Anaerobic Co-digestion Of Pig Manure Research Articles

Effect of Antibiotics and Thermophilic Pre-Treatment on Anaerobic Co-Digestion of Pig Manure and Corn Straw

The excessive use of antibiotics in the pig breeding industry leads to the accumulation of antibiotic residuals in the environment, which is attributed to the improper treatment of livestock excrements. Sulfamethoxazole (SMX) and Norfloxacin (NOR) are antibiotics used in pig breeding and veterinary medicines as growth promoters and antibacterial drugs. The aim of this study was to examine the effects of these antibiotics and thermophilic pre-treatment on methane (CH4) yield by anaerobic co-digestion (AcoD) of pig manure and corn straw under mesophilic temperature condition (35 ± 1 °C). We used antibiotics at a concentration of 0, 20 and 60 mg L−1 (three stages) in two lab-scale continuously stirred tank reactors. The first reactor was run using untreated fed and the second reactor was run with thermophilic (55 ± 1 °C) pre-treated fed. The results showed that the CH4 productions from reactor one were 205, 163 and 128 and from reactor two were 222, 185 and 173 mL CH4 g−1 VSadded, respectively. This elucidates that the presence of antibiotics had a negative effect on CH4 production. Moreover, thermophilic pre-treatment improved the performance of the anaerobic digestion and CH4 production.

Enhancement effect of biochar addition on anaerobic co-digestion of pig manure and corn straw under biogas slurry circulation

Based on the semi-continuous anaerobic co-digestion (AcoD) reactor, the effects of biochar addition on the internal environmental changes and gas production characteristics were studied under the condition of biogas slurry recirculation. The results showed that the addition of biochar enhanced the degradation and metabolic pathways of acetate and propionate, thereby reducing the concentrations of volatile fatty acids (VFAs), total ammonia and chemical oxygen demand by 55 %, 41 % and 61 %, respectively. The buffer system formed by the combination of NH4+ and VFAs of C2-C5 was also enhanced, thereby improving the stability of the system. The addition of biochar effectively increased the relative abundance of Bacteroidetes, Chloroflexi, Spirochaetota and Synergistota, and enhanced three methanogenic metabolic pathways. This study provides scientific support for the application of biochar to solve the system inhibition in mixed substrate semi-continuous AcoD process and provides technical support for the stable operation of biogas project.

Anaerobic Co-Digestion of Pig Manure and Rice Straw: Optimization of Process Parameters for Enhancing Biogas Production and System Stability.

The objective of this study was to optimize the process parameters of the anaerobic co-digestion of pig manure and rice straw to maximize methane production and system stability. In this study, batch experiments were conducted with different mixing ratios of pig manure and rice straw (1:0, 1:1, 1:5, 1:10, and 0:1), total solid concentrations (6%, 8%, 10%, 12%, and 14%), and inoculum accounts (5%, 10%, 15%, 20%, and 25%). The results show that a 1:5 mixing ratio of pig manure to rice straw, a 12% total solid content, and a 15% inoculum account yielded biogas up to 553.79 mL/g VS, which was a result of co-digestion increasing the cooperative index (CPI > 1). Likewise, the evolution of the pH and VFAs indicated that the co-digestion system was well-buffered and not easily inhibited by acidification or ammonia nitrogen. Moreover, the results of the Gompertz model's fitting showed that the cumulative methane production, delay period, effective methane production time, and methane production rate under optimal conditions were significantly superior compared to the other groups employed.

Methane Production Characteristics of an Anaerobic Co-Digestion of Pig Manure and Fermented Liquid Feed.

Methane production characteristics of anaerobic co-digestion of pig manure (PM) and fermented liquid feed (FLF) were investigated in a continuous digester under mesophilic conditions. The experiment followed three phases. PM alone was digested in phase I. In phases II and III, PM and FLF were mixed in a ratio of 95:5 and 90:10 (% v/v), respectively. The specific methane yields (SMYs) during phases I, II, and III were 238, 278, and 326.8 mLCH4·gVS−1-added, respectively. It was due to the effect of balancing the feedstock carbon-to-nitrogen ratio by adding FLF. This improvement can also be attributed to the readily biodegradable compounds in the FLF. The higher SMY obtained in this study showed a positive synergistic effect in the anaerobic co-digestion of PM and FLF. The results also indicate that adding the FLF positively affected and maintained a constant pH level, avoiding volatile fatty acid accumulation and ammonia inhibition in the anaerobic digestion (AD). Thus, this study provides valuable information regarding the usage of unused or wasted FLF as a co-substrate for the practical AD of PM. The production of fermented liquid additives such as FLF to improve the methane production from the AD of PM is a potential novel alternative to food waste recycling in Japan, besides compost and animal feeding.

