Sugarcane bagasse ash as fertilizer for soybeans: Effects of added residues on ash composition, mineralogy, phosphorus extractability and plant availability.

Sugarcane bagasse is commonly combusted to generate energy. Unfortunately, recycling strategies rarely consider the resulting ash as a potential fertilizer. To evaluate this recycling strategy for a sustainable circular economy, we characterized bagasse ash as a fertilizer and measured the effects of co-gasification and co-combustion of bagasse with either chicken manure or sewage sludge: on the phosphorus (P) mass fraction, P-extractability, and mineral P phases. Furthermore, we investigated the ashes as fertilizer for soybeans under greenhouse conditions. All methods in combination are reliable indicators helping to assess and predict P availability from ashes to soybeans. The fertilizer efficiency of pure bagasse ash increased with the ash amount supplied to the substrate. Nevertheless, it was not as effective as fertilization with triple-superphosphate and K2SO4, which we attributed to lower P availability. Co-gasification and co-combustion increased the P mass fraction in all bagasse-based ashes, but its extractability and availability to soybeans increased only when co-processed with chicken manure, because it enabled the formation of readily available Ca-alkali phosphates. Therefore, we recommend co-combusting biomass with alkali-rich residues to increase the availability of P from the ash to plants.

Closed-loop organic waste management systems for family farmers in Brazil.

Family farmers in Brazil could diversify their sources of income and improve agriculture practices by adopting circular economy principles on their farms. Closed-loop technological systems can be used to manage organic waste and produce fertiliser and biogas thereby generating revenue. Anaerobic Digestion (AD) is a proven technology that can produce digestate (i.e. fertiliser) and biogas from organic waste, although digestate application in soil and crops without treatment can have adverse effects. However, in practice, there is a lack of knowledge about the benefits of recycling organic waste in farming communities in Brazil. Therefore, the main aim of this paper is to provide conceptual design configurations of closed-loop systems that manage organic waste and generate revenue for small farms in Brazil. A literature review of selected technologies and interviews with Brazilian family farmers were used to inform the components of the proposed conceptual designs. The proposed designs are based on circular economy principles, incorporating AD, pyrolysis for biochar, hydroponics and vermifiltration in various configurations. A complete closed-loop system consisting of a 7.5 m3 digester, pyrolysis unit, a combined hydroponic and vermifilter unit and a shredder is estimated to cost around USD$1600 (R$ 6600). The flexibility of the proposed systems has the potential to increase resilience and income for small-scale farmers, whilst encouraging good practices for waste management. The conceptual designs can be used as a basis for further research and development of small-scale organic waste management solutions in Brazil.

Removal of synthetic sex hormones by hydrothermal carbonization.

One of the most prominent fields of environmental chemistry is the study and the removal of micro-pollutants from aqueous matrices. Analytical techniques for their identification and quantification are becoming more sensitive and comprehensive and, as a result, an increasing number of drugs have been detected in environmental samples. However, the literature shows that conventional treatments for drinking water and wastewater are not sufficient for remove these compounds. This study aims to check whether the process of hydrothermal carbonization (CHT) is effective in removing the synthetic sex hormones: ethinyl estradiol, gestodene and cyproterone acetate from aqueous samples. The system used in CHT basically consists of a pressurized reactor made of stainless steel and solutions of compounds of interest, both individual and mixed, with a concentration of 1.0 µg.L-1 and a pH range of 2.0 to 3.0. The maximum surface temperature in the reactor was about 180 °C, the internal pressure was 20 bar with 90 minutes for the reaction. Four experiments were conducted, one for each hormone and one with the three hormones together. In individual tests removal of the compounds was found to be 99.8% for ethinyl estradiol, 99.3% for gestodene and 100% for cyproterone acetate. For a mixture of the hormones treated under the same conditions, the mean values of CHT-removal of Ethinylestradiol, Gestodene and Cyproterone Acetate were 99.60%, 96.80% and 68.90%, respectively. The impact of the matrix effect may have affected the efficiency of the hormone removal process by CHT.