Abstract
In Thailand, the palm oil industry produces a huge amount of palm oil mill effluent (POME), mostly used for electricity generation through biogas production. Co-digestion with other waste can further improve biogas yield and solve waste management problems. Most previous studies relied on biochemical methane potential (BMP) assay or batch co-digestion to obtain the optimal mixing ratio, ignoring the kinetic part or treat it for sole discussion of the results. This work directly uses mechanistic models based on Monod kinetics to describe the experimental results obtained from the co-digestion of POME (40 ml, BMP = 281.2 mlCH4/gCODadded)) with chicken manure (CM) (0–50 g) and crude glycerol (Gly) (0–10 ml). The best mixing ratio between CM and POME was 5 gCM: 40 mlPOME (BMP = 276.9 mlCH4/gCODadded). The best ratio for Gly and POME was 2 mlGly: 40 mlPOME (BMP = 211.9 mlCH4/gCODadded). Adding Gly only 2 mlGly/40 mlPOME doubled the amount of biogas. Hence, crude glycerol is a good substrate for on-demand biogas output. The co-digestion increases the methane output but with a decreased yield. A multi-substrate Monod model was developed based on the levels of digestion difficulty. A partial-least squared fitting was used to estimate its main parameters. All parameters included in the model passed the significant tests at a 95% confidence level. The model can describe the experimental results very well, predict observable state variables of batch co-digestion, and allow a simple extension for continuous co-digestion dynamics. A limited continuous experiment was conducted to confirm the applicability of the model parameters of POME digestion obtained from BMP tests to predict a continuous AD. The results show good potential but must be carefully interpreted. It is generally possible and practical to directly obtain design and operational parameters from BMP assays based on only accumulated biogas curves and initial and final COD/VS.
Highlights
Introductionpalm oil mill effluent (POME) is the wastewater characterized by a thick-yellowish liquid, high organic contents, having chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in the range of 44,300–102,692 mg/L and 25,000–65,714 mg/L, respectively
Higher total solid (TS) in chicken manure (CM) than palm oil mill effluent (POME) indicates a higher fraction of non-degradable substrate present in CM
POME is a well-balanced substrate for the AD process, containing sufficient macro and micronutrients
Summary
POME is the wastewater characterized by a thick-yellowish liquid, high organic contents, having chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in the range of 44,300–102,692 mg/L and 25,000–65,714 mg/L, respectively. It is suitable for generating electricity through biogas. The concentration of oil and grease ranges from 4,000–9,341 mg/l, depending on milling processes [2, 3, 4, 5]. Characteristics of POME depends on the quality of the raw material (fresh palm-oil fruit bunches) and the efficiency of palm oil extraction processes [6]
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