Binary mixture composite adsorbents from crushed cockleshells and natural zeolites for river water treatment

Abstract

Development and maintenance of water treatment systems are extremely costly thus a cost-effective and environmental-friendly adsorbent is considered to be an attractive solution and was evaluated comprehensively in this research. The aim of this study was to assess the potential usage of dual-phase composite adsorbents from the mixtures of cockle shells and natural zeolites. This includes two important factors for dual-phase adsorbent development: 1) finding the optimal amount and exhaustive time of cockle shells and natural zeolites required in the jar test experiments; 2) determining the optimal mixture ratio of cockle shells relative to natural zeolites in the column experiments. River water samples were collected from the Desa Bakti River, Universiti Teknologi Malaysia where the total removal efficiencies of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total phosphorus (TP) and total nitrogen (TN) were monitored. Firstly, jar test experiments were carried out. Based on the experiments, the optimal amount was found to be 3 gL-1 for cockle shells and natural zeolites. The exhaustive time for both adsorbents was at day 3. Next, a series of mix ratios within the search area were selected using the Design Expert software. The D-optimal mixture (DMD) method was chosen from the software and an input obtained from the jar test experiment was used in order to generate a list of random mixture ratios. All generated mixture ratios were validated according to the sequence in the Easy Care Pipe System (ECPS). From the analysis provided by the software, the optimal mixture ratio was found to consist of 25% of natural zeolites and 75% of the cockle shells. The targeted values of the total removal were then compared with the experimental data. The percentage removal of BOD, COD, TP and TN were found to be 53.24%, 74.29%, 72.59% and 81.98% respectively. The adsorption mechanism was analytically explained using the adsorption isotherm to complement the results obtained from the jar and column tests. It was found that the cockle shells and natural zeolites in jar test experiments were best-fitted by the Langmuir isotherm. The dual-phase composite adsorbent consisting of cockle shells and natural zeolites in the column test was best fitted with the Yoon-Nelson and Thomas model .