Electrolytic biofilter system for rapid treatment of overflow pollution and operation method

Abstract

The invention relates to the technical field of sewage treatment equipment, in particular to an electrolytic biological filter system for rapid treatment of overflow pollution and an operation method, a bioelectrochemical system is coupled with a biological aerated filter to form the electrolytic biological filter system for rapid treatment of overflow pollution; the rapid electron transfer characteristic of a bioelectrochemical system is fully utilized, the denitrification rate of the biological aerated filter is improved, the treatment time can be greatly shortened under the same denitrification requirement, and the effect of rapidly treating overflow pollution in emergency is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment equipment, and in particular to an electrolytic biological filter system and an operation method for rapid treatment of overflow pollution. Background Art

[0002] In recent years, the water environment quality in most parts of my country has been significantly improved, but the problem of non-point source pollution cannot be ignored, especially the overflow pollution during the flood season. In particular, in old urban areas with combined drainage systems, urban areas with misconnected diversion pipes and imperfect diversion pipe network construction, the mixed discharge of urban rainwater and sewage during the flood season is extremely common. This situation is the main reason for the deterioration of river water quality during the flood season.

[0003] In order to deal with the problem of overflow pollution during the flood season, researchers have proposed many rapid treatment methods, such as storage, sedimentation, filtration, biological filter, artificial wetland, etc. The main purpose of these treatment methods is to quickly treat suspended matter and organic matter in the water to meet the requirements of discharge into the river and reduce the non-point source impact caused by rainfall overflow. However, due to the short treatment time, the treatment unit itself has only a relatively single performance, resulting in a single treatment method that cannot guarantee the simultaneous removal of multiple pollutants such as nitrogen, phosphorus, organic matter, and suspended matter to an ideal level. Among them, the aerated biological filter is a sewage treatment technology that integrates physical, biological, and chemical reaction processes. It has a certain removal performance for nitrogen, phosphorus, organic matter, and suspended matter in sewage. It is remarkable in the removal of suspended matter and organic matter, but due to the low bioavailability of organic matter in overflow sewage, the large treatment load and the overall aerobic environment, its biochemical removal efficiency of pollutants such as difficult-to-degrade organic matter, nitrogen, and phosphorus is low. Therefore, it is imperative to improve and upgrade the existing methods.

[0004] In recent years, bioelectrochemical systems have received extensive attention for their sustainability in energy and chemical production and their high efficiency in water treatment. The characteristics of bioelectrochemical systems that accelerate electron transfer, promote the transformation of pollutants such as nitrogen and phosphorus, and enhance the bioavailability of organic matter make them highly applicable in the rapid treatment of flood overflow pollution. The combination of bioelectrochemical systems and biofilters (electrolytic biofilter systems) can simultaneously achieve the high suspended solids removal performance of biofilters and the high nitrogen, phosphorus, and organic matter simultaneous reduction efficiency of bioelectrochemical systems. By utilizing the characteristics of bioelectrochemical processes to accelerate electron transfer and pollutant transformation, the flood overflow pollution treatment time is greatly reduced, which meets the needs of rapid treatment of flood overflow pollution with large water volume and strong short-term pollution. This technology can effectively reduce flood overflow pollution and achieve rapid purification of pollutants such as nitrogen, phosphorus, organic matter, and suspended matter in flood rainwater and overflow sewage. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide an electrolytic biofilter system and an operating method for rapid treatment of overflow pollution.

[0006] The present invention is realized by the following technical scheme: an electrolytic biofilter system for rapid treatment of overflow pollution, comprising a bioelectrochemical system and an aerated biofilter system, The bioelectrochemical system comprises a cell body 1, in which a bioanode and a biocathode are arranged, and the bioanode and the biocathode are connected to a power source. The aerated biological filter system comprises a second tank body. Sewage treated by the first tank body enters the second tank body. The second tank body is provided with an aeration device, a filtering device and a clear water outlet device.

[0007] Furthermore, the bioanode and the biocathode both comprise a conductive mesh cage, and an electrode body is arranged inside the conductive mesh cage.

