Table 4.

Biological processes for wastewater treatment

Treatment technology	Type of wastewaters	Removal efficiency	Highlights	References
Biological fluidized bed reactor	Coking	Ammonium nitrogen: 90, Phenol: 99, COD: 85	To assess the stability of nitritation under varying organic loading rates (OLR), a long-term experiment was conducted over a period of 200 days using a biological fluidized bed reactor (BFBR). The experimental data aligned with the predictions of a mathematical model, which identified the optimal conditions for achieving stable nitritation.	(Li et al. 2021)
Constructed wetland	Stabilizing pond effluent	BOD5:31 TN 15+ Ammonium nitrogen 90+	The effluent from the constructed wetlands exhibited decreased measurements of all measured parameters. The highest elimination rate was observed for ammonium nitrogen (>90%).	(Nguyen et al. 2019)
Oxic-anoxic-oxic, combined with chemical oxidation and sedimentation	Coking	MPAHs: 98.6 OPAHs: 83.9 NPAHs: 89.1%	For most low molecular weight methylated PAHs, PAHs, as well as some oxygenated PAHs and nitro PAHs, the main elimination mechanism was biodegradation. On the other hand, adsorption by dewatered sludge played a significant role in removing high molecular weight PAHs, as well as many OPAHs and NPAHs. However, to further eliminate the remaining semi-volatile PAHs (SPAHs) and PAHs in the treated effluents, advanced treatment methods are necessary.	(Saber et al. 2021)
Constructed wetland	Treated steel rolling	COD: 61 TP: 81 TN: 58	The results indicated that the horizontal flow constructed wetland (HFC) demonstrated effective elimination of turbidity, COD and total phosphorus. However, the average elimination rate of total nitrogen was only about 25%. It was observed that increasing the hydraulic retention time led to varying degrees of improvement in the elimination rate of contaminants in both HFC and horizontal flow subsurface flow artificial wetland (HFSAD).	(Zheng et al. 2021)
Anoxic/oxic/anoxic/oxic	Coking	COD: 90 and 87, Ammonium nitrogen 97 and 88	High molecular weight PAHs were found to be the predominant compounds in the untreated coking wastewater. These compounds exhibited significant degradation in the sequencing batch reactor with anoxic/oxic/anoxic/oxic configuration compared to the typically used anoxic/oxic/oxic process. The superior performance of the former in treating total nitrogen can be attributed to the higher abundance of Thiobacillus, SM1A02, and Thauera, which are likely the key factors driving the enhanced TN elimination in this system.	(Fan et al. 2021)