Abstract

A new integrated multi-environment wastewater treatment technology has been developed for high-rate removal of organic carbonaceous compounds and inorganic contaminants, notably nitrogen and phosphorus, as well as suspended solids. This technology uses two separate but interlinked reactors containing four zones with different environmental conditions of aerobic, microaerophilic, anoxic and anaerobic for biological treatment as well as two clarification zones and a filtration unit for efficient separation of solids from liquid. The first reactor of the treatment system is designed based on the concept of airlift reactors. The influence of operating and process parameters such as the hydraulic retention time (HRT) and superficial gas velocity (U G ) on the hydrodynamic characteristics of the first reactor was examined. The liquid circulation velocity, gas hold-up and overall volumetric oxygen transfer coefficient increase with the increase of superficial gas velocity, while the mean circulation time decreases with the increase of air flow rate. The theoretical analysis of time dependent changes in the volume of mixed liquor demonstrated that liquid circulates from 363 to 1686 times between the three zones of aerobic, microaerophilic and anoxic before 99% of the bioreactor's content is replaced by the added wastewater. At air flow rates higher than 30 L/min, the mixing performance of the first reactor resembles the patterns observed in continuous stirred tank reactors (CSTRs). Using the openings with the size of 1/2" between the riser and downcomer at air flow rates of 15-30 L/min provide higher mass transfer coefficient and better zone generation, suggesting an improved treatment performance of the system.