Prospect of anaerobic co-digestion of dairy manure: a review

Enhancing biogas generation from lignocellulosic biomass through biological pretreatment: Exploring the role of ruminant microbes and anaerobic fungi

Biogas production from Lignocellulosic Biomass (LB) via anaerobic digestion (AD) has gained attention for its potential in self-sustainability. However, the recalcitrance of LB cell walls pose a challenge to its degradability and biogas generation. Therefore, pretreatment of LB is necessary to enhance lignin removal and increase degradability. Among the different approaches, environmentally friendly biological pretreatment ispromising as it avoids the production of inhibitors. The ruminal microbial community, including anaerobic fungi, bacteria, and protozoa, has shown an ability to effectively degrade LB through biomechanical and microbial penetration of refractory cell structures. In this review, we provide an overview of ruminant microbes dominating LB's AD, their degradation mechanism, and the bioaugmentation of the rumen. We also explore the potential cultivation of anaerobic fungi from the rumen, their enzyme potential, and their role in AD. The rumen ecosystem, comprising both bacteria and fungi, plays a crucial role in enhancing AD. This comprehensive review delves into the intricacies of ruminant microorganisms' adhesion to plant cells, elucidates degradation mechanisms, and explores integrated pretreatment approaches for the effective utilization of LB, minimizing the impact of inhibitors. The discussion underscores the considerable potential of ruminant microbes in pretreating LB, paving the way for sustainable biogas production. Optimizing fungal colonization and ligninolytic enzyme production, such as manganese peroxidase and laccase, significantly enhances the efficiency of fungal pretreatment. Integrating anaerobic fungi through bioaugmentation during mainstream processing demonstrably increases methane production. This study opens promising avenues for further research and development of these microorganisms for bioenergy production.

Co-digestion of cow manure and food waste for biogas enhancement and nutrients revival in bio-circular economy

Anaerobic co-digestion (AcoD) with suitable substrate ratios may have the potential to improve biogas process and could play a better role in nutrient management for biocircular economy. The goal of this study was to enhance biogas yield from AcoD of cow manure (CM) and canteen food waste (CFW), and pertinent co-digestion of suitable substrate ratios for nutrient management i. e NPK from linear to biocircular economy, using ruminant intestinal fluid as a source of inoculum. A mesophilic (37 ± 1 °C) laboratory-scale AcoD with varying CFW/CM ratios of (0:1, 1:4, 2:3, 1:1, 3:2, 4:1, and 1:0) based on wet weight was performed. The AcoD systems of different CFW/CM ratios were evaluated with a loading rate of 400 g/L in the presence of 100 g cow intestinal fluid (CIF) inoculation. All experimental AcoD systems yielded greater biogas (147-300 cm3/g VS) than the mono-digestion in which only CM (135 cm3/g VS) and CFW (146 cm3/g VS) were digested anaerobically. The AcoD system of CFW/CM with 4:1 showed the highest biogas yield (300 cm3/g VS), and VS and COD reduction rate (39.51% and 65.15%, respectively), and nutrient contents (6.53%). Moreover, the experiment results were verified by modified Gompertz model. This work provided a window of opportunity to examine the anaerobic co-digestion technology beyond biogas production and to put the current low-cost technology to use for nutrient management and as a better component of the biocircular economy for agriculture in Pakistan in order to achieve sustainable development goals.

Hydrogen and Methane Production from Anaerobic Co-Digestion of Sorghum and Cow Manure: Effect of pH and Hydraulic Retention Time

The need for alternative energy sources is constantly growing worldwide, while the focus has shifted to the valorization of biomass. The aim of the present study was to determine the optimal pH and hydraulic retention time (HRT) values for treating a mixture of sorghum biomass solution with liquid cow manure (in a ratio 95:5 v/v) through anaerobic digestion, in a two-stage system. Batch tests were initially carried out for the investigation of the pH effect on bio-hydrogen and volatile fatty acids (VFA) production. The highest hydrogen yield of 0.92 mol H2/mol carbohydratesconsumed was obtained at pH 5.0, whereas the maximum degradation of carbohydrates and VFA productivity was observed at pH 6.0. Further investigation of the effect of HRT on hydrogen and methane production was carried out. The maximum yield of 1.68 mol H2/mol carbohydratesconsumed was observed at an HRT of 5 d, with H2 productivity of 0.13 L/LR·d. On the other hand, the highest CH4 production rate of 0.44 L/LR·d was achieved at an HRT of 25 d, with a methane yield of 295.3 mL/g VSadded, whereas at a reduced HRT of 20 d the process exhibited inhibition and/or overload, as indicated by an accumulation of VFAs and decline in CH4 productivity.

