Drinking water treatment sludge as an effective additive for biogas production from food waste; kinetic evaluation and biomethane potential test

Sludge Management at the Kraków-Płaszów WWTP—Case Study

Municipal wastewater treatment plants are good examples of facilities where the concept of a circular economy model can be effectively implemented by the recovery of energy as well as secondary and natural materials. That is why anaerobic co-digestion has become one of the most appealing renewable energy pathways and takes a key position within sludge-handling processes. This research looked into the feasibility of the utilization of water sludge from a water treatment plant in anaerobic co-digestion with sewage sludge. The experiments confirmed that anaerobic digestion of sewage sludge together with water sludge significantly improved fermentation gas (biogas) production. The best results were observed when water treatment sludge constituted 30% of the mass of sewage sludge (as volatile solids, VS). At this ratio, approximately 20% more biogas was produced in laboratory experiments compared to the biogas production from sewage sludge only. The results, once confirmed on a semi-technical scale, will help to develop a sequence of processes which would enhance biogas production. Both the technology and the final product offer a comprehensive solution for waste generated at water and wastewater treatment plants. The innovative approach allows for the use of various waste streams and their combined processing following the principle of the circular economy.

Composting and Anaerobic Digestion of Food Waste and Sewage Sludge for Campus Sustainability: A Review

Composting and anaerobic digestion have emerged as better options for managing food waste and sewage sludge at the campus level. This review highlights the characteristics of food waste and sewage sludge from various global higher education institutions. The composting and anaerobic digestion processes of food waste and sewage sludge will be reviewed and evaluated. Also, the adoption of composting and anaerobic digestion at various campus levels has been reviewed. The challenges and future direction, focusing on managing university campus composting and anaerobic digestion, are discussed as well. This review paper will significantly contribute to the understanding of the potential for managing and handling campus waste in a natural-friendly manner.

Bioprocesses for the recovery of bioenergy and value-added products from wastewater: A review

Wastewater and activated sludge present a major challenge worldwide. Wastewater generated from large and small-scale industries, laundries, human residential areas and other sources is emerging as a main problem in sanitation and maintenance of smart/green cities. During the last decade, different technologies and processes have been developed to recycle and purify the wastewater. Currently, identification and fundamental consideration of development of more advanced microbial-based technologies that enable wastewater treatment and simultaneous resource recovery to produce bioenergy, biofuels and other value-added compounds (organic acids, fatty acids, bioplastics, bio-pesticides, bio-surfactants and bio-flocculants etc.) became an emerging topic. In the last several decades, significant development of bioprocesses and techniques for the extraction and recovery of mentioned valuable molecules and compounds from wastewater, waste biomass or sludge has been made. This review presents different microbial-based process routes related to resource recovery and wastewater application for the production of value-added products and bioenergy. Current process limitations and insights for future research to promote more efficient and sustainable routes for this under-utilized and continually growing waste stream are also discussed.

Co-digestion of primary sewage sludge with drinking water treatment sludge: A comprehensive evaluation of benefits

Anaerobic co-digestion of primary sludge with two types of drinking water treatment sludge (DWTS), namely iron- or aluminum-rich DWTS (Fe- or Al-DWTS) were systematically evaluated by biochemical methane potential tests, kinetic modelling, downstream process parameters and microbial community analysis. Specific methane yields decreased approximately 19% to 123 mL·g^-1 VS, while the hydrolysis constant k_h decreased from 0.21 d^-1 to 0.18 d^-1 for Fe-DWTS at 10% to 40% dosages. On the contrary, specific methane yields decreased 45-55% for Al-DWTS, and k_h decreased to 0.14 d^-1 at 40% dosage. Significant removals (>95%) of phosphate and hydrogen sulfide were observed for Fe- and Al-DWTS additions at 40% dosage. Microbial community analysis revealed that Al-DWTS increased the abundance of most hydrogenotrophic methanogens, while Fe-DWTS increased the abundance of acetoclastic methanogens. Kinetic modelling further revealed that Fe- and Al-DWTS additions affected the hydrolysis and methanogenesis process kinetics and the methane yield differently.

Processing of Water Treatment Sludge by Bioleaching

Biological metal leaching is a technology used in the mining and biohydrometallurgy industries where microorganisms mediate the dissolution of metals and semi-metals from mineral ores and concentrates. The technology also has great potential for various types of metal-rich waste. In this study, bioleaching was used for sludge from water treatment. In addition to checking the applicability of the process to such a substrate, the influence of experimental conditions on the effectiveness of bioleaching of metals with sludge from water treatment was also determined, including sample acidification, addition of elemental sulfur, incubation temperature, and Acidithiobacillus thiooxidans-isolated strain. The measurement of metal concentration and, on this basis, the determination of bioleaching efficiency, as well as pH and oxygen redox potential (ORP), was carried out during the experiment at the following time intervals: 3, 6, 9, 12 days. After the experiment was completed, a mass balance was also prepared. After the experiment, high efficiency of the process was obtained for the tested substrate. The effectiveness of the process for most metals was high (Ca 96.8%, Cr 92.6%, Cu 80.6%, Fe 95.6%, Mg 91%, Mn 99.5%, Ni 89.7%, Pb 99.5%, Zn 93%). Only lower values were obtained for Al (58.6%) and Cd (68.4%).

Evaluation of Feasibility of Using the Bacteriophage T4 Lysozyme to Improve the Hydrolysis and Biochemical Methane Potential of Secondary Sludge

Anaerobic digestion (AD) of secondary sludge is a rate-limiting step due to the bacterial cell wall. In this study, experiments were performed to characterize secondary sludges from three wastewater treatment plants (WWTPs), and to investigate the feasibility of using bacteriophage lysozymes to speed up AD by accelerating the degradation of bacterial cell walls. Protein was the main organic material (67.7% of volatile solids in the sludge). The bacteriophage T4 lysozyme (T4L) was tested for hydrolysis and biochemical methane potential. Variations in the volatile suspended solid (VSS) concentration and biogas production were monitored. The VSS reduction efficiencies by hydrolysis using T4L for 72 h increased and ranged from 17.8% to 26.4%. Biogas production using T4L treated sludges increased and biogas production was increased by as much as 82.4%. Biogas production rate also increased, and the average reaction rate coefficient of first-order kinetics was 0.56 ± 0.02/d, which was up to 47.5% higher compared to the untreated samples at the maximum. Alphaproteobacteria, Betaproteobacteria, Flavobacteriia, Gammaproteobacteria, and Sphingobacteriia were major microbial classes in all sludges. The interpretation of the microbial community structure indicated that T4L treatment is likely to increase the rate of cell wall digestion.