Cost-Effective Upgrades to Wastewater Treatment Plants

Most of Bavaria’s wastewater treatment plants were built in the last century. Given the increasing demands on wastewater treatment and the growth of metropolitan areas, many of these plants are increasingly reaching their capacity limits. Improving sludge settling properties offers the opportunity to optimize existing facilities in a resource-efficient and cost-effective manner without having to build additional tank capacity.

01/01/2025 - 12/31/2026
Microscopic image of the sludge
Microscopic image of the sludge

Client:
Bavarian State Office for the Environment, Bavarian State Ministry of the Environment and Consumer Protection

Project Period:
2025–2026

People involved:
Prof. Dr.-Ing. Rita Hilliges
, M.Eng. Isabella Campestre

Contact via
wasser(at)hs-augsburg.de

Cost-Effective Upgrading of Wastewater Treatment Plants by Improving the Settling Properties of Activated Sludge

The term “aerobic granular sludge” (AGS) refers to compact activated sludge agglomerates that generally enable high settling rates. Thanks to improved settling properties, the biomass concentration in the biological stage can ideally be increased. This makes it possible, if necessary, to increase the plant’s capacity without having to expand the secondary clarifiers.

Microscopic images of the slurry from the upper section of the hydrocyclone (left) in Plant U (own illustration)
Microscopic images of the sludge from the hydrocyclone at the top of Plant U (own illustration)
Microscopic images of the slurry from the top of the hydrocyclone in Plant B (own illustration)
Microscopic images of the sludge from the top of the hydrocyclone in Plant B (own illustration)
Microscopic images of the slurry from the upper section of the hydrocyclone in Plant S (own illustration)
Microscopic images of the slurry from the upper hydrocyclone of Plant S (own illustration)
Microscopic image of the sludge from the hydrocyclone outlet of Plant U (own illustration).
Microscopic image of the sludge from the hydrocyclone outlet of Plant U (own illustration).
Microscopic image of the sludge from the hydrocyclone outlet of Plant B (own illustration).
Microscopic image of the sludge from the hydrocyclone outlet of Plant B (author's own illustration).
Microscopic image of the sludge from the hydrocyclone outlet of Plant S (own illustration).
Microscopic image of the sludge from the hydrocyclone outlet of Plant S (own illustration).

The goal of the research project was to provide scientific support to wastewater treatment plants where processes designed to improve sludge settling properties are already being used on an industrial scale. To this end, six pilot plants were examined; their operating data were analyzed, and the experiences of the plant operators were documented. 
In addition, a series of laboratory tests was conducted. These included, for example, determining the size distribution of the activated sludge, analyzing its settling properties, and conducting a microscopic examination of the sludge structure. The results obtained were compared with those from conventional wastewater treatment plants, SBR plants, and plants with a bio-P stage, which were examined and evaluated in a similar manner.

The investigations focused primarily on operational aspects, sludge properties, and sludge production, as well as on the process’s implications for future water law permitting procedures for such facilities.