Anaerobic Digestion Of Food Waste Research Articles

Two-phase anaerobic digestion of food waste: Effect of semi-continuous feeding on acidogenesis and methane production

In present investigation, effect of diverting acidogenic off-gas from leached bed reactor (LBR) to up-flow anaerobic sludge blanket (UASB) reactor during semi-continuous food waste (FW) anaerobic digestion was evaluated. In test LBR headspace pressure (3.3 psi) was maintained with intermittent headspace gas transfer into UASB. In control, same headspace pressure was maintained without gas transfer. The semi-continuous FW addition affected the characteristics and production of leachate in control and test LBR. The cumulative COD, total soluble products and methane yields were 1.26, 1.37 and 3 times higher in the test LBR than the control. The acetate and methane yields from test LBR were 697.8 g·kgVSadded−1 and 167.55 mL·gCOD−1feeding. Acidogenic gas transfer maintained low partial pressure of hydrogen and the hydrogen to carbon-di-oxide ratio in the headspace of LBR, which were thermodynamically favorable for microbial metabolism and concomitant high-rate production of acetate-rich volatile fatty acid and methane-rich biogas from FW.

Supplementation of KOH to improve salt tolerance of methanogenesis in the two-stage anaerobic digestion of food waste using pre-acclimated anaerobically digested sludge by air-nanobubble water

Air-nanobubble water (NBW) was applied to pre-acclimate anaerobically digested sludge that was then used as the inoculum in the two-stage anaerobic digestion (AD) of high saline (20 g NaCl/L) food waste (FW) to optimize NBW application in the AD of high saline FW. K+ was simultaneously supplemented during the methanogenic stage to resist the inhibition of salt on methanogens. Results showed that after the second pre-acclimation cycle, the inoculum activity was increased 27% in the Air-NBW supplemented reactor in comparison to the deionized water (DW) supplemented one. In the first-stage AD, H2 yield was enhanced by 46% in the Air-NBW pre-acclimated sludge reactor compared with the DW pre-acclimated sludge reactor. Besides, supplementation of KOH in the methanogenic stage could enhance methane production by 17–25% in the DW reactors at initial pH 7.5, 8.0, and 9.0 when compared to the control reactor (using NaOH adjusted initial pH to 7.5), respectively.

Integrated Use of Microalgae in Waste Water Purification and Processing of Food Industry Waste

The processing of liquid and solid waste from the food industry using microalgae is considered on the example of St. Petersburg enterprises. Waste water from Baltika Brewing Campaign and food waste from public catering enterprises were used in the work, using the example of food waste from the canteens of Peter the Great St. Petersburg Polytechnic University. Тhe possibility of purifying wastewater from the brewing industry using microalgae was studied. The obtained biomass of microalgae after purification of waste water from the food industry is proposed to be used to accelerate the processes of anaerobic digestion of food waste generated in the canteens of the Peter the Great St. Petersburg Polytechnic University. It has been shown that the addition of microalgae biomass is capable of accelerating the decomposition of food waste and producing more biogas with a maximum methane content.

Study on the performance of HNO3-modified biochar for enhanced medium temperature anaerobic digestion of food waste.

Biochar can help promote direct interspecies electron transfer (DIET) and increase methane production; the surface redox groups play a constructive role in these processes. This study attempted to improve the anaerobic digestion (AD) performance by modifying biochar with HNO3 to increase its redox activity. A comparative experimental study, raw biochar (BC0) and biochar treated with HNO3 for 6h (BC6), were conducted to investigate the effect of HNO3 treatment on the medium temperature AD performance of food waste. Both BC0 and BC6 can enhance CH4 yield and facilitate the degradation of volatile fatty acids. The enhanced yield of CH4 was 36% for BC0 and 90% for BC6, respectively. Biochar can also enhance methanogenesis, presumably owing to direct interspecific electron transfer (DIET). Compared with BC0, BC6 had a higher redox activity and a smaller conductivity. It was supposed that BC0 mediated DIET through its conductivity, whereas BC6 accelerated DIET by surface redox groups.

