Genome-resolved metagenomics links microbial dynamics to failure and recovery of a bioreactor removing nitrate and selenate from mine-influenced water

Selenium and concomitant anions removal in a fixed bed bioreactor to satisfy drinking water regulations and subsequent stability check of selenium-laden biosludge

This is the first successful report on selenium bio-attenuation to satisfy drinking water regulations as per Indian Standards (10 μg/L) in the presence of concomitant nitrate and sulfate from water sources utilizing a fixed bed bioreactor. The bioreactor was immunized with blended microbial culture and worked in downflow mode under anoxic conditions at 30 ± 2 °C for around 190 days under varying influent selenate (100-500 μg/L as selenium), nitrate (50 mg/L), sulfate concentrations (as per selenium removal) and necessary dose of acetic acid (as COD, a carbon source) in synthetic groundwater, operated at an empty bed contact time (EBCT) of 45-120 min. After supplying an adequate dosage of sulfate and alteration of EBCT, selenium was found to comply with drinking water regulations and nitrate was completely removed. X-ray diffraction and transmission electron microscopy analyses depicted nanocrystalline selenium sulfides (SeS and SeS2) formation as the possible mechanisms of selenium removal. Extended toxicity characteristic leaching procedure (TCLP) extractions confirmed a maximum selenium leaching of 52 and 282 μg/L during anoxic and oxic extractions, respectively. Long-term column leaching (>3-month equilibration) under aerobic conditions at pH 7 confirmed the produced precipitate to be essentially stable (∼0.14% Se leaching). This work exhibits the synchronous bioremoval of selenium and its co-anions from contaminated water complying with drinking water standards, and leaving a stable and non-hazardous selenium-laden biosludge.

Developing a versatile tool for studying kinetics of Selenate-Se removal from aqueous solution using a chemostat bioreactor

Understanding the impact of various parameters on the kinetics of dissolved selenium (Se) removal in bioreactors can be a challenging task, primarily due to the mass transfer limitations inherent in bioreactors employing attached growth configurations. This study successfully established a proof-of-concept for the efficient removal of Se from aqueous solutions using a chemostat bioreactor that relies solely on suspended growth. The research investigated the effect of selenate-Se feed concentrations under two distinct Se concentration conditions. One experiment was conducted at a considerably elevated concentration of 25 mg/L to impose stress on the system and evaluate its response. Another experiment replicated an environmentally relevant concentration of 1 mg/L, mirroring the typical Se concentrations in mine water. The bioreactor, featuring a working volume of 0.35 L, was operated as an anaerobic, fully mixed chemostat with hydraulic retention times (HRTs) ranging from 5 to 0.25 days. The outcomes revealed the chemostat's capacity to remove up to 25 mg/L of dissolved Se from water for all HRTs exceeding 1 day, under otherwise optimal conditions encompassing temperature, pH, and salinity. The research's significance lies in the development of a versatile tool designed to examine Se removal kinetics within a system devoid of mass transfer limitations. Furthermore, this study verified the ability of the bacterial consortium, obtained from a mine-influenced environment and enriched in the laboratory, to grow and sustain Se removal activities within a chemostat operating with HRTs as short as 1 day.

Degradation of starch-based bioplastic bags in the pelagic and benthic zones of the Gulf of Oman

The Gulf of Oman is becoming increasingly polluted with plastics, hence bioplastics have been considered 'a substitute', although their biodegradability in marine environments has not been well investigated. Most research has been performed on cellulose-based bioplastics, whereas starch-based bioplastics have proven to be a suitable, but less researched, alternative. This study is the first of its kind designed to investigate the degradability of two different types of starch-based bioplastic bags, available in the market and labeled as "biodegradable", in the pelagic and benthic zones of one of the warmest marine environment in the world. Fourier-Transform Infrared Spectroscopy (FTIR) showed a clear reduction in the presence of OH, CH, and CO in the bioplastic bags after 5 weeks of immersion. Thermo-Gravimetric Analysis (TGA) indicated degradation of glycerol, starch, and polyethylene. The biofouling bacterial communities on bioplastic surfaces showed distinct grouping based on the immersion zone. Candidaatus saccharibacteria, Verrucomicrobiae, Acidimicrobiia and Planctomycetia sequences were only detectable on bioplastics in the pelagic zone, whereas Actinomyces, Pseudomonas, Sphingobium and Acinetobacter related sequences were only found on bioplastics in the benthic layer. We conclude that starch-based bioplastics are more readily degradable in the Gulf of Oman than conventional plastics, hence could serve as a better environmentally friendly alternative.

The selectivity of electron acceptors for the removal of caffeine, gliclazide, and prazosin in an up-flow anaerobic sludge blanket (UASB) reactor

This study attempts to investigate the relationship between the dominance of reducing conditions and the biotransformation of pharmaceutical compounds, which has been scarcely reported in a continuous anaerobic treatment process. Previous batch experiments have discovered the possible implications of different reducing conditions on the biotransformation process, but have failed to reflect actual removal performance due to substrate limitations and other operational factors. Continuously operating reactors commonly receive wastewater stream containing a wide range of electron acceptors that diversify the growth of microorganisms in anaerobic treatment. The alteration of the dominance of reducing conditions in a continuous anaerobic reactor may result in the improvement of biotransformation performance compared to a single reducing condition in a substrate-limited batch experiment. The removal of psychostimulant caffeine (CAF), anti-diabetic drug gliclazide (GCZ), and anti-hypertensive drug prazosin (PRZ) were examined through the operation of an up-flow anaerobic sludge blanket (UASB) reactor under predominant methanogenic condition (Phase I) and simultaneous reducing conditions provided by a nitrate supplement (Phase II). The results revealed high biotransformation performance for all three compounds (73-> 99%) in both Phase I and Phase II experiments and fitted the pseudo-first-order model. The biotransformation rate of CAF and PRZ were relatively lower by 25% and 29%, while the GCZ rate improvement doubled in Phase II compared to Phase I. The outcome from 16s rRNA sequencing suggested that the biotransformation of the compounds may be driven by Firmicutes and Bacteroidota in both phases, and Burkhorderiales and sulfate-reducing bacteria species in Phase II. This study proved preferential of reducing conditions does not negatively affect the biotransformation performance of each pharmaceutical compound in a continuous anaerobic reactor, but they led to varying biotransformation rate, hence shifting the microbial diversity.