Analysis of Nutrient Removal using Membrane Thickening Aerobic Digestion

There are several long term water quality issues associated with discharging nutrients, specifically nitrogen and phosphorus into receiving water streams that are very difficult to manage. Due to these concerns many environmental regulatory agencies have either established nutrient discharge criteria or in the process of developing nutrient management plans. If a wastewater treatment plant is required to meet nutrient discharge limits the design of a sludge digestion system can be very critical especially for facilities that rely on biological nutrient removal (BNR) processes. This paper describes the membrane thickening aerobic digestion process technology that features advanced process control, techniques, and optimization that nearly eliminate nitrogen and phosphorus release in wastewater recycled to the head of the plant thereby protecting the effluent quality of a BNR activated sludge process. A membrane thickening aerobic digestion process offers this distinct advantage in contrast to other common biosolids handling processes without the need for chemical addition. There are up to sixteen operating membrane thickening aerobic digestion processes in the United States with several more in construction. Extensive nutrient data has been collected and evaluated from two existing operating facilities described in this paper then compared against the typical performance of other common biosolids handling processes such as anaerobic digestion, ATAD, aerobic digestion utilizing gravity thickening and decanting. After analyzing and comparing the results of these technologies it can be concluded that membrane thickening aerobic digestion offers the best nutrient management and removal performance in the liquid phase of a biosolids handling process.