wastewater of 40 g COD/L followed, testing several runs of gradually decreased hydraulic retention time, reaching steady-state conditions until the minimum of 4.2 days, while optimum performance was achieved at 5.6 days. The production of 9.51 ± 0.37 NLCH4/LFeed is considered quite promising for the high-rate anaerobic treatment plants development for olive mill wastewater valorization, without the need of co-digestion.

Stable, high-rate anaerobic digestion through vacuum stripping of digestate

This study coupled anaerobic digestion with vacuum stripping to achieve stable digestion at higher organic loading rates. Besides mitigation of ammonia inhibition, vacuum stripping of digestate improves solids solubilization and dewaterability due to vacuum-enhanced low-temperature thermal and mild-alkaline treatment under the vacuum stripping conditions (65 °C, 25–27 kPa, and pH 9). Batch vacuum stripping for 8 h removed 97.4–99.4% of ammonia, increased the dissolved fraction of volatile solids (VS) by 72.5%, and improved dewaterability with 30% decreases in time-to-filter and viscosity. The digesters having 2.9% of digestate replaced daily by vacuum stripped digestate were stable up to organic loading rate of 4.3 g-VS/Lreactor/d with biogas production at 3.15 L/Lreactor/d, while the digesters without stripping attained biogas production of 1.90 L/Lreactor/d at its highest stable organic loading rate of 2.5 g-VS/Lreactor/d. Acetoclastic Methanosaeta were the dominant methanogens, which became more resistant to ammonia stress in the digesters with vacuum stripping.

First proof of concept for full-scale, direct, low-temperature anaerobic treatment of municipal wastewater

Municipal wastewater constitutes the largest fraction of wastewater, and yet treatment processes are largely removal-based. High-rate anaerobic digestion (AD) has revolutionised the sustainability of industrial wastewater treatment and could additionally provide an alternative for municipal wastewater. While AD of dilute municipal wastewater is common in tropical regions, the low temperatures of temperate climates has resulted in slow uptake. Here, we demonstrate for the first time, direct, high-rate, low-temperature AD of low-strength municipal wastewater at full-scale. An 88 m3 hybrid reactor was installed at the municipal wastewater treatment plant in Builth Wells, UK and operated for 290 days. Ambient temperatures ranged from 2 to 18 °C, but remained below 15 °C for > 100 days. Influent BOD fluctuated between 2 and 200 mg L-1. However, BOD removal often reached > 85%. 16S rRNA amplicon sequencing of DNA from the biomass revealed a highly adaptable core microbiome. These findings could provide the basis for the next-generation of municipal wastewater treatment.

High-rate blackwater anaerobic digestion under septic tank conditions with the amendment of biosolids-derived biochar synthesized at different temperatures

Septic tanks have been widely used for blackwater treatment in developing countries, while high-rate septic tanks with improved methane recovery are yet to be achieved. This study investigated biosolids-derived biochar (synthesized at 300℃, 425℃, and 550℃) as an additive for developing high-rate septic tanks. The experiments were conducted with anaerobic bioreactors operated with synthetic blackwater under septic tank conditions. All biochar amended reactors demonstrated a steady increase in daily methane production for increasing OLR from 0.08 to 3 g COD/L/d. The control reactor showed significant process disturbances at OLRs ≥ 2 g COD/L/d with an accumulation of volatile fatty acids followed by pH drop. At OLR of 3 g COD/L/d, the daily methane production from biochar amended reactors was ~ 4.3 times higher than the control (300 vs. 70 mL per day). Biochar addition established a robust microbiome consisted of a higher abundance of hydrogenotrophic and acetoclastic methanogens and hydrogen-producing fermentative bacteria.

Microbial Community Redundancy and Resilience Underpins High-Rate Anaerobic Treatment of Dairy-Processing Wastewater at Ambient Temperatures.

