High Organic Loading Research Articles

Recent Advances in the Reactor Design for Industrial Wastewater Treatment by Electro-Oxidation Process

Refractory organic wastewater mainly includes wastewater from papermaking, textile, printing and dyeing, petrochemical, coking, pharmaceutical and other industries, as well as landfill leachate and its membrane-treated concentrate. The traditional biochemical method is difficult to adapt to its harsh conditions such as high toxicity, high organic load and high salinity. Compared to other methods, the electro-oxidation (EO) process owns the attractive characteristics of being clean and eco-friendly, highly efficient and producing no secondary pollution. EO systems mainly include electrodes, a reactor, a power supply and other basic units. The design of reactors with different electrodes was the key link in the application of EO technology. This paper mainly reported the different configurations of electrochemical reactors (ECRs) for refractory organic wastewater treatment, and summarized the advantages and disadvantages of them, including reactor structure, flow mode, operation mode and electrode construction. Compared with traditional reactors, the improved reactors such as 3D-ECR achieve higher mass transfer efficiency by increasing the contact area between the electrode and the fluid. Additionally, it has a higher removal rate of organics and a lower energy consumption. Finally, the future perspectives of the treatment of refractory organic wastewater by ECRs is discussed. This paper is expected to provide a reliable scientific basis for the real application of EO technology in refractory organic wastewater treatment.

Artificial aeration of an overloaded constructed wetland improves hypoxia but does not ameliorate high nitrogen loads

High organic loadings to constructed wetlands can result in water quality issues such as low dissolved oxygen and high ammonium concentrations, with artificial aeration a potential mitigation option. This study compared baseline (no aeration – NA), continuous aeration (CA), and intermittent aeration (IA) conditions to improve water quality in a tertiary treatment free water surface constructed wetland (FWS CW) with night time hypoxia/anoxia, and high nutrient concentrations. The response variables included dissolved oxygen (DO), total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), total phosphorus (TP), phosphate (PO43–-P), and dissolved organic carbon (DOC). In situ aeration and monitoring was performed from April to June 2021 in a large, field-scale FWS CW, the Laratinga wetlands Mount Barker, South Australia.The results demonstrated that DO increased by an average 2.11 mg L−1 from NA to CA during the night and 1.26 mg L−1 and 1.84 mg L−1 from NA to IA during the night and day respectively when averaging over the basins. The C/N ratio was very low and there was no significant influence of DO on DOC concentrations. There was no significant difference in TN concentrations with the application of aeration aside from a decrease in the channel at night from NA to IA, and an increase in NH4+-N resulted under IA compared with NA in Basin 1 and 2 during the day. This implies that the N loadings exceeded the wetland's ability to complete nutrient conversions at a rate that aligns with input rate. The concentrations of NO3−-N increased at night under CA and IA treatments suggesting that some nitrification was promoted, or there was inhibition of dissimilatory nitrate reduction to ammonium. The concentrations of TP and PO43–-P significantly increased with the aeration compared with no aeration, however there was no difference between the aeration treatments. This suggested that increased sediment resuspension during aeration increased P in the water. There was no change in DOC with the application of aeration. Overall, the DO increased with aeration application and may be able to better support the wetland ecology; however, the Laratinga wetland is overloaded and the capacity of the wetland to effectively transform and remove nutrients is inhibited, even with the application of artificial aeration.

Complexity of acclimatization substrate affects anaerobic digester microbial community response to organic load shocks

This study elucidated the changes in the short-term response to organic load shocks of the anaerobic digestion (AD) microbiome acclimatized to a simple substrate and a complex substrate. Batch vial reactors were inoculated with AD sludge acclimatized to either a simple (starch and hipolypeptone) or a complex (dog food and starch) substrate, both with carbon-to-nitrogen ratio of 25. Organic loads in the form of an easily degradable substrate mix (starch and hipolypeptone) with concentrations varying from 0 to 5 g VS/L were applied to the reactors. Runs utilizing the inoculum acclimatized to a complex substrate sustained its methane productivity despite the high organic load shocks which the inoculum acclimatized to a simple substrate was unable to handle efficiently. The alpha-diversity of the microbiome decreased with increase in organic load for inoculum acclimatized with a simple substrate but was unaffected for the case of the inoculum acclimatized with a complex substrate. LactobacillalesandCloacimonadales were inferred to be major players in starch degradation pathways for the inoculum acclimatized using a simple substrate as predicted by the bioinformatics package PICRUSt2. However, acclimatizing using a complex substrate did not support their growth and were replaced by Coriobacteriales which provided higher flexibility in terms of the predicted regulated metabolic functions. The predicted functional regulation of Synergistales and Syntrophales increased with acclimatization using a complex substrate which also showed increase in the flexibility of the microbiome towards handling organic load shocks. Acetoclastic pathway was upregulated with increase in organic load regardless of the acclimatization substrate while the hydrogenotrophic pathway was downregulated. Overall, acclimatization using a complex substrate increased the robustness and flexibility of the microbiome towards organic load shocks.

