Valorization of faecal and sewage sludge via pyrolysis for application as crop organic fertilizer

摘要

In developing countries, faecal sludge treatment facilities are non-existent in most cities and small towns resulting in untreated and improper disposal of sludge. In Ghana 85 % of faecal sludge produced each day is discharged into the earth with no effective treatment. Converting sewage and faecal sludge to biochar addresses the stigma of fertilizer obtained from human excreta, since the pyrolysis process guarantees a 100 % pathogen elimination, and enrich nutrients in faecal sludge biochar. The interest to convert sludge waste into biochar is that it ensures a pathogen free fertilizer. Sewage sludge and faecal sludge with sawdust were pyrolysed at different temperatures in this study. Sewage sludge (SSB1 -300 degrees C, 55B2-450 degrees C and 55B3-600 degrees C) as well as faecal sludge with sawdust (CTB1-300 degrees C, CTB2-450 degrees C and CTB3-600 degrees C) were both converted to biochar at 300 degrees C, 450 degrees C and 600 degrees C, respectively using an electric kiln. Physicochemical parameters such as Total Nitrogen (TN), Total Potassium (TK), Total Phosphorous (TP), Calcium (Ca), Magnesium (Mg), Organic Carbon (OC), Organic Matter (OM), Cadmium (Cd), Arsenic (As), Ash content, pH, Electrical Conductivity (EC), Moisture content, Porosity and Bulk Density and germination test were performed. It was found that at 300 degrees C nitrogen content, organic matter, bulk density, biochar yield and moisture content were high, and longer root lengths were observed as well. Biochars produced at 450 degrees C produced the longest shoot lengths. Also, biochars produced at 600 degrees C had high phosphorous, potassium, calcium and magnesium levels, high porosity, pH and high heavy metal concentration as well. The outcomes demonstrate that biochars produced at higher temperatures are high in heavy metal concentration, but were within acceptable limits for application in agriculture. Biochar produced at moderately lower temperature is favourable for agriculture purposes. SSB1-300 degrees C, SSB2-450 degrees C, CTB1 - 300 degrees C and CTB2 -450 degrees C had moderate pH and ash levels and so are less toxic to the growth of plants. Faecal sludge biochar produced at the three temperatures were suitable for use as fertilizer. The conversion of sludge waste into biochar will help improve faecal sludge management.