Improve Your Digester Performance HUBER Sludge Squeezer HSS – – – – – – – Low energy demand Constant homogenisation level Mechanical destruction of ﬁlamentary microorganisms Improved operating stability of digesters Reduction of “foaming“ in digesters Increased gas production of up to 30 % Reduction of sludge volume The Quality Company – Worldwide ➤ ➤ ➤ The Challenge Frequently, the anaerobic transformation of organic substances in digestion tanks is hindered by the insufficient flow in the plant and a critical biocoenosis composition. The flow problems are caused by the gel-like structure of the sewage sludge, which is aggravated by sludge thickening and leads thus to an increase in viscosity. The high viscosity impairs the mixing process and inhibits the contact between the organic substrate and anaerobic mixed biocoenosis within the digester. Due to the insufficient contact only part of the organic substances are transformed into sewage gas and filamentous microorganisms produce a flotate layer on top of the digested sludge inside the digester. The incomplete transformation of the organic substances in the sludge increases the sludge disposal volume, leads to poorer dewatering results and reduces the gas production in the digester. Excessive foam production caused by filamentous microorganisms may endanger the operating stability of the complete digestion process. Combating the production of foam using defoamers frequently remains unsuccessful so that the digester filling volume has to be reduced or, worst case, the digester needs to be aerated. Filamentous micororganisms lead to problems also in other plant parts, such as aeration tanks and secondary clarifiers, where they cause scum and bulking sludge. Due to the various undesired effects of these structure and substrate properties the costs for sludge disposal rise while the yield drops, as the availability of usable energy decreases due to the reduced gas production. Untreated thin sludge flocks Treated excess sludge structure ➤ ➤ ➤ The Solution These undesired properties regarding both the flow behavior of the sludge and anaerobic biocoenosis can be changed either by modifying the biological conditions within the complete purification process, or by changing the flow properties and mixed biocoenosis. Since it is impossible in most cases to influence all specific conditions and processes to such an extent that the physical sludge parameters can be changed and the occurrence of filamentous microorganisms reliably prevented, combating the symptoms is the most promising way. Previously available methods have focused on cell disruption by cavitation (ultrasonic or hydraulic methods), which requires a high energy density per volume for sludge treatment. Flow and circulation centres in a digestor with gas injection The new hydro-mechanical system with a special nozzle design achieves homogenisation and viscosity reduction of digested sludge at a low energy density. At the same time, the system inactivates filamentous microorganisms with the result that flotate layers or foam production within the digesters are to the greatest possible extent prevented. Due to the changed sewage sludge properties the flow in the digester improves, gas development increases and further sludge treatment, such as dewatering efficiency, is also improved. ➤ ➤ ➤ HSS HUBER Sludge Squeezer – The Design The sewage sludge homogeniser (Sludge Squeezer) consists of a mechanical treatment unit, which homogenises the digested and/or thickened excess sludge with a solids content of up to 8 % and improves its flowability. This increases the mass transfer area and improves material mixing inside the digester with the result of a higher gas production. Dependent on the specific gas yield the gas production can be increased to up to 30 %. Due to the special design of the treatment unit high flow velocities are induced. Their corresponding pressure distribution, however, lies below the cavitation limit. This system ensures a quiet plant operation, and in addition to the improved flowability inactivates filamentous microorganisms so that the tendency to foam production in the digester is minimised. The treatment can take place at virtually any point in the sludge cycle of the digestion and clarification plant. In special cases (if, for example, the sludge has a very low solids content of below 1.5 %) the integrated sludge atomisation can be designed so that a cavitation field is generated. The gas bubble implosion increases the treatment intensity if the solids content is low. Due to the automatically acting atomisation within the treatment unit a constantly high homogenization is achieved even with varying flows and solids contents. ➤ ➤ ➤ HSS HUBER Sludge Squeezer – The Process Sewage sludge homogenisation with the HUBER Sludge Squeezer is a two-stage process with a rebound-jet nozzle. In the first stage the sludge flocks are mechanically broken up, in the second stage the flocks are mixed into the sewage sludge via a hydrodynamic flow field and homogenised. This treatment leads to an increased mass transfer surface and increases thus the hydrolysis within the digestion process. The treatment is performed continuously with the HUBER Sludge Squeezer, while the complete plant is operated semi-continuously. At first, the intermediate storage tank of the treatment plant is filled with sewage sludge. (Valves V1 and V3 are open, all other valves are closed.) After tank filling the sewage sludge is pumped through the HSS and treated until the requested result is achieved. (Valves V2 and V4 are open, all other valves are closed.) After the end of the treatment process the plant is evacuated and the sewage sludge returned directly into the digestion cycle. (Valves V4 and V5 are open, all other valves are closed.) During the treatment process the sewage sludge is homogenised and a constant sewage gas increase is achieved after approx. 3 - 4 sludge ages. Increase in gas production Throughput (per system) Speciﬁc energy demand Up to 30 % 10 m3/h 0.97 kWh/m3 Result Discharge-Cycle V5 Macerator V1 PC-Pump Filling-Cycle Treatment-Cycle V3 V4 Hans Huber AG 0,2 / 1 – 3.2007 – 3.2007 Maschinen- und Anlagenbau Postfach 63 · D-92332 Berching Phone: + 49 - 84 62 - 201 - 0 E-mail: [email protected] Telefax: + 49 - 84 62 - 201 - 810 Internet: www.huber.de V2 Feed Subject to technical modification HUBER Sludge Squeezer HSS