RU2096350C1 - Method of disinfecting sediments from waste waters - Google Patents

Abstract

FIELD: waste water treatment. SUBSTANCE: invention relates to ways of reutilizing and processing sanitary and industrial sediments on waste disposal plants. Method includes preliminarily dehydrating sediment, granulation, and two-step heat treatment in fluidized bed using as heat carrier furnace gas at 200-400 C and temperature in bed 60-85 C in the first step and 120-140 C in the second step, after which gas release is dedusted. According to invention, gas streams after the two heat treatment steps are combined and kept for 2-3 s, and dedusting is carried out in fluidized bed of refluxed charge under adiabatic conditions and reflux rate 2.6 cu.m/h per 1 cu.m of static volume of charge. As reflux fluid, alkali solutions with pH at least 12 are used. EFFECT: achieved 100% worming of gas releases and meeting sanitary requirements. 2 cl

Description

 The invention relates to methods for utilization and processing of municipal and industrial sludge at wastewater treatment plants.

There is a method of disinfecting sewage sludge at treatment facilities, including preliminary sludge dewatering, granulation of a mixture of wet and dry sludge, its heat treatment at a temperature of 100 ^o C in a suspended layer created by an ascending stream of dried, dust-free and heated water vapor from the same sludge [ 1]
The disadvantage of this method is the presence in the exhaust gases generated simultaneously from the wet sediment during heat treatment in a suspended layer, viable helminth eggs.

The closest in technical essence and the achieved result to the alleged invention is a method of disinfecting sewage sludge, including preliminary dewatering of the sludge, granulation, heat treatment and purification of gas emissions from dust. The heat treatment according to this method is carried out in a fluidized bed in two stages when using flue gases supplied with a temperature of 200-400 ^o C as a coolant, while in the first stage, the temperature in the layer is maintained at 60-80 ^o C at a feed rate of 5-12 m / s, and on the second 120-140 ^o C. The method allows to obtain a completely decontaminated sewage sludge with maximum preservation of its organomineral composition [2]
However, the implementation of this method does not provide full compatibility with the environment in the helminthological relation of gas emissions formed at the stage of heat treatment of wet sediment in the fluidized bed. This is due both to the intensive evaporation of moisture from the precipitate at the first stage of its heat treatment, due to the high drying potential, and to the high velocity of the gas stream at its low temperature at the outlet of the layer. Intensive evaporation of moisture is accompanied by the removal of viable helminth eggs in the vapor-gas phase. The high speed of the flue gases leads to mechanical entrainment of the particles of the wet sediment containing helminth eggs, and thereby contributes to the pollution of the exhaust gases. The low temperature of the gases after the first stage of heat treatment and the short residence time of the exhaust gases in the sublayer space of the fluidized bed do not provide loss of viability of helminth eggs. These circumstances make gas emissions helminthologically dangerous.

 The invention consists in the following: the invention is aimed at solving the problem of deworming of gas emissions generated during the disinfection of sewage sludge.

 The solution to this problem is mediated by a new technical result. This technical result is achieved in that the gas flows after the first and second stages of heat treatment are mixed and held for 2-3 seconds in a preliminary deworming chamber with subsequent purification, which contributes to the loss of viability of helminth eggs.

Salient features of the claimed technical solution: the method of disinfecting sewage sludge includes preliminary sludge dewatering, granulation, two-stage heat treatment in a fluidized bed when using flue gases with a temperature of 200-400 ^o C at a temperature in the layer at the first stage of 60-85 ^o C, and the second 120-140 ^o C and the cleaning of gas emissions from dust.

Distinctive features: the gas flows after the first and second stages of heat treatment are mixed and held for 2-3 seconds, and they are cleaned in the fluidized bed of the irrigated nozzle under adiabatic conditions with a specific load on the irrigation fluid up to 2.6 m ³ / h • m ³ static volume of the nozzle. Alkaline solutions with a pH of at least 12 are used as irrigation fluid.

 Mixing gas flows after the first and second stages of heat treatment and keeping them for 2-3 seconds contribute to the loss of viability of helminth eggs due to an increase in gas temperature and an increase in contact time with the gas phase.