A comprehensive review on current status and future perspectives of microbial volatile fatty acids production as platform chemicals

Volatile fatty acids (VFA), the secondary metabolite of microbial fermentation, are used in a wide range of industries for production of commercially valuable chemicals. In this review, the fermentative production of VFAs by both pure as well mixed microbial cultures is highlighted along with the strategies for enhancing the VFA production through innovations in existing approaches. Role of conventionally applied tools for the optimization of operational parameters such as pH, temperature, retention time, organic loading rate, and headspace pressure has been discussed. Furthermore, a comparative assessment of above strategies on VFA production has been done with alternate developments such as co-fermentation, substrate pre-treatment, and in situ removal from fermented broth. The review also highlights the applications of different bioreactor geometries in the optimum production of VFAs and how metagenomic tools could provide a detailed insight into the microbial communities and their functional attributes that could be subjected to metabolic engineering for the efficient production of VFAs.

Effects of Mechanical Refining on Anaerobic Digestion of Dairy Manure

Mechanical refining (MR) is a cost-effective pretreatment in biochemical conversion processes that is employed to overcome biomass recalcitrance. This work studied the effects of MR on biogas and methane produced by the anaerobic digestion (AD) of dairy manure. The cumulative gas volume and yield from the AD of manure refined at 6k revolutions increased by 33.7 and 7.7% for methane and by 32.0 and 6.4% for biogas, respectively, compared to the unrefined manure. This enhancement was reached by increasing manure solubilization, reducing particle size, and achieving external fibrillation and internal delamination of fibers in manure. However, the highly refined manure (subjected to 60k revolutions) exhibited methane and biogas yields that were reduced by 9.5 and 1.5%, respectively. This decrease was observed because the pore structure was ruptured, and finely ground manure particles were aggregated together at high revolutions (60k), thereby inhibiting the release of organic matter from the manure. Therefore, this study indicates that the MR for pretreatment of dairy manure could have great potential for significantly enhancing AD of dairy manure. Further studies will include optimization of conditions of mechanical refining (i.e., mechanical intensity, process time), a continuous AD of dairy manure pretreated by the MR, and scale-up with cost evaluation.

Anaerobic co-digestion of acerola (Malphigia emarginata) agro-industry effluent with domestic sewage at mesophilic and thermophilic conditions

This study evaluated the effect of temperature on the anaerobic co-digestion of West Indian Cherry agro-industry effluent (EAV) and domestic sewage (EDT). The assays were performed in triplicates of reactor flasks using treatments with different mixture compositions (T1=5%EDT+95%EAV;T2=20%EDT+80%EAV;T3=30%EDT+70%EAV) and anaerobic sludge as inoculum (5g.L-1), at mesophilic (35°C) and thermophilic (55°C) temperatures. The analyses of soluble chemical oxygen demand (DQOs) and volatile fatty acids (AGV) were performed by determining the removal efficiency of the DQOs, the decay rate constant of the DQO (Kd), and the percentages of anaerobic biodegradability (%BD) and methanation (%M). The inoculum biomass of the treatments was observed through scanning electron microscopy at the end of the degradation process (12 days). Regardless of the temperature, the anaerobic digestion was considered efficient, with biodegradability above 60%. The mesophilic temperature favored the anaerobic co-digestion for all mixture compositions, presenting more diversified and structured biomass at the end of the assays, as well as higher removal efficiencies of the DQOs and methanization, especially for T3 at 35°C (63% and 51%, respectively). Furthermore, the kinetics of the degradation process proved to be more accelerated at mesophilic conditions (Kd 0.1d-1) and in the treatments with a higher percentage of sewage (T2M and T3M).

Treatment of Manure and Digestate Liquid Fractions Using Membranes: Opportunities and Challenges

Manure and digestate liquid fractions are nutrient-rich effluents that can be fractionated and concentrated using membranes. However, these membranes tend to foul due to organic matter, solids, colloids, and inorganic compounds including calcium, ammonium, sodium, sulfur, potassium, phosphorus, and magnesium contained in the feed. This review paper is intended as a theoretical and practical tool for the decision-making process during design of membrane-based systems aiming at processing manure liquid fractions. Firstly, this review paper gives an overview of the main physico-chemical characteristics of manure and digestates. Furthermore, solid-liquid separation technologies are described and the complexity of the physico-chemical variables affecting the separation process is discussed. The main factors influencing membrane fouling mechanisms, morphology and characteristics are described, as well as techniques covering membrane inspection and foulant analysis. Secondly, the effects of the feed characteristics, membrane operating conditions (pressure, cross-flow velocity, temperature), pH, flocculation-coagulation and membrane cleaning on fouling and membrane performance are presented. Finally, a summary of techniques for specific recovery of ammonia-nitrogen, phosphorus and removal of heavy metals for farm effluents is also presented.

