Abstract
Paper mills generate varieties of pollutants depending upon the type of the pulping process. The wastewaters discharged from these mills have high chemical oxygen demand (COD) and colour, in which indicating high concentrations of recalcitrant organics. This study was conducted using a Granular Activated Carbon – Sequencing Batch Biofilm Reactor (GAC-SBBR) of 3.0 L working volume, operated in an aerobic condition and packed with 200 gL-1 of 2-3 mm granular activated carbon (coconut shells) as a medium for the biofilm growth. For the six of months, the hydraulic retention time (HRT) was set at 36 hours and later it was adjusted to 24 hours in order to evaluate the performance of the system. The treated wastewater samples for these studies were taken from a recycled pulp and paper mill factory in Pahang, Malaysia with 4 different batch characteristics. The adsorbable organic halides (AOX) that had been determined and treated were pentachlorophenol (PCP), 2,3,4,5-tetrachlorophenol (2,3,4,5-TeCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,4-dichlorophenol (2,4-DCP), 2-chlorophenol (CP) and phenol at various concentration ranges. The Monod growth kinetic parameters for the process specific growth rate coefficient (µh), half saturation coefficient (Ks), endogenous decay coefficient (DH) and Yield coefficient (YH) obtained were 0.0037 hr-1, 65.23 mgL-1, 4x10-5 hr-1 and 0.36 mg/mg, respectively. Analysis of the growth kinetic parameters in GAC-SBBR had deduced that the system was suitable to operate on long biomass retention time (BRT) under anoxic condition. The results also indicated that the biofilm attached onto granular activated carbon (GAC) can substantially remove these recalcitrant organics in the wastewater, within the range of 10 – 100% AOX removal depending on the selected HRTs.
Highlights
Chloroorganic compounds such as phenol and chlorophenol have become a major concern to public health due to their toxicological and recalcitrant characteristics
The results indicated that the biofilm attached onto granular activated carbon (GAC) can substantially remove these recalcitrant organics in the wastewater, within the range of 10 – 100% AOX removal depending on the selected hydraulic retention time (HRT)
This study has shown that selection of a suitable HRT plays an important role in the chemical oxygen demand (COD) as well as in the AOXs removal
Summary
Chloroorganic compounds such as phenol and chlorophenol have become a major concern to public health due to their toxicological and recalcitrant characteristics. In order to remove these recalcitrant organics from industrial wastewater, the high costs activated carbon (AC) adsorption, as final treatment step is indispensable. This normal conventional adsorption technique has the disadvantages of inadequate exploitation of the adsorptive capacity, high cost of conventional thermal or chemical regeneration process for spent AC as well as decreasing adsorptive capacity of the AC, ultimate disposal problem, and toxic products such as chlorodibezodioxins might be generated in the thermal oxidation process (Kolb and Wilderer, 1997; Jaar and Wilderer, 1992). By introducing GAC inside the SBR, the GAC adsorption process was able to reduce the toxic effects of the pollutants and increase the stability of the pollutant removing system (Xiaojian et al, 1991; Caldeira et al, 1999; Jaar and Wilderer, 1992)
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