Characteristics of dissolved organic matter after treatment by clinoptilolite-amended activated sludge in association with coagulation processes

This study was performed to evaluate the physicochemical properties of dissolved organic carbons (DOC) in the effluents coming from a clinoptilolite amended activated sludge with regard to various sludge retention times (SRTs) singularly run or in combination with a coagulation process. First, four laboratory-scale activated sludge reactors were concurrently operated in SRT 5, 10, 20, and 40 days to treat the effluent from a primary settling tank in a municipal wastewater treatment facility. From the experiments, DOC in the effluents in terms of concentrations of hydrophobic/transphilic/hydrophilic compositions decreased with the increase of SRT. In between SRT 5 and 40 day, the fractions of them ranged from 28.5 to 30.2%, 15.3 to 16.3%, and 54.1 to 56.1%, which suggested that their distributions were not significantly influenced by SRT. The molecular weight distribution (MWD) of DOC in that effluent was observed; >3 kDa was in the range of 22.2 to 30.4%, 1 to 3 kDa 14.5 to 27.0%, and < 1 kDa 50.8 to 55.2%. Specific ultraviolet absorbance (SUVA; UV254 absorbance/DOC concentration) of <1 kDa of DOC was lower than 2.0 while that of >1 kDa was greater than 2.0, regardless of SRTs. Increasing SRT attributed to escalating the level of SUVA, but reducing down carbohydrate/protein (C/P) and BOD5/CODCr ratios. After coagulation, DOC was additionally removed by up to at the average of 33.1% for whole range of SRTs where hydrophobic/ transphilic/hydrophilic fractions were each removed in the range of 29.4 to 47.6%, 50.0 to 63.6%, and 10.5 to 20.0%, respectively. The MWD of DOC showed that the higher the molecular weight, the greater extent was removed. In line with, <1 kDa of DOC was the lowest removed in the range of 15.9 to 24.5%, where hydrophilic and low molecular weight (i.e. <1 kDa) in the effluent were greatest observed ranging from 63.8 to 68.8% and 62.4 to 68.4%, respectively.