Organic Overloading Research Articles

Solving the seasonality issue in sugarcane biorefineries: High-rate year-round methane production from fermented sulfate-free vinasse and molasses

Anaerobic digestion (AD) has been recently highlighted as the most efficient approach to manage vinasse in sugarcane biorefineries, providing both a renewable energy source (biogas) and a mineralized and nutrient-rich effluent suitable for agricultural use. However, the high sulfate concentrations (ca. 2 g L−1) present in vinasse and its seasonal availability (7–8 months) hinder the maximization of methane production in AD plants. This study investigated the use of sulfate-free vinasse (season) and molasses (off season), both pre-fermented in fermentative-sulfidogenic systems, as substrates to obtain enhanced year-round methane production in sugarcane biorefineries. Two second stage methanogenic structured-bed reactors operated at different temperatures (30 °C and 55 °C) were subjected to increasing organic loading rate (OLR) levels (1.0–20.0 kg COD m−3 d−1) in an experimental simulation of sequential periods of season, off season and season. An efficient start-up strategy enabled achieving operating stability in the full load project (10.0 kg COD m−3 d−1) in 37 d, which means anticipating the maximization of bioenergy production. Pre-fermenting vinasse and molasses was imperative for maintaining efficient organic matter conversion (80–90 %) into methane, regardless of the significant differences in lactate and phenols availability. A methane content in biogas ≥ 80 % and methane yield ≥ 330 NmL CH4 g−1COD were observed in both reactors, with no apparent observation of organic overloads. The results point towards a highly efficient strategy to maintain year-round high-rate biogas production from sugarcane vinasse, although the relatively high molasses demands can trigger an internal competition (with ethanol production) for substrate.

Kinetic modeling of anaerobic co-digestion with glycerol: Implications for process stability and organic overloads

The energy crisis, depletion of fossil fuels, and global waste issue highlight the need for sustainable and eco-friendly energy processes. In this study, the anaerobic co-digestion of sewage sludge (DS), milk sludge (MS), and food waste (FW) with glycerol (GL) from biodiesel production was investigated. Binary co-digestion of MS-GL, DS-GL, and FW-GL, as well as ternary co-digestion of MS-FW-GL and DS-FW-GL, were examined to determine the optimal combinations for biogas production and process stability. Adding 5% GL (v/v) increased methane yields by 88.78%, 405.82%, and 40.03% for binary mixtures and 55.57% and 298.53% for ternary mixtures, respectively. In addition, the ternary mixtures resulted in the accumulation of volatile fatty acids at 2136.96 mg/L and 1843.62 mg/L, respectively, causing a reduction in methane yield compared to that in binary mixtures. GL added to binary and ternary mixtures delayed optimal methanogenic activities, with higher hydrolysis rates and shorter lag times observed in single substrate-contained and binary mixture reactors. Ternary mixtures showed lower hydrolysis rates and longer lag times, indicating that methanogens required more time to adjust to the increased organic content. Co-digestion procedures using different substrate ratios should consider the risk of organic overloads, which can lead to system instability or failure.

Compact fluidic electrochemical sensor platform for on-line monitoring of chemical oxygen demand in urban wastewater