Effectiveness of layered inoculation in solid-state anaerobic co-digestion of pig manure and corn straw: Focus on macro-, micro-, and genetic-levels

Layered inoculation can achieve rapid start-up and promote methanation performance of anaerobic digesters. Daily specific methane yield (SMY) rapidly increased to 2.93 mL/g VS/d during 0–13 days, and cumulative SMY reached 212 mL/g VS in the solid-state anaerobic co-digestion (SS-AcoD) of pig manure and corn straw. Data were collected at macro-, micro-, and genetic-levels of each substrate layer. The results showed that layered inoculation could improve volatile fatty acids utilization and prevent adverse effects of high total ammonium nitrogen concentrations. Layered inoculation accelerated hydrolysis, acidification, and methanogenesis of substrates, as evidenced by the efficient inoculation of Bacteroidetes, Anaerolineales, Methanosphaerula, and Methanothrix, which were primarily from inocula. The various stages of SS-AcoD were synergistically initiated during the first 13 days, and acetoclastic pathway was boosted. These results further explain why layered inoculation is an efficient method for improving methanation performance of SS-AcoD and achieving efficient utilization of organic solid waste.

Effectiveness of Layered Inoculation in Solid-State Anaerobic Co-Digestion of Pig Manure and Corn Straw: Focus on Macro-, Micro-, and Genetic-Levels

Effectiveness of Layered Inoculation in Solid-State Anaerobic Co-Digestion of Pig Manure and Corn Straw: Focus on Macro-, Micro-, and Genetic-Levels

Evaluations of biochar amendment on anaerobic co-digestion of pig manure and sewage sludge: waste-to-methane conversion, microbial community, and antibiotic resistance genes

Effects of biochar on co-digestion of pig manure and dewatered sewage sludge under different total solids (TS) were investigated. Biochar could accelerate the start-up of methanogenesis and shorten the adaptation phase. At TS5%, the methane daily production in biochar group was 60.6% higher than the control; nevertheless, when TS increased, the gap between two groups gradually narrowed. Additionally, the change on antibiotics resistance genes (ARGs) was also affected by TS and the biochar addition. Moreover, biochar was beneficial to reduce ARGs in liquid phase. At TS14%, the total ARGs abundance in the liquid phase of biochar group was 41.4% lower than the control, among which the reduction rates of etB(P), sul1, rpoB2, macA, mupA and mupB were more prominent. These findings could provide useful guidance for developing ARGs elimination strategy before their release into the environment.

Stimulatory effects of biochar addition on dry anaerobic co-digestion of pig manure and food waste under mesophilic conditions.

The stimulatory effect of biochar addition on dry anaerobic digestion (AD) has been rarely investigated. In this study, the effects of commonly used biochars (bamboo, rice husk, and pecan shell) on dry co-AD were investigated using mesophilic batch digesters fed with pig manure and food waste as substrates. The results show that the specific methane yield was mildly elevated with the addition of biochars by 7.9%, 9.4%, and 12.0% for bamboo, rice husk, and pecan shell-derived biochar additions, respectively. Biochar did facilitate the degradation of poorly biodegradable organics. In comparison, there was no significant effect on the peak methane production rate by the supplementation of the selected biochars. Among the three mechanisms of enhancing methanogenesis by biochar (buffering, providing supporting surface, and enhancing electron transfer), the first two mechanisms did not function significantly in dry co-AD, while the third mechanism (i.e., enhancing electron transfer) might play an important part in dry AD process. It is recommended that the utilization of biochar for the enhancement of biomethanation in dry AD should be more focused on mono digestion in future studies.

Comparison of anaerobic co-digestion of pig manure and sludge at different mixing ratios at thermophilic and mesophilic temperatures

The objective of this study is to assess the effects of the mixing ratio on the methane production and digestate dewaterability of co-digestion of pig manure (P) and sludge (S). Batch experiments were carried out at five different P/S mixing ratios at mesophilic and thermophilic temperatures. Compared to sludge anaerobic digestion, co-digestion of pig manure with sludge increased methane yield 83.0%-136.5% at mesophilic temperature and 31.3%-68.0% at thermophilic temperature. The normalized capillary suction time (NCST) and total solids (TS) of sediment (centrifugal dewatering) increased when pig manure proportion of substrate increased. The NCST at thermophilic temperatures (4.87–17.58 s g−1-TSS) was higher than that at mesophilic temperatures (1.89–10.95 s g−1-TSS). However, the TS of sediment was close at thermophilic and mesophilic temperatures. The results indicated that anaerobic co-digestion of pig manure and sludge at a proper mixing ratio (P/S = 2:1) provides a good choice for energy recovery and land utilization.

