CS230233B1 - The method of biological sewage treatment with sulfur compounds - Google Patents

Abstract

According to the invention, the pH of the biologically treated wastewater is continuously maintained by the addition of alkali, for example sodium hydroxide, calcium hydroxide, calcium oxide, sodium carbonate, calcium hydroxide or wastewater with a pH higher than 7, in the range of 6 to 11, preferably 8.5 to 9.5, while the sulfide load of the mixed culture is maintained in the range of 0.05 to 2.0 kg. kg-1. d_íS2_, preferably 0.2 to 0.5 kg. kg-1. d'* 1S2-' and the sulfate load in the range of 0.05 to 20.0 kg. kg '1. . d^SzOs2", preferably 0.8 to 1.5 kg . kg-1. . d-1SzO3~2. When sulfide or thiosulfate ions higher than 100 mg l"1 occur in the flow to the biological treatment plant, 0.25 to 1 mol of sulfide ions and 0.5 to 10 mol of acid neutralization capacity are dosed per 1 mol of thiosulfate ions.

Description

According to the invention, the pH of the waste water purified biologically is continuously maintained by the addition of an alkali such as sodium hydroxide, calcium hydroxide, calcium oxide, sodium carbonate, calcium carbonate or waste water having a pH greater than 7 in the range of 6-11, preferably 8.5-9 5, the substance loading of the mixed culture sulfides being maintained in the range 0.05 to 2.0 kg. kg ^-1 . d ^_i S ^2, preferably from 0.2 to 0.5 kilograms. kg ^-1 . d ' ^{* 1} S ^2- ' and a thiosulphate load in the range 0.05 to 20.0 kg. kg ' ¹ .

. d 2 SzO ² , preferably 0.8 to 1.5 kg. kg ^-1 .

. d ^-1 SzO3 ~ ² .

In the presence of sulphide or thiosulphate ions greater than 100 mg l ^"1 in the biological wastewater flow is metered between 0.25 and 1 mole of sulfide ions and 0.5 to 10 moles of acid neutralizing capacity per 1 mol of thiosulphate ions.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to waste water treatment containing sulfur compounds.

Sulfur compounds are commonly found in a wide range of industrial waste water. They consist mostly of sultan, sulphides, sulphates, thiosulphates, organic sulfur compounds and sometimes also elemental sulfur. Virtually all of these forms are represented in some types of waste water from oil processing. These are mainly condensation water and water from scrubbing and drainage of petroleum products.

In terms of aquatic toxicity, sulphides and sultan are the most frequently cited among sulfur compounds. Depending on the type of test organism, their negative effect is already present in milligram concentrations or tens of milligrams per liter.

Other sulfur compounds show toxic effects only in concentrations in which they occur only rarely in wastewater. For example, thiosulfates do not interfere with activated sludge microorganisms even at concentrations of about 10 g. I ^-1 .

Microorganisms capable of oxidizing inorganic sulfur compounds include, in particular, sulfur bacteria and thionic bacteria. Most of these bacteria are able to grow in a strictly autotrophic environment, but there are cases where they also use organic compounds (eg Thiobacillus thiooxidans).

The development of thionic bacteria is usually accompanied by a decrease in pH due to the resulting sulfuric acid. However, most of these bacteria are resistant to low pH. For example, Thiobacillus thiooxidans can tolerate a pH of up to 0.6.

Thion bacteria may also be present in the activated sludge, which is a mixed culture. It would therefore be expected that the adaptation of activated sludge to sulfur compounds would be easy, even at concentrations of hundreds of milligrams per liter.

However, Aulenbach and Heukelekian report that activation cannot be permanently loaded with sulfides at a concentration greater than 50 mg. I ^-1 as activated sludge decomposes.

Lebedeva gives a limit concentration of sulphides of 44 mg. I ^-1 . On the other hand, thiosulfates do not interfere with the activated sludge even in concentrations corresponding to several grams per liter.

As has been found, the presence of sulfur compounds in wastewater can under certain circumstances lead to a sudden decrease in pH in activation. This decrease is accompanied by a deterioration of the cleaning effect of the activation, or a complete loss of the cleaning ability of the activated sludge.

