Abstract
A high-rate biological contactor process (HRBC) can be used as primary treatment instead of a clarifier to remove particulate, colloidal and soluble fractions of organic matter via biosorption plus flotation and divert it to anaerobic digestion for methane production, simultaneously reducing secondary aeration energy demand. Pilot and bench tests were conducted at a range of contact times (15-60 min) and contactor dissolved oxygen (DO) (0.2-2.0 mg/L) using waste activated sludge (WAS) from a trickling filter/solids contact (TF/SC) process in the HRBC. Biosorption performance was lowest when contact times were <30 min and unstable at DO < 0.5 mg/L. The overall average of 20% sCOD capture was similar to previous findings by others using WAS from conventional AS. The biomethane potential (BMP) of the HRBC float material can be as high as that of primary sludge (340-400 mL CH4/g VS), which is much greater than WAS. Operating the HRBC with a long contact time (>30 min) or with high DO (>1 mg/L) increases the amount of biosorption but reduces the BMP of the float. It was also found that biosorption only effectively occurs when a WAS is paired with the wastewater from the same facility.
Highlights
Municipal wastewater treatment plants (WWTPs) are large utility power consumers
850 mL of the biosorption effluent was placed in the dissolved air flotation (DAF) reactor (1-Litre plastic graduated cylinder fitted with an inlet/outlet valve located at the 300 mL level)
For the ffCOD removal, 16 mg/L and 30 mg/L ffCOD were removed for the 5 and 10% waste activated sludge (WAS) ratios respectively which represented 11 and 21% removal based on an average influent ffCOD of 146 mg/L. These results indicate that absorption is directly proportional to the amount of WAS. Both pilot and bench-scale test results showed that biosorption occurred using trickling filter/solids contact (TF/SC) WAS in the high-rate biological contactor (HRBC)
Summary
Municipal wastewater treatment plants (WWTPs) are large utility power consumers. The impact of HRT, DO, and TSS on the performance of the HRBC system using TF/SC WAS, the bio-methane potential (BMP) of the DAF thickened float and primary sludge, and the biosorption performance using WAS from various secondary treatment processes were evaluated. A Captivator pilot unit rated for 1,136 m3/d (300,000 gal/d) from Evoqua was used to examine the impact of HRT, DO and TSS on the HRBC system using TF/SC WAS and the BMP of the DAF thickened float material.
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