Chloroacetaldehyde removal by zero valent iron enhanced hydrolytic acidification pretreatment

Highlights

• ZVI enhanced hydrolytic acidification is a feasible technology treating chloroacetaldehyde.

• Chloroacetaldehyde posed toxicity to biological treatment.

• ZVI presented good dechlorination performance on chloroacetaldehyde.

• ZVI enhanced acetic acid yield under acidification process.

Abstract

Chloroacetaldehyde is a typical refractory toxic petrochemical wastewater to environment, whereas conventional treatment strategies in the wastewater treatment plants are inapplicable to transforming it into nontoxic forms. Therefore, we explored zero valent iron enhanced hydrolytic acidification solution to tackle this problem. Experimental results indicated that zero valent iron enhanced hydrolytic acidification technology possessed the capability to chloroacetaldehyde detoxication, 20.23% and 19.32% increasing dechlorination ratio achieved at initial CAE concentration of 50 and 100 mg/L with 5 g/L ZVI at 48 h. Moreover, ZVI reduced cell death resulted from 0.31, to 1.59 DNA/g VSS reduced at aforementioned parameters. Also, ZVI did not significantly affect predominant butyric acid-type fermentation, but it facilitated the total volatile fatty acids more 43.10, 26.06 and 25.39 mg COD/g VSS produced at 50 and 100 mg/L with at 48 h, particularly, it enhanced the yields of short-chain fatty acid Ac which can be directly used by microbes.

Introduction

Petrochemical industry generally including exploiting, extraction, refining, transporting and marketing processes which displaying highly a significant role in modern lives, more detailedly, it providing basic raw materials for other industries and producing a variety of products for the people's basic necessities in life. Rapidly increasing demand of chemical products over the last decades caused the petroleum consumption increased accordingly. According to the report from BP Statistical Review of World Energy, annual average growth of global petroleum consumption was 1.8%, that's to say, 1.7 million barrels/d in 2018 (BPSRWE, 2018). Relevant studies indicated that 3–3.5 m³ of petrochemical wastewater (PCWW) is generated per ton of crude oil refinery process (Siddique et al., 2017; Zhang and Fan, 2016), therefore, a great deal of PCWW are needed to be disposed or treated properly. However, that is a severe problem in the wastewater treatment originated from various pollutants concluded such as heavy metals, inorganic and specific organic pollutants. For instance, China announced a national standard refers to 60 kinds of PCWW specific organic pollutants (SOPs) and discharge limits in 2015. These contaminants have been proved to be toxic to microbial community existed in wastewater treatment plants (WWTPs) for exerting an extremely high impact on WWTPs stable operation, for example, benzene, toluene (Tobiszewski et al., 2012; Wu et al., 2015) and chlorinated organic compounds etc. posing toxicity to microbes in WWTPs. moreover, it can cause damage to water body, aquatic organism and cause human health harm (reproductive health, respiratory issues, psychological health and eve cancer etc.) through direct touch, food chain and other pathways (Axelsson et al., 2010; Di Salvo et al., 2015; Rovira et al., 2014), the reason was ascribed to CAE inhibited DNA and RNA synthesis etc (Kandala et al., 1990; Matsuda et al., 1996). As a result, exploring suitable disposal technologies or strategies is urgent and necessary to solve SOPs problem efficiently.

Some studies have been conducted to figure out SOPs treatment in recent years which are classified into physical, chemical and biological methods. Coagulation−flocculation, ozonation, membrane hybrid process, photodegradation, submerged membrane bioreactor (sMBR) and anaerobic expanded granular sludge bed (EGSB) etc. have been applied by many researchers to treat PCWW, although the major advantages of physical and chemical methods are high-efficiency and short-time, however, the disadvantages of them are high-cost and secondary pollution limiting their engineering application. Biological treatment is common and economical wastewater treatment methods, as for, chloroacetaldehyde (CAE), there is still only limited study reported. Recently, some explorations have clearly displayed that hydrolytic acidification (HA) pretreatment has the good potential to dispose PCWW (Wu et al., 2016), and (Yang et al., 2015) both discovered HA was fit for PCWW treatment, in addition, outstanding performance has been verified with respect to biodegradation improvement and toxicity reduction. At the same time, other impressive and good ways also used in SOPs removal is zero valent iron (ZVI), which is employed to detoxicate and treat 2,4-dinitroanisole (Shen et al., 2013), polychlorinated biphenyl (Long et al., 2014), p-chloronitrobenzene (Zhu et al., 2013), quinoline (Wang et al., 2019) and so on, the reason is due to ZVI's strong reduction effect.

In this study, we investigated the feasibility of ZVI enhanced HA technology to treat CAE in this paper. The effect of CAE initial concentration and ZVI were explored firstly to the yields and composition of volatile fatty acids (VFAs), then the dechlorination capacity of ZVI on CAE removal and the variation of extracellular polymeric substances (EPS) are studied. Finally, the mechanism of CAE detoxication by ZVI enhanced hydrolytic acidification are proposed.