Composting and vermicomposting of sewage sludge at various C/N ratios: Technological feasibility and end-product quality

• Published in: Ecotoxicology and environmental safety Vol. 263; p. 115255
• Main Authors: Dume, Bayu, Hanc, Ales, Svehla, Pavel, Michal, Pavel, Chane, Abraham Demelash, Nigussie, Abebe
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 15.09.2023; Elsevier
• Subjects: C/N ratio; Composting; Eisenia andrei; Sewage sludge; Vermicomposting; C/N ratio; Vermicomposting; Composting; Sewage sludge; Eisenia andrei
• ISSN: 0147-6513; 1090-2414
• DOI: 10.1016/j.ecoenv.2023.115255

Even though sewage sludge (SS) contains a high level of pollutants, it is rich in essential plant nutrients and has the potential to enhance soil fertility. However, the SS must be further treated through pre-composting plus vermicomposting to make it safe for use on food crops. More research and data are needed to determine how different carbon-to-nitrogen ratios (C/N) affect the feasibility and quality of composting vs vermicomposting of SS. Therefore, in this study we comprehensively evaluated the feasibility and end-product quality of compost and vermicompost produced from SS under different C/N ratios. SS was mixed with pelletized wheat straw (PWS) at various proportions to produce C/N ratios of 6:1, 18:1, 28:1, and 38:1, then pre-composted for 14 days followed by vermicomposting using the earthworm Eisenia andrei for 120 days. Agrochemical properties were measured at 0, 30, 60, 90, and 120 days. Results revealed significantly higher levels of agrochemicals in vermicompost compared to compost, including total potassium (37–88%) and magnesium (4.3–12%), nitrate nitrogen (71–98%), available potassium (53–88%), available phosphorus (79%), available magnesium (54–453%), available boron (48–303%), and available copper (2.5–82%). However, lower levels of ammonium nitrogen by (59–85%), available iron (2.3–51.3%), available manganese (29.7–52.2%), available zinc (10.5–29.8%), total carbon (0.75–4.5%), and total nitrogen (1.6–22.2%) were measured. Comparison of the various C/N ratios, showed that vermicompost with an 18:1 C/N ratio outperformed compost and demonstrated the highest earthworm population (165 pieces/kg). Thus, vermicomposting SS at an 18:1 C/N ratio is strongly recommended as a sustainable technology for producing high-quality vermicompost from SS. •Study evaluates the effect of different C/N ratios on compost/vermicompost from SS.•Vermicomposting reduced TC, C/N, pH, and NH4+; better maturity than composting.•Vermicompost had better agrochemical properties than compost.•An 18:1 C/N ratio yields the best results, including a high earthworm population.