Citation: Bekier, J.; Jamroz, E.; D˛ ebicka, M.; ´ Cwiel ˛ ag-Piasecka, I.; Kocowicz, A. Quantitative Carbon Changes of Selected Organic Fractions during the Aerobic Biological Recycling of Biodegradable Municipal Solid Waste (MSW) as a Potential Soil Environment Improving Amendment—A Case Study. Agriculture 2022, 12, 2058. https:// doi.org/10.3390/agriculture12122058 Academic Editors: Jolanta Kwiatkowska-Malina and Grzegorz Malina Received: 26 October 2022 Accepted: 29 November 2022 Published: 30 November 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). agriculture Article Quantitative Carbon Changes of Selected Organic Fractions during the Aerobic Biological Recycling of Biodegradable Municipal Solid Waste (MSW) as a Potential Soil Environment Improving Amendment—A Case Study Jakub Bekier , El ˙ zbieta Jamroz * , Magdalena D ˛ ebicka , Irmina ´ Cwiel ˛ ag-Piasecka and Andrzej Kocowicz Institute of Soil Sciences, Plant Nutrition and Environmental Protection, Wroclaw University of Environmental and Life Sciences, Grunwaldzka 53, 50-357 Wroclaw, Poland * Correspondence: elzbieta.jamroz@upwr.edu.pl Abstract: The aim of the investigation was to determine the quantitative changes of selected organic compounds during composting of municipal solid wastes (MSWs). The object of the study was a differently matured compost produced according the to open pile/windrow semi-dynamic technol- ogy from selectively collected biodegradable municipal solid waste. During the experiment, the temperature and moisture of the composted wastes were monitored. In the collected samples—taken from differently matured compost—the total organic carbon (TOC) and total nitrogen (TN) were determined. The organic matter fractionation method described by Stevenson and Adani et al. was adopted, which allows to determine the carbon content of the following groups of organic com- pounds: hydrophobic (HSC), hydrophilic (WEOC), acidophilic (C AC ), cellulose (CCEL), core-HA (ligno-humic, CALK) and residual carbon (non-hydrolysing, CR). The TOC and TN content, as well as the origin and quality of the starting materials, allow the product tested to be classified for fertiliser purposes. The most intense changes were observed during the thermophilic composting phase. In spite of the optimal technological conditions of the process, the predominance of the CR and CCEL fraction was observed, and the share of humic compounds did not exceed 30% TOC. The investigated compost met legal, ecological and economic criteria for products of biological recycling, thus can be used as a good organic amendment to improve the soil organic matter balance, stimulate the soil biodiversity and carbon sequestration. Keywords: humic substances; compost quality; municipal waste; transformation of organic com- pounds 1. Introduction Soil management and utilization should result in maintaining the soil quality, fertility and productivity, especially as stocks of soil organic carbon have declined in many agri- cultural systems all over the world. In the last decades there has been a growing interest in the use of alternative fertilizers, such as brown coal, biochar, composts produced from segregated biodegradable waste or biomass, as well as other organic amendments, in agri- cultural and horticultural production. Soil organic amendments are a good source of stable organic carbon and, due to the presence of good-quality nutrients, can be efficiently used to improve the balance of organic matter, enhance carbon sequestration and stimulate the activity of soil biodiversity [1–3]. Moreover, the increasing amount of waste requires a rea- sonable strategy in its management. It focuses mainly on: quantity and toxicity reduction, recycling and reuse, and energy recovery [1,2,4]. Urban waste management and processing is currently a priority in the environmental policy of many countries. As a consequence of increasing the pro-ecological awareness of citizens and governing elites, the development of those fields of science and technology, which allow a reasonable waste management, Agriculture 2022, 12, 2058. https://doi.org/10.3390/agriculture12122058 https://www.mdpi.com/journal/agriculture