INVESTIGATION OF PLASMA-OHMIC ELECTRIC FURNACES FOR GASIFYING CARBONACEOUSE WASTES

For the first time, the processes of reducing energy consumption of a plasma-ohmic electric furnace for the gasification of various carbon-containing wastes (municipal, biological, agricultural, and other organic wastes) were investigated. The effect of reducing the humidity, morphological composition of waste on energy consumption during plasma gasification of carbon-containing materials is shown. The possibility to exclude the process of preliminary drying from the production cycle of waste gasification has been revealed. In the modern world, one of the global trends in technology development is the continuous increase in the efficiency and environmental friendliness of carbon-containing waste management methods. The carbon-containing industrial waste includes: municipal (municipal solid waste (MSW)), agricultural (rice husk, etc.), industrial (wood waste, coal slimes, etc.) and biological (medical, biological sludge deposits (BIO) and etc.) Despite the different nature of this waste, they all consist of the same chemical elements: carbon, hydrogen, oxygen, nitrogen, chlorine, sulfur, ash (a complex of inorganic elements and compounds), water (moisture), but contain elements and compounds dangerous for the environment (pathogens, heavy metals, etc.). Gasification of carbon-containing wastes is a complex physico-chemical process with a large number of effects, a complete scientific explanation of which is far from completion.

Improvement of Biogas Yield by Pre-Treating Poultry Waste with Bacterial Strains

Poultry waste is increasingly used as a substrate for the methane fermentation process in a biogas plant. However, not all waste materials processed in the meat industry meet the criteria for optimal process management and cost-effective methane efficiency. An example may be centrifuged biological sludge, etc. Treatment of such material used as a substrate by introducing new metabolically and enzymatically active strains of bacteria could be beneficial for the fermentation process in a biogas plant and provide increased energy efficiency. The aim of the study was to compare the amount and quality of biogas obtained from biological sludge from the processing of poultry vaccinated with metabolically diversified bacterial inoculum after initial incubation of the batch before the actual process in a biofermenter. Laboratory tests were carried out in accordance with the guidelines contained in the DIN 38 414-S8 and VDI 4630 standards. Based on the obtained results, it was found that the optimized biological sludge can be used as a substrate in the methane fermentation process in a biogas plant. The material processed by the combination of bacterial strains marked with the symbols A/C, E/G, and F/H showed a significantly increased efficiency of biogas, including methane, compared to the non-grafted material. This is a good predictor for industrial applications, process feasibility, economic viability, and environmental sustainability that should be compiled based on the results obtained from this study.

Microaerobic Digestion of Low-Biodegradable Sewage Sludge: Effect of Air Dosing in Batch Reactors

The adoption of prolonged solid retention times during the biological treatment of urban wastewaters is a well-known strategy to reduce sewage sludge production. However, it also results in the production of a biological sludge with low percentages of biodegradable organic matter, also characterized by high humification degrees, which may hamper the anaerobic digestion treatment aimed at sludge stabilization. To accelerate the hydrolytic stage, the application of microaerobic conditions during the anaerobic digestion of low-biodegradable sewage sludge was investigated in this study. In particular, six bio-methanation tests of a real sewage sludge were carried out, introducing air in the bioreactors with doses ranging between 0 and 16.83 L air/kg VSin d, in order to evaluate the air dosage that optimizes the biomethane production and organic matter degradation. Notably, the lower air loading rates investigated in this study, such as 0.68 and 1.37 L air/kg VSin d, led to an increase in methane production of up to 19%, due to a higher degradation of total lipids and proteins. In addition, these microaerobic conditions also resulted in a decrease in the sludge humification degree and in lower volatile fatty acid accumulation.

