The tanning industry generates significant amounts of solid waste and post-production wastewater, which should be managed in accordance with the principles of the circular economy. Waste is generated at various technological stages of production. This comprises mainly solid waste and leachate. A comprehensive solution to the problem of disposal of this waste is very important from economic and environmental points of view. This work presents research for a technological production line designed for the comprehensive processing of post-production residues. In the present paper, the authors present an analysis related to the possibility of processing leather flesh side (mizdra) as a substrate for methane fermentation. The study showed an increased biogas production from solid waste after enzymatic hydrolysis up to 248 Nm³/Mg. Preliminary research on the system designed for pre-treatment of sewage from the technological line is also presented. The study showed a COD reduction of more than 30%. The possibility of energy management of the solid fraction directly from the processes carried out is demonstrated.

Solar energy is a promising and efficient source of electricity in countries with stable and high sunshine duration. However, in less favorable conditions, for example in continental, temperate climates, the process requires optimization to be cost-effective. This cannot be done without the support of appropriate mathematical and numerical methods. This work presents a procedure for the construction and optimization of an artificial neural network (ANN), along with an example of its practical application under the conditions mentioned above. In the study, data gathered from a photovoltaic system in 457 consecutive days were utilized. The data includes measurements of generated power, as well as meteorological records. The cascade-forward ANN was trained with a resilient backpropagation procedure and sum squared error as a performance function. The final ANN has two hidden layers with nine and six nodes. This resulted in a relative error of 10.78% and R² of 0.92–0.97 depending on the data sample. The case study was used to present an example of the potential application of the tool. This approach proved the real benefits of the optimization of energy consumption.

In the context of climate policy, measures are being taken around the world to reduce pollution. These have been intensified in the areas of transport, industry, and energy, with the goal of zero emissions. The role of the biogas plant in energy transition and as a waste treatment plant for disposal is very important. This article describes research on a dynamic anaerobic digestion (AD) process plant. The subject of this study was leather shavings, which is a problematic waste. The research presented here is intended to demonstrate the decomposition of the flesh in the process, to confirm its biogas yield, and to evaluate the biological and technical parameters of the process. High biochemical stability was achieved for each of the tests evaluated, and no specific technical requirements were demonstrated. The only technical aspect to be addressed during operation was sedimentation, which can be solved by preparing the mixture earlier or by changing the mixing method. This made it reasonable to investigate the material further in the context of an industrial project. The characteristics of protein degradation in the AD process resulted in a high methane content in the biogas, above 65%. It was also observed that the long conditioning time of biogas in the gas cushion favourably affected the proportion of methane in biogas. Analytical results confirmed 77.5% methane content, which was a very good result. This paper presents the results of a surprising effect of chromium, primarily Cr (III), on the performance of anaerobic digestion.

The possibility of anaerobic digestion of leather shavings regardless of tanning agent (chrome, vegetable, synthetic) were was investigated. The fermentation batch test (38 °C) was conducted in 2 L reactors according to modified German norm DIN 38314 S8 and standardized biogas guidance issued by the Association of German Engineers in Dresden, VDI 4630. Chemical pretreatment, using organic compounds for solubilization and organic salts for chrome leaching, was applied. Evaluation encompassed the dynamics of the process, final biogas/methane efficiency, as well as the influence of tanning agent type and pretreatment on fermentation. Results showed varying effects of pretreatment methods on methane production and biogas yields. Depending on the tanning of the agent, biogas yield increased by 37–3002%, 590–3198%, and 403–694%, for chrome, synthetic, and olive-tanned shavings, respectively, compared to the control sample (raw substrate). Findings underscore the need for further mechanistic understanding and optimization of pretreatment methods to maximize biogas production from leather wastes.

Agricultural production residues are an easily accessible raw material for energy recovery in a circular economy. Therefore, the possibility of biogas production from herb processing waste, namely common thyme (Thymus vulgaris L.), peppermint (Mentha × piperita L.), curled mint (Mentha crispa L.), and currants (woody stems and leaves), was investigated. In this study, the evaluation of the natural biodegradability of plant waste under conditions typical for an agricultural biogas plant was consciously carried out without the application of pre-treatment processes (shredding, steam hydrolysis, chemical treatment) to facilitate the methane fermentation process. The average values of biogas production efficiency ranged from 75 to 320 m³/mg DM for herb species and from 152 to 209 m³/mg DM for currant varieties under normal conditions. As part of laboratory tests, the elemental composition, i.e., C, H, N, S, O, was determined. Moreover, the analysis showed the energy potential of the tested waste in thermochemical processes (combustion). Garden thyme residues have particularly high energy potential, as indicated by the high calorific value, low nitrogen and sulfur content, and low ash content.