Simon Mills

Occupational exposure to aqueous film-forming foams (AFFF) can lead to elevated concentrations of per- and polyfluorinated alkyl substances (PFAS) in firefighter blood sera. AFFF are also one exposure source of PFAS in the general population because of their environmental persistence and solubility in groundwater. Because of the documented adverse health effects of PFAS, the primary concern to date in the fire services has centered on repeated use and exposure to AFFF. In this work, an additional PFAS exposure source for firefighters is presented: PFAS that are shed from their protective clothing. Textiles used as firefighter turnout gear were found to have high levels of total fluorine (up to 2%), and individual PFAS were identified and measured on new and used firefighting turnout gear. Used gear showed lower levels of PFAS as well as an increased migration into untreated material. A dust measurement from a textile storage area also suggests direct loss of PFAS from the fluoropolymers in the textiles. Because PFAS that are shed from the textiles used in turnout gear are more mobile, they represent another viable exposure source for firefighters that warrants further study.

Anaerobic digestion (AD) for waste, and wastewater, management was identified in the 1970s as a forerunner in the push for sustainability. The development of AD applications resulted in the discovery of “anaerobic granules,” which are multitrophic bio-aggregates comprising methanogenic consortia capable of digesting waste organics to methane-rich biogas suitable for use as a renewable bioenergy. In the intervening years the emergence of the anaerobic ammonium oxidizing (anammox) granule, aerobic granule, hydrogenic granule, oxygenic photogranule, and many other functionally-specialized granules, has opened new opportunities in wastewater treatment, and resource-recovery, biotechnology. As a single entity, a granule represents an entire community of microorganisms. This review compares three of the most influential types: the anaerobic (methanogenic), aerobic and anammox granule. The main characteristics, biochemical processes, and typical makeup of the microbial community in each type are discussed. Finally, the adoption of granules as an intriguing “playground” for experiments in microbial ecology is reviewed.

Harnessing microbial capabilities for metal recovery from secondary waste sources is an eco-friendly and sustainable approach for the management of metal-containing wastes. Soluble microbial products (SMP) and extracellular polymeric substances (EPS) are the two main groups of extracellular compounds produced by microorganisms in response to metal stress that are of great importance for remediation and recovery of metals. These include various high-, and low, molecular weight components, which serve various functional and structural roles. These compounds often contain functional groups with metal binding potential that can attenuate metal stress by sequestering metal ions, making them less bioavailable. Microorganisms can regulate the content and composition of EPS and SMP in response to metal stress in order to increase the compounds specificity and capacity for metal binding. Thus, EPS and SMP represent ideal candidates for developing technologies for selective metal recovery from complex wastes. To discover highly metal-sorptive compounds with specific metal binding affinity for metal recovery applications, it is necessary to investigate the metal binding affinity of these compounds, especially under metal stressed conditions. In this review we critically reviewed microbial EPS and SMP production as a response to metal stress with a particular emphasis on the metal binding properties of these compounds and their role in altering metal bioavailability. Furthermore, for the first time, we compiled the available data on potential application of these compounds for selective metal recovery from waste streams.

The retention of dense and well-functioning microbial biomass is crucial for effective pollutant removal in several biological wastewater treatment technologies. High solids retention is often achieved through aggregation of microbial communities into dense, spherical aggregates known as granules, which were initially discovered in the 1980s. These granules have since been widely applied in upflow anaerobic digesters for waste-to-energy conversions. Furthermore, granular biomass has been applied in aerobic wastewater treatment and anaerobic ammonium oxidation (anammox) technologies. The mechanisms underpinning the formation of methanogenic, aerobic, and anammox granules are the subject of ongoing research. Although each granule type has been extensively studied in isolation, there has been a lack of comparative studies among these granulation processes. It is likely that there are some unifying concepts that are shared by all three sludge types. Identifying these unifying concepts could allow a unified theory of granulation to be formed. Here, we review the granulation mechanisms of methanogenic, aerobic, and anammox granular sludge, highlighting several common concepts, such as the role of extracellular polymeric substances, cations, and operational parameters like upflow velocity and shear force. We have then identified some unique features of each granule type, such as different internal structures, microbial compositions, and quorum sensing systems. Finally, we propose that future research should prioritize aspects of microbial ecology, such as community assembly or interspecies interactions in individual granules during their formation and growth.