In search of the optimal inoculum to substrate ratio during anaerobic co-digestion of spent coffee grounds and cow manure

The inoculum to substrate (I:S) ratio is a crucial operating parameter during the start-up period of anaerobic digestion (AD) processes and this ratio shows high differentiation with respect to substrate composition. While spent coffee grounds (SCG) have started to gain attraction in AD as a co-substrate due to their vast production and promising methane potential, there is still not enough information on the operative environment of SCG-based biogas reactors. This study investigated the optimal I:S ratio during anaerobic co-digestion of SCG and cow manure. Biochemical methane potential tests were conducted at mesophilic conditions and the influence of I:S ratio on methane production and digestion stability was evaluated at a wide range of I:S ratios from 0.5:1 to 4:1 (volatile solids (VS) basis). Methane yields increased gradually starting from the I:S ratio of 0.5:1 up to 3:1 and the highest methane yield (225 mlCH₄ gVS^-1) was achieved at the I:S ratio of 3:1. Comparatively lower methane yields were obtained at the ratios of 3.5:1 and 4:1. Instable AD conditions were established at the lowest I:S ratio examined (0.5:1), which caused volatile fatty acid (VFA) accumulation. The results highlighted that anaerobic co-digestion of SCG and cow manure is a promising approach, while the I:S ratio should be well-maintained due to the high potential risk of rapid and/or excess VFA production of these feedstocks.

Effect of Pasteurisation on Methane Yield from Food Waste and Other Substrates in Anaerobic Digestion

The effect of pasteurisation and co-pasteurisation on biochemical methane potential values in anaerobic digestion (AD) was studied. Pasteurisation prior to digestion in a biogas plant is a common hygienisation method for organic materials which contain or have been in contact with animal by-products. Tests were carried out on food waste, slaughterhouse waste, animal blood, cattle slurry, potato waste, card packaging and the organic fraction of municipal solid waste (OFMSW); pasteurisation at 70 °C for 1 h was applied. Pasteurisation had increased the methane yields of blood (+15%) and potato waste (+12%) only, which both had a low content of structural carbohydrates (hemi-cellulose and cellulose) but a particularly high content of either non-structural carbohydrates such as starch (potato waste) or proteins (blood). With food waste, card packaging and cattle slurry, pasteurisation had no observable impact on the methane yield. Slaughterhouse waste and OFMSW yielded less methane after pasteurisation in the experiments (but statistical significance of the difference between pasteurised and unpasteurised slaughterhouse waste or OFMSW was not confirmed in this work). It is concluded that pasteurisation can positively impact the methane yield of some specific substrates, such as potato waste, where heat-treatment may induce gelatinisation with release of the starch molecules. For most substrates, however, pasteurisation at 70 °C is unlikely to increase the methane yield. It is unlikely to improve biodegradability of lignified materials, and it may reduce the methane yield from substrates which contain high contents of volatile components. Furthermore, in this experimental study, the obtained methane yield was unaffected by whether the substrates were pasteurised individually and then co-digested or co-pasteurised as a mixture before batch digestion.

Development of sustainable approaches for converting the organic waste to bioenergy

Dependence on fossil fuels such as oil, coal and natural gas are on alarming increase, thereby causing such resources to be in a depletion mode and a novel sustainable approach for bioenergy production are in demand. Successful implementation of zero waste discharge policy is one such way to attain a sustainable development of bioenergy. Zero waste discharge can be induced only through the conversion of organic wastes into bioenergy. Waste management is pivotal and considering its importance of minimizing the issue and menace of wastes, conversion strategy of organic waste is effectively recommended. Present review is concentrated on providing a keen view on the potential organic waste sources and the way in which the bioenergy is produced through efficient conversion processes. Biogas, bioethanol, biocoal, biohydrogen and biodiesel are the principal renewable energy sources. Different types of organic wastes used for bioenergy generation and its sources, anaerobic digestion-biogas production and its related process affecting parameters including fermentation, photosynthetic process and novel nano-inspired techniques are discussed. Bioenergy production from organic waste is associated with mitigation of lump waste generation and its dumping into land, specifically reducing all hazards and negativities in all sectors during waste disposal. A sustainable bioenergy sector with upgraded security for fuels, tackles the challenging climatic change problem also. Thus, intensification of organic waste conversion strategies to bioenergy, specially, biogas and biohydrogen production is elaborated and analyzed in the present article. Predominantly, persistent drawbacks of the existing organic waste conversion methods have been noted, providing consideration to economic, environmental and social development.

