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A variety of test procedures for determination of anaerobic biodegradability have been reported. This paper reviews the methods developed for determination of anaerobic biodegradability of macro-pollutants. Main focus is paid to the final mineralization of organic compounds and the methane potential of compounds. Hydrolysis of complex substrates is also discussed. Furthermore, factors important for anaerobic biodegradation are shortly discussed.

Polycyclic aromatic hydrocarbons (PAHs) are an important class of chemical pollutants that constitute a major component of total hydrocarbons in crude oils. Based on their poor water solubility, toxicity, persistence and potential to bioaccumulate, these compounds are recognized as high-priority pollutants in the environment and are of significant concern for human health. At oil-contaminated sites, PAH-degrading bacteria perform a critical role in the degradation and ultimate removal of these compounds. In April 2010, enormous quantities of PAHs entered the Gulf of Mexico from the thousands of tons of oil that were released from the ill-fated drilling rig Deepwater Horizon. In the ensuing months after the spill, intense research efforts were devoted to characterizing the microorganisms responsible for degrading the oil, particularly in deep waters where a large oil plume, enriched with aliphatic and low molecular-weight aromatic hydrocarbons, was found in the range of 1,000–1,300 m. PAHs, however, were found mainly confined to surface waters. This paper discusses efforts utilizing DNA-based stable isotope probing, cultivation-based techniques and metagenomics to characterize the bacterial guild associated with PAH degradation in oil-contaminated surface waters at Deepwater Horizon.

Biologically produced hydrogen (biohydrogen) is a valuable gas that is seen as a future energy carrier, since its utilization via combustion or fuel cells produces pure water. Heterotrophic fermentations for biohydrogen production are driven by a wide variety of microorganisms such as strict anaerobes, facultative anaerobes and aerobes kept under anoxic conditions. Substrates such as simple sugars, starch, cellulose, as well as diverse organic waste materials can be used for biohydrogen production. Various bioreactor types have been used and operated under batch and continuous conditions; substantial increases in hydrogen yields have been achieved through optimum design of the bioreactor and fermentation conditions. This review explores the research work carried out in fermentative hydrogen production using organic compounds as substrates. The review also presents the state of the art in novel molecular strategies to improve the hydrogen production.

Direct landspreading of anaerobic digestates is the most common digestate management strategy. Nevertheless, digestate post-treatment can be unavoidable, especially for environmental services providers operating large-scale anaerobic digestion (AD) facilities. This review aims to assess the technical feasibility of achieving value-added products from digestates from urban and/or centralized AD plants (UC-AD). An exhaustive effort was dedicated to identifying and clarifying the available processing technologies and specific issues that can be related to UC-AD digestates. The valorization options were classified according to the final product destination. The result is a useful information source for assessing digestate valorization pathway given a local market and context. Agriculture was the first destination to be considered, as it allows a more direct closing of nutrient and carbon cycles. Several processes exist either for concentrating desirable characteristics of digestates, enhancing organic matter stability or producing pure and reformulated fertilizers. Thermal conversion processes are either under development or full-scale demonstration. They allow to valorize the solids through the production of biofuels and/or biochar and in the coming future, to start a whole biorefinery system. Similarly, biomass harvesting processes such as microalgae are under upscaling, enabling to valorize the nutrients of the digestate liquid phase while producing renewable biomass from sunlight. Several value-added products were already obtained in laboratory to pilot conditions from UC-AD digestates, for example, biopesticides, biosurfactants and composite materials. Adding to technical challenges, the quality variation of digestates, regulation barriers, public acceptance and the difficult access to new markets are among the main obstacles to UC-AD digestates valorization into value-added products.

This paper is designed to provide an overview of the main membrane-assisted processes that can be used for the removal of toxic inorganic anions from drinking water supplies. The emphasis has been placed on integrated process solutions, including the emerging issue of membrane bioreactors. An attempt is made to compare critically recently reported results, reveal the best existing membrane technologies and identify the most promising integrated membrane bio/processes currently being under investigation. Selected examples are discussed in each case with respect to their advantages and limitations compared to conventional methods for removal of anionic pollutants. The use of membranes is particularly attractive for separating ions between two liquid phases (purified and concentrated water streams) because many of the difficulties associated with precipitation, coagulation or adsorption and phase separation can be avoided. Therefore, membrane technologies are already successfully used on large-scale for removal of inorganic anions such as nitrate, fluoride, arsenic species, etc. The concentrated brine discharge and/or treatment, however, can be problematic in many cases. Membrane bioreactors allow for complete depollution but water quality, insufficiently stable process operation, and economical reasons still limit their wider application in drinking water treatment. The development of more efficient membranes, the design of cost-effective operating conditions, especially long-term operations without or with minimal membrane inorganic and/or biological fouling, and reduction of the specific energy consumption requirements are the major challenges.

Anaerobic treatment processes have the advantages of cost-effectiveness, energy efficiency, low sludge yield and potential of resource recovery over conventional aerobic treatment methods and have been gaining increasing attention as an approach for future wastewater management. An important feature of anaerobic processes is the use of alternative electron acceptors to oxygen, which renders treatment flexibility in using redox active elements such as iron and sulfate from other waste materials. Co-treatment of acid mine drainage and municipal wastewater, as an example, has been shown to be an effective method for removing organic materials, metals, and phosphate from the both wastes. It also suggested the applicability of ferric reduction process in wastewater treatment. Most of the previous studies on ferric reduction process and iron reducers were conducted in natural systems such as sediments, soils and groundwater. This paper reviews the significance and fundamentals of the ferric reduction process, its utility for organics oxidation, controlling factors, reaction kinetics, microbial processes of iron reduction and its ecology. The paper also evaluates the suitability and discusses future aspects of using iron reduction for wastewater treatment. Knowledge gaps are identified in this paper for developing such innovative wastewater technology and process optimization.