CS251844B1 - Method of waste waters' final sedimentation by means of biological flotation's process intensification - Google Patents

Abstract

Method of wastewater treatment by intensification the process of biological flotation is carried out so that the slurry is continuously stirred in the bioreactor flocculation unit adding an alkaline salt, preferably calcium hydroxide and adjust the pH of the suspension to a pH of 8.5 to 10.0. Waste is used to heat the sludge heat of digesters, to supplement organic carbon can be added to the slurry add sludge water from methanizing in an amount of from 1 to 25% by volume process is enzymatic denitrification activity bacteria that are present in mixed culture of activated sludge.

Description

The invention relates to a process for the purification of waste water by intensifying the biological flotation process by increasing the activation of the denitrification activity of the mixed cell population.

The main factors in the treatment process are the high effect of wastewater treatment and the disposal or utilization of excess activated sludge with minimal energy costs and costs.

One of the intensive ways of sewage sludge thickening is the biological flotation process (author's certificate no. 228 403). This method of thickening biological, especially activated sludge, by altering their physical structure, consists in adding to the sludge oxygen-containing nitrogen compounds, preferably nitrates or nitrites, in an amount of 50 to 2000 gm ^- at a temperature of 5-45 ° C and at a pH of 5 to 45 ° C. 8.5 under anaerobic conditions. At the same time, changing the physical structure makes sludge dewatering easier.

The essence of the process is the enzymatic activity of denitrifying bacteria, which are present in a mixed culture of activated sludge. These facultatively anaerobic bacteria utilize nitrates as electron acceptors in the nitrate respiration process in the absence of molecular oxygen while utilizing the organic substrate. The resulting gases, especially nitrogen gas, are the cause of the flotation process.

In particular, temperature and oxygen conditions, an excess of NO ions to be fed to the system, and a high mass transfer between the phases are a precondition for the high efficiency of the biological flotation process.

The gas produced is formed by microscopic bubbles having a diameter of 10 to 220 µm which adhere to the surface of the flakes or form part of their internal structure.

The amount of gas produced by the bacteria in each flake should be sufficient to float it. The gas bubbles should not be released from the particles during the process, as they have not caused a high ascending velocity, combined surface tension, etc., causing disturbances in the flotation process. For these reasons, the presence of trace amounts of heteropolar substances (the remainder of oils, surfactants, etc.), which reduce the wettability of the activated sludge flakes, is appropriate.

The process of bubble dispersion formation during the denitrification process can be influenced by changing the conditions in the bioreactor. These factors, which may substantially affect the denitrifying enzyme activity and the amount and composition of the denitrifying gases, include in particular the pH of the environment, the temperature and mixing of the suspension.

The optimum pH range for the denitrification process is reported to be 6.5 to 7.5, with a pH of 6-8 achieving 70% efficiency (Moore, S.F. and Schroeder, E.D., Water Has., 5, 452-5, 1971).

Another factor that significantly affects the rate of denitrification reaction is temperature. The denitrification process is carried out at temperatures of 0 to 50 ° C. Increase the rate of enzymatic reactions with rising temperature can be expressed as temperature quotient of O, _O, i.e., the ratio of the rate of reaction at a certain temperature for their speed at a temperature 10 C lower. For the denitrification microorganisms, this quotient is between 1.5 and 2.0 (Dawson, RN and Murphy, KL: Adv. In Water Pollut. Res., 6, 671-83, 1972).

However, the reaction rate of the enzyme reactions only increases to a certain temperature according to 0.1 q. When the temperature is exceeded, when the rate of the catalyzed reaction reaches a maximum, reversal occurs and the activity of the enzymes decreases very rapidly due to the thermal inactivation of the protein component of the enzymes.

The reaction rate of the enzyme denitrification reaction is further influenced by the amount of mass transfer between the liquid medium and the nitrate present and the suspended phase biomass flakes. The intensity of the mass flow is dependent on the physical properties of the system, the concentration distribution, the hydrodynamic conditions of the process and, in particular, the size of the mesiphase surface. In an effort to intensify the biological flotation process, to obtain a microbial suspension with high specific denitrification efficiency and to achieve greater effluent contamination, optimum process conditions have been found.

At the same time, it is not known to use the thickening process concurrently to remove solutes from waste water.

It is an object of the present invention to provide a wastewater treatment process by intensifying the biological flotation process comprising adding an alkaline compound, preferably calcium hydroxide, to the continuous stirred slurry slurry in the bioreactor flocculation unit and adjusting the pH of the slurry to 8.5-10.0.