Filamentous microalgae as an advantageous co-substrate for enhanced methane production and digestate dewaterability in anaerobic co-digestion of pig manure

This study aimed at exploring filamentous microalgae (Tribonema sp.) as an advantageous co-substrate for anaerobic digestion (AD) of pig manure. Its impacts on the AD performance were assessed in terms of methane yield, energy conversion efficiency, digestion kinetics, and digestate dewaterability. The microalgae substantially improved methane yield, AD kinetics, and digestate dewaterability of the AD process. The enhancement in methane yield ranged from 2 to 27.4%, with the maximum enhancement (corresponding to an energy conversion efficiency of 81%) occurring at a mixing ratio of 1:1 (VS basis). The AD kinetics was improved as indicated by the increased hydrolysis rate constants and diminished lag time. The specific resistance to filtration (SRF) of the digestate decreased significantly with the increasing proportion of the microalgae in the co-substrates, which would facilitate digestate processing and valorisation. Subsequently, the high biomass productivity of the microalgae (441 mg/L/d) in liquid digestate would enable sustainable bioenergy production through nutrient recycling.

Multiple Substrates Anaerobic Co-Digestion: A Farm-Scale Biogas Project and the GHG Emission Reduction Assessment

UGlobal warming has become an increasingly inconvenient situation, indicating the importance of reducing greenhouse gas (GHG) emissions. Anaerobic co-digestion of multiple substrates is an effective way to utilize wastes and reduce GHG emissions. In this study, batch anaerobic co-digestion of pig manure, corn straw, and fruit and vegetable wastes (FVW) was performed in a laboratory and extended to a farm-scale biogas project. Laboratory test results showed a specific biogas yield of 420.18 mL/g VS when the ratio of pig manure, corn straw, and FVW was 100:20:1 (TS). A farm-scale biogas project was improved on the basis of laboratory studies, and an average specific volumetric biogas production rate of 1.22 m3/m3 d was obtained. For GHG emission reduction assessment, the open anaerobic pond of pig manure, solid waste disposal site of FVW, and uncontrolled burning of corn straw were used as baselines, obtaining a total GHG emission reduction of 303.08 t CO2 annually. The farm-scale biogas project could treat corn straw, pig manure, and fruits and vegetable wastes, achieving considerable environmental benefits.

Impact of total solids content on anaerobic co-digestion of pig manure and food waste: Insights into shifting of the methanogenic pathway

Dry anaerobic digestion (AD) has advantages over wet AD in treating high-solid organic wastes like livestock and food wastes, but an elevated total solids (TS) content would affect the AD performances. In this study, methane production of digesters co-digesting pig manure (PM) and food waste (FW) at different TS contents (R1, TS 5%; R2, TS 10%; R3, TS 15%; and R4, TS 20%) was assessed. The results showed the specific methane yield had no significant difference with the increase of TS contents from 5% to 15% (278.8–291.7 NmL/g VSadded), while it was reduced at a 20% TS content (259.8 NmL/g VSadded). Two peaks of total volatile fatty acids and daily methane production were observed in the high-solid digesters (R2-R4), while only one peak occurred in wet AD (R1). A new kinetics model was developed to describe the two-peak methane production behavior at high TS contents. The analysis on the microbial community structure clearly showed the different evolutions of methanogenic pathways in low and high solids content systems. In dry AD (R4), there was a general shifting from the acetoclastic pathway, to mixotrophic pathway and hydrogenotrophic pathway, with the dominance of mixotrophic and hydrogenotrophic methanogens.

Synergistic effect and supernatant nitrogen reduction from anaerobic co-digestion of sewage sludge and pig manure

The degradation kinetics of anaerobic co-digestion of pig manure (PM) and sewage sludge (SS) were investigated for a utility that has concerns on nitrogen in the digestate return stream. In this study, batch-scale anaerobic reactors were set up with SS/PM volatile solids (VS) ratios at 7:1, 14:1, 21:1, and mono-digestions of SS and PM. PM (239 mL/g VSadded) produced more methane than SS (182 mL/g VSadded). As a result, increasing PM in co-digestion also increased methane yield. Kinetic models indicated synergistic effects by co-digestion with a faster degradation rate, an increased cumulative methane yield, and a shortened digestion time. Despite total nitrogen increased in digestate, the total nitrogen in co-digestion supernatant was lowered, which interprets to a nominal impact to the mainstream treatment with the additional PM loading. Nitrogen content in dewatered biosolids is expected to increase between 39.5%–53.5% thus benefiting land application.

