RU2240291C2 - Process of biological treatment of waste waters - Google Patents

Abstract

FIELD: waste water treatment.

SUBSTANCE: process involves filtering waste water, settling, treatment with microorganisms and disinfecting treated effluents. Biological treatment is performed using three-sludge systems. First system, provided with settling-type sludge separator, functions with bacterial biocenosis and daily loadings on sludge at least 1 kg of biochemical oxygen demand per 1 kg of ashless substance of sludge. Second sludge system, provided with settling-type sludge separator, functions with nitrification-denitrification biocenosis, including association of heterotrophic and autotrophic bacteria, protozoa, and small organisms belonging to third trophic level, and daily loadings on sludge at least 200 g of biochemical oxygen demand per 1 kg ashless substance of sludge. Third system functions with nitrification and mineralization biocenosis preferably consisted of aquatic organisms belonging to third trophic level, animal plankton fixed in fibrous filler contained in construction space with daily loadings not superior to 1 kg dry substance of animal plankton, further provided with bubbler system, lines for removing faeces, pseudo-faeces, and died-off animal plankton toward waste water sediment treatment plants. Withdrawal of sediments is only effected from bioreactors of third sludge system.

EFFECT: increased efficiency of removal of biogenic elements from water, prepared high-ash non-decaying, rich in biogenic elements, waste water sediments, diminished volume of construction, and reduced power consumption.

2 cl, 1 dwg

Description

The invention relates to methods for wastewater treatment and can be used in utilities for the treatment of urban or similar industrial wastewater composition close to them.

The purpose of the invention is to increase the efficiency of removing biogenic elements (including phosphorus) from water, to obtain high-ash non-decaying wastewater sludge rich in biogenic elements, to reduce the volume of capacitive structures and the energy intensity of wastewater treatment processes.

It is known to use multi-stage aeration tanks [1] with immiscible sludge systems for the treatment of highly concentrated wastewater. The disadvantages of the method are: the bulkiness of structures; communication complexity; the need for the construction of sludge recirculation pumping stations and facilities for conditioning the precipitation before dehydration; high energy intensity.

The use of multi-stage displacer aerotanks [2] solves many problems, the work of which is based on the use of communities of attached and free-floating microorganisms in sewage treatment steps. An obstacle to the widespread use of the design and the biological wastewater treatment method incorporated in it is the rather high cost of the nozzle for holding microorganisms and scaffolds from corrosion-resistant material for its uniform placement in the volumes of capacitive structures, as well as the energy consumption of creating a constant effective mass transfer of the biocenosis attached to the nozzle with the wastewater being cleaned. The sludge of the first stages of wastewater treatment, mucus-forming accumulates the nozzle with hard-to-wash accumulations, their washing leads to rapid wear of the nozzle.

The closest to the achieved effect is the method embedded in the design of the treatment plant [3]. The bulkiness and energy intensity of the structure is reduced in the invention at the first cleaning stage due to the use of a two-core reactor and a thin-layer pulsed sludge separator with airlift return of the separated sludge from the exit of the second corridor to the entrance of the first corridor. The known device does not regulate the load on the sludge, does not separate the sludge according to the stages of purification and does not provide the mineralization of excess biomass of microorganisms.

The goal is solved in that in the method of biological wastewater treatment, freed from large mechanical impurities and sand at the stages of preliminary mechanical treatment, the following significant differences are provided:

- a three-sewage wastewater treatment system is used, in which the first sludge mixture mainly uses a highly loaded, fast-growing, heterotrophic biocenosis; the second sludge mixture uses nitridenitrifying biocenosis, including microorganisms of three trophic levels (bacteria, protozoa and small animals); the third silt mixture uses a nitrifying biocenosis of bacteria and hydrobionts, mainly of the third trophic level, predatory zooplankton;