[0008] Furthermore, a reference electrode is arranged between the bioanode and the biocathode.

[0009] Furthermore, a mud storage pool is provided at the bottom of the pool body.

[0010] Furthermore, the filtering device comprises a coarse filtering layer and a fine filtering layer which are sequentially arranged along the flow direction of the sewage.

[0011] Furthermore, it also includes a backwashing device, which includes a backwashing pump arranged at the bottom of the second pool body, and the backwashing pump is connected to the clean water outlet device.

[0012] Furthermore, the backwash device comprises a clean water tank connected to the clean water outlet device, and the backwash pump is connected to the clean water tank.

[0013] Furthermore, the clean water outlet device includes an overflow trough arranged at the upper end of the second pool body, and the overflow trough is distributed around the upper end of the second pool body.

[0014] An operating method of an electrolytic biofilter system for rapid treatment of overflow pollution comprises the following steps: S1, pretreatment, inoculate the activated sludge of the anoxic treatment section of the sewage treatment plant in tank body 1 and tank body 2, and energize the bioanode and biocathode, maintain a voltage of 0.1V, and continue for 20 days; S2, start, adjust the voltage to 0.5V, introduce sewage into the tank body, and start the aeration device at the same time; S3, run until clean water is detected at the outlet of the clean water device, maintain the voltage at 0.5V, the system starts to operate normally, the electroactive microorganisms enriched on the bioanode decompose organic matter and transfer the generated electrons to the biocathode; the electroactive microorganisms on the biocathode obtain electrons and reduce the nitrate nitrogen in the sewage near the biocathode to nitrogen gas.

[0015] The beneficial effects of the present invention are: 1. The bioelectrochemical system is coupled with the aerated biological filter to form an electrolytic biofilter system for rapid treatment of overflow pollution. The rapid electron transfer characteristics of the bioelectrochemical system are fully utilized to improve the denitrification rate of the aerated biological filter. Under the same denitrification demand, the treatment time can be greatly reduced, achieving the effect of emergency rapid treatment of overflow pollution; 2. Make full use of the bio-electrochemical process to break the degradation barrier of refractory organic matter, degrade macromolecular organic matter into small molecular organic matter with high bioavailability, improve the B / C ratio of sewage, and enhance denitrification performance; 3. Use the bio-electrochemical system to precipitate iron ions at the anode to enhance the system's flocculation and removal effect on phosphorus and suspended solids; 4. The front-end bio-electrochemical system not only serves as an enhanced treatment unit of the electrolytic biological filter system, but also plays the role of a primary sedimentation tank, preliminarily precipitating solid matter in the raw water to reduce the risk of clogging of the subsequent aerated biological filter, and precipitating and clarifying the backwash effluent during backwashing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the connection relationship between the components of Example 1; Figure 2 This is a schematic diagram of the connection relationship between the components of Example 2.

[0017] Among them: 1. Bio-motor; 2. Tank body 1; 3. DC regulated power supply; 4. Computer; 5. Resistor; 6. Multi-channel voltage data acquisition device; 7. Mud storage tank; 8. Mud discharge pipe; 9. Reference electrode; 10. Light ceramsite layer; 11. Water outlet switch; 12. Water outlet pipe; 13. Gravel supporting layer; 14. Aeration fan; 15. Clean water tank inlet pipe; 16. Backwash air path; 17. Water distribution trough; 18. Clean water tank; 19. Backwash pump; 20. Water distribution trough inlet switch; 21. Backwash water outlet switch. DETAILED DESCRIPTION

[0018] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0019] The following will be combined with the drawings in the embodiments of the invention to clearly and completely describe the technical solutions in the embodiments of the invention. Obviously, the described embodiments are only part of the embodiments of the invention, not all of the embodiments. Based on the embodiments of the invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the invention.

[0020] Example 1 like Figure 1 As shown, an electrolytic biofilter system for rapid treatment of overflow pollution includes a bioelectrochemical system and an aerated biofilter system.

