Saline oily wastewater treatment using Lallemantia mucilage as a natural coagulant: Kinetic study, process optimization, and modeling

[Display omitted] •A new natural coagulant (Lallemantia) for bilge water treatment was introduced.•About 87 % and 20 % of chemical oxygen demand and surfactant were removed.•The second-order kinetic model with R2 = 0.9642 was the best kinetic models.•Multivariate Adaptive Regression Splines (MARS) was validly used for the process.•Lallemantia mucilage could be used for treating saline oily wastewater economically. Saline oily wastewater is among the greatest environmental issues that requires effective treatment methods. The new trend of using natural coagulants to treat saline oily wastewater can help overcome the drawbacks of inorganic coagulants such as high costs, health risk, and large amounts of sludge. In the present study, the Lallemantia mucilage was used for the first time as a novel natural coagulant, which offered a remarkable performance in bilge water treatment at the optimum condition of coagulants dose = 10 mg/L, pH = 7.00, and contact time = 23.8 min with the maximum chemical oxygen demand (COD) removal efficiency of 87.57 % and influent COD of 1202.5 ± 8.5 mg/L. Also, at the optimum condition, Lallemantia mucilage could remove surfactant up to 20.6 % with influent concentration of 55 ± 0.4 mg/L. A quadratic polynomial with R2 = 0.9943 for COD removal showed a satisfactory fit and consistency. The predictability of Multivariate Adaptive Regression Splines (MARS) method with R2 = 0.95235 was significant compared to the Response Surface Methodology (RSM) with R2 = 0.9599. The second-order kinetic equation performed better in terms of kinetic determination with k = 0.00009, E = 1.42776E+13, and R2 = 0.9642 than the first-order model with k = 0.0159, E = 2.52237E+15, and R2 = 0.9431.