Animal Slurry Research Articles

Optimization of Recovery of Nutrients from Pig Manure Slurry through Combined Microbial Fuel Cell and Microalgae Treatment

Microbial fuel cells (MFCs) and microalgae–bacteria consortia represent two renewable and promising technologies of growing interest that enable wastewater treatment while obtaining high-value-added products. This study integrates MFCs and microalgae production systems to treat animal slurry, aiming to remove and recover organic and inorganic components while generating energy and producing biomass. The MFCs effectively eliminated Chemical Oxygen Demand (COD), organic nitrogen, and a portion of the suspended solids, achieving a maximum voltage of 195 mV and a power density of 87.03 mW·m−2. After pre-treatment with MFCs, the slurry was diluted to concentrations of 10%, 50%, and 100% and treated with microalgae–bacteria consortia. The results showed a biomass production of 0.51 g·L−1 and a productivity of 0.04 g·L−1·day−1 in the culture fed with 10% slurry, with significant removal efficiencies: 40.71% for COD, 97.76% for N-NH4+, 39.66% for N-NO2−, 47.37% for N-NO3−, and 94.37% for P-PO4−3. The combination of both technologies allowed for obtaining a properly purified slurry and the recovery of nutrients in the form of bioelectricity and high-value biomass. Increasing the concentration of animal slurry to be treated is essential to optimize and scale both technologies.

Tracing N2O from dairy processing sludge amended soil with visualizing microscale heterogeneity of NH3 and pH (Short Communication)

Nitrous oxide (N2O) emissions from organic waste and animal slurry contribute to climate change and endanger our ecosystems. For the development of efficient mitigation technologies, in-depth knowledge of emission processes is needed. This can be obtained by non-destructive, temporal measurements of in-situ soil profiles and the transformation of ammonium (NH4+) during events of emissions. Planar optode imaging is a non-destructive measuring method that can be used to visualize spatiotemporal changes of ammonia (NH3) and pH in soil systems. In this study, soil amended with dairy processing sludge (DPS) was incubated in static chambers for 23 days, and GHG emissions, NH3 concentrations and pH in the soil were measured simultaneously over time. The aim was to investigate the potential of applying different planar optodes to provide information that gives insight into processes of N2O emissions. The DPS was applied to the soil as a surface layer (SL), with untreated soil as a control (CK). We were able to measure N2O emissions while monitoring spatiotemporal changes of soil pH and NH3 concentrations. The visualized microscale heterogeneity of the soil contributed to a better understanding of N2O emission processes. While technical challenges (e.g., humidity sensitivity of the NH3 optode and airtightness of the chambers) still need to be overcome, the method is a promising non-destructive method to study soil processes after application of different types of soil amendments.

Assessment of transient hydrogen sulfide peak emissions caused by biogas plant operation

Odor nuisance is a major impediment for public acceptance and wider implementation of biogas plants. Knowledge on composition and dynamics of emissions from these plants is highly needed for development of robust mitigation solutions. In this study, odorant emissions were investigated from two biogas plants of different sizes and capacities. Measurements using proton-transfer-reaction mass spectrometer (PTR-MS) revealed that hydrogen sulfide was the main odorant and constituted 82% and 71% of the odor activity sums (SOAV) at the two studied plants, respectively. Long-term time-resolved measurements furthermore revealed that emissions were highly dynamic with distinct short-term emission peaks. By deploying an array of electrochemical sensors, the main sources of hydrogen sulfide emission were subsequently identified and correlated with operational data to identify the major causes for the highly fluctuating emissions. Addition of biomasses in the form of animal slurry to pre-tanks, were shown to be the major cause of periodic hydrogen sulfide emission within the range of 50–1200 ppm. Such hydrogen sulfide peak emissions could challenge odor abatement from biogas plants and should be taken into account when designing odor abatement technologies for biogas plants.

Improving Human Diets and Welfare through Using Herbivore-Based Foods: 2. Environmental Consequences and Mitigations.

