CS237020B1 - Biological aerobic wastewater treatment - Google Patents

Abstract

The invention relates to an aerobic method for treating wastewater from chemical, food and other production plants. Its essence is the treatment of wastewater entering biological oxidation by adding calcium salt to a value higher than 9.

Description

The invention relates to an aerobic method for treating wastewater from chemical, food and other production plants.

The aerobic method of biological wastewater treatment used so far is based on the biological destruction of organic matter, most often by the action of spontaneous cultures of microorganisms, which in an aerobic environment with a continuous supply of air or technical oxygen oxidize organic matter as their substrate. From the oxidation reactor, the so-called activation tank, a mixture of wastewater and activated sludge flows into the separation, so-called secondary settling tank. The separated purified wastewater flows into the recipient or for further treatment and utilization. The activated sludge with partially adsorbed pollutants captured at the bottom of the secondary settling tank is recirculated into the reactor. The increase in activated sludge, which occurs through the biosynthesis of the substrate — polluting organic substances — is removed from the system for further processing. The efficiency of treatment is proportional primarily to the relative concentration of pollutants and activated sludge ( — sludge load). A higher concentration of activated sludge allows for deeper destruction of organic matter and the resulting lower sludge load reduces the proportional increase in activated sludge. The poor sedimentation properties of activated sludge very often do not allow for perfect separation of activated sludge and wastewater in the settling tank, so that the resulting sludge components deteriorate the quality of the effluent. The desired high sludge concentration cannot be maintained in the oxidation reactor. Poorly sedimenting sludge is most often formed by non-compact cell clusters or an overgrown culture with a predominance of filamentous organisms. Such sludge has unsuitable properties for separation from a hydraulic point of view and makes further processing, i.e. thickening and dewatering for economic use, difficult.

The solution to the problem of improving the separation properties of activated sludge is based on the well-known knowledge that aerobic microorganisms respire carbon dioxide during the oxidation of organic matter in the activated tank and during separation in the final settling tank. Its higher concentration in the surrounding environment — in the activation tank, or in the final settling tank — makes it difficult for the diffusion processes through the cell membrane of microorganisms, which therefore change their shape from the economical and advantageous spherical shape from the point of view of gravitational separation, to a segmented or elongated one. With the increasing concentration of free carbon dioxide during the purification of polluting organic substances of predominantly carbohydrate type, the selection of microorganisms occurs — in polyculture, bacteria of elongated shapes or directly filamentous species with a significantly higher surface to volume or mass ratio prevail. In addition, non-spherical microorganisms, which are lightened by escaping carbon dioxide microbubbles, sediment poorly.

The above disadvantages found in aerobic treatment of wastewater containing primarily high molecular weight polysaccharides, amino acids and hydrocarbons, including chlorinated ones, with a characteristic ratio of BOD5: COD of 0.45 to 0.6 by low-load activation with a sludge load of L = 0.15 kg/kg D (removed BOD5 per organic dry matter content of sludge) are eliminated by the purification method according to the invention, in which the wastewater is alkalized with calcium compounds, such as hydroxide or calcium oxide, to a value higher than 9 before biological oxidation, so that 0.035 to 0.35 kg of Ca ^z+ is dosed per 1 kg of removed oxygen, measured by the conventional BOD5 method, thereby limiting the selection consequences for the selection of microorganisms by the limiting concentration of the metabolite (carbon dioxide) controlled by the reactions of carbon dioxide and calcium compounds, carbonation of calcium hydroxide, respectively by dissolving calcium carbonate to form calcium hydrogen carbonate.

The method according to the invention ensures that conditions are created for the reaction of the formed carbon dioxide with calcium hydroxide for the waste water entering the oxidation reactor. The formed hydrogen carbonate, or calcium carbonate, respectively, reduce the concentration of free carbon dioxide in the oxidation reactor and in the settling tank, even after the calcium salt dosing is temporarily stopped. In the environment of the activation and settling tanks, where biochemical reactions take place, a concentration gradient is created, which facilitates diffusion processes during the respiration of carbon dioxide through the cell membrane of microorganisms. At the same time, a desired concentration gradient of the metabolite — carbon dioxide is created in the activation tank between the inlet and outlet of the waste water and sludge. The resulting sludge is very compact; fibrous or segmented types of microorganisms are suppressed. The loaded sludge sediments very well in the settling tank. Its increased mineralization with calcium carbonate microcrystals slows down aerobic processes in the settling tank and during thickening and dewatering. Good sedimentation properties allow for an increase in the concentration of activated sludge in the activation tank. A decrease in sludge loading causes a desirable decrease in organic matter production. Biosludge mineralized with calcium carbonate thickens very well even at high surface loads in the thickening tank and dewaters well even without the addition of inorganic or organic flocculants. The increased calcium content in the waste sludge allows for its easier use in agriculture.