The process according to the invention makes it possible to purify the sulfur-containing waste water biologically without causing the above-mentioned negative phenomena. The principle of the invention is that the pH of the waste water purified biologically is continuously maintained by the addition of an alkali, for example: calcium hydroxide, calcium oxide, sodium hydroxide, sodium carbonate, calcium carbonate or waste water having a pH greater than 7 , preferably 8.5 to 9.5, wherein the material loading of the mixed culture sulfide is maintained in the range 0.05 to 2.0 kg. kg ^-1 . d S ² ~ ^_1, preferably from 0.2 to 0.5 kilograms. kg ^-1 . d ' ¹ S ² - and a thiosulphate load in the range 0.05 to 20.0 kg. . kg ^-1 . d ^-1 S2O3 ^2- , preferably 0.8 to 1.5 kg. . kg ^-1 . d ¹ S ² O ^{3 2} "at a temperature of 5 to 40 ° C, preferably 20 ° C.

An advantage of the process according to the invention is to ensure the trouble-free operation of the biological treatment plant, at a material load of activated sludge with sulfur compounds which has hitherto been considered toxic.

The process according to the invention is described in more detail below on several exemplary embodiments.

Example 1

In the laboratory model of continuous activation, a long-term experiment was performed with synthetic sewage in which the sulfide concentration was adjusted by adding standard sodium sulfide solution to the desired value. The pH of the water was adjusted with a sodium hydroxide solution so that it did not fall below 9. The age of the activated sludge was maintained at 10 days. The operation of the laboratory model was monitored by chemical analyzes performed at one to two-day intervals. The average values of the most important indicators are given in Tab. 1.

TABLE 1 Stage number zg ₂ - kg. ^From S2O3 ² . kg-1.d “ ¹ Time delay hours ^C S2- ^C S2O3 ² “ Přítok mg. if Outflow mg. if Přítok mg. if Outflow mg. 1 " 1 0,023 0,086 6.6 40 0 150 0 2 0.150 0.170 5.6 115 0 124 0 3 0,128 0.359 7.7 115 0 322 0 4 0,128 0.568 6.7 100 ALIGN! 0 433 71 5 0.300 0.158 25.4 760 0 - -

Example 2

In the same manner as in the previous example, another laboratory experiment was carried out. Instead of synthetic waste water, sulphide waste water was purified. The pH of this water was adjusted to 9 with a calcium hydroxide solution. The average values of the most important parameters are given in Table 2.

TABLE 2 Stage number zg2kg · kg “ ^From S2O3 ² “ ¹ . d “ ¹ Time delay hours c _S '2- ^C S2O3 ² “ PřítOK mg. I “ ¹ Outflow mg. I “ ¹ Přítok mg. I “ ¹ Outflow mg. 1 " ^: 1 1.01 0.92 24 980 0 840 0 2 1.42 0.92 28 1340 19 Dec 860 32 3 2.10 1.40 27 Mar: 1960 120 950 75 4 0 12.3 24 - - 8820 1754

Example 3

A concentration of 350 mg of thiosulfates was found in the inflow to the activation plant. I “ ¹ . Sulfides were not detected. The amount of waste water was 20 m ³ . h ^-1 . Alkaline waste water, whose KNK value is 25 mmol, was available to replenish the neutralization capacity. I ^-1 . The alkaline water did not contain toxic substances that could endanger the biological treatment plant.

Mixing ratio calculation:

Quantity of thiosulphates:

20.0.35 = 7 kg. h " ¹ = 62.5 mol. h ¹ .

Required optimal KNK:

2.62.5 = 125 moles. h ¹ .

The volume of the alkaline waste water stream added to increase the KNK was 125: 25 = 5 m ³ . h “ ¹ .

Claims (3)

SUBJECT Process for the biological treatment of sulfur-containing waste water, characterized in that the pH of the waste water treated is continuously maintained by the addition of an alkali, e.g. , in the range of 6 to 11, preferably 8.5 to 9.5, while the substance loading of the mixed sulfide culture is maintained in the range of 0.05 to 2.0 kg. kg ^-1 . d " ¹ S ² ", preferably 0.2 to 0.5 kg. kg ^-1 . d-iS ^2- and a thiosulfate load in the range 0.05 to 20.0 kg. kg ' ¹ . . d-iS2O3 ~ ² . 2. A process according to claim 1, characterized in that in the case of waste waters with a variable content of sulfur compounds, the presence of sulphide or thiosulphate ions in the inflow to a biological treatment plant exceeds 100 mg. I- ¹ , dosing starts with calcium hydroxide, calcium oxide, sodium or potassium hydroxide, sodium or calcium carbonate, or waste water having a pH greater than 7. Method according to Claims 1 and 2, characterized in that 0.25 to 5 moles of acid neutralizing capacity, preferably 0.75 to 1.5 moles, are added per mole of sulphide ions in waste waters with variable sulfur compound content, and for each mole of thiosulfate ions 0.5 to 10 moles of acid neutralizing capacity, preferably 1.4 to 3 moles.