Co-substrate For Anaerobic Digestion Research Articles

In-situ biomethanation of high CO content syngas in agricultural biogas digesters

To meet global energy demands, syngas with high CO content (>50 %) generated from hydrothermal gasification of agricultural residues or wood, could be utilized as a co-substrate in anaerobic digestion (AD) processes for conversion into CH4. This study investigated in-situ biomethanation using synthetic gas (55 % CO, 35 % H2, and 15 % CO2), mimicking wood gasification syngas, during AD of cow manure, the most abundant agricultural waste. A continuously stirred tank reactor (CSTR) served as a control and was fed only cow manure, while the other two reactors were fed syngas with or without gas recirculation at different gas loading rates (GLRs).In-situ syngas injection in AD of cow manure at GLRs ≤0.3 L LRV−1 d−1 improved overall CH4 productivity compared to the control (0.35 ± 0.1 vs. 0.29 ± 0.1 L LRV−1 d−1), though the CH4 content (45 ± 5 %) was lower than the control reactor (62 ± 3 %), indicating a need for biogas upgrading. Gas recirculation enabled higher CO and H2 conversion efficiencies of 99–100 % but considerably decreased CH4 productivity from cow manure. In-situ biomethanation enhanced the relative abundance of hydrogenotrophic methanogens, highlighting their role in syngas conversion to CH4.

Agricultural Plant Residues as Potential Co-Substrates for Biogas Production

Plant biomass can be used in many directions for bioenergy production. Biogas can be produced from a most diverse group of substrates compared to liquid or solid biofuels. The choice of substrates and technologies is crucial because it will allow getting the expected results. Not without significance is also the price and availability of substrates. Therefore, waste and residues are increasingly being used. Accordingly, the aim of the review was to analyze the potential of biogas production from agricultural plant residues and the effectiveness of using this feedstock as a co-substrate in anaerobic digestion. In this article, selected agricultural plant residues are collected, and their advantages and disadvantages as substrates for biogas production are described. Moreover, the effective technology of biogas production by anaerobic digestion on an industrial scale and calculations to obtain biogas and methane efficiency of the substrates are also included. In addition, the summarized biogas efficiency of selected plant agricultural waste under mesophilic conditions studied by many researchers is shown. On the basis of the analyzed results of this research, it can be concluded that agricultural plant residues have great potential as co-substrates for biogas production. It is important to experimentally determine both the biogas and the methane efficiency of the substrate, representing a potential raw material for the production of gaseous biofuels. The use of artificial neural networks in the prediction of biogas emission is future-proof and should facilitate the management of biogas plants. The use of waste from the cultivation and processing of plant raw materials will not only help to manage this waste rationally, but also contribute to the increase in production of renewable energy sources. Accordingly, the circular economy in terms of the management of agricultural plant residues to produce biogas will have a multi-faceted, positive impact on the environment. On the basis of this review, it can be concluded that numerous agricultural plant residues can be used as potential co-substrates for biogas production.

Promoting the overall energy profit through using the liquid hydrolysate during microwave hydrothermal pretreatment of wheat straw as co-substrate for anaerobic digestion.

Liquid hydrolysate (LH) derived from the microwave hydrothermal pretreatment (MHP) of wheat straw (WS) was anaerobically digested together with the solid residual to promote the overall energy profit. Different MHP temperatures (90, 120, 150, 180 °C) and retention times (10, 20, 40 min) were investigated. Increased MHP intensity generated plenty of VFAs (mainly acetate) and phenols in the LH, implying the double-side effect of LH on AD. The highest methane production of 227.92 mL CH4·gVS-1 Raw was obtained with MHP at 120 °C for 10 min, 21.53 % higher than the control. While, MHP at 180 °C for 40 min exhibited 29.02 % lower methane production (113.13 mL CH4·gVS-1 Raw) and 115.86 % longer lag phase (3.13 days) than the control. Butyrate fermentation endowed the treatment groups of 180 °C with resilience from the overload and inhibition. Methanosarcina was largely enriched by the abundant acetate in LH on the early stage of anaerobic digestion (AD), especially when with high MHP intensity. Increased abundance of Methanosaeta and Methanobacterium played a crucial role in maintaining methane production at the middle and later stage. The high number of species and evenness in methanogens community were beneficial for the startup of batch AD. Although negative net energy was obtained, the lower ratio of energy input and output compared with the most researches using the solid residual after MHP as the sole substrate for AD demonstrated the contribution of LH to the overall energy profit.

