Zinc oxide nanoparticle impact on solid waste anaerobic digestion and biogas production

Engineered nanoparticles incorporated into consumer products can enter the environment during the manufacture, use of the product and waste disposal. The effect of zinc oxide (ZnO) nanoparticle on anaerobic digestion was assessed using 250 mL batch digesters, fed with a blend of municipal solid waste and cow dung, spiked with 15 to 60 mg kg⁻ˡ shock dose of ZnO nanoparticle for 60 days at 35 ± 2 °C. The mean volatile fatty acid composition was 0.9 to 2.8 times higher in relation to the control. The difference was significant (p = 0.05) and suggests that the microbial community were unable to effectively use the available substrate although low ZnO concentration (15 mg kg⁻ˡ) exerted no pronounced adverse effect on the digestion process. Based on Archaea-specific phospholipid etherlipid (PLEL) derived saturated and monounsaturated isoprenoids, hydrogenotrophic and methylotrophic biomarkers were dominant with 1.0 to 2.3 times lower concentration in the ZnO nanoparticle spiked digester. The biogas produced was concentration-dependent and ranged from 1.1 to 4.3 times lower in the ZnO nanoparticle spiked digestate relative to the control. The results provide evidence on the inhibitory effect of ZnO nanoparticle on the performance, microbial richness and evenness during anaerobic digestion of municipal solid waste. Keywords: ZnO nanoparticle, municipal solid waste, anaerobic digestion, biogas, inhibitory effec

Evaluation of the impact of engineered nanoparticles on the operation of wastewater treatment plant

The effect of engineered nanoparticles (ENPs) mixture consisting of silver oxide, (Agg0[Silver Oxide Nanopartical], 20 nm), titanium dioxide, (TiO2[Titanium dioxide], 30-40 nm) and zinc oxide, (ZnO, 20 nm) compared with their bulk metal salts was evaluated against unspiked activated sludge (control) using 3 parallel pilot-scale treatment plants. The total concentration of the ionic species of Ag+ Ti[Silver + Titanium] and Zn(2+) in the effluent of the ENP spiked activated sludge (AS) was below limits of detection and> 99% of the spiked ENP were found in the waste activated sludge (WAS), whereas 39 – 58 % of Ag0[Silver Oxide Nanopartical], 51 – 63 % and 58 – 74 % of ZnO ion concentrations were recovered in the anaerobic digestate (AD) cake suggesting higher affinity of ENPs to WAS than to anaerobic digestate. ENPs induced a 2-fold increase of the microbial community specific oxygen uptake rate (SOUR) compared with the control and > 98 % of ammonia and 80 % of COD were removed from the AS suggesting that the heterotrophic biomass retained their ability to nitrify and degrade organic matter at the spiked ENP concentration. The floc size and cultivable microbial abundance was reduced in the ENP spiked AS with no apparent disruption of the overall AS process efficiency. However, scanning electron microscopic analysis clearly showed damage to specific microbial cells. The lipid fingerprint and 16S rRNA gene-based pyrosequencing evidenced the dominance of Proteobacteria, Firmicutes, and Bacteriodetes with a clear temporal shift in microbial community structure. The prominent nano-tolerant bacterial species identified were Acidovorax, Rhodoferax, and Comamonas whereas Methanocorpusculum and Methanosarcina were recovered in AS and were the dominant Archaea in the AD with 99 and 98 % similarities to the closest culturable relative. Their presence in the AS suggests tolerance to ENPs and oxygen-dependent respiration. V. fisheri activity was not sensitive to the ionic concentrations of the ENP or metal salt mixture in the digestate samples and illustrates the need to develop bioassay using indigenous wastewater microorganisms to detect the potential effect of ENP. Overall, unlike other xenobiotic compounds, ENPs can hasten the natural selection of microbial species in activated sludge and anaerobic digestion processes

Antibiotic Susceptibility of Coliform and Vibrio Species in Shellfishes from Estuary Chronically Contaminated with Polycyclic Aromatic Hydrocarbon

Polycyclic aromatic hydrocarbon (PAH) levels and antibiotic susceptibility of coliform and Vibrio species in swimming crab (Callinectes latimanus), mangrove oyster (Crassostrea tulipa), and periwinkle (Tympanotonus fuscatus) from Qua Iboe River and Cross River estuaries were assessed using standard procedures. Bacterial load in the shellfishes and surface water was 1.2 to 1.4 times higher than the control, but the difference was significant at p = 0.05. Total PAH level of 11.36 ± 0.3 mg kg-1 in C. latimanus, 17.57 ± 0.9 mg kg-1 in C. tulipa, and 13.88 ± 0.5 mg kg-1 in T. fuscatus compared to 7.51 ± 0.3 mg L-1 in the surface water and indicates 1.06 to 1.57 times higher PAH accumulation than in surface water and was significant (p = 0.05). The dominant coliform and Vibrio species in the shellfishes were Serratia marcescens, Enterobacter aerogenes, Escherichia coli, Klebsiella, Citrobacter diversus, and Vibrio alginolyticus, V. estuarianus, V. fischeri, V. fluvialis and V. parahaemolyticus. A mean of 21.2% difference between two study groups indicates that shellfishes were the main source of gastrointestinal illness with 43% median resistance to commercially available antibiotics. Accumulation of PAH and abundance of an emerging multiple antibiotic resistant bacterial strains is a cause of concern and potential health risk to consumers of the shellfishes. Keywords: Shellfish, coliform, Vibrio, polycyclic aromatic hydrocarbon, antibiotic resistanc

Evaluation of engineered nanoparticle toxic effect on wastewater microorganisms: current status and challenges

