Biochemical treatment of effluent from wet oxidation of emulsion waste liquid

1 test materials and methods

1.1 test materials

The main components of untreated emulsion waste liquid are non-ionic surfactant and its toxic assistant. The CODcr concentration of the aluminum cleaning waste liquid from an automobile air conditioner workshop is 50000 mg / L, and the test water is the effluent after oxidation at 200 ℃ and 220 ℃ for 2 hours. Under this condition, COD removal efficiency of 75% and 85% can be obtained with oxygen partial pressure of 1.2 MPa and reaction time of 2 h, respectively. It can be seen from the comparison that the unoxidized emulsion waste liquid is in the form of milky white slurry, and the oxidized effluent is transparent yellow or light yellow green, with a CODcr concentration of 8000-14000 mg / L and a pH value of about 4.20. The SBR aerobic test water is prepared by diluting the wet air oxidation effluent.

1.2 test equipment

Two drum batch biochemical treatment units (SBR) with volume of 3L and 2L were used in the experiment.

Among them, 3-L reactor is mainly used to study the influent CODcr concentration of 2000-3000 mg / L, and 2-L reactor is used for the influent COD of 1000-2000 mg / L. The operation cycle of SBR unit is 1D, the water inflow is 0.5h, the sedimentation is 1.5h, the drainage is 0.5h, the drainage and water inflow are 1 / 2 of the volume.

1.3 test method

Because the direct use of wet air oxidation effluent has little degradation effect under anaerobic condition, SBR test mainly investigated the biodegradation under aerobic condition. The oxidized effluent is diluted to a certain concentration, and then sent to the SBR reactor after adjusting the pH value, and then the aeration device is opened for reaction. After the reaction, the sedimentation and drainage are completed. Samples were taken every 2 hours after the influent, and 100 ml was taken in the middle of the aeration period for MLSS determination to understand its settling performance.

2 biochemical analysis

For industrial wastewater, if only B / C value is used to measure its biodegradability, it has great limitations. For the waste water containing chemical synthetic products, due to its complex composition, the method of high dilution is needed in the determination of BOD5, which is difficult to truly reflect the biodegradability of the waste water. However, the B / C value is a basic premise to judge the biodegradability. Therefore, the biodegradability of the effluent from wet air oxidation is investigated from many aspects before the biochemical test.

2.1 B/C value

Before oxidation, the B / C value of emulsion waste liquid is about 0.05-0.10, and its biodegradability is very poor. After oxidation at 200 ℃ and 1.2MPa oxygen partial pressure for 2h, the CODcr concentration in the effluent was about 12000 mg / L, and the average B / C value increased to 0.51; after oxidation at 220 ℃ and 1.2MPa oxygen partial pressure for 2h, the CODcr decreased from the original 50000 mg / L to about 9000 mg / L, and the average B / C value increased to 0.55. If only from the B / C value, the wastewater after wet air oxidation has good biodegradability.

2.2 biological toxicity change

The results show that the untreated emulsion waste liquid has high toxicity, which is equivalent to the toxicity of 0.12 mg / L mercuric chloride solution, while the waste water oxidized at 200 ℃ and 220 ℃ is only equivalent to the toxicity of 0.02 mg / L mercuric chloride solution.

2.3 change of waste water composition

According to the analysis of COD contribution rate, the non-ionic surfactant, mineral oil and other additives account for 80%, 10% and 10% respectively. The content of low-grade fatty acid (acetic acid) in the effluent is about 30% at 200 ℃ and 2 hours after oxidation, and its contribution rate as volatile acid is about 49% of COD. In the final effluent, there are not only volatile acid (such as acetic acid), but also small-molecule alcohols (such as methanol, ethanol, low-grade ether, low-grade ester, etc.), so it is estimated that the total amount of small-molecule organics can be more than 50%, so the toxicity is basically relieved Therefore, it is possible to further treat the wastewater by biochemical process.

3 SBR test results and discussion

The operation process of SBR process is generally divided into five stages: water inflow, reaction, sedimentation, drainage and idling. The main factor affecting the treatment process is aerobic aeration time. Therefore, the effect of aeration time on the organic matter removal rate under different influent load is mainly investigated. The concentration of sludge is 2500-6000 mg / L, the initial VSS / TSS is 0.60, and after normal operation, the VSS / TSS is about 0.87. The sludge has high activity and good settling performance.