HYDROTECH BIO is a biological treatment plant for domestic wastewater and for industrial effluent of similar composition. Organics, nitrogen and phosphorus compounds are removed in one vessel divided into an anaerobic, an anoxic and a meandering aerobic zone with a secondary clarifier.
The plant gathers into a single vessel what classical schemes spread over separate structures: an anaerobic zone for biological phosphorus removal, an anoxic zone for denitrification, a meandering aerobic zone for nitrification with fixed biofilm media, and a secondary clarifier. Combined aeration and two independently adjustable internal recirculation lines belong to the same layout; automatic control is provided according to the project.
It is meant for domestic wastewater and for industrial effluent of similar composition, where not only the organics but the nutrients have to be taken out. The application describes modular, containerised and stationary versions rated from 1 to 500 m³/day and above with several blocks connected in parallel: the same set of zones serves a single building and a village alike.
Alternating anaerobic, anoxic and aerobic zones is used in IFAS and MBBR schemes as well, and the limits of those solutions are of different kinds. The first is hydraulic: an aerobic zone working as a completely mixed volume passes part of the load through faster than the design time and holds another part in stagnant pockets, and contact time here is an average rather than a set quantity.
The second limit is recirculation in one direction, with no separate control of the flows: under a variable load there is nothing with which to strengthen denitrification and hold the biomass in the aerobic zone at the same time. The third concerns phosphorus: its biological removal proceeds only under strictly anaerobic conditions, and nitrates returned into that zone weaken the process even with the equipment in perfect order.
The anaerobic zone receives the raw wastewater and the return activated sludge from the secondary clarifier. Phosphorus-accumulating organisms work here only in the absence of free oxygen and of nitrates; the application names the target conditions — dissolved oxygen below 0.1 mg/l and nitrates below 0.5 mg/l. The return sludge is directed here alone, and not into the head of the aeration tank as in the classical schemes.
From the anaerobic zone the water passes into the anoxic one, where the internal recirculation pump delivers nitrate-bearing mixed liquor from the end of the aerobic zone: the nitrates are reduced to molecular nitrogen on the organic substrate of the raw water. The pump has two independently adjustable outlet lines — a return to the head of the aerobic zone at 50–150 % of the incoming flow and a feed into the anoxic zone at 100–300 %.
The first line raises the biomass concentration in the meandering channel, the second strengthens denitrification, and they are set separately — from the dissolved oxygen, nitrate nitrogen and sludge level sensors brought together on a programmable controller. The secondary clarifier inside the same vessel closes the scheme: the clarified water goes to polishing or discharge, the thickened sludge back into the anaerobic zone.
The aerobic zone is built neither as a single completely mixed volume nor as a straight channel, but as an extended meander with turns. The application sets the ratio of total channel length to width at L/W ≥ 8:1 — at such a ratio the regime approaches plug flow, and the concentration of the load falls along the path of the stream instead of levelling out across the reactor volume.
Contact time is then set by the geometry of the channel rather than by averaging, and a short circuit of the flow through the reactor is unlikely. The meander also gives room for fixed biofilm media along the path of the water: every point of the channel carries its own load on the biofilm rather than the average across the reactor. The application names the hydraulics of the meandering zone as one of the factors raising nitrogen and phosphorus removal.
The carriers are held in the aerobic zone permanently and need no stirring. A biofilm grows on their surface: the outer layers receive more oxygen, in the deeper ones the oxygen content is reduced. The application states that at dissolved oxygen below 0.5 mg/l conditions for simultaneous nitrification-denitrification arise in the deep layers: part of the nitrogen is removed inside the film itself.
The aeration is split by duty. Fine-bubble diffusers on the floor of the channel dissolve oxygen into the water; coarse-bubble diffusers, set along one side of the channel 50–200 mm above the floor, create a directed bubble flow that mixes and carries the mixed liquor without damaging the biofilm. Oxygen supply and mixing are separated, and the air for each duty is adjusted on its own.
Taken one by one, the elements of the scheme are known, and what sets HYDROTECH BIO apart is their combination. Attached biomass is used in MBBR and IFAS, but there the carriers are mobile and have to be kept in motion. The closest analogue by the design of the aerobic zone — a serpentine reactor with attached biomass — remains a single-zone one: it has neither the separation of zones, nor a second recirculation line, nor an integrated clarifier.
The target technical results of the application are total nitrogen removal of up to 85–93 %, total phosphorus of up to 80–90 %, a reduction of the working reactor volume by 20–35 % against units built on corridor-type aeration tanks, and a reduction of specific energy consumption by 15–30 % against MBBR/IFAS systems. These are declared targets rather than measurements on a working site, and each figure carries a comparison base of its own.
HYDROTECH BIO is SOLVIA's own technological development in the biological treatment of wastewater. The claim of the invention describes a vessel divided into anaerobic, anoxic and aerobic zones and a secondary clarifier, a meandering channel with L/W ≥ 8:1, fixed biofilm media, combined aeration and two adjustable internal recirculation lines. Structural parameters, the tuning regimes and the particulars of the layout are not disclosed in full in open materials and are selected for the individual project.
An MBR separates the treated water from the sludge with a membrane, but membranes call for maintenance, cleaning and protection from fouling. Here the separation is left to the clarifier and the work is shifted onto the biology and the hydraulics: separated zones, a regime close to plug flow, and adjustable recirculation. That choice pays where deep biological treatment is needed without membranes.
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