Fertiliser Properties of Wastewater Sludge and Sludge Ash - A Case Study from the Finnish Forest Industry

Juha Oksanen*, Risto Pöykiö, Olli Dahl

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

1 Citation (Scopus)
31 Downloads (Pure)

Abstract

In this case study we compared the fertiliser properties of an industrial wastewater treatment sludge and a sludge ash to the requirements of the Finnish Fertiliser Product Decree. The sludge was obtained from the activated sludge wastewater treatment plant of a Finnish non-integrated pulp mill. The sludge was furthermore incinerated at a laboratory in a muffle furnace (850 °C) to obtain sludge ash. The total Cd (4.9 mg/kg d.m.) concentration in the pulp sludge exceeded the Finnish limit value (1.5 mg/kg d.m.) for fertiliser products used in agriculture. In the sludge ash, the total concentration of Cd (39 mg/kg; d.m.) exceeded the Finnish limit value (25 mg/kg d.m.) for ash fertilisers used in forestry. These results restrict the potential reuse options of these residues. However, from the utilisation point of view, the enrichment of essential plant macro-nutrients was most notable, resulting to the following total concentrations of these elements in the sludge ash: P (26,000 mg/kg d.m.), S (40,000 mg/kg d.m.), K (11,000 mg/kg d.m.), Ca (83,000 mg/kg d.m.) and Mg (10,000 mg/kg d.m.). Therefore, we conclude that, the converting of sludge into ash may promote the reuse of this wastewater treatment residue to a more value-adding fertiliser by-product to be used as a soil improver and growing medium in landscaping or landfills sites or other closed industrial areas, where heavy metal limit values for fertilisers are not applied in Finland.

Original languageEnglish
Pages (from-to)63-78
Number of pages16
JournalEcological Chemistry and Engineering S
Volume30
Issue number1
DOIs
Publication statusPublished - 1 Mar 2023
MoE publication typeA1 Journal article-refereed

Keywords

  • ash
  • circular economy
  • extraction
  • fertiliser
  • pulp mill
  • sludge
  • waste
  • wastewater treatment

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