Electron donors and co-contaminants affect microbial community composition and activity in perchlorate degradation

Abstract

Although microbial reduction of perchlorate (ClO4(-)) is a promising and effective method, our knowledge on the changes in microbial communities during ClO4(-) degradation is limited, especially when different electron donors are supplied and/or other contaminants are present. Here, we examined the effects of acetate and hydrogen as electron donors and nitrate and ammonium as co-contaminants on ClO4(-) degradation by anaerobic microcosms using six treatments. The process of degradation was divided into the lag stage (SI) and the accelerated stage (SII). Quantitative PCR was used to quantify four genes: pcrA (encoding perchlorate reductase), cld (encoding chlorite dismutase), nirS (encoding copper and cytochrome cd1 nitrite reductase), and 16S rRNA. While the degradation of ClO4(-) with acetate, nitrate, and ammonia system (PNA) was the fastest with the highest abundance of the four genes, it was the slowest in the autotrophic system (HYP). The pcrA gene accumulated in SI and played a key role in initiating the accelerated degradation of ClO4(-) when its abundance reached a peak. Degradation in SII was primarily maintained by the cld gene. Acetate inhibited the growth of perchlorate-reducing bacteria (PRB), but its effect was weakened by nitrate (NO3(-)), which promoted the growth of PRB in SI, and therefore, accelerated the ClO4(-) degradation rate. In addition, ammonia (NH4(+)), as nitrogen sources, accelerated the growth of PRB. The bacterial communities' structure and diversity were significantly affected by electron donors and co-contaminants. Under heterotrophic conditions, both ammonia and nitrate promoted Azospira as the most dominant genera, a fact that might significantly influence the rate of ClO4(-) natural attenuation by degradation.

Enhanced bioremediation of RDX and Co-Contaminants perchlorate and nitrate using an anaerobic dehalogenating consortium in a fractured rock aquifer

“…4a). Although nitrate can be a competing electron acceptor for perchlorate reduction, high nitrate concentrations also have been shown to stimulate growth of perchlorate-reducing bacteria when nitrate is also reduced (Guan et al, 2015). The treatment GW-LNRP showed a gradual decline in perchlorate concentrations after 20 days of incubation (Fig.…”

“…Perchlorate is a common energetics booster and oxidant in a variety of rockets and munitions, and breakdown of nitrate-containing explosives in soil can result in elevated nitrate concentrations in groundwater at explosives-contaminated sites. These co-contaminants, which have similar reduction potentials (Guan et al, 2015), can act as more favorable electron acceptors for microbial metabolism than sulfate or RDX and delay the onset of sufficiently reducing conditions for RDX degradation. The presence of nitrate also provides a more readily available nitrogen source for microbial metabolism than available in RDX.…”

Perchlorate Removal in Microbial Electrochemical Systems With Iron/Carbon Electrodes

“…The aerospace fuels, explosives, and firecrackers could cause perchlorate contamination existing in the soil, groundwater, and drinking water. The perchlorate concentration can reach 3,700 mg/L in groundwater, 120 mg/L in surface water, and 811 μg/L in drinking water (Guan et al, 2015). It has been found in milk, urine, and blood (Cheng et al, 2004; Valentínblasini et al, 2005).…”

Electrochemically-induced in situ degradation of legacy munitions and insensitive high explosives in manufacturing wastewater

“…Research by Lorah et al(Lorah et al, 2022) emphasized the challenges these co-contaminants pose, even though the microbial consortium WBC-2 exhibited the capability to degrade RDX in their midst. Expanding on this, Guan et al (Guan et al, 2014) noted that both perchlorate and nitrate, due to their similar reduction potentials, can act as more favorable electron acceptors for microbial metabolism than sulfate or RDX, thus delaying the onset of conditions suitable for RDX degradation. This is complemented by insights from Hatzinger and Fuller (Fuller et al, 2015) , who posited that sulfate or methanogenic conditions are crucial for the in situ anaerobic bioremediation of RDX.…”