Valorisation of residues from municipal wastewater sieving through anaerobic (co-)digestion with biological sludge

The Circular and Green Economy principles is inspiring new approaches to municipal wastewater treatment plants (MWWTPs) design and operation. Recently, an ever-growing interest is devoted to exploring the alternatives for switching the WWTPs from being able to ‘simply’ removing contaminants from water to biorefinery-like plants where energy and material can be recovered. In this perspective, both wastewater and residues from process can be valorised for recovering nutrients (N and P), producing value added products (i.e. biopolymers), energy vectors and biofuels (i.e. bio-H2, bio-CH4 and bioethanol). As an additional benefit, changing the approach for WWTPs design and operation will decrease the overall amount of landfilled residues. In this context, the present research is aimed at evaluating the CH4 production potential of MWW screening units’ residues. While such a stream is typically landfilled, the expected progressive increase of biodegradable matter content due to the ban on single-use plastic along with the boost of bioplastics makes the investigation of different biochemical valorisation routes more and more interesting from an environmental and economical perspective. Thus, a full-scale data collection campaign was performed to gain information on screening residues amount and properties and to analyse the relationship with influent flowrate. The most relevant residue properties were measured, and lab-scale tests were carried out to evaluate the bio-CH4 potential.

Treatment of PCBs Contaminated Soil Via Aerobic Vermicomposting Process Amended with Biological Sewage Sludge

Background: During power plant operations, significant amounts of (PCBs)-contaminated soil are generated. PCBs enter the environment in various forms, causing toxicity in humans and other living organisms. Various technologies are used to remove PCBs from contaminated soils and sediments. Objectives: Bioremediation is an environmentally friendly method to improve areas infected with PCBs. In this study, to decontaminate PCB-contaminated soil, the effect of biological sludge in contaminated soil on the removal of PCBs was investigated in a vermicomposting process at different mix ratios. Methods: Mixtures of PCB-contaminated soil and biological sludge were prepared in sample containers at different mix ratios, and then, earthworms were added. Over 80 days, besides the reduction of PCBs, pH, volatile solid content, and fixed solid content changes were also examined. Results: The highest reduction in PCBs (47.4%) was reported in pilot D at a contaminated soil-to-biological sludge volume ratio of 1:4. Moreover, in the same pilot, the pH level decreased from 7.9 to 7.2, indicating a further decline compared to other pilots, attributed to the further reduction of volatile solids. The highest reduction in volatile solids occurred in pilot D, decreasing from 74.8% at the beginning of the experiment to 42.9% at the end. The largest amount of mineralization also occurred in the same pilot. Conclusions: In this study, it was found that Eisenia fetida worms, along with microorganisms in the biological sludge, could function properly at all volume ratios of contaminated soil to biological sludge and could purify contaminants in a vermicomposting process.

Investigating the reduction of BTEX in automotive paint sludge combined with biological sludge by vermicomposting process using Eisenia fetida

Background: Due to the fact that in the process of car painting in the automotive industry, sludge containing dangerous compounds of benzene, toluene, ethylbenzene, xylene which cannot be released into the environment without purification, is inevitably produced, this study was conducted to investigate the feasibility of removing BTEX (benzene, toluene, ethylbenzene, and xylene) from the paint sludge of Saipa Automotive Company using Eisenia fetida worms. Methods: This is an experimental study. First, mixtures with different proportions of sludge were prepared and loaded in suitable boxes. After preparing the desired sludge, their quantitative and qualitative characteristics were determined in terms of type and amount of BTEX, volatile materials, moisture content, and C/N ratio. Then, to check the changes in BTEX, sampling was performed on different days during 90 days. BTEX measurements were performed using GC-MS method (NIOSH Method 1501). Results: The results showed that in the best mixing ratio of sludge, the amount of benzene decreased from 3 mg to less than 0.01 mg in 30 days, toluene decreased from 1.5 mg to zero over a 45-day period, ethyl benzene was reduced from 7 mg to zero mg over 70 days, and xylene decreased from 18 mg to 0.9 mg over 90 days. In addition, in the same optimal mixing ratio, the amount of volatile organic matter, pH, and C/N ratio also had a decreasing trend in the vermicomposting process. Conclusion: According to the results, E. fetida worms are able to work in mixed sludge and have the ability to break down BTEX.