Search

This work investigated the effectiveness of free nitrous acid (FNA) in enhancing organic waste solubilization to improve biogas production in anaerobic digestion (AD). The results indicated that FNA pretreatment can enhance soluble organic content and control H 2 S odor in tested organic wastes, including food waste, sewage sludge, and their combination. However, a significant decrease (>50 %) in FNA concentration was found in the reactors, possibly due to denitrifier-driven NO 2 consumption. Biochemical methane potential (BMP) tests showed a 25 ± 8 % enhancement in CH - consumption. Biochemical methane potential (BMP) tests showed a 25 ± 8 % enhancement in CH 4 production in the reactors fed with mixed substrate pretreated with 2.9 mg FNA-N/L. However, the presence of NO 2 - (325.6-2368.0 mg N/L) in some BMP reactors, due to carryover from FNA pretreatment, adversely affected CH 4 production (>55 %) and prolonged lag time (>4.2 times). These findings are valuable for researchers and practitioners in waste management, offering insights for implementing FNA pretreatment to enhance the biodegradability of organic wastes in AD., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

A robust anaerobic digestion (AD) inoculum is key to a successful digestion process by providing the abundant bacteria needed for converting substrate to useable methane (CH 4 ). While transporting digester contents from one AD to another for digester startup has been the norm, transportation costs are high, and it is not feasible to transport wet inoculum to remote locations. In this study, the impact of preservation of AD inoculum via lyophilization was investigated for the purposes of digester startup and restabilization. The effect of lyophilizing inoculum on CH 4 production using food waste as the substrate was tested using biochemical methane potential (BMP) tests under the following conditions: (1) three inoculum sources, (2) two inoculum to substrate ratios (ISR), (3) two cryoprotectants, and (4) two inoculum growth phases. After lyophilization with skim milk, the three inocula produced 144-146 mL CH 4 /g volatile solids (VS) and 194-225 mL CH 4 /g VS at a 2:1 and 4:1 ISR, respectively, with 33-57% more CH 4 at the 4:1 ISR. Preservation with 10% skim milk exhibited complete recovery of CH 4 production, while 10% glycerol and 10% glycerol/skim milk mixture yielded 76% and 4% CH 4 recovery, respectively. Inoculum growth phase before preservation (mid-exponential or stationary growth phase) did not significantly affect CH 4 recovery. The study indicates that inoculum can be preserved via lyophilization using 10% skim milk as a cryoprotectant and reactivated for food waste digestion. The results provide a systematic quantification of the conditions needed to successfully preserve a mixed AD inoculum., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The methanogenic communities in alternative inocula and their potential to increase CH 4 production in mesophilic and psychrophilic dairy manure-based anaerobic digesters were examined. Quantitative-PCR and terminal restriction fragment length polymorphism (T-RFLP) profiles were used to determine archaeal and methanogenic community changes when three inocula (wetland sediment (WS), landfill leachate (LL), and mesophilic digestate (MD)) were incubated at 15, 25, and 35 °C for 91 and 196 days. After each incubation period, the inocula were used in biochemical methane potential (BMP) tests at the incubation temperatures. There was no significant correlation between inoculum mcrA gene copy numbers and CH 4 produced in BMP tests, suggesting that population size was not a distinguishing characteristic for predicting CH 4 production. Archaeal composition in LL and WS reactors generally converged with MD reactors after incubation at 25 and 35 °C for 196 days. These MD reactors had high relative abundance of TRF 302, likely Methanosaetaceae, and low acetic acid (0.62-1.61 mM). At 15 °C incubation, most reactors were associated with high acetic acid (1.61-133.6 mM) and dominated by TRF 199, likely Methanosarcinaceae. The LL reactor incubated at 25 °C for 91 days had higher relative abundance of TRF 199 and produced significantly higher CH 4 than WS and MD reactors in BMP test. In the future, it may be possible to create enrichment cultures that favor particular methanogens and use them as inoculum to benefit digesters at low mesophilic temperatures. Our data provides evidence that tailoring the archaeal community could benefit digesters operating under different conditions.

