Co-composting of palm oil wastewater sludge and biosolids

The present study deals with the co-composting of palm oil wastewater sludge (OS) and biosolids (BS) as a possible environmental friendly alternative to handle these wastes. Five laboratory scale composters, each containing 5 kg soil spiked with 10 % OS (mass basis) were used. Shredded empty fruit bunches (EFB) was used as bulking agent. The EFB to soil ratio for each composter was 1:2 (v/v). The carbon-to-nitrogen (C/N) and carbon-to-phosphorus (C/P) ratios were adjusted to 20:1 and 800:1 by adding urea (H2NCONH2) and potassium dihydrogen phosphate (KH2PO4) respectively to the composting mixture. The ratio of BS : (soil + OS) was varied as 0.0:1.0, 0.1:1.0, 0.5:1.0, 0.7:1.0 and 1.0:1.0. The moisture content was adjusted to 20 % and the experiment was conducted at room temperature. The results showed enhanced biodegradation due to biosolids addition. The optimum BS : (soil + OS) ratio was found to be 0.1:1 at which the oil and grease removal reached 86 % in the six week experimental duration. The experiment demonstrated the feasibility of composting at low temperatures (25-26 °C) and also pointed out that depending on the type of materials used it may not always be possible to adjust high levels of moisture content in composting piles.