Phytoremediation: An Option for Removal of Organic Xenobiotics from Water

Pollution by persistent organic pollutants (pesticides, pharmaceuticals, petroleum hydrocarbons, PAHs, PCBs, etc.) is an environmental problem that is recognized worldwide. In order to address this problem, cost effective technologies have been developed and evaluated for the decontamination of soil and water resources. Phytoremediation is a promising technology that uses plants and the associated rhizosphere microorganisms to remove, transform/detoxify, or accumulate organic and inorganic pollutants present in soils, sediments, surface or ground water, wastewater, and even the atmosphere. In fact, as a result of their sedentary nature, plants have evolved diverse abilities for dealing with toxic compounds in their environment. They, therefore, possess a variety of pollutant attenuation mechanisms that makes their use in remediating contaminated land and water more feasible than physical and chemical remediation. Currently, phytoremediation is used for treating many classes of organic xenobiotics including petroleum hydrocarbons, chlorinated solvents, polycyclic aromatic hydrocarbons, pesticides, explosives, pharmaceutical compounds and their metabolites, and it involves several decontamination mechanisms. There are several different types of phytotechnologies such as, for instance, treatment constructed wetlands. The aim of this work is to present a review on the application of phytoremediation technologies for water decontamination from persistent organic pollutants, with special emphasis focused on the removal of a class of emergent pollutants that has recently been receiving a lot of attention, the pharmaceutically active compounds. Within the realm of phytotechnologies, constructed wetlands for wastewater treatment are dedicated a special focus as these systems have been used with success for the removal of several different types of organic xenobiotics

Removal Processes of Pharmaceuticals in Constructed Wetlands

Over the latest years the occurrence of pharmaceutical residues in the environment has been motivating an increasing concern over the possible harmful effects of many of these pollutants to living organisms. In fact many reports are available in the literature about the detection of several of the most consumed pharmaceuticals, their metabolites and transformation products in wastewaters as well as surface and ground waters and even in drinking waters worldwide. This situation can be attributed to the general inadequacy of the conventional treatment processes used in wastewater treatment plants (WWTPs) in dealing with trace pollutants. The reason for the low efficiencies of conventional WWTPs for removal of pharmaceuticals is the fact that these plants were designed to remove bulk constituents of wastewater such as suspended solids, dissolved biodegradable organic matter, pathogens and nutrients and not for also dealing with trace pollutants in general. Due to the highly variable physical and chemical properties of these organic compounds, the efficiencies by which they are removed may vary substantially. Despite the low concentration levels at which pharmaceuticals are generally present in the environment, there is a significant potential for synergistic effects between compounds with similar modes of action or related therapeutic targets, which is enough to be of serious concern. Therefore, there is an urgent need to find ways of retaining and removing these pollutants before they reach the receiving water bodies. Optimization of the WWTP processes has been tried by increasing hydraulic and solid retention times, for example. In addition, some advanced technologies have been evaluated to decrease their discharge into water bodies. However, despite the sometimes high removal efficiencies attained, these processes are generally not cost-effective on a large scale. In fact, it remains a crucial necessity to find applicable technologies for removing pharmaceuticals from wastewater with higher efficiencies at reasonable cost of operation and maintenance. Constructed wetlands systems (CWS) are being increasingly used as an option to remove micropollutants, in particular organic xenobiotic compounds, from wastewaters. There is a vast range of studies highlighting the high efficiencies of these systems in removing a wide variety of compound types, including some pharmaceuticals. For this reason, this type of systems are being adopted as a tertiary treatment option in domestic wastewater treatment and, also, at least as part of the specialized wastewater treatment plants of some industries (such as chemical, dye, tannery, livestock, etc.). Often CWS have been studied under a “black box” approach where only influent and effluent pollutants concentrations were assessed and no further in-depth investigations were pursued. However, in order to use CWS as a more efficient response to new challenges such as those presented by the more recalcitrant micropollutants, a thorough characterization of the processes involved in pollutants removal in CWS is direly needed, as well as some understanding of the ways the several CWS components (solid matrix, vegetation and microorganisms) may interact with each other synergistically. This, in fact, has been an effort which increasingly has been undertaken in the most recent years as a new trend in CWS research, not only in field studies but also in numerous lab studies as well. As result of the increases knowledge of such processes and interactions, a better guidance in the selection and optimization of the CWS components for more specific applications becomes possible. In this work we intend to present a review of the main pharmaceutical removal and transformation processes in CWS, the roles played by the most important components of CWS in such processes and how the overall treatment system performance is affected by all these. Some attention will be given to the most recent studies published on this subject, especially those involving specific CWS application for the removal of pharmaceuticals and which focus on the characterization/optimization of processes or the selection of CWS components. Some of the questions remaining to be addressed about the removal mechanisms in CWS and the aspects of CWS operation that still require optimization will also be highlighted in this work

An international survey of mature students' uses of mobile devices in life and learning

