JP2004511346A - Method and apparatus for treating sewage or sewage sludge - Google Patents

Abstract

An improved method and apparatus for treating sewage or sewage sludge. In a method of treating sewage or similar organic sludge to produce a sterilized and dried product, drying the sludge to substantially the desired dry solids content of the product, and then removing the sludge. Adding an alkaline additive to the dried sludge for sterilizing and / or stabilizing to produce a product without subsequent drying by aeration.

Description

[0001]
(Technical field)
The present invention relates to a method and an apparatus for treating sewage sludge or similar organic sludge from industrial sites such as wastewater treatment plants.
[0002]
(Background technology)
European Patent EP 0 283 153 B1 discloses a method for treating wastewater sludge for making agricultural fertilizers which can be applied directly to the ground. The method comprises the steps of mixing sludge with an alkaline material of a particular fineness, increasing the pH of the mixture to at least 12 for at least one day, sterilizing, and then drying the mixture. Drying may be a) aerated and maintain a pH greater than 12 for at least 7 days until the solids level reaches and maintains a bulk density of at least 65%, or b) a solids level of at least 50%. This is done by aeration and heating to a temperature of at least 50 ° C. so as to reach and maintain the bulk density. In b) above, the temperature should not be so high as to destroy non-pathogenic organisms. Increasing the pH and drying reduces malodor, unwanted pathogens (eg, flies) attracted by viruses, bacteria, parasites and sludge, and effectively regenerates pathogens without eliminating beneficial non-pathogenic microorganisms. This is done to prevent growth. At least some of the temperature rise is due to an exothermic reaction with the alkali. The product can be cured in air for about 10 days after achieving the desired solid content. Drying and hardening are performed by a method of drying, inversion or other forced ventilation, the hardening or aeration time is determined based on the aeration procedure and other factors such as temperature and humidity, and In special cases, it is necessary to determine empirically whether or not the required end point has been reached. This involves taking a sample for measuring the solids content and testing for the following items:
[0003]
Animal virus-less than 1 plaque forming unit per 100 ml
Salmonella bacteria-less than 3 colony forming units per 100 ml
Parasites-less than 1 viable egg per 100 ml
・ Effective regrowth of pathogenic microorganisms-must not be
It also evaluates the reduction of odors in closed rooms to acceptable levels, and that this reduction is maintained indefinitely under all climatic conditions, and whether flies are not attracted to the product. At the same time, the presence of at least some beneficial non-pathogenic microorganisms must be established.
[0004]
When using method b) above, the minimum recommended time to maintain a temperature of at least 50 ° C. (but not so high as to eliminate non-pathogenic microorganisms) is at least 12 hours. The heat-treated alkali-stabilized dewatered sludge cake is then air-dried by intermittent rotation of the drying line until a solids content of at least 50% is achieved (while the pH is at least 3 days). Is maintained at 12 or more).
[0005]
GB 2 276 876 A, referred to in EP 0 283 153, cited above, uses an alkaline material containing free lime and stores and / or dries and / or composts the resulting mixture to provide sufficient mixture. Techniques for treating sewage sludge containing at least 15% by weight solids content by adding lime to achieve a pH of at least 10 are disclosed. Higher pH values, such as above 12, are not excluded, but it has been suggested that excellent reduction of pathogens is achieved at pH levels below 12 where less ammonia is evolved. Low ammonia means that the sludge to be treated and the surrounding discomfort are ameliorated and that the material to be treated carries a large amount of nitrogen, increasing the nitrogen value as fertilizer.
[0006]
The method of the above GB 2 276 876 discloses a method in which sludge is dewatered by, for example, a belt press, and the dewatered sludge is weighed using a weighing hopper (a suitable amount of alkali material is supplied to the hopper) to a mixer. With the step of measuring, the mixed material is fed to a skip and fed to the ground drying area, where the mixed material is rotated periodically, usually for up to 7 days. However, it is also suggested that the amount of calcium oxide introduced is sufficient to raise the pH to a value higher than 12, and indeed to be sufficient to ensure that it is maintained at a value higher than 12 for at least 12 hours. In this case, the mixture can be stored for at least 2 hours and applied directly to the ground.
