Principles and potential of thermal hydrolysis of sewage sludge to enhance anaerobic digestion.

Sewage sludge is rich source of carbon, nutrients, and trace elements and can be subjected to proper treatment before disposal to fulfill government legislation and protect receiving environments. Anaerobic digestion (AD) is a well-adopted technology for stabilizing sewage sludge and recovering energy-rich biogas and nutrient-rich digestate. However, a slow hydrolysis rate limits the biodegradability of sludge. In the present study we have attempted to explain the potential of thermal hydrolysis to enhance anaerobic digestion of sewage sludge. Thermal pretreatment improves biodegradability and recycling of the sludge as an excellent energy and nutrients recovery source at reasonable capital (CAPEX) and operational (OPEX) costs. Other pretreatments like conventional (below/above 100 °C), temperature-phased anaerobic digestion (TPAD), microwave and chemically mediated thermal pretreatment have also been accounted. This review provides a holistic overview of sludge's characterization and value-added properties, various techniques used for sludge pretreatment for resource recovery, emphasizing conventional and advanced thermal pretreatment, challenges in scale-up of these technologies, and successful commercialization of thermal pretreatment techniques.

Recent progress in microalgae-derived biochar for the treatment of textile industry wastewater.

Textile industry utilize a massive amount of dyes for coloring. The dye-containing effluent is released into wastewater along with heavy metals that are part of dye structure. The treatment of textile industry wastewater using conventional techniques (coagulation, membrane technique, electrolysis ion exchange, etc.) is uneconomical and less efficient (for a low concentration of pollutants). Moreover, most of these techniques produce toxic sludge, making them less environmentally friendly. Algae base industry is growing for food, cosmetics and energy needs. Algae biomass in unique compared to lignocellulosic biomass due to presence of various functional group on its surface and presence of various cations. These two characteristics are unique for biochar as a tool for environmental decontamination. Algae biomass contain functional groups and cations that can be effective for removal of organic contaminants (dyes) and heavy metals. Algae can be micro and macro and both have entirely different biomass composition which will lead to a synthesis of different biochar even under same synthesis process. This study reviews the recent progress in the development of an economically viable and eco-friendly approach for textile industry wastewater using algae biomass-derived absorbents. The strategy employed microalgal biochar to remove organic pollutants (dyes) and heavy metals from textile effluents by biosorption. This article discusses different methods for preparing algal biochar (pyrolysis, hydrothermal carbonization and torrefaction), and the adsorption capacity of biochar for dyes and heavy metals. Work on hydrothermal carbonization and torrefaction of microalgal biomass for biochar is limited. Variation in structural and functional groups changes on biochar compared to original microalgal biomass are profound in contract with lignocellulosic biomass. Existing Challenges, future goals, and the development of these technologies at the pilot level are also discussed.