Reusing Phosphorus: Engineering Possibilities and Economic Realities
Kvarnstrom, Elisabeth, Nilsson, Mats, Journal of Economic Issues
Recycling is becoming increasingly important in rich societies both in a physical sense and in the perceptions about desirable changes of economic activity and behavior. In both respects, the significance of recycling is greatest for the raw materials of agricultural, forest, and mineral origins. Recycling of phosphorus, i.e., secondary phosphorus originating from wastewater, is discussed in this paper.
The recycling of phosphorus from wastewater currently involves the reuse of sewage sludge in agriculture. In Sweden, 84 percent of the population is connected to wastewater treatment plants where phosphorus is removed from the wastewater [SCB 1995a], hence producing sludge containing high levels of phosphorus. The phosphorus content is 6,000 metric tons per year in Swedish wastewater treatment plant sludge. This represents approximately 30 percent of the commercial phosphorus fertilizer used yearly in Sweden [NV 1996].
The use of sewage sludge in agriculture has been discussed widely in Sweden during the 1990s. Far from resolving several important issues, such as the content of pollutants in the sludge and whether the content of phosphorus in sludge can be used by plants, the debate is still raging. The recoverability and value of phosphorus in sewage sludge depend on its quantity, location, and the sludge quality.(1) Sewage sludge is often favorably affected by the first criterion but unfavorably affected by the last two criteria.
Objectives and Method
This paper is interdisciplinary, and the objective is to investigate the factors determining the use of secondary phosphorus as viewed by the suppliers. Future secondary phosphorus alternatives, as viewed by the secondary phosphorus suppliers, are discussed. The method employed was to send a questionnaire (see Table 1) to 73 out of 288 municipalities in Sweden. The addressee was generally a sanitation engineer, who represents the supply side of the secondary phosphorus "market."
Background.' Sewage Sludge Use in Sweden
The macro-nutrients necessary for plant growth are nitrogen, phosphorus, and potassium. There is a constant flow of phosphorus from agriculture toward urban areas due to "exportation" of food. Around 60 percent of this phosphorus can be found in toilet waste [Kirchmann 1998].
In Sweden, about 30 percent of the sludge produced is reused in agriculture. However, the Recycling Act, passed by the Swedish government in 1994, states that a certain sludge quality must be reached to allow for the utilization of sludge within agriculture.2 An agreement on quality assurance for sludge utilization was reached in 1994 among the Swedish Environmental Protection Agency, the Federation of Swedish Farmers (LRF(3)), and the Swedish Water and Wastewater Association. Part of the agreement involved the establishment of national, regional, and local sludge utilization agreement councils, whose members include farmers and representatives from municipalities and consumer organizations. The establishment of these sludge councils has increased sludge utilization from 20 percent before the establishment of the councils to 30 percent in 1996 [NV 1996].
It is noteworthy that the allowed yearly deposition of cadmium(4) on arable land in Sweden is 1.75 g of Cd/ha. The same figure for the United States in 1994 was 1,900g/ha [Larsson 1995]. This indicates the stringent approach to sludge utilization in Sweden. Many municipalities conform to the strict regulations concerning sludge quality(5) but still do not find any use for their sludge [NV 1996].
In attempting to market their sludge, Swedish municipalities must also overcome the food industry's dislike of sludge utilization on crops. It is concerned with the transmission of heavy metals and organic compounds from sludge to humans via soil and animals. Several environmental organizations in Sweden are against the utilization of sewage sludge in agriculture. …