Addition of wood sawdust during the co-composting of sewage sludge and wheat straw influences seeds germination

• Published in: Ecotoxicology and environmental safety 2019-01, Vol.168, p.423-430
• Main Authors: Kebibeche, Hassiba, Khelil, Omar, Kacem, Mourad, Kaid Harche, Meriem
• Format: Article
• Language: English
• Subjects: Brassica rapa - physiology; Carbon - analysis; Chemical composition; Composting; Enterobacteriaceae - isolation & purification; Escherichia coli; Germination; Hydrogen-Ion Concentration; Lactuca - physiology; Lepidium sativum - physiology; Nitrogen - analysis; Phytotoxicity; Sanitation; Seeds - physiology; Sewage - chemistry; Sewage - microbiology; Sewage sludge; Soil - chemistry; Soil Microbiology; Streptococcaceae; Temperature; Triticum; Wheat straw; Wood; Wood sawdust
• ISSN: 0147-6513; 1090-2414
• DOI: 10.1016/j.ecoenv.2018.10.075

The objective of this study was to investigate the effect of addition of sawdust co-composted with sewage sludge and wheat straw on seeds germination. Two mixtures were piled and composted over 90 days. The first mixture (C1) was composed of sewage sludge and wheat straw, while the second mixture (C2) was composed of sewage sludge, wheat straw and wood sawdust. The results showed that the physicochemical parameters of both composts, i.e., temperature (> 55 °C in the thermophilic phase), moisture content (~ 30%). pH (6.73 for C1 and 7.19 for C2) and EC values (1.81 mS cm−1 for C1 and 1.32 mS cm−1 for C2) reached the required maturity standard. The values of C/N were below 12 indicating a high degree of maturity. Also, no bacterial pathogens were detected in the final composts. The concentration of total heavy metals has been reduced allowing the elimination of sewage sludge toxicity, confirmed by the germination index, which reached over 80%. Strong positive correlations were noticed between total Kjeldahl nitrogen of C2 and germination indexes of all the studied species. The obtained results indicate that the addition of wood sawdust increases the nitrogen content leading to slightly alkaline compost which influences seeds germination by reducing the phytotoxicity of sewage sludge. •Sawdust increases the nitrogen content of compost.•Compost with sawdust was slightly more alkaline.•The addition of wood sawdust reduces the maturity time of compost.•The use of sawdust as bulking agent reduces the phytotoxicity.•Positive correlation was noticed between nitrogen content and seeds germination.