• Energy Research

This article focuses on the end-of-life management of bio-based products by recycling, which reduces landfilling. Bio-plastics are very important materials, due to their widespread use in various fields. The advantage of these products is that they primarily use renewable materials. At its end-of-life, a bio-based product is disposed of and becomes post-consumer waste. Correctly designing waste management systems for bio-based products is important for both the environment and utilization of these wastes as resources in a circular economy. Bioplastics are suitable for reuse, mechanical recycling, organic recycling, and energy recovery. The volume of bio-based waste produced today can be recycled alongside conventional wastes. Furthermore, using biodegradable and compostable bio-based products strengthens industrial composting (organic recycling) as a waste management option. If bio-based products can no longer be reused or recycled, it is possible to use them to produce bio-energy. For future effective management of bio-based waste, it should be determined how these products are currently being managed. Methods for valorizing bio-based products should be developed. Technologies could be introduced in conjunction with existing composting and anaerobic digestion infrastructure as parts of biorefineries. One option worth considering would be separating bio-based products from plastic waste, to maintain the effectiveness of chemical recycling of plastic waste. Composting bio-based products with biowaste is another option for organic recycling. For this option to be viable, the conditions which allow safe compost to be produced need to be determined and compost should lose its waste status in order to promote bio-based organic recycling.

The textile industry is global, and most brands export their products to many different markets with different infrastructures, logistics, and regulations. A textile waste recovery system that works in one country may fail in another. European Union legislation (Directive (EU) 2018/851) mandates that post-consumer textile waste must be separately collected in all associated countries. This directive has also stated that, in January 2025, the rate of textile waste recycling in Europe should be increased. Local governments will be under pressure to improve the collection, sorting, and recycling of textiles. Supporting local governments could be part of a more long-term approach to managing high-value textile waste by implementing Extended Producer Responsibility, which would increase the recycling rate of textile companies. This would enable reuse of over 60% of recovered clothes, recycling into fibers of 35%, and only throwing away 5%. Today, most textile waste (85%) is disposed of as solid waste and must be disposed of through municipal or local waste management systems that either landfill or incinerate the waste. To increase reuse and recycling efficiency, textile waste should be collected and sorted according to the relevant input requirements. The dominant form of textile waste sorting is manual sorting. Sorting centers could be a future solution for intensifying the recycling of textile waste. Advances in textile waste management will require digitization processes, which will facilitate the collection, sorting, and recycling of textiles. It is very important that digitization will help to guide used products to recycling and encourage manufacturers to participate in the use and collection of product data. Currently, both the digitization of textile waste management and fiber recycling technologies are at the level of laboratory research and have not been implemented. The aim of this publication is to analyze the state of textile waste management, especially the various forms of recycling that involve a local governments and the textile industry.

This study assessed the effect of different lignocellulosic amendments and bulking agents on compost stability (based on a 4 day respiration activity test, AT4, and self-heating factor, SHF) and maturity (based on the nitrification index Initr and the ratio of C in humic acids, HA, to total organic carbon, TOC, in compost, CHA/TOC). With all feedstock compositions (FCs), the share of sewage sludge was 79% (wet mass). For FC1, wood chips (13.5%) and wheat straw (7.5%) were used as bulking agents and amendments; for FC2, instead of wood chips, energy willow was added; for FC3, pine bark (13.5%) and conifer sawdust (7.5%) were used. All FCs produced stable and mature compost; however, with FC2, the thermophilic phase last 3 days longer than with the other FCs. Moreover, an AT4 value below 10 g O2/kg dry mass (d.m.) was obtained the earliest with FC2 (after 45 days, ca. 15–20 days earlier than with other FCs). With FC2, Initr below 0.5 was obtained in ca. 60 days, 10 days earlier than with FC3 and 30 days earlier than with FC1. The highest net increases in HS (86.0 mg C/g organic matter (OM)) and HA (56.3 mg C/g OM) were also noted with FC2; with other FCs, the concentrations of these compounds were from 1.3- to 1.5-fold (HS) and from 1.4- to 1.9-fold (HA) lower. With FC2, the highest CHA/TOC (15.5%) was also noted, indicating that this compost contained the largest share of the most stable form of organic carbon. The rates of OM removal in the bioreactor ranged from 7.8 to 10.1 g/(kg d.m.·day). The rates of SH and HA formation ranged from 1.63 to 4.83 mg C/(g OM·day) and from 1.23 to 1.80 mg C/(g OM·day), respectively. This means that, through the choice of the amendments and bulking agents, the length of the composting time needed to obtain a stable and mature product can be controlled.

Although anaerobic digestion (AD) enables biogas production and facilitates renewable electricity production, its effluent must be post-treated before discarding it into the environment. However, during AD designing, the post-treatment step is often overlooked. This paper presents the kinetics and efficiency of nitrogen removal from effluent after AD of leachate from the aerobic stabilization of the organic fraction of municipal solid waste. A two-stage SBR system was used. An ammonium oxidation rate of 15.5 mg N-NH4/(L·h) ensured a 98% nitrification efficiency (I stage). For denitrification (II stage), alternative carbon sources (ACS) (molasses, crude glycerine, or distillery stillage) were used. Two volumetric exchange rates (n) were tested: 0.35 1/d (COD/N-NO3 ratio of 8) and 0.5 1/d (COD/N-NO3 of 7). With all ACS and COD/N-NO3 ratios, almost 100% of nitrate was denitrified; at the COD/N-NO3 of 8, biodegradable organics remained in the effluents. At the COD/N-NO3 of 7, the denitrification removal rates were lower (29.6-45.1 mg N-NOx/(L·h)) than at the ratio of 8 (72.1–159.5 mg N-NOx/(L·h)), because of temporal nitrite accumulation. The highest nitrate removal rates were obtained with molasses, the lowest with a distillery stillage. Considering the nitrate removal rate and the effluent COD concentration, molasses was recommended as the most effective carbon source for AD effluent treatment at the COD/N-NO3 of 7.