The paper presents research concerned with learner-driven innovative practice with mobile technologies and the interface between formal and informal learning. We build on our previous work investigating student use of personal devices for learning, work, social interaction and entertainment. A recent phase of the research included an international survey focusing on students registered on selected Masters and doctoral programmes in the UK, Sweden, Portugal, Hong Kong and Australia. The research gives an account of everyday uses and more unusual deployments of personal technologies by students from departments of education and technology. It illuminates learner choices and preferences, attitudes towards work–life boundaries, evolving social and cultural practices, and the impacts of technological change

Pilot-scale study on the removal of pharmaceuticals by LECA based SSF-constructed wetlands

In recent years, the occurrence and fate of pharmaceutically active compounds (PhACs) in the aquatic environment has been recognized as one of the emerging issues in environmental chemistry. Some compounds are just resistant to degradation in the sewage treatment plants (STPs) while others, although suffering partial degradation, still end up in receiving water bodies due to the large inputs received in STPs [1]. Clofibric acid (a metabolite from a series of widely used blood lipids lowering agents), ibuprofen (an anti-inflamatory non-prescription drug) and carbamazepine (an anticonvulsant and mood stabilizing drug) are some of the most frequently found PhACs in environmental monitoring studies [1]. Wastewater treatment by sub-surface flow constructed wetland systems (SSF-CWs) is a low-cost technology that has shown some capacity for removal of several organic xenobiotic pollutants, but fewer studies exist on pharmaceuticals behavior. The aim of the present work was to evaluate the efficiency of a pilot SSF-CW assembled with the plants cattail (Typha spp.) and a clay material (LECA 2/4) as support matrix, for the removal of three pharmaceuticals, namely ibuprofen (IB), carbamazepine (CB) and clofibric acid (CA), from contaminated wastewaters. Four beds were planted with pre-grown cattails (density of 80 plants/m2) and four were left unplanted to be used as controls. Experiments were conducted both in batch and in continuous mode with a flooding rate of 100%. Pharmaceutical concentrations were quantified by HPLC with UV detection at 210 nm (CB), 222 nm (IB) and 230 nm (CA). Solid phase extraction was used for sample pre-concentration whenever the measured pharmaceutical concentrations fell under the limit of quantification of the analytical method. The physico-chemical characterization of the support matrix material, LECA, involved the determination of properties such as pH, point of zero charge, electrical conductivity, apparent porosity, bulk density and hydraulic conductivity. In order to shed some light on the tolerance mechanisms developed by Typha spp. in the presence of these pharmaceuticals, biochemical and physiological parameters were evaluated. Typha spp. showed good tolerance to the presence of CA, CB and IB concentrations of 1 mg L-1, which is a value much higher than those usually reported in wastewaters. LECA alone was able to remove about 90% of the initial amounts of CB and IB in solution, and 50% of CA. IB was very susceptible to microbial degradation and up to 80% of the initial concentration could be removed by the microbial population present in the wastewater used. Overall, the CWS shows a higher removal performance for CA, CB and IB than any of its individual components (plants, support matrix, microorganisms) considered separately. CA proved to be the most resilient compound, which comes in agreement with other published data. However, this system enabled the removal of substantially higher amounts of CA than has previously been reported in other studies. The use of systems of this kind for the removal of pharmaceuticals from wastewaters seems like a promising alternative to the less efficient processes of conventional wastewater treatment

Using clay materials to remove pharmaceuticals from waters

Pharmaceutical active compounds (PhACs) have an important role in the treatment and prevention of disease in both human and animals. Ingested drugs are only partially absorbed by the organisms and studies have shown that the excreted compounds are only partially removed in the sewage treatment plants (STPs) [1]. Contaminated effluents are being released from the STPs and trace amounts of PhACs have been detected in wastewaters, surface and groundwaters worldwide [1]. Acidic pharmaceuticals like diclofenac, ibuprofen and clofibric acid are some of the most frequently detected compounds [1]. The concentrations detected are low (ng/L - μg/L) but, due to the very nature of these compounds, studies have shown damaging effects on the aquatic ecosystems [1]. Several different processed natural materials can be used as filter media in water and wastewater treatment systems. Some of these materials can additionally present functions which extend beyond the simple process of filtration. Their surface areas can constitute a support for microbial population growth in biofilters as well as support matrix for the development of macrophytes in sub-surface flow constructed wetland systems (SSF-CWS) [2] which are increasingly being used in sewage tertiary treatment. The efficiency of these biological systems in the removal of xenobiotics can be significantly enhanced by a greater capability of the support matrix to retain contaminants by sorption phenomena, ionic exchange or other physico-chemical processes [2]. The aim of the present work was to evaluate the efficiency of two different materials namely, Light Expanded Clay Aggregates [LECA] (in two different particle sizes) and sand, for the removal from water of three acidic PhACs, clofibric acid, diclofenac and ibuprofen. In addition, relationships were established between the compounds removal efficiencies and the physico-chemical properties of each material. A series of batch essays were carried out to study the sorption capacities of the different materials for the 3 chemical compounds. The influence of some experimental conditions, such as the contact time, the initial PhACs concentrations (1 mg/L up to 50 mg/L) and LECA particle size, were investigated. The media were sterilized before use in order to minimize any microbial development on the matrix and experiments were conducted in the dark to avoid any photocatalytic degradation reactions. The mineralogical composition of the materials was determined by X-ray diffraction and some physico-chemical properties were characterized. Samples of the contaminants’ aqueous solutions were collected over a range of contact times with the support matrix and the remaining concentrations in solution were determined by UV/Vis spectrophotometry. The results show that LECA has a good sorption capacity for acidic compounds. In contrast, sand does not exhibit any sorption capacity for any of the compounds tested. Not surprisingly, LECA with smaller particle sizes show higher efficiencies that larger grade LECA, due to a larger available surface area. However, the use of these smaller particle media at upper scales may present problems with hydraulic conductivities. From the results obtained, it can be concluded that expanded clay presents important advantages as a CWS support matrix or as a filter medium, because it has a good sorption capacity, a pH buffer capacity and an excellent control of hydraulic permeability. On the other hand, sand does not exhibit any sorption capacity that might enhance the performance of filters and CWS in the treatment of water contaminated with this type of contaminants

