Modeling the fate and effect of benzalkonium chlorides in a continuous-flow biological nitrogen removal system treating poultry processing wastewater

Salinity-mediated enhancement of quaternary ammonium compounds resistance and removal in endophytic bacteria LSE01

The widespread usage of quaternary ammonium compounds (QACs) as disinfectants during the COVID-19 pandemic poses significant environmental risks, such as toxicity to organisms and the emergence of superbugs. In this study, different inorganic salts (NaCl, KCl, CaCl2, MgCl2) were used to induce endophytes LSE01 isolated from hyperaccumulating plants. After five generations of cultivation under 80 g/L NaCl, the minimum inhibitory concentration (MIC) of LSE01 to QACs increased by about 3-fold, while its degradation extent increased from 8% to 84% for C12BDMA-Cl and 5%-89% for C14BDMA-Cl. Transmission electron microscopy (TEM) and three-dimensional fluorescence spectra indicated that the cells induced by high concentration of salt caused plasmolysis and secreted more bound extracellular polymeric substances (B-EPS); these changes are likely to be an important reason for the observed increased resistance and enhanced degradation extent of LSE01 to QACs. Our findings suggest that salt-induction could be an effective way to enhance the resistance and removal of toxic organic pollutants by functional microorganisms.

Short-term exposure to benzalkonium chloride in bacteria from activated sludge alters the community diversity and the antibiotic resistance profile

The continuous introduction of cleaning products containing benzalkonium chloride (BAC) from household discharges can mold the microbial communities in wastewater treatment plants (WWTPs) in a way still poorly understood. In this study, we performed an in vitro exposure of activated sludge from a WWTP in Costa Rica to BAC, quantified the changes in intI1, sul2, and qacE/qacEΔ1 gene profiles, and determined alterations in the bacterial community composition. The analysis of the qPCR data revealed elevated charges of antibiotic resistance genes in the microbial community; after BAC's exposure, a significant increase in the qacE/qacEΔ1 gene, which is related to ammonium quaternary resistance, was observed. The 16S rRNA gene sequences' analysis showed pronounced variations in the structure of the bacterial communities, including reduction of the alpha diversity values and an increase of the relative abundance of Alphaproteobacteria, particularly of Rhodospseudomonas and Rhodobacter. We confirmed that the microbial communities presented high resilience to BAC at the mg/mL concentration, probably due to constant exposure to this pollutant. They also presented antibiotic resistance-related genes with similar mechanisms to tolerate this substance. These mechanisms should be explored more thoroughly, especially in the context of high use of disinfectant.

Long-term evaluation of the effect of peracetic acid on a mixed aerobic culture: Organic matter degradation, nitrification, and microbial community structure

Peracetic acid (PAA) has been widely used as a disinfectant in many industries; its use in poultry processing is steadily increasing. However, information related to the potential inhibitory effect of PAA solutions (PAA and H₂O₂) on biological wastewater treatment processes used by the poultry processing industry is extremely limited. The work reported here assessed the long-term effect of PAA solution on aerobic degradation and nitrification in three bioreactors fed with poultry processing wastewater by quantifying the extent of COD removal and nitrification rates. Changes in culture viability, intracellular reactive oxygen species (ROS), and microbial community structure were also evaluated. COD removal and nitrification were not affected by H₂O₂ and PAA solutions added to the wastewater before feeding (indirect addition). However, both processes were significantly affected by high levels of H₂O₂ (i.e., 27 mg/L) and PAA solution (i.e., 60/8.4 mg/L PAA/H₂O₂) directly added to the reactors. Directly added PAA/H₂O₂ at 40/5.6 mg/L was the lowest dose resulting in nitrification inhibition. Fast recovery of COD removal and nitrification was observed when direct addition of H₂O₂ and PAA solution ended. Cell viability measurements revealed that the negative impact on nitrification was predominantly attributed to enzyme inhibition rather than to loss of cell viability. The impact on nitrification was not related to intracellular ROS levels. Microbiome analysis showed major shifts in community composition during the long-term addition of H₂O₂ and even more with PAA addition. No significant time-trend change in the relative abundance of ammonia-oxidizing bacteria or nitrite-oxidizing bacteria was observed, further supporting the conclusion that the negative impact on nitrification was attributed mainly to enzyme inhibition.

