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Abstract: Throughout Europe and the USA, forest ecosystem functioning has been impacted by long-term excessive deposition of acidifying compounds. In this study, we report on trends in stand deposition and soil solution fluxes of inorganic nitrogen (N) and sulphur (S) compounds over a 17-year period (1994–2010) in five ICP Forests monitoring plots in Flanders, northern Belgium. Deposition was dominated by N, and primarily NH4 +. Deposition of SO4 2− and NH4 + declined by 56–68% and 40–59% respectively. Deposition of NO− 3 decreased by 17–30% in deciduous forest plots, but remained stable in coniferous forest plots. The decrease of N and S deposition was parallelled by a simultaneous decline in base cation (BC = Ca2+ + K+ + Mg2+) deposition, resulting in a 45–74% decrease of potentially acidifying deposition. Trends in soil solution fluxes of NH4 +, NO3 −, SO4 2− and BC mirrored declining depositions. Nitrate losses below the rooting zone were eminent in both coniferous forest plots and in one deciduous forest plot, while net SO4 2− release was observed in two deciduous forest plots. Critical limits for BC/Al ratio were exceeded at the three plots on sandy soils with lower cation exchange capacity and base saturation. Soil solution acid neutralizing capacity increased but remained negative, indicating that soil acidification continued, as the start of recovery was delayed by a simultaneous decrease of BC depositions and short-term soil buffering processes. Despite substantial reductions, current N deposition levels still exceed 4–8 times the critical load for safeguarding sensitive lichen species, and are still 22–69% above the critical load for maintaining ground vegetation diversity. [Copyright &y& Elsevier]

Dredged sediments from the Leie catchment (Belgium) that were deposited on land between 70 and 10 years ago were characterized according to their physico-chemical properties, total metal concentrations and porewater composition. Actual and potential heavy metal availability was assessed by means of single extractions with 0.01 M CaCl 2 , 0.05 M EDTA and 0.43 M acetic acid. A modified version of the BCR (Community Bureau of Reference) extraction procedure, adapted to the elevated acid neutralizing capacity of the sediments, was applied. Information on element mobility was assessed and the used methodologies were critically evaluated. The favorable physico-chemical characteristics of dredged sediments from the catchment of the Leie River (N-Belgium) indicated a rather low actual heavy metal mobility. Based on CaCl 2 and EDTA extractions, the distribution of Cd, Zn and Ni between the solution and sorbed phase could be described as a function of pH and organic carbon content. Cd and Zn were found to be the elements with the highest potential availability, while Cu and Ni displayed a medium availability. It is stressed that different types of extractions deal with heavy metal mobility in a different way and that the measurement of “key-factors” such as the pH of the extracts can be helpful for the interpretation of the results. [ABSTRACT FROM AUTHOR]

Conventional wastewater treatment plants remove phosphorus, which is captured in sewage sludge. Increasing attention is paid to suitable process pathways that allow recovery and recycling of phosphorus. One of the processes under investigation is acid leaching and recovery of phosphorus, but this requires considerable chemical additives, which could be avoided by stimulating acidification via microbiological processes. This study investigated phosphorus leaching from sewage sludge by biogenic sulfuric acid, using Acidithiobacillus thiooxidans. Sulfur supplementation and solid to liquid ratio were varied to examine how these factors affected phosphorus leaching yield. Chemical leaching by sulfuric acid from sewage sludge and thermally-treated sludge was conducted to compare with bioleaching from sewage sludge. Sewage sludge samples were collected from wastewater treatment plants in Ghent, Belgium, and Delft, The Netherlands. Both bioleaching and chemical leaching were conducted at laboratory scale using shake flask technique, and highest phosphorus leaching yield and time was determined using one-way ANOVA statistical tests. Biogenic sulfuric acid produced by A. thiooxidans extracted phosphorus from both sludge samples. The highest phosphorus leaching yield observed was 48 ± 0% for 17 days from Ghent samples and 57 ± 4% for 27 days from Delft samples with 5.0% (w/v) sulfur supplementation and 1.0% (w/v) solid to liquid ratio. Chemical leaching took shorter than bioleaching, but the leaching yield was lower, i.e. 41 ± 1% for 4 h from Ghent samples, 44 ± 1% for 1 h from Delft samples, 48 ± 1% for 1 h from thermally-treated Ghent samples and 51 ± 2% for 4 h from thermally-treated Delft samples. During phosphorus bioleaching, pH increase was observed during the early stage which hampered the activity of A. thiooxidans and therefore increased phosphorus leaching time. This study suggests that creating conditions for A. thiooxidans to overcome acid neutralizing capacity of sewage sludge is needed to extract phosphorus effectively., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)