Abstract
Coal gasification wastewater is mainly from gas washing, condensation and purification processes in the gas furnace with high NH3-N (nitrogen in water in the form of free ammonia (NH3) and ammonium ion (NH4 +)), TN (total nitrogen) and refractory organics content, which will inhibit the subsequent biological treatment. The 'air stripping - hydrolysis acidification - air stripping' process was proposed as the pretreatment for coal gasification wastewater to improve the biodegradability and nitrogen removal, which could reduce the subsequent biological treatment load. The first-stage air stripping process before hydrolysis acidification could achieve a significant removal of NH3-N (97.0%) and volatile phenol (70.0%), reducing the corresponding toxicity on hydrolysis acidification. The group with air stripping had more abundant microbial communities and a more effective organic degradation performance in hydrolysis acidification than that without air stripping. The second-stage air stripping removed NH3-N released from hydrolysis acidification, and significantly reduced the TN concentration in effluent. The whole process achieved a TN removal from 2,000 ± 100 mg/L to 160 ± 80 mg/L, and a total phenols removal from 700 ± 50 mg/L to 80 ±20 mg/L.
Highlights
IntroductionIn typical coal gasification wastewater, the concentration of chemical oxygen demand (COD), NH3-N and total nitrogen (TN) can reach 22,000–35,000 mg/L, 3,000–5,000 mg/L and 6,000–8,000 mg/L, and the C/N (the ratio of the total amount of carbon in an organism to the total amount of nitrogen) only ranges between 3.5 and 4.4 (Feng et al ; Yu et al ; Wang et al ; Li et al ; Zhao et al )
In typical coal gasification wastewater, the concentration of chemical oxygen demand (COD), NH3-N and total nitrogen (TN) can reach 22,000–35,000 mg/L, 3,000–5,000 mg/L and 6,000–8,000 mg/L, and the C/N only ranges between 3.5 and 4.4 (Feng et al ; Yu et al ; Wang et al ; Li et al ; Zhao et al )
Based on the summary on pretreatment of coal gasification wastewater, this study proposed a combined process of air stripping and hydrolysis acidification to achieve the removal of phenols and ammonia with low cost and high efficiency
Summary
In typical coal gasification wastewater, the concentration of chemical oxygen demand (COD), NH3-N and total nitrogen (TN) can reach 22,000–35,000 mg/L, 3,000–5,000 mg/L and 6,000–8,000 mg/L, and the C/N (the ratio of the total amount of carbon in an organism to the total amount of nitrogen) only ranges between 3.5 and 4.4 (Feng et al ; Yu et al ; Wang et al ; Li et al ; Zhao et al ). The relatively low C/N in coal gasification wastewater determines the insufficiency of the carbon source in subsequent biological nitrogen removal. Coal gasification wastewater is a typical highly toxic, harmful and refractory wastewater
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