Enhanced solubilization of solid organics and methane production by anaerobic digestion of swine manure under nano-bubble water addition

Nano-bubble water (NBW) refers to water with a large number of nanoscale particle bubbles. The aim of this work was to study the mechanism of NBW addition into the anaerobic digestion (AD) of swine manure (SM). The results showed that the cumulative methane production from the NBW added reactor was 192-225 mL/g-VS and 19-39% higher than the control group (without NBW addition). Based on the analysis of soluble organics, NBW addition not only accelerated hydrolysis rates of proteins and carbohydrates, but also enhanced the production of VFAs. Moreover, mechanism analysis reveals that NBW with higher spin-spin relaxation time and absolute value of zeta potential might promote enzyme activity and the hydrolysis of organic solids. Simultaneously, the electron transport system activity of the methanogenic communities and electric conductivity were enhanced by NBW addition. This work implies that NBW addition is promising for enhancing AD for enhancement of methane production.

Understanding nitrogen recovery from wastewater with a high nitrogen concentration using microbial electrolysis cells

This study was aimed at understanding the effect of applied voltage, catholyte and reactor scale on nitrogen recovery from two different organic wastes (digestate and pig slurry) by means of microbial electrolysis cell (MEC) technology. For this purpose, MEC sizes of 100, 500 and 1000 mL were tested at applied voltages of 0.6, 1 and 1.4 V using either a phosphate-buffered solution or NaCl solution as the catholyte. By increasing the reactor size from 500 to 1000 mL, a decrease in the ammonia recovery efficiency from 47 to 42% was observed. The results also showed that the phosphate-buffered solution is preferable as the catholyte and that the voltage applied does not have a noticeable effect on current production and ammonia recovery. Low biodegradability of the wastes was identified as the main bottleneck.

Incorporating anaerobic co-digestion of steam exploded or ammonia fiber expansion pretreated sugarcane residues with manure into a sugarcane-based bioenergy-livestock nexus

The co-digestion of pretreated sugarcane lignocelluloses with dairy cow manure (DCM) as a bioenergy production and waste management strategy, for intensive livestock farms located in sugarcane regions, was investigated. Ammonia fiber expansion (AFEX) increased the nitrogen content and accelerated the biodegradability of sugarcane bagasse (SCB) and cane leaf matter (CLM) through the cleavage of lignin carbohydrate crosslinks, resulting in the highest specific methane yields (292-299 L CH₄/kg VSadded), biogas methane content (57-59% v/v) and biodegradation rates, with or without co-digestion with DCM. To obtain comparable methane yields, untreated and steam exploded (StEx) SCB and CLM had to be co-digested with DCM, at mass ratios providing initial C/N ratios in the range of 18 to 35. Co-digestion with DCM improved the nutrient content of the solid digestates, providing digestates that could be used as biofertilizer to replace CLM that is removed from sugarcane fields during green harvesting.

Co-digestion of oat straw and cow manure during anaerobic digestion: Stimulative and inhibitory effects on fermentation

Impacts of adding different amounts of cow manure (CM) on the anaerobic digestion (AD) of oat straw (OS) with total solids content (TS) values of 4%, 6%, 8% and 10% was assessed over 50 days using batch experiments. A modified Gompertz model was introduced to predict the methane yield and determine the kinetic parameters. The optimum addition was a 1:2 ratio of CM to the OS added, which resulted in a suitable C/N ratio of 27 and a higher degradation rate of lignocellulose. The best cumulative methane yield of 841.77 mL/g volatile solids added (VS_added) was 26.64% greater than that of digesting OS alone. In addition, the amount of CM added produced larger effects than that of changes in the TS. However, higher CM concentrations were found to be inhibitory. Clustering analysis could provide significant guidance for demonstrating project process and combining farming and animal husbandry.

