Solid–Liquid Separation of Animal Slurry

Abstract

Societies will inevitably have to recognise that animal excreta are not just a waste material requiring disposal, but a crucial raw material needed to boost plant production to feed a growing world population. If used appropriately, animal excreta can replace significant amounts of mineral fertilisers in areas with livestock production. Manure comprises animal excreta dissolved in water or mixed with straw, a substance made up of organic matter and used as an organic fertiliser in agriculture, where it contributes to the fertility of the soil by adding plant nutrients and organic matter (Figure 1.1). In the management chain before it is applied to soil, manure can also be used for energy production. The increasing focus on developing and using new technologies and management methods for manure handling is the consequence of both a huge increase in livestock production worldwide and specialisation in agriculture. Thus, in new production systems, traditional farms with a mixture of livestock and crop production are often replaced with landless livestock production units. These new livestock production systems may not have the capacity to recycle manure on-farm, which was a feature of many farming system in the past. The plant nutrients in manure can, if used appropriately, replace significant amounts of mineral fertilisers, and the organic matter can boost soil fertility (Text Box-Basic 1.1) and can be used for energy production. On the other hand, improper management and utilisation of manure results in loss of plant nutrients (Bouwman et al., 2012)(Figure 1.2), which are a limited resource, and this can be a risk to the global feed and food supply. For example, phosphorus (P) is a limited resource, with the mineable phosphate-rich rocks used for P fertiliser production projected to become exhausted within the next 60-130 years (Figure 1.3). In a 14-month period during 2007-2008, the global food crisis led to phosphate rock and fertiliser demand exceeding supply and prices increased by 700% (Cordell et al., 2009). This increase in cost may be mitigated by reducing P

Ammonium Fertilizers Production from Manure: A Critical Review

“…Alternatives for solids removal are mechanical filtration using screw presses or drainage through press or belt filters (22). In 2010, Hjorth et al (22) and in 2013 Christensen et al (26) reported extensive reviews of options for solid-liquid separation of animal slurries. Based on their studies, separation efficiency of mechanical separators for the removal of dry matter and N in descending order is as follows: centrifugation > sedimentation > nonpressurized filtration > pressurized filtration.…”

“…The efficiency of solid-liquid separation can be enhanced by addition of cations or polymers resulting in fine particles aggregation due to coagulation and/or flocculation (22,26). Flocculation will lead to production of a cleaner effluent which is desired before further ammonia recovery.…”

Nutrient Recovery From the Liquid Fraction of Digestate by Clinoptilolite

“…Further concentration of these nutrients in the liquid fraction could reduce transportation costs and potentially increase the fertilizer efficiency of the liquid fraction of digestate. Concentration techniques using water evaporation and ammonia stripping consume a great deal of energy and are usually rather costly . Treatment of digestate using an ion exchanger/adsorptive agent may therefore, present an attractive alternative, which has so far not been investigated.…”

Recovery of nutrients from biogas digestate with biochar and clinoptilolite

“…Further concentration of these nutrients in the liquid fraction could reduce transportation costs and potentially increase the fertiliser efficiency of the liquid fraction of manure and digestate. Concentration techniques using water evaporation and ammonia stripping consume a great deal of energy and are usually rather costly (Christensen et al, 2013;Fuchs & Drosg, 2013;Zarebska et al, 2015). Treatment of digestate using an ion exchanger/adsorptive agent may therefore present an attractive alternative.…”