Using ozonation-hydrolysis acidification to the pharmaceutical tail wastewater pretreatment

The presence of pharmaceuticals and personal care products (PPCPs) was first identified in surface and waste waters in the United States and Europe in the 1960s (Stumm-Zollinger & Fair 1965). PPCPs in the aquatic environment have been reported in the last few decades (Daughton & Ternes 1999). These pharmaceuticals can have serious effects on surface water resources and the purity of drinking water directly or indirectly. As the pharmaceutical wastewater includes many non-biodegradable substances, it is necessary to adopt complex processes to deal with the wastewater. Some different treatment methods reported can be used for the treatment of pharmaceutical wastewater such as physicochemical methods treatment which include screening, chlorination, coagulation/ flocculation, sedimentation, adsorption, reverse osmosis (Deegan et al. 2011), biological treatment methods (Suman Raj & Anjaneyulu 2005) and chemical oxidation methods (Khetan & Collins 2007). Biological treatment is usually combined with chemical oxidation used as a pre-treatment or post-treatment step. To completely eliminate pharmaceuticals from wastewater, the advanced oxidation methods may be required (Huber et al. 2005; Justo et al. 2013).

Because of expanded pharmaceutical products range and increased pollution components, the wastewater from the Northeast Pharmaceutical Factory of China disposed by the original anaerobic–aerobic biological process could not reach the standard of discharging to the urban sewage treatment plant using biological methods. It was necessary to improve the original process to increase the treatment efficiency. Pharmaceutical wastewater treated by the process of a pharmaceutical treatment station is usually called pharmaceutical tail water. The pharmaceutical tail water from the Northeast Pharmaceutical Factory treated by the anaerobic–aerobic biological process had the characteristics of poor biodegradability and included high concentrations of non-biodegradable substances which could not discharge to an urban sewage treatment plant using biological methods.

Ozone is a strong oxidizing agent widely used in water treatment with a high redox potential in the water (Loeb et al. 2012). Ozone oxidation and decomposition reaction is a free radical reaction, in which oxygen and hydroxyl radicals are formed through a series of reactions (Snyder et al. 2006). Hydroxyl radicals have stronger oxidation ability than oxygen and can decompose non-biodegradable substances (Janzen et al. 2011). Ozone plays a major role in wastewater treatment and thus ozonation has become a promising technology for the treatment of water and wastewater in the last few decades (Upadhyay & Shrivastava 2005). In ozonation, the ozone molecules rupture the target molecules and produce byproducts that are easily biodegradable. Ozone treatment usually improves the biodegradability of the wastewater. The improvement of biodegradability is an essential requirement environmentally for pharmaceutical effluents resistant to biological treatment (Lester et al. 2013). However, ozone selectively reacts with some organic matters, and ozone cannot completely decompose the organic matters in low dosages and short timescales. Ozonation must be used in combination with other water treatment technologies to achieve the ideal processing effects. Hydrolysis-acidification refers to the anaerobic process controlled in the anaerobic hydrolysis and acidification stage, in which acid-producing bacteria are used to change the non-dissolved organic mater into dissolved organic matter, to turned hardly biodegradable organic matter into easily biodegradable organic matter and to improve the biodegradability of wastewater.

The aim of the study was to dispose of pharmaceutical tail water with the ozonation–hydrolysis acidification, to improve tail water biodegradability and to improve treatment efficiency.

A gas–liquid mixing pump was used to convey pharmaceutical tail water into an ozonation pond equipped with an ozone generator with gas production (15 g/L), and sodium thiosulfate was used to absorb ozone tail gas. The influence and effluence BOD (biochemical oxygen demand), COD (chemical oxygen demand) were measured according to the experimental need.

After three months monitoring, some pollutants concentrations of pharmaceutical tail water were evaluated, and a 90% guarantee rate was used as an evaluation index of water quality guarantee rate. Evaluated concentrations of different water quality indexes were obtained under a given guarantee rate through statistical analysis of monitoring data, and the evaluated concentration is shown in Table 2.

In addition, the monitoring results showed that the pH of the pharmaceutical tail wastewater was alkaline, all data of pH were greater than 7, the maximum being 10. The BOD/COD ratio of pharmaceutical wastewater was lower than 0.20, which was difficult to be biodegraded. GC-MS was used to detect specific components of the COD in the tail water. The results measured by GC-MS showed that there were 51 types of organic substances, including alkanes, pyridine, aniline, ketone, ether and other heterocyclic compounds.

In the tests, BOD, COD, pH, SS, NH₃-N and organic substances were detected and the specific detection methods are shown in Table 3.

From Figure 2 it can be seen that the COD removal rate fluctuated and the guaranteed rate of COD removal increased along with the ozone dosage, increasing from 2.5 to 30 mg/L. At the ozone dosage of 30 mg/L the removal rate of COD was18.2% and the guaranteed rate reached 65% which shows that the ozone dosage of 30 mg/L is reliable.

The changes of organic substances types in the process are described in Tables 4 and 5. From the GC-MS test report it can be seen that organic compounds of pharmaceutical wastewater included alkanes, pyridine, aniline, ketones, ethers and other heterocyclic compounds, of which lipids accounted for the highest proportion. After ozonation the proportion of the alkanes elevated and the proportion of the other organic substances decreased. The cause of hydrocarbons alkanes elevating was that some heterocyclic organic substances were turned into hydrocarbons by ozonation. After hydrolysis the proportion of alkanes decreased, which testified that hydrolysis had an obvious effect on the long chain alkane.

1. The ozone unit test showed that with the ozone dosage increasing from 2.5 to 30 mg/L, the COD removal rate had been gradually improved.

2. The ozonation-hydrolysis acidification test indicated that COD removal rate of whole system was above 30% under ozone of 25 mg/L. After the ozonation-hydrolysis acidification process the B/C value of the pharmaceutical tail water was greater than 0.25, and biodegradability was enhanced.

3. The organic compounds in tail water included alkanes, pyridine, aniline, ketones, ethers and other heterocyclic compounds from the GC-MS test report. After hydrolysis the proportion of alkanes decreased, which testified that hydrolysis had an obvious effect on the long chain alkane.

4. After ozonation-hydrolysis acidification treatment, the pharmaceutical tail water was discharged into an urban sewage plant and mixed with domestic wastewater and the mixed wastewater treated by biological processes could meet national emission standards.