The use of engineered nanoparticles (ENPs) in a wide range of products is associated with an increased concern for environmental safety due to their potential toxicological and adverse effects. ENPs exert antimicrobial properties through different mechanisms such as the formation of reactive oxygen species, disruption of physiological and metabolic processes. Although there are little empirical evidences on environmental fate and transport of ENPs, biosolids in wastewater most likely would be a sink for ENPs. However, there are still many uncertainties in relation to ENPs impact on the biological processes during wastewater treatment. This review provides an overview of the available data on the plausible effects of ENPs on AS and AD processes, two key biologically relevant environments for understanding ENPs–microbial interactions. It indicates that the impact of ENPs is not fully understood and few evidences suggest that ENPs could augment microbial-mediated processes such as AS and AD. Further to this, wastewater components can enhance or attenuate ENPs effects. Meanwhile it is still difficult to determine effective doses and establish toxicological guidelines, which is in part due to variable wastewater composition and inadequacy of current analytical procedures. Challenges associated with toxicity evaluation and data interpretation highlight areas in need for further research studies

Enhanced biogas production from anaerobic co-digestion of lignocellulosic biomass and poultry feces using source separated human urine as buffering agent

Effect of source separated human urine as buffering agent compared to sodium bicarbonate and water in anaerobic co-digestion of lignocellulosic biomass and poultry feces was evaluated in laboratory scale reactor for 180 days at 37 ± 2°C. Mean biogas volume ranged from 37 ± 8 to 101 ± 18 mL gVS−1 in the urine buffered reactors which was 1–5 times higher than the bicarbonate and water buffered reactors and the difference was significant at p = 0. 05. Total volatile fatty acids (VFA) concentration ranged between 396 and 1,400 mg L−1 with a pH of 6.9 ± 0.3 and 7.8 ± 0.1, respectively. In contrast, VFA concentration ranged between 386 and 3,109 mg L−1 (pH 7.6 ± 0.2 and 4.8 ± 0.4) in sodium bicarbonate buffered digestate and control (water) respectively. The result indicates buffering capacity of urine on anaerobic co-digestion with positive effect on biogas production. The Archaeal isoprenoids included markers of aceticlastic and hydrogenotrophic methanogens with a relative abundance that ranged between 0.71–18, 3–55, and 2–59 μg g−1 dry matter in the water (control), bicarbonate and urine buffered digestate, respectively. The Archaeal abundance was 1.12 and 6 times higher in the combined female/male urine than the bicarbonate buffered digestate and the control, and the difference was significant at p = 0.05. Overall, this study demonstrates that human urine with no pharmaceutical loadings as a wetting and buffering agent is a promising option for anaerobic co-digestion with competitive edge over sodium bicarbonate on lignocellulosic biomass saccharification for enhanced biogas production

Aged-engineered nanoparticles effect on sludge anaerobic digestion performance and associated microbial communities

To investigate the potential effect of aged engineered nanoparticles (a-ENPs) on sludge digestion performance, 150 L pilot anaerobic digesters (AD) were fed with a blend of primary and waste activated sludge spiked either with a mixture of silver oxide, titanium dioxide and zinc oxide or a mixture of their equivalent bulk metal salts to achieve a target concentration of 250, 2000, and 2800 mg kg− 1 dry weight, respectively. Volatile fatty acids (VFA) were 1.2 times higher in the spiked digesters and significantly different (p = 0.05) from the control conditions. Specifically, isovaleric acid concentration was 2 times lower in the control digester compared to the spiked digesters, whereas hydrogen sulfide was 2 times lower in the ENPs spiked digester indicating inhibitory effect on sulfate reducing microorganisms. Based on the ether-linked isoprenoids concentration, the total abundance of methanogens was 1.4 times lower in the ENPs spiked digester than in the control and metal salt spiked digesters. Pyrosequencing indicated 80% decrease in abundance and diversity of methanogens in ENPs spiked digester compared to the control digester. Methanosarcina acetivorans and Methanosarcina barkeri were identified as nano-tolerant as their relative abundance increased by a factor of 6 and 11, respectively, compared to the other digesters. The results further provide compelling evidence on the resilience of Fusobacteria, Actinobacteria and the Trojan horse-like effect of ENPs which offered a competitive advantage to some organisms while reducing microbial abundance and diversity

Insights into the effect of mixed engineered nanoparticles on activated sludge performance

In this study, the effects, fate and transport of ENPs in wastewater treatment plants (WWTP) were investigated using three parallel pilot WWTPs operated under identical conditions. The WWTPs were spiked with (i) an ENP mixture consisting of silver oxide, titanium dioxide and zinc oxide, and (ii) bulk metal salts. The third plant served as control (unspiked). ENP effects were evaluated for (i) bulk contaminant removal, (ii) activated sludge (AS) process performance, (iii) microbial community structure and dynamics and (iv) microbial inhibition. ENPs showed a strong affinity for biosolids and induced a specific oxygen uptake rate two times higher than the control. The heterotrophic biomass retained its ability to nitrify and degrade organic matter. However, non-recovery of ammonia- and nitrite-oxidizing bacteria such as Nitrosomonas, Nitrobacter or Nitrospira in the ENP spiked reactors suggests selective inhibitory effects. The results further suggest that ENPs and metal salts have antimicrobial properties which can reduce synthesis of extracellular polymeric substances and therefore floc formation. Scanning electron microscopy evidenced selective damage to some microbes, whereas lipid fingerprinting and 454 pyrosequencing indicated a temporal shift in the microbial community structure and diversity. Acidovorax, Rhodoferax, Comamonas and Methanosarcina were identified as nano-tolerant species. Competitive growth advantage of the nano-tolerant species influenced the removal processes and unlike other xenobiotic compounds, ENPs can hasten the natural selection of microbial species in AS