Abstract
A pilot-scale experiment is carried out for treating mixed wastewater containing pharmaceutical wastewater (PW) and domestic wastewater (DW), by a process that is a combination of hydrolysis acidification-ozone-modified anaerobic–anoxic–aerobic-ozone (A2/O) (pre-ozone) or hydrolysis acidification-modified A2/O-ozone (post-ozone). The effects of different mixing ratios of PW and DW and pre-ozone treatment or post-ozone treatment on the removal of nitrogen and phosphorus and chemical oxygen demand (COD) are compared and studied. The optimal ratio of PW in mixing wastewater is 30%, which has the optimal COD removal efficiency and minimum biotoxicity to biological treatment. The pre-ozone treatment shows more advantages in removing nitrogen and phosphate but the post-ozone treatment shows more advantages in COD removal. Analysis of dissolved organic matter (DOM) demonstrates that post-ozone treatment has a more significant effect on the removal of fulvic acid and humic acid than the effect from the pre-ozone treatment, so the COD removal is better. Overall DOM degradation efficiency by post-ozone treatment is 55%, which is much higher than the pre-ozone treatment efficiency of 38%. Microbial community analysis reveals that the genus Thauera and the genus Parasegetibacter take great responsibility for the degradation of phenolics in this process. All the results show that the post-ozone treatment is more efficient for the mixed wastewater treatment in refractory organics removal.
Highlights
It has always been difficult to treat pharmaceutical wastewater (PW) to reach the effluent water quality standard, due to its characteristics of large differences in water quality and volume, complex composition, high pollutant content and poor biodegradability [1,2]
The chemical oxygen demand (COD) removal rate was stabilized in the later fourth stage when the instrument resumed normal operation. 70–80% of COD can be removed and COD in the effluent was about 80–120 mg/L in this system, which met the discharge standard of PW
This indicated that pre-ozone oxidation was performed, there were still some refractory organic matters left in the mixing wastewater, which could not be fully treated by biological treatment, thereby resulting in an increase of COD in the effluent
Summary
It has always been difficult to treat pharmaceutical wastewater (PW) to reach the effluent water quality standard, due to its characteristics of large differences in water quality and volume, complex composition, high pollutant content and poor biodegradability [1,2]. If biological treatment is carried out directly, the toxic substances in PW may affect the biological system, affecting the treatment effect [3,4]; many substances are heterocyclic organics which are difficult to eliminate by a biological treatment As a result, these toxic residues become micropollutants and enter into the environment. Many oxidation methods have been employed for destroying toxic organic pollutants, due to their capacity to destroy almost any organic contaminant [6]. Among those methods, ozone (O3 ) is often used to remove color and a variety of complex pollutants in water, due to its high oxidation
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