• Carbon-silica (C/SiO 2 ) thin films produced by sol–gel chemistry. • C/SiO 2 electrode fabrication at wafer-scale by photolithography / etching process. • Excellent electrochemical performance shown by the fabricated electrodes. • Electrochemical sensor integrated in a modular fluidic system for in-field use. • Cu NPs-modified C/SiO 2 sensor used for on-line analysis of COD in urban wastewater. The rapid expansion of urban areas has given rise to the generation of large amounts of wastewater that pose a growing pressure on the surrounding ecosystems. Effective water quality surveillance programs demand the implementation of in-field tests to monitor water safe discharge in the environment after being adequately treated. This paper describes the manufacturing and application of a miniaturized electrochemical sensor for measuring dissolved chemical oxygen demand (COD) in surface waters entering and exiting urban wastewater treatment plants (UWWTP). Thin-film carbon electrodes are produced on Si/SiO 2 substrates by a combined sol–gel material synthesis and photolithography/dry etching process at the wafer level and show superior electrochemical performance compared with the glassy carbon standard electrode. Three-electrode electrochemical cells of planar configuration are produced and the COD sensor is manufactured by electrodepositing copper nanoparticles (Cu NPs) on the working electrode under controlled potentiostatic conditions. A simple fluidic electrochemical sensor device is fabricated and allows for the Cu NPs electrodeposition as well as analytical sensor performance in an automatic fashion. A linear range up to 670 mg·L -1 O 2 and a limit of detection of 30 mg·L -1 O 2 are achieved. The ability of this electrochemical sensor approach to monitoring the soluble organic load of urban wastewater in real-time is evaluated by analyzing three samples collected in different locations of an UWWTP. The COD values estimated with the sensor are in excellent agreement with those obtained using the standard dichromate method provided by an accredited laboratory. This analytical platform provides a robust, user-friendly low-maintenance flow sensor approach for deployed analysis of COD that could aid to control the effectiveness of water treatment processes, especially when facing water influents containing organic overloads due to changing weather conditions or any anthropogenic phenomena.

Key players in syntrophic propionate oxidation revealed by metagenome-assembled genomes from anaerobic digesters bioaugmented with propionic acid enriched microbial consortia.

Propionic acid (HPr) is frequently accumulated in anaerobic digesters due to its thermodynamically unfavorable degradation reaction. Here, we identify key players in HPr oxidation and organic overloading recovery from metagenome-assembled genomes (MAGs) recovered from anaerobic digesters inoculated with HPr-enriched microbial consortia before initiating organic overloading. Two independent HPr-enrichment cultures commonly selected two uncultured microorganisms represented with high relative abundance: Methanoculleus sp002497965 and JABUEY01 sp013314815 (a member of the Syntrophobacteraceae family). The relative abundance of JABUEY01 sp013314815 was 60 times higher in bioaugmented bioreactors compared to their unaugmented counterparts after recovery from organic overloading. Genomic analysis of JABUEY01 sp013314815 revealed its metabolic potential for syntrophic propionate degradation when partnered with hydrogenotrophic methanogens (e.g., Methanoculleus sp002497965) via the methylmalonyl-CoA pathway. Our results identified at least two key species that are responsible for efficient propionate removal and demonstrate their potential applications as microbial cocktails for stable AD operation.

Analysis of the anaerobic digestion metagenome under environmental stresses stimulating prophage induction

BackgroundThe viral community has the potential to influence the structure of the microbiome and thus the yield of the anaerobic digestion process. However, the virome composition in anaerobic digestion is still under-investigated. A viral induction experiment was conducted on separate batches undergoing a series of DNA-damaging stresses, in order to coerce temperate viruses to enter the lytic cycle.ResultsThe sequencing of the metagenome revealed a viral community almost entirely composed of tailed bacteriophages of the order Caudovirales. Following a binning procedure 1,092 viral and 120 prokaryotic genomes were reconstructed, 64 of which included an integrated prophage in their sequence.Clustering of coverage profiles revealed the presence of species, both viral and microbial, sharing similar reactions to shocks. A group of viral genomes, which increase under organic overload and decrease under basic pH, uniquely encode the yopX gene, which is involved in the induction of temperate prophages. Moreover, the in-silico functional analysis revealed an enrichment of sialidases in viral genomes. These genes are associated with tail proteins and, as such, are hypothesised to be involved in the interaction with the host. Archaea registered the most pronounced changes in relation to shocks and featured behaviours not shared with other species. Subsequently, data from 123 different samples of the global anaerobic digestion database was used to determine coverage profiles of host and viral genomes on a broader scale.ConclusionsViruses are key components in anaerobic digestion environments, shaping the microbial guilds which drive the methanogenesis process. In turn, environmental conditions are pivotal in shaping the viral community and the rate of induction of temperate viruses. This study provides an initial insight into the complexity of the anaerobic digestion virome and its relation with the microbial community and the diverse environmental parameters.5iPig9MR3ASALE62Tsjw9nVideo

