title: Tetracycline remediation in simulated groundwater using wastepaper sludge ash based permeable reactive barrier
Creators: name: Al-Hashimi, O
Publisher: name: Liverpool John Moores University
Year: 2026

description: Provision of safe and reliable freshwater is a fundamental human right. Throughout history, a considerable number of people have relied on groundwater as their primary source for various purposes such as agriculture, industrial and daily activities. However, in recent decades, the growth of the population and increased anthropogenic activities led to soil pollution and to contamination of the available water resources by both organic and/or inorganic pollutants. This contamination poses a significant environmental threat and directly impacts all aspects of people's lives. Therefore, the focus of this research is to develop a new adsorbent that can effectively treat simulated groundwater (in the form of an aqueous solution) polluted by TC (Tetracycline antibiotic) using the PRB (Permeable Reactive Barrier) technique. The novelty lies in using a waste byproduct from the paper industry and sand to transform the inert sand into a reactive material, thereby creating a cost-effective raw material for the adsorbent. The raw materials and the newly synthesized sand have been determined by conducting a comprehensive set of characterization tests. These tests include the X-ray fluorescence analyzer (XRF), X-ray diffraction (XRD) analysis, scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), specific gravity measurements, the total carbon content, and particle size distribution. To achieve the optimal conditions for preparing the reactive sand with the highest adsorption capacity of TC, several synthesis parameters were identified. These parameters include maintaining a pH of 12, a molar ratio of Ca/Fe at 1/0.75, a ratio of 1:1 for FeCl3 to Sand, using 6 mL ethylene glycol solution, and drying the mixture at 95°C. During the batch tests, it was found that using 0.3g of the adsorbent, at pH 7 and an agitation, mixing speed of 200rpm for 3 hours, resulted in the removal of 91% of a 50mg/L TC solution in 100mL of deionized water. The kinetic results obtained from the adsorption process of TC onto the coated sand were well matched with the Pseudo second-order model, indicating that the chemisorption mechanism plays a dominant role in the removal. The intraparticle diffusion revealed that there are multiple linear portions in the relationship between the amount of adsorbed TC and the square root of time, suggesting that intra-particle diffusion also contributes to the removal of TC. Additionally, electrostatic attraction, hydrogen bonding, and intraparticle diffusion were identified as the primary mechanisms involved in the removal of TC by the prepared adsorbent. The conducted isotherm studies showed that the Langmuir model provided an excellent fit to the adsorption data, with a high determination coefficient (R2 &gt; 0.99). The highest adsorption magnitude observed was 21.96 mg/g and the characterization analyses indicated that the reactivity of the newly prepared sand was attributed to the formation of a calcium ferric oxide layer on the sand surface. This layer played a crucial role in adsorbing TC from the aqueous solution. Desorption tests demonstrated that only 0.17 mg/L of TC remained in the aqueous environment after 48 hours of contact time, highlighting the strong bonding between the contaminant and the solid phase. Furthermore, the exhausted adsorbent could be regenerated effectively using HCl and deionized water as washing agents to restore its removal efficiency. The fixed bed and column experiments revealed that increasing the flow rate and/or the initial concentration of TC while decreasing the bed depth led to reduced longevity of the bed, resulting in the rapid exhaustion of the reactive material. This behaviour was accurately described by the Adams-Bohart and Clark models. Longevity calculations demonstrated that employing a 1.35m PRB to treat a flow of 1.58 mL/min containing 50 mg/L of TC would keep the zone protected by the reactive wall for approximately 6 years. All the batch and fixed bed results were successfully simulated using artificial neural networks, enabling accurate predictions of the behaviour of the reactive material and the PRB in various environmental conditions within the limits of these experiments.