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

In this study, empty palm fruit bunch fibre was used for solids-liquid separation of palm oil mill wastewater and the sludge was sun-dried for potential uses as soil conditioner or solid fuel. The fibre was manually compressed into a wooden mould to obtain a fibre bulk density of 70 ​kg/m3. A composite wastewater sample was poured evenly over the surface of the fibre. The wet solids were sun-dried for 14 days to achieve a moisture content of 99% solids and up to 65% COD removal. Analysis of the dried sludge showed 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 oil mill wastewater sludge for use as sustainable soil conditioner or solid fuel. The effluent from the solids-liquid separation must be given additional treatment as it may still contain harmful constituents.