Wastewater treatment plants looking to meet new, more stringent effluent requirements, improve their energy efficiency and increase treatment capacity can benefit from a biological active-settling technology.
As a solution, we offer an innovative settler design that can easily be retrofitted to existing plant infrastructure.
Design
Elevate Operations With Advanced Pre-Treatment
Conventional primary clarifiers take a purely physical approach to the settling of particulate matter, where nitrogen and phosphorus removal is minimal. The Triple A Settler (AAA) — an acronym for Alternating Activated Adsorption — applies a flow-through sludge blanket that maximizes the redirection of organic carbon to anaerobic digestion, increasing nitrogen and phosphorus removal while improving the secondary treatment energy balance and performance.
This innovative settler design boosts primary clarification while minimizing chemical and energy consumption.
Combined Design Elements Provide Optimized Performance
The Triple A settler consists of a compact pre-treatment unit that integrates all features of an A-stage with a dual-tank-configuration to offer biomass activation, biomass recycling, sludge wasting and waste sludge thickening. This combination of features makes AAA well-suited to retrofit existing primaries at a hydraulic retention time of approximately two hours. The process principle is operational simplicity — the entire process is fully air-driven with no mechanical mixers or pumps.
The process goals are:
- Increasing capacity by removing:
- approximately 60% of chemical oxygen demand (COD).
- approximately 20% of nitrogen.
- approximately 30% of phosphorus.
- Reducing aeration demand at an increased methane yield through carbon redirection.
- Providing a net zero and/or net positive treatment plant.
- Integrating thickening to approximately 5% solids to directly feed digesters.
- Reduce cake-solids disposal via a high primary/secondary sludge ratio of approximately 0.7.
Advantages
Proven Success in Real Environments
Triple A was implemented at a brownfield facility at the Rottenburg wastewater treatment plant (WWTP) in Germany (46,000 PE). The process was retrofitted into existing tankage to help improve treatment capacity. The AAA system eliminated 66% COD (Figure 1) and 43% phosphorus on average and achieved an average total nitrogen elimination rate of 36%, as shown (Figure 2).
Figure 1: COD removal performance.
Figure 2: TN removal performance.Process
Elevate Operations With Advanced Pre-Treatment
The system’s typical process cycle is one hour (Figure 3) with each cycle consisting of at least four phases: inflow/outflow (30 minutes), wasting, aeration and settling (Figure 4).
In the first phase, the inflow drives the outflow through the effluent decanter. All other processes are air driven via blower air including aeration, mixing, air-lift sludge wasting and air-lock decanting. The aeration is oxygen-controlled at a standard set point of 0.5-1 mg/L dissolved oxygen (DO).
The sludge-wasting phase duration is dependent on the solids concentration present within the activation/settling tank which is typically kept in the range 1 and 2 g/L.
Triple A can be implemented at greenfield and brownfield sites on both small and large scales. Below, photos from the Alta Badia WWTP in Italy display the AAA container configuration and the construction process required to convert the sludge-hopper zones of the existing primary clarifiers to the AAA thickeners (Photos 1 and 2).
Components
The AirLock decanter follows a diving bell design, utilizing a pressurized air cushion to displace a water volume and prevent any sludge from entering the decanting system during the mixing/aeration process (Graphic 1). Photo 3 shows the top end of an AirLock decanter featuring the air pipe that fills and releases the air cushion.
AirLifts are employed to generate high-pressure suction to collect waste sludge during the short wasting phase which typically lasts two to three minutes. A collection pipe transfers the sludge to the adjacent thickener. Both the AirLift and the aeration system use the same source of process air. The AirLift and aeration system operate during the same cycle phase, when the AirLock decanter is full.
Distribution pipes are crucial for routing the raw sewage influent into the settled sludge blanket at the bottom of the reactor as well as for provisioning sufficient contact for biosorption. Computational fluid dynamics (CFD) support the optimum layout of distribution pipes, laterals and openings.
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