## 1 Introduction  
Water pollution is mainly caused by many sources such as industrialization activities, agricultural activities, and the release of improperly treated sewage into a water body [1]. It has now become more crucial to ensure the incoming pollutants into the water body do not adversely affect the carrying capacity of the water itself [2]. Various treatment methods such as coagulation-flocculation have been applied, and like any other conventional treatment, it shows promising pollutants removal performance. The coagulation process can be classified as a simple and effective treatment method with the use of divalent positively charged chemical coagulants [3]. The commonly used coagulants include metal salts coagulants such as aluminium sulphate or alum (Al\({}_{2}\)SO\({}_{4}\)), iron (III) chloride (FeCl\({}_{3}\)), polyaluminium chloride (PACI) and iron (II) sulphate (Fe\({}_{2}\)(SO\({}_{4}\))\({}_{3}\)). Despite their well-known performances, there are several disadvantages of using these chemical coagulants. It has been evidenced that the use of metal salts coagulant produces a large volume of toxic sludge, which can sometimes sufficiently be classified as scheduled waste. According to [PERSON] et al. (2018), it was estimated that the coagulation using chemical coagulant for big treatment plants produces around 60,000 tonnes of toxic sludge per year that requires high sludge treatment cost and proper treatment to ensure it did not cause further pollution. Besides, the use of the chemical coagulant without properly optimised dosing can chemically affect the treated water, where the residual chemical is remained in the treated water ([PERSON] et al., 2018). This residual chemical such as chlorine can then affect the health of water consumers. Henceforth, identifying other alternatives to replace the conventional chemical coagulant is vital. Alternatives for more environmentally friendly coagulants are natural coagulants that are composed of polymers from natural sources that were extracted from plants, animals, and algae ([PERSON] et al., 2018). The application of natural sources for water and wastewater treatment was also practised in other treatment technologies, such as biofiltration treatment ([PERSON] et al., 2018). Natural coagulant such as _Moringa oleifera_, _Jatropha curcas_, and _Opuntia ficus indica_ has been long tested for the removal of various pollutants. For example, _Moringa oleifera_ shows good removal of total suspended solids and colour exceeding 90% removal ([PERSON] et al., 2018). A natural coagulant is also having good antimicrobial properties in removing bacteria, coliform, and fungi with percentage removal exceeding 95% compared to metal salts coagulants with percentage removal less than 40% ([PERSON] et al., 2018). The common limitation of the natural coagulant arises due to the production in ensuring a continuous supply as the source of the coagulant can be affected based on the seasonal variation and the lifespan of the natural sources ([PERSON] et al., 2018). The good performance of natural coagulants in removing pollutants relies on their physical, chemical, and morphological properties. Different natural coagulant has different properties. For instance, _Moringa oleifera_ seeds rely on their superior protein content while _Jatropha curcas_ relies on its high carbohydrate or polysaccharide content which acts as an active coagulant agent ([PERSON] et al., 2018). Currently, researchers are still unable to conclude the main properties of these sources to be used as natural coagulants as different sources have different properties that make them suitable to be used as natural coagulants ([PERSON] et al., 2018). The extraction process using solvents such as acid, alkali, and alcohol can extract more active coagulant agents to improve the natural coagulant. Due to the different active agents comprised in the coagulant, they basically react differently towards the extraction process.