Sorption behavior of granular matrices for application in pharmaceutical removal by SSF constructed wetlands

In recent years, the occurrence and fate of pharmaceutically active compounds (PhACs) in the aquatic environment has been recognized as one of the emerging issues in environmental chemistry. Clofibric acid, ibuprofen and carbamazepine are some of the most frequently found PhACs in environmental monitoring studies. Some xenobiotics have already been successfully removed from contaminated waters using constructed wetlands (CW). Depuration of wastewaters in CWs is achieved by the concerted action between plant rhizomes, microorganisms and matrix component. CWs efficiency can be significantly improved by careful selection of the matrix, plants and microorganism used. Among several physico-chemical phenomena, sorption by the matrix plays an important role in the PhACs removal mechanism. It is important to select a matrix with a high sorption capacity, which depends on the physico-chemical properties of the material chosen. Previous studies carried out by the authors showed that expanded clay (LECA) presents a high sorptive affinity by clofibric acid [1]. The aim of the present work was to evaluate the capacity of LECA to remove other PhACs, namely ibuprofen and carbamazepine, and compare the results obtained with these pharmaceuticals with those obtained previously with clofibric acid. In addition, other materials were tested for the removal of clofibric acid and the results were compared with those obtained with LECA. The ultimate objective of this work will be to optimize the performance of this component in the overall performance of a constructed wetlands system designed for the removal of PhACs from wastewaters

Microalgal reactors: a review of enclosed system designs and performances

One major challenge to industrial microalgal culturing is to devise and develop technical apparata, cultivation procedures and algal strains susceptible of undergoing substantial increases in efficiency of use of solar energy and carbon dioxide. Despite several research efforts developed to date, there is no such thing as “the best reactor system”- defined, in an absolute fashion, as the one able to achieve maximum productivity with minimum operation costs, irrespective of the biological and chemical system at stake. In fact, choice of the most suitable system is situationdependent, as both the species of alga available and the final purpose intended will play a role. The need of accurate control impairs use of open-system configurations, so current investigation has focused mostly on closed systems. In this review, several types of closed bioreactors described in the technical literature as able to support production of microalgae are comprehensively presented and duly discussed, using transport phenomenon and process engineering methodological approaches. The text is subdivided into subsections on: reactor design, which includes tubular reactors, flat plate reactors and fermenter-type reactors; and processing parameters, which include gaseous transfer, medium mixing and light requirements

Removal of pharmaceuticals in constructed wetlands using Typha and LECA. A pilot-scale study.

An ever-increasing number of xenobiotic compounds are getting detected in environmental samples worldwide. Serious concern about the contamination of water resources and drinking water supplies has aroused from the prevalence of pharmaceutical residues in the aquatic ecosystems. Some pharmaceuticals such as ibuprofen, carbamazepine and clofibric acid are frequently detected in waters [1]. These compounds are generally quantified at low concentrations (at the ng/L or mg/L range) but, due to their persistence in the environment and to potentially cumulative effects in the organisms, studies have shown that these compounds can have some damaging effects on the aquatic ecosystems [1]. Several xenobiotic organic compounds have already been removed from contaminated waters using constructed wetlands (CW) where the processes occurring in natural wetlands can be optimized in engineered man-made ecosystems, specifically designed for wastewater treatment. Among several physico-chemical phenomena, sorption by the support matrix plays an important role in the contaminant removal mechanisms. It is important to select a matrix with a high sorption capacity, which will depend on the physico-chemical properties of the material chosen. Previous studies have shown that expanded clay (LECA) is capable to remove, by sorption, this type of substances from water [2]. CWs also take advantage of the ability of plants to adsorb, uptake and concentrate pollutants, as well as to release root exudates that enhance compound biotransformation and degradation. Wetland species such as the cattail (Typha spp.) have already been tested and found suitable for the removal of several organic compounds from wastewaters, being commonly used in CWs [3]. The aim of the present work was to evaluate the efficiency of a subsurface flow constructed wetland assembled with the plants Typha spp. and LECA as support matrix, for the removal of three pharmaceuticals, namely ibuprofen, carbamazepine and clofibric acid, from contaminated waters