Characteristics of antibiotic resistance genes in full-scale anaerobic digesters of food waste and the effects of application of biogas slurry on soil antibiotic resistance genes.

The fate of antibiotic resistance genes (ARGs) in full-scale anaerobic digestion (AD) of food waste (FW) and in the soil applied with biogas slurry has not been fully understood. In this study, 12 targeted ARGs and intI1 in FW, intermediate product, and biogas slurry from three full-scale ADwere analyzed. The results showed that subcritical water pretreatment was aneffective method for ARG attenuation, by which the absolute abundance of total targeted ARGs was removed by 99.69%. The predominant ARGs (ermB, tetM, and tetW) in FW were removed more than 99% after subcritical water pretreatment. The result of field experiments with biogas slurry as fertilizer showed that the absolute abundance of several ARGs (sul2, tetM, blaOXA-1, blaTEM) and intI1 accumulated significantly compared to the control group (CK) during three consecutive growth stages of the rice. The detected abundance of ARGs in paddy field soil increased from 190.50 (CK) to 8.87 × 104 copies/g (wet weight) (soil) during tillering stage, and increased from 4102.65 (CK) to 4.38 × 104 copies/g (wet weight) (soil) during heading time. Biogas slurry improved the soil nutrients (TN, AN, TP, and AP); meanwhile, the concentrations of total salt and Cl- increased. Network analysis indicated that 28 genera were the possible hosts of ARGs; variation partitioning analysis (VPA) indicated that microbial communities (contribution 59.30%) were the main factors that affected the fate of ARGs and intI1.

Digestate Post-treatment and Upcycling: Unconventional Moisturizing Agent for Food Waste In-Vessel Composting

Nowadays, Tunisia faces challenging environmental and energy issues which relate mainly to the implementation of an appropriate solid waste management system capable of dealing with the high production of biowaste on the one hand, and the increased need for water and energy resources on the other. Therefore, the current study is intended to develop a closed cycle technical concept treating mainly food waste (FW) through combined biological processes. In this approach, FW anaerobic digestion (AD) was destined to provide a valuable input material for FW in vessel-composting by exploiting the produced digestates. To this end, the gathered AD-effluents of three systems (D1, D2, D3) were entirely analyzed to select, as a further step, the most suitable one to be subject of the suggested post-treatment. Hence, several physiochemical parameters were examined as key performance indicators. It mainly consisted of moisture content, pH, C:N ratio and heavy metals contents. The current findings depicted that the generated digestates were characterized by a high moisture content which inspired its utilization as an unconventional moisturizing agent (MA) aiming to reduce the fresh water consumption during the composting process. Thus, two experimental setups were carried out to evaluate the effect of the selected digestate on FW-in-vessel composting process performance, as a non-standard MA inserted to A2, comparing to the unamended one (A1) which was moistened by fresh water. In fact, basing on the above-mentioned criteria, the relatively high C:N ratio (of around 15), as well as the relatively significant rate of the required macro- and micro-nutrients promoted the exploitation of biochar-rich digestate (D3) as not only an efficient unconventional MA, but also as a composting process booster. Furthermore, the results revealed that the addition of D3 improved significantly the composting process performance in terms of steering parameters including the attained temperature, MC and pH. When it comes to the maturity and stability assessment, the decreased profiles of C:N ratio, the nitrification index (NI), as well as the respiration activity (AT4) ascertained the fulfilment of the required conditions for both A1 and A2 to produce stable and mature end-products. However, regarding the compost quality, the examined concentrations of heavy metals met the requirement set by German standards and attested that both A1 and A2 generated highly-qualified products, rated as class B and A, respectively. Furthermore, it is noteworthy to mention that even the AD-effluents which were classified as an “inappropriate substrate” to be inserted to the composters, met the required criteria to be applied directly to land as a highly-qualified liquid biofertilizer. This latter ascertained, additionally, the efficiency and feasibility of the suggested closed cycle for a sustainable FW management.Graphic

Operational load enhancement for an anaerobic membrane bioreactor through ethanol fermentation pretreatment of food waste