Temperature is a critical factor affecting anaerobic digestion because it influences both system heating requirements and methane production. Temperatures of 35-37°C are typically suggested for manure digestion. In temperate climates, digesters require a considerable amount of additional heat energy to maintain temperatures at these levels. In this study, the effects of lower digestion temperatures (22 and 28°C), on the methane production from dairy digesters were evaluated and compared with 35°C using duplicate replicates of field-scale (FS) digesters with a 17-day hydraulic retention time. After acclimation, the FS digesters were operated for 12weeks using solids-separated manure at an organic loading rate (OLR) of 1.4kgVSm(-3)d(-1) and then for 8weeks using separated manure amended with manure solids at an OLR of 2.6kgVSm(-3)d(-1). Methane production values of the FS digesters at 22 and 28°C were about 70% and 87%, respectively, of the values from FS digesters at 35°C. The results suggest that anaerobic digesters treating dairy manure at 28°C were nearly as efficient as digesters operated at 35°C, with 70% of total methane achievable at 22°C. These results are relevant to small farms interested in anaerobic digestion for methane reduction without heat recovery from generators or for methane recovery from covered lagoon digesters., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Co-digestion of food waste with dairy manure is increasingly utilized to increase energy production and make anaerobic digestion more affordable; however, there is a lack of information on appropriate co-digestion substrates. In this study, biochemical methane potential (BMP) tests were conducted to determine the suitability of four food waste substrates (meatball, chicken, cranberry and ice cream processing wastes) for co-digestion with flushed dairy manure at a ratio of 3.2% food waste and 96.8% manure (by volume), which equated to 14.7% (ice-cream) to 80.7% (chicken) of the VS being attributed to the food waste. All treatments led to increases in methane production, ranging from a 67.0% increase (ice cream waste) to a 2940% increase (chicken processing waste) compared to digesting manure alone, demonstrating the large potential methane production of food waste additions compared to relatively low methane production potential of the flushed dairy manure, even if the overall quantity of food waste added was minimal., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

A co-digestion investigation was conducted using small-scale digesters in Costa Rica to optimize their ability to treat animal wastewater and produce renewable energy. Increases in methane production were quantified when swine manure was co-digested with used cooking grease in plug-flow digesters that operated at ambient temperate without mixing. The co-digestion experiments were conducted on 12 field-scale digesters (250 L each) using three replications of four treatment groups: the control (T0), which contained only swine manure and no waste oil, and T2.5, T5, and T10, which contained 2.5%, 5%, and 10% used cooking grease (by volume) combined with swine manure. The T2.5 treatment had the greatest methane (CH(4)) production (45 L/day), a 124% increase from the control, with a total biogas production of 67.3 L/day and 66.9% CH(4) in the produced biogas. Increasing the grease concentration beyond T2.5 produced biogas with a lower percentage of CH(4), and thus, did not result in any additional benefits. A batch study showed that methane production could be sustained for three months in digesters that co-digested swine manure and used cooking grease without daily inputs. The investigation proved that adding small amounts of grease to the influent is a simple way to double energy production without affecting other digester benefits., ((c) 2010 Elsevier Ltd. All rights reserved.)

