Electrochemical Oxidation Using BDD Anodes Combined with Biological Aerated Filter for Biotreated Coking Wastewater Treatment

Abstract

Coking wastewater is characterized by poor biodegradability and high microorganism toxicity. Thus, it is difficult to meet Grade I of Integrated Wastewater Discharge Standard of China by biological treatment technology; specifically, COD cannot meet above standard due to containing refractory organics. A novel coupling reactor, electrochemical oxidation using BDD anodes and biological aerated filter (BAF), has been developed for carbon and nitrogen removal from biotreated coking wastewater, focusing on COD, BOD5,NH4+-N, andNO3--N removal on operation over 90 days with average effluent value of 91.3, 9.73, 0.62, and 13.34 mgL−1, respectively. Average value of BOD5/COD and BOD5/NO3--N was enhanced from 0.05 to 0.27 and from 0.45 to 1.21 by electrochemical oxidation, respectively, with average energy consumption of 67.9 kWh kg−1COD. In addition, the refractory organics also were evidently mineralized in the unit based on the data of the three-dimensional fluorescence spectra. Meanwhile, its effluent provided excellent substrate for biological denitrification in BAF. At hydraulic retention time (HRT) of 13.08 h, about 12 mgL−1 NO3--N was depleted through denitrification, and it mainly occurred at top of 0.25 m height of BAF. Therefore, it is feasible to apply the coupling reactor for biotreated coking wastewater treatment and achieve desirable effluent quality.

Advances in treatment of coking wastewater – a state of art review

“…The coupling of Fenton's reagent with other methods in the form of photo-Fenton, electro-Fenton, sono-Fenton, and heterogeneous Fenton processes overcomes the limitations and improves its feasibility. Electrochemical oxidation is one of those technologies which have proved to be an emerging and promising alternative for wastewater treatment in recent decades (Sasidharan Pillai & Gupta 2016;He et al 2013;Wang et al 2015a). They are considered more advantageous than other oxidation processes because of several factors such as smaller footprint, absence of secondary waste generation, mild operating conditions, free of chemicals, and versatility to combine with other treatment techniques.…”

“…To prevent the recombination rate of photogenerated electrons and holes, Wei et al (2017) came up with a new hybrid technique called photoelectrocatalytic degradation which significantly improved the degradation and mineralization efficiency of phenolic compounds. Other AOPs like electrochemical oxidation (He et al 2013;Wang et al 2015a), wet air oxidation (Luan et al 2017), photocatalysis (Sharma & Philip 2014;Wlodarczyk et al 2016) and catalytic ozonation (Zhang et al 2018) have also been used as advanced treatment for achieving desirable effluent quality. However, high investment cost, severe conditions, sludge problems, and high catalyst limit the industrial-scale application of AOPs.…”

“…The system was able to remove 70.7% of total nitrogen and 55.8% of COD in 20 h at low energy consumption, removing the majority of the nitrogenous compounds. Combining the electrochemical treatment with biological treatment has also resulted in overall treatment of coking wastewater (He et al 2013;Wang et al 2015aWang et al , 2015b. For instance, when electrochemical oxidation was used as a pretreatment for biological aerated filter, over an operation of 90 days, desirable COD and nitrogen removal was achieved reaching the grade 1 discharge standards in China (Wang et al 2015a).…”

“…Combining the electrochemical treatment with biological treatment has also resulted in overall treatment of coking wastewater (He et al 2013;Wang et al 2015aWang et al , 2015b. For instance, when electrochemical oxidation was used as a pretreatment for biological aerated filter, over an operation of 90 days, desirable COD and nitrogen removal was achieved reaching the grade 1 discharge standards in China (Wang et al 2015a). Similarly in a low-cost graphite electrode-based hydrogen peroxide-assisted electrochemical oxidation, high removal of cyanide, phenol, thiocyanate and aniline was achieved under optimal conditions of 0.025 M hydrogen peroxide and 13.63 mA/cm 2 current density (Singh & Mishra 2018).…”

Efficient treatment of high-concentration sulfurous wastewater by using electrochemical oxidation process with Ti/SnO2–Sb anode and air cathode

“…Wang et al combined EO technology with biological aerated filter for advanced treatment of biotreated coking wastewater. At the current density of 75 mA cm −2 and HRT of 45 min, the COD was removed from 221.2 to 113.5 mg L −1 , and the EC was calculated as 67.9 kWh•kg COD −1 [30]. Zhu et al obtained EC of 64 kWh•kg COD −1 when also conducted study of advanced treatment of biologically pretreated coking wastewater using EO process [31].…”