[0021] The bioelectrochemical system includes a tank body 1, the lower end of the tank body 2 is an open cone, the bottom is a plane, and a mud pipe 8 is installed on the bottom surface to precipitate solid matter in the raw water and discharge it from the system, reduce the concentration of suspended solids in the inlet of the rear-end aerated biological filter to reduce the risk of clogging, and a bioelectrode is installed in the tank body 1. The bioelectrode includes a bioanode and a biocathode, wherein the bioanode is close to the sewage inlet side, and the bioanode and the biocathode both include a conductive mesh cage, which is made of a multi-layer stainless steel perforated mesh, the stainless steel perforated mesh has an aperture of 0.3 cm, a hole spacing of 0.1 cm, and a thickness of 3 mm, forming a conductive mesh cage with a thickness of 10 cm. The conductive mesh cage is rectangular, and the conductive mesh cage is filled with an electrode body, and the electrode body is composed of a diameter of 0.5-1 The activated carbon block is composed of 10000 square centimeters of activated carbon blocks, and the stainless steel perforated mesh mainly acts as a skeleton and a current collector. The activated carbon block is the main body of the bioelectrode, which plays the role of enriching electroactive microorganisms, denitrifying and removing phosphorus. The distance between the bioanode and the biocathode is 10 cm, and they are arranged vertically in parallel. The bioanode is close to the sewage inlet side, and the bioanode and the biocathode are connected to a power supply. Specifically, the power supply is a DC regulated power supply with an output voltage precision of 0.01 V. The DC regulated power supply is connected to the bioanode and the biocathode through an external circuit, thereby forming an electric potential difference between the bioanode and the biocathode. The DC regulated power supply is also connected to a resistor. Resistor 5 uses a cement resistor with good stability and a resistivity of 50-100Ω. A reference electrode is also installed between the bioanode and the biocathode, and the reference electrode uses Ag / AgCl2 standard reference electrode is connected to the negative channel of the multi-channel voltage data collector 6. At the same time, the biological anode and the biological cathode are connected to the two positive channels of the multi-channel voltage data collector 6 to record the potential of the biological anode and the biological cathode. The two ends of the resistor 5 are respectively connected to a pair of positive and negative channels in the multi-channel voltage data collector 6 to monitor the real-time voltage on the resistor and calculate the current data. The data output port of the multi-channel voltage data collector 6 is connected to the computer 4 for visualization to present real-time monitoring data. A water distribution trough inlet pipe is installed on the pool body 1 on the lower side of the biological electrode, and a water distribution trough inlet switch is installed. The sewage enters the pool body 1 from the upper end of the pool body 1, and after being treated by the biological electrode, it flows into the pool body 2 through the water distribution trough inlet pipe.

[0022] The aerated biological filter system includes a tank body 2. In this embodiment, the tank body 1 and the tank body 2 are separated by a partition. The tank body 2 is equipped with an aeration device, a filtering device and a clear water outlet device. Specifically, a water distribution trough is obtained by isolating the lower end of the tank body 2 through a horizontal support plate, and water distribution holes are processed on the support plate to evenly distribute water to the filtering device. The filtering device is installed on the upper end of the support plate. The filtering device includes a coarse filter layer and a fine filter layer distributed in sequence along the flow direction of the sewage, wherein the coarse filter layer includes a gravel support layer with a gravel diameter of 1-2 cm, and one or more of pebbles, quartz sand, zeolite, and expanded clay with the same particle size can also be selected. The fine filter layer includes a lightweight expanded clay layer with a diameter of 0.5-1 cm. The fine filter layer is the main reaction layer.

[0023] The aeration device includes an aeration fan and an aeration pipe. The aeration fan is installed on the second outer side of the pool body. The aeration pipe extends into the gravel support layer. Aeration holes are processed on the aeration pipe to evenly distribute air into the gravel support layer.

[0024] The clean water outlet device includes an overflow trough installed at the upper end of the second pool body. The overflow trough is distributed around the upper end of the second pool body. The clean water processed by the filtering device flows into the overflow trough. The overflow trough is connected to a water outlet pipe, and the water outlet pipe is equipped with a water outlet switch.