Availability and Co-Substrate Potential of Typha latifolia for Biogas Production in Funtua, Katsina State, Nigeria

In order to reduce global warming through fossil fuel utilization, biogas production from biodegradable biomass seems a sustainable alternative. This study evaluated the availability and co-substrate potential of T. latifolia for biogas production in Funtua, Katsina State Nigeria. A purposive sampling technique was used in selecting the wards that were used for this study. A 1204 metres transect was used for 32 quadrats; 19 of these were laid on the 953m contiguous land area at intervals of 50m; 9 quadrats covered 450m, 5 quadrats were on 250m, 3 on 153m, and 2 on 100m. The remaining 13 transects were laid on the 251m un-contiguous patches. Coordinates of various potentials sites were recorded using Global positioning system. There were an average of 27 T. latifolia stands per m2. A total of 32,388 of T. latifolia stands were recorded in the study area; Dukke ward (23,968), Makera (8,205) and Maska 216. T. latifolia is available in lqrge quantities, and a potential co substrate in anaerobic digestion for biogas production in Funtua. It is recommended that the study should be replicated in time later to establish a trend of the T. latifolia species in terms of population.

Enhancement of biogas production from cattle manure using glycerine phase as a co-substrate in anaerobic digestion

This study investigated the effect of glycerine phase on the anaerobic digestion of cattle manure under mesophilic conditions. The process was carried out in semi-continuous stirred tank reactors at a constant organic loading rate of 2.3 g VS/L·d and a hydraulic retention time of 30 days. It was found that the addition of 10% (as volatile solids) glycerine phase to cattle manure produced 3.1-times more biogas than cattle manure alone (237.5 L vs. 76.4 L) and a 10% higher methane content (69% vs. 59%). Biogas formation during co-digestion was strongly correlated with the concentrations of ammonium nitrogen (r = 0.89, p < 0.05) and volatile fatty acids (r = −0.71, p < 0.05), which resulted in a decrease in biogas production over time despite a stable pH value. The proposed use of glycerine phase could provide an advanced anaerobic digestion system that is technologically simple, has a positive energy balance, and produces upgraded biogas, although additional monitoring of the concentration of volatile acids and ammonium nitrogen is needed to maintain stable biogas production. These findings will be useful for reducing demand for non-renewable energy resources, and more broadly, they will assist in the shift from a traditional economy to a circular bioeconomy.

Determination of large microplastics: wet-sieving of dewatered digested sludge, co-substrates, and compost.

Dewatered digested sludge and compost may act as a conduit for microplastics (<5 mm) in terrestrial and subsequently aquatic systems. However, standardized methods for microplastics analyses are lacking. Thus, the aim is to demonstrate the applicability of wet-sieving as a way to quantify large microplastic particles (MPP, 1-5 mm) in dewatered digested sludge and compost. Additionally, we investigated the organic fraction of municipal solid waste, expired drinks and slaughterhouse waste used as co-substrate for anaerobic digestion at wastewater treatment plants (WWTP). Therefore, we collected samples from six WWTP and two biogas plants. These were then wet-sieved and potential MPP analysed via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). In dewatered digested sludge the amount of microplastics ranged from 0 to 326 MPP/kg TS (total solids) while compost contained 39-102 MPP/kg TS. Our results show that with 0-36 MPP/kg TS co-substrates are not necessarily a source of microplastics in WWTP. Furthermore, we found film to be the most abundant shape in the biogas plant samples, whereas, in WWTP samples film, fragments and fibers were detected the most. ATR-FTIR revealed that polyvinyl chloride, polyester, polypropylene, and polyethylene were the most abundant materials found across all samples.

Continuous Anaerobic Co-Digestion of Biowaste with Crude Glycerol under Mesophilic Conditions

A persistent topic of the anaerobic digestion of biowaste is the efficient use of co-substrates. According to Renewable Energy Sources Act the co-substrate input is limited to 10 percent of the average daily substrate feed in Germany. In this concern, the primary focus of this paper is to understand the suitability of crude glycerol in anaerobic digestion of biowaste. Two identical lab-scale anaerobic digester units were added with crude glycerol, and each unit was equipped with four identical fermenters. Unit A was fed with an average organic loading rate of 4.5 kg VS m−3 d−1, and the average organic loading rate of unit B was set at 5.5 kg VS m−3 d−1. The share of crude glycerol in the total feed was 0.77 percent of the fresh matter. The abort criterion is a ratio of the volatile organic acids and buffer capacity (FOS/TAC) in the fermenter above 1.2. The abort criterion was reached after 16 days. In summary, the results lead us to the conclusion crude glycerol is not suitable as a co-substrate for anaerobic digestion for several reasons.

