Design, modelling and development of filtration processes for household water treatment systems

Abstract

In small water treatment systems, cartridge filters are commonly employed due to their ease of use and small footprint. Readily available commercial filter types (spun, wound and pleated) of different micron ratings (10, 5 and 1) were tested for the removal of turbidity either alone or in series in simulated large volume pilot trials. An initial turbidity of 40±10 NTU was prepared using fine test dust (ISO 12103-1, A2) with the turbidity removal efficiency, pressure drop, and lifespan of the filters evaluated. In pilot trials, the volume of turbid water filtered varied from 0.85 m3 with a 1 micron wound filter to 6 m3 , with 5 and 1 micron pleated filters in series, which could be used for three filtration cycles. With the pleated filters, turbidity removal efficiency improved over time as a cake built up with the effluent turbidity reaching acceptable quality (<5 NTU). This criterion continued to be achieved with repeated cycles of washed pleated filters, significantly reducing the cost and improving sustainability of the HWT system. A comprehensive approach to simulation of particle removal in cartridge filtration using CFD was developed to simulate the fundamental mechanisms underpinning the removal of particles within the widely used 10 inch cartridge filter. Laboratory based validation studies confirmed the novel CFD model to accurately model removal of turbidity and predict the pressure drop across the filter with Root Mean Square Percentage Error (RMSPE) value being 2.46%, 1.49% and 1.95% for 1.2m, 3.6m and 4.8m mesh cells. The simulated location of particle deposition on the filter elements closely matched images taken at several stages during filtration experiments with the model aiding understanding of pattern of particle removal along and within the porous filter structure. A low-cost and multifunctional precoat layer and a simple precoating method were developed, achieving turbidity-free effluent with additional capability to effectively reduce the concentration of both organic matter and pathogenic microorganisms as well as protecting the surface of the filter, facilitating cleaning and re-use. Different test waters were prepared with A2 fine test dust (TD) and/or humic acid sodium salt (HA) to evaluate the performance of the system under different conditions. When tested with 60 mg/L of TD (40±10 NTU), the system effectively removed >95% of influent turbidity in large volume trials (>1000 L) when 1 micron pleated filters were precoated with either xii natural or calcined diatomaceous earth (DE); in comparison, with the un-precoated filter, filtrate turbidity never reached the 5 NTU target set by the WHO. A novel HWT system was implemented by fitting a T-Valve on the suction side of the feed pump to dose the coagulants, eliminating the need for an additional pump. Contact filtration using fibrous cartridge filters did not require frequent coagulant dose optimization due to the large surface area provided by the fibres on which the coagulant could be adsorbed. Both inorganic (alum) and polymeric (PDADMAC) coagulants provided filtrate turbidity of <5 NTU with concentrations as low as 8 and 0.45 mg/L, respectively.

Date of Award	Aug 2022
Original language	English
Sponsors	Vice Chanchellor's Research Scholarship
Supervisor	Patrick Dunlop (Supervisor), Dorian Dixon (Supervisor) & Nigel Ternan (Supervisor)