Preparation of Low-Cost Kaolin Based Tubular Ceramic and Chabazite Zeolite-Ceramic Composite Membranes: Application in Microalgae Recovery and Wastewater Treatment

Abstract

"The separation and purification process is an important aspect of downstream operation as it deals with great energy consumption and operational cost in chemical and several other industries. On the other hand, the need for wastewater treatment has increased alarmingly due to urbanization and industrialization. Specifically, the harmful effects associated with discharging untreated heavy metals containing wastewater to water bodies adversely impact mankind and aquatic life. Membrane separation is regarded as a clean and simple process; in particular, the use of low-cost ceramic membranes in the membrane separation process has gained enormous popularity owing to their outstanding thermal, chemical and mechanical properties. In this work, inexpensive kaolin clay based tubular ceramic membranes were prepared with different organic additives such as guar gum (GG), carboxymethyl cellulose (CMC) and hydroxypropyl methylcellulose (HPMC). Considering the fabrication ease and properties, the membrane prepared with HPMC as a binder displayed excellent characteristics such as porosity (40%), mechanical strength (25 MPa), along with good corrosion resistance. Also, the estimated cost of an optimized membrane (Kaolin-HPMC) is found to be 253 USD/m2 based on raw materials, energy consumption, manpower and equipment cost. The performance of the membrane was tested for recovery of microalgae from the culture broth, TiO2 separation from aqueous suspension, and oilfield-produced water treatment. The prepared membrane displayed complete recovery (100%) of microalgae from its broth and TiO2 nano particles from aqueous suspension. In case of oilfield-produced water treatment, the hybrid process of microfiltration followed by biological treatment efficiently reduced the COD of the treated water (COD: 11 mg/L), which was well below the discharge limits (COD: 250 mg/L) prescribed by the Central Pollution Control Board, Government of India. Furthermore, the prepared membrane was extended to use as a support to fabricate a mesoporous zeolite coated tubular ceramic composite membrane for the removal heavy metals from its aqueous solution. Different strategies were followed to fabricate the Chabazite zeolite composite membranes through the organic template-free hydrothermal synthesis method, such as coating the ceramic tubes solely on the interior surface, exterior surface and both sides. The experimental results revealed that the ceramic tube coated on both sides has the highest amount of zeolite loading, i.e., 1.82±0.18 g, along with porosity of 30.50±0.50%, water permeability of 1.74 L/m2 h bar and average pore diameter of 36 nm. Also, the estimated cost of both sides coated membrane is found to be 868 USD/m2. The performance of the membrane in separating heavy metal ions from their solutions was evaluated using Cd, Ni, Mg and Al salt in single, binary and tertiary mixtures. The membrane displayed the following salt rejection (R) trend: (99.9%) > (99.7%) > (99.5%) > (98.5%) in a single salt system at an applied pressure of 276 kPa, feed concentration of 1000 mg/L, and pH 3."