JPS6251677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a wastewater treatment method for removing impurities and achieving nitrification with unprecedented efficiency by means of a biological aeration device and an oxidized biomass-activated carbon aqueous slurry. Regarding. The wastewater produced by modern dense industrial societies requires increasingly complex treatment methods. Particularly demanding is the requirement to remove trace amounts of toxins and aquatic plant nutrients. Recently, giving effective treatment,
A method has been discovered that uses a combination of biological organic matter and fine solid absorbent adsorbents. The advantages of particulate solid adsorbents are generally due to the adsorption of microbially toxic substances, high settling of suspended solids during the clarification process, and maintenance of high solids content within the reactor. It is generally believed that the absorbent adsorbent must have a significant specific surface area, such as 100-2000 m ² /g, and that fresh absorbent adsorbent should be continuously applied to the wastewater at a fixed ratio. Commercial absorbents such as activated carbon, diatomaceous earth, etc. that meet the assumed requirements add significantly to the cost. Therefore, methods for recovering spent absorbent adsorbents have been the subject of much research. A number of activated carbon regeneration methods have been described using methods similar to those used in the production of conventional adsorbents, i.e. high temperature treatment of solids in a gaseous atmosphere of steam, carbon dioxide, carbon monoxide or oxygen. . Such methods are designed to restore the absorbent adsorbent to its original properties. Another recovery method is wet oxidation as taught by the inventions of US Pat. Nos. 3,386,922 and 3,442,798. This method has the advantage that it can be applied to aqueous slurries of expendable adsorbents, thus avoiding the costs of over-drying. In the patented invention of Schoeffel et al., wet oxidation is performed such that the absorbed adsorbent organic matter is substantially completely oxidized, a minimal amount of adsorbent is lost, and the recovered adsorbent approaches the original product in properties. Controlled by temperature, residence time and oxygen to adsorbed solids ratio. The use of powdered activated carbon in the biological treatment of wastewater to remove organic impurities and/or promote nitrification is disclosed in US Pat. No. 3,957,632; 3,904,518;
Nos. 3803029 and 3876536, and Canadian patents
It is described in the specification of No. 1006993. The method of the present invention comprises (a) preparing raw water with a mass of various acclimated aerobic microorganisms and powdered activated carbon in the presence of dissolved oxygen maintained above 1 ppm and a substantial reduction in chemical and biological oxygen demand; (b) separating the mixture of activated carbon and biological mass produced in step (a); (c) separating the mixture of activated carbon and biological mass obtained in step (b); (d) recirculating a portion of the mixture of activated carbon and biomass, preferably between 50 and 98%, to treat another portion of the raw water; (d) of the mixture of activated carbon and biomass obtained in step (b); The remaining amount is controlled while limiting the input amount of oxygen-containing gas so that the oxygen concentration in the exhaust gas is less than 7% by volume.
(e) The wet oxidized slurry of activated carbon and biomass obtained in step (d) is subjected to partial wet oxidation at a temperature of 200 to 260°C and a residence time of 30 to 60 minutes; (f) repeating steps (a) to (e) continuously; adding unused activated carbon only to the extent necessary to replace the resulting losses; (f) recycling the raw water for further treatment; (g) removing produced purified water that is substantially reduced in chemical oxygen demand, biological oxygen demand and ammonia nitrogen; By incomplete wet air oxidation of the adsorbed and associated organic matter, it can now be regenerated with virgin carbon or regenerated to its original properties when returned to the aerobic biophysical treatment process. It has been discovered that a slurry product is produced that improves process performance over that obtained using recovered carbon. In the biophysical system, the oxygen concentration of the exhaust gas is 7% by volume.
The return slurry or wet oxidation stream, which is less vigorously oxidized and contains some unoxidized soluble unadsorbed organic matter, as described in step (d), which is less than It has been discovered that feeding a different amount of carbon can accelerate the rate of conversion of ammonia nitrogen to nitrite and nitrate, an oxidation process commonly known as nitrification. A slurry of depleted carbonaceous adsorbent and excess biological material removed from the combined aerobic biological and physical adsorption treatment of wastewater at a temperature between 200°C and 260°C with a residence time of 30 to 60 minutes. When subjected to wet air oxidation and limiting the air supply rate to the oxidation process such that the oxygen concentration in the exhaust gas does not exceed 7% by volume, the product slurry is unexpectedly useful in the bio-physical treatment of wastewater. obtain certain characteristics. Wet oxidation under the above conditions imparts certain properties to the slurry. The suspended carbonaceous adsorbent has a completely different pore diameter-surface area distribution than typical man-made activated carbon, with the wet oxidized product having a diameter of 30 Å.
