30T ammonia nitrogen wastewater treatment project

I. Overview

1. Adopting the domestically advanced and mature blow-off + catalytic oxidation + biofilter treatment process, the process is reliable, mature, and in line with the domestic actual situation, and try to adopt new technology, new materials, practicality and advancement. Take care of both, practical and reliable.

2. The main facilities of wastewater treatment are mainly steel truss structure, which has compact structure, small floor space and reasonable layout. It can be considered to reduce the total investment and operating costs.

3. Make full consideration of the wastewater treatment facilities, and consider the necessary waterproof and antifreeze and anti-seepage measures according to regional climatic conditions.

4. The sludge generated in the wastewater treatment process is discharged into the sludge tank, and after aerobic digestion is stabilized, it is pressed into a mud cake for transportation to ensure reliable sludge outlet.

Second, the amount of wastewater treatment and the nature of wastewater:

1 Wastewater source and water volume:

The wastewater source is the high ammonia nitrogen wastewater after the cooling process of the fertilizer plant production process

a, the amount of wastewater: 30m3 / h

Third, the choice of wastewater treatment process:

According to the characteristics, functions, requirements and characteristics of wastewater discharge, the wastewater contains certain toxicity, B/C is relatively low, and ammonia nitrogen is high. Therefore, the denitrification and strong oxidation should be used to increase the B/C ratio of wastewater above 0.3. The remaining ammonia nitrogen and organic matter are removed in the biochemical system of the latter stage.

The company adopts the biological filter process, and the B/C ratio in the water after hydrolysis and acidification is about 0.35, which can greatly improve the biochemistry. According to the wastewater discharge standard, there is a limit of NH3-N. Therefore, in addition to considering the organic matter, we also consider denitrification in selecting the wastewater treatment process. In order to achieve this goal, we have selected a process that is mature and reliable in operation. Biofilter + N biofilter process.

V. Wastewater treatment process description:

1. Pre-processing system:

The pretreatment system consists of a mechanical grid, a regulating tank, a primary lifting pump, a pH adjusting sedimentation tank, an intermediate tank, an ammonia nitrogen stripping tower, and a final adjusting tank.

Nitrogen ammonia waste is collected into the grid well by the pipe network. There is a mechanical grille in the grid well to intercept large particles and fibrous impurities in the waste water, reduce the workload of the post-stage treatment system, and prevent the post-stage pipeline. And the blockage of the packing to ensure the smooth flow of the subsequent pipeline.

After removing the mechanical impurities of the large particles through the grid, the wastewater flows into the regulation tank by itself, and the grid well is a reinforced concrete structure and a conditioning pool. The elevation of the wastewater inlet is determined during the construction design, and the wastewater inflow is professionally connected to the grille inlet by the building design unit.

Due to the large daily variation of ammonia nitrogen wastewater, according to different production processes, the discharge and water quality of wastewater are inconsistent, resulting in large fluctuations in wastewater quality and water volume. Therefore, the adjustment tank should have sufficient capacity to enter the latter system. The water quality and water volume are stable, and a regulating tank is set in the process. The wastewater is adjusted and balanced in the water quality and water volume to ensure the stability of water quality and water volume in the downstream blowing system. A perforated aeration tube is arranged at the bottom of the pool, one can prevent precipitation of particles in the pool, and the second can play a role of pre-aeration, and at the same time, part of the ammonia nitrogen in the water can be removed to reduce the workload of the latter system.

The adjustment tank is a reinforced concrete structure with a design residence time of 8 hours.

There are two first-stage lifting pumps in the regulating tank, one for each, to increase the wastewater into the ammonia ammonia stripping system.

2. Ammonia nitrogen stripping system:

The ammonia nitrogen stripping system consists of a pH adjustment sedimentation tank, an intermediate tank, a secondary lift pump, an ammonia nitrogen stripping tower, a blow off circulation pump, a secondary lift pump, and a final neutralization tank.

