Управление вспуханием активного ила с помощью технологических параметров обработки сточных вод
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- Водное хозяйство
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УДК 628. 355. 5
ACTIVE SLUDGE BULKING CONTROL USING TECHNOLOGICAL PARAMETERS OF WATER TREATMENT
V. Yurchenko, Professor, Doctor of Technical Science, Ye. Voronova, Associate Professor, A. Astapova, master, KhNAHU
Abstract. As the result of researches there have been defined technological parameters of waste water treatment. These parameters will allow to control the active sludge bulking.
Key words: sludge volume index, dry weight, active sludge, bulking, sedimentation properties.
УПРАВЛЕНИЕ ВСПУХАНИЕМ АКТИВНОГО ИЛА С ПОМОЩЬЮ ТЕХНОЛОГИЧЕСКИХ ПАРАМЕТРОВ ОБРАБОТКИ СТОЧНЫХ ВОД
Аннотация. В результате проведенных исследований были установлены технологические параметры обработки сточных вод, с помощью которых можно управлять вспуханием активного ила.
Ключевые слова: иловый индекс, сухой вес, активный ил, вспухание, седиментационные свойства.
КЕРУВАННЯ СПУХАННЯМ АКТИВНОГО МУЛУ ЗА ДОПОМОГОЮ ТЕХНОЛОГІЧНИХ ПАРАМЕТРІВ ОБРОБКИ СТІЧНИХ ВОД
Анотація. В результаті проведених досліджень було встановлено технологічні параметри обробки стічних вод, за допомогою яких можна керувати спуханням активного мулу.
Ключові слова: муловий індекс, суха вага, активний мул, спухання, седиментаційні властивості.
Sedimentation of active sludge is its ability to form strong, quickly settling flakes. They are considered to be main active sludge technological properties playing the major role in maintenance of biological treatment constructions reliability necessary for purification of residential and industrial sewage.
Infringement of active sludge sedimentation properties results in so-called «bulking» of active sludge just increasing sludge index up to
values more than 150 ml/g. That leads to a phenomenon when active sludge does not have enough time to be separated completely from the treated liquid after two-hour upholding in a secondary settler. Active sludge starts to be taken out from secondary settler but it is not involved any more in the further process of water treatment. As a result there occur rather dangerous infringements in the operation of treatment constructions: technological ones that is steady reduction of sludge concentration in the system of «aerotank-secondary settler», ecological when sewage treatment reduction effect and the increased content of pollutants in processed water.
The main ecological danger of active sludge «bulking» is delivering of suspended substances into natural reservoirs from treatment constructions. Suppression of active sludge «bulking» in operaton of treatment constructions and prevention of this phenomenon considered to be one of the most actual problems of reliable protection of natural reservoirs from pollution with liquid industrial and anthropogenous waste products .
Purpose of the work and problem statement
The purpose of the work is to reveal technological parameters of sewage processing which control sedimentation properties of active sludge to develop ecologically safe technological methods of operative struggle against sludge «bulking» in treatment constructions.
Researches were carried out on Bezludovskie treatment constructions. The control of sewage treatment process and active sludge sedimentation properties was carried out by defining of a physical parameter namely water temperature penetrating into treatment constructions, technological parameters that is concentration of sludge dry substance (a doze of sludge) in aerotanks and regenerators, sludge index (the volume occupied with 1 g of active sludge after 30 minute settling), hydrochemical parameters — concentration of nitrates, hydrogen sulphide (sulfides).
Active sludge technological parameters control
The reason of active sludge «bulking» is an intensive filamentous bacteria development. In tests of active sludge samples the filamentous index was rather high (about 5−6). According to the results of the carried out tests executed with the help of microscopic researches , the following filamentous bacteria characteristics, being activators of «bulking», stipulated by the identification keys developed by Dutch scientist D. Eikelboom have been established: branching is not expressed- mobility is not observed- strings form is bent slightly- strings length constitutes 200 microns- diameter is 1,5−2,5 microns- the attached growth of bacteria to strings has not been marked- partitions between cells are well appreciable- painting by Gram is negative, painting by Neysser is negative, the test with Na2S is positive.
In total the established filamentous bacteria indications «bulking» activators are classified as Type 021N.
These bacteria refer to sulfur ones using restored compounds of sulfur in the metabolism. Therefore the probable reason of the development of filamentous bacteria Type 021N in biological treatment constructions can be the presence of hydrogen sulphide at entering sewage. Comparison of average sludge index in all aerotanks with concentration of sulfides in acting sewage reveals a positive correlation between these parameters (fig. 1). The increase of sulfides concentration in processable sewage coincides with the increase of sludge index up to extreme values — more 1000.
Fig. 1. Dynamics sludge index in aerotanks and sulfides concentration at entering sewage
A positive correlation between sludge index and sewage temperature has been marked. However this correlation is less obvious than the correlation between sludge index and sulfides concentration.
According to some scientists, filamentous bacteria have a higher temperature constant than monocelled bacteria. Temperature increase leads to the following: filamentous bacteria growth rate starts to outstrip the growth rate of monocelled bacteria. On the other hand, temperature increase activates anaerobic processes in water removal pipelines including processes of hydrogen sulphide formation which activate the development of filamentous bacteria Type 021N.
A positive correlation between sludge index in aerotanks and concentration of nitrates in the processed sewage is being marked (fig. 2). It is possible to explain nitrates influence on any oxygen mode in system of «aerotank-secondary settler» by the following: nitrates suppress anaerobic processes in secondary settler first of all hydrogen sulphide formation, and the total contents in system of «aerotank-secondary settler» decreases. And hydrogen sulphide is an obligatory condition of sulfuric filamentous bacteria development of Type 021N.
Fig. 2. Dynamics sludge index in aerotanks and entering sewage temperature
During the winter season the sludge index did not exceed 175 ml/g. During this period when mentioned above parameters correlating with sludge index (water temperature, concentration of sulfides in acting water and concentration of nitrates in the processed water) had constant values the correlation between the sludge index (in aerotanks and regenerators) and the doze of sludge has been marked. The correlation factor between the sludge index and the doze of sludge in aerotank constituted 0,86 in comparison with the regenerator where the factor of correlation
constituted 0,68. Probably this phenomenon is caused by features of active sludge sedimentation .
1. The activator of sludge «bulking» in the constructions is filamentous sulfuric bacterium Type 021N-
2. The sludge index increase is correlated positively with temperature and concentration of sulfides in acting sewage and also with sludge concentration in constructions-
3. There was marked a inversely proportional dependence among sludge index increase and concentration of nitrates in the processed water-
4. The marked parameters of sewage processing influencing on sedimentation properties of active sludge are being ecological factors of sulfuric filamentous bacteria development of Type 021N.
1. Очистка сточных вод: пер. с англ. / под
ред. М. Хенце, П. Армоэс, Й. Ля-Кур-Янсен и др. — М.: Мир, 2004. — 480 с.
2. Eikelboom D.H. Process Control of Activated
Sludge Plants by Microscopic Investigation. / D.H. Eikelboom. — London: IWA Publishing, 2000. — 163 р.
3. Wanner J. Activated Sludge Bulking and
Foaming Control / J. Wanner. — Lancaster: Technomic Publishing Co, 1994. — 327 p.
Статья поступила в редакцию 11 ноября 2010 г.