RU2415815C2 - Method of treating waste water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to treatment of concentrated waste water, particularly waste water from confectionary companies. Waste water which contains a large amount of organic contaminants undergoes primary settling to remove suspended substances. The treated water is then fed into a step I aerotank where is it aerated for 1.076 days while maintaining the dose of active sludge in amount of 3.4 g/l. A portion of the active sludge is removed in the settling tank. Further, the treated water is fed into a step II aerotank where it is aerated for 0.58 days while maintaining the dose of active sludge at 2.04 g/l. Before releasing into a water body, the treated waste water is fed into a settling tank to remove active sludge.

EFFECT: high efficiency of treating waste water.

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Description

The invention relates to a technology for the treatment of concentrated wastewater, in particular, confectionery enterprises.

A known method of wastewater treatment by flotation (see RF Patent No. 2104963, IPC C02F 1/52, 1998), in which contaminated wastewater of confectionery factories is treated.

However, this method has several disadvantages: the use of coagulants slightly reduces the BOD, the performance is limited when using reverse osmosis membranes, the operation of the facilities is much more complicated, the energy intensity of the cleaning process is increased, and, as a result, the investment and operating costs are increased. It was found that organic impurities contained in concentrated wastewater can be removed using reverse osmosis membranes with a pore diameter of not more than 10-15 · 10 ^-10 m. Currently, organic pollution of wastewater, in particular in the confectionery industry, is so great that special attention is paid to highly efficient methods of wastewater treatment under extreme loads on the treatment system.

The closest, in fact, is the technology of single-stage biological wastewater treatment in aeration tank (see RF Patent No. 2060965, IPC C02F 3/02, 1996), which includes aeration of wastewater with activated sludge in aeration tank, followed by separation or settling in the first steps of the secondary sump for 40-45 min with the return of circulating activated sludge from it to the aeration tank, clarification of the purified water from suspension by settling in the second stage of the secondary sludge for 75-80 min with the removal of excess activated sludge from it for treatment and disposal.

The analysis of this method shows that it is quite effective as applied only to wastewater, the quality indicators of which do not exceed: BOD _full = 250 mg / l, suspended solids 150 mg / l. However, the use of such a cleaning method as applied to concentrated wastewater with BOD values of more than 600 mg O ₂ / l and COD more than 1300 mg O ₂ / l, suspended solids 1,500 mg / l of confectionery enterprises, does not give the expected cleaning effect.

The technical task is to create an effective method of biological wastewater treatment using a two-stage aerobic scheme.

The technical result is an increase in the efficiency of wastewater treatment, as well as a significant reduction in the amount of organic pollutants entering surface water bodies with wastewater from the food industry.

It is achieved by the fact that waste water containing a large amount of organic impurities is subjected to primary sedimentation to remove suspended solids, fed to the first stage aeration tank, where it is aerated for 1.076 days and a dose of activated sludge of 3.4 g / l is maintained; then served in the sump to remove part of the activated sludge. Next, the water is fed into the second stage aeration tank, where it is aerated for 0.58 days and a dose of activated sludge of 2.04 g / l is maintained; then water is fed to the sump to remove activated sludge.

Example 1 of a specific implementation of the method.

The wastewater from the confectionery factory was supplied to a two-stage biological treatment model plant with preliminary sedimentation. The experimental setup consisted of models of aeration tanks with pneumatic aeration up to 10 l and models of sludge separators in the form of vertical settlers. Additional aeration of wastewater contributed not only to the oxidation of wastewater, but also their biological treatment, since as a result of this, the vital activity of aerobic microorganisms that decompose organic compounds is intensified.

Water supply and circulation of activated sludge in the system was carried out using a multi-channel metering pump. The installation model was a technological scheme of a two-stage wastewater treatment. Each stage had its own sludge separator; therefore, at all stages operating under flowing conditions, a biocenosis of activated sludge microorganisms was formed, which was most adapted to incoming contaminants and used a multicomponent substrate for its life activity. This significantly intensified the biological treatment process. The species composition of microorganisms of activated sludge was determined by the qualitative and quantitative composition of organic wastewater pollution.

The wastewater treatment process was controlled by BOD _{5 of the} source and purified water, the dose of sludge, the ash content of the sludge, the concentration of dissolved oxygen, and the sludge index. The considered parameters were determined by standard methods.

The quality of the initial runoff had the following indicators: BOD 600 mg / l, COD 1300 mg / l, suspended solids 1400 mg / l.

