Stabilization and sludge hygienization

OSS – oxyterm sludge system®

Autothermic aerobic termophilic stabilization of sludge

Use  

OSS is used for processing - stabilization and hygienization of sludge from all types of modern, especially low-rate, biological waste water treatment plants in aerobic conditions, on the level of the rigid hygienic requirements of the valid legislation in Czech Republic and most advanced EU Member States. The system’s capacity may be optimized for installations of 3000 - 35000 EI, in principle, however, the unit size is not limited in any regard.

Supplies      

The technological unit may be designed as a complex comprising pumping, thickening, stabilizing, hygienizing, homogenizing, dewatering and disposal. The technological unit may also be designed and implanted into the existing technological chain of the waste water treatment plant, comprising only stabilization, hygienization and homogenization. The latter variant makes maximum use of the already built objects and installed units. The supply also contains the independent control system.

Principle  of function

The excess sludge from biological treatment is processed in a complex way comprising suitable combination of aerobic stabilization by air and autothermic aerobic thermophilic aerobic sludge stabilization at temperatures above 55 °C, with the use of pure oxygen. Hygienization temperature is attained in an isolated reactor by using biologically mediated controlled oxidation of part of the biomass, during which energy is released, necessary for heating and maintaining the working temperature within the whole volume of the reactor. The unit does not depend upon any external heat energy source.

General  requirements for raw sludge properties

For the reason of already started anaerobic processes and possible development of methane (safety reasons) the fresh primary sludge is not suitable for processing using this technology. However, small quantities of long-term stored digested sludge (e.g. from small waste water treatment plants) do not cause problems.

Basic requirement for properties of the unprocessed input sludge:

•  average input solids should exceed 2.5%
•  organics content in the solids (AFDM) should exceed 35 - 40 %
•  chemical sludge content after condensation of phosphorus in the solids, should not exceed 20%
•  the sludge must not be in the anaerobic breakdown stage (development of hydrogen sulphide, etc.)

General requirements for processed sludge after autothermic thermophilic aerobic sludge stabilization process in the output from the homogenization tank, before dewatering:

•  medium solids, depending upon the input 2.5 - 4.5 %
•  organics content in the solids (AFDM) depending upon the input 20 - 45 %
•  enterococci - below 103 KTJ/g
•  salmonella - negative
•  the sludge is generally well-developable in centrifuge, currently in solids: 30 - 35 %

Therefore the sludge produced may be currently, directly applied in agriculture or for composting.

 Operation economy 

depends upon the price of consumed electricity, costs of final disposal of dewatered sludge outside the WWTP, upon the price and quantity of consumed oxygen and costs of dewatering (flocculant). The oxygen consumption represents ca. 30 - 45 % of the overall costs. The particular disposal costs in CR represent roughly CZK 2900 - 3500 per ton of solids in the raw input sludge (the price comprises the costs from the excess sludge withdrawal from the activation system up to its final disposal).