- the loads on the biocenosis of each sludge mixture are regulated: the load on organic substances on the first sludge mixture must be at least 1 kg of BOD is _full per 1 kg of ashless sludge substance per day; on the second sludge, the load on organic substances should be more than 0.2 kg of BOD _p per 1 kg of ashless sludge substance per day; on the third sludge mixture, the load on suspended solids carried out from the structures of the second sludge system should not exceed 1 kg of dry matter suspended in 1 kg of dry matter of zooplankton per day;

- removal of sediments, excess sludge from a set of structures of a three-silt biological wastewater treatment system is carried out exclusively from reactors of the third silt system;

- Reactors of all three stages of biological wastewater treatment are maximally performed by displacers due to division into compartments, aeration system for aerated sludge mixture inside compartments, placement of compartments relative to each other, peculiar placement of nozzles inside the third stage of water treatment.

Analysis of known technical solutions related to wastewater treatment methods showed that technical solutions containing the same set of essential features as the claimed method were not found. This allows us to conclude that the claimed method meets the criterion of "novelty."

Analysis of the identified significant features distinctive from the prototype showed that such or similar features in known technical solutions with the manifestation of the same properties were not found, which allows us to conclude that the claimed method meets the criterion of "significant differences".

The claimed combination of essential features allows to obtain a new, higher result, which is expressed in providing deeper wastewater treatment, especially in removing biogenic elements (nitrogen and phosphorus) from wastewater in the absence of reagent consumption, without adding additional volumes of capacitive structures. The allocated sewage sludge has neither a fecal smell nor a rotting smell; they contain 2–3 times more phosphorus, which increases their quality as an organomineral fertilizer.

The method is illustrated by the technological scheme of wastewater treatment and treatment of precipitates emitted at the treatment plant of the settlement (see drawing).

The scheme includes a wastewater stream 1 entering a sewage treatment plant (WWTP); screeners 2, sand traps 3, water measuring tray 4, distribution chamber 5, three-stage aerobic bioreactor 6, including an aerated tank 7 of the first sludge system with sludge separator 8, an aerated tank 9 of the second sludge system with sludge separator 10 and an aerated tank 11 with fiber frame system 12 13 of the third sludge system, communication 14 for the removal of sludge from the sewage treatment plant in the workshop 15 for mechanical dewatering after thickening in sludge separators 16. At the entrance of the bioreactor 6 into the distribution chamber 5 returns the stream 17 of superficial water from the sludge compactors and the filtrate 18 from the filter presses of the workshop 15 for mechanical dewatering of sediments.

The air 19 in the aerated tanks 7, 9 and 11 comes from the blower 20.

Dehydrated sludge (cake) 21 is stored in special sludge pads 22, from where it is transported for additional processing and certification before disposal as organic fertilizer.

The circulation of the first and second silt systems is provided by airlifts 23.

Biologically treated wastewater is discharged into building 24, where it is exposed to ultraviolet radiation (UV) in special devices and after UV is directed to release 25 into a surface water body or for reuse for technical needs of enterprises, irrigation of farmland and other purposes.

Large impurities of 26 wastewater from screeners 2 and sand 27 from sand traps 3 are discharged to specially designated places for processing and disposal.

The proposed scheme works as follows.

Wastewater (CB) flows by stream 1 to strainers 2, where they are freed from large (more than 5 mm) impurities 26 (rags, paper, fruit seeds, rubber products, gaskets, etc.). Next, the CBs in the sand traps 3 are freed from sand 27 and after recording the flow rate in the water metering tray 4, they enter the distribution chamber 5. The distribution chamber 5 also receives superficial water 17 from the sludge compactors 16 and the filtrate 18 with washing water from the filter presses of the mechanical sediment dewatering shop 15 ST

From chamber 5, CBs are distributed over parallel working sections of bioreactor 6 (for simplification, one section is shown in the drawing). The bioreactor section 6 consists of three stages. In the first stage there is an aerated reservoir 7 and a sludge separator 8 (for example, in the form of a thin-layer module).

From the sludge separator 8, the CBs are sent to the aerated tank 9 of the second stage, and the bulk of the sludge of the first cleaning stage separated from the CB is returned by airlift 23 to mix with the stream of CB coming into the aerated tank 7. The air 19 for aeration of the sludge mixture in the tank 7 comes from the blower 20 .

