Silver in urban wastewater

Abstract

As the use of consumer products is increasing, a similar increase of hazardous substances can be seen in sewage sludge in Swedish wastewater treatment plants (WWTPs). Silver (Ag) is a heavy metal with a high accumulation rate in soils when applying sewage sludge as fertilizer on arable land. Silver is therefore prioritized in REVAQ, a certificate system for Swedish WWTPs. The levels of Ag in the incoming water to the WWTP are today too high and must be reduced. This study aims to identify major diffuse emission sources of Ag and map out the inflow to, the stock (accumulated amount in the technosphere) and the outflow from Stockholm during 2012. In 2012, 62 kg silver was measured in the sludge in Henriksdal WWTP in Stockholm. Sources explaining 56 % of the measured amount of silver have been identified in this study, corresponding to 46 mg Ag per person and year. The sources with the largest contribution of silver are estimated to be textiles (19 %), urine and faeces (from for example amalgam fillings and food) (15 %) as well as cleaning products (7 %). The inflow of Ag to Stockholm during 2012 was estimated to 3 200 kg and the stock to 105 tons, where electric goods and appliances as well as silverware and jewellery together explain 94 % of the inflow and 98 % of the stock.