Stability of a New Banana Coagulant: Coagulation Performance and Macro-micro Characteristics

A type of banana peel (BP) coagulant and its antiseptic modifier (ABP) were prepared from a raw material of banana peel. Scanning electron microscope/energy dispersive spectrometer (SEM/EDS) and nanometer particle size analyzer were used to study the surface morphology/energy spectra and charge characteristics of BP and ABP. The influence of storage process on coagulation behavior, and macro and micro characteristics of BP and ABP was studied by using Jar tests in treating simulated humic acid (HA) water sample, ordinary camera, pH meter, viscometer, and UV-Vis spectrophotometer (UVA), respectively. Finally, coagulation performance of ABP was investigated, compared with that of polyaluminum chloride (PAC), and coagulation mechanism of ABP was simply analyzed. Results show that the surface morphology and element content of BP and ABP changed greatly compared with that of the raw material of banana peel:the atomic ratios of C/O and K/Na in banana peel, BP and ABP were 1.14, 0.49 and 0.38, and 28.9, 0.72 and 1.22, respectively. Turbidity and color removal by BP largely decreased with the increasing of storage time (85% and 75.4% at 0 d decreased to 52.6% and 44.3% at 11 d and 19.7% and 19.9% at 56 d, respectively). While ABP slightly decreased in turbidity and color removal first, followed by a slight increasing, and then almost tended to be stable (compared with that at 0 d, ABP only decreased by 2.6% and -1.2% at 56 d). With the increasing of storage time, BP posed different changes in macro and micro characteristics due to the erosion of microorganisms to BP, but ABP posed a basic stable state due to the addition of antiseptic stabilizer. ABP almost gave the same turbidity removal as PAC when dosage increased to 5 mg/L, but the suitable pH range (5-9) was less than that of PAC (3-11). The main coagulation mechanism of ABP and BP at 0 d was adsorption/bridging. The coagulation mechanism of ABP was a comprehensive effect conducted by natural organic polymers and microorganisms, rather than any of individual action of natural organic polymers or microorganisms.