Arsenic is a toxic metalloid and its pollution has become a global environmental problem. This paper reviewed the current knowledge on the speciation, toxicity and metabolism of arsenic in microalgae. A number of arsenic species are present in various microalgae. Due to the great toxicity of inorganic arsenic, microalgae may undergo different processes to reduce the arsenic toxicity, including cell surface binding, arsenite [As(III)] oxidation, arsenate [As(V)] reduction, methylation, transformation into arsenosugars or arsenolipids, chelation of As(III) with glutathione and phytochelatins, as well as excretion from cells. Several genes and enzymes involved in arsenic transformations have been identified and characterized. Many factors, especially nutrient elements (e.g., nitrogen and phosphorus) in cells and in culture, affect arsenic metabolic pathways of microalgae. Arsenic metabolism in the unicellular algae has gained considerable interest because these processes control not only the effectiveness of arsenic phycoremediation, but also the risk of arsenic contamination in algal products. Future research need to focus on (1) the regulative mechanisms of arsenic absorption, biotransformation and excretion at molecular level; (2) the effects of intracellular nutrient dynamics on arsenic speciation; (3) the impacts of culture regime on the arsenic metabolism in microalgae; (4) the transfer of arsenic species across aquatic food web in order to better evaluate the roles of microalgae in arsenic cycling.

Anaerobic process modelling is a mature and well-established field, largely guided by a mechanistic model structure that is defined by our understanding of underlying processes. This led to publication of the IWA ADM1, and strong supporting, analytical, and extension research in the 15 years since its publication. However, the field is rapidly expanding, in terms of new technology, new processes, and the need to consider anaerobic processes in a much broader context of the wastewater cycle as a whole. Within the area of technologies, new processes are emerging (including high-solids and domestic wastewater treatment). Challenges relating to these new processes, as well as the need to intensify and better operate existing processes have increased the need to consider spatial variance, and improve characterisation of inputs. Emerging microbial processes are challenging our understanding of the role of the central carbon catabolic metabolism in anaerobic digestion, with an increased importance of phosphorous, sulfur, and metals as electron source and sink, and consideration of hydrogen and methane as potential electron sources. The paradigm of anaerobic digestion is challenged by anoxygenic phototrophism, where energy is relatively cheap, but electron transfer is expensive. These new processes are commonly not compatible with the existing structure of anaerobic digestion models. These core issues extend to application of anaerobic digestion in domestic plant-wide modelling, with the need for improved characterisation, new technologies having an increased impact, and a key role for the linked phosphorous–sulfur–iron processes across the cycle. The review overall finds that anaerobic modelling is increasing in complexity and demands on the modeller, but the core principles of biochemical and physicochemical processes, metabolic conservation, and mechanistic understanding will serve well to address the new challenges.

Environmental management is crucial for sustainable growth and development. The use of microorganisms to clean up contaminated environment provides cheap alternative method to the conventional treatment methods. But the choice of easily grown, viable and effective natural occurring microorganism to do the cleaning is a major challenge. In this article we presented and reviewed the application of photosynthetic bacteria in bioremediation due to their utilisation of various kinds of pollutants, minimum nutrients requirement and the possibility of generating valuable products concomitantly cleaning the contaminated environment. Pollutants such as pesticides, heavy metals, dyes, crude oil and odour with the specific photosynthetic bacteria capable of degrading the pollutants were identified and discussed in this article. The possible value added products to be generated as well as the mechanism of degradation are also highlighted and discussed in the article. The utilisation of carbon dioxide and the generation of value added products while cleaning up polluted environment are the major advantages of using these bacteria in bioremediation and have both environmental and economic benefits.

Anaerobic digestion (AD) is a well-established technology used for the treatment of wastes and wastewaters with high organic content. During AD organic matter is converted stepwise to methane-containing biogas—a renewable energy carrier. Methane production occurs in the last AD step and relies on methanogens, which are rather sensitive to some contaminants commonly found in wastewaters (e.g. heavy metals), or easily outcompeted by other groups of microorganisms (e.g. sulphate reducing bacteria, SRB). This review gives an overview of previous research and pilot-scale studies that shed some light on the effects of sulphate and heavy metals on methanogenesis. Despite the numerous studies on this subject, comparison is not always possible due to differences in the experimental conditions used and parameters explained. An overview of the possible benefits of methanogens and SRB co-habitation is also covered. Small amounts of sulphide produced by SRB can precipitate with metals, neutralising the negative effects of sulphide accumulation and free heavy metals on methanogenesis. Knowledge on how to untangle and balance sulphate reduction and methanogenesis is crucial to take advantage of the potential for the utilisation of biogenic sulphide as a metal detoxification agent with minimal loss in methane production in anaerobic digesters.

