M. Timmerman

Sustainable intensive livestock production demands manure and exhaust air treatment technologies

Intensive livestock production is connected with a number of environmental effects, including discharges to soils and surface waters and emissions to the atmosphere. In areas with a high livestock density the low availability of nearby arable land, together with the preferred use of chemical fertilizer by arable farmers, results in high off-farm disposal costs for manure. Furthermore, ammonia abatement technologies, such as treatment of exhaust air, are important as ammonia emissions may account up to a quarter of the total nitrogen flux. Firstly, the paper describes and discusses the development of manure treatment in the Netherlands since the 1970s. Manure treatment processes that result in products that compete with and replace the use of chemical fertilizers can (partly) close the nutrient cycle again. From this point of view aerobic treatment of manure (nitrification/denitrification) can not be considered sustainable as nitrogen is taken out of the cycle at high environmental costs. Secondly, the state-of-the-art of techniques for treatment of exhaust air is presented. Besides ammonia, application of air treatment may also reduce environmental emissions of odour and particulate matter (dust). Both manure treatment and treatment of exhaust air are considered essential for sustainable livestock operations in areas with a high livestock density.

Optimizing the performance of a reactor by reducing the retention time and addition of glycerin for anaerobically digesting manure

Anaerobic digestion of manure is a widely accepted technology for energy production. However, only a minimal portion of the manure production in the EU is anaerobically digested and occurs predominantly in codigestion plants. There is substantial potential for biogas plants that primarily operate on manure (>90%); however, the methane yields of manure are less compared to coproducts, which is one of the reasons for manure-based biogas plants often being economically non-viable. Therefore, it is essential to begin increasing the efficiency of these biogas plants. This study investigated the effect of decreasing retention time and introducing a moderate amount of glycerin on the biogas production as methods to improve efficiency. An experiment has been conducted with two different manure types in four biogas reactors. The results of the study demonstrated that, first, it was possible to decrease the retention time to 10–15 days; however, the effect on biogas production varied per manure type. Secondly, the biogas production almost triples at a retention time of 15.6 days with an addition of 4% glycerin. The relative production-enhancing effect of glycerin did not vary significantly with both manure types. However, the absolute production-enhancing effect of glycerin differed per manure type since the biogas production per gram VS differed per manure type. Thirdly, the positive effect of the glycerin input declines with shorter retention times. Therefore, the effect of glycerin addition depends on the manure type and retention time.