This article aims to comprehensively review the anaerobic digestion (AD) process utilising the organic fraction of municipal solid waste (OFMSW) substrate. The AD of OFMSW has received considerable attention due to its significant energy and nutrient recovery as well as its greenhouse gas (GHG) mitigation potential. AD is a biological process involving treating and stabilising organic matter in the absence of oxygen accomplished by a consortium of microorganisms and occurs under hydrolysis, acidogenesis, acetogenesis, and methanogenesis phases. The hydrolysis phase is recognised as the primary rate-limiting step. Thus, exploring the ways to speed up the hydrolysis process will maximise biogas production. The key factors affecting the digestion efficiency include feedstock quality, pre-treatment process, design and selection of digestion process and process conditions including pH, temperature, carbon to nitrogen (C: N) ratio, organic loading rate and hydraulic retention time. The review reveals that solid-state anaerobic digestion (SSAD) is best suited for OFMSW due to its high solid concentration (>15%) and better process performance. The continuous digestion with thermophilic temperatures was found to be the best condition for high solid AD process. The plug flow and continuous stir tank reactors were the best performing options to control the biological conditions for the digestate post-treatment. Proper selection of the parameters for the whole process is crucial in ensuring process feasibility and economic sustainability of AD of OFMSW. The study revealed that the AD of OFMSW could play a significant role to mitigate waste and waste-related problems.

A comprehensive review on anaerobic digestion of organic fraction of municipal solid waste

Dyes (colorants) are used in many industrial applications, and effluents of several industries contain toxic dyes. Dyes exhibit toxicity to humans, aquatic organisms, and the environment. Therefore, dyes containing wastewater must be properly treated before discharging to the surrounding water bodies. Among several water treatment technologies, adsorption is the most preferred technique to sequester dyes from water bodies. Many studies have reported the removal of dyes from wastewater using biochar produced from different biomass, e.g., algae and plant biomass, forest, and domestic residues, animal waste, sewage sludge, etc. The aim of this review is to provide an overview of the application of biochar as an eco-friendly and economical adsorbent to remove toxic colorants (dyes) from the aqueous environment. This review highlights the routes of biochar production, such as hydrothermal carbonization, pyrolysis, and hydrothermal liquefaction. Biochar as an adsorbent possesses numerous advantages, such as being eco-friendly, low-cost, and easy to use; various precursors are available in abundance to be converted into biochar, it also has recyclability potential and higher adsorption capacity than other conventional adsorbents. From the literature review, it is clear that biochar is a vital candidate for removal of dyes from wastewater with adsorption capacity of above 80%.

https://www.mdpi.com/2073-4441/12/12/3561/pdf

Biochar as an Eco-Friendly and Economical Adsorbent for the Removal of Colorants (Dyes) from Aqueous Environment: A Review

Trends in renewable energy production employing biomass-based biochar.

Wastewater treatment may help to reduce water shortages, whilst concurrently recover energy and nutrients, leading to some of the exploitation of important sources being offset. Compared to other approaches, wastewater purification via adsorption is highly-desirable. The reason is that with this simple and better-to-regenerate technique, heavy metals could be removed even under lower concentration of metal ions. Due to numerous advantages and tunable physicochemical properties, biochar has received most attention for the control of water contamination. This contributes to the solving ecology issues. Significantly, the link between biochar and the rehabilitation of resources should be studied, so that the role of biochar during the wastewater and environmental treatment is well-comprehended and scale-up. In this review, the biochar production from biomass through different routes and their critical properties are critically reviewed and presented. In addition, the activation methods of biochar are also presented and thoroughly compared. More importantly, the application of biochar in heavy metal removal is scrutinized. The factors that affect the heavy metal adsorption capacity and performance are critically evaluated. Finally, limitations and future perspectives for biochar production and application in the removal of heavy metal from wastewater are highlighted in this review. 

Biomass-derived biochar: From production to application in removing heavy metal-contaminated water

Recent Advances in Thermochemical Conversion of Biomass

Hydrothermal carbonization (HTC) represents an efficient and valuable pre-treatment technology to convert waste biomass into highly dense carbonaceous materials that could be used in a wide range of applications between energy, environment, soil improvement and nutrients recovery fields. HTC converts residual organic materials into a solid high energy dense material (hydrochar) and a liquid residue where the most volatile and oxygenated compounds (mainly furans and organic acids) concentrate during reaction. Pristine hydrochar is mainly used for direct combustion, to generate heat or electricity, but highly porous carbonaceous media for energy storage or for adsorption of pollutants applications can be also obtained through a further activation stage. HTC process can be used to enhance recovery of nutrients as nitrogen and phosphorous in particular and can be used as soil conditioner, to favor plant growth and mitigate desertification of soils. The present review proposes an outlook of the several possible applications of hydrochar produced from any sort of waste biomass sources. For each of the applications proposed, the main operative parameters that mostly affect the hydrochar properties and characteristics are highlighted, in order to match the needs for the specific application.

https://www.mdpi.com/1996-1073/13/16/4098/pdf

Hydrothermal Carbonization as a Valuable Tool for Energy and Environmental Applications: A Review

Biomethane recovery from olive mill residues through anaerobic digestion: A review of the state of the art technology

Promoting energy recovery from recalcitrant agro-industrial wastes through anaerobic digestion: A review on olive mill residues

Almond shells represent an abundant agricultural waste which is annually produced in Sicily. Pyrolysis and gasification can be adopted to successfully modify its morphological and structural properties to produce graphitized porous material than can be used for environmental and energetical applications. The increase in pyrolysis and activation temperature led to pores formation and widening on the external surface as well as a re-organization of the internal structure toward a more graphitic one. Reaction temperatures tested were in the range of 600 °C to 1,000 °C, with 100 °C step increase, and the obtained material was characterized through SEM analysis. The samples prepared at 800 °C and 1,000 °C were further studied through TEM investigation. Aside from pore widening, as long as activation temperature was raised nano-onion carbon formations, characteristics or more graphitic structure were observed.

Manfredi P. Maniscalco

Papers

Hydrothermal Carbonization as a Valuable Tool for Energy and Environmental Applications: A Review

Biomethane recovery from olive mill residues through anaerobic digestion: A review of the state of the art technology

Promoting energy recovery from recalcitrant agro-industrial wastes through anaerobic digestion: A review on olive mill residues

Morphological and structural evolution of activated carbons from almond shells

Catalytic effect of alkali metals in volatilisation of solid biofuels during gasification