Synergistic effects of anaerobic co-digestion of whey, manure and fish ensilage

Biogas production potential of the three feedstocks fish ensilage, manure and whey was evaluated using biochemical methane potential (BMP) tests. Since anaerobic digestion of single substrates may be inefficient due to imbalances in the carbon-nitrogen ratio, degree of biodegradability and/or due to lack of nutrients needed by the microbial community, co-digestion of these substrates was also assessed, revealing synergistic effects and a particularly good effect of combining manure with fish ensilage. In this latter case, methane yields were up to 84% higher than the weighted average of the methane yields obtained with the individual substrates. The type of substrate was the dominating cause of variation in methane production rates and yields.

Anaerobic digestion for bioenergy production: Global status, environmental and techno-economic implications, and government policies

Anaerobic digestion (AD) is a mature technology that can transform organic matter into a bioenergy source - biogas (composed mainly of methane and carbon dioxide), while stabilizing waste. AD implementation around the world varies significantly, from small-scale household digesters in developing countries to large farm-scale or centralized digesters in developed countries. These differences in the implementation of AD technology are due to a complex set of conditions, including economic and environmental implications of the AD technology, and stimulus provided by a variety of polices and incentives related to agricultural systems, waste management, and renewable energy production. This review explores the current status of the AD technology worldwide and some of the environmental, economic and policy-related drivers that have shaped the implementation of this technology. The findings show that the regulations and incentives have been the primary factor influencing the steady growth of this technology, in both developing and developed countries.

Profits from pollutants: Economic feasibility of integrated anaerobic digester and nutrient management systems

There has been sustained interest from both environmental regulators and livestock associations to expand the use of anaerobic digester (AD) technology to mitigate greenhouse gas emissions. However, the generally profitable practice of codigesting off-farm organic waste could increase nitrogen and phosphorus content to the farm and exacerbate nutrient over-application concerns near large animal operations. We examine the economic feasibility of a broad set of dairy waste management systems composed of two technology groups that mitigate air and water pollution: an AD system that includes either animal waste input or combination animal/off-farm organic waste codigestion input and either compressed natural gas (CNG) or combined heat and power (CHP) output; and a filtration system that includes fiber separation, nutrient separation, and/or water recovery. We conclude that AD setups without codigestion are only economically feasible under limited conditions, but scenarios which use codigestion have the potential to contribute to nutrient over-application without nutrient separation technology. Trends for CNG and CHP match closely. Net present value (NPV) is greatest for AD with CNG scenarios. Estimated NPV for AD with CNG and environmental credits is $1.8 million and $39.7 million for dairies with 1600 and 15,000 wet cow equivalents, respectively. For these firm sizes, the addition of codigestion contributes $4.8 million and $47.3 million, respectively, to estimated NPV. Nutrient separation and water recovery both lead to decreases in scenario NPV with codigestion, but with the right policies, dairy owners may be willing to adopt AD with nutrient separation.

Methane and nitrous oxide emissions from Canadian dairy farms and mitigation options: An updated review

This review examined methane (CH4) and nitrous oxide (N2O) mitigation strategies for Canadian dairy farms. The primary focus was research conducted in Canada and cold climatic regions with similar dairy systems. Meta-analyses were conducted to assess the impact of a given strategy when sufficient data were available. Results indicated that options to reduce enteric CH4from dairy cows were increasing the dietary starch content and dietary lipid supplementation. Replacing barley or alfalfa silage with corn silage with higher starch content decreased enteric CH4per unit of milk by 6%. Increasing dietary lipids from 3% to 6% of dry matter (DM) reduced enteric CH4yield by 9%. Strategies such as nitrate supplementation and 3-nitrooxypropanol additive indicated potential for reducing enteric CH4by about 30% but require extensive research on toxicology and consumer acceptance. Strategies to reduce emissions from manure are anaerobic digestion, composting, solid–liquid separation, covering slurry storage and flaring CH4, and reducing methanogen inoculum by complete emptying of slurry storage at spring application. These strategies have potential to reduce emissions from manure by up to 50%. An integrated approach of combining strategies through diet and manure management is necessary for significant GHG mitigation and lowering carbon footprint of milk produced in Canada.

