Waste to energy: valorization of spent tea waste by anaerobic digestion

Sustainable management of tea wastes: resource recovery and conversion techniques

As the demand for tea (Camellia sinensis) has grown across the world, the amount of biomass waste that has been produced during the harvesting process has also increased. Tea consumption was estimated at about 6.3 million tonnes in 2020 and is anticipated to reach 7.4 million tonnes by 2025. The generation of tea waste (TW) after use has also increased concurrently with rising tea consumption. TW includes clipped stems, wasted tea leaves, and buds. Many TW-derived products have proven benefits in various applications, including energy generation, energy storage, wastewater treatment, and pharmaceuticals. TW is widely used in environmental and energy-related applications. Energy recovery from low- and medium-calorific value fuels may be accomplished in a highly efficient manner using pyrolysis, anaerobic digestion, and gasification. TW-made biochar and activated carbon are also promising adsorbents for use in environmental applications. Another area where TW shows promise is in the synthesis of phytochemicals. This review offers an overview of the conversion procedures for TW into value-added products. Further, the improvements in their applications for energy generation, energy storage, removal of different contaminants, and extraction of phytochemicals have been reviewed. A comprehensive assessment of the sustainable use of TWs as environmentally acceptable renewable resources is compiled in this review.

Re-flocculation reduces the effectiveness of sewage sludge pretreatment through hydrodynamic disintegration prior to anaerobic digestion

Circular economy model, based on the "make, use, reuse, remake, recycle" approach, is an alternative to progressive depletion of non-renewable fossil fuels. Sewage sludge can be a source of renewable energy obtained through the anaerobic conversion of their organic fraction into biogas. This process is mediated by highly complex microbial communities and its efficiency depends on the availability of substrates to microorganisms. Disintegration of the feedstock in the pre-treatment step may intensify the anaerobic digestion, but re-flocculation of disintegrated sludge (reassembly of the released fractions into larger agglomerates) may result in a reduced availability of the released organic compounds for microbes. Pilot-scale studies on re-flocculation of disintegrated sludge were conducted to select parameters for scaling-up the pre-treatment and intensifying the anaerobic digestion process in two large Polish wastewater treatment plants (WWTPs). Samples of thickened excess sludge from full-scale WWTPs were subjected to hydrodynamic disintegration at three energy density levels of 10 kJ/L, 35 kJ/L and 70 kJ/L. Microscopic analyses of disintegrated sludge samples were carried out twice: i) immediately after the disintegration process at a given energy density level, ii) and after 24-h incubation at 4 °C following the disintegration. Micro-photographs of 30 randomly selected fields of view were taken for each analysed sample. A method of the image analysis was developed as a tool to measure dispersion of sludge flocs to assess the re-flocculation degree. Re-flocculation of the thickened excess sludge occurred within 24 h after hydrodynamic disintegration. This was evidenced by a very high re-flocculation degree, reaching up to 86%, depending on the origin of the sludge and the energy density levels used for the hydrodynamic disintegration.