Anaerobic co-digestion of municipal waste sludge with grease trap waste mixture: Point of process failure determination

Using high-strength wastes, such as grease trap waste mixture (GTWM) from multiple commercial facilities, as a co-substrate in anaerobic digestion can contribute to a significant increase in methane production. However, challenges such as long chain fatty acids (LCFAs) accumulation, sludge flotation, washout and scum formation can lead to digester failure. In this study, the optimal operating condition to achieve the highest methane production from an anaerobic, semi-continuous flow, mesophilic co-digester at a solids retention time of 20 days was determined. The ratio of GTWM/sludge was increased based on volatile solids (VS) concentration from 10% to 50% in 10% increments. A 40% GTWM/sludge ratio was determined to be optimum in which up to 22%, 200% and 68% improvements in VS removal, daily biogas production and specific methane production, respectively, were observed with respect to control utilizing sludge only. Beyond a 40% GTWM/sludge, the anaerobic co-digester experienced failure and addition of biochar to mitigate LCFA inhibition to failing co-digester could not recover the process. Digester LCFA concentrations were also measured during stable and unstable digester operations.

Combined simultaneous enzymatic saccharification and comminution (SESC) and anaerobic digestion for sustainable biomethane generation from wood lignocellulose and the biochemical characterization of residual sludge solid

Simultaneous enzymatic saccharification and comminution (SESC) was used for large-scale anaerobic digestion of wood lignocellulose to generate methane and unmodified lignin. During SESC, 10% aqueous mixture of powdered debarked wood from various species was subjected to bead milling with hydrolytic enzymes to generate particles below 1 μm. This slurry was directly used as a cosubstrate for anaerobic digestion in a 500 L stirred-tank reactor. Temperature and hydraulic retention time (HRT) were maintained at 50 °C and 30 days, respectively. At stable operation periods, an average yield of 224 L of methane per kg of cedar was attained. Comparable yields were achieved with red pine, elm, oak, and cedar bark. High-throughput microbial analysis established the presence of a relevant community to support the elevated level of methane production. The stability of the unmodified lignin in anaerobic digestion was also confirmed, allowing for its recovery as an important by-product.

Food waste co-digestion in Germany and the United States: From lab to full-scale systems

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 CH4 potential (477–499 mLCH4/gVS) than maize and grass silage (368 and 331 mLCH4/gVS) and solid and liquid manure (243 and 91 mLCH4/gVS). Methane production in the full-scale DE system with 66% FW (by volume) was 882 m3CH4/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 CH4 potential (264–553 mLCH4/gVS), but due to the lack of heating in the full-scale system, 62% less CH4 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.

Viability of Using Glycerin as a Co-substrate in Anaerobic Digestion of Sugarcane Stillage (Vinasse): Effect of Diversified Operational Strategies

Vinasse, from sugar and ethanol production, stands out as one of the most problematic agroindustry wastes due to its high chemical oxygen demand, large production volume, and recalcitrant compounds. Therefore, the viability of using glycerin as a co-substrate in vinasse anaerobic digestion was tested, to increase process efficiency and biogas productivity. The effect of feeding strategy, influent concentration, cycle length, and temperature were assessed to optimize methane production. Glycerin (1.53% v/v) proved to be a good co-substrate since it increased the overall methane production in co-digestion assays. CH4 productivity enhanced exponentially as influent concentration increased, but when temperature was increased to 35°C, biogas production was impaired. The highest methane productivity and yield were achieved using fed-batch mode, at 30°C and at an organic loading rate of 10.1kgCODm-3day-1: 139.32molCH4m-3day-1, 13.86molCH4kgCODapplied, and 15.30molCH4kgCODremoved. Methane was predominantly produced through the hydrogenotrophic route. In order to treat all the vinasse produced by a mid-size sugar and ethanol plant, nine reactors with 7263.4m3 each would be needed. The energy generated by burning the biogas in boilers would reach approximately 92,000MWh per season and could save up to US$ 240,000.00 per month in diesel oil demand.

