In this research work, the new wastewater treatment process for the purification of dyeing wastewater containing polyester desizing agent has been developed with the combination of a electron accelerator and a submerged bioreactor. This newly developed process can treat the hard to degradable organic materials and can be applicable to the actual wastewater treatment plant.
The decomposition mechanism of organic material by accelerators is in the reduction oxidation reaction where organic materials are reacted with the radicals such as $e^-_{aq}$, H°, OH° and so on. These radicals are produced from the attack of electron beam to the water molecules. Generally, dyestuffs are oxidized by OH° in the hydrolysis. This means that oxidation is the dominant reaction. When it exceeds a certain G-value, it reach to the decoloring reaction. The decomposition degree of various dyestuffs can be measured by the analysis of TOC and TLC with Rf value. The initial Rf coefficient of a dyestuff was only one, but it could be destroyed into 3~4 after electron beam irradiation. Even though the TOC removal ratio of benzene showed 13.9~21.7% at 0.3kGy, but the concentration of benzene was less than 20%. This tells that the benzene can be removed more than 80%.
The analyzing results with GC-MS NIST library tell that the phenol was converted into hydroquinone, catechol, muconic acid, oxalic acid and acetic acid. The concentration of organic chlorinated compound in the dyeing wastewater was less than 10mg/ℓ. This compound was removed more than 95% at the irradiation of 0.3kGy. In addition to this, TCE and PCE showed the same removal characteristics and ratio. The intermediate products derived from the decomposition of PCE were analyzed as DCE, ClCH-C(OH)Cl2, ClCH-CHO, ClCH-COOH, ClCl=C(OH)Cl.
The polyester desizing agent was mainly composed of TPA and EG. When the TPA of 250mg/ℓ was irradiated, it was decomposed into benzoic acid, propanedioic acid, 2-pentenoic acid, silanol and trimethyl silane. The effect of electron beam on EG could be observed by the analysis of GC-MS. In here, the EG was decomposed into glycol aldehyde, formaldehyde, and hydroperoxide.
Aerobic biodegradability using active sludge was evaluated for the purpose of investigating the effect when the electron bean was irradiated into the dyeing wastewater containing polyester desizing agent. The removal efficiency of organic material was improved by 20~30% with the help of electron beam. There were no side effects such as sludge rising and sludge bulking took place in the irradiated wastewater.
During the experiment, we evaluated the activity of microorganisms. The value of measured dehydrogen activity enzyme (DHAe) was $20mgO_2/g$ VSS day. The coefficient of biodegradation is improved more than 1.5 times. Since the submerged bioreactors can sustain highly concentrated microorganism, it shows superior removal efficiency of the treatment of hard to degradable organic materials. In this research, we installed 1ton/day pilot plant. During the operation of this plant, we could determine the operation conditions for the separating membranes that is equipped in the bioreactor. This bioreactor was operated stable under the condition of 5 minutes suction pressure, 1 minutes reverse cleaning and the suction pressure of 200mmHg. In here we could minimize the contamination of membranes by keeping MLSS 5,000mg/ℓ constantly according to the operation cycle.
We constructed 1,000 ton/day actual plant in order to treat dyeing wastewater containing polyester desizing agent. This plant has 6 stage submerged bioreactors for the treatment of irradiated wastewater with a electron accelerator. When the 6 stage bioreactor is operated under the normal condition, we performed radio active tracer experiment to check the distribution of retention time. In addition to this, we can make sure that there is a dead volume in 1st stage reactor after applying 'perfect mixers in series model'. When the dyeing wastewater was treated with the combination of electron accelerator and 6 stage submerged bioreactor, the water quality regulation is satisfied. Furthermore, this combined treatment method guarantees at least 30% stable water quality. Also, we can discover many kinds of microorganisms such as Rotoria, Accella and Vorticella in the 6 stage bioreactor. The discovery of Arcella make us anticipate that the nitrification reaction takes place in the dead volume of 1st stage.
Through this research work, it was proved that the dyeing wastewater containing highly concentrated polyester desizing agent can be purified by the combined treatment method of electron accelerators and submerged bioreactors. Also, it can be concluded that the dyeing wastewater treatment facility can discharge the treated water with the stable water quality thanks to the addition of newly developed treatment process.