[0007]
The methods disclosed in both of these specifications are labor intensive, require subjective judgments (eg, evaluation of odors in a closed room), or biological methods that require days or weeks to obtain results. Obviously, it relies heavily on experimental results.
[0008]
For an effective treatment, it is necessary to mix the alkali with the dewatered sludge (although the dewatered sludge must be present only in the presence of enough water to cause the desired exothermic chemical reaction). , May contain substantial amounts of water). The final product is required to have a water content that is less than the appropriate amount in the exothermic stage, as is apparent from the disclosure in the above specification. In this case, the important thing of this method is that the product is finally dried, because the product is treated by drying. Drying, especially aeration by spinning rows, is not only labor intensive and floor spacer intensive, but also a slow drying method, exposing workers to excessive levels of ammonia and volatile organic compounds. I will.
[0009]
Prior art methods such as those disclosed in the above-mentioned EP 0 283 153 and GB 2 276 876 have other problems and disadvantages. For example, a relatively large amount (typically 30-50% by weight of wet sludge or 150-300% by weight of dry sludge) of alkaline material is required, and such a large amount of alkaline material is large in the end product produced by the process. Is to make up the proportions. This adds cost in three major ways. The first is the cost of providing a large amount of alkaline material. The second is the material cost when handling large volumes of mixed products by heat pulsing and drying line formation and rotation. Third is the transportation cost of removing end products from the site. Another important issue is that not only the relative proportion of nutrients such as nitrogen and phosphorus in the end product is reduced because the alkaline material makes up a large proportion of the end product, but also is fixed due to the high pH of the product It is to be. This reduces the value of the end product as an agricultural fertilizer. Also, because a large amount of alkaline material is added, a pH higher than 12 is maintained for an extended period of time, and the product may be categorized as a special waste by an administrative agency. Special waste requires special landfill disposal.
[0010]
It is difficult, if not impossible, to uniformly control, manage and measure the temperature of the dried product. Also, when using the method of EP 0 283 153, considerable problems with the odor of the product, more particularly with ammonia, actually occur both during production and in the finished product.
[0011]
It should be noted that U.S. regulations on the treatment of sewage sludge require stabilization as well as sterilization of the product (EPA Regulation 503). The latter is referred to as a vector attraction reduction requirement and is specified in regulation 503.33 (b). For the avoidance of doubt, as used herein, the terms "stabilizers" and "stabilization" refer to methods that meet the requirements for reducing vector attraction set forth in US EPA Regulation 503.33 (b). Shall be referred to.
[0012]
(Disclosure of the Invention)
The present invention overcomes the above problems and disadvantages and provides a new methodology for treating sewage sludge. The present invention is more efficient, less labor and space intensive, and easier to control (biotechnological testing, inaccurate manual sampling and dry solids content, temperature, And sewage sludge treatment method and apparatus which can perform both continuous treatment and online monitoring and management. This ensures the achievement of critical treatment steps that ensure pathogen destruction of the treated sludge and its subsequent long-term stability. More specifically, the tonnage of the final product produced after processing a given amount of sludge is greatly reduced, which can reduce manufacturing, handling and transportation costs. This is mainly due to the greatly reduced amount of sludge and the amount of alkaline material required to perform the sterilization. Another advantage provided by the reduced use of alkaline materials is cost savings. Also, unlike the methods disclosed in EP 0 283 153 and GB 2 276 876, the present invention does not involve the use of an aeration method such as drying. In addition, the floor space (or "footprint") required for the device of the present invention is greatly reduced. Further, the odor generated by the present invention is minimal and easily manageable. Also, the end product made by the process of the present invention is of high quality, has a high amount of available nutrients and is virtually odor free. Further, since the use of the alkali material is greatly reduced, the control of the process temperature and the reduction of the pH after the treatment can be achieved more efficiently.
