Marieke ten Hoeve

Life cycle assessment of pig slurry treatment technologies for nutrient redistribution in Denmark

Animal slurry management is associated with a range of impacts on fossil resource use and the environment. The impacts are greatest when large amounts of nutrient-rich slurry from livestock production cannot be adequately utilised on adjacent land. To facilitate nutrient redistribution, a range of different technologies are available. This study comprised a life cycle assessment of the environmental impacts from handling 1000 kg of pig slurry ex-animal. Application of untreated pig slurry onto adjacent land was compared with using four different treatment technologies to enable nutrient redistribution before land application: (a) separation by mechanical screw press, (b) screw press separation with composting of the solid fraction, (c) separation by decanter centrifuge, and (d) decanter centrifuge separation with ammonia stripping of the liquid fraction. Emissions were determined based on a combination of values derived from the literature and simulations with the Farm-N model for Danish agricultural and climatic conditions. The environmental impact categories assessed were climate change, freshwater eutrophication, marine eutrophication, terrestrial acidification, natural resource use, and soil carbon, nitrogen and phosphorus storage. In all separation scenarios, the liquid fraction was applied to land on the pig-producing (donor) farm and the solid fraction transported to a recipient farm and utilised for crop production. Separation, especially by centrifuge, was found to result in a lower environmental impact potential than application of untreated slurry to adjacent land. Composting and ammonia stripping either slightly increased or slightly decreased the environmental impact potential, depending on the impact category considered. The relative ranking of scenarios did not change after a sensitivity analysis in which coefficients for field emissions of nitrous oxide, ammonia and phosphorus were varied within the range cited in the literature. Therefore, the best technology to implement in a given situation depends on the environmental problem in question, local policy, cost and practicality.

Choosing co-substrates to supplement biogas production from animal slurry - a life cycle assessment of the environmental consequences.

Biogas production from animal slurry can provide substantial contributions to reach renewable energy targets, yet due to the low methane potential of slurry, biogas plants depend on the addition of co-substrates to make operations profitable. The environmental performance of three underexploited co-substrates, straw, organic household waste and the solid fraction of separated slurry, were assessed against slurry management without biogas production, using LCA methodology. The analysis showed straw, which would have been left on arable fields, to be an environmentally superior co-substrate. Due to its low nutrient content and high methane potential, straw yields the lowest impacts for eutrophication and the highest climate change and fossil depletion savings. Co-substrates diverted from incineration to biogas production had fewer environmental benefits, due to the loss of energy production, which is then produced from conventional fossil fuels. The scenarios can often provide benefits for one impact category while causing impacts in another.

Improving odour assessment in LCA—the odour footprint

PurposeOdour is an important aspect of systems for human and agricultural waste management and many technologies are developed with the sole purpose of reducing odour. Compared with greenhouse gas assessment and the assessment of toxicity, odour assessment has received little attention in the life cycle assessment (LCA) community. This article aims to redress this.MethodsFirstly, a framework for the assessment of odour impacts in LCA was developed considering the classical LCA framework of emissions, midpoint and endpoint indicators. This suggested that an odour footprint midpoint indicator was worth striving for. An approach to calculating an areal indicator we call “odour footprint”, which considers the odour detection threshold, the diffusion rate and the kinetics of degradation of odourants, was implemented in MATLAB. We demonstrated the use of the characterisation factors we calculated in a case study based on odour removal technology applied to a pig barn.Results and discussionWe produced a list of 33 linear characterisation factors based on hydrogen sulphide equivalents, analogous to the linear carbon dioxide equivalency factors in use in carbon footprinting, or the dichlorobenzene equivalency factors developed for assessment of toxic impacts in LCA. Like the latter, this odour footprint method does not take local populations and exposure pathway analysis into account—its intent is not to assess regulatory compliance or detailed design. The case study showed that despite the need for materials and energy, large factor reductions in odour footprint and eutrophication potential were achieved at the cost of a smaller factor increase in greenhouse emissions.ConclusionsThe odour footprint method is proposed as an improvement on the established midpoint method for odour assessment in LCA. Unlike it, the method presented here considers the persistence of odourants. Over time, we hope to increase the number of characterised odourants, enabling analysts to perform simple site-generic LCA on systems with odourant emissions.

