Distribution of Oxyphinic Elements in Sewage Sludge Fractions Based on Manganese and Nickel

Owing to the chemical composition of sewage sludge (SS), it may be used as an alternative to fertilizers; however, before land application, it must be assessed in terms of its contents of heavy metals considering their potential mobility in the soil. The aim of this study was focused on evaluating the potential mobility of oxyphinic elements – Mn and Ni in SS. The samples were collected from 4 different wastewaters treatment plants located in the Wielkopolska province at the same time points in 3 consecutive years. The levels of Mn and Ni were assessed using the BCR sequential method. The risk assessment code, and individual contamination factor were additionally calculated. The sewage sludge from small WWTPs was characterised by significantly lower amounts of metals in comparison to those originating from the large ones. It was found that both metals were dominant in loosely and relatively loosely bound fractions of all analyzed SS. It was confirmed by high values of risk assessment codes and individual contamination factor. Mn and Ni belonging to the group of oxyphinic elements showed significant similarities in the distribution of SS fractions. Large and rapidly activated pool of Mn and Ni may be a beneficial and valuable source of nutrients for plants, but certain dangers related to the possible accumulation of these elements in soils could be also considered.