Activated Sludge Process for Treatment of Refinery Alkaline Dregs Wastewater

Activated sludge method was used to treat the alkali residue wastewater after pretreatment in a refinery. Activated sludge was successfully domesticated with the target wastewater as a carbon source, and then the activated sludge was treated with domesticated activated sludge to treat the wastewater of the alkali refining wastewater to reduce its COD (chemical oxygen demand) value. The experimental results show that the activated sludge biochemical treatment has a high reduction effect on the COD value of the oil refinery alkali residue wastewater. With a hydraulic retention time of 24 h, the average removal rate of COD can reach 76% and the volume load is about 0.7 kg COD/(m3•d). After 10 days of operation, the total COD removal rate can reach about 74%. The effluent quality reached the national three-level emission standard (GB 8978-1996).

Oil refining alkaline residue wastewater is the spent alkali liquor produced during alkali refining of oil products in the petroleum refining process. Its main components are Na2S, mercaptan, thioether, thiophene, phenol, hydrazine and naphthenic acid, which are difficult to handle high-concentration organics. One of the wastewater. Currently, researchers have adopted a variety of processing technologies based on the characteristics of industrial wastewater, mainly high-temperature wet oxidation method and moderate wet air oxidation method. The Zimpro company first developed and developed an industrialized application device for wet air oxidation, and applied it to the treatment of hazardous petrochemical waste liquid and waste residue. This process has a higher treatment efficiency for organics and sulphides, but has a higher requirement for the reactor (high temperature and high pressure).

This kind of wet oxidation technology has better treatment effect on waste water, but the required equipment investment is large and the energy consumption is high. Nitrogenous compounds and polychlorinated biphenyls cannot be completely mineralized, which limits their wide application. Wright Chemical Company has cooperated with Korea's SK Group Institute of Biological Experiments for many years and applied SK's high-efficiency biological treatment technology to the treatment of high-alkaline residue waste water, creating the Wright Bio-Process. This process has a high degree of adaptability to changes in pollutant concentration, toxicant concentration, and salt content in wastewater.

However, the phenomenon of temperature increase during the operation of the process is relatively obvious, which will seriously reduce the dissolved oxygen capacity of the mud-water mixture in the reactor and reduce the microbial activity. Han Jianhua conducted an in-depth study on the wet oxidation treatment of sulfur-containing refinery alkaline slag, and proposed the 'Relaxed wet oxidation deodorization-acidification recovery of phenol or naphthenic acid-SBR process (the process flow of treating oil refinery alkali residue wastewater, and in 1998, in Shanghai A petrochemical enterprise designed an industrialized pilot plant, which can effectively oxidize the organic sulfides and inorganic sulfides in the spent caustic solution to sulfuric acid, eliminating the odor gas emissions during the further treatment of the spent caustic solution. The mild wet oxidation method has shortcomings such as incomplete treatment and strict requirements on the equipment, and it is very easy to generate carbon residue due to excessive temperature, leading to reactor pressure, seriously affecting the normal operation of the treatment device, and the biological method for treating organic wastewater is convenient and quick. The advantages of mildness, low energy consumption, low investment, no catalyst addition, and safe operation have received widespread attention from researchers.

The COD value of alkaline residue wastewater is generally from tens to hundreds of thousands

Because of its complex composition, it contains many refractory organics. Therefore, it is necessary to explore a new type of method for deep processing of oil refinery alkaline residue. In this experiment, activated sludge was successfully domesticated with the wastewater to be treated as a carbon source, and its effect on the treatment effect of the alkali residue wastewater from refining was investigated.