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Urbanization, industrialization, and natural earth processes have potentially increased the contamination of heavy metals (HMs) in water bodies. These HMs can accumulate in human beings through the consumption of contaminated water and food chains. Various clean-up technologies have been applied to sequester HMs, especially conventional methods including electrolytic technologies, ion exchange, precipitation, chemical extraction, hydrolysis, polymer micro-encapsulation, and leaching. However, most of these approaches are expensive for large-scale projects and require tedious control and constant monitoring, along with low efficiency for effective HMs removal. Algae offer an alternative, sustainable, and environmentally friendly HMs remediation approach. This review presents a state-of-the-art technology for potential use of algae as a low-cost biosorbent for the removal of HMs from wastewater. The mechanisms of HMs removal, including biosorption and bioaccumulation along with physical and chemical characterization of the algae are highlighted. The influence of abiotic factors on HMs removal and changes in algal biocomponents (including, carbohydrate, lipid, and protein) are discussed. Recent progresses made in the development of HMs-tolerant algal strains and the direction of future research toward the development of sustainable technology for advanced wastewater treatment and biomass production are covered.

Abstract Residential areas are being increasingly impacted by wildfire smoke that causes hazardous local ambient air quality conditions. Poor outdoor air quality also exacerbates the quality of indoor air as smoke particles penetrate the building envelope or the heating, ventilation, and air-conditioning (HVAC) filtration systems. In this work, we investigate the impact of wildfire-affected poor ambient air quality on indoor air particulate matter during a wildfire episode in June 2015 in interior Alaska. We measured size-resolved (0.3–10 μm) particle number counts (PNC; numbers/cm3) and calculated particle mass concentrations (PMC; μg/m3) outside and inside of three buildings in Fairbanks, Alaska, during this summer wildfire event. For comparison, the measurements were repeated during a no-wildfire period in summer 2017. Our results show that the fire episode increased the total PNC by factors of 189.4–244 in the outdoor air and by 19.5–150 in the indoor air compared to the total PNC measured during a non-fire season. The PNC was primarily dominated by particles in the size range 0.3–1 μm (> 99%) at all locations during the fire season, whereas the PMC was dominated by particles in the size range from 2.5 to 10 μm (40–67%). The indoor to outdoor ratio (I/O) of PNC during the fire season was significantly lower for an unventilated building (I/O = 0.13 ± 0.001) as compared to those with active (filtered) ventilation (I/O = 0.76 ± 0.11 and 0.62 ± 0.02), suggesting that lower efficiency filters (< Minimum Efficiency Reporting Value or MERV rating 11) often used in residential and public buildings may not control the infiltration of smaller smoke particles during a wildfire event. Although this study had a small sample size, the limited data collected here indicates that sheltering in a closed, non-ventilated building may be an effective strategy to reduce exposure to particulate matter during wildfires, given that there are no significant indoor source(s) of particulates and that the air leakage is insignificant. Finally, this study also shows that particulate mass concentrations (μg/m3) may not fully describe the relative differences between indoor and outdoor air quality especially during wildfire episodes.

Marine wastes extract (MWE), prepared from marine organic wastes, was used to develop an alternative nitrogen source for sulfate-reducing bacteria (SRB) in environments like acid mine drainage that are acidic in nature and contain high levels of sulfate and dissolved metals. The MWE contains 13.95 g L −1 of nitrogen, and other micronutrients like K, Na, P, S, Ca, Fe, Mg, Mn, Zn, Co, Cu and Ni, and has a C/N ratio of 0.107. A modified SRB medium (MSRB) was developed by replacing the commercial nitrogen source of standard SRB growth medium with MWE. MSRB was compared with modified Postgate B, Postgate B, and Widdel and Pfennig media, which contained bactopeptone and NH 4 Cl, as nitrogen sources. Results showed that the growth media could support a total microbial population of 2.8 × 10 12 –6.2 × 10 12 cells mL −1 with 96, 80, 92.5, and 65 % SRB in MSRB, Postgate B, modified Postgate B, and Widdel and Pfennig media, respectively. The sulfate reduction efficiency was 97, 87, 72, and 68 % at reduction rates of 12.41, 11.10, 4.35, and 8.8 mg L −1  h −1 , respectively, for the same media. We conclude that MWE could be a cost-effective substitute for commercially available nitrogen sources for SRB for large-scale treatment of sulfate-rich wastewater.

Sulfate reducing bacteria (SRB) mediated treatment of acid mine drainage is considered as a globally accepted technology. However, inadequate information on the role of nitrogen source in the augmentation of SRB significantly affects the overall treatment process. Sustenance of SRB depends on suitable nitrogen source which is considered as an important nutrient. This review focuses on the different nitrogen rich growth substrates for their effectiveness to support SRB growth and sulfate reduction in passive bioreactors. Compounds like NH 4 Cl, NH 4 HCO 3 , NO 3 − , aniline, tri-nitrotoluene, cornsteep liquor, peptone, urea, and chitin are reported to have served as nitrogen source for SRB. In association with fermentative bacteria, SRB can metabolize these complex compounds to NH 4 + , amines, and amino acids. After incorporation into cells, these compounds take part in the biosynthesis of nucleic acids, amino acids and enzyme co-factor. This work describes the status of current and the probable directions of the future research.