Shock loads change the resistance, resiliency, and productivity of anaerobic co-digestion of municipal sludge and fats, oils, and greases

Accidental organic overloading (shock loading) is a common cause of failure in the anaerobic co-digestion of fats, oils, and greases (FOG). Nonetheless, questions still remain about how shock loads alter an anaerobic digester's biogas productivity and response to future organic overloads. To address this knowledge gap, this study utilized short increases in OLR, or shock loads, to adapt one reactor to FOG co-digestion and compare its response to that of a non-adapted digester tested at similar organic loads. A long-term study was also conducted where sequential shock events and disturbance-to-failure events (with organic loading rates ranging from 2.5 to 9.0 g VS/L/d) were employed to study their effects on reactor stability and performance. When exposed to moderate and large shock loads (3.0 and 9.0 g VS/L/d, respectively), the anaerobic digester previously exposed to FOG shock loads had greater levels of resistance and resiliency. For a moderate shock, it took the non-adapted reactor 29.8, 43, 44, and 19 days longer than the adapted reactor to recover to the baseline levels for methane content, organic acids (OA), pH, and mcrA concentrations, respectively. For a large shock, the adapted and non-adapted reactors saw more similar recovery times with the non-adapted reactor requiring an additional 11, 18, 19, and 0 days longer than the adapted reactor to recover to baseline levels for methane content, OA, pH, and mcrA concentrations, respectively. However, exposure to successive large shock loads decreased the anaerobic digester's resistance and resilience. The length of time it took for the organic acid accumulation and methane content values to return to their pre-shock values generally increased with each successive large shock load. For OA, the reactor required 35, 39, and 43 days to recover from the first, second, and third large shocks, respectively, while the methane content recovery times were 27.5, 26.5, and 34.5 days for the same shock periods. Thus, this work demonstrates that there is a tipping point in which FOG shock loads, whether intentional or accidental, go from improving the overall robustness of an anaerobic digester to significantly deteriorating its overall performance.

Production of volatile fatty acids (VFAs) from five commercial bioplastics via acidogenic fermentation

The feasibility of producing volatile fatty acids (VFAs) from five commercial bioplastics via acidogenic fermentation by a non-pretreated anaerobic sludge was investigated. Mesophilic, anaerobic, acidogenic batch assays at 1, 10 and 20 g/L feed concentrations revealed the feasibility of producing VFAs from polyhydroxyalkanoates (PHA), i.e., PHB and PHBV, but not from PBS, PCL and PLA under the test conditions and time. However, only high PHA substrate concentrations (10–20 g/L) resulted in organic overloading and decreasing the pH of the culture broth down to 4–5, which in turn induced the accumulation of VFAs via kinetic imbalance between acidogenesis and methanogenesis. Gaseous carbon (C-CO2 and C-CH4) accounted for 8–35% of the total initial carbon, while C-VFAs represented 10–18%, mainly as acetate and butyrate. This study represents the first systematically assessed proof-of-concept to produce VFAs from PHA, which is key for the design of bioplastic-to-bioplastic recycling (bio)technologies.

Unraveling PHA production from urban organic waste with purple phototrophic bacteria via organic overload

The production of polyhydroxyalkanoates (PHA) with purple phototrophic bacteria (PPB) has been limited due to low yields and limited knowledge regarding the diverse routes used for carbon biosynthesis. The present study increases PHA accumulation yields using urban organic waste pretreated by steam explosion and acidogenic fermentation as substrate. Throughout the PPB-based photoheterotrophic process in an anaerobic membrane photobioreactor, the organic loading rate (OLR) was modified to increase the amount of PHA and biomass in the reactor. A maximum PHA accumulation of 42% (gPHA gBiomass−1) on a dry basis was achieved and maintained for 10 d for an OLR of 1 gCOD L−1 d−1, and hydraulic and sludge retention times of 2 and 6 d, respectively. This PHA accumulation capacity is the maximum obtained using a mixed culture of PPB fed with waste. Also, a medium-chain PHA (polyhydroxyhexanoate) has been quantified, enhancing the physicochemical properties and diversifying their industrial applications. Furthermore, we show novel alternatives to PHA accumulation: carbon storage as glycogen and extracellular polymers while deriving the excess electrons into hydrogen. Finally, a statistical study of microbial communities has settled the environmental variables with the most significant influence on these communities' variability. This work demonstrates the importance of acquiring a thorough understanding of carbon accumulation and electron allocation strategies of PPB under stressful conditions and shows promising results for a larger scale implementation of a PPB-based photobiorefinery, which could valorize urban organic waste to produce different high added-value products within the context of the circular bioeconomy.

