Environmental Biotechnology - Jordening and Winter
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2.5 Wastewater Composition and Treatment Strategies in the Food Processing Industry 69
2.5.7
Dairy Industry
Dairy products are classified into drinking milk, cream products, sour milk and milk mix drinks, butter, curd products, hard and soft cheeses, condensed milk, and dried milk. The difference between the listed products and the entire delivery amount is mainly due to the return of skimmed milk and whey and to the extraction of exhaust vapors during coagulation and drying of milk and whey.
For milk processing, the delivered raw milk is first – regardless of the production schedule – cleaned with separators, separated into cream and skimmed milk, and pasteurized. Cream is mainly used for the production of butter. Skimmed milk is processed into drinking milk, fresh milk products, and cheese, partly by adding cream or bacterial cultures. Skimmed milk and whey are the basic materials for the production of dried milk, lactose, and casein.
The wastewater produced in milk processing plants consists of cooling water, condensation water, sanitation water, and process water. The process water consists of the wastewater from the pretreatment, water losses during production, those residues that can no longer be used economically, washing water, detergents, rinsing and cleansing water, and water processing. In dairies the wastewater derives almost exclusively from cleaning of the conveyance and production implements. More than 90% of the organic solids in the wastewater result from milk and production residues. For the milk processing industry, wastewater discharge is almost always identical with loss of products that could otherwise be utilized or sold. This is a great incentive to decrease the production of wastewater by production-integrated measures. For untreated dairy wastewater, the following data are valid; peak values can even exceed these values (Table 2.10).
Dairy wastewater has only a small ratio of settleable solids. Thus, conventional mechanical procedures, such as settling tanks, are ineffective. Inevitable losses of fats can be retained in fat separators, which, however, have only a limited efficiency if the wastewater temperatures are comparatively high.
One major problem with dairies is the considerable variation in wastewater volume and concentration. Thus, as a first step after straining and a sand trap, it is recommended to install a mixing and equalizing tank (M+E tank). In the M+E tank wastewaters of different concentrations and pH are mixed, the wastewater flow is equalized, and partial biological degradation occurs, which can also result in a bio-
Table 2.10 Amounts and concentrations of dairy wastewater (Bertsch, 1997).
Wastewater |
BOD5 |
COD |
NO3-N N |
P |
Settleable pH |
Lipophilic |
Amount |
(g L–1) |
(g L–1) |
(mg L–1) (mg L–1) |
(mg L–1) |
Solids |
Substances |
(m3 t–1 |
|
|
|
|
(mL L–1) |
(mg L–1) |
of milk) |
|
|
|
|
|
|
1–2 |
0.5–2.0 |
0.5–4.5 |
10–100 |
30–250 |
10–100 |
1–2 |
6–11 |
20–250 |
|
|
|
|
|
|
|
|
|
70 2 Industrial Wastewater Sources and Treatment Strategies
logical neutralization. As a minimum volume, approx. 25% of the daily water flow has proved to be a favorable value, but it is also possible to adjust the facilities for daily or weekly equalization. With unaerated M+E tanks there is no biological degradation worth mentioning; instead, substance conversion (acidification) happens, which leads to the emergence of noxious odors. Aerated M+E tanks are mostly operated as washing-off reactors. They are able to reach BOD5 efficiency rates of 20%–60% for homogenized samples.
As a further pretreatment stage, a flotation implement is recommended, which can either replace the M+E tank or be downstream from it; this facility allows for the removal of fats and proteins, i.e., the major part of the organic pollutants.
Although more than 90% of the milk processing companies in Germany discharge their wastewater indirectly, direct discharge can under certain conditions be economically viable. Direct dischargers mostly have an activated sludge system, which should, if strong variations occur, be preceded by an M+E or a calimity tank. Since dairy wastewater has a tendency to develop bulking sludge, it is recommended to design the plant so that the microorganisms in the activated sludge are intermittently subjected to high loads, which can be achieved by installing an activated sludge system in plug flow design, by a preceding contact tank (selector), or by a SBR method (sequencing batch reactor: the process steps of filling, denitrification, aeration, sedimentation happen one after the other, but in the same tank).
