High Percentage Biosolids Digestion with Innovative Low Energy Technology

Baswood Corporation has worked with the Glasgow Water Company (GWC) to develop and refine its Aerobic/Anaerobic Integrated Microbial Succession (AIMS) technology, a patented biosolids digestion process that effectively reduces biosolids without the high energy requirements of other technologies. The AIMS technology was first installed at the GWC municipal wastewater treatment plant in Glasgow, KY in 2004. In 2007, the current configuration began operating as a demonstration installation for the digestion of biosolids produced by the GWC's activated sludge system. For the past three years, with the exception of a couple short test periods for treatment of primary wastewater (industrial and municipal), the Glasgow AIMS system has been continuously digesting biosolids.The AIMS system has maintained digestion rates of over 60% of the volatile suspended solids (VSS) in the processed biosolids. The technology accomplishes this with a hydraulic retention time (HRT) of just over 24 hours with both passive and active aeration, resulting in much lower horsepower (HP) requirements when compared to aerobic digestion. The process involves transferring the biosolids through a series of nearly identical fixed film reaction vessels, each containing a large, biologically diverse biomass. Each tank has aerobic, anoxic, and anaerobic zones, which allow the technology to maximize biological sequential digestion within a single process. These distinct environments work together to accelerate the digestion of biosolids.The most significant innovation of the patented AIMS technology is the DryCycle process. This occurs when a reaction vessel is taken off line for approximately 24 hours for the purpose of “pruning” the biomass. Removing the food source and dropping the liquid level in the vessel stresses the ecosystem, causing the healthy bacteria to feed upon weaker/older bacteria, as well as any retained residual biosolids. Before and after DryCycle vessel weight and volume measurements show biomass reductions ranging from 5% to 15%. In addition to increasing the digestion capacity of the system, the DryCycle works to maintain sufficient hydraulic flow characteristics within the biomass laden media. The system is designed so that the reactor vessels are cycled through the process, with one reactor vessel in DryCycle at all times.The GWC wastewater treatment plant (WWTP) consists of a primary clarifier, activated sludge system, secondary clarifiers, aerobic digester (secondary solids), anaerobic digester (primary solids), sludge drying beds and tertiary treatment processes. The biosolids discharged from the secondary clarifiers are either returned to the activated sludge system (RAS), wasted to the aerobic digester, or sent to the AIMS system for digestion. The digested secondary solids are either sent to drying beds or retained in a storage tank for land application. GWC has recently been required to adopt more stringent local limits in order to continue its land application practices.This paper will provide details of the AIMS technology and document its performance as a biosolids digester. It will also discuss the biosolids handling practices of GWC, and how it has affected its pretreatment program. Comparisons, such as energy consumption and dewatering characteristics, will be made between the GWC aerobic digester and AIMS system for biosolids digestion.