The effect of heat pre-treatment on the anaerobic digestion of high-solid pig manure under high organic loading level.

Since more and more large-scale farms appear in China and changes in fecal sewage source disposal, the production of high-concentration solid manure waste is also increasing, and its conversion and utilization are gaining attention. This study investigated the effect of heat pre-treatment (HPT) on the thermophilic anaerobic digestion (AD) of high-solid manure (HSM). Pig manure (PM) feed with a total solids of 13% was used for the HPT and subsequent anaerobic digestion (AD) test. The HPT was carried out at 60°C, 80°C, and 100°C, respectively, for 15min after the heating reached the set temperature. The results show that HPT led to PM feed COD solubilization, observing a maximum increase of 24.57% after pretreated at 100°C, and the treated PM feed under this condition received the maximum methane production potential of 264.64 mL·g-1 VS in batch AD test, which was 28.76% higher than that of the untreated group. Another semi-continuous AD test explored the maximum volume biogas production rate (VBPR). It involves two organic loading rates (OLR) of 13.4 and 17.8g VSadded·L-1·d-1. The continuous test exhibited that all the HPT groups could produce biogas normally when the OLR increased to the high level, while the digester fed with untreated PM showed failure. The maximum VBPR of 4.71LL-1·d-1 was observed from PM feed after pre-treated at 100°C and running at the high OLR. This reveals that thermal treatment can weaken the impact of a larger volume of feed on the AD system. Energy balance analysis demonstrates that it is necessary to use a heat exchanger to reuse energy in the HPT process to reduce the amount of energy input. In this case, the energy input to energy output (E i /E o ) ranged from 0.34 to 0.55, which was much less than one, suggesting that biogas increment due to heat treatment can reasonably cover the energy consumption of the pre-treatment itself. Thus combining HPT and high-load anaerobic digestion of PM was suitable.

Enhancing anaerobic co-digestion of primary settled-nightsoil sludge and food waste for phosphorus extraction and biogas production: effect of operating parameters and determining phosphorus transformation.

The study aimed to comprehensively determine P extraction efficiency and co-digestion of food waste (FW) and primary settled-nightsoil sludge (PSNS) process performance influenced by different hydraulic retention times (4, 7, 10, and 15days) and mixture ratios of FW:PSNS in substrates (100:0, 75:25, 50:50, 25:75, and 0:100). P-transformation was evaluated to identify P fractionation in both supernatant and sludge accumulated in reactors. The results showed that anaerobic co-digestion was inhibited by the accumulation of undigested feedstock due to higher %PSNS found in AD4 (25FW:75PSNS) and AD5 (100PSNS). A more stable process was found in AD2 (75FW:25PSNS) under hydraulic retention time (HRT) 15days in which COD removal efficiency and P release were 97.2 and 80.2%, respectively. This recommended condition allowed a high organic loading rate (OLR) at 12 gVS/L/day resulting in the highest biogas yield of 0.93 L/L/day. Distribution of P data demonstrated that most of P in feedstock was deposited and accumulated in sediment up to 97.8%. Poor biodegradability resulting from using shortened HRT led to high increased P-solid content in effluent. In addition, available P in effluents and accumulated P-solids in sediment obtained from the AcoD process has the potential to serve as sources for P recovery.

