Treatment Of ABS Resin Wastewater By Coagulation Coupled With Pressurized Dissolved Air Flotation

ABS resin wastewater is produced in the form of organic wastewater with high concentration in the production of ABS resin. It’s characterized with being emulsion and complicated substances, such as benzene series, acrylonitrile and its dimeric polymer, butyl benzene latex, ABS powder, ABS latex, oligomer, and so on. The ABS resin wastewater, with high suspended solid content, high toxic and harm organic compounds content and poor biochemical ability, is one of wastewaters which are difficult to be disposed in petrochemical industry. In recent years, with the increasing demand of ABS resin and increasing amount of ABS resin production units in China, the ABS resin wastewater discharge increases accordingly and pollution intensity is growing. Nowadays, the technique of physicochemical pretreatment – conventional biochemical treatment – deep processing is widely adopted by producer of ABS resin. However, some problems exists, such as poor performance of removing suspended substance and its harm influence on the following treatment of wastewater, blocking of pipe line and bonding microorganism, which have an effect on the performance of biochemical treatment, resulting in discharge water failing the national standards, thus causing economic losses to enterprises. Therefore, the key operation is the removal of suspended materials in ABS resin wastewater.In view of the difficultyof removing suspended solids thoroughly in ABS resin wastewater, the equipment blockage and unstable run of the existing conventional coagulation- air flotation, combining theoretical study and field test, this paper fully absorbed the advanced technology of dissolved air flotation both here and abroad, optimized the existing equipment of coagulation– dissolved air floatation, developed a wide flow channel releaser with good performance of anti-blocking, and optimized dissolving system with pressure and gas-water balance controlling system on a basis of the dissolving pressure requirement of wide flow channel releaser.Meanwhile, the screening of agents incoagulation- flotation for wastewater with different water qualities produced in the production of ABS resin was carried out, and the coagulation mechanism and optimal hydraulic condition was explored, and the optimization of operation parameters for dealing with ABS resin wastewater using the technique of improved coagulationcoupled with pressured dissolved air floatation was performed. Good performance is achieved to treat gel and emulsion wastewater with high concentration of suspended solid discharged from graft polymerization stage which is easy to be blocked using equipment of improved coagulationcoupled with pressured dissolved air floatation, such as good handling performance, stable run, no blockage of releaser and no breakdown of dissolved air system;there is still good performance on the conditions that the water qualities of feed water varies, resulting in smooth biochemical treatment, providing a reference for treating wastewater produced from ABS resin producers in China.The main achievements are as follows:(1) According to the problems that the slit of existing releaser of dissolved air for energy dissipation is too narrow, and the suspended solids leads to blockage easily, a new type of wide flow channel releaser was studied, which a hose fixed length and diameter was used to dissipate energy and a bigger pipe was used to release bubbles. The narrowest place of the whole reseaser was exceeded 3 mm, and the aperture size could be changed with the wastewater quality condition, so that the blockage was solved.(2) According to the problem that the wide flow channel releaser needs higher pressure of dissolved air compared to traditional releaser, the pressurized dissolved air system was optimized. A reflux pump and a dissolved gas cylinder were used for dissolving air, the pressure of the dissolved gas cylinder improved to 0.5~0.7 MPa, and the dissolved gas cylinder was placed horizontal so as to increase the contact area of gas-liquid interface and reduce the water level fluctuation. In order to guarantee the dissolved air efficiency and release effect of the pressurized dissolved air system and the pressure between gas and water in the dissolved gas cylinder reach balance, the pump pressure, air flow rate, the pressure of dissolved gas cylinder and the water level in dissolved air cylinder were optimized, so as to guarantee the pressurized dissolved air system balanced and stabled running. The results showed that under the condition of 8% gas water ratio, 0.6 MPa dissolved air pressure, the efficiency of dissolved air could reach 96%, which was finished within 30 s. Under the optimal condition of dissolved air system, the diameter of bubble was related with the length of the hose, the diameter of bubble was up to 38 μm under the condition of 0.6 MPa dissolved air pressure and 1.5m the length of the hose, met the requirement of air floatation.(3) The optimal chemicals were selected for ABS resin wastewater from 11 kinds of coagulants and 10 kinds of flocculants. The optimal chemical of butadiene polymerization section(area B) wastewater treatment was CaCl2, and the optimal dosage was 1500 mg/L; the optimal chemical of graft polymerization section(area C) wastewater treatment was coagulant R and flocculant FO4440 SSH, and the optimal complex ratio was 15:1; the optimal chemical of gelatinous drying section(area E) wastewater treatment was PAC and flocculant FO4440 SSH, and the optimal complex ratio was 7.5:1; the optimal chemical of mixed wastewater treatment was coagulant R and flocculant FO4440 SSH, and the optimal complex ratio was 40:1; the optimal chemical of the latex wastewater treatment was CaCl2 and flocculant FO4440 SSH, the optimal complex ratio was 7.5:1. Then, the cost of drug was analyzed that the wastewater from butadiene polymerization section mixed with graft polymerization section, and the wastewater from gelatinous drying section was individual, the treatment effect was the best, and could achieve better results in technology, economy and environment.(4) The coagulation mechanism mainly includes electric charge neutralization and adsorption and bridging of macromolecular polymer. The Zeta potential of colloids, the particle size distribution, and the appearance of the floc in ABS resin wastewater were analyzed. The effects of different coagulants on zeta potential, the effect of optimal coagulant on zeta potential, particle size distribution and the appearance of the floc, and the effect of different coagulants dosage on zeta potential and particle size distribution were discussed. It was showed that the zeta potential changed significantly by adding different coagulants, and the structure of flocs was compact, which was broke up uneasily by water flow and taken away easily by air bubbles.(5) The water quality characteristics of ABS resin wastewater from different production process were studied, and got the optimal hydraulic conditions of coagulation reaction. In allusion to the requirements of air flotation process for particle size and coagulation reaction degree, this paper improved coagulation reaction system, which combined with pipeline mixing and mechanical stirring. Then, it determined the chemical adding time of coagulant and flocculant.(6) The parameters of coagulation-dissolved air flotation were optimized for the pretreatment of ABS resin wastewater from different section. The optimum pH scope of wastewater was determined to provide reference for the wastewater treatment of ABS resin enterprises. For gelatinous drying section(area E) wastewater, the retention time of air flotation system was 12.5 min, the optimal reflux ratio was 40%, and the requirement of chemicals PAC and FO4440 SSH for pH was loose. For mixed wastewater, the retention time of air flotation system was 15 min, the optimal reflux ratio was 40%, and the optimal pH was 5~6. For latex wastewater, the retention time of air flotation system was 20 min, the optimal reflux ratio was 60%, and the optimal pH was 6~7. In order to investigate the stability of the treatment of ABS resin wastewater by the improved coagulation coupled with pressurized dissolved air flotation device, a continuous test for ABS graft polymerisation wastewater with high suspended solids was conducted under the determined optimum process conditions. During the continuous test, the wastewater pretreatment was effective. The SS removal rate was maintained above 90%, the effluent SS concentration was maintained below80 mg/L, and the effluent COD maintained below 1400 mg/L. This level of treatment was consistent even for widely varying influent quality and greatly reduced the subsequent biochemical treatment needed.