Animal-sourced foods are important for human nutrition and health, but they can have a negative impact on the environment. These impacts can result in land use tensions associated with population growth and the loss of native forests and wetlands during agricultural expansion. Increased greenhouse gas emissions, and high water use but poor water quality outcomes can also be associated. Life cycle analysis from cradle-to-distribution has shown that novel plant-based meat alternatives can have an environmental footprint lower than that of beef finished in feedlots, but higher than for beef raised on well-managed grazed pastures. However, several technologies and practices can be used to mitigate impacts. These include ensuring that grazing occurs when feed quality is high, the use of dietary additives, breeding of animals with higher growth rates and increased fecundity, rumen microbial manipulations through the use of vaccines, soil management to reduce nitrous oxide emission, management systems to improve carbon sequestration, improved nutrient use efficacy throughout the food chain, incorporating maize silage along with grasslands, use of cover crops, low-emission composting barns, covered manure storages, and direct injection of animal slurry into soil. The technologies and systems that help mitigate or actually provide solutions to the environmental impact are under constant refinement to enable ever-more efficient production systems to allow for the provision of animal-sourced foods to an ever-increasing population.

Working with cattle slurry on farms: emission and dispersion of hydrogen sulfide gas during stirring.

Over the past 15 years, there have been numerous fatalities related to working with animal slurry. Working with cattle slurry releases toxic gases, in particular, hydrogen sulphide (H2S), which can cause acute central nervous system toxicity, breathing difficulties, and death if exposed to high concentrations. Real-time measurements of H2S gas were taken over distance and time, during the stirring of cattle slurry on farms. Gas was measured at eight slurry stores with differing typical configurations of indoor or outdoor stores and with or without slatted flooring. Highest H2S gas levels were measured from indoor stores under slatted floors, and generally at positions closest to the stirrer or the point of maximum stirring, with levels decreasing with distance from source. Most of the data indicate H2S gas levels increase very rapidly after stirring starts, and mostly decline to baseline levels within 30 min post start of stirring. There were, however, circumstances where gas levels remained high and only started to decline once the stirrer had stopped. H2S gas levels at all farms, at all positions measured were consistently below 10 ppm within 30 min of the stirrer being stopped. The current data highlight areas of the farm and ways of working that have the potential for workers and others to be at risk of exposure to toxic slurry gases. The area should be left to ventilate naturally for at least 30 min after the stirrer has been stopped before re-entering buildings. Influencing the design of stirring equipment and future slurry stores would likely reduce the risk of worker exposure to slurry gases.

Effects of combined application of animal slurry and mineral fertiliser on rice yield and soil nitrogen cycle microbes

Effects of combined application of animal slurry and mineral fertiliser on rice yield and soil nitrogen cycle microbes

Agro-industrial by-products as alternative additives for the agronomic valorization of pig slurry through pH modification

The use of animal slurry in modern agricultural systems is receiving considerable attention, mainly due to the latest increase in chemical fertilizer prices. However, the use of raw animal slurry to fertilize horticultural crops can, on the one hand, lead to significant ammonia emissions and, on the other hand, be an important source of zoonotic pathogens. Therefore, proper treatment is required. The present study explored the modification of the pH value of pig slurry using by-products from different agro-industrial activities as a strategy to control these two problems. Three approaches were used, namely acidification and biological acidification (bio-acidification) to pH 5 and alkalization to pH 9.5. The most promising of the 14 different additives and additive combinations initially considered should be able to reach the target pH at a dose of less than 20% (m/m). The presence of Salmonella and the number of Escherichia coli colony forming units (CFU) were evaluated in the slurry for each selected treatment. To ensure that treated slurry remains of interest as an organic fertilizer, the impact of treated slurry on plant germination and nitrogen (N) availability was also assessed. The by-products from the brewing and yeast industry failed to reduce the pH to 5. In fact, the bio-acidification of pig slurry was only possible with additives rich in carbon. Although slurry sanitization (<1000 CFU E.coli g−1 slurry) was not guaranteed by all treatments, a reduction in E.coli numbers was observed with all additives. The ammonium content of the treated slurry was significantly reduced (up to 20%) with treatments involving bio-acidification. N mineralization was evidenced for all additives used for slurry alkalinization but no N mineralization was observed when using acidification with H2SO4 or by-product spent acid. The phytotoxicity bioassay showed that most additives do not have a negative impact on germination. The results presented here suggest that agro-industrial by-products are capable of modifying the pH of pig slurry. Depending on the pH modification strategy and additive used, treated slurry may be safer and of higher fertilizing value than untreated (raw) slurry.

