Insights into multisource sludge distributed in the Yangtze River basin, China: Characteristics, correlation, treatment and disposal

Unraveling temperature effects on caproate and caprylate production from waste activated sludge

This study explored the impact of different temperatures on the continuous production of medium-chain fatty acids (MCFAs) from waste activated sludge (WAS). Experimental results showed that there was almost no MCFAs accumulation at 55 °C. Both 25 °C and 37 °C were suitable for MCFAs production, with 25 °C favoring high-value caprylate production. The metagenomic and metatranscriptomic analysis highlighted reverse β-oxidization as the main chain elongation (CE) cycle. The lack of CE-related microorganisms and enzymes at 55 °C hindered MCFAs production, in contrast to the heightened activity observed at 25 °C and 37 °C, with peak activity at 25 °C leading to increased longer-chain MCFAs synthesis. 37 °C promoted hydrolysis and acidification, resulting in a accumulation of higher short-chain fatty acids, but further elongation to MCFAs would be hindered by product toxicity. This research concludes that 25 °C is the most effective temperature for the production of WAS-derived MCFAs, offering significant economic advantages.

Evaluating energy balance and environmental footprint of sludge management in BRICS countries

Climate change is driving global endeavours to achieve carbon neutrality and renewable energy expansion. Sludge, a nutrient-rich waste, holds energy potential yet poses environmental challenges that need proper management. We conducted a comprehensive life cycle assessment to evaluate the energy balance and environmental footprint of the most commonly used sludge management scenarios in BRICS countries, namely Brazil, Russia, India, China, and South Africa. Technologies such as incineration and anaerobic digestion with energy recovery units (i.e., cogeneration unit) maximize energy balance and minimize the environmental footprint, with incineration showing a superior performance. Shifting sludge management scenarios from the worst to the best can boost energy production by 1.4-98.4 times and cut the environmental footprint by 1.5-21.4 times. In 2050, these improvements could lead to a 98-fold boost in energy generation and a 25-fold drop in carbon emissions, according to the Announced Pledges Scenarios. Optimizing parameters such as volatile solids and anaerobic digestion efficiency further boosts energy output and minimizes the environmental footprint. This study offers robust evidence to support sustainable sludge management and thus promote energy recovery and carbon neutrality goals, guide technological transitions, and inform policymaking for sustainable development.

Biosolids, an important route for transporting poly- and perfluoroalkyl substances from wastewater treatment plants into the environment: A systematic review

The pervasive presence of poly- and perfluoroalkyl substances (PFAS) in diverse products has led to their introduction into wastewater systems, making wastewater treatment plants (WWTPs) significant PFAS contributors to the environment. Despite WWTPs' efforts to mitigate PFAS impact through physicochemical and biological means, concerns persist regarding PFAS retention in generated biosolids. While numerous review studies have explored the fate of these compounds within WWTPs, no study has critically reviewed their presence, transformation mechanisms, and partitioning within the sludge. Therefore, the current study has been specifically designed to investigate these aspects. Studies show variations in PFAS concentrations across WWTPs, highlighting the importance of aqueous-to-solid partitioning, with sludge from PFOS and PFOA-rich wastewater showing higher concentrations. Research suggests biological mechanisms such as cytochrome P450 monooxygenase, transamine metabolism, and beta-oxidation are involved in PFAS biotransformation, though the effects of precursor changes require further study. Carbon chain length significantly affects PFAS partitioning, with longer chains leading to greater adsorption in sludge. The wastewater's organic and inorganic content is crucial for PFAS adsorption; for instance, higher sludge protein content and divalent cations like calcium and magnesium promote adsorption, while monovalent cations like sodium impede it. In conclusion, these discoveries shed light on the complex interactions among factors affecting PFAS behavior in biosolids. They underscore the necessity for thorough considerations in managing PFAS presence and its impact on environmental systems.