Anaerobic digestion (AD) of food waste (FW) tends to result in the accumulation of volatile fatty acids (VFA), especially a large quantity of propionic acid that is inevitably produced. Propionic acid has a significant inhibitory effect on AD at a concentration far lower than acetic acid. Therefore, anaerobic digestion cannot be operated at an excessively high load. We proposed an AD system that used a considerable amount of starch-rich food waste for ethanol fermentation as a pretreatment and reported that it improved methane concentration in biogas with a low propionic acid accumulation even under high-load operation. This study examined whether ethanol fermentation pretreatment (EP) of food waste can contribute to high-load operation on AD using an anaerobic membrane bioreactor (AnMBR). This involved a sequential bath experiment using FW that was saccharized before fermentation to ethanol. The results are compared with those for FW without pretreatment. The organic loading rate (OLR) was stepwise increased to 43.5 g COD/L/d by increasing the feed OLR, the hydraulic retention time (HRT) was six days and methane content was 71%–74%, which is thrice the capability of the control series and the highest load in the reports of medium temperature AD of FW. Furthermore, the primary methanogens were tolerant to ammonia inhibition. Correspondingly, the ammonium produced improved the buffering capacity of AD at high load. Functional archaeal and bacterial communities in the two reactors were examined. The abundance of hydrogenotrophic methanogens in AnMBR are determined to highlight the impact of the EP for FW disposal through 16S rRNA sequence analysis. Because there were multiple methanogens that use hydrogen, the higher decomposition of the substrate was attributable to the maintenance of a lower hydrogen partial pressure. It contributed to create a virtuous cycle with the EP. This study demonstrates the performance of the EP during high loading and long-term AD operation using an AnMBR; moreover, ultra-high load is achieved by changing the metabolic pathway.

Modelling and analysis for biogas production process simulation of food waste using Aspen Plus

Researchers around the world are earnestly investigating the production of biogas from food waste as it is rich in organic content, and it has high potential to become a sustainable source for second-generation biofuels. The anaerobic digestion process is used to produce biogas but due to its complex nature, the process is still not efficient and productive. Current research on the production of biofuel out of food waste using two-stage digesters has shown promising results in increasing the biogas production rate and methane yield. Existing literature demonstrates only a few studies that have simulated a two-stage digester setup at thermophilic conditions for the anaerobic digestion of food waste at different fat concentrations, organic loading rates variation, and hydraulic retention times. Therefore, the purpose of this research was to simulate the anaerobic digestion of food waste using Aspen Plus at increasing Organic Loading Rates and Hydraulic Retentions Time and using 3 different fat concentration levels (20%, 40%, and 60%). The simulation used a two-stage digester setup at thermophilic (55 °C) conditions. The Aspen Plus simulation results demonstrated that at an Organic Loading Rate of between 2 l/day and 5 l/day and at a fat concentration level of 40% and 60%, the highest methane content achieved was 74.82% and 77.10%, respectively. The simulation results provided the data that can be used for future experimental projects for biogas research and development at an industrial level.

Why is biogas production and not food donation the Swedish political priority for food waste management?

The management of food waste is high on the political agenda. This study will analyze and discuss why biogas production has become the politically prioritized management method for food waste in Sweden, ahead of other alternatives such as donation to people in need. This study shows that biogas is the preferred alternative because food losses are framed as a waste issue, evaluated from an environmental and economic perspective. However, if food losses had been evaluated from a social perspective, and consideration given to the potential of food waste to address food insecurity, the evaluations could well have resulted in other priorities. In practice, there is no conflict between donation and anaerobic digestion of food waste. The edible food waste can be donated, while the inedible waste can be recycled. However, such an approach would require different ambitions and policies, which would bring actors together and ultimately improve the conditions for food donations and people living in food insecurity.