2.5.8
Fruit Juice and Beverage Industry
Natural mineral waters and spring waters are collected and bottled at the location of the source spring. Table water consists of drinking water or natural mineral water to which salts are added. Refreshment beverages are produced from water, flavoring substances, sugar or sweetener, and carbon dioxide. The technology of fruit juice production can, in a simplified manner, be divided into the production stages of washing, grinding, refining, filtering, heating, recooling, and bottling.
The wastewater produced in these three industrial branches consists of the following streams (some do not occur in every branch): wastewater from cleaning bottles and containers and from bottling, rinsing and washing water, exhaust vapor condensate, wastewater from the production facilities, wastewater from surface cleaning (floors of the production sheds and the parts of the yards where production takes place), and wastewater from cleaning the conveyor facilities.
Wastewater produced in the mineral water industries contains the following components: adhesive materials and fibrous substances, cleaning alkalis and acids, and soiling from the deposit bottles. For soft drinks, one has to consider the fact that the wastewater additionally contains organic pollutants (with a high ratio of carbohydrates, a large part of it being sugar), which derive from residues and product losses. For the fruit juice industry, product losses – in particular the loss of fruit concentrates – and the sugar, which is often added, are a considerable part of the wastewater pollution. The COD of fruit juices ranges from about 50 g L–1 (tomato juice) to about 200 g L–1 (apricot juice); 1 kg of glucose (or of fructose) is equivalent to
2.5 Wastewater Composition and Treatment Strategies in the Food Processing Industry 71
1066 g COD. Besides the wastewater, the fruit juice industry also produces cooler sludge, filtration residues, sludge from clarifying agents, pomace, and kieselguhr. Because of their high pollution potential, these substances should be the focus of production integrated measures. If possible, they should be utilized or disposed of separately.
The specific wastewater amounts and pollutant concentrations of the three industry branches are presented in Table 2.11. For companies in the fruit juice industry, one has to differentiate between those that do only bottling, only processing, and both processing and bottling. It is apparent that the wastewater from the beverage industry has low nitrogen and phosphorous values in relation to the BOD. The pH can range from 3.5–11.5. At the time of contact with the product the pH is mostly within the acidic range.
To meet the discharge limits of the municipal sewer system, it is often necessary to equalize the pH peaks and sometimes to reduce the temperature (discharge limit in most cases: <35 °C). Thus, a wastewater pretreatment plant could – in addition to a straining station – consist of only a neutralization stage. Because of the high cost of chemicals, biological neutralization is usually recommended, e.g., in an aerated mixing and equalizing tank, which, used as a washing-off reactor, achieves BOD5 elimination rates between approx. 35% (daily equalization) and >50% (weekly equalization). Particular heed, however, should be paid to the alkaline water from the bottle washing machines, as it might be necessary to collect this water in a separate container and to discharge it in controlled doses.
Extensive wastewater pretreatment can be successfully done with anaerobic reactors in the fruit juice industry. Two-stage implements (first stage: acidification reactor with mixing and equalization function; second stage: methane reactor) have proved to be advantageous. At volumetric loads in the methane reactor of up to >10 kg COD m–3 d–1 the COD elimination rate amounts to about 80%.
For direct discharge into waterways, the activated sludge system with cascade design has proved to be viable; it is operated at sludge loads of <0.1 kg BOD5 kg–1
Table 2.11 Specific wastewater amounts and concentrations in mineral water, refreshment beverage, and fruit juice industry (ATV, 1999).
|
Specific Demand |
BOD5 |
COD |
N |
P |
|
(m3 1000 L–1 drink) |
(mg L–1) |
(mg L–1) |
(mg L–1) |
(mg L–1) |
|
|
|
|
|
|
Mineral water and |
0.9–1.3 (mineral) |
|
|
|
|
beverages |
1.1–3.3 (beverages) |
110– 800 |
200– 1600 |
2–35 |
0–18 |
Fruit juice |
|
250–1000 |
1500– 3000 |
1.2–10 |
1.5–12 |
(bottling only) |
|
|
|
|
|
Fruit juice |
|
1700–4000 |
2500–45 000 |
5–30 |
3–15 |
(production only) |
|
|
|
|
|
Fruit juice (pro- |
|
400–2000 |
400– 3000 |
9–25 |
2–14 |
duction + bottling) |
|
|
|
|
|
|
|
|
|
|
|
72 2 Industrial Wastewater Sources and Treatment Strategies
MLSS d–1. Because of the low nitrogen and phosphorous amounts in the raw wastewater, it is generally necessary to add these substances. For reuse of deposit bottles, denitrification may be necessary because, as part of the label glue, nitrogen is added to the water. Moreover, one has to deal with the danger of bulking sludge.
