Novel K-enriched organomineral fertilizer from sewage sludge-biochar: Chemical, physical and mineralogical characterization

Pyrolysis of municipal solid waste compost: Pilot plant evaluation as a sustainable practise of waste management

To evaluate the potential of compost based on municipal solid waste (MSW) and 20% legume pruning under a pyrolysis process, generated products, including solids (biochar), liquids (bio-oil), and gases (non-condensable gases), through experimentation in a pilot plant with a fluidized bed reactor at 450°C and gas chromatography/mass spectrometry have been analysed. In addition, the compost kinetic behaviour by thermogravimetric analysis (TGA), using the Flynn-Wall-Ozawa (FWO) method, has been investigated. Four different reaction zones, associated with lignocellulosic materials (hemicellulose, cellulose, and lignin) with a first step for water evaporation, in TGA curve have been observed. A biochar with low stability and aromaticity, considering high and low O/C and H/C ratios, respectively, has been obtained. The obtained pyrolytic liquids contain a high concentration of phenolic compounds because of a significant presence of lignins and other high molecular weight compounds in the original material. Moreover, the generated non-condensable gases consist mainly of short-chain compounds, such as alcohols, aldehydes, and alkenes produced from hemicellulose, cellulose, and proteins.

Micropollutants in biochar produced from sewage sludge: A systematic review on the impact of pyrolysis operating conditions

Biochar obtained from sewage sludge serves as a valuable soil amendment in agriculture, enhancing soil properties by increasing the nutrient content, cation exchange capacity, water retention, and oxygen transmission. However, its utilisation is hampered by the presence of micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs). Previous studies indicate that the type and amount of micropollutants can be significantly adjusted by selecting the right process parameters. This literature review provides an overview of how (1) pyrolysis temperature, (2) carrier gas flow and type, (3) heating rate, and (4) residence time affect the concentration of micropollutants in biochar produced from sewage sludge. The micropollutants targeted are those listed by the European Biochar Certificate (EBC) and by the International Biochar Institution (IBI), including PAHs, PCDD/Fs, PCBs and VOCs. In addition, per- and poly-fluoroalkyl substances (PFAS) are also considered due to their presence in sewage sludge. The findings suggest that higher pyrolysis temperatures reduce micropollutant levels. Moreover, the injection of a carrier gas (N2 or CO2) during the pyrolysis and cooling processes effectively lowers PAHs and PCDD/Fs, by reducing the contact of biochar with oxygen, which is crucial in mitigating micropollutants. Nevertheless, limited available data impedes an assessment of the impact of these parameters on PFAS in biochar. In addition, further research is essential to understand the effects of carrier gas type, heating rate, and residence time in order to determine the optimal pyrolysis process parameters for generating clean biochar.

Synthesis of tapioca starch/palm oil encapsulated urea-impregnated biochar derived from peppercorn waste as a sustainable controlled-release fertilizer

Nutrient leaching and volatilization cause environmental pollution, thus the pursuit of developing controlled-release fertilizer formulation is necessary. Biochar-based fertilizer exhibits slow-release characteristic, however the nutrient release mechanism needs to be improved. To overcome this limitation, the approach of applying encapsulation technology with biochar-based fertilizer has been implemented in this study. Black peppercorn waste was used to synthesize urea-impregnated biochar (UIB). Central composite design was used to investigate the effects of pyrolysis temperature, residence time and urea:biochar ratio on nitrogen content of UIB. The optimum condition to synthesize UIB was at 400 °C pyrolysis temperature, 120 min residence time and 0.6:1 urea:biochar ratio, which resulted in 16.07% nitrogen content. The tapioca starch/palm oil (PO) biofilm formulated using 8 g of tapioca starch and 0.12 µL of PO was coated on the UIB to produce encapsulated urea-impregnated biochar (EUIB). The UIB and EUIB pellets achieved complete release of nitrogen in water after 90 min and 330 min, respectively. The nutrient release mechanism of UIB and EUIB was best described by the Higuchi model and Korsmeyer-Peppas model, respectively. The improvement of water retention ratio of UIB and EUIB pellets was more significant in sandy-textural soil as compared to clayey-textural soil. The EUIB derived from peppercorn waste has the potential to be utilized as a sustainable controlled-release fertilizer for agriculture.

Dynamics of potassium released from sewage sludge biochar fertilizers in soil

The solid product of sewage sludge (SS) pyrolysis, called SS biochar (SSB), is rich in carbon and nutrients, such as phosphorus (P), nitrogen (N), calcium (Ca), and zinc (Zn). However, SSB has a low potassium (K) concentration because it is released with water during the final stage of sewage treatment. The enrichment of SSB with mineral sources of K can solve the low supply of K in SSB and produce an organomineral fertilizer with a slow release of K. However, the dynamics of K release from these enriched fertilizers in different soil types remain unclear. This study investigated the dynamics of K release from biochar-based fertilizer (BBF) in the form of pellets and granules in two soil types (clayey and sandy) and natural silica. An incubation experiment was conducted for 60 days, and replicates were evaluated at prescribed time intervals. After the incubation period, the levels of K available in the solid fraction were determined, and the dynamics of K release were evaluated using four nonlinear regression models. BBFs achieved a slower release of K than the mineral KCl. The dynamics of K release were affected by the physical form of BBF, such that the pelleted BBF exhibited the slowest K release. Furthermore, regarding the concentration detected in the solid phase, the total released was highest in clayey soil, followed by sandy soil and natural silica. The enriched BBFs reduced K release throughout the experimental period, behaving as slow-release fertilizers with the potential to optimize K uptake by plants throughout the growth cycle. Further studies are required to evaluate K leaching and retention in the soil profile when biochar-based fertilizers are applied.

Assessing potassium release in natural silica sand from novel K-enriched sewage sludge biochar fertilizers

Enrichment of biochars to produce slow nutrient release fertilizers with minimal losses to the environment is a promising strategy. However, the release of potassium (K) from biochar-based fertilizer produced from sewage sludge (SS) is still poorly studied. In the present 30-day incubation study, the dynamics of K release were evaluated from SS biochar-based fertilizers enriched with potassium chloride (KBF) in different forms, subjected to two levels of silica sand moisture (10 and 20%). The KBF was evaluated in the form of granules, pellets and powder, in addition to pure KCl mineral fertilizer. During the incubation period water-soluble K extractions were performed, where the K contents were adjusted to K release kinetic models. An additional experiment was performed to assess the effect of KBFs and KCl on K leaching. In general, at both moisture levels all KBFs presented a slower K release compared to pure KCl mineral fertilizer, reducing the release rate by up to 77%. The K release dynamics were affected by the type of biochar fertilizer (granule, pellet and powder) and the silica sand moisture level. The behavior of KBFs as slow-release fertilizers is strongly dependent on the silica sand moisture level. At the 10% moisture level, biochar fertilizers in the form of pellets and granules can be classified as slow-release fertilizers with the potential to increase the efficiency of K use in agriculture. Furthermore, compared to the chemical fertilizer, KBF reduced the amount of leached K, diminishing the risk of this nutrient polluting the groundwater. Our results must be further assessed in real conditions using soil as a suitable medium for agronomic and environmental evaluation. Therefore, future studies should consider the dynamic of K and other nutrients from KBFs in distinct soil types.