Using food waste (FW) as a co-substrate in anaerobic digestion (AD) results in increased energy production, decreases in greenhouse gas emissions, and recycles the FW nutrients back to the land for producing crops. This research investigated food waste AD systems in the United States (US) and Germany (DE) that co-digested FW with dairy manure at the lab and full-scale. In DE, the post-consumer FW had 32–49% more CH 4 potential (477–499 mL CH4 /g VS) than maize and grass silage (368 and 331 mL CH4 /g VS) and solid and liquid manure (243 and 91 mL CH4 /g VS). Methane production in the full-scale DE system with 66% FW (by volume) was 882 m3 CH4 /d, which was 37% higher than the laboratory results due to the 86-day retention and 42 °C AD conditions in the field. The pre-consumer FW in the US had a similar CH 4 potential (264–553 mL CH4 /g VS), but due to the lack of heating in the full-scale system, 62% less CH 4 was produced than the lab-based potential. While DE requires pasteurization of FW for AD and bans FW bans to landfills, the US does not have specific requirements for FW treatment in AD or federal FW landfill policies, with a few forthcoming FW bans in some municipalities and states. As FW diversion and utilization in AD systems is expected to grow, it is important to understand the effect of FW in biogas production and nutrient content, comparisons between lab and field-scale results, and the effect of policy on FW utilization. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Metal nanoparticles (NPs) were added to anaerobic digestion (AD) of poultry litter. • Adding Ni NPs (12 mg/L) increased CH 4 production by 38.4% (368 mL CH 4 /g VS). • Fe, Co and Fe 3 O 4 NPs added individually also increased CH 4 with no effect on H 2 S. • Higher concentrations of NP mixtures greatly reduced H 2 S with no effect on CH 4. • A method for extraction of NPs from digestate for SEM detection was developed. Abstract The effects of metal nanoparticle (NP) addition during anaerobic digestion (AD) of poultry litter was tested using two sequential experiments: Exp. A) four NPs (Fe, Ni, Co, and Fe 3 O 4) at three concentrations; and Exp. B) NP combinations (Fe, Ni, and Co) at four concentrations. Scanning electronic microscopy (SEM) and elemental analysis were used to confirm NP inclusion after dispersion (before AD) and track nanoparticles post-AD, and new technique for NP extraction post-AD was developed. Before AD, NPs ranged from 30.0 to 80.9 nm for Fe, Ni, and Co, and 94.3 to 400 nm for Fe 3 O 4. Methane production increased with NPs addition compared to poultry litter-only, with the highest increases observed with NPs concentrations (in mg/L) of 12 Ni (38.4% increase), 5.4 Co (29.7% increase), 100 Fe (29.1% increase), and 15 Fe 3 O 4 (27.5% increase). Nanoparticle mixtures greatly decreased H 2 S production. The SEM post-AD detected Fe, Ni, and Fe 3 O 4 at concentrations ≥100 mg/L. [ABSTRACT FROM AUTHOR]

Lasalocid is an antibiotic from the group of carboxylic ionophores, and it is commonly used in cattle and poultry as a coccidiostat and for growth promotion. The widespread use and persistence of lasalocid have led to its detection in the environment. The objective of this study was to determine the fate and effect of veterinary ionophore lasalocid during the anaerobic digestion of dairy manure. Duplicate plug flow field-scale digesters were operated using either non-amended dairy manure or dairy manure amended with 1 or 5 mg/L lasalocid. Results showed that lasalocid was reduced approximately 75% during anaerobic digestion. Methane production from digesters treating manure amended with 1 and 5 mg/L lasalocid were comparable with CH4 production from the duplicate digesters operated without added lasalocid. These results suggest that anaerobic digestion can be used to reduce lasalocid levels in dairy manure, and lasalocid did not affect digester stability at concentrations expected in dairy manure. [ABSTRACT FROM AUTHOR]

There is growing concern about residual antibiotics and feed additives in the manure of treated animals because of the effects of these residues in the environment. Monensin is the most widely used ionophore coccidiostat in the U.S. The objective of this study was to determine the fate and effect of monensin during the anaerobic digestion of dairy manure. Duplicate plug flow field-scale digesters were operated using non-amended dairy manure and dairy manure amended with monensin to 1 and 10 mg/L for 56 days at 30°C at an organic loading rate of 1.4 kg VS/m3-d and 17-day hydraulic retention time. Results showed that monensin was reduced approximately 70% during anaerobic digestion. Methane production from digesters using manure amended with 1 mg/L monensin was comparable to that from digesters operated without added monensin. However, digesters using manure amended with 10 mg/L monensin yielded 75% less methane than digesters using manure without added monensin. These results suggest that anaerobic digestion is an effective treatment for reducing, but not eliminating, monensin in dairy manure. Monensin did not reduce methane production at concentrations expected in dairy manure at recommended dosage rates. [ABSTRACT FROM AUTHOR]

