Study On Treatment Of Caffeine Wastewater By Micro-electrolysis And SBR Process

Caffeine wastewater was from the synthetic caffeine production process, which was a high concentration and refractory organic wastewater. The characteristics of the wastewater were high organic content, nitrogen content, chrome and poor biodegradability. The wastewater would result in serious environmental pollution problems if not treated effectively. At present the caffeine wastewater treatment method was rarely reported. China was a big country at the production of caffeine, so to find a comprehensive and effective way to deal with wastewater caffeine was an urgent task.Considering the composition and characteristics of wastewater, the micro-electrolysis method combined with the SBR was chosen to treat caffeine wastewater. Micro-electrolysis method aimed at enhancing the biodegradability of wastewater and removing chrome of the wastewater; SBR process could efficiently remove the organic substance of wastewater and had a certain biological nitrogen removal capacity.Using micro-electrolysis to treat caffeine wastewater, influential factors of micro-electrolysis which can optimize the reaction conditions and the mechanism of micro-electrolysis were studied. The results showed that: The micro-electrolysis method to pre-treat caffeine wastewater achieved good results. The optimum reaction conditions were as follows: influent pH was 5, HRT 60min, the concentration of the influent was raw water, iron carbon ratio (the accumulation of volume ratio) was 1 : 1, normal temperature reaction. Under these conditions, removal rate of COD was up to 46.8%, ammonia nitrogen 62.6% chrome 93.5%, BOD / COD could be from the initial 0.23 to 0.48. And micro-electrolysis got a good removal efficiency in heavy metals such as nickel, cadmium, lead. The major pollutants in caffeine wastewater was a purine heterocyclic organic compounds which was structural stability, not biodegradable and contained chromophore and auxochrome. Through the micro-electrolysis treatment, the macromolecules of nitrogen-containing heterocyclic opened bond and broke ring and generated easily biodegradable small molecules such as amide and urea, improve the wastewater biodegradability, and greatly reduce the wastewater chrome. Using micro-electrolysis to pre-treat caffeine wastewater and the inherent advantage of acidic wastewater, the need of pH adjustment process for wastewater eliminated, the cost of wastewater treatment reduced and the treatment process simplified. Then using the SBR process to treat wastewater after pretreated, the changes of substance inside the reactor with the time in aeration, the effect of treatment influenced by temperature, volume load and so on and kinetics of activated sludge were studied. The results showed that: with the aeration time elapsed, COD continued to decline until invariablenes. NO2-, NO3-continued to decline until nondetects, but ammonia nitrogen present a persistent increase until stability, which resulted from hydrolysis of amide and urea substances. When the volume load of COD was 1.26g·L-1·d-1, the water temperature controlled at 36℃, aeration reaction time was 34h, the effect of treatment was best. The removal rate of COD was up to 93.7%, the effluent COD was 131mg·L-1, and reached emission standards (GB21904-2008). The process of SBR to treat caffeine wastewater could be divided into three phases: 0 ~ 6h, 8 ~ 22h, 24 ~ 34h. Each stages could fit zero-order kinetic equation. After regression analysis, the substance degradation rate constants of three stages were: K01 = 0.0204h-1, K02 = 0.0048 h-1, K03 = 0.0129 h-1.