SOLVIA Retrofit Module is an engineering module for the retrofit of septic tanks, concrete vessels and local treatment works that are already built. It is installed inside the existing vessel and forms a zone of aeration, recirculation and biological treatment within it: the shell stays as it is, what changes is the process its volume runs.
A retrofit starts not from a clean sheet but from an existing shell: a septic tank, a concrete reservoir, a holding vessel or an old local treatment works that has run in a simplified mode for years and in practice only settles the water. The aim is not to add air to such a shell but to change how it works, taking the volume out of passive settling or anaerobic holding into a managed system of biological wastewater treatment.
The set of elements is chosen for the individual site, after a survey: a guide airlift tube with a diffuser, a compressor and an air line, a recirculation zone with a directed flow outlet, biofilm media, a settling zone with return of activated sludge, a dissolved oxygen sensor and elements of automation. What enters the scope is decided by the condition of the particular vessel, not by a standard scheme.
On many sites septic tanks, concrete vessels and old local treatment works are already built, and their shell is often still serviceable. A septic tank as such remains first of all a settling tank: it holds back part of the suspended solids, the fats and the sediment, but takes out dissolved organics unevenly, while inside the volume an anaerobic environment builds up — an environment short of oxygen.
Old accumulated sludge together with organics and fats sets off septicity in that environment, and with it come odour, hydrogen sulphide and unstable operation of the whole system. Pumping the sludge out gives a temporary result: if the hydraulics of the volume and the biological process inside it stay as they were, the odour and the turbid discharge return, and on sites with a variable load this shows especially plainly.
A guide tube is lowered into the vessel, and air from the compressor is fed into its lower part through a diffuser set there. The bubbles rise and carry the water with them: the liquid is drawn into the tube from below, takes up air on the way up and is thrown back into the main volume, closing an internal circulation. The air serves two duties at once — it supplies the biological process with oxygen and it mixes the contents, drawing in the lower layers.
What separates SOLVIA Retrofit Module from the simple variant, an aerator merely lowered into a septic tank, lies exactly here: what matters is not the presence of bubbles but the controlled movement of the flow. With air fed at a single point the rest of the volume stays still, a small aerated zone forms inside, and anaerobic sludge goes on accumulating in the far corners — and the odour and the unstable treatment come back by the same road.
The geometry of the shell is set beforehand and is not open to alteration, so it is the module that is fitted to it. The choice covers the size of the guide tube, the air flow rate, the type of diffuser, the position of the lower inlet windows, the direction of the flow outlet and the place of the module inside the vessel, and along with them the presence of a settling zone and the possibility of returning sludge. The aim of that work is not to aerate the water but to create a circulation loop inside the existing vessel.
In part of the configurations biofilm media are placed in the volume. They give an additional surface for microorganisms to attach to, on which a more stable biofilm forms, and for sites with a variable load this matters especially: the flow and the composition of the effluent change over the day and over the season, while attached biomass helps the system to work more steadily. Both standard media and bioactive materials for the particular duty are used.
Biological treatment answers not only the task of breaking down the load but also the task of separating the water from the biomass. A well mixed volume with no quiet stretch sends turbid water carrying sludge particles to the outlet, so a retrofit provides a place where the flow calms down, the activated sludge separates from the treated water and returns to the aerated part.
What that place turns out to be depends on the design of the existing vessel: a separate chamber, an internal partition, a settling compartment, a baffle in front of the outlet or a T-piece drawing the water off. Whether such a zone can be arranged in a ready shell is assessed beforehand, together with the rest of the geometry. What makes the retrofitted volume complete technologically is precisely the combination of aeration, circulation and settling.
In the extended scope a dissolved oxygen sensor is fitted. It shows whether there is oxygen not only inside the airlift tube but in the main volume of the aerated zone as well, and by it one sees whether the air is sufficient, whether there is an overload, whether the diffuser works properly and whether the circulation reaches the remote parts of the vessel.
In the more developed variants automation is added to the sensor: regulation of the air supply, alarm signalling, monitoring of the compressor, level sensors, remote monitoring and SCADA. For small sites this is a simple control system, for hotels and residential complexes an automation with remote access. The site is improved step by step: first aeration and circulation, then biofilm media, settling, automation and service.
SOLVIA Retrofit Module is SOLVIA's own engineering development, aimed at the retrofit of existing septic tanks, reservoirs and local treatment works. The technology is being developed as a practical solution for sites where the efficiency of treatment has to be raised, the odour reduced, the biological process improved and the infrastructure already in place put to use. Structural particulars, design parameters, tuning regimes and individual technological solutions are not disclosed in open materials; neither is the composition of the special bioactive materials.
No: the module is not a solution for every existing shell, and before it is applied the site is surveyed. The dimensions and working volume of the vessel, the water depth, the condition of the shell and of the partitions, the level of accumulated sludge, the inlet and outlet arrangement, the point of discharge, the flow and the character of the load are all assessed. Only after that inspection is it settled whether the site suits a retrofit and what configuration of the module is needed.
Tell us about your site — our engineer will prepare a process design, a specification and a quotation within one business day.