Three tubular anaerobic digestion (AD) systems were installed in Haiti to treat black water (toilet-based wastewater), including a three cell 36 m 3 clinic digester (CD), a two cell 2 m 3 hotel digester (HD), and a three-cell 3 m 3 farm digester (FD) for worker use. During digestion, total coliforms were reduced by 99.1%, E. coli by 98.5%, and chemical oxygen demand (COD) by 93.6%. Nutrients in the effluent averaged 99.4 mg/L NH 4 + and 10.6 mg/L PO 4 2− , producing an effective organic fertilizer. Average biogas production in CD was 108 L/d, with 65.4% CH 4 . Survey participants (n = 573) were willing to pay $0.10–0.30 per use for sanitation facilities. Seventy-two percent of the rural population surveyed in Cange, Haiti lacked access to improved sanitation due to financial constraints. The economic analysis calculated an investment cost for a shared toilet AD systems of $16–$47 (USD) per person based on daily use at design capacity. [ABSTRACT FROM AUTHOR]

Although there are a variety of commercially available biological and chemical treatments for removal of hydrogen sulfide (H2S) from biogas, managing biogas H2S remains a significant challenge for agricultural digesters where labor and operational funds are very limited compared to municipal and industrial digesters. The objectives of this study were to evaluate headspace aeration for reducing H2S levels in low cost plug flow digesters and to characterize the relationship between the liquid surface area and H2S oxidation rates. Experiments with replicate field scale plug flow digesters showed that H2S levels decreased from 3500 ppmv to <100 ppmv when headspace oxygen levels were 0.5 to 1%. Methane production was not affected by aeration rates that resulted in headspace oxygen levels of up to 1%. Pilot scale experiments using 65 to 104 L desulfurization units showed that H2S oxidation rates increased with increases in liquid surface area. These results support the hypothesis that H2S oxidation rates are limited, in part, by the surface area available for oxygen transfer, and can be increased by growth of biofilms containing H2S oxidizing bacteria. Maximum removal rates corresponded to 40 to 100 g S m-2 d-1 of liquid surface area at biogas retention times of 30 to 40 min. [ABSTRACT FROM AUTHOR]

Forage radish, a winter cover crop, was investigated as a co-substrate to increase biogas production from dairy manure-based anaerobic digestion. Batch digesters (300 cm 3 ) were operated under mesophilic conditions during two experiments (BMP1; BMP2). In BMP1, the effect of co-digesting radish and manure on CH 4 and H 2 S production was determined by increasing the mass fraction of fresh above-ground radish in the manure-based co-digestion mixture from 0 to 100%. Results showed that forage radish had 1.5-fold higher CH 4 potential than dairy manure on a volatile solids basis. While no synergistic effect on CH 4 production resulted from co-digestion, increasing the radish fraction in the co-digestion mixture significantly increased CH 4 production. Initial H 2 S production increased as the radish fraction increased, but the sulfur-containing compounds were rapidly utilized, resulting in all treatments having similar H 2 S concentrations (0.10–0.14%) and higher CH 4 content (48–70%) in the biogas over time. The 100% radish digester had the highest specific CH 4 yield (372 ± 12 L kg −1 VS). The co-digestion mixture containing 40% radish had a lower specific CH 4 yield (345 ± 2 L kg −1 VS) but also showed significantly less H 2 S production at start-up and high quality biogas (58% CH 4 ). Results from BMP2 showed that the radish harvest date (October versus December) did not significantly influence radish C:N mass ratios or CH 4 production during co-digestion with dairy manure. These results suggest that dairy farmers could utilize forage radish, a readily available substrate that does not compete with food supply, to increase CH 4 production of manure digesters in the fall/winter. [ABSTRACT FROM AUTHOR]

Pilot-scale digesters (850 L) were used to quantify CH 4 and H 2 S production when using forage radish cover crops as a co-digestion feedstock in dairy manure-based digesters. During two trials, triplicate mixed digesters were operated in batch mode with manure-only or radish + manure (27% and 13% radish by wet weight in Trial 1 and 2, respectively). Co-digestion increased CH 4 production by 11% and 39% in Trial 1 and 2, respectively. As H 2 S production rapidly declined in the radish + manure digesters, CH 4 production increased reaching high levels of CH 4 (⩾67%) in the biogas. Over time, radish co-digestion lowered the H 2 S concentration in the biogas (0.20%) beyond that of manure-only digestion (0.34–0.40%), although cumulative H 2 S production in the radish + manure digesters was higher than manure-only. Extrapolated to a farm-scale (200 cows) continuous mixed digester, co-digesting with radish could generate 3150 m 3 CH 4 /month, providing a farmer additional revenue up to $3125/month in electricity sales. [ABSTRACT FROM AUTHOR]

