References

1. R. Li, H. Meng, L. Zhao, H. Zhou, Y. Shen, X. Zhang, J. Ding, H. Cheng, J. Wang, Study of the morphological changes of copper and zinc during pig manure composting with addition of biochar and a microbial agent, Bioresour. Technol., 291 (2019) 121752, doi: 10.1016/j.biortech.2019.121752.
2. M.M. He, G.M. Tian, X.Q. Liang, Phytotoxicity and speciation of copper, zinc and lead during the aerobic composting of sewage sludge, J. Hazard. Mater., 163 (2009) 671–667.
3. S. Li, D. Li, J. Li, G. Li, B. Zhang, Evaluation of humic substances during co-composting of sewage sludge and corn stalk under different aeration rates, Bioresour. Technol., 245 (2017) 1299–1302.
4. J. Wu, Y. Zhao, H. Qi, X. Zhao, T. Yang, Y. Du, H. Zhang, Z. Wei, Identifying the key factors that affect the formation of humic substance during different materials composting, Bioresour. Technol., 244 (2017) 1193–1196.
5. R. Sidełko, I. Siebielska, B. Janowska, A. Skubała, Assessment of biological stability of organic waste processed under aerobic conditions, J. Cleaner Prod., 164 (2017) 1563–1570.
6. R. Sidełko, K. Seweryn, B. Walendzik, Optimization of composting process in real conditions, Rocz. Ochr. Srodowiska, 13 (2011) 681–691.
7. G. Zheng, T. Wang, M. Niu, X. Chen, C. Liu, Y. Wang, T. Chen, Biodegradation of nonylphenol during aerobic composting of sewage sludge under two intermittent aeration treatments in a full-scale plant, Environ. Pollut., 238 (2018) 783–791.
8. M.P. Bernal, J.A. Alburquerque, R. Mora, Composting of animal manures and chemical criteria for compost maturity assessment. A review, Bioresour. Technol.,100 (2009) 5444–5453.
9. J. Doublet, F. Francou, M. Poitrenaud, S. Houot, Sewage sludge composting: influence of initial mixs on organic matter evolution and N availability in the final composts, Waste Manage., 30 (2010) 1922–1930.
10. D. Gonzalez, J. Colon, D. Gabriel, A. Sanchez, The effect of the composting time on the gaseous emissions and the compost stability in a full-scale sewage sludge composting plant, Sci. Total Environ., 654 (2019) 311–323.
11. X. Zhao, B. Li, J. Ni, D. Xie, Effect of four crop straws on transformation of organic matter during sewage sludge composting, J. Integr. Agric., 15 (2016) 232–240.
12. T. Głąb, A. Żabiński, U. Sadowska, K. Gondek, M. Kopeć, M. Mierzwa-Hersztek, S. Taborc, Effects of
    co-composted maize. sewage sludge. and biochar mixs on hydrological and physical qualities of sandy soil, Geoderma, 315 (2018) 7–35.
13. D. Kulikowska, S. Sindrewicz, Effect of barley straw and coniferous bark on humification process during sewage sludge composting, Waste Manage., 79 (2018) 207–213.
14. L. Wang, Y. Li, S.O. Prasher, B. Yan, Y. Ou, H. Cui, Y. Cui, Organic matter, a critical factor to immobilize phosphorus, copper, and zinc during composting under various initial C/N ratios, Bioresour. Technol., 289 (2019) 121745, doi: 10.1016/j.biortech.2019.121745.
15. X. Zhang, S. Dou, B.S. Ndzelu, X.W. Guan, B.Y. Zhang, Y. Bai, Effects of different corn straw amendments on humus composition and structural characteristics of humic acid in black soil, Commun. Soil Sci. Plant Anal., 51 (2020) 107–117.
16. H.N. Guo, L.X. Wang, H.T. Liu, Potential mechanisms involving the immobilization of Cd, As and Cr during swine manure composting, Sci. Rep., 10 (2020) 16632, doi: 10.1038/s41598-020-73894-4.
17. R. Sidełko, A. Chmielinska-Bernacka, Application of compact reactor for methane fermentation of municipal waste, Rocz. Ochr. Srodowiska, 15 (2013) 683–693.
18. X. Xiao, Y. Chang, F. Lai, H. Fang, C. Zhou, Z. Pan, J. Wang, Y. Wang, X. Yin, H. Huang, Effects of rice straw/wood sawdust addition on the transport/conversion behaviors of heavy metals during the liquefaction of sewage sludge, J. Environ. Manage., 270 (2020) 110824, doi: 10.1016/j.jenvman.2020.110824.
19. N. Rich, A. Bharti, S. Kumar, Effect of bulking agents and cow dung as inoculant on vegetable waste compost quality, Bioresour. Technol., 252 (2018) 83–90.