The surface area is much less in case of pores less than 30 ~
The surface area is significantly higher for pores with a diameter of 600 Å. Wet oxidized solids also differ significantly from commercially available activated carbon in elemental composition. Such differences are shown in the table below. [Table] Solid
(modified carbon)
The remainder of the matter is inorganic. Another feature of the wet oxidized slurry of depleted carbonaceous adsorbent produced by the method of the present invention is the presence of low molecular weight oxygenated organic compounds in the solution phase. C _1-4 alcohol,
Aldehydes, ketones, acids and esters have been identified. Its concentration is such as to give a chemical oxygen demand (COD) of 3000-15000 mg/ and a biological oxygen demand (BOD) of 2000-10000 mg/.
It has been discovered that unoxidized, soluble, unadsorbed organic matter is an exceptional biological substrate. Extensive experimental work has conclusively demonstrated that the use of this wet oxidized slurry in place of commercially available activated carbon provides significant improvements over conventional methods, particularly in the extent and rate of nitrification. First, a certain amount of commercially available activated carbon is charged into the reactor of a biological device, and then the biological wastewater treatment device is operated continuously, and the slurry removed from the device is
It has been discovered that generation of the desired wet oxidized slurry can be effectively achieved by periodically initiating controlled wet oxidation. A wet oxidized slurry with optimal properties is produced after 2-3 days of operation. Thereafter, desired wastewater treatment operations are maintained by limiting the addition of unused activated carbon to the system to the amount needed to replenish normal process losses. Raw wastewater that can be treated by the method of the invention can be obtained from domestic, municipal or industrial sources, including sewage and industrial wastewater or mixtures thereof. This method is particularly effective for wastewater containing significant amounts of ammonia nitrogen. The procedure will be further illustrated with reference to the accompanying drawings. Continuously flowing wastewater 1 enters a mixing chamber 2 where blending with biomass and absorbent adsorbent takes place.
Introduce unused activated carbon in step 9 . mixture reactor
3 , where the dissolved oxygen flows to a sparger,
The value is maintained above 1 ppm by any known device for contacting the liquid with the oxygen-containing gas, such as a fixed membrane reactor or a side flow pressure vessel. Alternating aerobic-anaerobic zones are also possible in the reactor. From the reactor, the mixture is sent to Clarifier 4 ,
There, suspended solids settle and the amount of dissolved oxygen is 0~
2 ppm and biological conversion of nitrate and nitrite to elemental nitrogen (denitrification) may occur. Purified/clear water 5 overflows from 4 . The slurry 6 of absorbent adsorbent and biodegradant is removed from the Clarifair, after which a portion of the slurry, preferably 50-98% thereof, is returned to the mixer 2 and the remainder is treated by the wet oxidation reactor 10. . Depending on process requirements, reactor 10 can be used intermittently. Excess inert inorganic ash material 8 is blown down from the wet oxidation reactor and the wet oxidized slurry 7 is passed to mixer 2 . The method of the invention can be initiated in a number of ways. For example, start the wastewater flow and start the wastewater oxygenator. The wastewater may contain a sufficient number of microorganisms to initiate biological action, and the wastewater may also contain a sufficient number of microorganisms to initiate biological action .
Sewage, etc. may be added to the In either case, the number of microorganisms will increase, so that the mixture in the reactor will contain a mass of microorganisms, characteristically in the range of 1000 to 5000 mg/ml, as measured by inert volatiles. Activated carbon is then added in an amount sufficient to provide 500-50000 mg/, preferably about 3000-15000 mg/volatile activated carbon. The term "volatile" refers to carbon that is derived from organic sources; most commercially available activated carbons contain between 5 and 30% ash (minerals).
"Volatile activated carbon" refers to the organic or non-inorganic (not ash) portion of activated carbon. Alternatively, the activated carbon may be charged at the beginning and the biomass then allowed to accumulate. 5000 ~ in the presence of activated carbon
Biomass concentrations as high as 10000mg/ can be achieved. In any event, once the desired level of activated carbon and biomass concentration is established, the process for generating the preferred absorbent adsorbent slurry can begin. A portion of the thickened slurry removed from the clarifier 4 is directed to a wet oxidation reactor 10. The reaction temperature, residence time and compressed gas:oxygen in solids weight:weight ratio of the slurry determine the yield of active oxygenated absorbent adsorbent. The volumetric flow rate of the thickened slurry directed to the wet oxidation, the concentration of solids in the thickened slurry, the yield in the wet oxidation and the ash blowdown rate determine the active oxygenated adsorbed solids. The rate at which the wastewater is returned to the wastewater treatment reactor 3 is determined. The initial amount of activated carbon introduced into the wastewater reactor 3 and any additional activated carbon 9 added determines the total amount of activated carbon charged to the device. In aeration equipment, residence time (hydraulic
The mixed liquor aeration time, also known as detention time (HDT), is from 0.5 to 24 hours, and the solids residence time is from 2 to 50 days. The temperature is ambient (5-30°C). The invention is further illustrated by the following examples. Example 1 A pilot plant arranged according to the flowchart in the accompanying drawings was set up to determine the performance of a bio-physical device in the treatment of municipal wastewater. During a period of 33 days, designated Period A, only unused activated carbon was added to the mixture in the wastewater treatment reactor. During the next 46 day period, designated Period B, the thickened slurry was separated, wet oxidized, and the active oxygenated absorbent adsorbent slurry was returned to the wastewater treatment reactor. As shown in Table 1, the residence time of solids in the wastewater input into the equipment during period A is longer than 30 days, and the wastewater input into the equipment during period B when the environment inside the equipment is in a steady state. The residence time of the solids inside was 30 days.
