Intensive aerobic bioconversion of sewage sludge and food waste into fertiliser.

The aim of this research was to verify the possibility of recovering the nutrients present in sewage sludge and vegetable food waste as fertiliser after aerobic thermophilic intensive bioconversion. The process was performed in a closed reactor under controlled conditions of aeration, stirring and pH, at a temperature of 60 degrees C, after addition of a starter bacterial culture of Bacillus thermoamylovorans SW25. End product with the best fertilising properties was obtained when sewage sludge, mixed with food waste, CaCO3 and an artificial bulking agent was thermally pretreated. The content of volatile solids and organic carbon decreased from 82.8% to 62.3% and from 37.7% to 32.5% of total solids (TS) respectively, during 12 days of bioconversion. The stable organic fertiliser produced was a powder with moisture content of 5%. Furthermore, 3.4% of nitrogen, 0.4% of phosphorus and 2.9% of potassium were also present. Addition of 10-15g of this fertiliser to 1 kg of poor fertility soil increased the growth of different plants by 113-164%.