Carica papaya seeds-derived coagulant for water treatment

Abstract

Papaya, or also known as carica papaya is a common fruit grown in many tropical climate countries. Following its mass consumption, papaya fruit wastes such as peels and seeds are generated around 15 to 20% of the fruit’s weight. Hence, the needs arise to either to reduce waste or reuse it into other forms that can be beneficial. Natural coagulants are gaining interest as they are environmentally friendly compared to chemical coagulants. Therefore, the aim of this study is to utilize discarded papaya seeds in becoming the natural coagulant to treat turbid water. The objective of this study is to characterize physico-chemical and morphological properties of carica papaya seed-derived natural coagulant, to determine the optimum operating conditions of carica papaya seed-derived natural coagulant in treating synthetic water and to investigate performance efficiency of carica papaya seeds-derived natural coagulant in treating different classes of river water. Initially, the collected carica papaya seeds were processed by washing, deshelling, drying at 50°C for 24 hours and grinding prior to physico-chemical and morphological characterization. Jar test was conducted based on 2-level factorial design, followed by Response Surface Methodology (RSM) in order to determine the optimum operating conditions of coagulant dosage, pH and initial turbidity on turbidity removal and coagulation activity. For comparison purpose, alum was used. The effectiveness of carica papaya seeds-derived natural coagulant was then tested on different classes of rivers. Class III, Class IV and Class V river water was represented by Skudai River, Melana River and Tukang Batu River respectively. The effectiveness of carica papaya seeds as coagulant was determined based on the removal of turbidity, chemical oxygen demand (COD), ammoniacal nitrogen, nitrite, nitrate, phosphorus and coliforms. Based on the findings, the deshelled carica papaya seeds contained 3.9% moisture content, which resulted towards high yield of 99.2%. The isoelectric point of carica papaya seeds derived natural coagulant was at pH 6 while the surface charge was recorded as +0.4 meq/g. The coagulant also contained minimum concentration of iron and sufficiently high protein content of 363 mg/g. Factorial analysis of carica papaya seeds-derived coagulant revealed that most main and interaction terms are significant, excluding interaction between pH and initial turbidity on turbidity removal. Based on the RSM analysis, at optimum condition of 196 mg/L dosage, pH 4 and initial turbidity of 500 NTU, the papaya seeds were capable to remove turbidity up to 93% with coagulation activity of 85%. Actual observations using the optimum conditions resulted to 88% turbidity removal and 83% coagulation activity. Meanwhile for alum, at optimum condition of 197 mg/L dosage, pH 6.3 and initial turbidity of 425 NTU, the recorded turbidity removal and coagulation activity was 98% and 98%, respectively. Actual observations using the optimum conditions resulted to 94% turbidity removal and 93% coagulation activity. Carica papaya seeds derived natural coagulants were also able to obtain high removal turbidity (87.6%), nitrite (86.2%) and nitrate (82.3%) for river of Class III while for river of Class IV, the natural coagulant obtained higher removal of only turbidity (88.3%) and nitrite (92.2%). This natural coagulant was also able to remove 57.6% and 62.1% of total coliform and Escherichia coli, respectively from Class III river water, which then verifies the antimicrobial properties of the studied natural coagulant. In conclusion, carica papaya seeds have proved its potential ability in becoming effective natural coagulant and able to treat synthetic kaolin water as well as river water of Class IV and below at designated optimum conditions.