Potential of _Carica papaya_ Seed-Derived Bio-Coagulant to Remove Turbidity from Polluted Water Assessed through Experimental and Modeling-Based Study  
[PERSON]  
1 School of Civil Engineering, Faculty of Engineering, Universite Teknologi Malaysia (UTM),  
Jober Bahru Shalyn 81310, Joho, Malaysia; ami94 [EMAIL_ADDRESS] (A.H.A.); [EMAIL_ADDRESS] (N.S.Z.); [EMAIL_ADDRESS] (L.Z.Z.); burhanudud@hahod  
reported for their applications in wastewater treatment. Bio-coagulants have been obtained from various plant species such as _Morringa oleifera_[9; 10], _atropha curcas_[1; 11], tannin [12], banana peels [13; 14] and _Bagasse_[10]. These studies have shown that bio-coagulants pose promising treatment performance and thus stand a great chance in replacing the conventional chemical coagulants. Not limited to promising treatment performance, the used bio-coagulants in water and wastewater treatment produce non-toxic and lesser volume of sludge and the bio-coagulant itself is highly degradable unlike chemical coagulants. Besides, application of bio-coagulant in water treatment can eliminate the cost of purchasing and importing chemicals as the raw materials for bio-coagulants can be obtained locally [12].  
_Carica papaya_, commonly known as papaya has been a popular fruit throughout the world. It tends to grow in tropical or subtropical regions and its international trade has been recorded worth nearly 200 million US $ in 2009. Consumption of papaya fruits results in a mass production of food wastes, particularly the discarded papaya peels and seeds which constitutes 15-20% of its weight [15]. Hence, it is essential to minimize the quantity of the papaya waste by utilizing it in various aspects including as the bio-coagulant in wastewater treatment. To date, there is lack of study investigating the performance of _Carica papaya_ seeds as the bio-coagulant in either water or wastewater treatment. Moreover, the chemical characteristics of the papaya seeds such as protein and functional groups which are responsible as an active coagulation agent remains indeterminate. According to [PERSON] et al. [16], the fat residues that are associated with protein in the bio-coagulant increase aggregation by forming cluster thus, promotes the coagulation process. Active coagulant agent can be extracted using various solvents such as distilled water, alcohol, acid (H\({}_{2}\)SO\({}_{4}\)) and alkali (NaOH). Different solvents affect the extracted bio-coagulants differently. Among others, the used of distilled water without additional chemicals is the most preferable as the use of chemicals could alter the initial pH of the treated water or wastewater. Furthermore, chemical-free bio-coagulant produces less sludge [17].  
Besides the chemical characterization, there is also lack of knowledge in terms of the interaction effects and optimization among the prevalent operating parameters of the coagulation process. Existing study on papaya seeds as bio-coagulant was mainly focused on the single effect (by applying one-factor-at-a-time approach) of either dosage or pH towards the turbidity removal [2; 18]. According to [PERSON] and [PERSON] [19], the relationship between different parameters plays an important role in identifying the optimum conditions for the coagulation process. Response Surface Methodology (RSM) utilizes mathematical and statistical models in identifying the optimum operating parameters to achieve a higher process efficiency [18].  
Therefore, this study was conducted to assess the potential of deshelled _Carica papaya_ seeds as the bio-coagulant in treating the polluted turbid water. The bio-coagulant extracts obtained from deshelled _Carica papaya_ seeds were characterized for protein, functional groups by Fourier Transform Infrared (FTIR) spectroscopy, and Field-Emission Scanning Electron Microscopy (FESEM). The optimization of the turbidity removal process and coagulation activity was achieved using RSM to enhance the destabilization of the pollutant particles.