The wastewater is upgraded into the pH regulating tank by the first-stage lifting pump. At the same time, the pH of the wastewater is adjusted by adding alkali solution to adjust the pH value to 11. Under the alkaline condition, the ammonia nitrogen in the water is converted into free ammonia, and after precipitation, it enters the intermediate water tank. The secondary lift pump is sent to the stripping tower for ammonia nitrogen stripping. The inlet water temperature is about 30 °C, which is suitable for the ammonia nitrogen stripping temperature. When the water temperature is too low, steam heating is required. The system uses the steam system and the stripping process. In the process of transferring free ammonia to the atmosphere, the ammonia nitrogen partial pressure in the water surface of the stripping tower is small, and ammonia nitrogen enters the atmosphere with the air through the blast, and at the same time, some substances such as phenol, cyanide and sulfide in the water body can be separated. . The tail gas from which the ammonia nitrogen is blown out is discharged into a high air diffusion of 15 m (or can enter the ammonia spray tower to recover ammonia chloride through the acid liquid). The effluent from the stripping tower is lifted into the pH neutralization tank, and the acid solution is added for stirring and neutralization, so that the pH value is adjusted to 7-8 and then enters the post-stage catalytic oxidation system.

The stripping tower adopts a water circulation structure and has three-stage spraying to improve the efficiency of stripping. The first-stage spray utilizes the pre-stage ammonia-nitrogen wastewater spray, and the second-stage and third-stage sprays use the circulating pump to recirculate.

3. Catalytic oxidation system:

The catalytic oxidation reactor adopts ozone, ultraviolet light, nanometer titanium dioxide catalyst combined with normal temperature catalytic oxidation treatment system, and catalyzes the oxidation of water to flow into the subsequent biochemical treatment system.

Because the wastewater contains cyclic organic compounds and some toxic substances (such as sulfides, cyanides and phenols), the factors affecting the biochemical system are mainly long-chain aliphatic hydrocarbons, polycyclic aromatic hydrocarbons and naphthenes and toxic substances. It is difficult to biochemically degrade, which brings great difficulty to the biochemical treatment of wastewater. Therefore, a catalytic oxidation reactor is arranged in the pretreatment system for the degradation of polymer chains and the oxidation of toxic substances into non-oxidizing oxides.

Ozone is a strong oxidant. Ozone dissolved in water is relatively stable under acidic conditions. However, when pH or water temperature rises, ozone is easily decomposed. The decomposition process of ozone is a free radical chain reaction.

In the chain reaction, the ozone molecule O3 reacts with OH- to form superoxide radical (·O2—) and superoxide radical (HO2·), and superoxide radical·O2—reacts with O3 and combines with H+ to form hydrogenation. Ozone free radicals (HO3·), then HO3· are decomposed into oxygen molecules O2 and hydroxyl radicals (·OH). • OH has a stronger oxidation capacity than O3 and plays an important role in the ozone treatment process. (Compared with the reaction rate constants of ozone, hydroxyl radical and some organic compounds, see Table 1.) Some OH and O3 combine to form ozone hydroxyl radical (O3OH·), and O3OH· decomposes oxygen molecules to HO2·. · There is a chemical equilibrium relationship between O2. This completes a loop, and the generated ·O2 - then interacts with O3 to initiate a chain reaction in the next cycle.

Hydroxyl radicals are very active, and the rate constants are generally at least seven orders of magnitude higher than the reaction rate constants of ozone with the organics when reacted with most organics.

Under the combination of ultraviolet light and nanometer titanium dioxide catalyst, the ozone oxidation process can produce a larger amount of strong oxidizing hydroxyl radicals, and the high molecular organic matter is a carbon oxyhydroxide. Under the combined action of ozone and ultraviolet light, A strong redox reaction occurs to remove the oxidative decomposition of organic matter in the wastewater, resulting in low molecular weight organic matter. After the combined oxidation of ozone and ultraviolet light, the B/C ratio of the wastewater is increased to 0.3 or more to improve the biodegradability of the biochemical system of the latter stage.

4. Biochemical treatment system:

The biochemical treatment system consists of a reduction reaction tank, a lift pump, a pulse water distributor, a hydrolysis acidification tank, a DC biofilter, an N biofilter, a discharge tank, a backwash fan, a biochemical fan, a backwash water pump, and a backwash water collection tank. composition.

Since the catalytic oxidation effluent contains a large amount of active oxygen having oxidizing ability, if it directly enters the biological system, it will inhibit the growth of microorganisms in the water, and a sodium hydrogen sulfite reducing agent is added to the reduction reaction tank to mainly reduce the oxidizing active oxygen in the water. In order to facilitate the cultivation of microorganisms in the biochemical system of the latter stage, the effluent from the reduction reaction tank is lifted by the lift pump into the post-stage hydrolysis acidification tank.

The hydrolysis acidification tank utilizes an acidification and hydrolysis section of the anaerobic reaction.