High-solid anaerobic co-digestion of pig manure with lignite promotes methane production

High-solid anaerobic digestion is a common practice to treat organic wastes, but its efficiency of methane production is poor. In this study, the effect of high-solid anaerobic co-digestion (HS-AcoD) of pig manure with lignite (0%–64% based on total solid) on methane production at 37 °C was investigated. The results showed that pH, alkalinity, total ammonia nitrogen, and free ammonia decreased with the increasing ratios of lignite addition during HS-AcoD. After HS-AcoD for 30 days, the highest cumulative methane yield of 175.90 mL g−1 volatile solid was obtained for the treatment with 2% lignite addition, which was 9.26% higher compared with the control treatment without lignite addition (CK). However, the highest cumulative methane yield (the 8% lignite addition treatment) was 36.51% higher than CK after HS-AcoD for 12 days. The modified Gompertz model was fitted well to the methane production (R2 ≥ 0.9863). The synergistic effects of HS-AcoD with lignite ranged from 8.84 to 14.58% when lignite addition accounted for 2–50%. Structural equation models indicated that lignite mainly represented the indirect effect on cumulative methane yield by impacting C/N, pH and total ammonia nitrogen during HS-AcoD. High-throughput sequencing demonstrated that HS-AcoD of pig manure with lignite highly enhanced the relative abundance of Methanosaeta for methanogenesis. Overall, the results suggested that lignite addition could enhance the methanogenes’ activities and improve the methane production during HS-AcoD of pig manure with lignite.

Fate of antibiotic resistance genes during high-solid anaerobic co-digestion of pig manure with lignite

Lignite could be used to promote methane production during high-solid anaerobic co-digestion (HS-AcoD) of pig manure, however, the effects of lignite amendment on the fate of ARGs during HS-AcoD are unknown. Here, we explored the influence of lignite (0%, 8%, 16%, 32%, and 64%) on the fate of ARGs during HS-AcoD of pig manure. The results showed that 16% lignite reduced the absolute abundance of ARGs by 28.71% compared with the 0% lignite treatment. Variation partitioning analysis suggested the combined effect of microbial community, mobile genetic elements (MGEs) and environmental factors was the major driver shaping the pattern of ARGs. The potential hosts of ARGs were Bifidobacterium, Lactobacillus, Tissierella and Streptococcus. Structural equation models analysis suggested lignite indirectly impacted the pattern of ARGs by significantly reducing the abundance of microbial community and MGEs. These findings give an insight into the mechanistic understanding of the lignite influence on the reduction of ARGs during HS-AcoD.

Anaerobic Co-digestion of Pig Manure and Spent Coffee Grounds for Enhanced Biogas Production

The selection of appropriate co-substrates is very important to the feasibility of an anaerobic co-digestion process. A proper choice of co-substrate compositions leads to system balance and increased methane generation. Spent coffee grounds (SCG) are an unexploited material produced in large quantities which seems suitable for anaerobic digestion. During this study SCG were tested for biogas production in both batch and continuous reactors. Specifically, the biochemical methane potential of SCG was calculated in serum bottle test reactors at two different inoculum to substrate ratios (ISRs). In addition, co-digestion of SCG with liquid pig manure as co-substrate was monitored in a pilot scale continuously stirred tank reactor. Maximum methane production was similar at both ISRs, indicating no inhibition effects. Moreover, results from continuous experiments show that the methane production rate increased significantly after the addition of SCG to the digester. The reactor treating the liquid pig manure produced approximately 0.12 Lbiogas/Lreactor/d before the addition of SCG and 1.4 Lbiogas/Lreactor/d after the addition. The average removal of dissolved chemical oxygen demand increased from 20 to 40% after the addition of SCG. The concept of co-digestion could be a promising perspective for anaerobic digestion units as it increases methane production significantly.

Characterization of microbial community dynamics during the anaerobic co-digestion of thermally pre-treated slaughterhouse wastes with glycerin addition.