[0025] The backwashing device also includes a backwashing device, which includes a backwashing pump connected to the bottom of the second pool body, and the backwashing pump is connected to the clean water outlet device. Specifically, the backwashing device includes a clean water tank connected to the clean water outlet device, the clean water tank is distributed at the lower end of the water distribution trough, and is sealed and isolated from the water distribution trough. The backwashing pump is connected to the clean water tank. A submersible pump is selected as the backwashing pump and installed in the clean water tank. The outlet pipe of the backwashing pump extends into the water distribution trough. The clean water tank and the outlet pipe are connected through the clean water tank inlet pipe. The overflow trough is also connected to a backwashing water outlet pipe. A backwashing water outlet switch is installed on the backwashing water outlet pipe, and the outlet of the backwashing water outlet pipe extends into the first pool body.

[0026] In addition, the aeration fan is also connected to a branch pipe into the water distribution tank, so as to aerate and disturb the water distribution tank during the backwashing process, and also efficiently flush the water distribution tank.

[0027] An operating method of an electrolytic biofilter system for rapid treatment of overflow pollution comprises the following steps: S1, pretreatment, inoculate activated sludge from the anoxic treatment section of the sewage treatment plant in tank body 1 and tank body 2, the inoculation amount is to submerge the bioanode, biocathode, gravel support layer and lightweight expanded clay layer, control the concentration of activated sludge to 3g / L, and then ensure fluidity, the bioanode and biocathode are energized, maintain a voltage of 0.1V, and continue for 20 days. In this process, the bioanode and biocathode are enriched with microorganisms, among which the bioanode enriches organic matter degrading bacteria and electroactive bacteria, such as Arthrobacter and Geobacter; the biocathode enriches denitrifying bacteria and electroactive bacteria, such as Caldilinea, Denitromonas, Thillbacilius, etc., and the most dominant bacteria Arthrobacter and Thillbacilius account for 18.73% and 4.80% of the corresponding electrodes, respectively. The voltage is maintained at 0.1 V to utilize the electrochemical microbial selection characteristics to enrich electroactive bacteria. Starting with too high a voltage (such as 0.5 V) can easily cause oxidation of the iron electrode, resulting in a positive shift in the electrode potential, making the cathode potential too high, and the denitrification environment cannot be formed. The lightweight ceramsite layer forms the main reaction layer and forms a biofilm on the filler surface of the gravel support layer. S2, start, installed beside the combined rainwater overflow outlet, with an inlet pool in front of the system, connect the overflow pipeline of the combined rainwater network to the inlet pool, and let the overflow sewage flow from the inlet pool into the tank body 1. Adjust the voltage to 0.5V, and let sewage flow into the tank body 1. At the same time, turn on the aeration device and test the water out of the clear water device; S3, operation, monitoring of sewage and effluent, judging the treatment effect of the system by monitoring ammonia nitrogen, nitrate nitrogen, total nitrogen, total phosphorus, total suspended solids and chemical oxygen demand, maintaining the voltage at 0.5V, the system starts to operate normally, the electroactive microorganisms enriched on the bioanode decompose organic matter and transfer the generated electrons to the biocathode; the electroactive microorganisms on the biocathode obtain electrons and reduce the nitrate nitrogen in the sewage near the biocathode to nitrogen gas, during which the potential of the biocathode relative to the reference electrode is maintained at -0.5~-0.6 V, and the potential of the Ag / AgCl2 solid standard reference electrode relative to the standard hydrogen reference electrode is +0.199 V, relative to the reference electrode, the bioanode is maintained below 0V. The bioanode above 0V is prone to iron electrode oxidation, resulting in a gradual increase in the anode potential, thereby increasing the cathode potential as well, and ultimately failing to form a denitrification environment near the electrode. During operation, sewage enters the tank body through the water inlet pipe. The sewage first passes through the bioanode. The electroactive microorganisms enriched on the bioanode can decompose organic matter and transfer the generated electrons to the bioelectrode. The electrons are transferred to the biocathode through an external circuit. The electroactive microorganisms on the biocathode obtain electrons and reduce the nitrate nitrogen in the sewage near the biocathode to nitrogen gas. This process simultaneously accelerates the removal of organic matter and nitrate nitrogen. In addition, the biocathode converts protons in the water into H2 under the catalysis of microorganisms, and under the action of the cathode microorganisms, the hydrogen autotrophic denitrification process occurs to further strengthen the denitrification process. The removal of nitrate nitrogen; on the bioanode, the electrochemical process under the catalysis of microorganisms will initially degrade the difficult-to-degrade organic pollutants into small molecular organic matter that is easier to be used by microorganisms, thereby improving the B / C ratio of the second inlet water of the next-level tank body, which is conducive to the progress of its biochemical reaction. The iron ions precipitated in the system will flocculate and settle the phosphorus and solid matter in the sewage to the bottom of the bioelectrochemical system tank, and will be transported to the sludge storage tank 7 by the bottom mud discharge pipe 8. The effluent of the bioelectrochemical system enters the aerated biological filter from the water distribution tank 17. The sewage passes through the aerated aerobic area, and the ammonia nitrogen in the sewage is oxidized to nitrate nitrogen through nitrification. Subsequently, the organic matter and nitrate nitrogen are simultaneously reduced through denitrification in the anaerobic and anoxic microenvironment formed by the light ceramsite filter layer, and escape from the system in the form of nitrogen gas. Subsequently, the effluent flows into the clear water tank 18 or is further discharged into the natural water body; S4, backwashing. When the electrolytic biofilter system for rapid treatment of overflow pollution has been running for a period of time, the stable water level of the bio-electrochemical system determines that the water head loss of the aerated biofilter has increased, and serious blockage has occurred, and the filtering function cannot be performed normally. At this time, the backwashing process begins. When the backwashing process begins, stop the sewage inlet, close the water tank inlet switch 20 and the water outlet switch 11 of the aerated biofilter cloth, and the aeration pipe; open the backwashing gas line 16 switch, and the air is purged at 10-15 L / (m 2*s) for 3-5 min, then open the backwash water path 19 and the backwash outlet switch 21 at the same time, pump the clean water in the clean water tank 18 into the backwash tank, and then wash the clean water with a speed of 5-10 L / (m 2 *s) for air-water combined backwashing for 5-10 minutes, and finally close the backwashing gas line 16, wash with water for 5-10 minutes, and the backwashing water flows into the tank body 1 through the backwashing outlet 21. After sedimentation, the sediment enters the mud storage tank 7 through the mud discharge pipe 8. This process can greatly improve the simultaneous removal of refractory organic matter, nitrate, phosphorus and ammonia nitrogen in the overflow polluted water body; After backwashing is completed, return to step S1.

