Halogenated organic compounds constitute one of the largest groups of environmental pollutants as a result of their wide spread use as herbicides, insecticides, fungicides, solvents, hydraulic and heat transfer fluids, plasticizers, and intermediates for chemical syntheses. Because of their toxicity, bioconcentration, and persistence, and the uniquitous distribution of halogenated compounds in the biosphere has caused public concern over the possible effects on the quality of life.
The purpose of this study was to development biological process for treatment of wastewater including refractory material. The contents of this research were consisted of five parts. First topic is degradation and toxicity of 2,4,6-TCP in anaerobic system, second topic is suggestion of mechanism for organic removal in single sludge anaerobic-aerobic process, third topic is continuous operation for single sludge anaerobic-aerobic process using USB (up-flow sludge blanket) reactor, forth topic is treatment of wastewater including 2,4,6-TCP single sludge anaerobic-aerobic process using USB and fifth topic is suggestion of degradation mechanism for 2,4,6-TCP in single sludge anaerobic-aerobic process.
In first topic, the research is to find the relationship between organic content and toxic compound in anaerobic system. In an attempt to investigate the degradation and the effect of toxic compound on methane fermentation, 2,4,6-TCP was used as a toxic compound. As the 2,4,6-TCP showed more toxic at low COD concentration, the effects of toxicity can be relieved by increased organic loading rate when toxicants were introduced to anaerobic reactors. When toxicants were fed to the anaerobic treatment system, the stable operation could be maintained by higher biomass concentration indicating that the high-rate anaerobic treatment such as UASB system would be better than conventional anaerobic processes in these cases. As organic concentration increased, 2,4,6-TCP concentrations in the serum bottles decreased proportionally resulting in the drop of toxicity in the anaerobic system. The 2,4,6-TCP fed into UASB reactor was dechlorinated under methanogenic conditions, resulting in the formation of dechlorinated products, such as 2,4,-DCP, 4-CP and phenol. Thus succession treatment must be needed to remove intermediate products as 2,4-DCP, 4-CP and phenol.
USB reactor shows hydraulic characteristics of plug flow type in hydraulic retention 1 hr and rotating speed of mixer 0 and 3 rpm.
In third experiment, mechanism for uptake, degradation, storage and release of susbstrate for single sludge using anaerobic-aerobic system was suggested for readily biodegradable organic material and refractory material. Readily biodegradable organic material was released by-products and refractory organic material was released raw material without degradation. In the anaerobic conditions sludge, glucose acclimated sludge with sulfate in single sludge anaerobic-aerobic system was uptake and release more than glucose acclimated sludge without sulfate. However, in aerobic condition sludge, acclimated glucose sludge without sulfate was uptake and release more than acclimated glucose sludge with sulfate.
USB reactor used for treatment of high strength organic wastewater. The volume ratios of aerobic and anaerobic reactor were 1, 1.7 and 2.1. At large volume ratio of aerobic to anaerobic reactor, COD increased cause growth of filamentous bacteria because of high COD concentration of anaerobic reactor effluent. Thus volume ratio of aerobic to anaerobic reactor may be important factor of operation and design on the treatment of high strength organic material using single sludge anaerobic-aerobic system. SS concentrations in the USB reactor maintained average 30000 mg/l to 50000 mg/l. This will be indicated that USB reactor could be played function of thickener.
In the acclimated and unacclimated 2,4,6-TCP sludge, organic material affected uptake and release of refractory material. The uptake of 2,4,6-TCP for acclimated 2,4,6-TCP sludge with organic was 91.9 % of without organic and uptake of 2,4,6-TCP for unacclimated 2,4,6-TCP sludge with organic was 83.3 % of without organic. While The release of 2,4,6-TCP for acclimated 2,4,6-TCP sludge without organic was 81.1 % of sludge with organic and release of 2,4,6-TCP for unacclimated 2,4,6-TCP sludge with organic was 58.4 % of sludge without organic. 2,4,6-TCP in the sequential anaerobic and aerobic conditions was degraded thoughtfully without intermediate products. 2,4,6-TCP was up-taken and released during anaerobic period and degraded and released during aerobic period.
During the continuous operation, 2,4,6-TCP was degraded thoughtfully to mineral without intermediate products. Degradation mechanism for refractory material in the single sludge anaerobic-aerobic system has two processes. One is uptake and release under anaerobic condition and the other is degradation and release and uptake under aerobic condition.
The conclusions of this research as follows.
Degradation of 2,4,6-TCP using anaerobic digestion process produce intermediate product such as 2,4-DCP, 4-CP and phenol and need succession treatment to degrade thoughtfully.
The removal mechanism of single sludge using sequential anaerobic-aerobic system has four functions. The first is uptake, second is storage, third is release and last is degradation. There are two difference, one is readily biodegradable organic, other is refractory organic such as 2,4,6-TCP. After uptake organic, readily biodegradable organic release by-products but refractory organic release raw organic.
High strength wastewater can be treated in single sludge anaerobic-aerobic system using USB reactor. Here, USB reactor for anaerobic condition can be used instead of thickener because there are high strength SS concentration.
Refractory material(2,4,6-TCP) was degraded to mineral thoughtfully without intermediate products in the single sludge anaerobic-aerobic system. 2,4,6-TCP was up-taken and released during anaerobic period and released and degraded during aerobic period. Thus 2,4,6-TCP can be treated without succession treatment by single sludge anaerobic- aerobic system.