Microbial community dynamics during the anaerobic co-digestion of pig manure, pasteurized slaughterhouse waste and glycerin were studied in a lab-scale CSTR. The feed composition was optimized through progressive co-substrate additions for enhanced methane production and organic matter removal without accumulation of intermediate compounds. Microbial community structure of biomass samples was studied by means of qPCR and DGGE profiling of 16S rRNA genes (Bacteria and Archaea), and genus-specific qPCR of the methyl coenzyme M reductase gene (mcrA), which encodes for an enzyme universally involved in methanogenesis. The composition of the dominant bacterial populations remained relatively stable, when compared to those in the influent, but the highest changes were observed upon the introduction of glycerin. Biodiversity of archaea was restricted to a few representatives of the genera Methanosaeta and Methanosarcina, but Methanospirillum sp. was detected only when glycerin was introduced in the feeding. Glycerin supplementation coincided with the strongest increase in methane yield (from 0.22 to 0.64m3CH4m-3d-1).

Anaerobic co-digestion of pig manure and food waste; effects on digestate biosafety, dewaterability, and microbial community dynamics

This study assessed the effect of varying pig manure (PM)/food waste (FW) mixing ratio and hydraulic retention time (HRT) on methane yields, digestate dewaterability, enteric indicator bacteria and microbial communities during anaerobic co-digestion. Three 10 L digesters were operated at 39 °C, each with a PM/FW feedstock composition of 85%/15%, 63%/37% and 40%/60% (volatile solids basis). While the PM/FW ratio was different among reactors, the organic loading rate applied was equal, and increased stepwise with reducing HRT. The effects of three different HRTs were studied: 41, 29, and 21 days. Increasing the proportion of FW in the feedstock significantly increased methane yields, but had no significant effect on counts of enteric indicator bacteria in the digestate or specific resistance to filtration, suggesting that varying the PM/FW feedstock composition at the mixing ratios studied should not have major consequences for digestate disposal. Decreasing HRT significantly increased volumetric methane yields, increased digestate volatile solids concentrations and increased the proportion of particles >500 µm in the digestate, indicating that decreasing HRT to 21 days reduced methane conversion efficiency High throughput 16S rRNA sequencing data revealed that microbial communities were just slightly affected by changes in digester operating conditions. These results would provide information useful when optimizing the start-up and operation of biogas plants treating these substrates.

Effect of magnetite powder on anaerobic co-digestion of pig manure and wheat straw

This study investigated the effects of different amounts of magnetite powder (i.e., 0g, 1.5g, 3g, 4.5g, 6g) on the anaerobic co-digestion of pig manure (PM) and wheat straw (WS). The variations in pH, alkalinity, cellulase activity (CEA), dehydrogenase activity (DHA) and methane production, were analyzed by phases. Correlation of the activities of the two enzymes with methane production was also analyzed, and the Gompertz model was used to evaluate the efficiency of anaerobic digestion (AD) with the addition of magnetite powder. The results showed that magnetite powder had significant effects on the anaerobic co-digestion of PM and WS. The maximum total methane production with the addition of 3g of magnetite powder was 195mL/g total solids (TS), an increase of 72.1%. The CEA and DHA increased with magnetite powder in the ranges of 1.5–4.5g, 1.5–6g, respectively, while the methane production showed a better correlation with DHA than with CEA. Using the Gompertz model, the efficiency of AD was optimal when adding 3g magnetite powder, with higher methane production potential (206mL/g TS), shorter lag-phase time (14.9d) and shorter AD period (44d).

Anaerobic Co-digestion of Pig Manure with Dried Maize Straw

The anaerobic co-digestion of pig manure (PM) with dried maize straw (DMS) was studied at 35 °C with a volatile solid (VS) ratio (VSPM/VSDMS) of 1:2 in a continuously stirred tank reactor, and the digestions of mono-PM and mono-DMS were evaluated under the same conditions. The organic loading rates (OLRs) of 2, 3, and 4 g VS/L/d were studied and found to correspond to hydraulic retention times (HRTs) of 60, 40, and 30 d, respectively. Under the condition of long HRT and low OLR, PM could be degraded completely. The co-digestion of PM with DMS showed the most stable performance in TAN, whereas TAN in mono-PM increased with the increase of OLR. The specific methane yield (SMY) did not have a linear correlation with OLR, since HRT changed with different OLR. The maximum average SMY in the co-digestion reactor was 272 mL/g VS-fed at an OLR of 3 g VS/L/d and an HRT of 40 d. The SMY in mono-DMS digestion was the lowest and it decreased with the increase of OLR.