Solids-liquid separation and solar drying of palm oil mill wastewater sludge: Potential for sludge reuse

In this study, empty palm fruit bunchfibre was used for solids-liquid separation of palm oil mill wastewater andthe sludge was sun-dried for potential uses as soil conditioner or solid fuel. Thefibre was manually compressedinto a wooden mould to obtain afibre bulk density of 70 kg/m3. A composite wastewater sample was pouredevenly over the surface of thefibre. The wet solids were sun-dried for 14 days to achieve a moisture content of<10%. The mass of each mould was determined daily after sunset throughout the drying period. The nutrientscontent and calorific value of the dried sludge were determined using standard methods. The solids-liquid sep-aration process was able to achieve>99% solids and up to 65% COD removal. Analysis of the dried sludgeshowed nutrients content (% of dry weight) of 0.84 for total nitrogen, 0.15 for phosphorus and 0.49 for potassium.The mean calorific value of the dried sludge was 17.1 MJ/kg. The results show the potential of sun-dried palm oilmill wastewater sludge for use as sustainable soil conditioner or solid fuel. The effluent from the solids-liquidseparation must be given additional treatment as it may still contain harmful constituents.