Investigations on Biogas Recovery from Anaerobic Digestion of Raw Sludge and Its Mixture with Agri-Food Wastes: Application to the Largest Industrial Estate in Oman

Recent developments in metallic-nanoparticles-loaded biochars synthesis and use for phosphorus recovery from aqueous solutions. A critical review

Phosphorus (P) represents a major pollutant of water resources and at the same time a vital element for human and plants. P recovery from wastewaters and its reuse is a necessity in order to compensate the current important depletion of P natural reserves. The use of biochars for P recovery from wastewaters and their subsequent valorization in agriculture, instead of synthetic industrial fertilizers, promotes circular economy and sustainability concepts. However, P retention by pristine biochars is usually low and a modification step is always required to improve their P recovery efficiency. The pre- or post-treatment of biochars with metal salts seems to be one of the most efficient approaches. This review aims to summarize and discuss the most recent developments (from 2020- up to now) in: i) the role of the feedstock nature, the metal salt type, the pyrolysis conditions, and the experimental adsorption parameters on metallic-nanoparticles-loaded biochars properties and effectiveness in recovering P from aqueous solutions, as well as the dominant involved mechanisms, ii) the effect of the eluent solutions nature on the regeneration ability of P-loaded biochars, and iii) the practical challenges facing the upscaling of P-loaded biochars production and valorization in agriculture. This review shows that the synthesized biochars through slow pyrolysis at relatively high temperatures (up to 700-800 °C) of mixed biomasses with Ca- Mg-rich materials or impregnated biomasses with specific metals in order to from layered double hydroxides (LDHs) biochars composites exhibit interesting structural, textural and surface chemistry properties allowing high P recovery efficiency. Depending on the pyrolysis's and adsorption's experimental conditions, these modified biochars may recover P through combined mechanisms including mainly electrostatic attraction, ligand exchange, surface complexation, hydrogen bonding, and precipitation. Moreover, the P-loaded biochars can be used directly in agriculture or efficiently regenerated with alkaline solutions. Finally, this review emphasizes the challenges concerning the production and use of P-loaded biochars in a context of circular economy. They concern the optimization of P recovery process from wastewater in real-time scenarios, the reduction of energy-related biochars production costs and the intensification of communication/dissemination campaigns to all the concerned actors (i.e., farmers, consumers, stakeholders, and policymakers) on the benefits of P-loaded biochars reuse. We believe that this review is beneficial for new breakthroughs on the synthesis and green application of metallic-nanoparticles-loaded biochars.

Conversion of Industrial Sludge into Activated Biochar for Effective Cationic Dye Removal: Characterization and Adsorption Properties Assessment

This paper presents an in-depth characterization of a raw industrial sludge (IS-R) and its KOH-activated biochar pyrolyzed at 750 °C (IS-KOH-B) followed by their application to remove a cationic dye from aqueous solution. Materials characterization shows that compared to the IS-R, the IS-KOH-B has improved structural, textural, and surface chemical properties. In particular, the IS-KOH-B’s BET surface area and total pore volume are about 78 and 6 times higher than those found for the IS-R, respectively. The activated biochar efficiently retained the cationic dye under wide experimental conditions. Indeed, for an initial dye concentration of 50 mg L−1, removal yields were assessed to be more than 92.5%, 93.5%, and 97.8% for a large pH range (4–10), in the presence of high contents of competing cations (3000 mg L−1 of Ca2+, Mg2+, Na+, and K+), and a low used adsorbent dose (1 g L−1), respectively. The Langmuir’s adsorption capacities were 48.5 and 65.9 mg g−1 for of IS-R and IS-KOH-B, respectively, which are higher than those reported for various adsorbents in the literature. The dye removal was found to be monolayer, spontaneous, and endothermic for both the adsorbents. Moreover, this removal process seems to be controlled by chemical reactions for IS-KOH-B whereas by both physico–chemical reactions for IS-R. This study demonstrates that the raw industrial sludge and especially its KOH-activated derived biochar could be considered as promising adsorbents for the removal of dyes from aqueous solutions.

The dairy biorefinery: Integrating treatment process for Tunisian cheese whey valorization

In order to set up a cost-efficient biorefinery in a Tunisian dairy industry, the production unit effluents are recovered. The main objective is to develop an optimum method for the production of bioethanol from whey. An energy analysis as well as environmental and economic analyses are performed for a bioethanol production plant. Four production scenarios are examined in order to determine the most provident as well as the less polluting ones. The process and cost models were developed using SuperPro Designer software which a simulation program that is able to estimate both process and economic parameters. This software uses energy and mass balances. The model can be used to assess the efficiency, the resources consumption, the profitability and the environmental impact of each scenario. The results demonstrate that the third scenario, in which a reverse osmosis procedure is added to concentrate the whey, a continuous stoichiometric reaction procedure is integrated to model the biotransformation in the fermenter and where streams are added in order to recycle the biomass, produces the highest amount of bioethanol with 1.65 MT/year but the second one (where no streams were added) is the most profitable one with revenues as high as 570 000 $/year. The corresponding cost of ethanol production is 0.271 US $ ethanol per liter. The net present value (NPV) and the return on investment (ROI) of each scenario are positive. Such result indicates that all these investments could be undertaken in order to find an eco-friendly issue for the dairy industry effluents. Cheese whey could serve as an alternative raw material for producing ethanol.

Olive Mill by-Products Thermochemical Conversion via Hydrothermal Carbonization and Slow Pyrolysis: Detailed Comparison between the Generated Hydrochars and Biochars Characteristics

In this research work, an ecofriendly approach was adopted for the treatment of two abundant liquid and solid agricultural wastes generated by olive mill industry: olive mill wastewater (OMWW) and raw olive pomace (ROP). It consists, firstly of the impregnation of ROP by OMWW and the conversion of the resulting impregnated sample (IROP) into hydrochars and biochars through hydrothermal carbonization (HTC) and slow pyrolysis methods, respectively. The impact of the treatment temperature on the physico-chemical properties of the derived chars was assessed by various analytical techniques. The hydrochars production yields were found to be higher than the biochars ones and associated to the lower temperature used. However, the generated biochars possess higher carbon percentage and lower volatile matter contents. In addition, the increase of the hydrothermal and pyrolysis carbonization temperatures shows an increase of macro-elements contents and a significant decrease of the O/C ratios which led to an enhancement of the high heating value for both hydrochars and biochars. The FTIR and Boehm titration analysis highlighted a significant alteration of the biochars surface chemistry compared to hydrochars evidenced by the lower amount of functional groups. The collected data emphasize on the efficient potential application of hydrochars and biochars for agricultural and environmental applications, respectively. Furthermore, it was noted that both chars have high energetic potentials and could be used for co-firing with coal in industrial boilers.

Waste Strategies Development in the Framework of Circular Economy

Current studies proposed that more that 2bn tons of solid waste/year are produced globally [...]