Abstract
The coal gasification wastewater figures prominently among types of industrial effluents due to its complex and phenolic composition, posing great difficulty for conventional water treatment processes. Since the coking wastewater is toxic and mutagenic to humans and animals, treatment of coal gasification wastewater is genuinely necessary. In this study, we established a lab-scale A2O (Anaerobic-Anoxic—Oxic) with moving bed biological reactor (MBBR) system and evaluated some water indicators of wastewater pretreated with internal electrolysis, of wastewater output of the established A2O-MBBR system, and of the wastewater treated by the combination thereof. The wastewater was taken from a coking plant at Thai Nguyen Iron and Steel Joint Stock Company in Vietnam. COD, BOD5, NH4+-N, phenol, and pH of the input coal gasification wastewater were 2359, 1105, 319, 172 mg/L, and 8 ± 0.1, respectively. The conditions of internal electrolysis were as follows: 720 min of reaction time, pH = 4, 25 g/L Fe-C dosage, and 100 mg/L PAM dosage. After internal electrolysis process, the removal of COD, BOD5, NH4+-N, and phenol were 53.7%, 56.7% 60.5%, and 73.3%, respectively. After 24 h of treatment, the treatment efficiencies of the combined treatment process are as follows: 100% phenol removal, 71.3% of TSS removal; 97.7% reduction of BOD5, and 97.1% reduction of COD; total N content reduced by 97.6%; total P content decreased by 81.6%; and NH4+-N content decreased by 97.5%. All above indicators after treatment have met QCVN 52: 2017/BTNMT (column A) Vietnamese standard for steel industry wastewater.
Highlights
The coal gasification wastewater is among the most difficult-to-treat wastewaters due to its complex and phenolic composition, which contains a large number of organic compounds and cyanide [1].Since it is toxic and mutagenic to humans and animals, treatment of coal gasification wastewater is genuinely necessary
We aimed to improve treatment process for real coking wastewater by comparing water indicators of effluents treated by various processes including internal electrolysis with Fe-C materials, the A2O-moving bed biological reactor (MBBR) integrated system, and a combinational process in which internal electrolysis treatment preceded the A2O-MBBR
The results showed that Fe-C internal electrolysis materials had decomposed 73.32% of phenol, 51.02% of TSS, 56.70% of BOD5, 53.74% of COD, 34.98% of total nitrogen, 47.20% of total phosphorus, and 60.10% of NH4 + -N
Summary
The coal gasification wastewater is among the most difficult-to-treat wastewaters due to its complex and phenolic composition, which contains a large number of organic compounds and cyanide [1].Since it is toxic and mutagenic to humans and animals, treatment of coal gasification wastewater is genuinely necessary. Physicochemical pretreatment processes involved the removal of phenol and NH3 from highly concentrated pollutants to facilitate the subsequent biological treatment and might include extraction, extraction, and autoclaving, filler, flocculation, dilution, electrochemical, Fenton, and oxidation [2,3,4,5]. Such pretreatment methods still present certain disadvantages such as high treatment cost, technological complexity, and generation of secondary pollution. The treatment method could be utilized in a wide range of industries ranging from textile and pharmaceutical to treatment of domestic and coking wastewater [5,6,7,8,9]
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