Resource recovery from the anaerobic digestion of food waste is underpinned by cross-kingdom microbial activities

As the human population grows on the planet so does the generation of waste and particularly that of food waste. In order to tackle the world sustainability crisis, efforts to recover products from waste are critical. Here, we anaerobically recovered volatile fatty acids (VFAs) from food waste and analysed the microbial populations underpinning the process. An increased contribution of fungi relative to bacteria was observed throughout the reactor operation, with both kingdoms implicated into the main three steps of anaerobic digestion occurring within our systems: hydrolysis, acidogenesis and acetogenesis. Overall, Ascomycota, Proteobacteria and Firmicutes were found to drive the anaerobic digestion of food waste, with butyrate as the most abundant VFA likely produced by Clostridium using lactate as a precursor. Taken together we demonstrate that the generation of products of added-value from food waste results from cross-kingdoms microbial activities implicating fungi and bacteria.

Monitoring of Food Waste Anaerobic Digestion Performance: Conventional Co-Substrates vs. Unmarketable Biochar Additions.

This study proposed the selection of cost-effective additives generated from different activity sectors to enhance and stabilize the start-up, as well as the transitional phases, of semi-continuous food waste (FW) anaerobic digestion. The results showed that combining agricultural waste mixtures including wheat straw (WS) and cattle manure (CM) boosted the process performance and generated up to 95% higher methane yield compared to the control reactors (mono-digested FW) under an organic loading rate (OLR) range of 2 to 3 kg VS/m3·d. Whereas R3 amended with unmarketable biochar (UBc), to around 10% of the initial fresh mass inserted, showed a significant process enhancement during the transitional phase, and more particularly at an OLR of 4 kg VS/m3·d, it was revealed that under these experimental conditions, FW reactors including UBc showed an increase of 144% in terms of specific biogas yield (SBY) compared to FW reactors fed with agricultural residue. Hence, both agricultural and industrial waste were efficacious when it came to boosting either FW anaerobic performance or AD effluent quality. Although each co-substrate performed under specific experimental conditions, this feature provides decision makers with diverse alternatives to implement a sustainable organic waste management system, conveying sufficient technical details to draw up appropriate designs for the recovery of various types of organic residue.

Bioelectrochemical Enhancement of Methanogenic Metabolism in Anaerobic Digestion of Food Waste Under Salt Stress Conditions

Bioelectrochemical anaerobic digestion, a promising concept, has been proven to improve anaerobic digestion (AD) performance in methane production. However, it has been challenged by the unstable performances attributed to high-salt stress in food waste (FW). In this study, an Fe anode-assisted bioelectrochemical anaerobic digester (R1) was proposed to facilitate FW treatment. Batch experiments were conducted under different salt stresses to understand the impact of Fe-carbon microbial electrolysis cells on the performance of AD of FW. The results indicated that R1 achieved the highest specific methane yield of 0.15 L/g VS·day–1 as compared with the controls after being exposed to 20 g/L Na+. As demonstrated from metagenomic and metaproteomics analysis, the gene abundance and enzyme activity of salt-tolerant microbial communities were improved with the presence of an Fe anode in AD, which might be achieved by participating in the biosynthesis of key kinases or altering the metabolic pathways of cells. Methanothrix, a dominant species of salt-tolerant methanogenic archaea, could rely on CO2 reduction by using iron electrodes as an electron contact to facilitate methane metabolism. The enzyme of sodium transport ATPase 5 capability in excreting Na+ from the cell and regulating the cell penetration was enriched in R1, thereby significantly improving the salt tolerance under high salinities.

Long-term operation of anaerobic digestion of food waste under simplified conditions: effect on reactor performance

