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The search for sustainable municipal solid waste management in urban areas has become a dire need as the generated unprecedented volumes of waste eventually end up in landfills and emits greenhouse gas (GHG). To offer sustainable waste management in Dhaka, Bangladesh, the performance of incineration, anaerobic digestion, and hydrothermal carbonization (HTC) based Waste to Energy (WtE) processes were assessed and compared. The population and the GDP of Dhaka North City Corporation from 2015 to 2023 were used to estimate the MSW generation rate with an empirical multivariable linear regression model. In 2023 around 3600 tons/day of MSW was generated which was 35 % higher than in 2015. The IPCC decay models, ZODM, FODM, and modified triangular model (MTM) yielded 87.3, 41.3, and 38-k tonnes of CH 4 generation, respectively. The power generation from incineration-based plants can fall from 30 MW to 3 MW if the moisture content of MSW increases from 70 % to 90 %. Anaerobic digestion produces 34 MW of power. The Optimization of the HTC operating parameters was done and it demonstrates substantial energy potential (up to 65 MW with co-feeding of 420 tons/day of hydrochar with 426 tons/day of plastic from MSW) and GHG emission reduction (221.5 %) compared to landfilling. Additionally, HTC-derived wastewater presents an opportunity for nutrient recovery with 8.16 and 2.66, 0.3 tons/day of K, Na, and P reclamation potential, respectively. A comparison of different scenarios in plastic recycling in incineration and sensitivity analysis for three WtE schemes were conducted. Thus, the study provides a rigorous assessment of different pathways to offer a comprehensive framework for sustainable MSW management that contributes to a cleaner urban environment. • Over 9 years, the estimated increase of MSW generation in Dhaka city is by 35 %. • Up to 34 MW power can be obtained from anaerobic digestion of MSW. • Using 420 tons/day of MSW hydro-char, 65 MW of net power generation is possible. • 8.16, 2.66 and 0.3 tons/day of K, Na, and P are recoverable from HTC by-product. • HTC was found as a sustainable WtE process with remarkable GHG mitigation potential. [ABSTRACT FROM AUTHOR]

Herein, the valorization of vegetable and fruit waste was assessed via hydrothermal carbonization (HTC) and anaerobic digestion (AD) in terms of product characterization and energy requirements. HTC was conducted at reaction temperatures between 150 ºC and 190 ºC, and residence times between 20 min and 40 min. The increase in the process severity resulted in hydrochars with higher carbon contents and higher energy densification ratios. AD was performed in two different ways. i.e., batch and semi-continuous reactions. From the batch experiments a methane yield of 300 L CH 4 /kg VS was obtained, while for the semi-continuous, the average specific methane production estimated (for HRTs from 75 to 50 days) was 213 ± 32 L CH 4 /kg VS. To estimate the energy requirements, mass and energy balances were performed considering the basic stages of each process to obtain a suitable biofuel material. In this sense, it was concluded that for this specific waste, AD was a more suitable process with a positive energy net balance. On the contrary, HTC presented a negative energy net balance being required 1.29 MJ/kg of fresh food waste. A combined HTC-AD treatment may be an efficient method to take advantage of both technologies leading to higher energy efficiencies and other valuable products. [Display omitted] • A carbon-rich solid product is obtained from HTC of fruit and vegetable waste. • The higher the severity of the HTC, the better the fuel properties of the hydrochars. • The energy recovered by HTC is higher than that of AD (923 MJ vs. 867.1 MJ). • Batch and semi-continuous anaerobic digestion experiments were performed. • AD presented a positive energy balance, while HTC showed negative outputs. [ABSTRACT FROM AUTHOR]

Biochar is discussed as an option for climate change mitigation via C sequestration and may promote sustainable resource efficiency. Large-scale field trials and commercial business with char materials have already started. Therefore char materials have to be assessed for toxic compounds. We tested genotoxic effects of different hydrochars and biochars with the Tradescantia micronucleus test. For this purpose chromosomal aberrations in pollen cells of Tradescantia in the form of micronuclei were evaluated microscopically after defined exposition to extracts from char materials. Hydrochars from hydrothermal carbonization mostly exhibited significantly negative results. Additional germination experiments with hydrochar showed total germination inhibition at additions above five percent v/v in comparison to biochar. However, biological post-treatment of previously toxic hydrochar was successful and toxic effects were eliminated completely. Some post-treated hydrochars even showed growth stimulating effects. Our results clearly demonstrate the necessity of risk assessment with bioindicators. The chosen tests procedures can contribute to biochar and hydrochar characterization for safe application. [Copyright &y& Elsevier]

An efficient method of synergetic dechlorination and reduction of heavy metals risk is crucial for the clean resource utilization of sewage sludge (SS) and polyvinyl chloride (PVC). In this work, SS was upgraded to hydrochar using co-hydrothermal carbonization (HTC) with PVC at different mixing ratio (30─70%) at 230 °C. Transformation behaviors of chlorine and heavy metals in hydrochars, along with fuel properties, were evaluated. The results illustrated that Mn and Zn could be effectively removed during co-HTC and low ratio addition of PVC was beneficial for reducing the toxicity of Ni and As. Meanwhile, compared with the HTC of single PVC, co-HTC with SS could further improve the dechlorination efficiency (69.49─81.35%). Particularly, the blending ratio of SS to PVC at 7:3 showed high fuel ratio and HHV (13.58 MJ/kg) with desirable combustion performance. These findings offered a potential approach to convert SS and PVC into clean solid fuel. [Display omitted] [ABSTRACT FROM AUTHOR]