A note on sewage sludge - risk assessments and fertilization value for Orgprints

Background In 2012 the Coordination Program Network of European Transnational Research in Organic Food and Farming Systems called for research on sustainable and efficient management of phosphorus and use of secondary fertilizers within organic agriculture. Recognizing that the mineral resources of natural phosphorous world-wide (suitable for extraction) are expected to meet requirements for the next 100 years only, a special focus on efficient use of existing P from alternative sources such as processed farm fertilizers, municipal waste and waste from the food industry, was highlighted among other points of interest. Oelofse et al. (in press) discuss the implications of phasing out conventional nutrient supply in organic agriculture which has been emphasized by a decision by Danish Organic farmers to ban import of manure and straw from conventional farms by 2021. Alternative strategies to ensure nutrient supply will require a tapestry of small solutions. One element of this tapestry is to review the volume and type of nutrient sources available in alternative, non-farm organic waste streams, and consider their suitability for use in organic systems. One lesson emerging from this study is that it will be impossible to cover the need for P fertilization in non-dairy farms without resorting to reuse of sewage sludge, which is in line with the ideas of one of the forefathers of organic agriculture, Sir Albert Howard, was a very strong proponent of the recycling of organic waste (Heckman J, 2006). Oelofse et al. (in press) assessed that a decision to allow the use of sewage sludge in one form or other will require a discussion of principles, and is perhaps an issue which requires discussion within organic agriculture about whether this can be a considered a breach of principles, a compromise or a fulfillment of the organic ideology of working with closed cycles. In the following sections a number of recent studies of risk related to agricultural use of sewage sludge are reviewed, as a contribution to the discussion of potential for use in organic agriculture. Furthermore a very tentative assessment of the fertilization value of sewage sludge and its derived products is developed.