Ampelodesmos mauritanicus pyrolysis biochar in anaerobic digestion process: Evaluation of the biogas yield

The integration of different conversion technologies can strongly contribute to the biomass potential exploitation. To this aim, the use of intermediate pyrolysis biochar is analyzed in this paper as an alternative co-substrate in anaerobic digestion. The specie Ampelodesmos mauritanicus has been specifically chosen in this case for its capacity to tolerate, accumulate and, in some cases, degrade organic and inorganic pollutants. The biochar, produced under intermediate pyrolysis conditions at 450 °C, 500 °C and 550 °C, has been here considered for a biomethane potential assessment. The intermediate pyrolysis process improves the herbaceous bioavailability and promotes the microbial activity by reducing the digestion lag phase. Three reactors, namely B450, B500 and B550, have been considered in this study. Acclimatized cow manure from food wastes digestion has been used as inoculum with 5 g of biochar. The reactors have been continuously monitored for 15 days keeping the temperature fixed at 37 °C. Excluding the inoculum contribution, an accumulated methane production of 465–540.4 ml CH4/g-VS has been measured with an LHV evaluated in the range 25.8–26.9 MJ/kg. The modified Gompertz equation has been then used to describe the influence of biochar production temperature on methane conversion. A lag phase of 1.8, 2.2 and 3.8 days respectively for B450, B500 and B550, has been estimated showing an inverse proportionality to the biochar production temperature. The biomass to biogas energy conversion analysis reveals a reduction in the efficiency with the biochar production temperature increase. This fact is attributed to the steep reduction in volatile solids occurring by increasing the pyrolysis process severity. As a whole, the paper present a novel approach to possibly combine phytoremediation and production of renewable energy by using Ampelodesmos mauritanicus.

Olive Mill Industrial Waste as Co-substrate in Anaerobic Digestion with Aim at its Energetic Exploitation

The aim of this paper is to assess the feasibility of the co-digestion of olive mill industrial waste with urban sewage sludge from wastewater treatment plants (WWTP). These wastes include olive mill solid waste (OMSW) and olive mill effluent (OME). This co-digestion process enables the energetic exploitation of OMSW and/or OME and introduces an environmental solution for their highly pollutant compounds. The behaviour of both co-substrates was studied using biochemical methane potential assays. To determine the optimal proportions of each co-substrate, different quantities of OME and OMSW were added to a constant quantity of substrate (urban sewage sludge) and put to test. A small amount of digested sludge from WWTP was used as an inoculum to accelerate the pace of the reactions. Thus, the optimal proportions between substrate and co-substrate were defined. The samples containing OMSW showed a biodegradability around 23%, slightly above that of the substrate on its own (21.3%). Moreover, biogas production in samples containing OMSW was significantly superior to samples containing substrate only. Nevertheless, the samples containing OME as a co-substrate presented an inferior biodegradability (20.3%) to that of the substrate on its own. Similarly, biogas production in OME co-digestion remained within the usual values of urban sewage sludge biogas production. In all cases, the system remained stable and the energetic efficiency of the process was improved in comparison to the digestion of substrate only. Therefore, co-digestion with urban sewage sludge proves to be a cost-effective method for OMSW and OME environmental management.

Anaerobic co-digestion of different wastes in a UASB reactor

Anaerobic co-digestion has made a greater impact on the biogas production from mixing different type of waste. In this research, sewage sludge (SS) and cow manure (CM), was used as a primary waste along with kitchen waste (KW), yard waste (YW), floral waste (FW) and dairy wastewater (DWW) as co-substrate for anaerobic digestion. Mixtures with a ratio of 1:2 ratio is fed into a single stage up-flow anaerobic sludge blanket (UASB) reactor. Digestion was carried out in a mesophilic temperature range for 20 days. pH and VFA were measured and ranged from 5 to 7.5 and 3500–500 mg/L, respectively, for all the mixtures throughout the digestion period. Percentage of COD removal efficiency after 20 days was found to be in the range of 76–86%. The maximum biogas production rate was found to be 4500 mL/day. Characterization of the final residue from each of the digesters was carried out by Scanning Electron microscope, Energy dispersive, thermogravimetric, FTIR Spectra, and Atomic microscope. Thermal analysis reveals that spent sludge can be potential waste energy sources.

Co-digestion of chicken manure and microalgae Chlorella 1067 grown in the recycled digestate: Nutrients reuse and biogas enhancement

The present investigation targeted on a sustainable co-digestion system: microalgae Chlorella 1067 (Ch. 1067) was cultivated in chicken manure (CM) based digestate and then algae biomass was used as co-substrate for anaerobic digestion with CM. About 91% of the total nitrogen and 86% of the soluble organics in the digestate were recycled after the microalgae cultivation. The methane potential of co-digestion was evaluated by varying CM to Ch. 1067 ratios (0:10, 2:8, 4:6, 6:4, 8:2, 10:0 based on the volatile solids (VS)). All the co-digestion trials showed higher methane production than the calculated values, indicating synergy between the two substrates. Modified Gompertz model showed that co-digestion had more effective methane production rate and shorter lag phase. Co-digestion (8:2) achieved the highest methane production of 238.71mL⋅(g VS)−1 and the most significant synergistic effect. The co-digestion (e.g. 8:2) presented higher and balanced content of dominant acidogenic bacteria (Firmicutes, Bacteroidetes, Proteobacterias and Spirochaetae). In addition, the archaea community Methanosaeta presented higher content than Methanosarcina, which accounted for the higher methane production. These findings indicated that the system could provide a practicable strategy for effectively recycling digestate and enhancing biogas production simultaneously.