There is a lack of knowledge about the composition and particle size distribution of the <80 mm fraction mechanically separated from residual municipal solid waste (rMSW) and the stabilized residual (SR) after aerobic stabilization in a full-scale MBT plant. Therefore, the composition of the particle size fractions (>60 mm, 60–40 mm, 40–10 mm) of the <80 mm fraction and SR, collected in all seasons (summer (S), autumn (A), winter (W), spring (Sp)), was determined. Biodegradable waste (vegetable waste, other organic waste, paper, cardboard) constituted from 44.1% (A) to 54.3% (Sp) of the <80 mm fraction and it decreased to 8.5% (W) to 17.1% (S) in the SR, after effective biodegradation. In SR, the smaller particle size fractions (up to 40 mm) predominated. The main contaminants in SR were plastic, glass, metal, and other waste. Hierarchical clustering indicated that the composition of the particle size fractions of SR was more similar across four seasons than that of the <80 mm fraction. After stabilization and separation, the share of contaminants increased in the SR size fractions, which means that their recovery before landfilling may be profitable. This suggests a new direction in waste management that would be consistent with the principles of a circular economy, in which a waste product, like SR, which previously could only be landfilled, becomes a source of secondary materials.

Challenges associated with plastic waste management range from littering to high collection costs to low recycling rates. Effective collection of plastics is obviously an important step in the management of plastic waste and has an impact on recycling rates. For this reason, several countries have transformed their collection systems in recent decades. Collecting more plastic packaging comes at a cost, as the feedstock for the sorting process becomes more complex and leads to cross-contamination within the sorted fractions. Therefore, a balance must be obtained between some elements, such as the design of packaging, collection and recycling rates, and finally, the quality of fractions that have been sorted. Further investment to improve pretreatment, sorting, and recycling technologies and simpler recyclable packaging designs are, therefore, key to further increasing plastic recycling rates. It is essential to possess more data, especially on the type of containers and plastics, and examine how often unsorted waste is collected. The automated waste collection monitoring system is a step forward in automating manual waste collection and sorting. Multi-sensory artificial intelligence (AI) for sorting plastic waste and the blockchain sorting platform for the circular economy of plastic waste are forward-looking activities that will increase the efficiency of recycling plastic waste. This review focuses on the development of collection systems and sorting processes for post-consumer plastic recycling. The focus is on best practices and the best available technology. Separate collection systems for recyclable plastics are presented and discussed along with their respective technical collection and sorting solutions, taking into consideration that progress in separation and sorting systems are implicitly linked to approaches to waste collection.

To produce a valuable final product from anaerobic digestion (AD), one of the preferred methods of organic recycling, high quality feedstock must be ensured. In this study, separately collected real biowaste (B) was used, consisting of 90% food waste and 10% green waste. The priority issues of AD are both high methane production (MP) and high organics removal efficiency (as organic matter, OM and dissolved organics, and DCOD), which may be improved after pre-treatment. In this study, the effect of hydrothermal pre-treatment (BHT) and enzymatic additives (BE) on MP and organics removal from biowaste in mesophilic (37 °C) conditions was analyzed. To assess the adequacy of pre-treatment application, biowaste without treatment (BWT) was used. Pre-treatment of biowaste prior to AD affected the maximal MP, the removal effectiveness of both OM and DCOD, and the kinetic parameters of these processes. For BWT, the maximal cumulative MP reached 239.40 ± 1.27 NL/kg OM; the kinetic coefficient of MP (kCH4) and the initial MP rate (rCH4) were 0.32 ± 0.02 d−1 and 76.80 ± 1.10 NL/(kg OM·d), respectively. After hydrothermal pre-treatment, the MP of BHT (253.60 ± 1.83 NL/kg OM) was 6.3% higher than BWT. However, the highest MP was found for BE, 268.20 ± 1.37 NL/kg OM; to compare, it increased by 12.1% and 5.5% with BWT and BHT, respectively. However, the kinetic parameters of MP were highest with BHT:kCH4 0.56 ± 0.02 d−1 vs. 0.32 ± 0.02 d−1 (BWT) and 0.34 ± 0.02 d−1 (BE); rCH4 141.80 ± 0.02 NL/(kg OM·d) (BHT) vs. 76.80 ± 1.10 NL/(kg OM·d) (BWT) and 89.80 ± 0.50 NL/(kg OM·d) (BE). The effectiveness of OM removal was highest with BE, similarly to the MP with the use of an enzymatic additive. The kinetics of OM removal (rOM, kOM) were highest with BHT, similarly to the kinetics of MP (rCH4, kCH4). The highest effectiveness of OM and, consequently, its lowest final content obtained with BE means that the organics were used most efficiently, which, in turn, may result in obtaining a more stable digestive system.