Kerry J. Howe

Use of ATR/FTIR spectrometry to study fouling of microfiltration membranes by natural waters

Attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectrometry provided insight into the chemical nature of deposits on polypropylene microfiltration membranes after filtration of two North American surface waters. The spectra of the foulants were easy to distinguish from the spectra of the membrane material. The results did not show strong evidence for the presence of carboxylic acid, carboxylate, phenolic, or hydroxyl functional groups in the foulants, although these functional groups are common in natural waters. ATR/FTIR also indicated the presence of inorganic foulants; the ratio of inorganic to organic foulants varied between the two water sources. The spectra of the foulants were significantly more distinct than spectra of other natural waters, suggesting that relatively few components present in Medina River and Beaver Lake surface waters may adsorb to this membrane material. ATR/FTIR appears to be a valuable tool for studying membrane fouling by natural waters.

Ozone and biofiltration as an alternative to reverse osmosis for removing PPCPs and micropollutants from treated wastewater

This pilot-scale research project investigated and compared the removal of pharmaceuticals and personal care products (PPCPs) and other micropollutants from treated wastewater by ozone/biofiltration and reverse osmosis (RO). The reduction in UV254 absorbance as a function of ozone dose correlated well with the reduction in nonbiodegradable dissolved organic carbon and simultaneous production of biodegradable dissolved organic carbon (BDOC). BDOC analyses demonstrated that ozone does not mineralize organics in treated wastewater and that biofiltration can remove the organic oxidation products of ozonation. Biofiltration is recommended for treatment of ozone contactor effluent to minimize the presence of unknown micropollutant oxidation products in the treated water. Ozone/biofiltration and RO were compared on the basis of micropollutant removal efficiency, energy consumption, and waste production. Ozone doses of 4-8 mg/L were nearly as effective as RO for removing micropollutants. When wider environmental impacts such as energy consumption, water recovery, and waste production are considered, ozone/biofiltration may be a more desirable process than RO for removing PPCPs and other trace organics from treated wastewater.

Fouling indices for low pressure hollow fiber membrane performance assessment.

This study evaluated the use of fouling indices to describe low pressure membrane fouling. One critical aspect of this study was the use of a bench-scale hollow fiber membrane system that imitated full-scale operation (constant flux with automatic hydraulic backwash and chemical cleaning). Fouling indices were based on a resistance-in-series model. Two different hollow fiber membrane types (membrane A and B) were tested with water from two water utilities (A and B) and three other natural sources (oligotrophic, algal bloom impacted, and wastewater impaired). The bench-scale testing included use of the same membrane as utilized at Utility B. Most fouling was reversible by hydraulic backwash and chemical cleaning. Specific flux and fouling indices for the bench-scale system were higher than those determined from full-scale data but fouling index ratios were comparable, suggesting a similar fouling nature. At similar organic loading, fouling was specific to water source and membrane type, i.e., no generalization on the impact of water source was possible. Full-scale data were compared with bench-scale data to validate the use of fouling indices. Fouling indices based on a resistance-in-series are useful tools to describe membrane performance data for both raw and pretreated water, for different water sources, and different membrane types.

Effect of membrane bioreactor solids retention time on reverse osmosis membrane fouling for wastewater reuse.

The effect of the solids retention time (SRT) in a membrane bioreactor (MBR) on the fouling of the membranes in a subsequent reverse osmosis (RO) process used for wastewater reuse was studied experimentally using a pilot-scale treatment system. The MBR-RO pilot system was fed effluent from the primary clarifiers at a large municipal wastewater treatment plant. The SRT in the MBRs was adjusted to approximately 2, 10, and 20 days in three experiments. The normalized specific flux through the MBR and RO membranes was evaluated along with inorganic and organic constituents in the influent and effluent of each process. Increasing the SRT in the MBR led to an increase in the removal of bulk DOC, protein, and carbohydrates, as has been observed in previous studies. Increasing the SRT led to a decrease in the fouling of the MBR membranes, which is consistent with previous studies. However, the opposite trend was observed for fouling of the RO membranes; increasing the SRT of the MBR resulted in increased fouling of the RO membranes. These results indicate that the constituents that foul MBR membranes are not the same as those that foul RO membranes; to be an RO membrane foulant in a MBR-RO system, the constituents must first pass through the MBR membranes without being retained. Thus, an intermediate value of SRT may be best choice of operating conditions in an MBR when the MBR is followed by RO for wastewater reuse.

