T. E. Cloete

Nanotechnology and water treatment: applications and emerging opportunities.

Nanotechnology, the engineering and art of manipulating matter at the nanoscale (1–100 nm), offers the potential of novel nanomaterials for treatment of surface water, groundwater, and wastewater contaminated by toxic metal ions, organic and inorganic solutes, and microorganisms. Due to their unique activity toward recalcitrant contaminants and application flexibility, many nanomaterials are under active research and development. Accordingly, literature about current research on different nanomaterials (nanostructured catalytic membranes, nanosorbents, nanocatalysts, and bioactive nanoparticles) and their application in water treatment, purification and disinfection is reviewed in this article. Moreover, knowledge regarding toxicological effects of engineered nanomaterials on humans and the environment is presented.

Lignocellulose biodegradation: Fundamentals and applications

Lignocelluloses are the building blocks of allplants and are ubiquitous to most regions ofour planet. Their chemical properties make it asubstrate of enormous biotechnological value.The basic chemistry of cellulose,hemicellulose, and lignin has a profound effecton lignocellulose tertiary architecture. Theseintricate associations constitute physical andchemical barriers to lignocellulose utilizationand biodegradation in natural and man-madeenvironments. Overcoming these barriers is thekey to unlocking the commercial potential oflignocellulose. Understanding lignocellulosedegradation under natural conditions forms thebasis of any lignocellulose-based application.A variety of microorganisms and mechanisms areinvolved in the complete biodegradation oflignocellulose in natural environments rangingfrom soil and rumen ecosystems to the termitehindgut. The primary objective oflignocellulose pretreatment by the variousindustries is to access the potential of thecellulose and hemicellulose encrusted by ligninwithin the lignocellulose matrix. Currentworking technologies based on the principles ofsolid-state fermentation (SSF) are brieflyreviewed. The use of unsterile lignocellulosicsfor bioremediation purposes holds promise forcost-effective environmental clean-upendeavors. Novel lignocellulose-basedapplications have found functionality intextile, biological control, and medicalresearch fields and might be exploited there inthe near future. Ultimately, lignocellulosewill probably accompany man to his voyages intospace for interest in this field isintensifying. Therefore, proper management oflignocellulose biodegradation and utilizationcan serve to improve the quality of theenvironment, further mans understanding of theuniverse, and ultimately change local economiesand communities.

Biofouling and Biocorrosion in Industrial Water Systems

Corrosion associated with microorganisms has been recognized for over 50 years and yet the study of microbiologically influenced corrosion (MIC) is relatively new. MIC can occur in diverse environments and is not limited to aqueous corrosion under submerged conditions, but also takes place in humid atmospheres. Biofouling of industrial water systems is the phenomenon whereby surfaces in contact with water are colonized by microorganisms, which are ubiquitous in our environment. However, the economic implications of biofouling in industrial water systems are much greater than many people realize. In a survey conducted by the National Association of Corrosion Engineers of the United States ten years ago, it was found that many corrosion engineers did not accept the role of bacteria in corrosion, and many of them that did, could not recognize and mitigate the problem. Biofouling can be described in terms of its effects on processes and products such as material degradation (bio-corossion), product contamination, mechanical blockages, and impedance of heat transfer. Microorganisms distinguish themselves from other industrial water contaminants by their ability to utilize available nutrient sources, reproduce, and generate intra- and extracellular organic and inorganic substances in water. A sound understanding of the molecular and physiological activities of the microorganisms involved is necessary before strategies for the long term control of biofouling can be format. Traditional water treatment strategies however, have largely failed to address those factors that promote biofouling activities and lead to biocorrosion. Some of the major developments in recent years have been a redefinition of biofilm architecture and the realization that MIC of metals can be best understood as biomineralization.

Resistance mechanisms of bacteria to antimicrobial compounds

Abstract A range of antimicrobial compounds (bactericides) commonly termed biocides, microbicides, sanitizers, antiseptics and disinfectants are available, all of which are claimed by their producers to kill bacteria. Resistance has been defined as the temporary or permanent ability of an organism and its progeny to remain viable and/or multiply under conditions that would destroy or inhibit other members of the strain. Bacteria may be defined as resistant when they are not susceptible to a concentration of antibacterial agent used in practice. Traditionally, resistance refers to instances where the basis of increased tolerance is a genetic change, and where the biochemical basis is known. Antimicrobial substances target a range of cellular loci, from the cytoplasmic membrane to respiratory functions, enzymes and the genetic material. However, different bacteria react differently to bactericides, either due to inherent differences such as unique cell envelope composition and non-susceptible proteins, or to the development of resistance, either by adaptation or by genetic exchange. At low concentrations bactericides often act bacteriostatically, and are only bacteriocidal at higher concentrations. For bactericides to be effective, they must attain a sufficiently high concentration at the target site in order to exert their antibacterial action. In order to reach their target site(s), they must traverse the outer membrane of the gram negative bacteria. Bacteria with effective penetration barriers to biocides generally display a higher inherent resistance than those bacteria which are readily penetrated. The rate of penetration is linked to concentration, so that a sufficiently high bactericide concentration will kill bacteria with enhanced penetration barriers. It has been indicated that susceptible bacterial isolates acquire increased tolerance to bactericides following serial transfer in sub-inhibitory concentrations. Whereas the basis of bacterial resistance to antibiotics is well know, that of resistance to antiseptics, disinfectants and food preservatives is less well understood. Three mechanisms of resistance that have been reported include: • limited diffusion of antimicrobial agents through the biofilm matrix, • interaction of the antimicrobial agents with the biofilm matrix (cells and polymer), • enzyme mediated resistance, • level of metabolic activity within the biofilm • genetic adaptation • efflux pumps and • outer membrane structure.

