Recovery of valuable nitrogen compounds from agricultural liquid wastes: potential possibilities, bottlenecks and future technological challenges

Agricultural liquid livestock wastes are an important potential source of valuable nitrogen-containing compounds such as ammonia and proteins. Large volumetric quantities of these wastes are produced in areas with a high livestock production density. Much technological research has been carried out in the past to recover nitrogen compounds from livestock wastes, usually within the framework of a more or less complete waste treatment process. A large part of this research did not result in applicable technology due to various technical and/or economical reasons. However, increasing interest in both the negative environmental aspects of agricultural liquid wastes and in recycling of valuable compounds promote further development of technologies for recovery valuable nitrogen compounds. In this paper the most important technologies to recover nitrogen compounds as valuable products are briefly discussed and evaluated. For each technology the stage of development, the applicability and the obtained experience is discussed. The evaluation covers biological conversion techniques like enzyme synthesis from ammonium and production of algae, chemical processes such as precipitation of fertiliser compounds and separation techniques such as stripping, partial condensation, and membrane chemo-sorption. It is emphasised that practical implementation of a technology can only be successful if both liquid animal waste producers and potential buyers and users of products of the treatment processes are heavily involved in the development of technology - a development that should start at farm level.