[0028] The present embodiment provides an electrolytic biofilter system operation method for rapid treatment of overflow pollution. The test results are shown in Attached Table 1.

[0029] Schedule 1

[0030] In Table 1, the control group is the test data of 24 hours of operation without opening the biological anode and biological cathode. In comparison, the pollutant removal performance of this system is greatly improved compared with the single aerated biological filter technology. When the denitrification demand is the same, the system can shorten the processing time. The system's removal performance of nitrate nitrogen has been greatly enhanced, and the B / C ratio of the effluent from the first pool has increased by 32%. During the test, it was found that maintaining the electrode activity of the microbial electrochemical system in the first pool and enriching and culturing electroactive bacteria are the top priorities. The transfer of electrons between microorganisms and electrodes by electroactive bacteria is a prerequisite for the microbial electrochemical enhanced pollutant removal process. Therefore, the startup process of the system is crucial. The single aerated biological filter technology has a very slow aeration process. The presence of makes its denitrification environment poor and its nitrate nitrogen removal process is hindered. To improve its nitrate nitrogen removal rate, the dissolved oxygen content must be controlled. However, it is extremely technically difficult to achieve sufficient dissolved oxygen for oxygen-consuming processes such as ammonia oxidation and COD oxidation in one device while creating an anoxic or anaerobic environment that is conducive to the denitrification process. This is because the contact time between sewage and filler, the internal flow state, oxygen transfer and other conditions or processes are complex and changeable. Therefore, even if precise control is achieved, the maintenance process is extremely difficult. The system divides the anaerobic, anoxic process and the aerobic process into two tanks, creating conditions conducive to their respective processes, which can effectively avoid the above problems.

