Advanced Treatment And Reuse Of Citric Acid Production Wastewater

Pollution of water environment, water shortage and improvement of sewage discharge standard, which are considered as the driving forces for the development of industrial wastewater reuse.Industrial wastewater reuse as an alternate water source is becoming an important way to realize the target for water-saving and emission-reduction,meanwhile to control water-pollution.In the thesis, which focus on secondary effluent of the citric acid production wastewater of Xielian company, a combined process of Fenton/BAF/RO was established for advanced treatment aiming at reuse in the recirculated-cooling water.The Fenton oxidation is studied as a pre-treatment process for sequencing BAF. The parameters influencing the COD removal of wastewater, namely pH, ferrous ion and hydrogen peroxide concentrations have been optimized. More than 75% COD is removed under the optimized conditions as of 2 h reaction time, pH 3.5 and dosages of 30% H₂O₂ and FeSO4 at 0.9 ml/L and 223.4mg/L, respectively. The optimum operating conditions for later sedimentation is that pH is 8.57, the concentration of Na2CO3 is 800 mg/L, the dosage of PAM is 0.5mg/L.The pilot plant was started up by the way of inoculation and cultivating biofilm on packings. The COD removal rate of BAF was investigated with full consideration of the influence of two major controlling factors such as hydraulic loading rate and gas-liquid ratio. The optimum operating conditions are that hydraulic loading rate is 3.47m3/(m2·h), and gas-liquid ratio is 1.Under these conditions, the influence of the height of filter was tested.Fenton's reaction has proved to be a feasible technique for the wastewater under study. It improved the biodegradability of wastewater, promoted the biofilm growth of BAF. To reduce the cost and the H₂O₂ concentration for maximum waste degradation,α=(B/C)/H₂O₂ and COD removal loading of BAF as criteria are introduced to test the oxidation degree. With the pH around 4.0, the H₂O₂ dosage of 0.42ml/L,the effluent COD is about 13mg/L, B/C of effluent is 0.43,αis maximum.After the removal of pretreatment of organic and hardness, RO system ran stably, the electrical conductivity of effluent is 15⁴5μs/cm. The effluent satisfied the requirements of industrial recirculated cooling-water.