Highlights: [•] ATAs were conducted on four food processing wastes at 2%, 5%, 15% and 30% (by volume). [•] There were significant decreases in pH, with media addition, at each inclusion rate. [•] Above 5% inclusion, all four food processing wastes showed signs of toxicity. [•] Without co-digestion, CH4 production may be inhibited with food processing wastes. [Copyright &y& Elsevier]

Bioplastics have emerged as a viable alternative to traditional petroleum-based plastic (PET). Three of the most common bioplastic polymers are polyhydroxybutyrate-valerate (PHBV), polylactide (PLA), and cellulose-based bioplastic (CBB). This study assessed biodegradation through anaerobic digestion (AD) of these three bioplastics and PET digested with food waste (FW) at mesophilic (35 °C) and thermophilic (55 °C) temperatures. The four plastic types were digested with FW in triplicate batch reactors. Additionally, two blank treatments (inoculum-only) and two PHBV treatments (with FW + inoculum and inoculum-only) were digested at 35 and 55 °C. The PHBV treatment without FW at 35 °C (PHBV-35) produced the most methane (CH4) normalized by the volatile solids (VS) of the bioplastics over the 104-day experimental period (271 mL CH4/g VS). Most bioplastics had more CH4 production than PET when normalized by digester volume or gram substrate added, with the PLA-FW-55 (5.80 m3 CH4/m3), PHBV-FW-55 (2.29 m3 CH4/m3), and PHBV-55 (4.05 m3 CH4/m3) having 848,275 and 561%, respectively, more CH4 production than the PET treatment. The scanning electron microscopy (SEM) showed full degradation of PHBV pellets after AD. The results show that when PHBV is used as bioplastic, it can be degraded with energy production through AD. [ABSTRACT FROM AUTHOR]

Abstract: A nine-month co-digestion investigation was conducted in Costa Rica to optimize animal wastewater treatment, renewable energy production, and fertilizer creation using 12 Taiwanese-model, plug-flow digesters (250 L each) constructed of tubular polyethylene and PVC piping, operating without mechanical or heating components. The experiment tested three replications of four treatment groups: the control (T0), which contained only swine manure, and T2.5, T5, and T10, which contained 2.5%, 5%, and 10% used cooking grease (by volume) combined with swine manure. T2.5 had the greatest methane production (45 L d−1), a 124% increase from the control. No adverse effects were observed from co-digesting 2.5% grease in terms of organic matter removal, pathogen reduction, grease removal, and pH. Chemical oxygen demand (COD) was reduced 94.7% to 1.96 g L−1, fecal coliforms and Escherichia coli were reduced 99.2 and 97.1%, respectively, and grease removal was 99.9%. The average effluent pH (7.05) and alkalinity in T2.5 was within the optimal range for methanogens and increased significantly during the nine-month experiment, likely due to adaptation of the methanogenic organisms to the influent grease concentrations. Total nitrogen concentration decreased 34.0%, and NH4-N increased 97.1% during digestion in T2.5, with no significant differences between T2.5 and T0. There was less phosphorus reduction with co-digestion, with 181 mg g−1 of total phosphorus (TP) in T2.5 and only 90.6 mg g−1 of TP in T0, resulting in lower N:P ratios in the grease treatment groups due to the greater concentration of phosphorus in the effluent. [Copyright &y& Elsevier]