High-rate anaerobic digestion (AD) is a reliable, efficient process to treat wastewaters and is often operated at temperatures exceeding 30°C, involving energy consumption of biogas in temperate regions, where wastewaters are often discharged at variable temperatures generally below 20°C. High-rate ambient temperature AD, without temperature control, is an economically attractive alternative that has been proven to be feasible at laboratory-scale. In this study, an ambient temperature pilot scale anaerobic reactor (2 m3) was employed to treat real dairy wastewater in situ at a milk processing plant, at organic loading rates of 1.3 ± 0.6 to 10.6 ± 3.7 kg COD/m3/day and hydraulic retention times (HRT) ranging from 36 to 6 h. Consistent high levels of COD removal efficiencies, ranging from 50 to 70% for total COD removal and 70 to 84% for soluble COD removal, were achieved during the trial. Within the reactor biomass, stable active archaeal populations were observed, consisting mainly of Methanothrix (previously Methanosaeta) species, which represented up to 47% of the relative abundant active species in the reactor. The decrease in HRT, combined with increases in the loading rate had a clear effect on shaping the structure and composition of the bacterial fraction of the microbial community, however, without affecting reactor performance. On the other hand, perturbances in influent pH had a strong impact, especially when pH went higher than 8.5, inducing shifts in the microbial community composition and, in some cases, affecting negatively the performance of the reactor in terms of COD removal and biogas methane content. For example, the main pH shock led to a drop in the methane content to 15%, COD removals decreased to 0%, while the archaeal population decreased to ~11% both at DNA and cDNA levels. Functional redundancy in the microbial community underpinned stable reactor performance and rapid reactor recovery after perturbations.

High-Rate Anaerobic Digestion of Waste Activated Sludge by Integration of Electro-Fenton Process.

Anaerobic digestion (AD), being the most effective treatment method of waste activated sludge (WAS), allows for safe disposal. The present study deals with the electro-Fenton (EF) pretreatment for enhancing the WAS biogas potential with low-cost iron electrodes. The effect of pretreatment on the physicochemical characteristics of sludge was assessed. Following EF pretreatment, the pH, conductivity, soluble chemical oxygen demand (SCOD), and volatile fatty acids (VFA) increased to 7.5, 13.72 mS/cm, 4.1 g/L, and 925 mg/L, respectively. Capillary suction time (CST) analysis highlighted the dewaterability effect of EF on WAS, as demonstrated by the decrease in CST from 429 to 180 s following 30 min of pretreatment. Batch digestion assays presented an increase in the biogas yield to 0.135 L/g volatile solids (VS) after 60 min of EF pretreatment in comparison to raw sludge (0.08 L/g VS). Production of biogas was also found to improve during semi-continuous fermentation of EF-pretreated sludge conducted in a lab-scale reactor. In comparison to raw sludge, EF-pretreated sludge produced the highest biogas yield (0.81 L biogas/g VS) with a high COD removal rate, reaching 96.6% at an organic loading rate (OLR) of 2.5 g VS/L. d. Results revealed that the EF process could be an effective WAS disintegration method with maximum recovery of bioenergy during AD.

Improved Mixing System for Anaerobic Sequencing Batch Reactors

HighlightsA novel single-jet mixing system was designed for ASBR digesters.Mixing energy was reduced to the point that solids were only partially suspended in the reactor vessel.The partial mixing system increased effluent quality as measured by suspended solids content.The partial mixing system increased solids retention, allowing hydraulic retention time (HRT) to be reduced to at least 7.5 days while maintaining solids retention time (SRT) above 100 days.The partial mixing system did not reduce biogas production rate nor biogas yield.Abstract. An anaerobic sequencing batch reactor (ASBR) is a high-rate anaerobic digestion system ideally suited for the treatment of liquids with high organic strength and low solids content. Biota are retained in an ASBR by settling solids prior to decanting effluent from the top of the reactor. Solids retention time (SRT) can be managed separately from hydraulic retention time (HRT) in an ASBR. One problem encountered with ASBRs is poor solids retention due to inefficient solids settling. A novel mixing system in which solids are only partially mixed in the reactor prior to decanting was investigated in a series of three experiments. A battery of six 30 L ASBR reactors were fed a mixture of dilute swine manure (0.30% TS, 0.20% VS) and raw glycerol. In a side-by-side comparison of two reactors operated at an organic loading rate (OLR) of 0.30 g COD L-1 d-1 with 15-day HRT and two feeding cycles per day, the partially mixed reactor outperformed the fully mixed reactor as measured by effluent quality (130 vs. 350 mg VSS L-1), SRT (354 vs. 52 days), and VS removal efficiency (88% vs. 79%). In a replicated study of five reactors operated at 0.31 g COD L-1 d-1 OLR, 15-day HRT, and two feeding cycles per day before and after switching from full to partial mixing, the partially mixed reactors showed significantly (p = 0.05) better performance as measured by effluent quality (100 vs. 382 mg VSS L-1), SRT (760 vs. 72 days), and VS removal efficiency (85% vs. 71%). Biogas production did not significantly change with the change from full to partial mixing in the five replicated reactors, i.e., average biogas yield was 0.81 and 0.77 L biogas g-1 COD with partial and full mixing, respectively. Effluent quality, SRT, VS removal efficiency, and biogas yield did not significantly change when the OLR was increased from 0.31 to 0.62 g COD L-1 d-1 and HRT was reduced from 15 to 7.5 days in a replicated study of six partially mixed reactors. A mass balance of COD across the six partially mixed reactors showed that endogenous respiration of retained biomass accounted for approximately 50% of the biogas produced by an ASBR with SRT exceeding 400 days. Keywords: Anaerobic digestion, Anaerobic sequencing batch reactor, ASBR, Biogas, Glycerol, Hydraulic retention time, Mixing, Operation, Performance, Solids retention time, Swine manure.