Management of reject streams from hybrid membrane processes applied to phenolic compounds removal from olive mill wastewater by adsorption/desorption and biological processes

This work studies the valorisation of the concentrates obtained through membrane processes for the purification of olive oil washing wastewater (OOWW). The adsorption with resins/desorption process, followed by a biological treatment with sequencing batch reactor SBRs. Three different wastewater samples were treated: an ultrafiltration reject stream (UF-R), with a high organic load and low content of phenolic compounds; a nanofiltration reject stream (NF-R), which rich in phenolic compounds and with medium organic load; a stream concentrated by forward osmosis (FO-C) with high organic content and concentration of phenolic compounds. Through the adsorption/desorption process, it was possible to recover 90 % and 73 %, which corresponds to 1.69 and 1.66 g∙L−1 of the total phenolic compounds reject streams of NF-R and FO-C, respectively. With the SBRs, it was possible to eliminate around 80 % of the organic matter present in the effluent of adsorption, and also 90 % of the remaining phenolic compounds in the case of UF-R. The results obtained are promising since, on the one hand, a high recovery of phenolic compounds was achieved and, on the other hand, a large part of the organic matter of the remaining streams after adsorption was eliminated. In this way, a solution for the management of the membrane reject streams is proposed, allowing a circular economy in the wastewater treatment of olive oil processing.

Optimization and microbial diversity of anaerobic co-digestion of swine manure with waste kitchen oil at high organic loading rates

Anaerobic co-digestion of swine manure (SM) and waste kitchen oil (WKO) was conducted to evaluate the effect of high organic loading rates (OLRs) on biogas production efficiency and microbial changes. Combinations of different loading rates of SM and WKO, with total OLRs from 2 to 8 g VS (volatile solid)/L/d, were evaluated in a laboratory-scale study. While feeding more than 4 g VSSM/L/d did not result in higher biogas production in both mono- and co-digestion scenarios, the addition of WKO increased the total OLR up to 6 g VS/L/d without significant reduction of system productivity. Biogas yields of M2O1 (2 g VSSM/L/d + 1 g VSWKO/L/d) and M4O2 were 910 ± 35 and 849 ± 85 mL/g VSfed which were 25.2 % and 16.9 % higher than the mono-digestion of M2, respectively. A significant increase of bacterial alpha-diversity (Shannon index) was observed in M2O1, at 233.0 ± 3.6 compared with 218.7 ± 5.1 of M2 (p < 0.05). Less bacterial alpha-diversity and accumulation of volatile fatty acids were observed in M4O1 and M4O2, suggesting their potential instability. When digesters were fed with M2, the introduction of 1.4 g VSWKO/L/d or more did not increase biogas yield and could cause system imbalance. The study suggests the limit of WKO could be increased when higher OLRs of SM were applied but should not be more than 4 g VSSM/L/d, and ratio between SM and WKO should be considered to avoid failure. Some of the system disturbances took up to three months to show.

Do increased organic loading rates accelerate aerobic granulation in hypersaline environment?

It is a common sense that high organic loading rate (OLR) leads to the faster formation of aerobic granular sludge (AGS), while the effects of increased OLR on the direct development of salt-tolerant aerobic granular sludge (SAGS) in hypersaline wastewater is still unknown. In this study, four identical sequencing batch reactors (SBRs) were directly fed with 3% salinity wastewater and operated at different OLRs to cultivate SAGS. Granules firstly appeared on Day 10, 7, 5, and 8, and dominated on Day 23, 16, 10, and 13 in four SBRs operated under OLR of 2.4, 3.6, 4.8, and 7.2 kg COD/m3·d, respectively. The former three granules matured on Day 29 (D50 of 550 µm), 25 (D50 of 639 µm), and 25 (D50 of 808 µm), respectively, while the loose and fluffy filamentous granules cultivated under the highest OLR failed to reach the traditional criterion of AGS. Overall, increased OLR could accelerate the formation of AGS that had larger sizes and lower microbial diversities. However, unlike salt-free wastewater, the appropriate OLR for rapid formation of compact AGS in hypersaline wastewater was only 3.6 kg COD/m3·d, since the higher OLRs with higher hydraulic selection pressure led to the massive sludge loss and the formation of instable fluffy granules during granulation period. Bacterial community analysis revealed Corynebacterium, Marinobacterium, Paracoccus, Halomonas, and Vibrio were the main genera in four SBRs, in which Corynebacterium had certain abundance at all OLRs, and Vibrio and Paracoccus favored low OLR, while Halomonas and Marinobacterium dominated the SBRs with high OLRs. This study contributed to a better understanding of SAGS granulation under different OLR conditions in hypersaline wastewater.

Effect of organic shock loading on anaerobic performance of pumice-reinforced up-flow anaerobic sludge bed for incineration leachate treatment

The research and application of leachate in the treatment of leachate in UASB reactors are increasing, but UASB also has problems such as poor resistance to organic load impact and unstable operation. In order to improve the anaerobic performance stability of an up-flow anaerobic sludge bed reactor (UASB) subjected to high organic loading shock, pumice was added to the leachate from the incineration. The reinforcement effect of pumice on the anaerobic efficiency of the reactor was studied by increasing the influent load. The results showed that with a gradual increase in the influent organic load [11.6‒66.6 kg COD/(m3∙d)] and without the addition of pumice, irreversible acidification took place in the reactor (R1) when the influent load reached 14.51 kg COD/(m3∙d). The average methane output and content were reduced to 39.7 L/d and 66.16%, respectively. In contrast, the reactor (R2) with pumice could still be operated stably when the influent organic load reached 40.04 kg COD/(m3∙d). The COD removal rate reached 91.80%, and the average methane output and content were increased by 42.30% and 15.20%, respectively. The results of analyzing the sludge microbial community structure in the reactor showed that the adding of pumice could selectively enrich the methanogenic bacterium methanosaeta, promote the decomposition of volatile fatty acid (VFA), effectively mitigate the acid inhibition effect of VFA on the anaerobic reactor, and enhance the balance between acidogenic bacteria (Chloroflexi and Proteobacteria) and methanogenic bacterium (Methanosaeta) to a great degree. These results prove that the addition of pumice filler can reinforce the resistance of UASB to organic loading.

A novel bio-flocculation combined with electrodialysis process: Efficient removal of pollutants and sustainable resource recovery from swine wastewater

High organic matter load and nutrient concentration in swine wastewater could lead to soil and water pollution by inappropriate land irrigation. To solve the above problem, this study developed an eco-friendly bio-flocculation combined with electrodialysis (BF-ED) process, in which BF could effectively reduce the probability of ED membrane fouling and replaced subsequent biochemical treatment by ED process. High removal of TS (100 %), TP (100 %), and COD (95.68 %) from raw swine wastewater could be obtained via BF pretreatment, while high recovery efficiency of nutrient ions (98.8 % K+ and 84.3 % NH3-N) was achieved after ED process. Besides, dissolved organic matter was effectively removed after BF treatment, which was beneficial to reduce membrane fouling of ED reactor. Nutrient ions recovery from swine wastewater could be used as agricultural fertilizers. The proposed approach not only solve the problem of swine wastewater purification, but also realize the environmentally sustainable swine wastewater.

Rapid cultivation of aerobic granular sludge in laboratory scale sequencing batch reactor

Aerobic granular sludge (AGS) is known as excellent biological treatment for wastewater industry, high organic load wastewater and adsorption of heavy metal. AGS have some advantages such as higher density, higher biomass retention, simultaneous nutrient removal and higher tolerance to toxicity. The aim of this research is to use sequencing batch reactor (SBR) to cultivate AGS in the short time (28 days) in laboratory scale. Experimental condition that we use to cultivate AGS are based on this parameter: 1.5 hours of total cycle time, 50 % of exchange ratio, 3 hours of HRT and 3 l/min air flow rate. Even the AGS cultivation successfully achieve in 28 days with pH around 7-9, DO 3.6 mg/l, SVI 232.6 mg/l, and MLSS 500 mg/l, it is still need more time to generate more mature AGS to breakdown organic molecule in the wastewater.

GREEN APPROACH FOR THE TREATMENT OF TEXTILE WASTEWATER USING MICROBIAL FUEL CELL AND BIOELECTRICITY PRODUCTION

Microbial fuel cell (MFC) is a green and promising alternative for saving the depleting nonrenewableresources. In the present research, MFC technology is utilized to bring aboutdetoxification of textile wastewater with simultaneous production of electricity. Textile wastewaterhas a high pH value, high concentrations of dyes, organic pollutants, suspended solids, chlorides,nitrates, heavy metals (high BOD and COD values). The high organic load in the wastewatermakes it function as the useful substrate for microorganisms in MFC. Experimental results showedthat MFC using textile wastewater gave excellent electrical output of 546 mV after 60 h of operationIt has been found under the operating conditions of the experiments, there was 90–95% reductionin colour, TDS, BOD and COD of the textile wastewater.

Susceptibility of Clostridium sporogenes Spores to Selected Reference Substances and Disinfectants.