The waste heat of the digestion units can be used to heat the sludge slurry and, to replenish the organic carbon, sludge water from the methanization stage can be added in an amount of from 1 to 25% by volume.

It has been found that the change in pH significantly affects the rate of the denitrification reaction.

The rate of conversion of nitrate to nitrogen gas is dependent on the nitrite concentration in the reaction mixture. Read the concentration of nitrites in the environment has a feedback inhibitory effect on the activity of the first enzyme in the denitrification process - nitrate reductase and thus significantly inhibits the nitrate conversion.

The accumulation of nitrites in the environment is due to the lower activity of the second enzyme in the chain citrate reductase in the more acidic pH range (pH <7.2). As the pH decreases, the percentage of NgO, which is extremely water-soluble, increases significantly in the denitrification off-gas, and thus does not form a bubble dispersion suitable for the flotation process, thereby reducing the separation effect.

It has been found that by increasing the pH up to pH 10, the denitrification process can be accelerated and thus the residence time of the suspension in the bioreactor by more than 50% can be shortened, while at the same time intensifying the organic substrate.

At the same time, by increasing the pH, phosphorus accumulated in the suspended phase, thereby significantly reducing the inorganic phosphate content of the effluent. The principle of elimination of organic phosphates from biological sludge sludge is based on their precipitation into insoluble forms with calcium ions trapped in biological flakes. In this reaction, the calcium ions supplied by the flotation agent, i.e., calcium nitrate, can be used. utilize calcium ions present in the waste water.

At the same time, the ratio of the source of organic carbon and nitrogen to phosphorus influences the removal of inorganic phosphates from waste water. Phosphate accumulation also occurs at the limit. The lack of the source of macronutrients can be solved by adding sludge water. Accumulated phosphate can also serve as a source of phosphorus for cell growth in the absence of external phosphate. It has been found that increasing the temperature from 25 ° C to 35 ° C using a mixed activated sludge culture can achieve = 2.1 while increasing the pH to 8, 5 O _1Q * 2.4.

By controlled mixing of the suspension in the bioreactor, the interfacial surface and thus the mass transfer necessary for the rapid enzymatic reaction is substantially increased, without releasing the gas bubbles formed during the denitrification process from the flakes. Controlled mixing was performed on a model apparatus using a low speed stirrer (10-20 min ¹ ) and in a pilot plant model using a static mixer. The specific denitrification rate was increased by 200% over the unmixed system.

The biflotation process is accompanied by a reduction of organic contamination and thus the secondary effluent is purified. It has been found that the organic pollution of the effluent, indicated by the biochemical oxygen demand, is reduced by an average of 60%, based on the chemical oxygen consumption value of 40%.

251S44

Organic flue gases in the waste water serve as an electron donor for the denitrification process and at the same time they are biosorbed in the spatial structure of the sludge.

Intensification of the blotting process, resp. As a result of the above-mentioned conditions, there is also a significant reduction in organic contamination.

Hall:

VL

POJCHSK

BOD ₅ ^{In the} analytical evaluation of the biological flotation process the following sizes were used: all substances, dimension (gl ^-1 ) = nitrate concentration, dimension (mg.I ^- ') = inorganic phosphate, dimension (mg.l ¹ ), ³ chemical consumption oxygen, dimension (mg.l ¹ ) ³ biochemical oxygen demand, dimension (mg.l ¹ ) = specific denitrigation rate ^{3 3} cons. conc. NO? - residual conc. NO] -i __ ^{J J} (mg.g ~ .h) all substances. Sas

All substances (VL) were determined gravimetrically by drying the sample at 105 ° C to constant weight. Spectrometric methods were used to determine nitrate and phosphate concentrations; in the first case by reaction with sodium salicylate, in the second case with molybdenum after reduction with ascorbic acid; chemical oxygen demand (COD), indicating organic water contamination, was performed by the dichromate method; biochemical oxygen demand (BOD ^) by the dilution method. These measurements were performed according to the recommended methods of Horáková et.al (Methods of chemical analysis of water, ecriptum ICT Prague 1981).

In the following, the invention is illustrated in the examples without being limited thereto. The present invention is also associated with the design of a bioreactor, the elements of the metering and the control of the process that is being developed for the purpose of intensifying biological denitrification flotation.

