article · Chemical Engineering Journal Advances
Untreated shipboard bilgewater poses severe environmental hazards to marine ecosystems and maritime operations. To address this, an integrated physico-chemical treatment process was tested on synthetic bilgewater. The system combines chemical coagulation and flocculation using alum with fixed-bed column adsorption using biochar derived from rice husks. Under optimised coagulation conditions, the process removed 84.67 percent of chemical oxygen demand and 46.31 percent of surfactants. The subsequent biochar adsorption column achieved 96.6 percent surfactant removal at an optimal flow rate and bed depth, operating primarily through physisorption mechanisms. Modelling of the adsorption data enabled the design of both pilot-scale and large-scale units. The estimated operating cost for the complete on-board treatment system was calculated at 2.51 US dollars per cubic metre, providing a basis for future validation with real bilgewater.
Discharging shipboard bilgewater directly into the sea harms marine organisms and disrupts maritime transport activities. Developing simple, low-cost purification systems that utilise agricultural by-products such as rice husks offers a practical pathway to mitigate water pollution. This research demonstrates an effective treatment sequence that significantly reduces harmful organic contaminants before water is released into the marine environment.
This technology provides an on-board water treatment solution for shipping operators and maritime transport vessels seeking cost-effective compliance with discharge standards. The process uses inexpensive rice husk biochar and standard alum, with a projected operating cost of 2.51 US dollars per cubic metre. However, the system has only been tested on synthetic bilgewater at laboratory scale, meaning it requires further testing on real bilgewater from operating ships before commercial deployment.
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Discharging shipboard bilgewater (SBW) into seas and oceans without proper treatment could poison marine organisms and negatively impact transportation-related activities. This study focuses on the treatment of synthetic SBW using a simple and cost-efficient physico-chemical process. This treatment system included coagulation-flocculation (CF) using alum coagulant and fixed-bed column adsorption using rice husk-derived biochar (RHB). The optimization and effect of CF process parameters, viz., pH, fast stirring speed, and alum dosage, on surfactant and COD removal efficiencies were studied using a central composite design-response surface methodology (CCD-RSM). At optimum conditions (pH of 6.4, rapid mixing speed of 160 rpm, and coagulant dosage of 140 mg/L), the surfactants and COD removal efficiencies were 46.31±1.48% and 84.67±2.61%, respectively. The adsorption column optimum conditions were flow rate= 5 mL/min and bed depth= 16 cm, giving a surfactant removal efficiency of 96.6%. The primary adsorption mechanism was physisorption, including electrostatic attraction, hydrogen bonding, pore-filling, and hydrophobic interaction, as revealed by SEM, EDX, and FTIR characterizations. The adsorption data fitted well with Thomas model predictions, giving the best kinetic constant (KTh)= 0.305 mL/min/mg and equilibrium surfactant uptake (qo)= 11.05 mg/g (R2= 0.996). The Thomas model's coefficients were successfully used to predict the breakthrough curves and determine the column dimensions for pilot-scale (3 L/h) and large-scale (300 L/h) fixed-bed adsorption units. The estimated cost for the on-board treatment of SBW by the proposed system was 2.51 US$/m3. Future studies are required to implement the proposed combined coagulation/flocculation/adsorption system to treat real SBW from medium-sized ships.
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DOI: 10.1016/j.ceja.2023.100520
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