Anaerobic digester microbiome dynamics in response to moderate and failure-inducing shock loads of fats, oils and greases

Accidental organic overloading (shock loading) is common during the anaerobic co-digestion of fats, oils and greases (FOG) and may lead to decreased performance or reactor failure due to the effects on the microbiome. Here, adapted and non-adapted lab-scale anaerobic digesters were exposed to FOG shocks of varying organic strengths. The microbiome was sequenced during the recovery periods employed between each shock event. Non-failure-inducing shocks resulted in enrichment of fermentative bacteria, and acetoclastic and methylotrophic methanogens. However, sub-dominant bacterial populations were largely responsible for increased biogas production observed after adaptation. Following failure events, early recovery communities were dominated by Pseudomonas and Methanosaeta while late recovery communities shifted toward sub-dominant bacterial taxa and Methanosarcina. Generally, the recovered microbiome structure diverged from that of both the initial and optimized microbiomes. Thus, while non-failure-inducing FOG shocks can be beneficial, the adaptations gained are lost after a failure event and adaptation must begin again.

Thermodynamics of volatile fatty acid degradation during anaerobic digestion under organic overload stress: The potential to better identify process stability

Anaerobic digestion (AD) operating under organic overload stress usually increases the potential for process instability, leading to significant economic and ecological consequences. Volatile fatty acids (VFAs) accumulation is regularly considered a major factor during AD and their degradation is subject to thermodynamic constraints. To date, no study has systematically investigated the mechanisms of VFA degradation on process stability from the perspective of thermodynamics. Hence, increased substrate-to-inoculum ratio was applied in this study to simulate organic overload stress using batch tests with Hybrid Pennisetum. As a result, VFAs accumulation increased, accompanied by decreased methane yield, slower methane production kinetics and even severe process instability. Metagenomic analysis demonstrated that the accumulated propionate and butyrate were degraded by methyl-malonyl-CoA and the β-oxidation pathway while syntrophic acetate oxidation was preferred during acetate degradation. The deviation of stability parameters to varying degrees from the recommended threshold values was observed. However, a subsequent thermodynamic analysis revealed that moderate organic overload stress merely retarded the syntrophic oxidation of propionate, butyrate, and acetate. As a result, the methanogenic activity decreased, and the lag phase of AD was extended, but no adverse thermodynamic effects actually occurred. Changes in the Gibbs free energy for syntrophic propionate and acetate oxidation have the potential to better identify process stability. This study provided novel insights into the underlying thermodynamic mechanisms of VFA degradation and may have important implications for improving the current diagnostic mode for AD process stability.

Application of biochar and alkalis for recovery of sour anaerobic digesters

Commercial digesters handling complex waste and organic overloading often encounter unbalanced conditions or failures. With limited studies on the digester recovery from an industry-based waste stream, a complex and high-strength digestate containing up to 79 g COD l−1 from acidified commercial digester was investigated for biochar and alkaline treatments. The addition of biochar and calcium hydroxide successfully decomposed excessive volatile fatty acid up to 18.9 ± 2.5 g l−1 and resumed methane production. The maximum methane yield was obtained from the digester amended with biochar (373.4 ± 6.0 ml g COD−1), followed by calcium hydroxide (350.1 ± 2.5 ml g COD−1). Calcium hydroxide treatment showed a shorter lag phase than the biochar by 44%. Methane production could not be recovered by using sodium hydroxide or untreated digester. This study provides a strategic approach to justify the use of alkalis for restoring sour digesters from industry-based waste streams.

