Elsevier

Chemosphere

Volume 155, July 2016, Pages 100-108
Chemosphere

Toxicological characterization of a novel wastewater treatment process using EDTA-Na2Zn as draw solution (DS) for the efficient treatment of MBR-treated landfill leachate

https://doi.org/10.1016/j.chemosphere.2016.04.045Get rights and content

Highlights

  • A novel wastewater treatment process using EDTA-Na2Zn as DS was investigated.

  • The water recovery rate of landfill leachate was high by using EDTA-Na2Zn as DS.

  • The treatment of LL using EDTA-Na2Zn as DS kept high retention rate of pollutants.

  • The method of EDTA-Na2Zn as DS could effectively eliminate the acute toxicity of LL.

  • Landfill leachate treated by EDTA-Na2Zn had no toxicity effects on cells.

Abstract

Landfill leachate has become an important source of environmental pollution in past decades, due to the increase of waste volume. Acute toxic and genotoxic hazards to organisms can be caused by landfill leachate. Thus, how to efficiently recover water from landfill leachate and effectively eliminate combined toxicity of landfill leachate are the most pressing issues in waste management. In this study, EDTA-Na2Zn as draw solution (DS) was used to remove the toxicity of membrane bioreactor-treated landfill leachate (MBR-treated landfill leachate) in forward osmosis (FO) process, and nanofiltration (NF) was designed for recovering the diluted DS. Zebrafish and human cells were used for toxicity assay after the novel wastewater treatment process using EDTA-Na2Zn as DS. Results showed that the water recovery rate of MBR-treated landfill leachate (M-LL) in FO membrane system could achieve 66.5% and 71.2% in the PRO and FO mode respectively, and the diluted DS could be efficiently recovered by NF. Toxicity tests performed by using zebrafish and human cells showed that M-LL treated by EDTA-Na2Zn had no toxicity effect on zebrafish larvae and human cells, but it had very slight effect on zebrafish embryos. In conclusion, all results indicated that EDTA-Na2Zn as DS can effectively eliminate toxicity of landfill leachate and this method is economical and eco-friendly for treatment of different types of landfill leachate.

Introduction

Landfill leachate is a complex mixture of inorganic and organic compounds. It is generated through the precipitation, infiltration, compaction and degradation of waste mass at landfill sites (Kjeldsen et al., 2002). Landfill leachate can leak into groundwater and migrate for considerable distances to the rivers, leading to acute toxic and genotoxic hazards to aquatic organisms (Maqbool et al., 2011). A serious threat to public health and the environment caused by landfill leachate impelled it to become one of the most significant environmental pollution (Widziewicz et al., 2012). Due to the toxic effects of coexistent heavy metals on microbes, the biological treatment of landfill leachate is very difficult (Sawaittayothin and Polprasert, 2007). The treatment of landfill leachate and water recovery are the pressing issues that need to be solved (Neczaj et al., 2005).

Forward osmosis (FO) has been regarded as an important new water treatment technology, because of the plenty of advantages, such as no aid pressure (Klaysom et al., 2013, Coday et al., 2014), high rejection of many pollutants (Cath et al., 2006, Cartinella et al., 2006) and low membrane fouling propensity (Hoover et al., 2011, Lutchmiah et al., 2011). Recently, FO was widely used to solve many environmental and industrial problems in seawater desalination, industrial and municipal wastewater treatment (Cornelissen et al., 2008, Wang et al., 2014, Zhang et al., 2014, Kong et al., 2014). However, there are many barriers in the development process of FO technique. The decrease of the osmosis pressure for DS is one of major barriers. The drive force for FO system is the osmotic difference of feed solution (FS) and DS. The osmosis difference increases with the enhancement of infiltration efficiency. Thus, the DS with high osmosis pressure is necessary. The diluted DS in the process of the FO leads to decrease of the osmosis pressure, therefore the DS needs to be regenerated or separated to restore high osmosis pressure, which is energy-intensive and cost-intensive in the FO system. Suitable DS and low-energy regeneration technology are the key factors to determine the economic feasibility of the FO technique.