Cow Manure Composting by Microbial Treatment for Using as Potting Material: An Overview

Dairy industry is flourishing in Saudi Arabia for the last two decades producing milk and milk products to meet the population needs. Simultaneously, it is also producing large amount of dairy waste (animal manure) posing a serious environmental issues. Vermicomposting (conversion of animal manure into compost by bacterial treatments) is considered as one of the safest means for efficient management and to mitigate environmental pollution issues resulting from land disposal of raw dairy wastes. The main objective of this studywas to summarize different processes of vermicomposting and identified the most important bacteria species suitable for vermicomposting using animal manure especially the cowdung. The review showed that among the different bacteria species, Eisenia fetida is the most efficient and commonly used bacteria for vermicomposting to develop compost using cow dung (dairy manure). Overall,this review has highlighted the various vermicomposting technologies, various bacteria species involved in vermicomposting, effect on soil and plant growth as well as the benefits of using compost prepared by way of vermicomposting. The study showed a lot of potential for the production of compost by vermicomposting technology using appropriate bacteria species which is safe, friendly and is associated with minimum environmental issues for safe land disposal of dairy waste (animal manure) with minimum possible environmental issues for the adjacent population.

Reduction of volatile fatty acids and odor offensiveness by anaerobic digestion and solid separation of dairy manure during manure storage

Volatile fatty acids (VFA) play an important role in the biodegradation of organic wastes and production of bioenergy under anaerobic digestion, and are related to malodors. However, little is known about the dynamics of VFA during dairy manure storage. This study evaluated the characteristics of VFA in dairy manure before and after anaerobic co-digestion in a laboratory experiment using eight lab-scale reactors. The reactors were loaded with four different types of dairy manure: (1) liquid dairy manure from a freestall barn, (2) mixture of dairy manure and co-digestion food processing wastes at the inlet of an anaerobic digester, (3) effluent from the digester outlet, and (4) the liquid fraction of effluent from a solid separator. Four VFA (acetic, propionic, butyric, and 2-methylbutyric acids) were identified and quantified in weekly manure samples from all reactors. Results showed that the dominant VFA was acetic acid in all four manure sources. The off-farm co-digestion wastes significantly increased the total VFA concentrations and the proportions of individual VFA in the influent. The dairy manure under storage demonstrated high temporal and spatial variations in pH and VFA concentrations. Anaerobic digestion reduced the total VFA by 86%-96%; but solid-liquid separation did not demonstrate a significant reduction in total VFA in this study. Using VFA as an indicator, anaerobic digestion exhibited an effective reduction of dairy manure odor offensiveness.

Invited review: Sustainability of the US dairy industry

The US dairy industry has realized tremendous improvements in efficiencies and milk production since the 1940s. During this time, farm and total cow numbers have decreased and average herd size has increased. This intensification, combined with the shift to a largely urban public, has resulted in increased scrutiny of the dairy industry by social and environmental movements and increased concern regarding the dairy industry's sustainability. In response to these concerns, a group of scientists specializing in animal welfare, nutrient management, greenhouse gas emissions, animal science, agronomy, agricultural engineering, microbiology, and economics undertook a critical review of the US dairy industry. Although the US dairy system was identified as having significant strengths, the consensus was that the current structure of the industry lacks the resilience to adapt to changing social and environmental landscapes. We identified several factors affecting the sustainability of the US dairy industry, including climate change, rapid scientific and technological innovation, globalization, integration of societal values, and multidisciplinary research initiatives. Specific challenges include the westward migration of milk production in the United States (which is at odds with projected reductions in precipitation and associated limitations in water availability for cattle and crops), and the growing divide between industry practices and public perceptions, resulting in less public trust. Addressing these issues will require improved alignment between industry practices and societal values, based upon leadership from within the industry and sustained engagement with other interested participants, including researchers, consumers, and the general public.

Sustainability of soil fertility and the use of lignocellulosic crop harvest residues for the production of biofuels: a literature review

Use of lignocellulosic crop harvest residues for liquid or gaseous biofuel production may impact soil quality, long-term soil fertility and the major determinants of the latter, stocks of soil organic carbon and nutrients. When soil organic carbon stocks of mineral cropland soils are to be maintained, there is scope for the removal of lignocellulosic harvest residues in several systems with much reduced tillage or no tillage. The scope for such removal might be increased when suitably treated residues from the conversion of harvest residues into biofuel are returned to cropland soils. For mineral cropland soils under conventional tillage, the scope for the production of liquid biofuels from harvest residues is likely to be less than in the case of no-till systems. When fertility of cropland soils is to be sustainable, nutrients present in suitably treated biofuel production residues have to be returned to these soils. Apparently, the actual return of carbon and nutrients present in residues of biofuel production from crop harvest residues to arable soils currently predominantly concerns the application of digestates of anaerobic digestion. The effects thereof on soil fertility and quality need further clarification. Further clarification about the effects on soil fertility and quality of chars and of co-products of lignocellulosic ethanol production is also needed.