Abstract: Methane production, electricity production, and wastewater transformations were quantified for a digestion system that combines biogas from a swine digester and dairy digester in Costa Rica. The low-cost, plug-flow digesters were not heated and were operated in the lower portion of the mesophilic range (25–27°C). The dairy digester produced 27.5m3/day of biogas with 62.6% methane and reduced organic matter (COD) by 86%. The swine digester produced 6.0m3/day of biogas with 76.4% methane and reduced COD by 92%. Combining biogas from a swine and dairy digester, increased electricity production due to the higher biogas production rate of the dairy farm and the higher quality biogas obtained from the swine farm. The farm’s 2-h peak electricity demand (12.9kW/day) was 81.8% met. The electricity was produced using manure equivalent to the quantity excreted by 5 dairy cows and 40 pigs remaining in corrals 100% of the time. The $21,000 capital cost of the digester project will be recovered in 10.1 years through electricity savings and reductions in wastewater fines. If the generator were more appropriately sized for the farm, the capital recovery time would have been 7.6 years. [Copyright &y& Elsevier]

Seven low-cost digesters in Costa Rica were studied to determine the potential of these systems to treat animal wastewater and produce renewable energy. The effluent water has a significantly lower oxygen demand (COD decreased from 2968mg/L to 472mg/L) and higher dissolved nutrient concentration (NH4-N increased by 78.3% to 82.2mg/L) than the influent water, which increases the usefulness of the effluent as an organic fertilizer and decreases its organic loading on surface waters. On average, methane constituted 66% of the produced biogas, which is consistent with industrial digesters. Through principle component analysis, COD, turbidity, NH4-N, TKN, and pH were determined to be the most useful parameters to characterize wastewater. The results suggest that the systems have the ability to withstand fluctuations in the influent water quality. This study revealed that small-scale agricultural digesters can produce methane at concentrations useful for cooking, while improving the quality of the livestock wastewater. [Copyright &y& Elsevier]

• Unmodified biochar added to a digester resulted in 90.5% H 2 S removal efficiency. • The biochar particle size did not significantly affect the H 2 S removal efficiency. • Iron-impregnated biochar resulted in complete removal of H 2 S from the biogas. • Activated carbon was not effective when used as an in-situ desulfurization agent. • Biochar addition did not significantly affect the methane yield during digestion. Corn stover biochar (CSB) and maple biochar (MB) were added into anaerobic digesters and evaluated for hydrogen sulfide (H 2 S) reductions. This was the first study to show Fe-impregnated biochar can eliminate H 2 S production. The novel study evaluated biochar addition on H 2 S reduction and nutrient concentrations using three experiments to test the effect of: 1) biochar concentration, 2) biochar particle size, and 3) Fe-impregnated biochar using triplicate lab-scale reactors. At the highest biochar dose (1.82 g biochar/g manure TS), H 2 S production was 90.5% less than the control treatment (351 mL H 2 S/kg VS). Biochar particle size did not significantly affect H 2 S concentration. The Fe-impregnated biochar (0.5 g biochar/g manure TS) reactors had no H 2 S detected in the CSB-Fe system. Methane (CH 4) in the biochar and control treatments were not significantly different in all three experiments. The results show that biochar added to digesters can significantly reduce H 2 S production without affecting CH 4 production. [ABSTRACT FROM AUTHOR]

Currently, there are challenges with proper disposal of cassava processing wastewater, and a need for sustainable energy in the cassava industry. This study investigated the impact of co-digestion of cassava wastewater (CW) with livestock manure (poultry litter (PL) and dairy manure (DM)), and porous adsorbents (biochar (B-Char) and zeolite (ZEO)) on energy production and treatment efficiency. Batch anaerobic digestion experiments were conducted, with 16 treatments of CW combined with manure and/or porous adsorbents using triplicate reactors for 48 days. The results showed that CW combined with ZEO (3 g/g total solids (TS)) produced the highest cumulative CH4 (653 mL CH4/g VS), while CW:PL (1:1) produced the most CH4 on a mass basis (17.9 mL CH4/g substrate). The largest reduction in lag phase was observed in the mixture containing CW (1:1), PL (1:1), and B-Char (3 g/g TS), yielding 400 mL CH4/g volatile solids (VS) after 15 days of digestion, which was 84.8% of the total cumulative CH4 from the 48-day trial. Co-digesting CW with ZEO, B-Char, or PL provided the necessary buffer needed for digestion of CW, which improved the process stability and resulted in a significant reduction in chemical oxygen demand (COD). Co-digestion could provide a sustainable strategy for treating and valorizing CW. Scale-up calculations showed that a CW input of 1000–2000 L/d co-digested with PL (1:1) could produce 9403 m3 CH4/yr using a 50 m3 digester, equivalent to 373,327 MJ/yr or 24.9 tons of firewood/year. This system would have a profit of $5642/yr and a $47,805 net present value. [ABSTRACT FROM AUTHOR]

