Method of engineering calculations of bioreactors for biological treatment of natural water and advanced treatment of sewage
Relevance of research. In order to intensify the processes of natural and sewage treatment in agricultural water supply and sewage systems, a number of measures have been proposed, some of which are the use of biological methods of water purification with the help of attached hydrobionts in bioreactors (BR) with fine-fiber loading.
For the first time he raised the question of the expediency of microbiological methods for purification of natural waters, Professor P.I. Gvozdiak, who claims that the microbiological method can clean any contaminated water, significantly improve the efficiency of water purification, improve the quality of purified water and reduce its cost. With the biological method of neutralizing underground waters, the specific Gallonella ferruginea iron bacteria, due to their catalytic action, quickly oxidize Fe2+, and the resulting iron hydroxide Fe(OH)3 accumulate in a compact form, which significantly increases the dirt of contact clarifying filters (CСF) and the duration of the filtration cycle.
The purpose of the research. To develop a method of mathematical modeling of processes of biological purification of natural and sewage in the BR and methods of engineering calculations of these structures for determining their optimal structural and technological parameters.
Principle of BR work. Microorganisms inhabiting a biofilm, which is formed on the surface of filaments of fibrous fluid, oxidize substances that are in the source water, oxygen in the air, while receiving energy for their livelihoods. After intense aeration, the initial water enters the BR and is evenly distributed between the threads of the fibrous boom, flowing over the surface on which the biofilm is formed with aerobic microorganisms. At the same time, processes such as adhesion, sorption, diffusion, destruction, oxidation, etc. occur, which results in the rapid removal of oxidizing substances and the formation of new substances.
BR has the following functions:
- biochemical oxidation of impurities present in the source water;
- removal of gases from the water to eliminate bubble colmatation in the subfilter space of the CCF;
- ensuring a constant rate of water filtration during the filtration cycle due to an increase in the water level in it by changing the pressure loss on the CCF from hf.0 (at a clean loading) to hf.max (at the end of the filtration cycle).
Mathematical model and algorithm of engineering calculations BR. For a mathematical description of the processes of water purification in the BR, it is necessary to establish the balance of the change in the concentration of contamination in the biofilm, the liquid film and the volume of the source water, which is located between the fibrous threads and moves from top to bottom. BR perform the role of air separators, the area of which must be taken from the calculation of the velocity of the downstream water flow not more than 0,05 m/s and the duration of water in it for at least 1 minute.
Engineering calculations lead in the following sequence:
- for the estimated flow of water through the BR Qe, m3/h, the accepted number of threads of the fibrous load N and the cross-sectional area of one thread, determine the cross-sectional area of the BR and the velocity of water flow in the BR;
- to ensure the required time for water in the BR with a duration of te≥1 min at the limit velocity of water in the BR Vl= 0,05 m/s its height should be not less than He.min≥3 m;
- for preliminary calculations, we take the estimated values of the output constants and coefficients defined in the special literature: Kc = 0,025 - 0,080 m/h; A = 0,01 – 0,04 m/h; δp = 0,1 – 0,2 mm;
- according to laboratory studies, we find the maximum specific bristle content of BR, the duration of the filtracycle in the zone of accumulation of contaminants and the duration of washing BR in its given intensity;
- specify the estimated values of Hb and Cfand the efficiency of water purification in the BR.
Conclusions. The required working height of the loading BR depends on the depth of the water treatment C0 / Сf, is directly proportional to the water filtration rate Vf and inversely proportional to the number of threads in the unit of loading БР. The developed methodology of engineering calculations BR can determine their rational design and technological parameters, based on the requirements of providing the required time for water in the BR at the marginal velocity of the downward movement of water and the calculated efficiency of water purification from impurities.
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