In the aerated tank 7, heterotrophic bacteria consume easily digestible organic substances, nutrients and oxygen introduced into the water from the air, give rise to mucus-forming complexes that flocculate suspended matter of CB, which provides good sedimentation properties of the sludge of the first sludge system. Desilter 8 ensures that the concentration of heterotrophic bacteria is sufficient for flocculation of suspended solids of the SW with any fluctuations in flow rates and pollution concentrations observed in urban NE with the use of airlifts 23 into the aerated tank 7 to mix with SV

The volume of the tank 7 and the parameters of the sludge separator 8 should provide such a mass of heterotrophic bacteria in the sludge of the first sludge system so that the load on the sludge is not less than 1 kg of BOD _p per 1 kg of dry ash-free substance of the sludge mixture per day. Such a load ensures the presence in the sludge mixture of predominantly rapidly growing heterotrophic bacteria with certain surface properties and a specific enzyme system rich in ATP. The need for such bacteria in phosphorus is 3 or more times higher than microorganisms of activated sludge working in traditional aeration tanks of sewage treatment plants in settlements.

The entire growing biocenosis of heterotrophic bacteria and the suspended matter flocculated by it are washed out from the sludge separator 8 with a stream of purified CB into the aerated reservoir 9 of the second sludge system, providing a guaranteed inflow for the biocenosis of the second sludge system of the nutrients that make up the suspended substances, and the simplest and small animals will get a loop of heterotrophic bacteria, sludge mixture from a set of microorganisms removed from the sludge separator 8 and 10 returned from the sludge separator 10 by means of airlifts 23 hydrobionts of the second sludge system Together with nitrates obtained in aerated tank 9 due to the vital activity of autotrophic nitrifying nitrogen ammonium bacteria, it provides denitrification and elimination of nitrogen in the form of nitrogen gas molecules. The food for denitrifiers is the organic matter of suspensions, flocculated in the first sludge system, but not fed on fast-growing heterotrophic bacteria.

The low load on the biocenosis of the sludge of the second sludge system (not more than 200 g of BOD _p / kg of dry ashless sludge substance per day) ensures complete nitrification of ammonium nitrogen, eating out the heterotrophs of the first sludge system by the simplest and small animals and good sedimentation properties of the sludge mixture. Desilter 10 ensure that a sufficient concentration of biomass of aquatic organisms of the second sludge system is maintained in the aerated tank 9, but does not hold the excess of the growing biocenosis and it is washed with the flow of CB into the aerated tank 11. In the aerated tank 11, the sludge received from the CB from the sludge separators 10 is in contact with the fiber nozzle 13, evenly distributed in the volume of the tank 11 with the help of frames 12, and is adsorbed on it due to the presence of electric (positive) potential in the fibers during the movement of water . Active sludge of the second sludge system carries a negative potential. The 13th trophic level hydrobionts living on the fiber nozzle (predatory zooplankton) eat out the sorbed biocenosis, secreting feces and pseudo-feces of high ash content (up to 67%) and stability. The amount of fibrous nozzle and predatory zooplankton is maintained so that the daily load of suspended solids from the sludge separator 10 into the reservoir 11 by mass of suspended solids does not exceed 1 kg of sludge dry matter per 1 kg of dry matter of predatory zooplankton hydrobionts biomass.

In this case, complete sedimentation of sludge and clarification of CB to the concentration of suspended solids at the CB outlet to building 24 to the disinfection unit at a level of 3-5 mg / l are observed, while feces and pseudo-feces accumulate at the bottom of the tank 11 and are partially retained on the fibrous nozzle, wilting and creating the illusion of a large biomass of predatory zooplankton or a large amount of sludge from the second sludge system detained but not processed by zooplankton. Therefore, in the community of hydrobionts of the biocenosis of the third sludge system, there should be worms, ticks, mollusks and other cultivators that do not allow strong silting of the nozzle, transporting feces and pseudo-feces, as well as dead individuals to the bottom of the reservoir 11. The shape of the fibrous nozzle in the reservoir 11 should contribute to the flow of processes trapping sludge particles of the second sludge system, as well as slipping 11 feces and pseudo-feces onto the bottom of the tank.