2.5.9
Breweries
Beer of course contains both alcohol and carbonic acid. In Germany, legal regulations prescribe that it may be produced only from malt (germinated and ‘oasted’ barley), hops, yeast, and water. The different kinds of beer (lager, stout, top-ferment- ed, bottom-fermented) are produced mainly by varying the original wort concentrations and by using different kinds of malt and yeast.
After malting, the main operation steps of beer production are wort production, fermentation, storing, filtration, and bottling. Prior to its fermentation into alcohol, the starch contained in the malt (which in Germany is obtained from barley) has to be converted into fermentable sugar.
Residues and wastewater flow fractions occur in the brewing room, in the fermentation and storage cellars, in the filter and pressure tank cellar, during dealcoholization, and during bottling (bottle, barrel, other containers). Brewery wastewater is prone to heavy variation with regard to volume and concentration in the single flow fractions. Where production-integrated measures have already been applied, one can assume the following characteristics for the entire wastewater flow of an average brewery (Table 2.12).
Brewery wastewater has a comparatively high temperature (25–35 °C). With decreasing wastewater volume the temperature tends to rise to 40 °C. It is likely that the pH values vary strongly. In companies that reuse deposit bottles, the wastewater from the bottle washing generally has alkaline pH values. Acidic wastewater may at times result from cleaning processes and from regeneration by ion exchange techniques (for water processing). The nitrogen consists mainly of organic nitrogen (albumen, yeast) and to some extent of nitrate (nitric acid). Furthermore, the wastewater is likely to be contaminated by cleaning and detergent agents, as well as by kieselguhr and by particles arising from abrasion of bottles and shards.
Through production-integrated measures, considerable contributions to the reduction of amounts and loads, temperature, solids content, and pH can be achieved. Some very important measures are the retention and separate disposal of cooler sludge, kieselguhr, and yeast and the addition of lye.
Table 2.12 Brewery wastewater amounts and concentrations (Rüffer and Rosenwinkel, 1991).
Specific Wastewater |
BOD5 |
COD |
N |
P |
Settleable Solids |
Amount |
(mg L–1) |
(mg L–1) |
(mg L–1) |
(mg L–1) |
(mL L–1) |
(m3 100 L–1 beer) |
|
|
|
|
|
0.25–0.60 |
1100–1500 |
1800–3000 |
30–100 |
10–30 |
10–60 |
|
|
|
|
|
|
2.5 Wastewater Composition and Treatment Strategies in the Food Processing Industry 73
For wastewater pretreatment, the first step should be the removal of settleable solids, such as shards, labels, spent hops, bottle caps, etc., by suitable screens and strainers. To neutralize the mainly alkaline wastewater it is common to use carbonic acid from the fermentation or flue gas. It is also possible to biologically neutralize the alkalis with the carbon dioxide that is produced during the BOD degradation. Because of the heavy variations, it is always recommended to use an equalization tank, which can be run as an aerated mixing and equalizing tank with a biological partial purification (the elimination rates of these washing-off reactors range from approx. 35% with daily equalization and >50% with weekly equalization) or which may serve as an unaerated pretreatment tank or acidification reactor for the anaerobic plant. For the anaerobic pretreatment of brewery wastewater the most common implements are UASB and EGSB reactors, which usually are run without heating the wastewater (reactor temperatures are in the range of 24–36 °C).
For the full-scale purification of brewery wastewater to direct discharge quality, aerobic activated sludge systems have proved to be best, because of the need to eliminate nitrogen and phosphorous. The activated sludge system can either be the sole treatment stage or be post-positioned to an anaerobic plant or an aerobic trickling filter unit. Another reasonable solution is the use of SBR methods (sequencing batch reactor), in which all treatment steps are run one after the other, but in the same tank.
