ScienceAsia 25 (1999) : 121-126 |doi: 10.2306/scienceasia1513-1874.1999.25.121

Treatability of Dye Wastewaters by Conventional and Anoxic + Anaerobic/Aerobic SBR Processes

Jintana Pansuwan^a, Thongchai Panswad^a,* and Jin Anotai^b

ABSTRACT: Several studies have reported that the color in dye wastewaters could be removed effectively by a combined biological treatment, ie, anaerobic digestion followed by aerobic degradation. Therefore, the Phoredox or anaerobic/aerobic process, which is a biological phosphorus (BPR) system, seems to be a very good combination for the decolorization of dye wastewater from the textile industry. This study compared the performance of conventional and anoxic+anaerobic/aerobic (A+A/A) sequencing batch reactors (SBRs) in removing organic matter, total kjeldahl nitrogen and color. The two SBR systems with 8 days of sludge age were operated under the same feeding, reacting, settling and withdrawal periods. However, the 10-hour reaction period of the conventional SBR was totally aerobic whereas that of the A+A/A system was separated into 2 hours of anoxic+anaerobic followed by 8 hours of aerobic conditions. The feed wastewaters contained specific target dyes, ie, disperse, sulfur and reactive dyes, which were collected directly from the treatment plants of local textile factories. At the steady state, it was found, as expected, that both systems were able to reduce the chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) of the wastewaters to the same extent. The phosphorus removal efficiency of the A+A/ A system was not so good, approximately only twice as high as that of the conventional system due to limited volatile fatty acids and anaerobic contact time. The visual color removal of the A+A/A system was impressive and seemed to be a step ahead of the conventional system. The anaerobic digestion is considerably a necessary step for decolorization of dye wastewaters. Disperse dye was degraded to form non-color by-products whilst the sulfur and reactive dyes were degraded to yield colored by-products which were readily degraded under aerobic environment. The apparent color removal efficiencies of both models measured in terms of color intensity as space unit (SU) and ADMI were, however, not convincing. This is probably due to turbidity and/or solute interference during the color measuring process.

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a Department of Environmental Engineering, Chulalongkorn University, Bangkok 10330, Thailand.
b Department of Environmental Engineering, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand.

* Corresponding author: Tel: +66-2-218 6669 Fax: +66-2-218 6666 E-mail: pthongch@chula.ac.th

Received 29 Jan 1999