ABSTRACT Anaerobic digestion under simplified conditions can contribute to food waste decentralised management. However, there is an absence of knowledge on the effect of long-term operation under these conditions. This study aimed to evaluate the operational conditions of an anaerobic reactor treating food waste after long-term operation without temperature control and low-intensity mixing. For this, a demonstration-scale reactor (18.8 m3) was operated for 160 days, while stability parameters were used to control the applied organic loading rate (OLR). Stability parameters indicated that the reactor was operated at stable conditions with an OLR of 0.3 kg VS m−3 d−1, while it was overloaded at an OLR of 0.4 kg VS m−3 d−1. This was observed through high value of intermediate and partial alkalinity ratio (IA/PA ratio), 2.5, and low values of bicarbonate alkalinity and pH, 1800 mg CaCO3 L−1 and 6.8, respectively. Moreover, there was a change in the concentration of intermediated metabolites, with a higher content of propionate and acetate, 1080 and 3775 mg L−1, respectively. Consequently, the methane production rate was decreased from 0.12 to 0.08 m3 CH4 m−3 d−1 and methane yield from 0.43 to 0.15 m3 CH4 kg VS−1. The reactor instability at a relatively low OLR was most probably due to hydrodynamic factors caused by the accumulation of recalcitrant material. Therefore, this material reduced the reactor performance and requires attention for a sustainable long-term operation.

Methane Production of Food Waste Anaerobic Digestion Recovered from NaCl Inhibition by Water Dilution

One of the significant challenges of food waste anaerobic digestion (AD) is the negative effect of high NaCl concentrations. This study investigated the effects of NaCl fluctuation on the methane generation of food waste AD under thermophilic and mesophilic conditions. Particularly, the effects of the shock loading of high NaCl concentration with/ without water dilution treatment were investigated. Generally, the methane generation decreased with increasing NaCl concentration. In addition, the sensitivity of the thermophilic AD to NaCl concentrations (5-10 g/L) was higher than that of the mesophilic AD. Furthermore, with an increase in the NaCl concentration from 0 to 30 g/L, the accumulative methane volumes of the thermophilic reactors decreased from 210 to 45 mL/gVS, and those of the mesophilic reactors decreased from 265 to 67 mL/gVS. Additionally, the pH of digestate decreased with increasing NaCl concentration. In contrast, the concentrations of the chemical oxygen demand and volatile fatty acid increased with increasing NaCl concentration. These results indicated that a shock loading of NaCl significantly reduced methane generation. In addition, the methane generation rates could be recovered up to 64-72% using water dilution as a remedial measure. Further investigation using 16S rRNA analysis revealed that the predominant genus of the methanogens shifted from Methanoculleus to Methanosarcina after the removal of the osmotic stress using water dilution.

Enhancing the performance of thermophilic anaerobic digestion of food waste by introducing a hybrid anaerobic membrane bioreactor

The thermophilic anaerobic digestion of food waste was a long-term challenge for maintaining process stability. A hybrid submerged anaerobic membrane bioreactor (AnMBR), integrating 27%(v/v) polyurethane sponge as fixed carriers were therefore investigated at (50 ± 2) °C. The organics removal efficiencies, COD mass balance, and membrane filtration performance were investigated in a 75-days continuously operated experiment. The results showed that methane production reached 0.31 L/(kg·COD) under an organic loading rate of 7.3 kg·COD/(m3·d). The low concentration of total volatile fatty acids of 247 ~ 274 mg/L and a high proportion of Methanosarcina (>97%) represented the high stability of the thermophilic process. Approximately 21% of biomass grew on the carriers in the hybrid AnMBR and induced a much lower suspended solids concentration and viscosity of bulk sludge. Noticeable lower trans-membrane pressure was consequently observed. The affecting factors identified by PCA analysis proved the advantages of the hybrid AnMBR for alleviating membrane fouling formation.

Prediction of biogas production rate from dry anaerobic digestion of food waste: Process-based approach vs. recurrent neural network black-box model

The stability of dry anaerobic digestion (AD) of food waste (FW) as well as the resulting methane gas generation was investigated from the perspective of system dynamics. Various organic loading rates were applied to the system by modifying the water content in the FW feed and solid retention time (SRT). The excessive organic loading due to the accumulation of volatile fatty acids (VFAs) from the feed with 80% water content during the short SRT (15 and 20 d) caused system failure. In contrast, more intermediate materials, such as VFAs, was easily converted into methane at higher water contents. In addition, the biogas production rate of dry AD was effectively predicted based on SRT, soluble chemical oxygen demand, total VFA, total ammonia, and free ammonia using a recurrent neural network—the so-called “black-box” model. This implies the feasibility of applying this data-based black-box model for controlling and optimizing complex biological processes.