Example 1

Using 500 ml of the starting of the return activated sludge from a mechanical-biological sewage treatment odpadníbh total solids content of 8.38 gl ^1, pH 6.95, temperature of 18.5 ° C and the specific denitrifying rate of 17.25 mg.g ^"1 .h ” ¹ . The slurry was divided into five parts. In the first fraction, the original pH was maintained, in the second fraction, the pH was adjusted to 6.0 with concentrated sulfuric acid, followed by 30% sodium hydroxide to pH 7.9; 8.5 and 9.0. In all proportions of the sludge suspension, the nitrate content was increased by the addition of 10% by weight. calcium chloride solution to a concentration of 173.0 mg.] ¹ MO].

The progress of nitrate degradation for 60 minutes was monitored in all proportions. Table 1 shows the resulting specific denitrification rates for the slurry under the original conditions and at the adjusted pH. Increase, resp. the decrease in specific divitrification rate is also expressed in% by weight. specific denitrification rates of untreated activated sludge.

Table I

6.95 6.00 7.90 8.50 9.0 mg.g ¹ .h ^-1 17.25 15.49 21.71 24.30 25.70 % wt. 100.00 89.80 125.80 140.90 149.00

By increasing the pH to 9.0, for example, the specific denitrification rate increased by 49.0% by weight.

Example 2

1 sludge slurries from a mechanical-biological wastewater treatment plant with a total content of 4.79 g / ^l , pH 7.0 and a temperature of 25 ° C were divided into three parts and the conditions of denitrification were further adjusted. In the first part the original pH and temperature were maintained, in the second part the pH was maintained at 7.0 and was placed in a thermostat at 35 ° C, in the third part the pH was adjusted to 8.5 with sodium hydroxide and the slurry was temperature of 35 ° C. The nitrate content was increased to 173.24 mg.l ^-1 in all three cases by the addition of a 10% solution of technical calcium nitrate.

Nitrates elimination and organic contamination reduction were monitored at selected time intervals. The results are summarized in Table 11, where specific denitri-

fictional speed and chemical drop Table 11 oxygen consumption in% by weight, after a reaction time of 105 minutes. pH 7.0 Mp: 35 ° C pH 8.5 Mp: 35 ° C Time Bin pH 7.0 Mp = 25 ° C no; J mg.l COD mg.l ^-1 no; J -1 mg.l COD mg.l ' ¹ no; J - -1 mg.l ' COD mg.l 0 173.24 541.0 173.24 54,, 0 173.24 541.0 15 Dec 120,00 57.94 57.94 30 91.00 33.24 25.29 45 81,00 362.0 14.71 326.0 8.68 289.0 60 52.94 2.57 1.47 75 51,00 1.47 1, 03 105 31, 03 238.0 1.47 208.0 1.03 169.9 ^v N07 3 16.97 35.63 40.62 mg.g ""! ¹ Reduction COD % wt. 56.01 61.55 68.76

By the ratio of specific denitrification rates at temperatures differing by 0 ° C the temperature quotient Q, q can be expressed. Increasing the temperature from 25 ° C to 35 ° C was obtained temperature quotient _{Q] 0} = 2.10.

By increasing the temperature from 25 ° C to 35 ° C while increasing the pH from 7.0 to 8.5, a temperature quotient of _Q10 = = 2.39 was obtained.

Example 3

In 200 l sludge suspension of mechanical-biological sewage treatment plant with a total content of 5,59 gl ^-1 , inorganic phosphate 38,8 mg.l ^-1 , pH 7,43, at a temperature of 7 ° C and specifically by tritration 15.04 mg.g speed ^{"1st!» "1} was adjusted to pH 8.5 with calcium hydroxide and then was kept constant for 120 minutes.

The sludge easpension was dosed in a stirred vessel with potassium nitrate to a nitrate concentration of 100 mg.l At selected time intervals for 120 minutes, the progress of nitrate and inorganic phosphate degradation was monitored. The specific denitrification rate and the percentage of phosphate removed were calculated from the results obtained. It has reached the specific denitrifying rate of 21.57 mg.g ^'1. h " ¹ , ie its increase by 43% by weight compared to untreated sludge. An increase of pH to 8.5 resulted in 28.9 wt. removal of the inorganic phosphate present, while for untreated sludge to 12.4 wt. removal.

Example 4

Recovered activated sludge from mechanical-biological Waste Water Treatment Plant with average concentration of all substances 4,5 gl ^- ', content of organic substances according to the value of chemical oxygen demand 4,10 mg.l ^- ', according to biochemical oxygen consumption 198 mg.l ^- ', pH 6.95 teplotš and 16.5 ° C was zahušlován biological flotation unit to a usable volume of 10 flotaSnlm NP in the amount of about 5.5 m ^ .h ^- 'compositions used and delayed by 1.0 h.