 Standing for less than two seconds is associated with a decrease in the effectiveness of disinfection. Holding for more than three seconds leads to an increase in hardware volumes and therefore is not economically feasible.

 When cleaning gas emissions in a fluidized bed of an irrigated nozzle, helminth eggs are subjected to the combined action of mechanical, temperature and chemical factors.

 Intensive chaotic movement of nozzle bodies with high speed, their pulsations and strong multiple collisions cause a violation of the integrity of the shells of helminth eggs.

Under adiabatic conditions in the fluidized bed of the irrigated nozzle, a limit temperature is set equal to the temperature of the wet thermometer (52-53 ^o C), which allows for 100% death of helminth eggs. The load on the irrigation fluid should not exceed 2.6 m ³ / h • m ^{3 of the} static volume of the nozzle. An increase in the load above the specified value leads to a decrease in the temperature in the layer, a decrease in the contact time, and, as a result, a decrease in the disinfection efficiency.

 The use of alkaline solutions as an irrigating liquid is associated with their pronounced ovicidal effect, which consists in the destruction of the shells of the first half of the shell and the dissolution of the lipoprotein and lipoid components of the shells of its inner half.

 The use of alkaline solutions with a pH of less than 12 significantly reduces the disinfecting effect.

 It has been experimentally established that only the implementation of the combination of the above essential features allows us to ensure a 100% degree of deworming of gas emissions generated during the disinfection of wastewater.

 The essence of the invention is illustrated by the following examples.

Example 1. Pre-dehydrated and granular sludge sludge station for wastewater treatment with a moisture content of 80 wt. subjected to a two-stage heat treatment in a fluidized bed. As a heat carrier, flue gases with a temperature of 300 ^o C. are used. In the first stage, gases are supplied at a speed of 8 m / s and the temperature in the layer is maintained at 80 ^o C. The temperature of the layer in the second stage is 140 ^o C.

The gas flows after the first and second stages of heat treatment are mixed, for example, in a tangential mixer, and then kept for 2 seconds in a preliminary deworming chamber, which is a large diameter isometric gas duct. Gas purification and its final disinfection are carried out in an apparatus with a fluidized bed of an irrigated nozzle operating in adiabatic conditions. As nozzle bodies, for example, polymer rings of 40x20x2.5 mm in size are used. Irrigating liquid NaOH solution with pH 12. The load on the irrigating liquid is 2.1 m ³ / h • m ³ . There are no viable helminth eggs in the gas phase.

Example 2. Under the conditions of example 1, the gases are held in a preliminary deworming chamber for 3 seconds. The irrigating liquid is a KOH ₃ solution with pH 13. The load on the irrigating liquid is 2.6 m ³ / h • m ³ . There are no viable helminth eggs in the gas phase.

Example 3. Under the conditions of example 1, the aging time of the gases in the preliminary deworming chamber is 2 seconds. As the irrigated liquid, Ca (OH) ₂ solutions with pH 12 are used. The load on the irrigated liquid is 1.9 m ³ / h • m ³ . The gas phase does not contain viable helminth eggs.

Example 4. Under the conditions of example 1, the gas holding time is -0.5 seconds. The irrigation liquid is a KOH solution with pH 10, the load on the irrigation liquid is 3.2 m ³ / h • m ³ . In the gas phase, single viable helminth eggs are present.

 Using the proposed method of disinfecting sewage sludge provides 100% deworming of gas emissions and their compliance with sanitary-helminthological requirements.

Claims (2)

1. The method of disinfecting sewage sludge, including preliminary sludge dewatering, granulation, two-stage heat treatment in a fluidized bed, when using flue gases with a temperature of 200 400 ^o C as a heat carrier, at a temperature in the layer at the first stage of 60 85 ^o C, and at the second 120 140 ^o C, and cleaning gas emissions from dust, characterized in that the gas flows after the first and second stages of heat treatment are mixed and held for 2 3 s, and cleaning is carried out in a fluidized bed of the irrigated nozzle in adiabatic conditions at a specific load of up to 2.6 m ³ / h • m ^{3 of the} static volume of the nozzle.  2. The method according to claim 1, characterized in that the alkaline solutions with pH ≥ 12 are used as the irrigation liquid.