Evaluation of different natural waste materials as bio-coagulants for domestic wastewater treatment

Abstract

The process of removing pollutants from wastewater is a significant challenge for many countries due to the high cost of current technologies and the continuous increase in water consumption. Several methods are used to treat wastewater, but their efficiency varies according to the quality of the treated effluent and the technology used. In this study, seven natural waste materials: Moringa leaves, Chitosan, Opuntia, Pomegranate peel, Lupin straw, Sugarcane bagasse, and tea were prepared, characterized, and utilized as bio-coagulants for domestic wastewater treatment. Jar test experiments were carried out for the bio-coagulants using the coagulation/flocculation procedure. The optimum dose and time were tested for the bio-coagulants and the experiments were performed at pH 7.5 and at 25 °C. The presence of surface functional groups such as -COOH, -CN and –OH and the formation of surface adsorbents were characterized using Fourier transform infrared (FT-IR) spectroscopy and electron microscopy (SEM) analysis. All bio-coagulants were effective in removing contaminants from wastewater. The tested bio-coagulants removal efficiency increased with increasing doses until equilibrium was reached. The maximum removal percentage of Moringa, Chitosan, Opuntia, Pomegranate, Lupin, Sugarcane bagasse, and tea waste residue was observed at the optimal dose of 0.8 g/L. Pomegranate showed the highest pollutant removal efficiency. Chitosan and Lupin showed moderate efficiency for chemical oxygen demand (COD), biological oxygen demand (BOD5), total suspended solids (TSS), phosphate (PO4), ammonia (NH3), nitrate (NO3), turbidity, total Kjeldahl nitrogen (TKN), total nitrogen (TN), and total organic carbon (TOC). The highest adsorption capacities achieved for Opuntia in terms of TSS, COD, BOD5, PO4, NH3, NO3, TKN, TN, and TOC were 367.42, 625, 450, 82, 3.5, 3.83, 10.43, 8.21, 18.64, and 231.66 mg/g, with corresponding average removal efficiency of 85%, 88.25%, 88.07%, 90.32%, 90.29%, 93.82%, 90.23%, 92.23%, and 95.69%, respectively, due to the presence of cracked texture with porous adsorption sites. The research work suggested that the materials could be considered eco-friendly, low-cost, and effective bio-coagulants for wastewater treatment.