SmartAeration is an engineering system for the control of aeration at biological treatment works. The oxygen supply and the mixing of the mixed liquor are carried by separate loops, and each loop is driven by a quantity of its own: the oxygen one by the demand of the biological process, the mixing one by the minimum hydraulic intensity required.
An aeration tank takes a large share of the electricity of the works, and the air fed into it works on two duties at once: it saturates the mixed liquor with oxygen and holds the activated sludge in suspension. Control is usually run from a single parameter — most often dissolved oxygen — or is not run at all, and then the blower simply stays on. SmartAeration separates the two duties and gives each a loop of its own with its own test of sufficiency.
It is meant for biological treatment works with an aerated reactor: municipal and package plants, the works of hotel and residential complexes, industrial sites. The development suits new construction and existing structures alike, where diffusers, blowers and control logic are modernised without replacing the plant as a whole. It is neither a single instrument nor one setting for every site: the make-up of the unit and its regimes are chosen for the particular aeration tank.
Air in an aeration tank lets the microflora oxidise the organics and at the same time keeps the sludge flocs in suspension, so that they neither settle nor leave stagnant pockets behind. The two duties make different demands. Oxygen demand follows the load and shifts through the day; mixing calls for no such quantity of air — the minimum hydraulic intensity at which the sludge does not settle is enough for it.
Control by dissolved oxygen alone sees only the first of them. There is then oxygen enough and possibly mixing too little: the sludge settles, stagnant pockets appear, and the contact between the wastewater and the biomass gets worse. The opposite safeguard — supplying air with a margin so that mixing is guaranteed — sets the airflow by the worst case and is paid for in blower power and in wear.
The split rests on a physical difference between the types of aeration. Fine-bubble elements transfer oxygen into the water more efficiently, but once the airflow drops they may fail to mix the whole volume of the reactor. Coarse-bubble aeration transfers oxygen worse, but as a means of mixing and of keeping the sludge from settling it can be effective. The same cubic metre of air does different work depending on the element it passes through.
The oxygen loop is therefore driven by the actual demand of the biological process, while the mixing loop comes in only when the first no longer provides the hydraulic activity required. If the fine-bubble aeration mixes well enough, no extra air is supplied at all; if its delivery has fallen below the hydraulic minimum, the second loop is raised by just as much as it takes to keep the sludge suspended.
The difference shows in the night regime. The inflow of wastewater falls, the oxygen demand falls with it, and the system cuts the air delivery. Cutting it too deeply would settle the activated sludge, and the plant would meet the morning peak with the sludge on the floor. Separate loops let the oxygen delivery drop to what the process needs without dropping below the hydraulic threshold.
The unit is assembled from fine-bubble aeration, an additional mixing loop, sensors of dissolved oxygen, of airflow and of pressure, a control cabinet holding the algorithm that computes the delivery, and a link to the plant automation or to SCADA. The set is not fixed: on a working site part of that is already in place, and only what the chosen control logic lacks is replaced or added.
The three measured quantities serve not only the calculation of the delivery but the diagnosis. A fall in dissolved oxygen means the process is short of air at the delivery set. A rise of pressure in the air main points to fouled diffusers or to resistance in the pipework itself. A discrepancy between the actual airflow and the set one calls for a check of the supply equipment, and it shows before the deviation reaches the quality of treatment.
Works built without automation drift away from their own design over the years: the flow and the composition of the effluent change, and so do the number of users, the seasonal peaks, the state of the diffusers and of the blowers, the properties of the activated sludge and the hydraulics inside the reactor. Replacing the plant outright is not the only answer to such a drift — part of it is removed by changing diffusers, redistributing the air, fitting sensors and altering the control logic.
Where the boundary between those two answers runs is decided by a survey, not by a catalogue. The volume of the aeration tank, the daily and hourly flow, the organic load, the concentration of activated sludge, the aeration scheme in place and the presence of stagnant pockets show what the plant is short of: air, its distribution, or the control of it. The development answers for the control and in part for the distribution, whereas a shortage of reactor volume remains a matter for a deeper reconstruction.
SmartAeration is SOLVIA's own engineering development aimed at the efficiency and the controllability of aeration at wastewater treatment works; it is meant for practical use in existing and in new systems of biological treatment. The technical solutions are protected within the developer's patent strategy. The internal control algorithms, the design parameters and the particulars of tuning are not disclosed in open materials, and the regime for a given plant is chosen from a survey of it.
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