Filtered sludge filters filtered by sedimentators of the third sludge system have high transparency, low suspension, therefore, after UV disinfection, it can be used for technical needs, irrigating farmland and other purposes.

Sewage sludge discharged from the reservoir 11 via communications 14 is heavily flooded, therefore, they need to be thickened. To thicken the sludge are sent to sludge compactors 16, from where after settling, the superfluous water is discharged by stream 17 to the distribution chamber 5, and the compacted sludge to the mechanical sediment dewatering shop 15 on filter presses. The filtrate 18 and water from washing the fabric of the filter presses are sent to the distribution chamber 5, and the cake 21 is stored on the sludge pads 22 in preparation for disposal.

To clarify the parameters of the ST cleaning process and to prove the achievement of the set goals, we give an example of the method implementation at the treatment plant with a capacity of 500 m ³ / day.

Example

Sewage treatment plant Esto-Sadok on Krasnaya Polyana near the city of Sochi accepts a daily discharge of waste water of 500 m ³ / day. Due to the presence at the sewage treatment plant of an average cost of SW after screeners with 1.5 mm openings that trap both waste and sand, the hourly flow rate of SV no more than 25 m ³ / h enters the bioreactor. The concentration of contaminants in the NE at the entrance to the bioreactor with a three-loop system in terms of BOD _p is 180 mg O ₂ / L, suspended solids 130 mg / L, ammonium nitrogen 22 mg / L; phosphorus - 4.3 mg / l.

The reservoir of the first sludge system has a volume of 26 m ³ , including a thin-layer pulsating sludge separator inside it with a volume of 9 m ³ . The biomass of the first sludge system is retained in the tank - 76 kg by dry matter and 55 kg by ash-free substance (ash content of 28%, silt concentration - 2.9 g / l by dry matter).

500 m ³ / day · 180 g / m ³ = 90 kg of BOD _p and not less than 60 kg of BOD _p / day are oxidized by the biocenosis of the first silt system per day. For aeration of the sludge mixture in the tank of the first sludge system, 50 m ³ / h of air is supplied, including for the operation of the airlift to drain the sludge mixture from the sludge separator back into the tank.

The removal of suspended solids from the sludge separator to the second aerated tank of the second sludge system was 170 mg / l, the BOD _p decreased to 70 mg О ₂ / l, ammonium nitrogen decreased to a concentration of 16 mg / l, phosphorus decreased to 2.5 mg / l.

The tank of the second sludge system with a volume of 58 m ³ with a sludge separator inside with a volume of 9 m ³ has a total biomass of activated sludge - 185 kg dry matter and 140 kg dry ash (ash content of about 30%, sludge concentration is approximately 3.2 g / l dry substance).

Up to 35 kg of BOD _p and not less than 28 kg of BOD _{p are} oxidized per day in the tank of the second sludge system. The load on the sludge is 200 g BOD _p / kg ash-free substance sludge per day.

As a result of the vital activity of microorganisms of the second sludge system in wastewater flowing from the sludge separator of the second reservoir, the value of BOD _p does not exceed 20 mg O ₂ / L; the concentration of suspended solids decreased to 120 mg / l, ammonium nitrogen decreased to 0.35 mg / l, nitrites did not exceed 0.02 mg / l; nitrates were kept at 5.3 mg [N-NO $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$ ], the concentration of phosphorus in the filtrate was 1.3 mg / L. Air consumption for aeration - 70 m ³ / h, including air supply to the airlift.

The bioreactor of the third sludge system has two equal compartments with a total volume of 27 m ³ with a total weight of a fiber nozzle of a ruff of 81 kg and a weight of hydrobionts of at least 100 kg with an ash content of up to 40%. Considering the presence of feces and pseudo-feces on the nozzle with an ash content of at least 47%, it is possible to take the biomass of hydrobionts by dry matter of at least 60 kg.