High rate anaerobic digestion of swine wastewater in an anaerobic membrane bioreactor

Efficient treatment of swine wastewater at a high rate would facilitate the development of a sustainable pig industry. In this study, to investigate methane fermentation and membrane filtration performance, an anaerobic membrane bioreactor was operated under mesophilic conditions for 207 days during four stages, with a hydraulic retention time (HRT) decreasing from 5 to 3, 2, and 1 day, and a changing of solid retention time/hydraulic retention time (SRT/HRT) ratio from 18,18 to 8 and 3.2. The results showed that a higher volumetric methane production of 1.63 L/(L·d) and a lower VFAs concentration (<200 mg/L at stable stage) could achieved when the HRT was 1 day and SRT/HRT ratio was only 3.2. The specific methanogenic activity slightly decreased under the shorter HRT, and with SRT/HRT shortening, hydrogenotrophic Methanocorpusculum tended to dominate in bulk sludge while acetoclastic Methanosaeta dominated in the biofilm. Membrane fouling was observed after 4 months with a flux decline and a significant increase in trans-membrane pressure. A serial cleaning test indicated that organic pollutants contributed highly to the membrane fouling.

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.

Simulation of two-dimensional attainable regions and its application to model digester structures for maximum stability of anaerobic treatment process

Unlike high-rate anaerobic digesters that employ some mechanism to retain microbial sludge mass, low-rate systems use sufficiently long hydraulic retention times to ensure process stability, which becomes economically unattractive for treating large quantities of waste. This study presents the use of attainable region to develop a new strategy to enhance the stability of low-rate digesters. By considering three digestion cases, diary manure only (batch 1) or diary manure with granular (batch 2) or lagoon (batch) sludge as innoculum, the following findings were obtained. (1) For a given concentration of volatile acids in an anaerobic digester, higher concentrations of methanogenic archae can be attained using a digester structure (combination of different digesters) as opposed to single digester. (2) For a given digested substrate, a change in the source of inoculum results in a change in the limits of achievability by the system (attainable limits for batches 1, 2 and 3 were 46.486(g/L)2, 5.562(g/L)2 and 0.551(g/L)2, which resulted in performance improvements of 118.604%,175.627% and 200.436% respectively), and hence optimal digester structure. The evidence from this study suggests that the technique can be used to simultaneously improve process stability, define performance targets and propose digester structures required to achieve a given target.

Influence of Pre-Hydrolysis on Sewage Treatment in an Up-Flow Anaerobic Sludge BLANKET (UASB) Reactor: A Review

The up-flow anaerobic sludge blanket (UASB) process has emerged as a promising high-rate anaerobic digestion technology for the treatment of low- to high-strength soluble and complex wastewaters. Sewage, a complex wastewater, contains 30–70% particulate chemical oxygen demand (CODP). These particulate organics degrade at a slower rate than the soluble organics found in sewage. Accumulation of non-degraded suspended solids can lead to a reduction of active biomass in the reactor and hence a deterioration in its performance in terms of acid accumulation and poor biogas production. Hydrolysis of the CODP in sewage prior to UASB reactor will ensure an increased organic loading rate and better UASB performance. While single-stage UASB reactors have been studied extensively, the two-phase full-scale treatment approach (i.e., a hydrolysis unit followed by an UASB reactor) has still not yet been commercialized worldwide. The concept of treating sewage containing particulate organics via a two-phase approach involves first hydrolyzing and acidifying the volatile suspended solids without losing carbon (as methane) in the first reactor and then treating the soluble sewage in the UASB reactor. This work reviews the available literature to outline critical findings related to the treatment of sewage with and without hydrolysis before the UASB reactor.