The potential of surplus grass production as co-substrate for anaerobic digestion: A case study in the Region of Southern Denmark

AbstractThis paper presents an assessment of the surplus grass production in the Region of Southern Denmark, and the perspectives of utilizing it in local biogas production. Grass production represents a significant role in the Danish agricultural sector. However, statistical data show an excess production of averagely 12% in the period 2006–2012. Based on spatial analyses and statistical data, the geographical distribution of grass production and consumption was estimated and mapped for the Region of Southern Denmark. An excess production of grass was estimated for several of the municipalities in the Region of Southern Denmark, but the excess production was found to be quite sensitive to the management practice of the grass fields and the productivity of the grass. The yields of excess grass estimated in the sensitive and conservative scenario were found to be sufficient to serve a sole co-substrate in 2–8 biogas plants using animal manure as primary feedstock. The yields in the intensive scenario were assessed to be sufficient to serve a sole co-substrate in 8–16 biogas plants. Alternatively, at least 31% of the regionally produced maize which is exported to the biogas sector could annually be substituted by methane produced from the production of excess grass. The intensive scenario was estimated to have significantly higher grass yields than the sensitive and conservative scenario. The environmental impacts of intensified agricultural management should, however, be assessed carefully in order to ensure that the ecosystems are not increasingly being burdened. The potential of utilizing residual grass for energy production in the region or as an alternative to the maize exported to Northern Germany, was concluded to seem as a promising possibility for a sustainable development of the regional biogas sector. Furthermore, it could provide incentives for establishing new biogas plants in the region and thereby increase the share of manure being digested anaerobically, which could help extrapolate the environmental and climate related benefits documented for the use of digested animal manure as fertilizer on agricultural land.

Anaerobic digestion of crude glycerol: a review

Several researchers have used crude glycerol as a source of substrate for methane production and power generation, which is a way of adding value to this residue that has a high chemical oxygen demand (COD) and is rich in impurities. This review article summarizes recent data and discussions on the use of crude glycerol as substrate and co-substrate for anaerobic digestion. In general, the dilution of glycerol has been used to avoid problems of inhibition due to the presence of inorganic salts of chloride and sulphates, and due to accumulation of metabolites. However, other methods have been proposed, such as the use of halo-tolerant biomass. It can be concluded that the anaerobic digestion of crude glycerol is technically viable, and an anaerobic reactor treating 25 m3 per day of crude glycerol can produce 4.4 MW of thermal energy, which can be converted to 4.4 GW of heat or 1.2 GW of electricity.

The optimisation of food waste addition as a co-substrate in anaerobic digestion of sewage sludge.

Food waste has been regarded as the main source of various environmental pollution in Korea due to the high volatile solids (VS) and moisture content caused by the features of dietary habits. The feasibility of food waste as a co-substrate in anaerobic digestion of sewage sludge was investigated in mesophilic and thermophilic conditions using batch tests. Cumulative methane production, dissolved organic carbon (DOC) and volatile fatty acids (VFA) were monitored to find the optimal mixing ratios of food waste and sewage sludge for the enhanced performance of co-digestion. It was observed that adequately mixed food waste led to the enhanced methane production both at mesophilic and thermophilic conditions. However, a conventional linear regression conducted for the optimisation of co-substrate mixing ratios was not accurate in describing exact methane production trends of co-digestion because of the different biodegradability of substrates. Therefore, a remodified Gompertz equation showing nonlinear relationship between variables was developed to find exact information with the same experimental data obtained at 2g VS/l generally used in biochemical methane potential (BMP) tests. Based on an influential parameter, methane production rate (MPR), the optimal mixing ratios of food waste were 39.3% and 50.1% in mesophilic and thermophilic conditions, respectively. To confirm the application of the remodified Gompertz equation, secondary batch tests were conducted with the substrate concentrations of 1-4g VS/l. In overall range tested, the confident mixing ratios of food waste was adjusted to 30-40% and 40% in mesophilic and thermophilic conditions, respectively. The most significant factor for enhanced performance was the improved organic carbon content provided by additional food waste.