Spatial and temporal evolution of organic foulant layers on reverse osmosis membranes in wastewater reuse applications.

Advanced treatment to remove trace constituents and emerging contaminants is an important consideration for wastewater treatment for potable reuse, and reverse osmosis (RO) can be a suitable technology to provide the necessary level of treatment. However, membrane fouling by biological and organic matter is a concern. This research examined the development of the RO membrane fouling layer using a bench-scale membrane bioreactor operating at different solids retention times (SRTs), followed by a custom-designed RO test cell. The RO test cell contained stacked plates that sandwich five sheets of RO membrane material, which can be extracted for autopsy at separate times over the course of an experiment without disturbing the remaining membranes. The MBR-RO system was run continuously for 2 weeks at each SRT. The RO membranes were stained for live and dead cells, protein, and carbohydrate-like materials, and visualized using confocal laser scanning microscopy. Images of the stained foulant layers were obtained at different depths within the foulant layer at each time point for all SRT conditions. As the RO foulant layer developed, changes occurred in the distribution and morphology of the live cells and carbohydrates, but not the proteins. These trends were similar for all three SRT conditions tested. RO membrane fouling increased with increased MBR SRT, and the highest SRT had the highest ratios of live to dead cells and carbohydrate-like material to dead cells. The autopsied membranes were also analyzed for protein and carbohydrate content, and it was found that the carbohydrate concentration on the membranes after 14 days increased as the SRT increased.

Supercapacitive microbial desalination cells: New class of power generating devices for reduction of salinity content

Graphical abstract Supercapacitive Microbial Desalination Cell is here presented with unprecedented performances. Anode and cathode act as negative and positive electrode of an internal supercapacitor that is discharged and self-recharged. Maximum power of 3 W m−2 is recorded.

Head loss characteristics of a fibrous bed in a pwr chemical environment

This paper examines the generation and effect of secondary materials created by chemical reactions between dislodged fiberglass insulation debris and simulated cooling system water that would be present within the containment of a pressurized water reactor following a loss-of-coolant accident (LOCA). Corrosion and subsequent precipitation of metals (aluminum, iron, zinc, and calcium) pose an important safety concern because the surface area of exposed metal inside containment represents a large potential source term of chemical debris products that may be capable of blocking the recirculation sump. The Advisory Committee on Reactor Safeguards (ACRS) cited the presence of gelatinous material recovered from the Three Mile Island containment pool after its 1979 accident and noted that the formation of adverse chemical products had not been previously examined under Generic Safety Issue 191 (GSI-191) research program. Based on small-scale tests, the following key issues related to corrosion and precipitation were investigated: 1. Do credible corrosion mechanisms exist for leaching metal ions from bulk solid surfaces, and if so, what are the typical reaction rate constants?2. Can corrosion products accumulate in the containment pool water to the extent that they might precipitate as new chemical species at pH and temperature levels that are relevant to the LOCA accident sequence?3. How do chemical precipitants affect the head loss across an existing fibrous debris bed? Findings from these tests confirmed that corrosion of metal can occur and that artificially induced metallic precipitants can cause substantial additional head loss.

Predicting the partitioning of organic compounds through Polymer materials: Quantum mechanical applications

AbstractHazardous organic compounds can permeate gas pipelines and geomembranes made of organic polymer materials in landfills and leak into the surrounding environment, contaminating groundwater. ...