The study of treatment functions of activated sludge/contact aeration combined system

The activated sludge/contact aeration (AS/CA) combined system was created by adding biological contact filters into the rear sector of the activated sludge tank. The system contains both suspended and fixed microorganisms. This combined system presents the advantages of both AS system and CA system. It also improves the disadvantages of these two individual systems. A special feature is that the AS/CA system can enhance the removal ratios of the true color, oil and grease.
Both AS/CA and AS-only systems were tested to treat the synthetic domestic sewage. The BOD, COD and color removal ratios of both treatment systems were compared. The results showed that the pollutant removal ratios of the AS/CA system were higher than those of the AS-only system. When the oil and grease was spiked into the sewage, oil and grease concentrations were gradually increased from 15 mg/L to 60 mg/L. When the influent oil and grease concentration was 60 mg/L, the effluent concentration of the AS system was 13 mg/L, which was higher than 10 mg/L, the effluent standard of oil and grease. However, in the AS/CA system, the effluent oil and grease concentration was 8 mg/L, which was under the regulated standard. When the influent oil and grease concentrations reached 120 mg/L, the effluent concentrations of both systems exceeded the regulated standard.
A pilot treatment plant was constructed and located in a slaughterhouse. The AS/CA system was operated with eight-hour hydraulic retention time (HRT), and the results indicated that average effluent COD = 71 mg/L (94% removal ratio), BOD = 29 mg/L (91% removal ratio), SS = 43 mg/L (86% removal ratio), and true color = 47 unit (84% removal ratio). The AS/CA system can treat the oil and grease concentration from 54 mg/L to 7 mg/L (87% removal ratio). In the case of slaughterhouse wastewater treatment, the sludge presented as golden color in AS and CA tanks. The effluent water quality can meet Taiwan’s regulation, and the AS/CA system was much more stable.
In terms of the removal ratios of SS, BOD and COD of the leachate, these ratios in AS/CA system are 10.3%, 6.4% and 4% higher than those ratios in AS system, respectively. The AS/CA system efficiently decomposes the leachate, resulting in a 35.2% ~ 42.5% removal ratio of COD and a 59.9% ~ 65.4% removal ratio of BOD.
Under eight hours of HRT, the AS/CA system was able to treat restaurant wastewater which had fluctuating quality, and to reduce the standard deviations of COD and BOD from 115.8 and 158 to 40.5 and 8.8, respectively.
The kinetic parameters derived through the linear regression analysis of COD data yielded a volume loading P value of 625 g/m3•day for the AS tank, greater than 233 g/m3•day for the CA tank. The p value of 455 g/m3•day for the complete AS/CA system was between those for AS and CA tanks. The Ks values of 41 mg/L for the AS tank was greater than 20 mg/L for the CA tank.
Denaturing Gradient Gel Electrophoresis (DGGE) analysis was applied to samples taken from activated sludge system, contact aeration system, and AS/CA system. The analytical results suggested that when these three systems were compared, the microbe diversity and quantity of the combined system was relatively high.