Abstract
The growing production of coke and, consequently, coke wastewater is a significant problem for the environment. Coke wastewater, because it contains high amounts of toxic substances, is classified as an extremely hazardous industrial wastewater. The treatment of such wastewater requires a combination of advanced physicochemical and biological methods. The aim of the research was to investigate the effectiveness of the application of the ultrasonic disintegration of coke wastewater in a sequencing batch reactor (SBR). The tests were conducted in two stages, wherein the first stage involved determining the most favorable sonication conditions, that is, time and amplitude. The authors used the following amplitudes: 31 µm; 61.5 µm; 92 µm; 123 µm and times: 120 s; 240 s; 480 s; 960 s. The second stage focused on treating coke wastewater in SBRs (Reactor A—a proportion of coke wastewater in the mixture: 5%, 10%, and 20%; reactor B—sonicated coke wastewater, proportion in mixture: 5%, 10%, 20%). The efficiency of the treatment process was determined based on the rate of removal of selected parameters: chemical oxygen demand (COD), total organic carbon (TOC), inorganic carbon (IC), ammoniacal nitrogen (N-NH4), total nitrogen (TN), the course of pH changes. The study revealed that sonication of coke wastewater increased biodegradability and reduced its toxicity. The use of the preliminary sonication of coke wastewater before biological treatment improved the degree of removal of the tested parameters by approximately 10%. The volumetric ratio of coke wastewater in the mixture had the greatest impact on the obtained results. The use of an ultrasound field allows the treatment process to be executed with a coke wastewater addition exceeding 10%. In addition, it was found that in order to increase the coke wastewater treatment efficiency, one should optimize individual phases in the SBR and the pollution load.
Highlights
The production of coke is growing year by year
chemical oxygen demand (COD) was determined according to standard methods (APHA, 1999) [46], with the bichromate method using a Dr/4000 spectrometer by HACH, (APHA, 1999) [46]; Total organic carbon (TOC), total carbon (TC), inorganic carbon (NC), and total nitrogen (TN) were determined using a total organic carbon (TOC) 10 C Analyzer PX by Kiper, with an AS 40 autosampler by Dione; Ammoniacal nitrogen (N-NH4 ) was determined using the titration method according to standard methods (APHA, 1999) [46]; pH was determined using the potentiometric method,; All analyses were triplicated
The aim of the analysis was to determine the difference in the values of the studied indicators depending on the combination of tests (the variables in the combinations were amplitude (A), sonication time (t), the portion of coke wastewater in the treated mixture: 5% coke wastewater (CW), 10% Coke Wastewater (CW), and 20% CW, and whether the process carried out in the reactor was assisted with the ultrasonic field-sequencing batch reactor (SBR) + UD or the non-aided ultrasonic field-SBR)
Summary
The production of coke is growing year by year. According to the forecast for 2021, global production will exceed 900,000 Mg per year. Most of the coking plants are located in Asia, while around 10% of global production comes from the European Union. Per every Mg of coke, 0.6 to 1.6 m3 of wastewater is generated. The removal of pollutants from coke oven wastewaters is a significant issue due to the environmental impact of these compounds. The technological cycle of coke oven wastewater treatment is based on the conventional arrangement, i.e., the physical separation of larger solids by means of grids and/or grates, chemical coagulation for the removal of suspensions, and the precipitation of inorganic contaminants and biological nitrification/denitrification systems for the elimination of ammonia and soluble (DOC) organics. The purified wastewater, after the treatment process, can be used in wet coke quenching or disposed of in the environment [1,2,3,4]
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