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Sugar beet press pulp (SBP) accumulates as a by-product in sugar factories and it is generally silaged or dried to be used as animal food. Rising energy prices and the opening of the European Union sugar market has put pressure on the manufacturers to find alternatives for energy supply. The aim of this project was to develop a technology in the treatment of SBP that would lead to savings in energy consumption and would provide a more competitive sugar production from sugar beets. These goals were met by the anaerobic digestion of SBP for biogas production. Lab-scale experiments confirmed the suitability of SBP as substrate for anaerobic bacteria. Pilot-scale experiments focused on process optimization and procedures for a quick start up and operational control. Both single-stage and two-stage process configurations showed similar removal efficiency. A stable biogas production could be achieved in single-stage at a maximum volumetric loading rate of 10 kgCSB/(m3·d). Degradation efficiency was 75% for VS and 72% for COD. Average specific gas production reached 530 NL/kgCODSBP or 610 NL/kgVSSBP. (CH4: 50 to 53%). The first large-scale biogas plant was put into operation during the sugar processing period 2007 at a Hungarian sugar factory. Digesting approximately 50% of the SBP (800 t/d, 22%TS), the biogas produced could substitute about 40% of the natural gas required for the thermal energy supply within the sugar processing.

Activated sludge bulking caused by the filamentous bacteria 021N, was repeatedly detected in the mixed liquor of a beet sugar mill treatment plant, equipped with an aerated selector. The organic pollution of the waste water consisted of about 70% easily degradable dissolved substrate (sugar, fatty acids). Only in cases when the elimination of the readily biodegradable substrate from the liquid phase in the selector was incomplete a rapid increase of filamentous bacteria could be detected consistently. The readily biodegradable substrate is predominantly removed in the selector by uptake and storage by the biomass. The oxygen demand for the storage in the selector depends on the kind of substrate. To obtain storage capacity in the selector, the sludge must have the opportunity to regenerate the capacity for substrate storage in the aeration tank. In the case of overloading and/or oxygen and/or nutrient deficiency the storage capacity can not be regenerated and the aerobic selector loses its effectiveness. From the findings about the factors influencing the elimination of the readily degradable substrate in the selector, a simple calculation method for dimensioning of aerobic selectors as well as a simulation model have been developed. In two plants, (60,000 m3/d, 40 t COD/d) that were built according to these findings it could be verified that the growth of 021N can be avoided effectively by using aerobic selectors, dimensioned with the developed calculation method. The results could be proved by successful operation of the treatment plants during the last two years. In a paper mill plant the SVI reaches values of 300 to 600 ml/g caused by the filamentous bacteria Type 0041 and Type 1701. Some days after installing an “adequate aerobic selector system” the growth of filamentous bacteria could be suppressed and the SVI reached values of 60 to 90 ml/g.

In industrial wastewater, especially from food industry, the concentrations of the organic compounds are usually high, whereas the contents of nitrogen and phosphorus are often low. For the aerobic treatment, the addition of nutrients to the industrial wastewater can be required. For ecological and economic reasons, this nutrient addition must be kept to a minimum. Unintentional nitrification and denitrification lead to an additional demand of nitrogen and should therefore be avoided at such plants. Observations from two treatment plants (50 000 m3/d, 40 t COD/d) proved that the nitrogen dosage can be controlled by monitoring the ammonia concentration. If the control procedure also considers the N/COD ratio in the raw wastewater (including the N dosage) and the organic sludge load of the last couple of days, very low effluent concentrations (NH4–N in the range of 0.3–0.5 mg/l) can be achieved and the nitrogen dosage is low. If there are periods with nitrogen in excess, too, a minimum nitrification capacity has to be maintained by means of nitrogen addition in periods of deficiency. A control procedure for phosphorus addition is to keep a fixed P/COD-ratio in the raw wastewater (including P dosage). The PO4–P concentration is monitored in order to limit the maximum phosphorus dosage. Following this procedure, considerable savings of phosphorus have been achieved, keeping very low effluent concentrations (average Total-P<0.3 mg/l).

Activated sludge bulking caused by the filamentous bacteria 021N, was repeatedly detected in the mixed liquor of a beet sugar mill treatment plant, equipped with an aerated selector. The organic pollution of the waste water consisted of about 70% easily degradable dissolved substrate (sugar, fatty acids). Only in cases when the elimination of the readily biodegradable substrate from the liquid phase in the selector was incomplete a rapid increase of filamentous bacteria could be detected consistently. The readily biodegradable substrate is predominantly removed in the selector by uptake and storage by the biomass. The oxygen demand for the storage in the selector depends on the kind of substrate. To obtain storage capacity in the selector, the sludge must have the opportunity to regenerate the capacity for substrate storage in the aeration tank. In the case of overloading and/or oxygen and/or nutrient deficiency the storage capacity can not be regenerated and the aerobic selector loses its effectiveness. From the findings about the factors influencing the elimination of the readily degradable substrate in the selector, a simple calculation method for dimensioning of aerobic selectors as well as a simulation model have been developed. In two plants, (60,000 m3/d, 40 t COD/d) that were built according to these findings it could be verified that the growth of 021N can be avoided effectively by using aerobic selectors, dimensioned with the developed calculation method. The results could be proved by successful operation of the treatment plants during the last two years. In a paper mill plant the SVI reaches values of 300 to 600 ml/g caused by the filamentous bacteria Type 0041 and Type 1701. Some days after installing an “adequate aerobic selector system” the growth of filamentous bacteria could be suppressed and the SVI reached values of 60 to 90 ml/g.

The presence of easily degradable compounds from food industries frequently leads to bulking problems. The paper describes a new process that has been developed for a dairy in Austria. Because of the increase in production the treatment plant receiving the wastewater up to now was not able to handle the increased loads. Therefore detailed studies for treatment alternatives have been undertaken which led to a completely new concept. The excess sludge of the urban treatment plant is contacted with the concentrated dairy waste in a separate contact tank. In this tank the easily degradable substrate from the industrial waste is mainly adsorbed to the biological sludge and after a mechanical dewatering transferred to the anaerobic digester where it yields an increased gas production. The filtrate of the dewatering process is completely free from biodegradable material and can without danger of bulking be fed to the aeration tank. The process has been in operation for more than one year and has fulfilled all expectations.

The primary driving force for re-investments in wastewater treatment plants in Austria - and also other countries in Central Europe - is at present not an increase in load to treatment but a marked increase in effluent requirements to be fulfilled. (The re-investments necessary for sludge handling and treatment remain outside this paper.) Within a period of 20 years, the load specific requirements on aeration tank volume rose five- to tenfold, when Lv = 2.0 kg BOD5/(m3d) was the starting value, and roughly doubled for final clarifiers. In addition, the importance of the application and expansion of primary sedimentation decreased as well. This development over time in Central European countries as well as the need to utilize previous investments as long as possible - 35 to 60 years for civil works are common as periods of depreciation - indicate that investments in new plant at any location in the world have to consider the possible whole life cycle of a plant and that plant hydraulics becomes the “key hook” for expandability.

As indicated by the rapidly changing effluent standards in Austria, new wastewater-treatment plants must be designed so that upgrades can be made efficiently. To that end, plant design becomes a primary consideration. Pretreatment, primary sedimentation, aeration, and final clarification have to be expandable at different ratios. Design considerations are discussed: from the outlet of aeration to the outlet of final sedimentation, from the outlet of the primary tank to the outlet of aeration, from the lift station to the outlet of primary sedimentation, and from final clarification to aeration. Recommendations for optimal wastewater-treatment plant design are proposed, and an example of plant development over time is presented.