Research on the susceptibility of the spores of anaerobic bacteria such as Clostridium sporogenes or Clostridioides difficile is vital for assessing the sporicidal activity of disinfectants. The diverse susceptibility of anaerobic bacteria spores may lead to different disinfection parameters being determined by laboratories that prepare spore suspensions to test sporicidal effectiveness. The tests were performed using the suspension method according to PN-EN 13704:2018-09. In order to assess the susceptibility of the C. sporogenes spores, the criterion established for the C. difficile ribotype 027 spores was used in accordance with PN‑EN 17126:2019-01. The susceptibility of the C. sporogenes spores to glutardialdehyde corresponded to the susceptibility ranges established for the C. difficile ribotype 027 spores. The C. sporogenes spore suspension was susceptible to low concentrations of peracetic acid (0.01%). A disinfectant containing peracetic acid as the active substance showed high sporicidal activity at a low concentration (1%), a short contact time (15 minutes), and a high organic load (3.0 g/l bovine albumin + 3.0 ml/l sheep erythrocytes), as compared to a disinfectant with glutardialdehyde, which was sporicidal at a higher concentration (2.5%), at a longer contact time (60 minutes) and lower organic conditions (3.0 g/l bovine albumin). There is a need to define the minimum susceptibility criteria for the C. sporogenes spores to the reference substances most often found in disinfectants with sporicidal activity. Excessive susceptibility of the C. sporogenes spores to reference substances may result in low-performance parameters of disinfection products with sporicidal activity and lead to ineffective disinfection in practice.

High-speed treatment of low strength domestic wastewater for irrigation water production in pilot-scale classical, moving bed and fixed bed hybrid MBRs

To evaluate the treatability of domestic wastewater under conditions of low hydraulic retention time and high organic loadings, 3 pilot-scale automatically controlled membrane bioreactors (MBRs) as classical (C-MBR), moving bed (MB-MBR), and fixed bed (FB-MBR) were established and operated for a total of 268 days. Established pilot plants were compared in terms of treatment performance, membrane fouling, irrigation water criteria, and power consumption values. Results obtained have shown that all three systems were able to achieve more than 93% removal of chemical oxygen demand (COD) in an average hydraulic retention time (HRT) of 1 hour, and MB-MBR and FB-MBR were superior in terms of total nitrogen (TN) and total phosphorus (TP) removals. It has been determined that MB-MBR and FB-MBR are also advantageous in terms of power consumption. Especially it has been found that FB-MBR can produce better quality irrigation water with 40% lower power consumption than C-MBR under the same conditions. It was concluded that biofilm-supported hybrid systems could be a practical application in the fight against increasing water scarcity and global warming, both in obtaining clean water with less power consumption and in protecting human and environmental health.

Prequalification of flotation sludge for a sustainable increase in biogas production and in regard of demand-driven feeding strategy

Co-substrates can increase gas production in a digester significantly. The characteristic properties of substrates, depending on the amounts added, influence the processes in the digester reactor. As a consequence, they can have an impact on the buffer capacity, pH value, C:N ratio, dewaterability of the digested sludge and introduce contaminants to the digester among others. In the future, a discontinuous digester feeding could contribute to the demand-driven energy supply by WRRFs. Due to the increasing instability caused by fluctuating organic load, higher demands are placed on the selection of co-substrates. This study examined to what extent flotation sludge from dairy companies is suitable for a sustainable co-digestion. In addition, it should be evaluated whether flotation sludge is applicable for demand-driven feeding strategies. It was shown that flotation sludge has positive effects on the reactor as well as a significant increase in biogas production and a high degree of degradation of at least 80%. Even at high organic loads pH remained at a high level at around 7.5 due to the high alkalinity of the substrate. Nonetheless, addition of more than 20 w-% flotation sludge lead to a significant decrease of the dewaterability of the digested sludge.

Effect of Water Organic Load and Total Ammonia Nitrogen on Broilers’ Humoral Immune Response Against Newcastle Disease Virus Vaccination in Egypt

