Heat shock protein 47 stress responses in Chinese hamster ovary cells exposed to raw and reclaimed wastewater

Abstract

As wastewater reclamation and reuse becomes more widespread, risks of exposure to treated wastewater increase. Moreover, an unlimited number of pollutants can be identified in wastewater. Therefore, comprehensive toxicity assessment of treated wastewater is imperative. The objective of this study was to perform a comprehensive toxicity assessment of wastewater treatment systems using stress response 10 bioassays. This powerful tool can comprehensively assess the toxicity of contaminants. In this study, samples from conventional activated sludge treatment, membrane bioreactors (MBRs) with different pore sizes and sludge retention times (SRTs), rapid sand filtration, coagulation, nano-filtration (NF) and reverse osmosis (RO) were investigated. The results of stress response bioassays confirmed that the secondary effluent showed higher stress response than influent indicating that biological treatment 15 generates toxic compounds. The results obtained from molecular weight fractionation of water samples demonstrated that organic matter with a higher molecular weight fraction (>0.1μm) causes toxicity in secondary effluent. Furthermore, supernatant from MBR reactors showed toxicity regardless of SRT. On the other hand, stress response was not detected in MBR permeates except for an MBR equipped with a larger pore size membrane (0.4μm) and with a short SRT (12 days). While rapid sand filtration could not 20 remove the toxic compounds found in secondary effluent, coagulation tests, operated at an appropriate pH, were effective for reducing stress response in the secondary effluent. Experimental findings also showed that stress response was not detected in cases of NF and RO permeate subsequent to MBR treatment.

Microfiltration, Nano-filtration and Reverse Osmosis for the Removal of Toxins (LPS Endotoxins) from Wastewater

“…This is probably caused by the fact that small molecules aggregated together into larger molecules and were then removed by MBR. Knowing that the detected toxicity was somehow correlated to the existence of microbial by-products and precisely LPS endotoxin [2], therefore we can conclude that LPS endotoxin can be removed by MBR and the removal is enhanced by their aggregation into larger molecules. However, selection of the pore size of the membrane will be important because the size (MW) of organic matter and the aggregates, showing endotoxicity, are strongly dependent on SRT.…”

“…Similarly, Guizani et al [2] applied heat shock protein (HSP) assays to the membrane permeates. The HSP is a very sensitive measurement (bio-assay test) of stress response in cells exposed to pollutants.…”

“…To study the effect of SRT on stress response, HSP assays were applied to the supernatant of mixed liquor of the two MBRs with SRT50 and SRT12, respectively [2]. The supernatants showed significant stress response, and in both cases, the stress was significant in samples including higher MW fractions (> 0.1 um).…”

“…Nano-filtration (NF) and reverse osmosis (RO) membranes have been increasingly used in wastewater reclamation in recent years for the production of clean water from sewage, benefiting due to their improvement in terms of energy consumption [2]. For the time being, they are almost employed in all wastewater treatment plants producing potable water quality.…”

“…As assumed and with some incertitude, Lipo-polysaccharide (LPS) endotoxin materials, a bacterial byproduct [1] found in treated wastewater, are a potential threat for human health [2][3][4][5].…”