A New Strategy to Handle Peak Loads in Membrane Bioreactor (MBR) Processes Using Oxygen

A new system of handling peak BOD loads using high purity oxygen (HPO) and the In-Situ Oxygenator (I-SO™) mechanical mixer in membrane bioreactors (MBR) is proposed. The I-SO™ system allows efficient use of HPO in conventional open (non-covered) aeration tanks, for both greenfield and retrofit MBR installations. Economic analyses were conducted for the new method and the results are compared with those for conventional air-based diffuser systems. Wastewater flow and BOD demand patterns from a municipal wastewater treatment plant (WWTP) were used for the analyses. The average flow rate and BOD of the WWTP were 29,500 m3/day and 195 mg/L, respectively. Due to the extremely high oxygen transfer efficiency (OTE) of the I-SO™ system (89.9% on average), operating costs were only slightly higher than those of an air-based fine pore diffuser system (with an OTE of 7.0% at 10 g/L MLSS). Furthermore, the I-SO™ system with HPO could save a significant capital cost due to its simple design and wide range of oxygenation capacity. In fact, the I-SO™ system provides high OTE (90%) at dissolution rates while transferring up to 2.59 ton/day of oxygen at 10 g/L MLSS. It can also easily provide higher O2 dissolution capacity for peak loads at reduced OTE. For example, the I-SO™ system described here provides an OTE exceeding 90%, at average loads (1.81 ton/day of O2), and can dissolve 3.36 ton/day of O2 to meet peak loads at an OTE of 66%. Estimated annual cost savings (including capital amortization) were estimated at 293,000 with the I-SO™ system and HPO, while providing additional non-financial benefits.