Experimental and model-based comparison of wind tunnel and inverse dispersion model measurement of ammonia emission from field-applied animal slurry

Volatilization of ammonia from field-applied animal slurry is a significant problem. Accurate emission measurements are needed for inventories and research, but are not provided by all measurement methods. Wind tunnels may give emission values substantially above or below micrometeorological results, which have been shown to be accurate. This limitation reduces the utility of wind tunnel results, which make up a large fraction of available measurements. The present work focused on understanding wind tunnel measurement error by comparing micrometeorological and wind tunnel measurements with the aid of a semi-empirical model. Ammonia loss from digestate after field application was measured in high time resolution in three field trials using wind tunnels and the backward Lagrangian stochastic (bLS) dispersion technique simultaneously. Differences in measured emission were interpreted using the ALFAM2 model, and measurements were used to evaluate the model. Results showed that wind tunnel and bLS methods provided different cumulative emission estimates, although there were similarities in measured emission dynamics. The ALFAM2 model was generally able to reproduce emission dynamics for both measurement methods, but only when differences in mass transfer between the two methods were incorporated in an experimental parameter set. This important result suggests that: 1) the simple structure of the ALFAM2 model captures the essential physical and chemical processes controlling emission and 2) the two measurement methods differ only (or mainly) through mass transfer above the slurry/soil surface and rain. Therefore, with careful selection of wind tunnel air flow it should be possible to approximately match emission that occurs under open-air conditions. But without temporal variation in air flow, actual emission dynamics cannot be captured. This work provides a template for integrating and comparing measurements from different methods, and suggests it is possible to use wind tunnel measurements for model evaluation and even parameter estimation.

Nitrogen availability in digestates from full-scale biogas plants following soil application as affected by operation parameters and input feedstocks

Biogas operation parameters are usually optimised to enhance biogas yields while ignoring digestate quality. This study evaluated the effects of varying operation parameters and input feedstocks used in co-digestion with manure on digestate properties and N turnover in soil for 80 days. Net inorganic N release (% of N input) from digestates varied significantly (p < 0.001) due to their contrasting properties. Temperature, hydraulic retention time (HRT), manure type and input feedstocks significantly influenced soil inorganic N release. Animal slurry co-digested with energy crops had the highest average net soil inorganic N release at 67 %, while co-digestion with straw-based feedstock had the lowest at 56 %. Feedstock type greatly influenced the choice of digesting temperature and HRT, with most energy crop-based feedstocks digested at <50 days HRT. Digestate properties NH4+ -N/total N, C/N and total carbon concentration significantly influenced net inorganic N release in soil. A better understanding of the effects of biogas operation variables on nutrient availability and digestate fertilising properties could help design and optimise the anaerobic digestion process to increase biogas yields and N fertiliser value of the digestates.

Microbial Fuel Cell Using a Novel Ionic Liquid-Type Membrane–Cathode Assembly for Animal Slurry Treatment and Fertilizer Production

The implementation of a microbial fuel cell for wastewater treatment and bioenergy production requires a cost reduction, especially when it comes to the ion exchange membrane part and the catalysts needed for this purpose. Ionic liquids in their immobilized phase in proton exchange membranes and non-noble catalysts, as alternatives to conventional systems, have been intensively investigated in recent years. In the present study, a new microbial fuel cell technology, based on an ionic liquid membrane assembly for CoCu mixed oxide catalysts, is proposed to treat animal slurry. The new low-cost membrane–cathode system is prepared in one single step, thus simplifying the manufacturing process of a membrane–cathode system. The novel MFCs based on the new low-cost membrane–cathode system achieved up to 51% of the power reached when platinum was used as a catalyst. Furthermore, the removal of organic matter in suspension after 12 days was higher than that achieved with a conventional system based on the use of platinum catalysts. Moreover, struvite, a precipitate consisting of ammonium, magnesium, and phosphate, which could be used as a fertilizer, was recovered using this membrane–cathode system.

Responses of CH4, N2O, and NH3 emissions to different slurry pH values of 5.5–10.0: Characteristics and mechanisms