Alternative Carbon and Electron Allocation Hold the Key to Pha Production from Ofmsw Fermentation Eluents with Ppbs Via Organic Overloading

Alternative Carbon and Electron Allocation Hold the Key to Pha Production from Ofmsw Fermentation Eluents with Ppbs Via Organic Overloading

Co-digestion of wastewater treatment sewage sludge with various biowastes: A comparative study for the enhancement of biogas production

The objective of the present study is to improve the anaerobic digestion of sewage sludge viaco-digestionwith biowastes. In the study, anaerobic co-digestion of sewage sludge and six organic waste materials as possible co-substrates for enhancement of bio-methane potential were carried out. Furthermore, the possible impact of the co-digestion on digested sludge content in terms of volatile solids (VS), Chemical oxygen demand (COD), and total solids (TS) were examined. Firstly, physicochemical characterization of sewage sludge as the anaerobic digestion feedstock was carried out before anaerobic digestion to obtain their composition. Characterizations such as proximate and ultimate analysis were carried out using a Hach spectrophotometer, a laboratory oven, and a furnace. The characterization feedstock results showed that the sludge contains a reasonable amount of COD, organic matter, TS, and VS along with the inhibitory compounds which shows potential for a high yield of methane in biogas production, as long as the stability of anaerobic digestion is maintained throughout the process. The results show that the sewage sludge has great methane potential during biogas production quantified as 28.6 g CH4/kg feed. When compared to sewage sludge mono digestion, biomethane yield was increased by 3–6 times when thick co-substrates were used. Although high solid content co-substrates generated significantly more methane gas, they also increased the risk of organic overloading. Co-substrates such as molasses, food waste, animal manure, and fresh produce waste performed well at 25% co-digestion ratios. Furthermore, all other solid co-substrates co-digestion resulted in increased VS and COD residuals in digested sludge, withexception of manure. Most of the liquid co-substrates studied here, on the other hand, had a significant synergistic effect, enhancing the removal of TS, VS, and COD during anaerobic digestion.

Anaerobic digestion of vinasse in fluidized bed reactors: Process robustness between two-stage thermophilic-thermophilic and thermophilic-mesophilic systems

Two-stage anaerobic digestion (AD) is a solution for the biodegradation of complex wastes, but the best association of temperatures between acidogenesis and methanogenesis is unclear. Our study investigated whether it is best to associate a thermophilic acidogenic reactor with a thermophilic or a mesophilic methanogenic reactor and results were compared to single-stage AD. The effect of increasing the organic loading rate (OLR from 2.7 to 24.7 kg COD/m3/d) in thermophilic and mesophilic second-stage methanogenesis of two-stage AD was also assessed. A thermophilic acidogenic reactor (R2-H2-Thermo) treating sugarcane stillage fed thermophilic (R2-CH4-Thermo) and mesophilic (R2-CH4-Meso) methanogenic reactors. A single-stage methanogenic thermophilic reactor was used as control (R1-CH4-Thermo). Reactors R2-CH4-Thermo and R2-CH4-Meso showed similar performance at OLR of 2.7–13.3 kg COD/m3/d, but the latter achieved the highest methane production rate at 24.7 kg COD/m3/d (3.2 L CH4/d/L – 78% higher than R2-CH4-Thermo). The two-stage system (R2-H2-Thermo + R2-CH4-Meso) achieved the best energetic yield: 5.5 kJ/g COD, which was 41% higher than the single-stage system. Operation of a second-stage reactor at mesophilic temperature is the most suitable for vinasse AD due to its flexibility, robustness, and stability of CH4 production, even in situations of organic overload and accumulation of toxic components. Digestate at ambient temperature is also more adequate for fertirrigation.

