James S. Taylor

Influences of molecular weight, molecular size, flux, and recovery for aromatic pesticide removal by nanofiltration membranes

Abstract Eleven aromatic pesticides were used for a removal study using a 4040 spiral-wound polyamide nanofiltration (NF) membrane. The influences of molecular weight, molecular size (length and width), flux, and recovery were studied. The molecular weights of these pesticides are from 198 Da to 286 Da. Molecular sizes were determined by theoretical calculation for their length and width by “Hyperchem” based on their structures and orientation. Furthermore, the study held constant for two operated recoveries and fluxes to determine their effects. The results showed that the NF membrane can remove pesticides from 46% to 100% based on their molecular weights, lengths, fluxes and recoveries. The rejections were increased as the molecular weight increased, and a sharp increase to complete rejection (100%) was observed around MW 200 Da. Therefore, a molecular weight cut-off (MWC) of 200 Da can be determined for this membrane from this result. In addition, the results showed the molecular length was more significant than molecular width for these pesticides. The rejections were not only dependent on molecular weight and length, but also on operational flux and recovery. For a particular pesticide in the two operational fluxes and recoveries, the highest percent rejections occurred on high flux and low recovery, and lowest percent rejection occurred on low flux and high recovery, which would indicate the basic diffusion control theory.

Fouling behavior of a pilot scale inside-out hollow fiber UF membrane during dead-end filtration of tertiary wastewater

A series of pilot-scale filtration experiments were performed systematically under various operating conditions to investigate the fouling behavior of ultrafiltration (UF) membranes to treat tertiary wastewater for resuse. All experiments were conducted using a pilot system, which consisted of six inside-out capillary polyether sulfone UF membrane modules (molecular-weight cutoff = 150,000 Da), arranged in parallel configuration. The pilot unit was operated in dead-end filtration mode and the membranes were frequently backwashed with chlorinated water. Results of this research clearly indicated that the productivity of the UF membranes, measured by the specific water flux (Kw), declined much faster as operating flux increased. This observation was attributed to enhanced solid and organic loading to the membrane surface at higher operating fluxes. Furthermore, the analysis of Kw variation against filtrate volume showed larger productivity reduction per foulant mass loading during operation at high flux rates, suggesting the formation of more compact cake layers which were not easily removed during backwashing. Pilot study results also demonstrated that increasing backwashing with chlorine addition significantly improved membrane productivity, primarily due to enhanced foulant removal by organic oxidation and biogrowth control. In addition, flux enhancement per backwashing volume increased with decreasing time between backwashing events. Ferric chloride pretreatment also markedly enhanced membrane productivity by increasing particle floc size, which led to decreased pore plugging, reduced cake layer resistance, and enhanced backwashing efficiency.

Simplified Analysis of Contaminant Rejection During Ground- and Surface Water Nanofiltration Under the Information Collection Rule

A simple, closed-form analytical expression based on the homogenous solution diffusion model is derived for contaminant removal during nanofiltration (NF) of ground and surface water. Solute permeation and back-diffusion coefficients were used as fitting parameters to model rejection characteristics of four thin-film composite NF membranes under conditions typical of drinking water NF. Nonlinear fits of the model to experimental data suggests that the United States Environmental Protection Agencys (USEPA)s Information Collection Rule protocol for bench-scale studies could be improved to obtain greater precision of the mass transfer coefficients. The model was found to fit rejection data for several water treatment contaminants including total organic carbon, precursors to total organic halide, four trihalomethanes and nine haloacetic acids containing chlorine and bromine, calcium and total hardness, alkalinity and conductivity. The simplified approach to mass transfer calculations from multisolute systems suggests that feed water recovery has a stronger influence on contaminant rejection than permeate flux. Evidence for coupled transport of divalent inorganic ions is also presented. Even though the model developed does not account for ion coupling and cannot be applied in a purely predictive mode, it can assist in the better design and interpretation of data obtained from site-specific pilot-scale water treatment NF studies conducted in support of plant design.

Surface water treatment using nanofiltration -- pilot testing results and design considerations

Integrated membrane systems (IMS) were pilot tested for treatment of a high TOC river water. Pretreatment methods included microfiltration, in-line coagulation-microfiltration, and coagulation-sedimentation-filtration. Fouling was minimized at lower flux, lower recovery and with the addition of a biocide. Such experiments incurred no fouling. A cellulose acetate nanofilter was susceptible to biological degradation therefore a biocide was necessary to ensure membrane integrity. A polyamide membrane was sensitive to oxidation by monochloramine and rejection characteristics were compromised. The rate of fouling between the three nanofilters tested increased with increasingly negative surface charge and increasing surface roughness. Organic adsorption therefore did not follow the charge-repulsion theory but may have been negatively influenced by the greater surface area associated with a rougher surface. Modeling of productivity decline by a form of the resistance model using permeate volume and TOC concentration provided a better fit than that of the linear model of productivity with time. Rejection of organic and inorganic parameters increased with decreasing nanofilter molecular weight cut-off (MWCO). Rejection was influenced by diffusion and size exclusion mechanisms. Log removals of Bacillus subtilis spores by IMS ranged from 5.4 to 10.7 log with the highest removals achieved by microfiltration pretreatment followed by a low (200 dalton) MWCO polyamide nanofilter.