A 10% calcium nitrate solution was used as the flocculating agent. The slurry was dosed to a nitrate concentration of 120 mg.] / * ´. The nitrate concentration at the effluent from the flotation bioreactor and reduction of organic pollution was monitored for one month.

Ρσ for the next month, the pH of the sludge suspension and the inlet to the flotation unit were adjusted to 8.5 with calcium hydroxide, and the residence time was shortened from 1.0 hour to 0.5 hours.

An average nitrate concentration of 25 mg.l ** was achieved at the effluent from the flotation unit. Calculated specific denitrification rate was 11.7 mg.g ** '** .h', while adjusting the pH to 8.5 was increased to 17.0 mg.g ^{- and} H ^- '.

The organic pollution of the sludge water discharged from the flotation unit at pH 6.95 was on average 229 mg.l ^- according to COD, respectively. 82, BOD. These values correspond to 44.1 wt. (according to COD) resp. 58.6 wt. (according to BOD) reduction of organic contamination.

When the pH was adjusted to 8.5, the organic contamination of the sludge discharged from the flotation unit was on average 206.1 mg.l ^- ^ according to COD, resp. These values correspond to 49.7% by weight of BOD. (according to COD) resp. 64.8 wt. (according to BOD) reduction of organic pollution.

Example 5

In the biological flotation unit with a usable flotation volume of 10 m ^, biological flotation tests of a mixture of return activated sludge and sludge water from methanization stage β with high organic pollution were performed. Tests were performed at high hydraulic load eyatému 19-22 m ^ .m ^ .d ^- '. The amount of water supplied to the sludge flotation test rozmetl ranged from 290 to 1 360 H ^- ', whereby 1,100 ** H' corresponds to the total production of sludge water from metanizačního stage.

The residence time of the activated sludge and sludge water mixture in the flotation unit ranged from 0.81 to 0.96 hours, the pH of the mixture was adjusted in the flocculation unit with 30% sodium hydroxide to 8.5, the temperature of the mixture was 20 ° C.

The measured and calculated values are shown in Table III. During the flotation process, there was a substantial reduction of organic matter in the mixture of activated sludge and sludge water from the methanization stage. The reduction was 43% by weight. (not COD) resp. 73 $ wt. (based on BOD ^).

Table 111

Flow rate Q lh ¹ Time delay h T ° c PH NOZ dose mg.l ¹ NÁTOK BSK _R NO mg.l ' VL β · Γ ' OUTLET COD mg.l ' BOD _{K mo} 1-1 mg.l no; mg.l ' ^{1 VL} -1 g.1 ¹ COD mg.l ' ¹ Porter activated 7200 sludge 290 0.96 20 May 8.5 76 6,708 858 434 13.4 2,716 441 171 30 Kalová water 2,508 940 535 41, 0

Porter aktivo- _ 144 20 May 8.5 64 8,900 2,508 1 037 '1 940 473 535 21.5 41.0 ⁹ · ®53 678 41 36 sludge, sludge water 360 0.92 Returnable assets 8 571 7,100 180 7.7 sludge, sludge water 095 0.81 20 May 8.5 55 11,306 820 - 5,998 12.3 176 14 Refundable ύ ⁷ Vanya activated sludge Sewage Water Star 638 915 0.90 20 May 8.5 65 7,570 5,440 691 1 567 354 535 14.2 6,189 31.4 431 106 27 Mar:

According to the process of the invention, the pollution of the effluent from the flotation bloreactor indicated by the value of biochemical oxygen consumption is from 50 to 80% by weight, according to chemical oxygen consumption from 30 to 70% by weight, while the activated sludge is thickened. The inorganic phosphate content is also reduced by up to 30% by weight. The residence time of the sludge suspension in the flotation bloreactor can be reduced by an average of 50% by the process according to the invention.

Claims (3)

SUBJECT OF THE INVENTION Process for the purification of waste water by intensifying the biological flotation process, characterized in that an alkaline compound, preferably calcium hydroxide, is added to the continuously stirred sludge suspension in the flocculation unit of the bloreactor and the pH of the suspension is adjusted to a value of 8.5 to 10.0. 2. A process for the purification of waste water by intensifying the biological flotation process according to claim 1, characterized in that the waste heat of the expanding units is used to heat the sludge suspension. 3. A process for the purification of waste water by intensifying the biological flotation process according to claim 1 or 2, characterized in that, to replenish the organic carbon, the sludge slurry from methanization stage is added in an amount of from 1 to 25% by volume.