Example 1

Wastewater from the production of viscose staple, caprolactam, vinyl chloride, agricultural products and sewage wastewater from the company and the city in the amount of 10,500,000 ^m3 /year was neutralized according to the original technology with 7 to 10% Ca (OH) 2 suspension to pH values of 6.5 to 8, then subjected to primary sedimentation, further biological oxidation in activation tanks and from there led to the final sedimentation tank and finally to the recipient.

raw water — inflow COD (mg/1)

BOD5 (mg/1) undissolved substances (mg/1) water from the first sediment-COD (mg/1) ce BOD5 (mg/1) undissolved substances (mg/1) water after settling tanks — COD (mg/1) outflow BOD5 (mg/1) undissolved substances (mg/1)

Wastewater in all three profiles of the treatment plant is evaluated daily based on the analysis of poured samples taken every 2 hours.

Since mid-1981, this wastewater has been treated using the method according to the invention. For the suction of vertical pumps that pump wastewater after the 1st sedimentation into the activation

year 1980 January to June 1981 622 679 256 132 579 567 270 276 112 92 275 233 73 61 91 66

tanks, a 7 to 10% suspension of calcium hydroxide is supplied through a rubber pipe, the pH of the wastewater entering the activation tank reaches values of 9 to 11. The dose is 0.20 to 0.35 kg of Ca ²⁺ per 1 kg of removed organic pollution — O2 (measured by the usual method of determining BOD5). The dosage is constant, the flow rate of this so-called milk of lime is adjusted once a week.

July to December 1981 year 1982 year 1983 raw water — influent COD (mg/1) 595 517 603 BOD5 (mg/lj) — 241 288 insoluble matter (mg/1) 118 120 124 water from the first session- COD (mg/lj) 538 461 536 mentation BOD5 (mg/lj) 237 216 226 insoluble matter (mg/lj 121 89 123 water for settling- COD (mg/1) 192 174 209 ky — drain BOD5 (mg/1) 38 27 28 ... ' . insoluble matter (mg/1) 69 43 36

By using the method according to the invention, the dewatering capabilities of sludges were significantly improved; the specific filtration rates of untreated sludge decreased from values of 5.10 ³ to 9.10 ¹⁴ m/kg to values of 2.10 ^u to 5.10 ¹² m/kg. Example 2

Wastewater from the production of dried soups and soup extracts, including rinsing and cooling water, as well as sewage wastewater from the plant and housing estate for about 30 residents in the amount of 120,000 ^m3 /year, were subjected to primary sedimentation in a slotted tank, then biological oxidation in an activation tank and from there led to a settling tank and finally to the recipient.

inlet for cleaning cleaning drain year 1981 COD (mg/1) 2195 233 BOD5 (mg/lj) 1047 36.4 insoluble matter (mg/1) 558 56 January to July 1982 COD (mg/1) 1813 215 BOD5 (mg/lj) 1066 30.3 insoluble matter (mg/1) 425 66

Due to the occurrence of poorly sedimenting, partly fibrous sludge, the method according to the invention was adopted, i.e. alkalizing the wastewater at the point of inflow until activation by dosing powdered calcium oxide into the inflow to the treatment plant.

VIII. to XII. 1982 COD (mg/1)

BOD5 (mg/1) undissolved substances (mg/1)

1983 COD (mg/1]

BOD5 (mg/1) undissolved substances (mg/1)

The sludge content in the activation was increased 2.5 times (maintained at about 5 to 7 kg/mj) and the filamentous bacteria in the sludge were completely suppressed; sludge indices are maintained at 100 ml/g.

amount of 15 kg/day (one-time), which represents a specific dose of 0.12 to 0.035 kg of Ca ²⁺ per 1 kg of removed organic pollution 02 (BOD5).

sewage treatment plant drain

1666 235 910 21.3 578 38 1914.3 192.1 1088 15.7 409.8 6.3

The sludge from this wastewater drains quickly in the sludge field and is of great interest, especially among gardeners, due to its humus-forming matter and calcium content.

Claims (1)

A method of biological aerobic treatment of waste water from chemical, food and similar plants with pollution predominantly polysaccharides, amino acids and hydrocarbons, including chlorinated, in which the waste water is first subjected to biological oxidation and then sedimentation, characterized by the invention the biological oxidation adjusts to a value greater than 9 by adding a calcium compound such as hydroxide or calcium oxide in an amount of 0.035-0.35 kilograms of Ca ²⁺ per kg of BOD5 (O2) removed.