Animal slurry storage is a significant source of greenhouse gas (GHG) and ammonia (NH3) emissions. pH is a basic but key factor that could pose great influence on gas emissions, but the simultaneous evaluation of its influence on GHG and NH3 emissions and the understanding of its underlying mechanism are not enough. In this work, pH was adjusted between 5.5 and 10.0 by a step of 0.5 unit by adding lactic acid and sodium hydroxide (NaOH) properly and frequently to the stored slurry during a 43-day storage period. The cumulative NH3 emissions were linearly correlated with the slurry pH, with R2 being 0.982. Maintaining the slurry pH at 5.5–6.0 could reduce NH3 emissions by 69.4%–85.1% compared with the non-treated group (CK). The pH ranges for maximum methane (CH4) and nitrous oxide (N2O) emissions were 7.5–8.5 and 6.5–8.5, respectively, and the slurry under pH 7.5–8.5 showed the highest GHG emissions. Acidification to pH 5.5 helped reduce the CH4, N2O, and total GHG emissions by 98.0%, 29.3%, and 81.7%, respectively; while alkalinization to pH 10.0 helped achieve the mitigation effects of 74.1%, 24.9%, and 30.6%, respectively. The Pearson's correlation factor between CH4 and the gene copy of mcrA under different pH values was 0.744 (p < 0.05). Meanwhile, the correlation factors between N2O and the gene copies of amoA, narG, and nirS were 0.644 (p < 0.05), 0.719 (p < 0.05), and 0.576 (p = 0.081), respectively. The gene copies of mcrA, amoA, narG, and nirS were maintained at the lowest level under pH 5.5. These results recommended keeping slurry pH lower than 5.5 with lactic acid can help control GHG and NH3 emissions simultaneously and effectively.

Improving removal of combined veterinary antibiotics and mitigating their negative impacts during anaerobic digestion of swine manure using modified bentonite

This study investigated the potential of modified bentonite (MB) material in mitigating the negative effects of combined veterinary antibiotics (CVAs) on anaerobic digestion (AD) process treating swine manure. Four CVAs (i.e., Oxytetracycline (OTC), Tetracycline (TC), Norfloxacin (Norf), and Sulfadiazine (SDZ)) were selected as they are most frequently detected in swine manure; and anaerobically incubated for 30 days under mesophilic conditions (37 °C) and with addition of different MB weights (1, 5, and 10 g L−1). Results showed that 1, 5, and 10 g L−1 of MB enhanced the removal of CVAs from 61.5 (no MB addition) to 72.7, 86.4, and 91.4 %, respectively. CVAs removal was accredited to biodegradation rather than adsorption to MB. Norf was rapidly transferred to solids causing an adsorption competition and decreasing co-antibiotics removal, while it was fast removed when MB was added. When 10 g L−1 of MB were added, the CVAs' adsorption competition diminished and their inhibition on CH4 production decreased from 27 % to 1.7 %. MB addition lowered the impact of CVAs significantly by maintaining pH stability, enhanced COD removal, decreased the VFAs accumulation, and improved the activity of bacteria and archaeal communities. The cost analysis showed that MB additions to AD would reduce cost by 52 % than applied methods for animal slurry pre-treatment or post-digestive treatment for reducing antibiotic residues. These findings suggests that using MB as an environmentally-friendly and commercial additive holds promise for reducing CVAs and eradicating their negative impacts with safe digestate disposal to land applications.

Effects of self-produced lactic fermentation (SPLF) on GHG and VSC emissions during swine slurry storage

Self-produced lactic fermentation (SPLF) is a new valued utilization technology, but its impact on gas emission remains unclear. The objective of this study is to investigate the effect of replacing the H2SO4 additive with SPLF on greenhouse gas (GHG), and volatile sulfur compound (VSC) emissions from swine slurry storage in a laboratory-scale study. In this study, SPLF is directed toward producing lactic acid (LA) through the anaerobic fermentation of slurry and apple waste under the most suitable conditions, with the LA concentration kept at 10,000–52000 mg COD/L and the pH remaining within 4.5 during the following 90 days of slurry storage. Compared with that in the slurry storage treatment (CK), the GHG emissions decreased by 86% and 87% in the SPLF and H2SO4 groups, respectively. The low pH (i.e., less than 4.5) inhibited the growth of Methanocorpusculum and Methanosarcina and resulted in very low mcrA gene copies in the SPLF group, leading to a reduction in CH4 emissions. The methanethiol, dimethyl sulfide, dimethyl disulfide, and H2S emissions in the SPLF group were reduced by 57%, 42%, 22%, and 87% and increased by 2206%, 61%, 173%, and 1856% in the H2SO4 group, respectively. Therefore, SPLF can be an innovative bioacidification technology for effectively reducing GHG and VSC emissions from animal slurry storage.