The cleaning option under consideration was characterized by the following features: the volumes of the first and second cleaning stages were 8.0 and 10.0 L, respectively, the aeration time was 0.73 days and 1.15 days, the concentration of activated sludge in aeration tanks was maintained on average 3.6 g / l and 2.2 g / l. The wastewater flow rate in the model plant remained constant and amounted to 0.012 m ³ / day.

The specified cleaning mode allowed to achieve the following results. After the first stage of biological treatment, BOD of wastewater decreased by 66%, COD by 73%. At the output, the main indicators of BOD and COD were 36 mg O ₂ / L and 48 mg O ₂ / L, respectively. Other indicators of wastewater quality, such as nitrogen compounds, did not exceed the maximum permissible values.

The data obtained testified to the possibility of discharge into the city sewer for subsequent treatment and discharge into a water body.

Example 2

The wastewater from the confectionery factory entered the two-stage biological treatment model plant with preliminary sedimentation. The experimental setup consisted of models of aeration tanks with pneumatic aeration up to 10 l and models of sludge separators in the form of vertical settlers. Additional aeration of wastewater contributed not only to the oxidation of wastewater, but also their biological treatment, since as a result of this, the vital activity of aerobic microorganisms that decompose organic compounds is intensified.

Water supply and circulation of activated sludge in the system was carried out using a multi-channel metering pump. The installation model was a technological scheme of a two-stage wastewater treatment. Each stage had its own sludge separator; therefore, at all stages operating under flowing conditions, a biocenosis of activated sludge microorganisms was formed, which was most adapted to incoming contaminants and used a multicomponent substrate for its life activity. This significantly intensified the biological treatment process. The species composition of microorganisms of activated sludge was determined by the qualitative and quantitative composition of organic wastewater pollution.

The wastewater treatment process was controlled by BOD _{5 of the} source and purified water, the dose of sludge, the ash content of the sludge, the concentration of dissolved oxygen, and the sludge index. The considered parameters were determined by standard methods.

The quality of the initial runoff had the following indicators: BOD 600 mg / l, COD 1300 mg / l, suspended solids 1400 mg / l.

The treatment option under consideration was characterized by the following features. The volumes of the first and second stages of purification were 12.4 and 8.8 L, respectively, the aeration time was 1.076 days and 0.58 days, the concentration of activated sludge in aeration tanks was maintained on average 3.4 g / L and 2.04 g / L. The wastewater flow rate in the model plant remained constant and amounted to 0.012 m ³ / day.

The specified cleaning mode allowed to achieve the following results. After the first stage of biological treatment, BOD of wastewater decreased by 92%, COD by 84%. At the output, the main indicators of BOD and COD were 17 mg O ₂ / L and 22 mg O ₂ / L, respectively. Other indicators of wastewater quality, such as nitrogen compounds, did not exceed the maximum permissible values.

The data obtained indicated the possibility of discharge into the water body without further treatment.

It is known that the biological treatment of concentrated wastewater of food enterprises is most reliably described by the equations of enzymatic reactions. The obtained experimental data allowed us to analyze the process of two-stage biological wastewater treatment of confectionery enterprises in the absence of oxygen limitation of the process.

For the considered examples, the constants of the equations of enzymatic reactions were calculated. The calculation of constants was carried out on the basis of the analysis of data from two cleaning schemes. The resulting constants ρ _m , K _L , φ are 357, 130, 1.6 for the first stage and 90, 6.5, 6.2 for the second stage, respectively.

The obtained values allow us to optimize the wastewater treatment process of this production. In the process of research, the optimal treatment regimes were identified, namely: the residence time of wastewater in the first and second stages, which is 27.98 hours and 18.72 hours, respectively. Calculated volumes of structures for the implementation of the scheme.

An analysis of experimentally obtained indicators and calculated optimization parameters of the purification process show that two-stage purification of concentrated wastewater is the simplest and less capital-intensive way of biological wastewater treatment of confectionery enterprises containing a large amount of organic pollution.

Claims (1)

A method of wastewater treatment, including mechanical wastewater treatment followed by biological treatment in an aeration tank, characterized in that the waste water containing a large amount of organic impurities is subjected to primary sedimentation to remove suspended solids, purified in the first stage aeration tank, where the wastewater is aerated for 1,076 days, while maintaining a dose of activated sludge in an amount of 3.4 g / l; then the wastewater is fed to the sump, where part of the activated sludge is removed, then the wastewater is similarly treated in the second stage aeration tank, where the wastewater is aerated for 0.58 days and the activated sludge dose is maintained at 2.04 g / l, after which the wastewater is fed into the sump to remove activated sludge.