about us | careers | terms & conditions | intranet | extranet | sitemap | contact us
   
Skip Navigation Links
Home
Skip Navigation Links
Knowledge Hub
Skip Navigation Links
Research
Skip Navigation Links
Resources & Tools
Skip Navigation Links
Learning
Skip Navigation Links
Events
Skip Navigation Links
News & Media
Skip Navigation Links
FET Water
Skip Navigation Links
SCM
Skip Navigation Links
Mine Water Atlas
Login | Register
Go Search
     
Fate and behaviour of engineered nanoparticles in simulated wastewater and their effect on microorganisms
Expanded Title:The emerging and numerous advantages related to nanotechnology and nanomaterials (NMs) incorporated in the variety fields of studies ranging from catalysis, water treatment materials to environmental remediation and biomedicine have raised concerns for public and environment. Nanomaterials especially zinc oxide and silver are increasingly applied in consumer products such as sunscreen, fashion, electronic appliances and varieties of medical equipment have been produced over the past years and such products are expected to increase. However, substances from these NMs might increasingly be released into wastewater treatment plant (WWTP) and their fate and ecotoxicological effects on the microbial population of wastewater systems are still lacking as such effects can ultimately inhibit the performance of these systems. On the microbial front, activated sludge usually consists of various microbial strains of bacteria including their extracellular products, and 9% protozoan population. But the presence of NMs in the system can inhibit these essential microbial communities and cause detrimental effects on the performance of wastewater treatment systems. NMs are reported to exert antimicrobial properties through different mechanisms, e.g. adsorption on the cell wall, degrading the lipopolysaccharide molecules and then NMs accumulating inside cells; generation of reactive oxygen species that cause oxidation; causing damage to deoxyribonucleic acid (DNA) thereby dismantling cell replication abilities. However, such information is insufficient in relation to impact on the biological processes during wastewater treatment. It has been suggested that the fate and behaviour of NMs change with the presence of natural organic matter, contaminants and extracellular polymeric substances (EPS) leading to the precipitation of these NMs in the sludge. These nano-wastes can then represent an environmental risk if disposed at landfills. This project therefore investigated the potential impact of ENMs on wastewater treatment plants using laboratory scale activated sludge based wastewater treatment systems (OECD 303A). The present study aimed to investigate the physicochemical behaviour, chemical effect, fate, potential impacts on microbial population (particularly the bacteria and protozoa), and to examine the resistance limits of these organisms after their exposure to engineered nanoparticles (ENMs). Overall, the results obtained indicated the suitability of the OECD 303 A method used to assess the fate and behaviour of ZnO ENPs in WWTPs and their effect on microbes. In light of low concentrations of ZnO ENPs found in the treated effluent attained as a result of their removal with the waste activated sludge (WAS), it is predicted that there will be low likelihood of ZnO ENPs release and dispersion into the aquatic systems from WWTPs as point sources. Finally, the elevated concentration of ZnO ENPs in the sludge therefore necessitates additional treatment steps to ensure mitigation of possible dispersion of ENPs from various disposal mechanisms such as landfilling, incineration, and agricultural applications. The fate and behaviour of ZnO ENPs in wastewater were also found to be impacted upon by the presence of electrolytes, ionic strength, organic matter and pH during the activated sludge wastewater treatment. Thus, the release of zinc from ZnO ENPs suspension in wastewater was found to be more significant under acidic conditions and low ionic strength. However, the release of zinc from ZnO ENPs in wastewater was comparatively lower compared to the release from de-ionized water. This indicates the release of the nanomaterials into water from sediments and sludge is not likely if the pH conditions are around neural pH. In addition, under alkaline conditions, a large fraction of the metal-oxide ENPs showed strong tendency to settle out in the sewage sludge bio-solid rather than being dissolved or dispersed in the filtrate. The depositions of ENPs on sludge suggest their removal by abiotic, bio-sorption and bio-solid settling mechanisms. Furthermore, the size of ZnO ENPs was found to significantly increase upon exposure to wastewater matrix, an observation that suggests the sorption and stabilization capacity of synthetic organic matter from domestic waste and natural organic matter (NOM) such as humic substances. Under the conditions of this study, which simulated the real WWTPs, the consortium of bacteria collected from a well operated WWTP and employed in the aeration chamber, were able to remove the organic matter in the wastewater spiked with ZnO ENPs. Both COD and DOC were not significantly affected by changes in ENPs concentration, a phenomenon suggesting adaptation ability of microorganisms responsible for organic matter degradation during activated sludge wastewater treatment upon long term exposure to ENPs. Toxicity of ENPs demonstrated a pH-dependence towards selected single bacterial isolates and the consortium of protozoan and bacterial isolates. Exposure of target bacterial and protozoan isolated to ENPs results in cell growth reduction, which progressively lead to cell inhibition. The toxicity effects of the target ENPs towards wastewater bacterial and protozoan population may diminish the performance of biological treatment processes and affect the efficiency of wastewater treatment plants in producing effluent of high quality on a long term. Based on the results obtained in this study, some gaps were identified for future work and these include; I. Investigation of the bacterial species highly sensitive to the presence of ZnO ENPs, in order to understand which stages of the activated sludge wastewater treatment processes are more affected by the presence of nanoparticles. This will help to develop methodologies to overcome the potential adverse effects of ENPs; ii. Investigations on the impacts of ENP sludge accumulation on sludge treatment processes, such as anaerobic digestion. iii. Elucidation of the mechanism governing ENPs accumulation on sludges and biofilms and assess possible mitigation of their long-term impacts.
Date Published:14/11/2016
Document Type:Research Report
Document Subjects:Wastewater Management - Sewers
Document Format:Report
Document File Type:pdf
Research Report Type:Consultant
WRC Report No:KV 350/16
ISBN No:978-1-4312-0762-6
Authors:Chaúque EFC; Zvimba JN; Ngila JC; Musee N; Mboyi A; Momba MNB
Originator:WRC
Organizations:University of Johannesburg; CSIR; Tshwane University of Technology
Document Size:10 020 KB
Copyright 2017 - Water Research Commission Designed By: Ceenex