Co-digestion of dairy manure with waste organic substrates has been shown to increase the methane (CH4) yield of farm-scale anaerobic digestion (AD). A gummy vitamin waste (GVW) product was evaluated as an AD co-digestion substrate using batch AD testing. The GVW product was added at four inclusion levels (0%, 5%, 9%, and 23% on a wet mass basis) to a co-digestion substrate mixture of dairy manure (DM), food-waste (FW), and grease-waste (GW) and compared to mono-digestion of the GVW, DM, FW, and GW substrates. All GVW co-digestion treatments significantly increased CH4 yield by 126–151% (336–374 mL CH4/g volatile solids (VS)) compared to DM-only treatment (149 mL CH4/g VS). The GVW co-digestion treatments also significantly decreased the hydrogen sulfide (H2S) content in the biogas by 66–83% (35.1–71.9 mL H2S/kg VS) compared to DM-only (212 mL H2S/kg VS) due to the low sulfur (S) content in GVW waste. The study showed that GVW is a potentially valuable co-digestion substrate for dairy manure. The high density of VS and low moisture and S content of GVW resulted in higher CH4 yields and lower H2S concentrations, which could be economically beneficial for dairy farmers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conductive NPs potential to improve AD performance was critically discussed. • Impact of different NPs and sizes on AD biogas quantity and quality are elucidated. • The interactions of AD microorganisms and DIET with the aid of NPs were reviewed. • The role of NPs in biochemical pathways direction and metabolites utilization are covered. Anaerobic digestion (AD) is a biochemical process that converts waste organic matter into energy-rich biogas with methane as the main component. Addition of electric electro-conductive, such as that nanoparticles (NP), has been shown to improve biogas generation. Interspecies electron transfer and direct interspecies electron transfer (DIET) using conductive materials is one of the mechanisms responsible for observed increases in CH 4. This article discusses the effect of the type and size of electro-conductive NPs on improving microbial degradation within AD systems, as well as the effect of electro-conductive NPs on microbial community shifts and syntrophic metabolism. Limitations and future perspectives of using NPs in an AD system is also discussed. [ABSTRACT FROM AUTHOR]

• Tracked nanoparticle (NP) use, degradation, and uptake in an AD-hydroponics system. • NP use increased CH 4 production by 23.7% during anaerobic digestion (AD). • NP addition temporarily ceased H 2 S production, with an average reduction of 56.3%. • The AD treated with NPs had 1,160–19,400% higher NP concentrations in the effluent. • Harvested lettuce had 21.0–1,920% more NP uptake, yet, well below toxic thresholds. Nanoparticle (NP) use can increase biological activity and adversely impact the environment. This study was the first to quantify biogas increases with NP mixtures during continuous anaerobic digestion (AD) of poultry litter and NP uptake in crops through tracking: 1) CH 4 and H 2 S production from a NP mixture (Fe, Ni, and Co) in 30 L continuous digester (AD1) for 278 days compared to a control digester (AD2) without NP addition, 2) NP degradation during digestion, 3) using AD effluent with and without NP addition as a fertilizer, and 4) plant uptake of NPs. With NP inclusion, CH 4 production increased by 23.7%, and H 2 S was reduced by 56.3%. The AD1 effluent had 1,160–19,400% higher NP concentrations and the lettuce biomass had 21.0–1,920% more NPs than lettuce fertilized with the AD2 effluent. This study showed that the effects of NPs remaining in the AD effluent must be considered. [ABSTRACT FROM AUTHOR]

