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Summary of common calculation formulas for anaerobic reactors!

来源:环保工程师 作者: 阅读:326 网友评论0 Updated: 2019-12-10 11:31 Source: engineer of environmental protection: Reading: 326 2010 0 comments

For quite some time, anaerobic digestion has lagged far behind the development of aerobic biological treatment in theory, technology and application. Since the 1960s, the world ’s energy shortage has become increasingly prominent. This has led to a re-understanding of anaerobic digestion processes, a large number of studies on the design of treatment processes and reactor structures, and methane recovery have made the theory and Practice has made great progress and has been widely used.

At present, anaerobic microorganism treatment is an indispensable treatment section in the high-concentration organic wastewater treatment process. It is better that aerobic microorganism treatment not only has low energy consumption, but also can produce biogas as a secondary energy source. The higher the anaerobic reaction volume load, the better the oxygen reaction is much higher, and the investment for the same amount of COD anaerobic reaction is lower.

In the operation of the anaerobic reactor, the rising flow rate, hydraulic retention time, and volume load, etc., how are these data calculated? Today we will talk about the five most commonly used calculation formulas in the daily operation of anaerobic reactors.

Rising flow rate

Up flow Velocity is also called Superficial Velocity or Superficial Loading Rate. Assuming that the inlet water flow (including the circulation of the outlet water) of an upward flowing reactor is Q (m3 / h) and the cross-sectional area of the reactor is A (m2), the rising flow rate u (m / h) can be defined as:

In the formula:

u – ascending flow rate in meters / hour

Q-Inlet water flow of the reactor, in cubic meters / hour

A-cross-sectional area of the reactor in square meters

Hydraulic retention time

Hydraulic Retention Time (Hydrolic Retention Time) is short for HRT. It actually refers to the average residence time of wastewater entering the reactor in the reactor. Therefore, if the effective volume of the reactor is V (m3)

In the formula:

HRT-hydraulic retention time

V-reactor volume in cubic meters

Q-Inlet water flow of the reactor, in cubic meters / hour

If the reactor height is H (m), then: because Q = uA, V = HA

Therefore, HRT can also be expressed as the following formula, that is, the hydraulic retention time is equal to the ratio of the reactor height to the rising flow rate.

In the formula:

HRT-hydraulic retention time

H-reactor height in meters

u-ascending flow rate in meters / hour

3. Organic load in the reactor

The Organic Loading Rate (OLR) of the reactor can be "divided into two expressions: volume loading rate (VLR) and sludge loading rate (SLR).

VLR refers to the amount of organic pollutants in wastewater received per unit volume of the reactor, and its unit is kgCOD / (m3d) or kgBOD / (m3d). Assuming that the inlet water concentration is pw (kgCOD / m3 or kgBOD / m3) and the flow rate is q (m3 / d), then:

In the formula:

VLR-Volumetric load

Q-Inlet water flow of the reactor, in cubic meters / hour

Pw-Influent concentration in kgCOD / m3

V-reactor volume in cubic meters

4. Specific methanogenic activity of sludge

Specific Methanogenic Activity is the maximum rate of methanogenesis per unit mass of anaerobic sludge under certain conditions. Its unit is mlCH4 / (gVSS? D), m3CH4 / (kgVSS? D), or gCODCH4 (gVSS? D)

Specific methanogenic activity is an important parameter for sludge properties. Specific methanogenic activity is determined by a special method, which does not refer to the actual methanogenic rate of the sludge in the reactor, but indicates the potential methanogenic capacity of the sludge. Because the specific methanogenic activity is affected by many factors, such as temperature, substrate concentration and composition, the specific methanogenic activity measured under different conditions is different.

Because the reactor load depends on the amount of sludge in the reactor, the specific methanogenic activity of the sludge and the situation where the sludge and wastewater are mixed, the specific methanogenic activity is the reactor load and An important parameter for efficiency.

In the anaerobic process of COD in the dissolved wastewater entering the anaerobic reactor, it is converted into methane, a small amount of cellular material and underutilized VFA. Because the amount of cellular material and VFA is relatively small, and for the anaerobic treatment of dissolved wastewater, methanogenesis is a rate-limiting step. Therefore, the maximum expected load of the reactor can be approximately expressed as:

In the formula:

Ps-average concentration of sludge in the reactor, kgVSS / m3;

U-specific methanogenic activity of sludge, kgCODch4 / (kgVSS? D);

fc-mixing coefficient of sludge and wastewater, fc = 1 for well-mixed reactors.

5. Sludge residence time in the reactor

Sludge Retention Time (SRT) is also called mud age. Extending SRT is the main design idea of all high-speed anaerobic reactors. In other words, a high SRT is the basic guarantee for high-speed and efficient operation of the anaerobic reactor.

In a continuously operating anaerobic reactor:

or

In the formula:

Ps-average sludge concentration in the reactor, unit kgTSS / m3 or kgVSS / m3;

Ps'-average sludge concentration in the effluent, the unit is the same as Ps

V-reactor volume in m3

Q-daily wastewater treatment volume in m3 / d.

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