The palm oil industry produces liquid waste called POME (palm oil mill effluent). POME is stated as one of the wastes that are difficult to handle because of its large production and ineffective treatment. It will disturb the ecosystem with a high organic matter content if the waste is disposed directly into the environment. The authorities have established policies and regulations in the POME waste quality standard before being discharged into the environment. However, at this time, there are still many factories in Indonesia that have not been able to meet the standard of POME waste disposal with the existing treatment technology. Currently, the POME treatment system is still using a conventional system known as an open pond system. Although this process can reduce pollutants’ concentration, it will produce much sludge, requiring a large pond area and a long processing time. To overcome the inability of the conventional system to process POME is believed to be a challenge. Extensive effort is being invested in developing alternative technologies for the POME waste treatment to reduce POME waste safely. Several technologies have been studied, such as anaerobic processes, membrane technology, advanced oxidation processes (AOPs), membrane technology, adsorption, steam reforming, and coagulation. Among other things, an AOP, namely photocatalytic technology, has the potential to treat POME waste. This paper provides information on the feasibility of photocatalytic technology for treating POME waste. Although there are some challenges in this technology’s large-scale application, this paper proposes several strategies and directions to overcome these challenges.

Disposal of palm oil mill effluent (POME), which is highly polluting from the palm oil industry, needs to be handled properly to minimize the harmful impact on the surrounding environment. Photocatalytic technology is one of the advanced technologies that can be developed due to its low operating costs, as well as being sustainable, renewable, and environmentally friendly. This paper reports on the photocatalytic degradation of palm oil mill effluent (POME) using a BiVO4 photocatalyst under UV-visible light irradiation. BiVO4 photocatalysts were synthesized via sol-gel method and their physical and chemical properties were characterized using several characterization tools including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), surface area analysis using the BET method, Raman spectroscopy, electron paramagnetic resonance (EPR), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The effect of calcination temperature on the properties and photocatalytic performance for POME degradation using BiVO4 photocatalyst was also studied. XRD characterization data show a phase transformation of BiVO4 from tetragonal to monoclinic phase at a temperature of 450 °C (BV-450). The defect site comprising of vanadium vacancy (Vv) was generated through calcination under air and maxima at the BV-450 sample and proposed as the origin of the highest reaction rate constant (k) of photocatalytic POME removal among various calcination temperature treatments with a k value of 1.04 × 10−3 min−1. These findings provide design guidelines to develop efficient BiVO4-based photocatalyst through defect engineering for potential scalable photocatalytic organic pollutant degradation.

Photocatalytic oxidation is one of the technologies to overcome pollution that can be applied for air and water purification. TiO2 has been widely used as a photocatalyst, however, several disadvantages of TiO2 including low absorption of visible or solar radiation, rapid recombination of electron and hole as well as low stability limits its practical applications especially for wastewater treatment. Thus, to overcome this problem, this study aims to develop highly adsorbent photocatalyst using TiO2/SiO2 composites with sugarcane bagasse waste act as SiO2 source. The experimental results show that the photocatalytic performance of TiO2/SiO2 composite in the decolorization of methyl orange exhibits three-fold enhancement compared to neat TiO2. Several catalyst characterizations were obtained including X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray fluorescence (XRF). Characterization data show that a phase transformation was obtained from amorphous to crystalline phase by increasing TiO2 content. These results proved that the feasibility of SiO2 from sugarcane bagasse waste coupled with TiO2 can be utilized for wastewater degradation.

The biosilica shell of marine diatoms has emerged as a unique matrix for photocatalysis, owing to its sophisticated architecture with hierarchical nanopores and large surface area. Although the deposition of titania nanoparticles on diatom biosilica has been demonstrated previously, their photocatalytic activity has been tested only for degradation of pure compounds, such as dyes, nitrogen oxide, and aldehydes. The efficiency of such photocatalysts for degradation of mixtures, for instance, industrial wastewaters, is yet to be investigated. Furthermore, reports on the lattice structures and orientation of nanotitania crystals on biosilica are considerably limited, especially for the underexplored tropical marine diatoms. Here, we report an extensive characterization of titania-loaded biosilica from the tropical Cyclotella striata diatom, starting from freshly grown cell cultures to photodegradation of wastewaters, namely, the palm oil mill effluent (POME). As Indonesia is the largest palm oil producer in the world, photocatalytic technology could serve as a sustainable alternative for local treatment of POME. In this study, we achieved a 54% loading of titania on C. striata TBI strain biosilica, as corroborated by XRF analyses, which was considerably high compared to previous studies. Through visualization using HR-TEM, supported by SAED and XRD analyses, nanocrystal TiO2 appeared to be trapped in an anatase phase with polycrystalline characteristics and distinct crystallographic orientations. Importantly, the presence of C. striata biosilica lowered the band gap of titania from 3.41 eV to around 3.2 eV upon deposition, enabling photodegradation of POME using a broad-range xenon lamp as the light source, mimicking the sunlight. Kinetic analyses revealed that POME degradation using the photocatalysts followed quasi-first-order kinetics, in which the highest titania content resulted in the highest photocatalytic activity (i.e., up to 47% decrease in chemical oxygen demand) and exhibited good photostability throughout the reaction cycles. Unraveling the structure and photoactivity of titania-biosilica catalysts allows transforming marine diatoms into functional materials for wastewater photodegradation.