2.5.10
Distilleries
Distilleries produce alcohol for human consumption by fermentation and distillation of agricultural products that contain sugar or starch. Some of this alcohol is also used for vinegar production and in the pharmaceutical and cosmetics industries. In companies that produce spirits, the alcohol is diluted to make it potable and is enhanced with flavor additives. Quite a large number of rather small fruit schnapps distilleries exist.
For the production process, it is important that raw materials containing starch be turned into sugar by enzymes, fermented into ethanol, and then distilled, whereas raw materials containing sugar are only fermented and then distilled. Wine is only distilled. Normally, the first steps are mechanical disintegration of the fruit and mashing with water. In some instances, the saccharification must be artificially boosted. After fermentation is finished, the raw spirit (approx. 80 vol.% alcohol) is cleaned of its distillation residues (slops) by a first distillation. In a further refining step, either a so-called fine spirit (approx. 86 vol.% alcohol) is produced by a second discontinuous distillation, or a fine spirit or neutral alcohol (approx. 96 vol.% alcohol) is produced by continuous rectification. The residues of this second refinement step are called singlings.
Depending on the raw product and production methods, distilleries produce washing water, steaming water or fruit water, slops, and cleaning water. The specific wastewater amounts, as well as the concentrations of the major components, are listed in Table 2.13.
742 Industrial Wastewater Sources and Treatment Strategies
Table 2.13 Specific wastewater and slops amounts and concentrations in distilleries (ATV, 1999, 2003).
|
Amount |
COD |
BOD5 |
TKN |
P |
|
(m3 100 L–1) |
(g L–1) |
(g L–1) |
(g L–1) |
(mg L–1) |
|
|
|
|
|
|
Washing water (potatoes) |
0.2–0.5 m3 t–1 |
|
0.3–1.7 |
|
|
Slops |
|
|
|
|
|
– wine |
0.81–0.88 |
10–39 |
6–25 |
0.24–0.45 |
0.044–0.092 |
– potatoes |
0.5–1.0 |
72 |
44 |
2.5 |
|
– grain (wheat) |
0.79–0.97 |
71 |
32 |
2.8 |
0.19 |
|
|
|
|
|
|
Washing water is produced only during the cleaning of potatoes or roots, which is mostly done by the suppliers. During steaming of the potatoes a mixture of condensate and fruit water emerges, which as a rule is added to the mash. Modern methods of unpressurized starch breakdown (DSA methods), however, do not produce any steaming water. Since singlings derive from the distillate of the first distillation stage, they contain absolutely no solids and are hardly polluted. For the bottling of spirits, almost exclusively new bottles are used, so that cleaning water derives only from washing the implements, containers, and factory sheds and is not highly polluted.
Slops contain a high amount of organic acids, proteins, minerals, trace elements, unfermentable carbohydrates, or – especially with fruit slops – high solids ratios (cores, stalks, stones, skins), which result in very high COD and BOD5 values as well as in low pH.
In wastewater treatment the slops are of particular importance, since the other fractions of the wastewater can normally be discharged into the wastewater sewage without further treatment. Thus, slops should, if possible, be collected and utilized separately from the wastewater flow. The most common utilization method for slops from grain, potatoes, or fruit is direct feeding in cattle farming (if necessary, after thickening with decanters). If direct feeding is not possible, one should consider spreading on agricultural fields (if necessary, after anaerobic treatment of the slops in a factory-owned biogas plant or after injection as cosubstrate into a municipal digestion tank). Only if these two utilization methods are not possible, may the slops wastewater be mixed with the other production wastewater flow. Direct discharge, however, is then possible only with sufficiently powerful municipal wastewater treatment plants. In any case, the wastewater should be neutralized as a major pretreatment step. Another point one has to consider is the danger of bulking sludge development and hydrogen sulfide emission (corrosion, odors).
