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The production of bovine slurry and its subsequent storage are significant sources of ammonia (NH 3) and greenhouse gases (GHGs). Chemical acidification of manures has been shown to significantly reduce these emissions. Waste products, derived from food processing and on-farm practices, may be used as "natural" acidifiers. However, the efficacy of these products in reducing pH and any subsequent emissions are unknown. Commercial "slurry improvers" or "additives" may also be a viable mitigation option; however, their effectiveness is questionable. This study investigated the efficacy and cost of a range of waste and commercial amendments and a chemical acidifier, ferric chloride (FeCl 3), to identify the most effective amendment for NH 3 and GHG emissions reduction. Ammonia abatement potential was observed for 5% sugar beet molasses (67% reduction), 7% apple pulp (49% reduction), and 7% grass silage (38% reduction). Methane (CH 4) emissions were reduced only by spent brewers' grain, sugarbeet molasses, and grass silage effluent at the higher inclusions (i.e. amounts added), with reductions ranging from 15% to 70%. Carbon dioxide (CO 2) emissions were significantly increased with the addition of waste amendments. Commercially available additives had little impact on emissions, with the exception of one treatment, which reduced CH 4 by approximately 10%. Ferric chloride reduced NH 3 emissions by 20%–68%, CH 4 by 6%–65%, and CO 2 by 6%–38%, depending on the inclusion. All waste amendments had low marginal abatement costs ranging from -€0.46 to €0.88 kg−1 NH 3 abated compared to FeCl 3 and commercial amendments (€1.80 to €231 kg−1 NH 3). This incubation experiment demonstrated that a range of on-farm and industry waste streams could be valorised to reduce NH 3 emissions. However, many of these may result in higher CH 4 and CO 2 emissions due to input of labile carbon sources. Therefore, based on the results of the current study, it is recommended that sugarbeet molasses and ferric chloride, at 5% and 1.1% inclusions respectively, be examined in field experiments. [Display omitted] • Farm waste products may be used to reduce NH 3 and GHG emissions. • Ferric chloride and sugarbeet molasses reduced emissions. • A cost saving of ∼ €0.46 kg−1 NH 3 was achieved using waste amendments. • Commercial products were ineffective in abating NH 3 and GHG emissions. [ABSTRACT FROM AUTHOR]

Cattle and cow slurry storage is a significant source of agricultural greenhouse gas (GHG) and ammonia (NH3) emissions. While acidification has been demonstrated to significantly reduce these emissions, a knowledge gap exists to identify a range of chemical amendments that are safe, suitable and cost effective to mitigate both GHG and NH 3 gases simultaneously. The current study showed that ferric chloride, sulphuric acid, alum and acetic acid were extremely effective at abating emissions, with NH 3 reduced by 96%, 85%, 82% and 73%, respectively. In terms of methane (CH 4), ferric chloride, alum, sulphuric acid and acetic acid reduced emissions by 98%, 96%, 95% and 94%, respectively. Previous studies have found that the reduction of >pH 6 can inhibit the release of these gases; however, the effectiveness can vary depending on each amendment's composition. The cost benefit analysis, assessed the amendments in terms of both gaseous emissions reduction and net cost. Sulphuric acid, acetic acid, ferric chloride and alum ranked best, respectively. Currently, the cost of implementing these amendments is, at best, cost neutral. Therefore, incentivising chemical amendments for the abatement of GHG and NH 3 gases from slurry storage is needed. This incubation experiment is an effective means of pre-screening amendments before they are explored at pilot or full scale with subsequent field application. Future research should consider the assessment of cheaper on- and off-farm alternative waste streams as slurry amendment. Image 1 • Acidification of cattle and dairy slurry was investigated. • Target pH of 5.5 resulted in a 96% reduction in NH 3 and 98% reduction in CH 4. • Ferric chloride reductions were independent of pH value. • Cost analysis revealed financial incentives are needed for scaled implementation. [ABSTRACT FROM AUTHOR]

North Atlantic European grassland systems have a low nutrient use efficiency and high rainfall. This grassland is typically amended with unprocessed slurry, which counteracts soil organic matter depletion and provides essential plant micronutrients but can be mobilised during rainfall events thereby contributing to pathogen, nutrient and metal incidental losses. Co-digesting slurry with waste from food processing mitigates agriculture-associated environmental impacts but may alter microbial, nutrient and metal profiles and their transmission to watercourses, and/or soil persistence, grass yield and uptake. The impact of EU and alternative pasteurisation regimes on transmission potential of these various pollutants is not clearly understood, particularly in pasture-based agricultural systems. This study utilized simulated rainfall (Amsterdam drip-type) at a high intensity indicative of a worst-case scenario of ~11 mm hr−1 applied to plots 1, 2, 15 and 30 days after grassland application of slurry, unpasteurised digestate, pasteurised digestate (two conditions) and untreated controls. Runoff and soil samples were collected and analysed for a suite of potential pollutants including bacteria, nutrients and metals following rainfall simulation. Grass samples were collected for three months following application to assess yield as well as nutrient and metal uptake. For each environmental parameter tested: microbial, nutrient and metal runoff losses; accumulation in soil and uptake in grass, digestate from anaerobic co-digestion of slurry with food processing waste resulted in lower pollution potential than traditional landspreading of slurry without treatment. Reduced microbial runoff from digestate was the most prominent advantage of digestate application. Pasteurisation of the digestate further augmented those environmental benefits, without impacting grass output. Anaerobic co-digestion of slurry is therefore a multi-beneficial circular approach to reducing impacts of livestock production on the environment. Unlabelled Image • Co-digesting cattle slurry with food processing waste mitigates environmental impacts. • Lower microbial, nutrient and metal concentrations in runoff from digestate compared with slurry. • Reduced microbial runoff from digestate was the most prominent difference compared with slurry. • Pasteurisation further improved the environmental benefits of amending soils with digestate. [ABSTRACT FROM AUTHOR]