Novel Vortex Powered Aeration: Performance Of A Large Scale System In An Abattoir Wastewater Treatment Plant

Introduction
The Vortex Powered Aerator Standard is a novel patented wastewater aeration technology (provided by VorTech Water Solutions Ltd) that adopts cyclonic flow with advanced flexible control to achieve high treatment efficiency in activated sludge systems. The innovation was recently deployed at a large-scale industrial abattoir as part of an onsite wastewater treatment plant (WwTP) upgrade. The challenge at the facility (which processes circa 274 livestock per day) was to provide a low total expenditure aeration solution for an activated sludge system, to enhance resource efficiency, reduce trade effluent charges, reduce carbon emissions, and minimize noise pollution. This paper will provide a first summary of the full-scale technical performance of the innovative VPA solution, following the first six months of operation at this site.
Challenges and Objectives
An abattoir WwTP recently underwent a major upgrade to include a new activated sludge treatment facility. The abattoir originally had basic treatment consisting of a balance tank and dissolved air floatation (DAF), prior to discharge to the local municipal sewer network. Prior to the upgrade, the average biochemical oxygen demand (BOD5) and ammonium concentrations in the final discharged effluent were of the order of 1,500 to 2,500 mg/L and 100 to 250 mgN/L respectively. Site operators identified that continuing operations in this fashion was not sustainable due to several concerns: - The effluent concentrations discharging to the sewer were high relative to municipal waste, and furthermore these concentrations fluctuated seasonally. This mounted pressure on the downstream municipal WwTP. - Each cubic meter of effluent discharged to the sewer was subject to a trade effluent charge ranging from $2.32 to $2.52 per m3. With flows through the plant of the order of 200 to 300 m3/day, the cost of trade effluent alone ranged from $15,900 to $18,600 per month. - The DAF system was operated at full capacity to maximize BOD5 removal and to minimize trade effluent charges. This resulted in significant quantities of chemical usage which also incurred a heavy monetary cost and carbon footprint at the facility. Based on the above, the operator decided to upgrade the existing treatment plant to a full activated sludge treatment facility using sustainable aerobic and anoxic treatment. However, the site posed several unique challenges and objectives which influenced the choice of aeration technology at the facility: - Electricity prices had risen considerably, particularly in 2021. With aeration accounting for a significant portion of a typical treatment plant's electricity bill1, there was a major priority to consider the most energy efficient aeration system. - Noise pollution was a serious consideration as the nearest domestic dwelling less than 50 m away from the proposed location of the aeration tank. - Pollutant concentrations such as BOD5, ammonium and total nitrogen were known to increase at times by as much as 300%, therefore system control flexibility was crucial.
Solution
The solution was to intercept the DAF effluent line with a new activated sludge system comprising Vortex Powered Aeration (VPA), an aerobic-anoxic fully mixed reactor and a clarifier (see Figure 1 and https://www.youtube.com/watch?v=-H5RetXpZEY). The balance tank and solids holding tank were also upgraded, with new tanks along with mixers and pumping lines. Following the aeration tank, water gravitates to a clarifier where mixed liquor settles, and clarified supernatant is discharged to the sewer. The aerobic-anoxic reactor comprised a 17.05 m diameter glass lined steel tank with a liquid depth of 5.1 m and had a volume of 1,168 m3. A Vortex Powered Aeration Standard-5 (VPA-S5; 63 kW) system and a submersible mixer (10 kW) were installed in the activated sludge tank. An advanced control interface was provided to address rapidly varying demands at the facility.
Results Summary
The full paper will present results pertaining to oxygen transfer, aeration efficiency, process efficiency, noise, aerosols, and maintenance, along with projected lifecycle cost and carbon emission savings over 20 years. Key results are outlined as follows: - Micro- to fine-bubble characteristics, velocity and turbulence distributions (supported by computational fluid dynamics simulations) indicated desirable conditions for oxygen transfer with no detrimental impact on sludge floc. - In-process oxygen uptake rates were measured to be as high as 130 kgO2/h which were catered for by the 63 kW VPA, implying excellent in process aeration efficiencies2,3. - The average BOD5 and ammonium removal efficiencies were 98% and 99% respectively (see Figure 2). - The specific energy consumption was measured using the energy consumed per mass of BOD5 equivalent removed and the energy consumption per unit livestock processed. Compared to another similarly sized abattoir facility (owned by the same client) which uses fine bubble diffused aeration (FBDA), the VPA reduced the kWh/kgBOD5 equivalent removed and kWh/unit livestock processed by 30% and 41% respectively (see Figure 2). - Very low noise and no splashing or aerosol generation was recorded at the facility. - Inspection of the pump (the only moving part of the VPA), after circulating 5 million tonnes of activated sludge, demonstrated no sludge or fibrous build up on the pump or guide vanes, demonstrating low maintenance requirements for the machine. Conclusion & Impact This paper will provide a first, full-scale technical performance summary of the innovative Vortex Powered Aeration system in a large-scale abattoir WwTP. Technical in-situ performance data pertaining to oxygen transfer, aeration efficiency, process efficiency, noise, aerosols, and maintenance will be presented and discussed. The VPA's energy efficiency performance was compared to a similarly sized abattoir facility which uses FBDA, and a 30% reduction in specific energy consumption (using the BOD5 equivalent metric) was noted. Furthermore, the electricity consumed in treatment on the basis of livestock units processed was 41% lower than the facility utilizing FBDA. In financial terms, this report demonstrates that the VPA system will save the facility circa $82,000 per annum. Costs per livestock processed will fall from $4.48 to $3.02, costs per cubic meter of effluent discharged will fall from $2.39 to $1.63, and there will be a 20-year total lifecycle saving of $1.23M.