RESUMEN
In recent years, increasing attention has been paid to the possibility of converting waste materials, e.g. manure, bio-waste, green waste, waste from the water and sewage industries (e.g. post-fermentation sludge), and agri-food waste into biochars (BCs) by pyrolysis. The ability of biochar to improve soil health and fertility is driving growing interest in its use as a soil amendment. A high soil stability of BCs and their excellent nutrient sorption properties are the main reasons for the superiority of such materials over other organic soil amendments. In addition, BCs can retain soil-relevant compounds, including humic substances (HSs). Since most of the resources used to produce humic fertilisers are non-renewable, the effluent from anaerobic digestion of sewage sludge (reject water, RW), which contains high levels of HSs, is considered a promising target for their recovery. In this study, the potential of ten BCs derived from pine, oak, straw, sunflower, and digestate at different pyrolysis temperatures for the recovery of HSs from RW was evaluated. The sorption of HSs on the applied BCs was conducted using contact method for 24 h and then determined spectrophotometrically. The most effective sorbents for HSs from RW were BCs obtained from straw in the low and high temperatures with the sorption capacity of 3.10 mg g-1 and 5.31 mg g-1, respectively. It was observed that the BCs produced from the same biomass at different pyrolysis temperatures had different sorption capacities for FA, HA, and a mixture of these compounds. The results indicated that BCs obtained from sunflower at different temperatures and oak at high temperature were the most promising sorbents for the recovery of HSs from RW. Such materials have the potential to be applied to soil and were selected for further evaluation due to their ability to enhance soil quality and immobilize pollutants. Further studies will assess their effectiveness in different soil conditions, their stability and persistence, and their impact on plant health and growth.
RESUMEN
Biochar application has been reported to improve the physical, chemical, and hydrological properties of soil. However, the information about the size fraction composition of the applied biochar as a factor that may have an impact on the properties of soil-biochar mixtures is often underappreciated. Our research shows how sunflower husk biochar (pyrolyzed at 650 °C) can modify the water retention characteristics of arable sandy soil depending on the biochar dose (up to 9.52 wt.%) and particle size (<50 µm, 50-100 µm, 100-250 µm). For comparison, we used soil samples mixed with biochar passed through 2 mm sieve and an unamended reference. The addition of sieved biochar to the soil caused a 30% increase in the available water content (AWC) in comparing to the soil without biochar. However, the most notable improvement (doubling the reference AWC value from 0.078 m3 m-3 to 0.157 m3 m-3) was observed at the lowest doses of biochar (0.95 and 2.24 wt.%) and for the finest size fractions (below 100 µm). The water retention effects on sandy soil are explained as the interplay between the dose, the size of biochar particles, and the porous properties of biochar fractions.