Abstract
With stringent wastewater discharge limits on nitrogen and phosphorus, membrane bioreactor (MBR) technology is gaining popularity for advanced wastewater treatment due to higher effluent quality and smaller footprint. However, higher energy intensity required for MBR plants and increased operational costs for nutrient removal limit wide application of the MBR technology. Conventional nitrogen removal requires intensive energy inputs and chemical addition. There are drivers to search for new technology and process control strategies to treat wastewater with lower energy and chemical demand while still producing high quality effluent. The NPXpress is a patented technology developed by American Water engineers. This technology is an ultra-low dissolved oxygen (DO) operation for wastewater treatment and is able to remove nitrogen with less oxygen requirements and reduced supplemental carbon addition in MBR plants. Jefferson Peaks Water Reuse Facility in New Jersey employs MBR technology to treat municipal wastewater and was selected for the implementation of the NPXpress technology. The technology has been proved to consistently produce a high quality reuse effluent while reducing energy consumption and supplemental carbon addition by 59% and 100%, respectively. Lab-scale kinetic studies suggested that NPXpress promoted microorganisms with higher oxygen affinity. Process modelling was used to simulate treatment performance under NPXpress conditions and develop ammonia-based aeration control strategy. The application of the ammonia-based aeration control at the plant further reduced energy consumption by additional 9% and improved treatment performance with 35% reduction in effluent total nitrogen. The overall energy savings for Jefferson Peaks was $210,000 in four years since the implementation of NPXpress. This study provided an insight in design and operation of MBR plants with NPXpress technology and ultra-low DO operations.
Highlights
Regulations related to the nitrogen and phosphorus concentrations in the discharged wastewater are becoming more stringent
It is recommended that the aeration tank has a dissolved oxygen (DO) level of 2.0 mg/L for optimum nitrogen removal [17,19]
Before the NPXpress conversion, the DO level in the aeration tanks of Jefferson Peaks Water Reuse Facility (WRF) was higher than 2.0 mg/L
Summary
Regulations related to the nitrogen and phosphorus concentrations in the discharged wastewater are becoming more stringent. Compared to conventional activated sludge systems, the operating costs of MBR systems are still quite high due to air scouring for membrane cleaning and aeration demand for carbon and nitrogen removal [3]. Conventional nitrogen removal requires substantial oxygen input for nitrification and supplemental carbon source for denitrification. There have been significant interests in the recent past in the development of new nitrogen removal processes that reduce energy and chemical requirements for conventional nitrification-denitrification processes and can be applied to optimize MBR plants. Several recent advanced approaches in nitrogen removal technology include intermittent aeration, simultaneous nitrification and denitrification (SND), and the enrichment of novel microorganisms such as anaerobic ammonium oxidation (anammox) and ammonia oxidizing archaea (AOA) [4,5]. Studies have shown that aeration energy can be saved by using an intermittent aeration process to create a so-called “swing-zone” while achieving a similar level of nitrification and denitrification efficiency compared to continuous aeration processes [6,7,8]
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