Micro-organism rejection by membrane systems

The removal of micro-organisms by membrane systems was investigated using single-element membranes and five species of micro-organisms in a plant setting at East St. Louis, MO. Single-element membranes included a cellulose acetate ultrafilter (UF), a polysulfone microfilter (MF), a cellulose acetate (CA) nanofilter (NF), and two composite thin-film (CTF) nanofilters. Micro-organism challenge studies were conducted using raw, alum coagulated-settled, and finished plant water. Model micro-organisms consisted of Clostridium perfringens (strain 26) spores (~1-5 μ m) for bacteria simulation, MS-2 (~0.025 μ m), and PRD-1 (~0.1 μ m) phage for virus rejection and Cryptosporidium parvum oocysts (~4-6 μ m) and Giar dia lamblia cysts (~8-14 μ m) for cyst rejection. Sixty-eight observations of micro-organism rejection were gathered over 1 year of operation in eight separate challenge events where micro-organisms were spiked separately and as a mixture. The composite thin-film nanofilters provided significantly better...

Potable Water Quality and Membrane Technology

Requirements for potable water quality have changed dramatically from the late 1970s due to enhanced regulation of pathogens and disinfection by-products. Consequently, new treatment technology and analytic techniques are required to meet this challenge, affecting clinics, laboratories, universities, and other organizations involved in the analysis and treatment of potable water. The changing health effects and regulations affecting potable water treatment and associated applications of membrane technology are discussed.

Comparison of NF/RO membrane performance in integrated membrane systems

Abstract Within the framework of the project ‘Integrated multi-objective membrane systems for control of microbials and DBP precursors, funded by AWWARF and USEPA, four integrated membrane systems (IMSs) for surface water treatment were investigated. The identified IMSs are based on pretreatments including slow sand filtration, bank filtration, coagulation-sedimentation-rapid filtration (CSF) and ultrafiltration respectively. The IMSs were tested on three locations in the US and three locations in The Netherlands. One of the primary objectives of the project was to compare membrane performance, a conventional NF system applied to ground water was used as a reference. Membrane performance was studied by normalising process data towards the mass transfer coefficient (MTC) and normalised feed channel pressure drop (NPD). Results show that a soil passage is to be preferred, especially when the water can be extracted under anaerobic conditions; such an IMS leads to a low cleaning frequency at low costs. When soil passage is not possible due to local circumstances, ground water conditions can be approximated by slow sand filtration after a CSF pretreatment. Since slow sand filtration is a space consuming technique, an IMS was investigated based on ultrafiltration after CSF pretreatment. After optimization of both CSF pretreatment and ultrafiltration no significant fouling of the RO membranes was observed.

Pilot scale microfiltration at Manitowoc

Microfiltration of Lake Michigan Water for the production of drinking water was investigated using a 60 GPM Memcor microfiltration pilot plant for nine months at Manitowoc WI. The performance characteristics of a microfiltration pilot plant for varying surface water conditions were analyzed and modeled. Statistical regression was used to determine and develop quantitative relationships between time of operation and several operational variables for water quality and productivity. Direct filtration of a alum pretreated feed water was found to greatly increase time of operation between cleanings for temperatures below 48°F. The investigation found the turbidity and particle counts of the microfiltered water was less than the same for the finished water produced by the conventional alum coagulation, sedimentation and filtration process. Cleaning frequencies of 21 or more were predicted. Based on the results of this investigation, a recommendation was made to use microfiltration as the treatment process of choice for the treatment of Lake Michigan Water.

Influences of Water Treatment Process on Iron and Copper Release in Distribution System

A pilot study was conducted to assess the effect of water quality changes on iron and copper release in distribution systems. Three finished waters were prepared from groundwater source by conventional treatment, lime softening and reverse osmosis (RO). To mimic desalinated seawater, sea salts were added to RO treated water. Both lime softening and RO treatment significantly decreased the calcium concentration and alkalinity of groundwater. During a yearlong investigation, the impact of seasonal changes on iron and copper release was also evaluated. The results showed that groundwater after lime softening slightly increased iron release potential but significantly decreased copper release. Desalination water caused much higher iron release but lower copper release than conventionally treated groundwater. Blended water with conventional groundwater and desalination water resulted in intermediate iron release but much high copper release. Both iron and copper release could be accelerated by temperature increase.