Biogas production from the liquid waste of distilled gin production: Optimization of UASB reactor performance with increasing organic loading rate for co-digestion with swine wastewater

This study is the first test that proves high rate anaerobic digestion as an efficient technological process for the treatment of gin spent wash. The gin spent wash was co-digested in UASB reactors with swine wastewater, which provided nutrients and alkalinity. The process was optimized by increasing the proportion of gin spent wash in the feed, and thus the organic loading rate (OLR) up to reactor failure. Stable high- efficiency operation was reached at an OLR as high as 28.5 kg COD m−3 d−1, yielding 8.4 m3 CH4 m−3 d−1 and attaining a COD removal of 97.0%. At an organic loading rate of 32.0 kg COD m−3 d−1, the process became unstable and the reactor underwent over-acidification that drastically lowered the pH and suppressed methanogenesis. The failure of the reactor was caused by a combination of an organic overloading and alkalinity deficit that uncoupled acidogenesis and methanogenesis.

Operational strategy of high rate anaerobic digester with mixed organic wastes: effect of co-digestion on biogas yield at full scale

ABSTRACTThe present research work is aimed at providing an economically feasible solution for the farmers to exploit the mixed organic wastes (MOW) as resources for the generation of biogas based electrical power and utilize the same for irrigation purpose to reduce the dependence on electricity board. A full scale biomethanation plant has been installed based on anaerobic gas lift reactor (AGR) technology to analyse, understand the operational parameters of anaerobic digestion and assess the performance of a high rate biomethanation plant by co-digesting the MOW such as poultry litter (PL), cattle manure (CM) and napier grass (NG) at ambient temperature. The biomethanation plant was incorporated with inline pre and post-processing unit assembly. The plant was fed with 1000 kg of MOW per day having 250 kg of total solids, about 178–200 kg of volatile solids and operated continuously for 52 weeks under ambient temperature. Electrical power generated (84.5–104 kWh/day) from biogas (65–80 m3/day) containing methane (40–48 m3/day) was used for operating the water pumps for agricultural purpose and the digestate (115–130 kg/day) was exploited as organic manure for growing crops in the same field. Napier grass was grown in the same land and other feedstocks were procured from the nearby area at the cost of $10–$15 per ton. Around 6 acres of land was being cultivated using the biogas based power generated from the MOW that was being used for growing vegetables and maize.

Resolving stability issue of thermophilic high-rate anaerobic palm oil mill effluent treatment via adaptive neuro-fuzzy inference system predictive model

Abstract Palm oil mill effluent is a highly polluting and corrosive liquid waste generated from crude palm oil processing. Its varying characteristics depending on the crop season and loading rate of the milling process complicate the handling of anaerobic digestion of palm oil mill effluent. To ease monitoring and aid decision making to handle operation anomalies, this study adopts Adaptive Neuro-Fuzzy Inference System with hybrid learning algorithm and subtractive clustering to predict the output from a thermophilic high-rate anaerobic digester treating palm oil mill effluent. Influent pH, chemical oxygen demand, organic loading rate and historical data of effluent pH, chemical oxygen demand and total suspended solids were utilized to build the model for output prediction of treated effluent (pH, chemical oxygen demand and total suspended solids). Trained models were validated with experimental data. The models were able to predict the effluent pH, chemical oxygen demand and total suspended solids satisfactorily with average error of less than 8.32% and standard deviation of less than 7.65% with closely followed pattern between the actual values and simulated results. The viability of adaptive neuro-fuzzy inference system in modelling palm oil mill effluent using thermophilic high-rate anaerobic digester is further demonstrated by coefficient of determination, R2 of 0.82, Root Mean Square Error of 0.0377, Index of Agreement of 0.95 and d-factor of 0.0496.