The chemical control of biofouling in industrial water systems

Oxidising and non-oxidising biocides are commonly used in an attempt to control biofouling in industrial water systems. Many of these programmes, however, fail due to the incorrect selection and application of these chemical compounds. Knowledge of the organisms to be eliminated and system hydraulics are important operational parameters in ensuring the successful application of chemical control programmes. A further complicating factor is the build up of bacterial resistance to many of these compounds. One way of limiting resistance is the alteration of oxidising and non-oxidising biocides at the correct miminum inhibitory concentration and using these in combination with surface active compounds to dislodge any biofilm. A variety of surface monitoring techniques are in use in order to monitor the success of biofouling control programmes. Unfortunately none of these techniques are ideal and results have to be considered very carefully.

The potential of nanofibers and nanobiocides in water purification

Electrospun nanofibers and nanobiocides show potential in the improvement of water filtration membranes. Biofouling of membranes caused by the bacterial load in water reduces the quality of drinking water and has become a major problem. Several studies showed inhibition of these bacteria after exposure to nanofibers with functionalized surfaces. Nanobiocides such as metal nanoparticles and engineered nanomaterials are successfully incorporated into nanofibers showing high antimicrobial activity and stability in water. Research on the applications of nanofibers and nanobiocides in water purification, the fabrication thereof and recently published patents are reviewed in this article.

Germination of Lepidium sativum as a method to evaluate polycyclic aromatic hydrocarbons (PAHs) removal from contaminated soil

Abstract The sensitivity of Lepidium sativum germination to polycyclic aromatic hydrocarbons (PAHs) was investigated in soil(s) artificially and historically contaminated with mixtures of PAH. The level of germination of L. sativum decreased with increasing concentration of the PAH in the artificially contaminated soil, while no germination occurred in the historically polluted soil. At a concentration of 1000 and 50 ppm , the germination levels were 75%, respectively. The same germination levels, as a function of PAH concentration, were observed when a non-ionic surfactant was present in the soil(s). When used during phytoremediation of PAH, the germination level of L. sativum was inhibited during the first weeks, after which germination increased, possibly due to PAH dissipation from the soil. The data suggest that the germination of L. sativum can be used to monitor the removal of PAH pollutants from soil.

Emerging Waterborne Infections: Contributing Factors, Agents, and Detection Tools

Because microorganisms are easily dispersed, display physiological diversity, and tolerate extreme conditions, they are ubiquitous and may contaminate and grow in water. The presence of waterborne enteric pathogens (bacteria, viruses, and protozoa) in domestic water supplies represents a potentially significant human health risk. Even though major outbreaks of waterborne disease are comparatively rare, there is substantial evidence that human enteric pathogens that are frequently present in domestic water supplies are responsible for low-level incidence of waterborne microbial disease. Although these diseases are rarely debilitating to healthy adults for more than a few hours to a few days, enteric pathogens can cause severe illness, even death, for young children, the elderly, or those with compromised immune systems. As the epidemiology of waterborne diseases is changing, there is a growing global public health concern about new and reemerging infectious diseases that are occurring through a complex interaction of social, economic, evolutionary, and ecological factors. New microbial pathogens have emerged, and some have spread worldwide. Alternative testing strategies for waterborne diseases should significantly improve the ability to detect and control the causative pathogenic agents. In this article, we provide an overview of the current state of knowledge of waterborne microbial pathogens, their detection, and the future of new methods in controlling these infectious agents.

The role of extracellular exopolymers in the removal of phosphorus from activated sludge.

Biological phosphorus removal in activated sludge systems is thought to be a result of the action of polyphosphate accumulating organisms (PAO). However, not all phosphorus removed can be accounted for by PAO. A method for the qualitative in situ characterization of PAO cell clusters and closely associated extracellular exopolymers (EPS) is described. X-ray microanalysis was performed on samples from two activated sludge plants situated in Pretoria, South Africa. Analysis was done by means of scanning electron microscopy combined with energy dispersive spectrometry (EDS). Cell clusters with associated EPS, on average, contained between 57% and 59% phosphorus, while EPS alone contained, on average, between 27% and 30% phosphorus. Results suggest that phosphorus removal in activated sludge might be due not only to PAO, but also by EPS acting as a phosphorus reservoir.

Evaluation of the impact of disinfection processes on the formation of biofilms in potable surface water distribution systems

In this study, surface water was used to evaluate the impact of disinfection processes (chlorination, chloramination, ozonation, UV irradiation and hydrogen peroxide) on biofilm formation in potable water distribution systems. Biofilm formation was obvious, even in the presence of residual disinfectant concentrations (16.5 mgl −1 hydrogen peroxide, 1 mg −1 monochloramine, 0.2 mgl −1 free chlorine) within the first day after disinfection in the laboratory scale unit. The yield in viable count was higher on stainless steel coupons than on cement coupons within the first 8 days. Viable bacteria numbers on cement coupons were similar (±2 log cfu.cm −2 ) in chlorinated, ozonated and in the control. Biofilm formation was related to the depletion of residual disinfectant concentration. Monochloramine and hydrogen peroxide had a longer residual effect controlling growth of biofilm cells in the system for a longer period before regrowth occurred. Once no residual concentrations could be detected there was no significant difference between the viable bacterial counts on any of the coupons in the various systems.