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Bio-fabrication of ZnO films using plants, enzymes, and microorganisms has been recognized as an environmentally friendly procedure as an alternative to physical and chemical methods. In this research, the optical and structural properties of ZnO thin film have been investigated using UV-Vis spectrophotometer, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The ZnO films was prepared by spin-coating the mixed solution of Zn(NO3)2 and watermelon (Citrullus lanatus) peel extract on glass substrate. The ZnO films were then annealed at 400°C for 3h. The UV-Vis absorbance spectra show the strong absorption peaks occurs over a range of wavelengths of 220-380nm, and 190-235 nm for pre-annealed and annealed samples, respectively. The optical band gap of the samples was influenced by the heat treatment. The as-prepared samples synthesized at pH 8 is 3.73 eV and increased up to 5.4 eV after annealed at 400 °C for 3 h. This result suggested that pre-annealed sample has better photocatalytic activity compared to the annealed samples. The XRD pattern of the ZnO films exhibits the ZnO diffraction peaks that correspond to the hkl of hexagonal wurtzite structure. SEM image shows that the morphology of ZnO samples are spherical and rod-like microstructure.

Abstract-Palm oil mill effluent is waste produced from palm oil processing activities. This waste are comingfrom condensate water, process water and hydrocyclone water. The high levels of contaminants in the palm oil mill effluent causes the waste becomes inappropriate to be discharged to water body before processing, one of the most major contaminants in wastewater is fats, oils and COD.This study investigated the effectiveness of chemically activated bentonite that serves as an alternative to reduce the COD in adsorption and floatation based palm oil effluent waste processing. Natural bentonite was activated by using nitrit acid and benzene. In the existing adsorption material to improve COD reduction capability whereas the flotation method was used to further remove residual effluent which is still remain after the adsorption process. An adsorption columns which operated in batch was used in the present study. By varying the circulation time and adsorbent treatment (activated and non-activated), it was shown that percentage of COD reduction reached 75% at the circulation time of 180 minutes for non activated adsorbent. On the other hand the percentof COD reduction in adsorption and flotation process using activated bentonite reached as high as 88% and 93% at the circulation time of 180 minutes.

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