Environmental consideration of dairy wastewater treatment using hybrid sequencing batch reactor

In this study, biological treatment of dairy wastewater industry was investigated. Two units, conventional sequencing batch reactor (CSBR) and hybrid sequencing batch reactor (HSBR) were -1 -1 operated, with the same source at organic loading rates (OLRs) of 1.75, 2.33, and 3.50 g COD L d . The seed sludge was collected from a treatment plant situated in an Egyptian Starch, Yeast and Detergents Company. The operating sequence of both CSBR and HSBR systems consisted of five steps: fill (2 h), react (aerobic: 19 h and anoxic: 1 h), settle (1 h), draw (0.5 h) and idle (0.5 h). In 2- 3 the hybrid system, plastic balls with specific surface area of 900 m m and porosity of 94% were randomly equipped at the bottom of the reactor. Results showed that, in the two reactors, the chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) removal efficiencies decreased with increasing OLRs. However, better performance was observed in the hybrid system. In the -1 -1 HSBR, at increasing the OLR from 1.75 to 3.50 g COD L d , COD and TKN removal efficiencies decreased from 98 to 92% and from 92 to 83%, respectively. Similarly, in the CSBR, removal of COD decreased from 88 to 76% and removal of TKN decreased from 71 to 54%, at the same range of OLR. Moreover, the hybrid system obtained higher specific substrate utilization rates (0.096-0.13 -1 -1 h ) and biomass growth yield coefficient (0.25-0.67 g VSS g COD), as compared to the CSBR. Good performance of the HSBR was explained by the wide variation of microbial community dominated in the system, including suspended heterotrophs and attached nitrifiers. The conventional treatment systems could be upgraded to handle higher organic loads by adding packed media in the biological units.