Nitrogen fertiliser value of bioacidified slurry

Bioacidification of animal slurry has proven to be a good alternative to traditional acidification with sulfuric acid for reducing ammonia emissions. However, the fertiliser value of the bioacidified slurry is yet to be determined before a whole-system assessment can be made. The N fertiliser value of pig slurry either untreated or bioacidified with glucose and/or fermented brown juice (BJ) was investigated in a pot experiment with maize (Zea mays L.) grown in a greenhouse. The slurry treatments were either pre-acidified with sulfuric acid to pH 6.5 or 5.5 before bioacidification, or bioacidified without pre-acidification. Plant growth was good in all treatments, but the bioacidified treatments showed a lower mineral fertiliser equivalence (MFE) value than the non-bioacidified treatments. Average MFE values were 71 %, 62 %, 59 % and 41 % for the non-bioacidified (noC), glucose (glu), glucose and brown juice (glu + BJ20) and brown juice (BJ50) treatments respectively. This reduction was most likely caused by immobilisation of N due to the addition of easily available C from the substrates. The fertiliser value was not affected by the pH, C/N ratio and C content of the treatments, while a positive correlation was found with NH4 + -N content. Pre-acidification positively affected MFE, probably due to higher nutrient availability. Further studies on the effect of different inclusion rates of substrates for bioacidification and the effect of application method on the fertiliser value, as well as studies under field conditions, are needed before recommendations can be made about bioacidification as an alternative to traditional acidification.

Impact of Sandy Soil Amendment with Dairy Slurry Treated through pH Adjustment on Nutrient and Coliform Leaching

Livestock farming produces high volumes of animal slurry that can be sanitized using low-cost treatments by pH adjustment, reducing pathogen contamination, and promoting slurry valorization as a safe fertilizer. This work aims to evaluate the impact of sandy soil amendment with dairy slurry treated by pH adjustment on the potential release of nutrients and coliforms into groundwater. A laboratory soil column leaching experiment was conducted and the surface application of six treatments was tested: raw dairy slurry, dairy slurry acidified with H2SO4, dairy slurry alkalinized with KOH, alkalinized/neutralized dairy slurry, mineral fertilizer, and a control. The fertilizer application rate was 0.08 g N kg−1 dry soil. Leachates were analyzed for pH, electrical conductivity, N-NH4+ and N-NO3−, macro- and micronutrients, and fecal coliforms. Results showed that amendment with dairy slurry led to significantly lower nitrate leaching potential than mineral fertilizer (maximum 16.1 vs. 50.4%). The use of hygienized slurry by alkalinization decreased the potential leaching of coliforms relative to raw slurry. However, incomplete sanitization by acidification strongly promoted coliform leaching and the risk of groundwater contamination. It can be concluded that the use of alkalinized dairy slurry is a safer solution than raw slurry with regard to the risk of groundwater pollution.

A Detailed Database of the Chemical Properties and Methane Potential of Biomasses Covering a Large Range of Common Agricultural Biogas Plant Feedstocks

Agricultural biogas plants are increasingly being used in Europe as an alternative source of energy. To optimize the sizing and operation of existing or future biogas plants, a better knowledge of different feedstocks is needed. Our aim is to characterize 132 common agricultural feedstocks in terms of their chemical composition (proteins, fibers, elemental analysis, etc.) and biochemical methane potential shared in five families: agro-industrial products, silage and energy crops, lignocellulosic biomass, manure, and slurries. Among the families investigated, manures and slurries exhibited the highest ash and protein contents (10.3–13.7% DM). High variabilities in C/N were observed among the various families (19.5% DM for slurries and 131.7% DM for lignocellulosic biomass). Methane potentials have been reported to range from 63 Nm3 CH4/t VS (green waste) to 551 Nm3 CH4/t VS (duck slurry), with a mean value of 284 Nm3 CH4/t VS. In terms of biodegradability, lower values of 52% and 57% were reported for lignocelluloses biomasses and manures, respectively, due to their high fiber content, especially lignin. By contrast, animal slurries, silage, and energy crops exhibited a higher biodegradability of 70%. This database will be useful for project owners during the pre-study phases and during the operation of future agricultural biogas plants.