Most artificial fish passes have been developed in Northern temperate rivers and are designed to serve large, migratory sport fish species (mostly salmonids). Experience in construction and maintenance of fish passes show that salmon-criteria are not adequate for flat-land rivers and non-sport fishes. Consequently, over the last decade, design criteria have changed to take requirements of target species into account. Extrapolation of these concepts to rivers in the Southern Hemisphere with different hydrological conditions and fish community composition is not straight forward. This review focuses on requirements for an adequate hydraulic design of passes for non-sport fish species bodied (<15 cm) threatened by small hydropower dams (with a typical head of 3–5 m). First, fragmentation of fish populations due to river obstructions that impede longitudinal movements is introduced from the perspective of environmental sustainability, taking the Chilean indigenous freshwater fish species as a study case. Subsequently, relevant properties of fish passages are reviewed, and experimental issues for maintenance in captivity and determination of swimming abilities in the laboratory are presented. Following dimensional considerations controlling scales for an adequate hydraulic design of fish passes, involving fluid, flow, fish, and pass properties are discussed. Finally, we postulate that successful passage design should consider habitat connectivity as the key concept for preservation of this highly threatened native fish fauna.

Biofilters are popular as an alternative method for treatment of volatile air pollutants like hydrogen sulphide originating from wastewater treatment plants. Despite several advantages over conventional chemical systems, one of the concerns of biological treatment of hydrogen sulphide is the production of large volumes of neutral or acidic leachate which needs to be treated or disposed safely. Instead of treating as an unwanted product, a waste stream of weakly acidic leachate can be thought of as a sulphur resource. This paper provides an overview of recent literature on the removal of H₂S from contaminated air in an aerobic environment and discusses the possibility of recovering sulphur from contaminated air with special emphasis on polluted air originating from wastewater treatment plants. We also add our perspectives on future research and development needs in this area.

Abiotic stresses collectively are responsible for crop losses worldwide. Among various abiotic stresses, drought and salinity are the most destructive. Different strategies have been adopted for the management of these stresses. Being complex traits, conventional breeding approaches have shown less success in improving salinity and drought stress tolerance. Roles of compatible solutes in salinity and drought stress tolerance have been studied extensively. At physiological level, osmotic adjustment is an adaptive mechanism involved in drought and/or salinity tolerance and permits the maintenance of turgor pressure under stress conditions. Increasing evidences from series of in vivo and in vitro studies involving physiological, biochemical, genetic, and molecular approaches strongly suggest that osmolytes such as ammonium compounds (polyamines, glycinebetaine, b-alanine betaine, dimethyl-sulfonio propionate and choline-O-sulfate), sugars and sugar alcohols (fructan, trehalose, mannitol, D-ononitol and sorbitol) and amino acids (proline and ectoine) perform important function in adjustment of plants against salinity and drought stresses. Thus, aim of this review is to expose how to osmoprotectants detoxify adverse effect of reactive oxygen species and alleviate drought and salinity stresses. An understanding of the relationship between these two sets of parameters is needed to develop measures for mitigating the damaging impacts of salinity and drought stresses.

Management of municipal solid waste is a global problem and is faced by all developing countries. The rapid pace of increase in population, economic growth, urbanization and industrialization is coupled with accelerated solid waste generation. In most of the developing countries wastes are either scattered in urban centers or disposed off unplanned in low lying areas or open dumps. The lack of infrastructure for collection, transportation, treatment and disposal of solid waste, proper solid waste management planning, insufficient financial resources, technical expertise and public attitude have made the situation exasperating due to which several environmental and health related problems are increasing. Though, there are many negative issues related to solid waste, it also provides many opportunities that not only mitigates its negative impact but also helps in meeting the demand for energy and employment generation as well as in soil health improvement. Keeping in mind the present situation the current review was planned with the objective to overlook the challenges and opportunities faced during urban solid waste management in developing countries like India.

The consumption of water contaminated with bacteria poses significant health risks around the world, which brings into focus the need for the effective and efficient detection of microorganisms in water. Current technology for water-quality monitoring is based on frequent sampling and culturing methods which are time-consuming and do not allow a rapid decision making process. There is a clear need for rapid and more convenient analytical methods that enable their wide use and feed into regulatory and decision-making processes. PCR-based methods, DNA sequencing and immuno-fluorescence methods are promising strategies for pathogen detection. Development of new biosensing methodologies is currently under way that will open new avenues for the fast and cost-efficient detection of pathogens. In this review, we summarize recent advances and developments for monitoring pathogenic and biological agents in water samples.