The ideal DS has the following characteristics: high solubility and low molecular weight leading to high osmosis pressure; good compatibility with membrane and less reverse salt diffusion resulting in better stability; simple regeneration or separation process with low operating costs. Recent studies on DS have achieved significant advances, which facilitate the FO to be widely used in practice. For instance, Lutchmiah et al. (2014) investigated the feasibility of zwitterions used as DS and proved that the highly soluble zwitterions produced similar water fluxes to NaCl. Hau et al. (2015) found that the surfactant as DS could achieve water fluxes of 4.9 L m−2 h and 1.2 L m−2 h. Ryan et al. (2014) reported that addition of salts with divalent and organic ions at relatively low concentrations could effectively reduce reverse salt flux and maintain high water flux. Ge et al. (2012) reported that polyelectrolytes were used as a DS and found that they could be separated from water by low pressure-driven or heating processes. Zhao et al. (2015) found that the diluted polyacrylamide solution could maintain high viscosity and be used directly for polymer flooding to increase oil yield. Zhao et al. (2016) found that a series of EDTA complexes (EDTA-Na2Mg, EDTA-Na2Ca, EDTA-Na2Mn and EDTA-Na2Zn) had high solubility in water, moderate molecular size, expanded molecular structure, nontoxicity, low viscosity and relatively high osmotic pressure. These characteristics were favorable for FO performance and the regeneration of EDTA complexes, which ensured the feasibility of EDTA complexes as a new class of competent draw solutes. Therein, EDTA-Na2Zn possessed the best property, because it is easily regenerated by nanofiltration and is freely soluble in water (Hau et al., 2014).

Commonly, biological oxygen demand (BOD), chemical oxygen demand (COD) and total organic carbon (TOC) were the primary physico-chemical parameters to evaluate water quality after wastewater treatment. Nevertheless, these physico-chemical parameters might not be suitable for evaluating the developmental toxicity to organisms caused by waste water (Ma et al., 2005). To better understand the toxicological characterization of the waste water treatment, aquatic organisms should be used to demonstrate the elimination of developmental toxicity of waste water (Ma et al., 2005). Zebrafish (Danio rerio) is a favorite model for the studies on DNA damage and toxicology (Pei and Strauss, 2013, Dai et al., 2014, Bian and Pei, 2016). The fish at early developmental stages are very susceptive to toxic substances (McKim, 1995). Bioassays with zebrafish embryos and larvae have been regarded as a faster and more cost-effective way for toxicity testing of pollutants in environmental water and sediment samples (Carlsson et al., 2009). Thus, the detection of detoxification efficiency of wastewater treatment by using zebrafish model is a useful method to predict the potential health effects.

In this study, EDTA-Na2Zn solution was used as DS to deal with MBR-treated landfill leachate (M-LL). The effects of DS concentration, membrane orientation and membrane cleaning in the FO process were tested and the maximum recovery rate of the FO process with EDTA-Na2Zn as DS for M-LL was also determined. To evaluate the detoxification efficiency of EDTA-Na2Zn as draw solution, zebrafish and human cells were used as biological model to test the toxicity of M-LL extracted by EDTA-Na2Zn (E-MLL). Our studies here indicated that E-MLL had no toxicity effects for zebrafish larvae and human cells. EDTA-Na2Zn can effectively eliminate developmental toxicity and acute toxicity of M-LL, indicating that EDTA-Na2Zn as draw solution can be considered as a simple and eco-friendly technology to treat landfill leachate.

Section snippets

Ethics statement

The animal protocol for this study was approved by the Institutional Animal Care and Use Committee of Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences (Approval ID: ZKCQY0063) and by the Animal Care and Use Committee of Chongqing in China.

Chemicals and membranes

EDTA-Na2Zn was purchased from KeLong Chemical Co., Ltd (Chengdu, Sichuan, China). The FO membranes prepared by TFC polyamide and NF membrane were purchased from Hydration Technologies Innovation (HTI, Albany, USA) and TS80

Effect of DS concentration on water flux

The result in Fig. 1 showed that when the DS concentration was raised from 0.5 M to 0.9 M, the initial water flux increased from 3.9 L m−2 h−1 to 8.0 L m−2 h−1 in the PRO mode and 1.8 L m−2 h−1 to 4.6 L m−2 h−1 in the FO mode. Higher DS concentration generated greater osmotic driving force, which in turn led to higher water flux across the membrane, but the increase of water flux was not directly proportional to the DS concentration, because of the concentration polarization. Meanwhile, the

Conclusion

The novel method using EDTA-Na2Zn as draw solution not only possessed high water recovery rate and high retention rate of pollutants for M-LL, but also effectively eliminated toxicity of M-LL. Although it is quite difficult to remove the combined toxicity of landfill leachate, EDTA-Na2Zn may become a potential alternative in wastewater treatment to effectively eliminate combined toxicity of landfill leachate in the future. Here, toxicity tests were performed by using zebrafish embryos, larvae

Conflict of interest

The authors declare no conflict of interest.

Acknowledgements

The authors are grateful for supports from the Hundred Talents Program of Chinese Academy of Sciences (to D.S.P.), the Scientific Research Starting Foundation for Returned Overseas Chinese Scholars from Ministry of Education (to A.P.N and D.S.P.), the National Natural Science Foundation of China (Grant No. 51503205 to X.W.), the Key Application and Development Program of Chongqing Science and Technology Commission (Grant No. cstc2014yykfC20004 and cstc2014yykfC20002 to D.S.P.), the CAS ″Light

References (28)

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These authors contributed equally to the manuscript.

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