Optimization of E. coli Inactivation by Benzalkonium Chloride Reveals the Importance of Quantifying the Inoculum Effect on Chemical Disinfection

Optimal disinfection protocols are fundamental to minimize bacterial resistance to the compound applied, or cross-resistance to other antimicrobials such as antibiotics. The objective is twofold: guarantee safe levels of pathogens and minimize the excess of disinfectant after a treatment. In this work, the disinfectant dose is optimized based on a mathematical model. The model explains and predicts the interplay between disinfectant and pathogen at different initial microbial densities (inocula) and dose concentrations. The study focuses on the disinfection of Escherichia coli with benzalkonium chloride, the most common quaternary ammonium compound. Interestingly, the specific benzalkonium chloride uptake (mean uptake per cell) decreases exponentially when the inoculum concentration increases. As a consequence, the optimal disinfectant dose increases exponentially with the initial bacterial concentration.

Impacts of quaternary ammonium compounds on membrane bioreactor performance: Acute and chronic responses of microorganisms

Quaternary ammonium compounds (QACs) are emerging contaminants with the extensive applications in a variety of fields. However, little is known about their potential impacts on activated sludge and performance of biological wastewater treatment processes. In this work, the effects of benzalkonium chloride (BAC, a kind of QACs) on acute and chronic responses of microorganisms and on MBR performance were systematically investigated. The results showed that a low concentration (0.5-2.0 mg BAC/g SS) caused no significant effects on activated sludge property. In contrast, an elevated concentration of BAC led to severer inhibition on activated sludge and key enzyme activity (e.g., dehydrogenase activity) in both short-term and long-term exposure, thus deteriorating the pollutant removal efficiency. Compared with the control MBR (R1) and the reactor with 0.5 mg/L BAC (R2), the removal efficiency of ammonia in R3 with 5.0 mg/L BAC at identical hydraulic retention time (4.3 h) and sludge retention time (30 d) was decreased, i.e., ammonium removal efficiency in R1∼R3 was 95.4 ± 6.1, 93.4 ± 8.1 and 89.3 ± 17.6%, respectively. Moreover, MBR tests showed that membrane fouling was aggravated in the presence of high-concentration BAC. Long-term exposure to BAC reduced microbial community diversity and enriched the BAC-resistant microbes. For instance, the abundance of Pseudomonas genus in R3 was increased from 0.02% to 14.9% with the increase of operation time. Microbial community structure was changed to resist the environmental stress induced by BAC during long-term exposure, thus decreasing the inhibition effects.

Surfactants in aquatic and terrestrial environment: occurrence, behavior, and treatment processes

Surfactants belong to a group of chemicals that are well known for their cleaning properties. Their excessive use as ingredients in care products (e.g., shampoos, body wash) and in household cleaning products (e.g., dishwashing detergents, laundry detergents, hard-surface cleaners) has led to the discharge of highly contaminated wastewaters in aquatic and terrestrial environment. Once reached in the different environmental compartments (rivers, lakes, soils, and sediments), surfactants can undergo aerobic or anaerobic degradation. The most studied surfactants so far are linear alkylbenzene sulfonate (LAS), quaternary ammonium compounds (QACs), alkylphenol ethoxylate (APEOs), and alcohol ethoxylate (AEOs). Concentrations of surfactants in wastewaters can range between few micrograms to hundreds of milligrams in some cases, while it reaches several grams in sludge used for soil amendments in agricultural areas. Above the legislation standards, surfactants can be toxic to aquatic and terrestrial organisms which make treatment processes necessary before their discharge into the environment. Given this fact, biological and chemical processes should be considered for better surfactants removal. In this review, we investigate several issues with regard to: (1) the toxicity of surfactants in the environment, (2) their behavior in different ecological systems, (3) and the different treatment processes used in wastewater treatment plants in order to reduce the effects of surfactants on living organisms.

Nitrification recovery behavior by bio-accelerators in copper-inhibited activated sludge system

Copper (Cu) is a toxic heavy metal which can cause inhibitory effects on nitrification process in biological wastewater treatment systems. However, few studies have done to dose accelerators into Cu-inhibited activated sludge system to promote bioactivity recovery of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). In this study, four ingredients of bio-accelerators were developed and dosed in five parallel SBRs. The effluent NH4(+)-N, NO2(-)-N and NO3(-)-N concentrations, specific oxygen uptake rate (SOUR), and Cu distribution were investigated to assess the bioactivity recovery effects. Results showed that, among biotin, L-aspartic acid and cytokinin, L-aspartic acid was the most effective for the fast bioactivity recovery of nitrifying bacteria. The combination of these three substances was optimum and Cu-inhibited activated sludge system could be 100% recovered in 8 days. The bio-accelerators proposed in this study can be potentially applied in the emergency treatment in biological wastewater treatment systems.