Rapid initiation of methanogenesis in the anaerobic digestion of food waste by acclimatizing sludge with sulfidated nanoscale zerovalent iron

Although coupling of sulfidated nanoscale zero-valent iron (S-nZVI) into anaerobic digestion of food waste (FW) for improving methanogenesis has been reported, the specific role of S-nZVI during start-up process and its influence on subsequent methanogenesis and system stability remains unknown. In this study, S-nZVI was added into the unacclimatized sludge system to investigate its influence on microbial acclimatization and methanogenic performance. During acclimatization phase, CH4 production improved and VFAs transformation facilitated with the addition of S-nZVI. Furthermore, enzymatic activity analysis and electrochemical measurements presented direct evidence that electron transfer capacity of acclimatized sludge was significantly improved. S-nZVI favored the transition of microbial community to a robust and specialized population. During evaluation phase, acclimatized sludge still exhibited strong methanogenic ability, but the microbial community inevitably changed under the stress of FW. This research provides a novel perspective on initiating anaerobic digestion of FW for shorter start-up time and stronger methanogenesis.

Considering syntrophic acetate oxidation and ionic strength improves the performance of models for food waste anaerobic digestion

Current mechanistic anaerobic digestion (AD) models cannot accurately represent the underlying processes occurring during food waste (FW) AD. This work presents an update of the Anaerobic Digestion Model no. 1 (ADM1) to provide accurate estimations of free ammonia concentrations and related inhibition thresholds, and model syntrophic acetate oxidation as acetate-consuming pathway. A modified Davies equation predicted NH3 concentrations and pH more accurately, and better estimated associated inhibitory limits. Sensitivity analysis results showed the importance of accurate disintegration kinetics and volumetric mass transfer coefficients, as well as volatile fatty acids (VFAs) and hydrogen uptake rates. In contrast to the default ADM1, the modified ADM1 could represent methane production and VFA profiles simultaneously (particularly relevant for propionate uptake). The modified ADM1 was also able to predict the predominant acetate-consuming and methane-producing microbial clades. Modelling results using data from reactors dosed with granular activated carbon showed that this additive improves hydrogen uptake.

Potential production of struvite from the anaerobic digestion of food waste: analysis in one-phase and two-phase configurations

Abstract Anaerobic digestion (AD) of food waste (FW) has been gaining more interest as it has potential for the production of organic amendments with high struvite (NH4MgPO4·6H2O) content, which is a nutrient of great interest in sustainable agriculture. In this study, the influence of AD of FW in one- and two-phase configurations on methane production and the potential for struvite formation using digestate was evaluated. It was found that the two-phase is more efficient as its organic loading rate is 18% higher than that of one-phase configuration. In addition, the two-phase yielded a higher methane content in biogas (>60%) and a higher organic matter transformation in each of the AD stages (>20%); further, the digestate complied with the regulatory requirements for the use of organic amendments, thereby being deemed as a Type-B material with a struvite precipitation potential, exceeding 80%, as opposed to the digestate from one-phase configuration, which may represent a revenue of up to US$ 26,505 per year.

Dynamic interaction mechanism of environment, microorganisms, and functions in anaerobic digestion of food waste with magnetic powder supplement

The reutilisation of food waste for the production of clean energy was promoted by supplementing magnet powder in anaerobic digestion (AD). This study found that adding 5% magnet powder optimally increased the amount of biogas produced by 61.9%, and the pH and volatile fatty acids (VFA) content had the greatest correlation with biogas production. A further metagenomics analysis in the early, middle, and late stages of the AD revealed that interaction between bacteria and archaea had highest explanation rate for pH and VFA changes rather than enzymes. Moreover, the 5% magnet powder increased the proportion of the CO2 methanogenesis and decreased the acetate methanogenesis on day 15 of peak biogas production. And it was an innovative discovery that conversion of tetrahydromethanopterin S-methyltransferase to methane increased, which is an important common node of methanogenesis metabolic and may be the fundamental reason for the increase in biogas production caused by magnetic powder.