Mike B. Dixon

A coagulation–powdered activated carbon–ultrafiltration – Multiple barrier approach for removing toxins from two Australian cyanobacterial blooms

Cyanobacteria are a major problem for the world wide water industry as they can produce metabolites toxic to humans in addition to taste and odour compounds that make drinking water aesthetically displeasing. Removal of cyanobacterial toxins from drinking water is important to avoid serious illness in consumers. This objective can be confidently achieved through the application of the multiple barrier approach to drinking water quality and safety. In this study the use of a multiple barrier approach incorporating coagulation, powdered activated carbon (PAC) and ultrafiltration (UF) was investigated for the removal of intracellular and extracellular cyanobacterial toxins from two naturally occurring blooms in South Australia. Also investigated was the impact of these treatments on the UF flux. In this multibarrier approach, coagulation was used to remove the cells and thus the intracellular toxin while PAC was used for extracellular toxin adsorption and finally the UF was used for floc, PAC and cell removal. Cyanobacterial cells were completely removed using the UF membrane alone and when used in conjunction with coagulation. Extracellular toxins were removed to varying degrees by PAC addition. UF flux deteriorated dramatically during a trial with a very high cell concentration; however, the flux was improved by coagulation and PAC addition.

Nanofiltration for the removal of algal metabolites and the effects of fouling

Nanofiltration (NF) has been shown to be an effective way of removing organic micropollutants from drinking water due to its size exclusion properties. A rapid bench scale membrane test unit was utilised to trial six NF membranes to remove the algal metabolites, microcystin, cylindrospermopsin, 2-methylisoborneol (MIB) and geosmin (GSM). Membrane fouling due to the algal metabolites was observed for both charged and neutral metabolites. MIB and GSM were removed effectively by low molecular weight cut-off (MWCO) membranes but less effectively by a higher MWCO membrane. Removal of MIB and GSM by the higher MWCO membrane was improved as the membrane fouled. Microcystin was initially removed to above 90% by tight NF membranes but fouling of several membranes caused decreased percent removals over time. Tight NF membranes afforded removals of 90-100% for cylindrospermopsin, while removal by the higher MWCO membrane was lower but improved with time due to fouling.

The impact of optimised coagulation on membrane fouling for coagulation/ultrafiltration process

Abstract This work aimed to demonstrate the effect of optimised coagulation on minimise fouling for coagulation–ultrafiltration process. Coagulation as pretreatment has the potential to mitigate fouling and enhance flux. Operating parameters were tested by a matrix of experiments for various mixing conditions and coagulant doses. In coagulation experiments, varied shear forces were applied to generate different floc characteristics in order to assess the effect on membrane fouling. Floc properties were investigated with an optical monitoring technique to identify structure, size and growth of flocs. It was shown that stronger flocs are of advantage for fouling mitigation and that the coagulant dosage is crucial for the performance of filtration. The impact of water quality was assessed using general water quality parameters and organic characterisation techniques to investigate the performance of each treatment step. The treatment efficiency was further assessed based on comparing the molecular size fract...

Chemometric approaches to data assessment for a long-term case study of MIEX pretreatment performance

Abstract A specifically designed pilot plant facility located at the Mount Pleasant Water Treatment Plant in South Australia was used to investigate the efficiencies of several drinking water treatment processes, including (1) magnetic ion exchange (MIEX) as a pretreatment followed by conventional coagulation treatment, (2) conventional coagulation at pilot the plant alone, (3) MIEX followed by microfiltration (MF), and (4) MF alone. Dissolved organic matter (DOM) removal efficiency of the treatment processes and more importantly the treated water quality was assessed using dissolved organic carbon (DOC) measurement and together with the changes in the chromophoric organics character based on their molecular weight profiles determined by high-performance size exclusion chromatography (HPSEC) were also reported. Cluster analyses (CAs) were performed using the HPSEC peak area (after separated by peak fitting), and supported by DOC, UV absorbance at 254 nm, and SUVA in order to compare treatment efficiencies...

Santa Barbara, Curacao desalination plant expansion using NanoH2O thin film nanocomposite (TFN) SWRO membrane

AbstractThe Santa Barbara desalination plant, located in the South of the Curacao Island, was built and commissioned by Degremont in 2005. The plant production capacity was 18,000 m3/d—consisting of three double-pass trains—which supplied about 45% of the average drinking water consumption of the Island. However, to fulfill the increasing demand of potable water, the plant owner, Aqualectra, added a fourth train to produce 7,100 m3/d, totaling a production capacity to 25,100 m3/d. The new train is single-pass and its product blends with the product from the other three trains. Based on an innovative technical approach, Aqualectra and Degremont awarded NanoH2O the supply of the seawater RO membranes for the fourth train. The proposed membrane design by NanoH2O offered the following: (i) 29% less SWRO elements per train than the existing first-pass trains; reducing the number of pressure vessels from 92 to 65; (ii) the same operating feed pressure as the existing first-pass trains while the system flux is s...

Improving second-pass permeate quality using thin film nanocomposite (TFN) membranes

AbstractSince the initial development of thin film nanocomposite (TFN) reverse osmosis membranes, a concerted effort has been made to optimize performance in first-pass seawater applications in order to lower energy usage. As the potential for greater energy savings can be harder to achieve in brackish water (BW) and second-pass seawater applications, increased membrane rejection is an attractive goal for many BW plants. A pilot plant was identified in Israel utilizing ground water with total dissolved solids of 2,900 ppm that suited an experiment to demonstrate the potential for TFN membranes to provide better salt rejection at the same projected feed pressures as standard Thin Film Composite (TFC) BW membranes. The pilot was undertaken using TFN membranes (400 square foot elements) in Stage 2 of the Lahat BW desalination facility. Eight (8) elements were loaded in a single pressure vessel. Feed water was taken from the concentrate of the plant’s Stage 1 train and had an average conductivity of 5,864 μS/...