Quaternary ammonium compounds (QACs): a review on occurrence, fate and toxicity in the environment

Quaternary ammonium compounds (QACs) are widely applied in household and industrial products. Most uses of QACs can be expected to lead to their release to wastewater treatment plants (WWTPs) and then dispersed into various environmental compartments through sewage effluent and sludge land application. Although QACs are considered to be aerobically biodegradable, the degradation is affected by its chemical structures, dissolved oxygen concentration, complexing with anionic surfactants, etc. High abundance of QACs has been detected in sediment and sludge samples due to its strong sorption and resistance to biodegradation under anoxic/anaerobic conditions. QACs are toxic to a lot of aquatic organisms including fish, daphnids, algae, rotifer and microorganisms employed in wastewater treatment systems. And antibiotic resistance has emerged in microorganisms due to excessive use of QACs in household and industrial applications. The occurrence of QACs in the environment is correlated with anthropogenic activities, such as wastewater discharge from WWTPs or single source polluters, and sludge land application. This article also reviews the analytical methods for determination of QACs in environmental compartments including surface water, wastewater, sewage sludge and sediments.

Prolonged exposure of mixed aerobic cultures to low temperature and benzalkonium chloride affect the rate and extent of nitrification

The combined effect of benzalkonium chloride (BAC) and prolonged exposure to low temperature on nitrification was investigated. Ammonia oxidation at 22-24°C by an enriched nitrifying culture was inhibited at increasing BAC concentrations and ceased at 15 mg BAC/L. The non-competitive inhibition coefficient was 1.5±0.9 mg BAC/L. Nitrification tests were conducted without and with BAC at 5mg/L using an aerobic, mixed heterotrophic/nitrifying culture maintained at a temperature range of 24-10°C. Maintaining this culture at 10°C for over one month in the absence of BAC, resulted in slower nitrification kinetics compared to those measured when the culture was first exposed to 10°C. BAC was degraded by the heterotrophic population, but its degradation rate decreased significantly as the culture temperature decreased to 10°C. These results confirm the negative impact of quaternary ammonium compounds on the nitrification process, which is further exacerbated by prolonged, low temperature conditions.

The biodegradation of monomeric and dimeric alkylammonium surfactants

Quaternary ammonium compounds (QACs) are salts known for having antiseptic and disinfectant properties. These compounds are toxic to aquatic organisms and should thus be removed from wastewater before its discharge into surface waters. The biodegradation of QACs takes place in the presence of microorganisms under aerobic conditions. The susceptibility of these compounds to degradation depends on numerous parameters. A number of them, such as the structure-adsorption on solids, and concentration of the QACs, as well as the presence of additional substances, have been reviewed in this article. Moreover, the biodegradability of new dimeric alkylammonium salts, i.e., cationic gemini surfactants, has been discussed and compared with that of anionic and nonionic geminis. The biodegradation study of monomeric and dimeric alkylammonium surfactants show that they are not easily degraded. The degradation process is very complex and strongly depends on the structure of the compound, adsorption-desorption processes on sludge, type of microorganism consortia and the presence of anions. Alkylammonium surfactants with biological motifs, like amide, peptides or carbohydrates, are much better degraded.

Removing and Recovering Phosphate from Poultry Wastewater Using Amorphous Ceramics

A novel and effective technique for phosphate from poultry wastewater was developed using amorphous ceramics. Amorphous ceramics, which showed high performance for phosphate removal and recovery from poultry wastewater, were synthesized using unlimitedly available, inexpensive materials such as silica fume and lime. Dissolved phosphate in poultry wastewater can be deposited as a solid on the surface of amorphous ceramics. Phosphate content on the surface of amorphous ceramics could reach 14.20%. The phosphate removal and recovery process and mechanism was revealed by a series of characterizations, such as XRD, FESEM, BET, and so on. The present study demonstrated that amorphous ceramics have great potential as a novel, beneficial material for removing and recovering phosphate from poultry wastewater.