Succession of marine bacteria in response to Ulva prolifera-derived dissolved organic matter

Increasing macroalgal blooms as a consequence of climate warming and coastal eutrophication have profound effects on the marine environment. The outbreaks of Ulva prolifera in the Yellow Sea of China occurring every summer since 2007 to present have formed the world’s largest green tide. The green tide releases huge amounts of dissolved organic matter (DOM) to the seawater, causing an organic overload. However, how marine bacteria respond to this issue and the potential impact on the marine environment are still unclear. Here, we monitored the highly temporally resolved dynamics of marine bacterial community that occur in response to Ulva prolifera-derived DOM by performing a 168-h microcosm incubation experiment. DOM inputs significantly increased bacterial abundances within 6 h, decreased bacterial diversity and triggered clear community successions during the whole period of incubation. Vibrio of Gammaproteobacteria robustly and rapidly grew over short timescales (6–24 h), with its relative abundance accounting for up to 52.5% of active bacteria. From 24 to 48 h, some genera of Flavobacteriia grew rapidly, which was more conspicuous at a higher DOM concentration than at a lower concentration. The genus Donghicola of Alphaproteobacteria was predominant at later time points (>48 h). This bacterial community succession was accompanied by significant variations in the activity of 12 different extracellular enzymes, resulting in a rapid reduction of dissolved organic carbon by 74.5% within the first 36 h. In summary, our study demonstrates rapid successions of bacterial community and extracellular enzyme activity after DOM inputs, suggesting that the bacterial response to Ulva prolifera-derived organic matter may contribute to environmental restoration and may pose a health threat due to the bloom of potential pathogenic Vibrio.

Thermophilic biodigestion of fermented sugarcane molasses in high-rate structured-bed reactors: Alkalinization strategies define the operating limits

Energetic exploitation of sugarcane-derived byproducts via anaerobic digestion (AD) has recently been highlighted as an alternative to the conventional ethanol-producing approach. In this context, the thermophilic (55 °C) methane production from fermented molasses was assessed in the long-term (>200 d) continuous operation of two anaerobic structured-bed reactors. Two types of alkalinization strategies, namely, NaHCO3 dosing (RM1) and NaOH dosing coupled to effluent recirculation (RM2) were compared, as well as different levels of organic loading rate (OLR) and hydraulic retention time (HRT) were applied to reach limiting operating conditions. Both alkalinization strategies provided an equivalent buffer control up to an OLR of 7.5 kg-CODt m−3 d−1, from which unwanted accumulation of organic acids was observed in RM2. NaHCO3 dosing enabled doubling the OLR (15.0 kg-CODt m−3 d−1) without performance deterioration, i.e., organic matter removal > 80.0% and maximum methane yield values. A detailed assessment of the food-to-microorganism ratio demonstrated the maintenance of stable operating conditions at excess substrate availability (>3.0 g-CODt g−1VSS d−1) in the feeding chamber (FDC) of the reactors, in which substrate conversion exceeded 70.0%. Organic overloads occurred only when biomass retention reached a saturation level in the FDC, hampering the uptake of volatile organic acids, regardless of the operating condition. In any case, the wide range of operating conditions (OLR = 2.5–15.0 kg-CODt m−3 d−1 and HRT = 24.0–36.0 h) associated with maximized methane production characterized a highly flexible process, which enables varied design arrangements in full-scale AD plants.

Evaluation of the performance of covered lagoon digester in terms of the solids loading

The use of anaerobic digesters to convert residual biomass for energy use and nutrient recovery has been increasingly indicated by the operational simplicity and added value of the treatment by-products. However, the levels of solids present in the influents to be treated directly influence the operation and management of the system. Thus, the objective of the study was to evaluate the performance of covered lagoon digesters in terms of the solids loading in the swine wastewater treatment system. The study was performed in a farm located in Zona da Mata Mineira. The monitoring took place from September 2018 to August 2019. The influent flow of waste was estimated based on the analysis of monthly water consumption on the farm. The collection and sampling took place weekly, the influents and effuents were analyzed in terms of the solids loading of total solids (TS) and volatiles solids (VS). The mean total flow distributed to the two digesters was 102.3 m³.d-1, with a mean hydraulic retention time (HRT) of 24.5 days. The results ranged from 1.14 to 2.83% for TS at the start of treatment. In most of the monitored months, anaerobic digesters were being fed with organic overload in terms of VS, which consequently affected the efficiency of the system, which were 33.6% for TS and 39.5% for VS.