Slops from molasses distilleries often retain very high residual COD ratios after biological treatment. Here, evaporation of slops to a dry solids content of approx. 75% with ensuing separation of potassium sulfate (fertilizer) and utilization of the evaporated slops as an additive for cattle feed has proved to be a suitable utilization method. The condensed exhaust vapors from the evaporation unit are often subjected to anaerobic secondary purification.
References 75
References
General Literature
Andreadakis, A. (Ed.), Pretreatment of industrial wastewaters II, Water Sci. Technol.
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Andreadakis, A., Christoulas, D. G. (Eds.), Pretreatment of industrial wastewaters,
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ATV, Industrieabwasser – Lebensmittelindustrie, 4th Edn., Berlin 2000: Ernst & Sohn.
ATV, Industrieabwasser – Dienstleistungs und Veredelungsindustrie, 4th Edn., Berlin 2001: Ernst & Sohn.
ATV-DVWK, Empfehlungen zum Korrosionsschutz von Stahlteilen in Abwasserbehandlungsanlagen durch Beschichtungen und Überzüge, ATV Merkblatt-M 263
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ATV, Richtlinien für die Bemessung und Gestaltung von Regenentlastungsanlagen in Mischwasserkanälen, ATV Arbeitsblatt-A 128 (1992).
Ballay, D., IAWQ Programme Committee (Ed.), Water Quality International ’96, Part 7: Agro-industries waste management, appropriate technologies, Water Sci. Technol. 1996, 34.
Britz, T. J., Pohland, F. G. (Eds.), Anaerobic digestion VII, Water Sci. Technol. 1994, 30.
Brauer, H., Produktions und produktintegrierter Umweltschutz, In: Handbuch des Umweltschutzes und der Umweltschutztechnik (Brauer, H., Ed.) Vol. 2. Heidelberg 1996: Springer-Verlag.
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Special Literature
Sugar Factories
ATV, Reinigung organisch verschmutzten Abwassers, Korrespondenz Abwasser 1979, 3, 156–161.
ATV, Abwasser aus Zuckerfabriken, Korrespondenz Abwasser 1990, 3, 285–290.
ATV-DVWK, Abwasser in der Zuckerindustrie,
ATV-DVWK Merkblatt-M 713 (2004). Jördening, H.-J., Produktionsintegrierter Um-
weltschutz in der Zuckerindustrie,
Handbuch des Umweltschutzes und der Umweltschutztechnik (Brauer, H., Ed.) Vol. 2, pp. 616–635. Heidelberg 1996: Springer-Verlag.
Jördening, H.-J., Abwasserreinigung in Zuckerfabriken, ATV-Seminar: Abwasserbehandlung in der Ernährungs und Getränkeindustrie, Essen 1997.
Jördening, H.-J., Zuckerfabriken, In: Lehrund Handbuch der Abwassertechnik (ATV, Ed.), 4th Edn., pp. 43–64. Berlin 2000: Ernst & Sohn.
Nyns, E.-J., The Anaerobic Treatment of the Wastewater of the Sugar Refinery at Tienen, Report prepared for the European Commission Directorated General for Energy Thermic Programme. Namur, Belgium 1994: Institut Wallon.
Starch Factories
Althoff, F., Betriebserfahrungen mit einer an- aerob/aerob-Betriebskläranlage in der Weizenstärkeindustrie, ATV-Seminar: Anaerobtechnik in der Abwasserbehandlung, Magdeburg 1995.
ATV, Abwasser der Stärkeindustrie, Korrespondenz Abwasser 1992, 8, 1177–1203.
76 2 Industrial Wastewater Sources and Treatment Strategies
ATV, Abwasser der Stärkeindustrie, Gewinnung nativer Stärke, Herstellung von Stärkeprodukten durch Hydrolyse und Modifikation, Korrespondenz Abwasser 1994, 7,
1147–1174.
ATV-DVWK, Abwasser der Stärke-Industrie: Gewinnung nativer Stärke, Herstellung von Stärkeprodukten durch Hydrolyse und Modifikation. ATV-DVWK Merkblatt-M 776
(2002).
Austermann-Haun, U., Stärkefabriken, ATVSeminar: Abwasserbehandlung in der Ernährungs und Getränkeindustrie, Essen 1997.