20. D. Wu, Z. Wei, F. Qu, T.A. Mohamed, L. Zhu, Y. Zhao, L. Jia, R. Zhao, L. Liu, P. Li, Effect of Fenton pretreatment combined with bacteria inoculation on humic substances formation during lignocellulosic biomass composting derived from rice straw, Bioresour. Technol., 303 (2020) 122849,
    doi: 10.1016/j.biortech.2020.122849.
21. S. Wu, Z. Shen, C. Yang, Y. Zhou, X. Li, G. Zeng, S. Ai, H. He, Effects of C/N ratio and bulking agent on speciation of Zn and Cu and enzymatic activity during pig manure composting, Int. Biodeterior. Biodegrad., 119 (2017) 429–436.
22. R. Sidełko, B. Walendzik, M. Smuga-Kogut, B. Janowska, K. Szymański, A. Głowacka, A. Leśniańska, Impact of reduced straw content on the sewage sludge composting process, Arch. Environ. Prot., 46 (2020) 70–77.
23. A. Jouraiphy, S. Amir, M. El Gharous, J.C. Revel, M. Hafidi, Chemical and spectroscopic analysis of organic matter transformation during composting of sewage sludge and green plant waste, Int. Biodeterior. Biodegrad., 56 (2005) 101–108.
24. D. Kulikowska, Z.M. Gusiatin, K. Bułkowska, K. Kierklo, Humic substances from sewage sludge compost as washing agent effectively remove Cu and Cd from soil, Chemosphere, 136 (2016) 42–49.
25. S. Xu, L. Li, J. Zhan, X. Guo, Variation and factors on heavy metal speciation during co-composting of rural sewage sludge and typical rural organic solid waste, J. Environ. Manage., 306 (2022) 114418, doi: 10.1016/j.jenvman.2021.114418.
26. F. Ingelmo, M.J. Molina, M.D. Soriano, A. Gallardo, L. Lapeña, Influence of organic matter transformations on the bioavailability of heavy metals in a sludge based compost, J. Environ. Manage., 95 (2012) S104–S109.
27. F. Laborda, E. Bolea, M.P. Górriz, M.P. Martín-Ruiz, S. Ruiz- Beguería, J.A. Castillo, A speciation methodology to study the contributions of humic-like and fulvic-like acids to the mobilization of metals from compost using size exclusion chromatography-ultraviolet absorption-inductively coupled plasma mass spectrometry and deconvolution analysis, Anal. Chim. Acta, 606 (2008) 1–8.
28. A. Veeken, K. Nierop, V.D. Wilde, B. Hamelers, Characterisation of NaOH-extracted humic acids during composting of a biowaste, Bioresour. Technol., 72 (2000) 33–41.
29. A. Leśniańska, B. Janowska, S. Sidełko, Immobilization of Zn and Cu in conditions of reduced C/N ratio during sewage sludge composting process, Energies, 15 (2022) 4507, doi: 10.3390/en15124507.
30. K. Gondek, M. Mierzwa-Hersztek, M. Kopec, Mobility of heavy metals in sandy soil after application of composts produced from maize straw, sewage sludge and biochar, J. Environ. Manage., 210 (2018) 87–95.
31. D. Kulikowska, Kinetics of organic matter removal and humification progress during sewage sludge composting, Waste Manage., 49 (2016) 196–203.
32. J. Kang, Z. Zhang, J.J. Wang, Influence of humic substances on bioavailability of Cu and Zn during sewage sludge composting, Bioresour. Technol., 102 (2011) 8022–8026.
33. Interreg South Baltic 2018, STEP, Sludge Technological Ecological Progress—Increasing the Quality and Reuse of Sewage Sludge, Project No. STHB.02.02.00-32-0110/17. Available at https://www.step-interreg.eu/pl/ (Accessed on 28 October 2020).
34. H. Yu, B. Xie, R. Khan, G. Shen, The changes in carbon. nitrogen components and humic substances during organic-inorganic aerobic co-composting, Bioresour. Technol., 271 (2019) 228–235.
35. Y. Chen, Y. Chen, Y. Li, Y. Liu, H. Li, H. Jiang, X. Luo, P. Tang, L. Chen, H. Yan, Evolution of humic substances and the forms of heavy metals during co-composting of rice straw and sediment with the aid of Fenton-like process, Bioresour. Technol., 333 (2021) 125170, doi: 10.1016/j.biortech.2021.125170.
36. M. Shi, Z. Wei, L. Wang, J. Wu, D. Zhang, D. Wei, Y. Tang, Y. Zhao, Response of humic acid formation to elevated nitrate during chicken manure composting, Bioresour. Technol., 258 (2018) 390–394.
37. A. Kabata-Pendias, Trace Elements in Soils and Plants, CRC Press, London, 2010.
38. StatSoft Electronic Statistic Textbook PL 2006. Available at http://www.statsoft.pl/textbook/stathome.html (Accessed on 30 September 2006).