Because the catalytic oxidation of water contains some polymer organic matter, suspended COD and some oil substances, it is difficult to biodegrade when entering the biochemical filter. The hydrolysis is mainly to decompose the high molecular organic matter in the wastewater into low molecular weight. The biochemical organic matter is beneficial to the removal of the biofilter in the latter stage, and the removal rate of the suspended matter in the acidified water is 70%, which can effectively prevent the blockage of the biofilter in the latter stage.

The hydrolysis acidification tank is a steel crucible structure with a designed residence time of 6 hours. The hydrolysis acidification tank is watered and mixed by a pulse water distributor. The pre-stage wastewater is sprayed with water to suspend the sludge to increase the wastewater and pollution. The contact area of the mud, while uniformly arranging the water in the hydrolysis acidification tank.

5. Biofilter:

The biological filter is a biological treatment device which is mainly based on the biofilm method and has the characteristics of filtration. In this type of device, the inlet water and the intake air enter from the bottom of the ceramsite filter layer. Due to the heterogeneity of the filter layer particle size, the upper filter material has a smaller particle size, and the lower layer filter material has a larger particle size, which is equivalent to The filter has numerous intercepting interfaces and has the characteristics of large dirt retention capacity and long operating period.

The horizontal flow is used to make the spatial filtration better, and the air can bring the solid material into the depth of the filter bed, which can obtain high load and uniform solid matter in the filter, thereby prolonging the backwash cycle. , to reduce the cleaning time and the amount of gas and water used in cleaning.

The cutting effect of the filter layer on the bubbles makes the residence time of the bubbles in the filter tank prolonged, and the utilization rate of oxygen is improved.

The organic matter in the wastewater is adsorbed and degraded when passing through the filter layer, so that the water is purified. The biological filter is divided into two grades and is made of light ceramsite filler. The filler has the advantages of large specific surface area and long service life, and is corrosion resistant. The aeration method uses a single-hole membrane aerator.

The first section of the DC aerated biological filter mainly removes carbonized organic matter in the wastewater, and at the same time functions as a nitrification and denitrification. In this section of the filter, the dominant heterotrophic bacteria grows from the bottom inlet end to the height of the filter tank. At the surface of the water outlet, the concentration of organic matter is decreasing, and the degradation rate is also decreasing. At the inlet end, due to the high concentration of organic matter, the heterotrophic microorganisms are in the logarithmic growth phase, the microbial concentration is high, the BOD loading rate is also high, and the degradation rate of organic matter is fast, while the autotrophic bacteria are in a state of inhibition; In the filter tank, the concentration of organic matter decreases continuously from bottom to top along the water flow, the heterotrophic microorganisms are in the period of deceleration and proliferation, the microbial membrane grows slowly, and the autotrophic microorganisms are in a proliferating state, and the organic matter in the final effluent of the DC aerated biological filter is already in existence. Lower level.

The most important feature of the biological filter is that the gas and water are in the same direction. The new type of lightweight ceramsite filler is used as the carrier, and the microbial membrane grows on the surface and the inner cavity space. When the wastewater flows from the bottom to the filter layer. The microbial membrane provides aerobic degradation of the organic matter in the wastewater under the condition of providing aeration and oxygen supply in the lower part of the filter layer, and nitrating part of the ammonia nitrogen in the wastewater to be decomposed into nitrogen nitrate or nitrite. The filtered water is periodically backwashed by the treated effluent to remove the aged microbial membrane proliferating on the surface of the filter to ensure the activity of the microorganism.

The second stage N aerated biological filter mainly performs complete nitrification and decomposition of ammonia nitrogen in the wastewater. In the filter tank, due to the low concentration of organic matter, the heterotrophic microorganisms are less, and the dominant strain is autotrophic nitrifying bacteria. The ammonia nitrogen in the wastewater can be completely oxidized to N2 and H2O.

Since the biological filter is blocked by the biofilm after running for a period of time, it needs to be backwashed regularly. The backwashing drainage contains a large amount of suspended matter, and the buffer pool is used in the process for the storage of the biofilter backwashing drainage. The water storage capacity of the single filter is backwashed, and the submersible sewage pump is installed in the buffer pool for the water quantity improvement, and the wastewater is upgraded and then enters the hydrolysis acidification tank.

The N aerated biological filter effluent flows into the discharge pool, the discharge pool functions as a storage water in the process, and the regular water backwash water used in the biological filter, and the remaining water is discharged through the overflow.