The wet oxidation was carried out at 200° C., the residence time was 60 minutes, and the oxygen content in the effluent gas was less than 7% by volume. Compressed air was the oxygen source. The biomass:absorbent weight/weight ratio was 0.4:1.0. Table 1 shows details of the operation and results. The concentration of influent wastewater will increase during period B due to the increase in climate temperature.
Despite the increase in BOD and
The performance performance with respect to COD was just as high in Period B as it was in Period A. Ammonia removal through biological nitrification could not occur during period A. In contrast, about 84% ammonia removal was obtained in period B. In this case, wet oxidation regenerated carbon was used in the biological treatment equipment, and the biological nitrifier was stimulated by the soluble fraction and/or the regenerated carbon. Table 1 In Table 1, solids residence time, an indicator of wastewater treatment, is the average time that solids remain in the device before being discharged. SRT is equal to total solids aerated/total solids discharged per day. Mixed liquid aeration time is also known as residence time (HDT). HDT is the length of time that wastewater is aerated. HDT is equal to the aerator capacity/flow rate per unit time. The aeration capacity is the capacity of the mixed liquid in the aeration device, as shown by 3 in the figure. Volatile activated carbon in the aeration zone (g) is the weight of volatile activated carbon contained within the aeration vessel.
The carbon concentration in the reactor is obtained by dividing the carbon weight by the reactor volume. In period A, the volatile activated carbon in the aeration zone is 608 g/72. Volatile activated carbon input rate is a measure of the mass of fresh (virgin + recycled) carbon added per unit volume of wastewater flowing into the device. Example 2 The treatability of wastewater consisting of 60% domestic sources and 40% industrial sources was tested both in a pilot plant and in a full-scale installation of the type illustrated by the accompanying drawings. Note that the actual-scale device refers to a device of a scale used to actually perform wastewater treatment. Various wet oxidation temperatures were used in the generation of active absorbent adsorbent slurries from depleted absorbent adsorbent-biomass mixtures. Table 2 shows details of the operation data and results. This example demonstrates consistent high performance with generation of active oxygenated absorbent adsorbent slurry at wet oxidation temperatures ranging from 200 to 250°C. [Table] Example 3 From the wet oxidized slurry of Example 2,
The solid absorbent was recovered by washing and drying.
Chemical analysis, surface analysis and adsorption relative efficiency of standard test substances were obtained. Table 3 shows the results. This example shows that the active oxygenated adsorbent produced according to the present invention has significantly different characteristics than the starting activated carbon. The above examples illustrate the excellent performance of these generation absorbent adsorbents. 【table】

[Brief explanation of the drawing]

The figure is a flowchart of one embodiment of the wastewater treatment method of the present invention. 2... Mixer, 3... Reactor, 4... Clarifier, 10... Wet oxidation reactor.

Claims (1)

[Claims] 1. A method for treating raw water, comprising: (a) treating the raw water with a mass of various acclimated aerobic microorganisms and powdered activated carbon in the presence of dissolved oxygen maintained at an amount greater than 1 ppm; (b) separating the mixture of activated carbon and biological mass produced in step (a); (c) recirculating a portion of the mixture of activated carbon and biological mass obtained in step (b) to treat another portion of the raw water; (d) recirculating a portion of the mixture of activated carbon and biological mass obtained in step (b); The remaining amount is controlled while limiting the amount of oxygen-containing gas input so that the oxygen concentration in the exhaust gas is less than 7% by volume.
(e) The wet oxidized slurry of activated carbon and biomass obtained in step (d) is subjected to partial wet oxidation at a temperature of 200 to 260°C and a residence time of 30 to 60 minutes; (f) repeating steps (a) to (e) continuously; adding unused activated carbon only to the extent necessary to replace the resulting losses; (f) recycling the raw water for further treatment; (g) removing the produced purified water having substantially reduced chemical oxygen demand, biological oxygen demand and ammonia nitrogen. 2 The product of step (d) contains 20 to 60% carbon and 1 to 60% hydrogen.
2%, organic nitrogen 1-3%, organic oxygen 5-20%, and the balance is 3000-15000mg/chemical oxygen demand.
2. A method according to claim 1, characterized in that the slurry is an active absorbent adsorbent slurry having a composition of inorganic matter in the aqueous phase with a biological oxygen demand of 2000 to 10000 mg/. 3 The concentration of volatile activated carbon in step (a) is 500
3. The method according to claim 1 or 2, characterized in that the amount is ~50000 mg/. 4. Process according to any one of claims 1 to 3, characterized in that from 50 to 98% of the mixture is recycled in step (c).