Organic Waste Conversion Via Continuous Anaerobic Co-Digestion of Oil Palm Empty Fruit Bunches and Cow Manure: Evaluation of Feeding Regime on Methane Production

Abstract Anaerobic co-digestion of oil palm empty fruit bunches with cow manure was studied. The research focus was on the evaluation of feeding different solid concentrations of the substrate in the on-going process of anaerobic digestion. The solid concentrations ranged from 0.5 to 12% TS. Results of the study showed that the maximum methane production could be reached with the reactor digesting substrates with 4 to 8% TS, in which the methane produced was from 1300 to 1400 mL per day. A significant drop of pH from 7.02 to 5.97 occurred when the reactor was digesting substrates with 10 and 12% TS. Acidic condition caused by organic matter overloads lowered the efficiency of organic conversion represented in the low removal of COD, which was only 22.4%. This finding is highly significant for the waste management industries in terms of dealing with the digester upset due to the digestion of large amount of organic wastes.

Moving average convergence and divergence indexes based online intelligent expert diagnosis system for anaerobic wastewater treatment process

Anaerobic wastewater treatment process is efficient but unstable due to various disturbances, such as refractory organics and influent organic overloading. Therefore, sensitive and accurate status diagnosis is important for reasonable control to improve the stability of anaerobic process. In this study, an online intelligent expert diagnosis system for anaerobic process was established based on moving average convergence and divergence (MACD) indexes of gas- and liquid-phase parameters, combined with online monitoring system and expert diagnosis database. The effect of this diagnosis system was verified through refractory organics and organic overloading shock experiments. Results showed that this diagnosis system could make rapid, accurate and comprehensive diagnosis, predictions and early-warning. MACD algorithm could enhance pattern recognition capacity of status parameters, overcome the lagging of anaerobic process and filter irregular noisy fluctuations of status parameters. MACD index of H2 partial pressure is suitable as sensitive early-warning indicator in the initial shock stage.

Rapid recovery of methane yield in organic overloaded-failed anaerobic digesters through bioaugmentation with acclimatized microbial consortium

Acidification during anaerobic digestion (AD) due to organic overloading is one of the major reasons for process failures and decreased methane productivity in anaerobic digesters. Process failures can cause the anaerobic digesters to stall completely, prolong the digester recovery period, and inflict an increased operational cost on wastewater treatment plants and adverse impacts on the environment. This study investigated the efficacy of bioaugmentation by using acclimatized microbial consortium (AC) in recovering anaerobic digesters stalled due to acidosis. Overloading of digesters with food waste leachate (FWL) led to the accumulation of volatile fatty acids (11.30 g L−1) and a drop in pH (4.67), which resulted in process failure and a 22-fold decline in cumulative methane production compared to that in the initial phase. In the failure phase, the syntrophic and methanogenic activities of the anaerobic digester microbiota were disrupted by a significant decrease in the abundance of syntrophic populations such as Syntrophomonas, Syntrophorhabdus, Sedimentibacter, and Levilinea, and the phylum Euryarchaeota. Bioaugmentation of the failed digesters by adding AC along with the adjustment of pH resulted in the prompt recovery of methane productivity with a 15.7-fold higher yield than that in unaugmented control. The abundance of syntrophic bacteria Syntrophomonas and phylum Euryarchaeota significantly increased by 29- and 17-fold in the recovered digesters, respectively, which showed significant positive correlations with methane productivity. Methanosarcina and acetoclastic Methanosaeta played a major role in the recovery of the digesters; they were later replaced by hydrogenotrophic Methanoculleus. The increase in the abundance of genes associated with biomethanation contributed to digester recovery, according to the functional annotation of 16S rDNA amplicon data. Thus, bioaugmentation with AC could be a viable solution to recover digesters experiencing process failure due to organic overloading.