This study determined the effect of incorporating a microbial electrolysis cell (MEC) with an anaerobic digester (AD) in a single chamber. The study evaluated three treatments: a combined AD-MEC operated for 23 days (AD-MEC-23); a combined AD-MEC operated with the MEC running for 5 days followed by no MEC for the subsequent 18 days (AD-MEC-5); and an AD operated for 23 days (AD-only). Food waste was the digestion substrate at an inoculum to substrate ratio of 1:1 (VS basis). Cumulative methane and hydrogen during the batch test in AD-MEC-23 (9.4 L CH4 , 3.39 L H2 , 2.8 L CO2 ) was higher than AD-MEC-5 (7.6 L CH4 , 2.2 L H2 , 4.6 L CO2 ), and AD-only (7.4 L CH4 , 0.2 L H2 , 5.8 L CO2 ). The results also showed that using the MEC continuously inside the digester (AD-MEC treatment) reduced CO 2 concentration to approximately 4% at the end of the experimental period, thereby, increasing the useful gases (CH 4 and H 2 ) concentrations to a maximum of 95.8%, with an average of 71.9% CH 4 , 17.4% H 2 and 10.7% CO 2 over the 23-day digestion period in the AD-MEC-23 reactor. Additionally, the COD removal in AD-MEC-23 was 12% higher than AD-only. The volumetric current was 108.7 A/m 3 based on MEC volume and 17.3 A/m 3 based on total AD-MEC volume, while the current density was 1.35 A/m 2 (cathode surface area). The total energy produced from the AD-MEC-23 (414 kJ) was higher than AD-MEC-5 (325 kJ) and AD-only (295 kJ), with an increase of energy production of over 400% output energy compared to the input energy to power the MEC. The results showed that the novel MEC design incorporated into an AD reactor increased the biogas quality, overall energy production, and waste treatment. [ABSTRACT FROM AUTHOR]

Algal turf scrubbers (ATS) and anaerobic digesters (AD), when combined, remove nutrients from eutrophic water while producing renewable energy through biogas production. Algal biomass was produced from an ATS system that used tipping buckets to introduce riverine water in pulses onto a flow-way with a mesh screen installed to facilitate algal attachment. This study was the first to determine methane (CH 4) production from AD of a micro- and macro-algae polyculture, harvested from an ATS, using lab-scale reactors under batch and semi-continuous feeding regimes. The lab-scale study was followed by a pilot-scale (7 m3) ATS-AD study, the largest scale study of biogas production from ATS-derived algae. Batch digestion of 'wet' algae (93% moisture) produced 158 ± 13 L CH 4 /kg VS, which was higher than algae with a lower moisture content (≤62% moisture). Continuing use of 'wet' algae as the substrate, the 2 L semi-continuously-fed lab system yielded a maximum CH 4 production value of 144 ± 7 L CH 4 /kg VS, with 60%–62% CH 4 in the biogas. The 7 m3 pilot-scale system produced 107 ± 15 L CH 4 /kg VS, with 66.4% CH 4 in the biogas. Scale-up calculations showed that a 1 ha ATS system could capture 8.73 kg N, 1.18 kg P, and 52.5 kg C/ha-d, with the resulting algae being used in AD to produce biogas for direct heating (2.8*108 J) or to power a 1.13 kW generator. While the total energy output from the 1 ha ATS-AD system is relatively low, energy production from the AD system is a supplemental benefit to an ATS system that captures nutrients from eutrophic water. This ATS-AD system could contribute to the overall Chesapeake Bay cleanup, especially in nutrient hot-spots, like the Baltimore Harbor, where high nutrient concentrations support high algal productivity, which would provide substrate for on-site energy production from AD. Unlabelled Image • Biomass from algal turf scrubber (ATS) that removed nutrients from eutrophic waters. • Methane production from ATS biomass was 158 L CH 4 /kg VS with 'wet' algae (TS = 7%). • Max CH 4 production in semi-continuous reactors was 144 L CH 4 /kg VS with 20-day HRT. • 7 m3 pilot-scale digester produced 107 L CH 4 /kg VS, with 66.4% CH 4 in the biogas. • Scale-up to 1 ha would remove 8.7 kg N/d, 1.18 kg P/day and produce 1.13 kW of power. [ABSTRACT FROM AUTHOR]