Full-Scale Investigation of Methane and Ammonia Mitigation by Early Single-Dose Slurry Storage Acidification

The effects of early acidification with sulfuric acid of animal slurry in concrete storage tanks to pH 5 on methane and ammonia emissions have been investigated on two cattle and two pig slurry storage tanks in full scale. The tanks’ up- and down-wind concentrations were measured online by cavity ring-down spectroscopy (CRDS). The inverse-dispersion method (IDM), using a backward Lagrangian stochastic (bLS) model, was used to determine the emission rates. The results show that CH4 emissions after single-dose acidification of slurry tanks in the early summer were reduced by 95 ± 14% and 95% ± 6% for cattle and pig manure, respectively, compared to the emissions measured before acidification. The reductions occurred even though pH increased during the storage with and without addition of fresh slurry. After acidification, NH3 emissions were comparable to or lower than when a natural crust was present. A supplementary experiment on small-scale slurry containers was conducted to investigate the pH development when fresh slurry was added to the acidified slurry. The influence of pH development on the long-term emission dynamics of methane is discussed by comparing the large-scale and small-scale studies. The study presents the first full-scale documentation that slurry acidification is a promising technology for mitigation of methane from slurry storage.

Effectiveness of mechanical separation for reducing ammonia loss from field-applied slurry: Assessment through literature review and model calculations

To assess solid-liquid separation as a technology to reduce ammonia (NH3) emission from storage and field application of animal slurry, it is necessary to consider a possible higher NH3 loss from the solid fraction after application than from raw slurry, as well as losses during storage. A literature review was conducted, and a case study was developed for Denmark, including cattle slurry, pig slurry, and biogas digestate applied by trailing hose, trailing shoe, or open slot injection at five different periods of the year. Standard storage emission factors were used and emission factors after field application were estimated using the ALFAM2 model with input data for dry matter (DM), pH, total ammoniacal nitrogen (TAN), and separation efficiency all from the literature compilation. In general, a clear reduction in the emission factors after application of the liquid fraction was found relative to application of raw slurry in the literature data. Case study results provide some evidence that separation of cattle slurry or digestate, followed by storage and subsequent application by trailing hose or trailing shoe of the liquid fraction and broadcast application of the solid fraction reduces overall NH3 loss, with a higher reduction when the solid fraction is incorporated by plowing after 4 h. This effect was not present for pig slurry. For all slurry types when the raw slurry and liquid fraction is applied by open slot injection, the overall reduction in emission due to separation is not present or even negative.

Effects of the Addition of Different Additives before Mechanical Separation of Pig Slurry on Composition and Gaseous Emissions

The treatment of animal slurry is used to improve management on a farm scale. The aim of this laboratory study was to assess the effects of the addition of the additives biochar, alum and clinoptilolite before the mechanical separation of whole pig slurry (WS) on the characteristics and emission of NH3, N2O, CO2 and CH4 from solid (SF) and liquid fractions (LF). The additives were mixed with WS (5% w/w), followed by separation, in a total of 12 treatments with 3 replicates, including the controls and WS with additives. Gaseous emissions were measured for 30 d by a photoacoustic multigas monitor, and initial characteristics of the slurries were assessed. The results indicated that the separation of the WS modified the initial physicochemical characteristics and increased the GWP emissions of the SF and LF, but not the NH3 losses. However, the addition of additives before separation increased the nutrient value and reduced the GWP emissions from the SF and LF. Additionally, just the additive alum was effective in the reduction of E. coli. The additives led to significant reductions in NH3 and N2O emissions, with higher reductions in NH3 losses for alum (51% for NH3) and similar N2O losses for all additives (70% for N2O) observed, whereas the CO2 and CH4 emissions were reduced by biochar (25% for CO2 and 50% for CH4) and alum (33% for CO2 and 30% for CH4) but not by clinoptilolite. Although the additives had a positive effect on slurry management, it can be concluded that the addition of alum before mechanical separation has the potential to be the best mitigation measure because it improves the nutrient content and sanitation and decreases gaseous losses from slurry management.

Bio-acidification of animal slurry: Efficiency, stability and the mechanisms involved

Slurry acidification is effective for reducing gaseous emissions during slurry storage. However, an alternative to sulfuric acid traditionally used is needed. This study investigated the efficiency of slurry bio-acidification treatment by adding different types and amounts of fermentable substrates to initiate and sustain the fermentation process. The carbon pools in the slurry were quantified to understand the mechanisms involved during the bio-acidification. Substrate addition efficiently reduced slurry pH during storage via lactic acid production. Substrates with a low pH proved beneficial in initiating the fermentation process, but higher glucose dosage did not produce the highest lactic acid concentration. Once the treated slurries reached pH 4.2 during the fermentation process, the production of lactic acid was promoted and provided substrate was still available, the weaker volatile fatty acids were avoided, resulting in lower CH4 emissions. In conclusion, bio-acidification could replace the sulfuric acid to reduce gaseous emissions during slurry storage.