[0031] Example 2 like Figure 2As shown, an electrolytic biofilter system for rapid treatment of overflow pollution is shown. Different from Example 1, in the tank body one, sewage flows into the tank body one from the lower side of the biological electrode and flows out of the tank body one from the upper side of the biological electrode. The bioanode and the biocathode are horizontally parallel and arranged. The bioanode is located at the lower side, which can make the sewage pass through the bioanode and the biocathode better in sequence. The effluent of the tank body one enters the tank body two after passing through the overflow trough, and then passes through the lightweight ceramsite layer and the gravel supporting layer from top to bottom in sequence and flows into the clean water tank, and then is discharged. In this embodiment, the water distribution trough is retained, and then mixed with the airflow of the backwashing gas path during the backwashing process, and the lightweight ceramsite layer and the gravel supporting layer are backwashed. The backwashing outlet pipe is not connected to the tank body one, but is connected to a separate sewage tank (not shown in the figure). Compared with Example 1, this embodiment can better remove suspended matter. The disadvantage is that the sewage greatly disturbs the bioanode when flowing upward in the tank body one, and regular maintenance is required.

[0032] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An electrolytic biofilter system for rapid treatment of overflow pollution, characterized in that: Including bio-electrochemical system and aerated biological filter system, The bioelectrochemical system comprises a cell body 1, in which a bioanode and a biocathode are arranged, and the bioanode and the biocathode are connected to a power source. The aerated biological filter system comprises a second tank body. Sewage treated by the first tank body enters the second tank body. The second tank body is provided with an aeration device, a filtering device and a clear water outlet device.

2. The electrolytic biofilter system for rapid treatment of overflow pollution according to claim 1 is characterized in that: The bioanode and the biocathode both include a conductive mesh cage, and an electrode body is arranged inside the conductive mesh cage.

3. The electrolytic biofilter system for rapid treatment of overflow pollution according to claim 1 is characterized in that: A reference electrode is arranged between the bioanode and the biocathode.

4. The electrolytic biofilter system for rapid treatment of overflow pollution according to claim 1 is characterized in that: A mud storage pool is arranged at the bottom of the pool body.

5. The electrolytic biofilter system for rapid treatment of overflow pollution according to claim 1, characterized in that: The filtering device comprises a coarse filtering layer and a fine filtering layer which are sequentially arranged along the flow direction of the sewage.

6. The electrolytic biofilter system for rapid treatment of overflow pollution according to claim 1 is characterized in that: It also includes a backwashing device, which includes a backwashing pump arranged at the bottom of the second pool body, and the backwashing pump is connected to the clean water outlet device.

7. The electrolytic biofilter system for rapid treatment of overflow pollution according to claim 6 is characterized in that: The backwash device comprises a clean water tank connected to the clean water outlet device, and the backwash pump is connected to the clean water tank.

8. The electrolytic biofilter system for rapid treatment of overflow pollution according to claim 1 is characterized in that: The clean water outlet device comprises an overflow trough arranged at the second upper end of the pool body, and the overflow trough is distributed around the second upper end of the pool body.

9. The method for operating an electrolytic biofilter system for rapid treatment of overflow pollution according to claim 1, characterized in that: The following steps are included: S1, pretreatment, inoculate the activated sludge of the anoxic treatment section of the sewage treatment plant into the tank body 1 and the biotank body 2, and energize the bioanode and biocathode, maintain a voltage of 0.1V, and continue for 20 days; S2, start, adjust the voltage to 0.5V, introduce sewage into the tank body, and start the aeration device at the same time; S3, run until clean water is detected at the outlet of the clean water device, maintain the voltage at 0.5V, the system starts to operate normally, the electroactive microorganisms enriched on the bioanode decompose organic matter and transfer the generated electrons to the biocathode; the electroactive microorganisms on the biocathode obtain electrons and reduce the nitrate nitrogen in the sewage near the biocathode to nitrogen gas.

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