Low-quality drinking water (DW) has a negative impact on poultry immunity raising the risk of emerging infections. The current trial used experimentally contaminated broilers’ DW to study its effect on humoral immunity compared to 2 control groups. A total of 450 unsexed 1-day-old Cobb chickens were randomly allocated into 6 groups (75 birds in 5 replicates per group). DW of (T1) had 24 ppm chemical oxygen demand (COD), (T2) 12 ppm COD, (T3) 15 ppm total ammonia nitrogen (TAN), (T4) 5 ppm TAN, (T5) normal tap water (TW), (T6) TW with immunostimulant (IMU FORT®) a day before and after vaccination. Birds were subjected to the NDV DW vaccination program, serum was collected weekly, antibody (Ab) titers were measured along 6 weeks, lymphoid organs somatic indices (OSI) were evaluated after carcass evisceration at the end of the trial (42nd day), and Postmortem lesions were examined. Groups showed differences in Ab titers however, the 3rd and 6th weeks showed significant differences (p≤0.05), at the 3rd week T3 titers were significantly higher than T1, T2 but lower than T4, T6, and at the 6th week T6 titers were significantly higher than T1, T3, T4 but T5 was significantly lower than T3. The lowest OSI was in T3 which records 0.475, 0.133, 0.101 for thymus, bursa, and spleen, respectively while T6 was the highest. Broilers’ DW which has a high organic load (COD) and TAN, significantly decreases Ab titers and OSI. Both good quality DW and immunostimulant supplementation have a positive effect on NDV vaccines’ immune response.

Food Waste Management for Biogas Production in the Context of Sustainable Development

In the context of increasing pressure regarding the sustainable utilization of food waste in a circular economy, one of the trends is their biological transformation, through anaerobic digestion, into biogas as a renewable source of energy. We presented the physical-chemical properties of the main categories of food waste from different sources: dairy, meat, and poultry, fish, fruit and vegetable, cereal and bakery, brewing and winery industries, and others. Due to the high organic load, the presence of a multitude of nutrients, and an insignificant amount of inhibitors, food waste can be successfully used in the biogas production process in co-digestion with other materials. Physical (mechanical and thermal), chemical (alkali, acid, and oxidative), and biological (enzymatic, bacterial, and fungal) techniques have been widely used for pretreatment of different substrate types, including food waste. These pretreatments facilitate the degradation of pretreated food waste during anaerobic digestion and thus lead to an enhancement in biogas production. The purpose of this study is to review the situation of food waste generated in the food industry and to formulate the main trends of progress in the use of this waste in the anaerobic digestion process.

Performance of an anaerobic sequencing batch reactor operating under high organic loading in treatment of biodiesel wastewater.

Performance of an anaerobic sequencing batch reactor operating under high organic loading in treatment of biodiesel wastewater.

Influence of organic load on biogas production and response of microbial community in anaerobic digestion of food waste

Organic load (OL) is one important parameter influencing performance of anaerobic digestion, yet it is unclear how it affects the biogas composition and microbial community. This work investigated the influence of OL on biogas production from food waste (FW) and the response of microbial community. Results showed that the main biogas component was methane at low OLs (<10 g VS/L) while it turned into hydrogen at high OLs (>10 g VS/L). The optimum methane and hydrogen yields were 184.4 and 61.3 mL/g VS, corresponding to the OLs of 4 and 20 g VS/L, respectively. Analysis of microbial community indicated that high OLs leaded to the decrease of hydrolysis bacteria and methanogen while it helped to increase the relative abundance of hydrogen-producing bacteria. This study cast an insight that it is essential to control the OL and reinforce the hydrogenogen to obtain high output of hydrogen energy.

Enhancing anaerobic digestion of food waste with granular activated carbon immobilized with riboflavin

Previous studies have shown that anaerobic digestion of food waste can be enhanced by addition of conductive materials that stimulate direct interspecies electron transfer (DIET) between bacteria and methanogens. However, at extremely high organic loading rates (OLRs), volatile fatty acids (VFAs) still tend to accumulate even in the presence of conductive materials because of an imbalance between the formation of fermentation products and the rate of methanogenesis. In this study, granular activated carbon (GAC) immobilized with riboflavin (GAC-riboflavin) was added to an anaerobic digester treating food waste. The GAC-riboflavin reactor operated stably at OLRs as high as 11.5 kgCOD/ (m3·d) and kept VFA concentrations below 69.4 mM, COD removal efficiencies, methane production rates, and biogas methane concentrations were much higher in the GAC-riboflavin reactor than the GAC- and non-amended reactors. Transcripts associated with genes that code for proteins involved in DIET based metabolism were somewhat more highly expressed by Methanothrix in the GAC-riboflavin reactor. However, it is unlikely that riboflavin acted as an electron shuttle to stimulate DIET. Rather, it seemed to provide nutrients that enhanced the growth of microorganisms involved in the anaerobic digestion process, including those that are capable of DIET.