Advances, trends and challenges in the use of biochar as an improvement strategy in the anaerobic digestion of organic waste: a systematic analysis.

A recently strategy applied to anaerobic digestion (AD) is the use of biochar (BC) obtained from the pyrolysis of different organic waste. The PRISMA protocol-based review of the most recent literature data from 2011-2022 was used in this study. The review focuses on research papers from Scopus® and Web of Knowledge®. The review protocol used permits to identify 169 articles. The review indicated a need for further research in the following challenges on the application of BC in AD: i) to increase the use of BC in developing countries, which produce large and diverse amounts of waste that are the source of production of this additive; ii) to determine the effect of BC on the AD of organic waste under psychrophilic conditions; iii) to apply tools of machine learning or robust models that allow the process optimization; iv) to perform studies that include life cycle and technical-economic analysis that allow identifying the potential of applying BC in AD in large-scale systems; v) to study the effects of BC on the agronomic characteristics of the digestate once it is applied to the soil and vi) finally, it is necessary to deepen in the effect of BC on the dynamics of nitrogen and microbial consortia that affect AD, considering the type of BC used. In the future, it is necessary to search for new solutions in terms of the transport phenomena that occurs in AD with the use of BC using robust and precise mathematical models at full-scale conditions.

Optimization of lignocellulolytic bacterial inoculum and substrate mix for lignocellulose degradation and product quality on co-composting of green waste with food waste.

The present study evaluates the effect of the mixing ratio of substrates and inoculation with lignocellulolytic bacteria on green waste (GW) and food waste (FW) co-composting. A Box-Behnken design was used to simultaneously optimize the lignocellulose degradation (%LD) and end-product quality. The best operational conditions were 4.85*105 CFU g-1 of Bacillus sp. F3X3 and 1.44*106 CFU g-1 of Paenibacillus sp. F1A5 with a substrate mixture containing 50% GW, 32.5% unprocessed FW, 2.5% processed FW, 13% sawdust, and 2% phosphate rock; with a C/N ratio of 27. Under these conditions, the %LD was 33% and the end-product has pH 8.3, TOC 22,4%, TN 1,7%, and a germination index of 103%. Therefore, the product complies with quality standards for organic fertilizers. The results of this study allow the identification of appropriate strategies to optimize GW composting, increasing the degradation of lignocellulose and improving the end-product quality.

Evaluation of mixing ratio and frequency of turning in the co-composting of biowaste with sugarcane filter cake and star grass.

This work studied the effect of mixing ratio (MR) and turning frequency (TF) in biowaste composting (BW) with sugarcane filter cake (SFC) and star grass (SG), both on process performance (temperature, static respiration index, total organic carbon, total nitrogen and total phosphorus) and on product quality (pH, cation exchange capacity, electrical conductivity, organic matter, nutrients, stability, maturity, total coliforms and faecal coliforms), through the Principal Components Analysis (PCA). The Pearson correlation coefficients were calculated for all the quality parameters. A joint effect of mixing ratio and turning frequency was demonstrated, highlighting the importance of studying the operational parameters simultaneously. The results of the PCA showed that the best operating conditions and therefore higher product quality is achieved with a TF of twice a week and MR between 20 and 30% of SFC or SG. Additionally, it was found that a frequency of one turn per week generates the lowest product quality, regardless the co-substrate and the MR. The best treatment corresponded to BW composting with MR of 20% SFC and TF of two turnings per week. The obtained results allow to optimize the operation in composting facilities.