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

Abstract

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 <10%. The mass of each mould was determined daily after sunset throughout the drying period. The nutrients content and calorific value of the dried sludge were determined using standard methods. The solids-liquid separation process was able to achieve >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.