Up to 60 kg of suspended solids were delivered per day to the biocenosis of the third silt system.

The air requirement was 30 m ³ / h.

The quality parameters of the treated wastewater are as follows: suspended solids - 3 mg / l; BOD ₅ ≤ 3 mg O ₂ / L; ammonium nitrogen - 0.25 mg / l; phosphorus - 1.3 mg / l, nitrite nitrogen - 0.005 mg / l, nitrate nitrogen - 5.3 mg [N-NO $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$ ] / l.

Up to 40 kg of dry matter of wastewater sludge with an ash content of 47% was removed daily from the bottom of bioreactors of the third stage. After compaction, the sediment volume was about 1 m ³ / day.

Thus, the effect of removing phosphorus from wastewater was 70%, nitrogen - 75%, BOD _full - 96.6%, suspended solids - 97.6%, air demand - 7.2 m ³ / m ^{3 of} wastewater, specific volume of structures 0.222 m ³ / m ³ waste water. The specific energy consumption of the treatment plant was 0.24 kWh / m ^{3 of} effluent.

For comparison, a treatment plant of the KU-400 type provides phosphorus removal by no more than 30%, nitrogen - 60%; BOD _full - 92%; suspended solids - 89% with air requirements up to 10 m ³ / m ³ , specific volume of structures up to 1.3 m ³ / m ³ , specific energy consumption - 0.5 kWh / m ³ .

The yield of sewage sludge is about the same in weight, and 1.5 times more in volume at the KU-400 plant.

The phosphorus content in the sewage sludge is more than 2 times higher by the proposed method in comparison with the traditional one.

The goal of increasing the efficiency of removal of nutrients has been achieved (the proportion of phosphorus removed during the cleaning process doubles), the ash content of the precipitate increased from 35% to 47%, and the amount of phosphorus in them doubled. The volume of required reservoir facilities decreased by more than 5 times, the specific air consumption for conducting the biological treatment process was reduced by a third, the specific energy consumption was halved.

Sources of information

1. Auth. St. USSR No. 929598, class C 02 F 3/02, 1980.

2. Auth. St. USSR No. 1463721, 1985.

3. RF patent No. 2183592, cl. C 02 F 3/02, 2002.

Claims (2)

1. A method of biological wastewater treatment, including filtering water to isolate large mechanical impurities, settling to trap sand, treating wastewater with microorganisms to remove dissolved and colloidal organic substances from the water, as well as nutrients and subsequent disinfection of treated wastewater to destroy pathogenic microorganisms before release in surface water or for reuse, characterized in that the biological treatment is carried out using a three-force system emy, wherein the first sludge system operates with bacterial biocoenosis and daily loads on yl least 1 kg _BOD per 1 kg of ashless substance sludge, and is provided with a cyclone separator of the settling type, second-sludge system working with nitrification-denitrifying biocoenosis, including community heterotrophic and autotrophic bacteria, protozoa and small animals of the third trophic level, the daily load on the sludge is not more than 200 g of BOD is _full per 1 kg of ash-free sludge substance and equipped with a sludge separator of the sludge type, the third sludge system works with a nitrifying and mineralizing biocenosis, mainly consisting of hydrobionts of the third trophic level, zooplankton, fixed in the volume of the building, equipped with a fiber nozzle, a system of bubblers for introducing oxygen and creating circulating flows of water and sludge flowing from the second sludge system through a fiber nozzle populated by zooplankton, with daily loads of not more than 1 kg of dry matter of zooplankton, fixed on the fibrous nozzle of the third silt system, is equipped with pecifications to remove faeces and dead zooplankton psevdofekaly on facilities for the processing of sewage sludge. 2. The method according to claim 1, characterized in that the removal of sediment, excess activated sludge from a set of structures of a three-sewage system for biological wastewater treatment is produced exclusively from bioreactors of the third sludge system.