Austermann-Haun, U., Seyfried, C.F., Stärkefabriken, In: Lehr- und Handbuch der Abwassertechnik (ATV, Ed.), 4th Edn., pp. 65– 91. Berlin 2000: Ernst & Sohn.
Seyfried, C. F., Saake, M., Stärkefabriken, Stärkezucker und Stärkesirupherstellung, In: Lehrund Handbuch der Abwassertechnik
(ATV, Ed.), Vol. V, pp. 182–219. Berlin 1985: Ernst & Sohn.
Vegetable Oil and Shortening Production
ATV, Organisch verschmutzte Industrieabwässer, Korrespondenz Abwasser 1979, 11, 664–667.
ATV, Organisch verschmutzte Industrieabwässer, Korrespondenz Abwasser 1981, 9, 651–656.
Heinrich, D., Speisefett/Speiseölfabriken, ATV-Seminar: Abwasserbehandlung in der Ernährungs und Getränkeindustrie, Essen
1997.
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Potato Processing Industry
ATV, Abwässer der Kartoffelindustrie, ATV Merkblat-M 753 (1985).
ATV-DVWK, Abwasser aus der Kartoffelverarbeitung, ATV Merkblatt-M 753 (2004).
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(ATV, Ed.), 4th Edn., pp. 155–171. Berlin 2000: Ernst & Sohn.
Slaughterhouses
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ATV, Behandlung und Verwertung von Reststoffen aus Schlachtund Fleischverarbeitungsbetrieben, ATV Regelwerk Abwasser: Abfall, ATV Merkblatt-M 770 (1995).
Blaha, M.-L., Schlachthofabfälle; Mengenanfall und Inhaltsstoffe, Die Fleischwirtschaft 1995,
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Dairy Industry
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ATV, Abwasser bei der Milchverarbeitung,
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Fruit Juice and Beverage Industry
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Breweries
ATV, Reinigung hochverschmutzten Abwassers, 1.18 Brauereien, Korrespondenz Abwasser 1977, 6, 182–186.
Rosenwinkel, K.-H., Entwicklungstendenzen bei der Brauereiabwasserbehandlung, Braue- reiabwasser-Seminar, Institut für Siedlungswasserwirtschaft und Abfalltechnik der Universität Hannover (26.03.1996).
Rosenwinkel, K.-H., Schrewe, N., Brauereien und Malzfrabriken, In: Lehrund Handbuch
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Seyfried, C. F., Verfahrenstechnische Grundlagen der Brauereiabwasserbehandlung, Brauerei- abwasser-Seminar, Institut für Siedlungswasserwirtschaft und Abfalltechnik der Universität Hannover (26.03.1996).
Seyfried, C. F., Rosenwinkel, K.-H., Brauereien und Malzfabriken, In: Lehrund Handbuch der Abwassertechnik (ATV, Ed.), 3rd Edn., Vol. V, pp. 509–549. Berlin 1985: Ernst & Sohn.
Distilleries
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3
Activated Sludge Process
Rolf Kayser
3.1
Process description and historical development
3.1.1
Single-stage process
About 1910, investigations started on the treatment of wastewater simply by aeration (e.g., Fowler and Mumford in Manchester [1]). Ardern and Lockett [2] in Manchester conducted similar experiments but after a certain aeration period they stopped aeration, let the flocs settle, decanted the supernatant, added more wastewater, and repeated the cycle again and again. After buildup of a certain amount of biomass they obtained a fully nitrified effluent at an aeration period of 6 h. The settled sludge they called ‘activated sludge’. The first technical scale plant was a fill- and-draw activated sludge plant, which today is called the SBR process. Since at that time the process had to be operated manually, they had a lot of operational problems, and therefore, the next plant was built in what is called today the conventional mode (Fig. 3.1).
An activated sludge plant is characterized by four elements:
•An aeration tank equipped with appropriate aeration equipment, in which the biomass is mixed with wastewater and supplied with oxygen.
Fig. 3.1 Flow diagram of an activated sludge plant.
Environmental Biotechnology. Concepts and Applications. Edited by H.-J. Jördening and J. Winter Copyright © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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