Modelling the potential of slurry management technologies to reduce the constraints of environmental legislation on pig production

Limits on land applications of slurry nitrogen (N) and phosphorus (P) are used to restrict losses of nutrients caused by livestock production. Here, we used a model to assess technologies that enable a more even geographic distribution of slurry nutrients to land. Technologies included were screw press slurry separation, with or without solid fraction composting, centrifuge separation with or without liquid fraction ammonia (NH3) stripping, and anaerobic digestion. Regulatory constraints were placed first on the application in slurry of N, then P, then N and P both on the producing (donor) and receiving (recipient) farms. Finally, a constraint preventing an increase in donor farm NH3 emissions was imposed. Separation had little effect on N losses per unit mass of slurry, but NH3 stripping led to a reduction. Centrifuge separation allowed a greater increase in pig production than a screw press, especially with P regulation. NH3 stripping was only advantageous with N regulation or when combined with NH3 scrubbing of pig housing ventilation air, when donor farm NH3 emissions were a constraint. There was a production penalty for using composting or anaerobic digestion. The choice of appropriate slurry management option therefore depends on the focus of the regulation. Nuanced and therefore complex regulations are necessary to take advantage of synergies and avoid cross-policy conflicts and incongruencies.

Environmental impacts of combining pig slurry acidification and separation under different regulatory regimes - A life cycle assessment.

Global livestock production is increasing rapidly, leading to larger amounts of manure and environmental impacts. Technologies that can be applied to treat manure in order to decrease certain environmental impacts include separation and acidification. In this study, a life cycle assessment was used to investigate the environmental effects of slurry acidification and separation, and whether there were synergetic environmental benefits to combining these technologies. Furthermore, an analysis was undertaken into the effect of implementing regulations restricting the P application rate to soils on the environmental impacts of the technologies. The impact categories analysed were climate change, terrestrial, marine and freshwater eutrophication, fossil resource depletion and toxicity potential. In-house slurry acidification appeared to be the most beneficial scenario under both N and P regulations. Slurry separation led to a lower freshwater eutrophication potential than the other scenarios in which N regulations alone were in force, while these environmental benefits disappeared after implementation of stricter P regulations. With N regulations alone, there was a synergetic positive effect of combining in-house acidification and separation on marine eutrophication potential compared to these technologies individually. The model was sensitive to the chosen ammonia emission coefficients and to the choice of inclusion of indirect nitrous oxide emissions, since scenarios changed ranking for certain impact categories.

Life cycle inventory modeling of phosphorus substitution, losses and crop uptake after land application of organic waste products

PurposeLife cycle assessments (LCAs) that attempt to provide advice on treatment options for phosphorus (P) containing organic waste products encounter problems related to the quantification of mineral P fertilizer substitution, P loss and crop P uptake after land application. The purpose of this study was to develop a relatively easy to use life cycle inventory model, known as PLCI, that could be used to estimate these values.MethodsA life cycle inventory model for P was developed, which estimates the effect of an application of organic waste followed by ordinary fertilizer management in the modeling period. This was compared with a simulation without the initial waste application. The difference in mineral P fertilizer application (substitution), P loss and crop P uptake was then calculated and expressed as a proportion of the amount of waste applied. As an example, the effect of an initial application of mineral fertilizer, sewage sludge and ash on two farm types was simulated. These results were applied in an LCA case study of different sewage sludge treatment options.Results and discussionFarm type influenced the P fertilizer substitution, loss and crop uptake factors. The application on an arable farm showed a substitution of 28 to 31%, relatively low P loss and a large spread in crop P uptake for the different P sources, compared with the pig farm. Application on a pig farm showed no mineral P substitution. For substitution, mineral fertilizer outperformed waste product fertilizer with a short modeling period, due to higher immediate P availability, which was not the case with a long period. The LCA case study showed that the P substitution factor had an influence on the environmental impact categories climate change and depletion of reserve-based abiotic resources while the P loss factor influenced freshwater eutrophication. Application of the P loss and substitution factors generated from the PLCI model resulted in higher environmental burdens and lower savings than using conventional factors.ConclusionsThe soil P status mainly affected P substitution and loss, with the fertilizer type only having a small influence when soils had a low P status. The PLCI model can facilitate more coherent and rigorous estimates of P substitution and loss to be used in LCA studies involving application of waste products on agricultural land. This is important since P substitution and loss can have an important influence on impact categories, such as freshwater eutrophication and resource depletion.