Evaluation of Four Farm-scale Systems for the Treatment of Liquid Pig Manure

In some regions in the Netherlands, high pig concentrations and limited availability of arable land have led to a surplus of manure which results in high off-farm manure disposal costs. The aim of manure treatment is to lower manure transport costs by reducing the volume and to improve market prospects by changing the nutrient composition. The objective of this study was to promote the introduction of manure treatment in the Netherlands by giving research support to farmer initiatives and providing them with data on the actual performance of their system with regard to product composition, mass flows, gaseous emissions, and economic feasibility. Four farm-scale systems for treatment of liquid pig manure were studied: two systems for mechanical separation, one for nitrification/denitrification, and one for evaporation. The results showed that a wide range of manure products could be obtained that differ in dry matter, N, P, and K content. The emission of ammonia and odour varied from 1·8 to 55 g t−1 [manure] and from 3·8×103 to 1·3×107 [European odour units] t−1 [manure], respectively. The nitrification/denitrification showed the highest emission of greenhouse gases (48 kg [carbon dioxide equivalents] t−1 [manure]), mainly nitrous oxide (N2O), whereas the emission of the other systems was 12–17 kg [CO2-eq.] t−1 [manure]. The critical success factor for the operation of the manure treatment installations turned out to be not of technical but of economical nature. The manure treatment costs, including variable and fixed cost, varied from 7 to 17 € t−1 (excluding value added tax). To be cost effective in comparison with the disposal of untreated manure, these costs must be balanced out by the sale or the lower disposal costs of the manure products. As market prospects and disposal costs for manure and its products differ from case to case, no generally preferred manure treatment technique can be pointed out from this study, as local market circumstances must be taken into account.