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Influence of Decreasing Supplementation to Transformation of Chemical Forms of Ni, Zn and Cu During Composting of Sewage Sludge

Sidełko Robert, Janowska Beata, Leśniańska Aleksandra, Kraszewska Katarzyna, Grabowska Karina

Rocznik Ochrona Środowiska

2021

Tom 23

580--593

This paper pertains to the influence of decreasing supplementation to transformation of chemical forms of Ni. Zn and Cu during composting of sewage sludge. A universally used supplementing material constituting a rich source of organic carbon is straw. Addition of straw to sewage sludge is aimed at increasing C/N proportion up to at least 15 due to the risk of formation of toxic forms of nitrogen, concentration of which in sewage sludge is exceptionally high. We have presented in this paper the results of speciation research of three elements applying Tessier’s sequential extraction. It’s been proven that decreasing of straw share in the composted mixture with sewage sludge down to the level of C/N value below the admissible value, has a beneficial effect on the allocation of tested heavy metals towards the forms that are permanently bound in compost matrix. A systematic increase of organic (IV) and residual (V) fractions share and decrease of mobile forms of heavy metals content in bioavailable fractions i.e. ion-exchange (I) and carbonate (II) has been ascertained.

Impact of reduced straw content on the sewage sludge composting process

Sidełko Robert, Walendzik Bartosz, Smuga-Kogut Małgorzata, Janowska Beata, Szymański Kazimierz, Głowacka Anna, Leśniańska Aleksandra

Archives of Environmental Protection

2020

Vol. 46, no. 4

70--77

The main objective of presented research work was the assessment of the impact of reduced straw content, as organic carbon source, on the course of sewage sludge composting process. During the research work performed in industrial conditions, the composting process going in periodically overturned windrows differing in proportion of dehydrated sludge, straw and structural material being 4:1:1 and 8:1:2 respectively, was observed. The consequence of increase of sludge concentration with relation to straw was decrease of C:N ratio in the input material from 11.5 to 8.5. The following parameters were analyzed as indicators for the assessment of the composting process: contents of fulvic acids (FA), humic acids (HA), lignin, cellulose and hemicellulose as well as absorbance in UV/VIS (λ=280, 465 and 665 nm) range. The results obtained have indicated that the increase of sludge content extends the elevated temperature (T>50°C) period from 42 days to approximately 65 days. Our tests did not confirm that limitation of straw content added to sewage sludge had any adverse effect on the course of composting. PI index (HA/FA), which qualifies the compost as mature in the first case – No 1, exceeds limit value of 3.6 on the 83rd day whereas, in the second case No 2, on the 48th day.