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Biomass on growth carrier material in a fluidized-bed reactor
To remove organic matter, phosphorus and nitrate from wastewater biological processes are used.A high process stability, even in case of hydraulic jumps, underload and overload of the system, a nearly completely elimination of nitrogen and very ambitious target values for the required discharge parameters are to achieve with a sewage treatment process by combining activated-sludge process and fluidized-bed biofilm process.
This biological technology for processing of removal nutrients while traditional wastewater treatment has been developed by us since 1989. This turbulent biofilm technology was put into operation at more than 170 WWTP`s with a capacity 50 to 50.000 PE.
The major part of the micro-organisms required for wastewater treatment settle down on cylindrical carrier material which is mechanically and biologically persistent. Diameter of carriers is general 3 to 8 mm, the length 4 to 8 mm with a specific surface of 800 to 950 m2/m3 bulk volume. Micro-organisms with special metabolic efficiencies concentrate in the biofilm on the growth carrier material in dependence on the oxygen conditions in the arranged stages are anaerobiers (acidifying organisms, organisms for eliminate phosphorus), facultative anaerobiers (denitrifiers) or aerobiers (nitrifiers).
The finely divided and dissolved organic substances and nutrients are converted into biomass, in both, very good settleable activated-sludge flocs and biofilm on the carrier material. The biomass on the growth carriers has a high degree of specialisation of the micro-organisms especially for nutrient removal, nitrification and denitrification and also for acidifying of organic substances. The concentration of micro-organism in the aeration tanks is approximately for to five times higher than in a simple activated sludge process tank
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The quantity of the higher biomass concentration results in a increase in efficiency and increase of process stability without detrimental effect on the secondary settling tank. According to the dimensioning of the final sedimentation tanks the dry solid concentration in the aeration basins for the settleable micro-organism will be selected as 3 to 5 kg DS/m3 , although the real concentration of dry solids including biomass on the carrier material general is 12 to 16 kg DS/m3. The biomass on the carrier material accorded not the dimensioning of the final sedimentation tanks and this share is very much higher then the activated-sludge flocs. Carrier-fixed micro-organisms remain in the corresponding process stage in case of hydraulic jumps or excess sludge removal by a special hydraulic retention system witch can not block. The system is absolutely clog-proof.
A primary advantage of this process technology is, that the quantity of growth carrier material can be adapted to the degree of design and/or purification requirements. The efficiency potential of suspended activated-sludge flocs (for phosphorus removal) and of micro-organisms in form of a biofilm on the growth carrier material (in anaerobic zones for acidifying of organic matter, in anoxic zones without aeration and for denitrification in an fluidised bed with filter effect as well as in aerated aerobic zones in dependence on the intensity of air introduction in an ideally mixed turbulent or fluidised bed for nitrification) are, thereby, effectively combined with each other.
As a essentially advantage of this technology can the quantity of carrier material adapted to standards on purification efficiency without consequence to required reactor volume. Seasonally pollution load can therefor exactly reliable treated. Effluent concentrations for phosphorus 0,1..0,5 mg/l, for NH4 N 0,1 0,6 mg/l, CSB 23 60 mg/l can dependent on quantity of carrier material achieved.
The comparison showed that this process is therefore the most economical (low investment and operating costs) and technically most advantageous process technology for the wastewater purification with the highest operational safety as a result of process according to the state of the art. The special process technology makes it possible to eliminate phosphorus and nitrogen even in traditional wastewater treatment plants with a significant smaller volume of the biologically reactors. This is very important for a effective recovery.
The aeration basins are cascade tanks. Hence, at the intake in each stream a denitrification tank is separated for the denitrification of return sludge, the inflowing waste water and a part of the internal recirculation for the denitrification. The capacity of this partial flume must be so that anaerobic conditions are ensured in the following downstream phosphate release step. It will be equipped with agitators.
As the next step the volume up to the partition wall is used as phosphorus release step. The biomass on the carriers in this tank acidifies and hydrolyses the organic matter in the waste water. The return sludge takes of these easily assimilable substances, stores them as hydroxybutanoic acid and releases the stored polyphosphate (Valutingranula) to the liquid phase. A precondition for this is that there is neither dissolved oxygen nor oxygen chemically bonded as nitrate present in this reactor part. The growth carriers are stirred with an agitator as a floating layer in the reactor. This layer acts as a floating granular filter and, hence, filters out all coarse and rough dispersed organic matter which are then hydrolysed by the biofilm of the carrier material.
The separation of the metabolic processes of the biofilm (acidification and hydrolysis) from the metabolic processes of the return sludge (phosphate storage and denitrification) results in a high degree of specialisation of the micro-organisms which happens because such short retention periods are sufficient. The residual phosphate content can be separated as flocculent with dosing of Me3+ salts.
The next section of the activation tank is used as the subsequent control step in order to compensate weekly or seasonal load fluctuations. This reactor section can be used both for denitrification and nitrification. It will be equipped with aerators and agitators.
The nitrification and denitrification steps are filled at the outset with carrier material at 10 to 60 %. This corresponds to a biofilm load of 2,7 to 8 g BOD per mē biofilm. Thus, a total nitrification is possible at 450 % recirculation. The max. carrier material filling more than 60%, so that there is a sufficient margin for load peaks or extensions. The existing shearing forces in the turbulent bed guarantee, thereby, a highly active thin biofilm. The micro-organisms are supplied with oxygen by means of fine-bubble aeration. The required oxygen will be introduced to the system via membrane aerators. These entrain oxygen from the atmosphere, keep the basin mixed and the carrier material is brought to turbulence. The oxygen input to the wastewater is determined by the submergence of the membrane aerators. The tank depth selected is the maximum at which the blowers can efficiently work. A depth of 5 m is chosen.
A degassing zone should be provided at the end of the activation and before the outlet trough. There the formed CO2, the residual air and other gaseous substances will escape. The internal recirculation pump for the denitrification will be installed in this degassing zone. Each pump is variable speed controlled. These pumps extract simultaneous carrier material to the denitrification zone.
Dimensioning of sewage treatment plants according to processes are based on the technological combination of activated-sludge biology with turbulent biofilm process.
This is the carrier material:
