A recent study performed at the Beaudesert Sewage Treatment Plant in Queensland, Australia, discovers how one trickling filter plant maximizes existing infrastructure to improve nitrogen removal from treated wastewater.

By Yu Dai, CH2M HILL Process Technologist

Yu Dai was co-author of a paper entitled “Enhanced Nitrogen Removal in Trickling Filter Plants,” recently published by the International Water Association (IWA).

Beaudesert Sewage Plant - Queensland, Australia

Due to the technology limitation of the existing filter process, the Beaudesert Sewage Treatment Plant in Queensland, Australia, has been struggling to meet modern treatment standards, in particular in regards to nutrient reduction requirements. Upgrading the plant to the widely-adopted activated sludge process would resolve the issue; however, it is not financially justified because there are plans to build a new sewage treatment plant in an adjacent catchment (new development) within five years, and the flow from the Beaudesert STP would utilize this new plant. Therefore, a feasibility study was initiated to investigate the best economic option to optimize the current system’s performance and maximize the treatment capacity. The study evaluated ways to help the plant reliably meet the discharge licence and cope with the projected population growth until the proposed new sewage treatment plant is constructed and operating to successfully divert sewage from the Beaudesert plant.

Tracking and analyzing data trends over the past several years indicated this ancient Beaudesert trickling filter plant had been consistently achieving substantial nitrogen reduction—an exceptional accomplishment for this type of process configuration. Exploring the ‘mystery’ behind this exceptional performance, the team leading the study hoped to uncover a way to boost the system performance.

By selectively sampling the process streams of interest and measuring the relevant nitrogen content of the samples, the team discovered that the nitrogen reduction origin was the primary sedimentation tanks. A considerable amount of nitrate was re-circulated from the trickling filters to the primary sedimentation tanks and was denitrified in the settlers. This was an interesting and unprecedented phenomenon and no doubt an inspiring breakthrough to the study.

Determined to solve the mystery behind the plant’s performance, the team further investigated whether the denitrification performance in the primary sedimentation tanks could be used to lower the effluent nitrogen level, seeking answers to questions such as: what is the determining factor for the process improvement, and what is the limitation of this superb nitrogen reduction process?

With a number of question left unanswered, a nine day site trial was designed to test the system and determine the system’s potential reserve nitrogen reduction. In order to test high flows, one of the two trickling filters was shut down and a temporary recycle stream was set up via a portable diesel pump to provide higher recirculation flows matching the increased influent flows. The trial results proved to be very promising and led to the conclusion that the plant could achieve a higher degree of nitrogen reduction under the current process configuration and assets, as long as minor process modifications were implemented, such as increasing the capacity of the recycle pump station.

The findings of this feasibility study are of great benefit to not just the Beaudesert trickling filter plant, but also to the similar trickling filter plants worldwide not originally designed for any degree of nutrient removal. The outcomes of this work demonstrate the ability of these plants to effectively improve their effluent quality and positively improve performance relative to their receiving environments.

If you are interested in learning more about this project, you can purchase and download a copy of the full report on IWA Publishing Online.

Yu Dai is a process technologist with the Water Business Group in CH2M HILL’s Brisbane office. She has more than ten years of experience in the wastewater and water treatment process design and development area. Graduating with a PhD in Advanced Water Management Centre at UQ, she has been involved in a number of wastewater and water treatment plant upgrading strategy works and design works. She takes great initiative to provide clients the quality service and deliverables within the set time frame. Yu Dai specializes in the areas of biological nutrient removal, continuous flow and sequencing batch reactor (SBR) process design and monitoring, wastewater and water treatment process design and modeling (BioWinTM), process control and optimization.