The thermochemical transformation of sewage sludge (SS) to biochar (SSB) allows exploring the advantages of SS and reduces possible environmental risks associated with its use. Recent studies have shown that SSB is nutrient-rich and may replace mineral fertilizers. However, there are still some questions to be answered about the residual effect of SSB on soil nutrient availability. In addition, most of the previous studies were conducted in pots or soil incubations. Therefore, the residual effect of SSB on soil properties in field conditions remains unclear. This study shows the results of nutrient availability and uptake as well as maize yield the third cropping of a three-year consecutive corn cropping system. The following treatments were compared: (1) control: without mineral fertilizer and biochar; (2) NPK: with mineral fertilizer; (3) SSB300: with biochar produced at 300 °C; (4) SSB300+NPK; (5) SSB500: with biochar produced at 500 °C; and (6) SSB500+NPK. The results show that SSB has one-year residual effects on soil nutrient availability and nutrient uptake by maize, especially phosphorus. Available soil P contents in plots that received SSB were around five times higher than the control and the NPK treatments. Pyrolysis temperature influenced the SSB residual effect on corn yield. One year after suspending the SSB application, SSB300 increased corn yield at the same level as the application of NPK. SSB300 stood out and promoted higher grain yield in the residual period (8524 kg ha−1) than SSB500 (6886 kg ha−1). Regardless of pyrolysis temperature, biochar boosted the mineral fertilizer effect resulting in higher grain yield than the exclusive application of NPK. Additional long-term studies should be focused on SSB as a slow-release phosphate fertilizer.
The sewage sludge (SS) use in agriculture has been limited by the Brazilian legislation to a few situations, mainly as a precautionary measure due to inorganic pollutants and pathogens. Thus, a large amount of SS has been accumulated in landfills, with no prospect of use, generating great concern for governments and society. Thermal treatment via pyrolysis has stood out as an option for SS recycling, transforming it into a carbon-rich product known as SS biochar (SSB). Biochar from SS showed good potential to be used for agricultural and environmental purposes. The present study aimed to evaluate the influence of pyrolysis at 300°C on the physical, chemical, morphological and mineralogical characteristics of SSB. In general, pyrolysis increased total carbon, total nitrogen, macro and micronutrient contents, except potassium. Pyrolysis also increased heavy metals (HMs) concentration in SSB. However, HMs values remained below the maximum limits allowed according to the legislation on SS agricultural use. X-ray analysis showed that both SS and SSB present silica (SiO2) as the main mineral. Pyrolysis also increased the SS surface area (SA) and porosity. In general, results of the present study prove showed that pyrolysis is a technological alternative to enable SS use as a sustainable input in agriculture.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.