PhD defence

Jerke de Vries: From animals to crops

Animal manure is a key component that links crop and livestock production as it contains valuable nutrients for the soil and crop. The aim of this thesis, was to provide knowledge and insight into the environmental consequences of current and future strategies for manure management. The environmental consequences of the following technologies were assessed: mono- and co-digestion of liquid manure; high-tech separation of liquid manure with further dewatering of the liquid fraction; and segregating fattening pig urine and feces inside the housing system. Applying a structured design approach enabled the design of new strategies for integrated manure management that prevented pollution swapping. The approach proved to be successful because the environmental impact reduced throughout the manure management chain by at least 57% and more than doubled the nitrogen use efficiency compared to current North Western European manure management practices.

Abstract:

Animal manure is a key component that links crop and livestock production as it contains valuable nutrients for the soil and crop. Manure is also a source of environmental pollution through losses of nutrients, such as nitrogen (N) and phosphorus (P), and losses of carbon (C). These losses are largely determined by the way manure is managed. Technologies to reduce nutrient and C losses from manure mainly focused on reducing a single emission while unwillingly increasing another emission at the same time; a phenomenon called pollution swapping. To prevent pollution swapping, we need to gain insight into the integral environmental consequences of technologies and use these insights to (re)design the manure management chain. The aim of this thesis, therefore, was to provide knowledge and insight into the environmental consequences of current and future strategies for manure management.

The environmental consequences of the following technologies were assessed: mono- and co-digestion of liquid manure; high-tech separation of liquid manure with further dewatering of the liquid fraction; and segregating fattening pig urine and feces inside the housing system. Following, we designed new strategies for integrated manure management that prevent pollution swapping, and assessed the environmental consequences of these strategies. Life cycle assessment was used to calculate the environmental impacts of current and future strategies. For the design, we adapted and used a structured approach to engineering design to create new strategies for integrated manure management.

It was concluded that mono-digestion of liquid manure reduced the environmental impact compared to conventional manure management, but has a low potential to produce bio-energy. Co-digestion with waste and residues, such as roadside grass, increased bio-energy production and further reduced the environmental impact. Co-digestion with substrates that compete with animal feed increased bio-energy production, but also the overall environmental impact from producing a substitute for the used co-substrate. Separating liquid manure into liquid and solid fractions with further de-watering of the liquid fraction increased the environmental impact compared to manure management without processing. A combination of separation and anaerobic mono-digestion of the solid faction reduced climate change and fossil fuel depletion. Segregating fattening pig urine and feces in the housing system reduced climate change, terrestrial acidification, and particulate matter formation and provided a sound basis for environmentally friendly manure management.

Applying a structured design approach enabled the design of new strategies for integrated manure management that prevented pollution swapping. The approach proved to be successful because the environmental impact reduced throughout the manure management chain by at least 57% and more than doubled the nitrogen use efficiency compared to current North Western European manure management practices.