[0013]
According to a first aspect of the invention, in a method of treating sewage or similar organic sludge to produce a sterilized and dried product, the sludge is substantially reduced to a desired dry solids content of the product. Drying, and then adding an alkaline additive to the dried sludge to sterilize and / or stabilize the sludge and produce a product without subsequent aeration drying. Is provided.
[0014]
There are a number of advantages resulting from the approach of drying prior to sterilization or performing sterilization as a result of drying (the present invention differs from post-sterilization drying as disclosed in EP 0 283 153 and GB 2 276 876). ing). After drying, the weight and volume of the sludge is significantly reduced compared to the output of the raw material. The total amount of alkaline additive required for sterilization (and / or stabilization) of the mixture may be very small. This has the advantage of greatly reducing costs and reducing the tonnage of product associated with a given amount of wet sludge starting material. Although the amount of alkali additive used is small, excellent long term sterilization and stabilization profiles are obtained. Also, end products with excellent high dry solids content can be easily made. The higher the dry solids content of the product, the better the long-term stability of the final product. There is no need for time- and space-intensive and costly drying steps, such as drying or other aeration techniques. The process of the present invention can be used for treating raw sludge feedstock, which has the advantage of eliminating the need for expensive sludge digestion steps. However, the method of the present invention can also be used to treat digested sludge feedstock.
[0015]
Alkali additives can be added to the dried sludge at a mixing ratio of sludge dry solids of 25% by weight or less, preferably 20% or less, most preferably 15% or less. This represents a very low proportion of the product finally formed, but is surprisingly sufficient to sterilize and / or stabilize the sludge and to produce a high quality product. .
[0016]
Preferably, the alkaline additive comprises lime, which is advantageously ground or atomized. It has been found that the greater the surface area associated with the lime treated in this manner, the better the sterilization and stabilization process. Drying of sludge is performed by a thin film dryer, and the dryer can be formed by a horizontal one-pass indirect heating thin film dryer. Such a dryer is manufactured by Buss-SMS GmbH (Pratteln, Switzerland). These dryers operate on a plow flow basis, i.e., first in first out (FIFO), with the advantage that the sludge residence time in the dryer is accurately established. Further, the sludge can be completely sterilized during the drying process.
[0017]
The sludge can be dried to a dry solids content of greater than 50%, preferably in the range of 52-65%. The advantage of limiting drying to this range is that sludge with a high fiber content (such sludge has the risk of igniting or exploding later in the dried sludge) is not produced.
[0018]
The method of the present invention may further include a step of dewatering the sludge before further drying the sludge to produce a dewatered sludge cake.
[0019]
The drying step of the sludge can perform partial or complete sterilization of the sludge. This helps to keep the amount of alkaline additive required to a minimum. Further, since the sludge is not dried at a high pH, the odor accompanying this drying step does not include ammonia. On the contrary, volatile species or gases are created such as volatile organic compounds, hydrogen sulfide and various mercaptans, which can be easily removed by biological filters, scrubbers or regenerative thermal oxidizers. The effect is that the odor associated with sludge treatment can be significantly reduced (ammonia and certain volatile organic compounds are a major source of such odors). If an indirect design dryer is used, only the non-condensable gas stream needs to be scrubbed, thus minimizing the gas volume and thus the scrubber size.
[0020]
The product can be discharged continuously. Sterilization and / or stabilization of the mixture can be performed in a first-in, first-out (FIFO) hopper, with or without recirculation of the mixture.
[0021]
Raw waste, such as mowed grass and leaves, can be added to the sludge prior to drying the sludge to a substantially desired dry solids content.
[0022]
The gas is removed during sterilization and can be introduced into a dryer used for drying sludge. One advantage is that the particles, ammonia and volatile organic compounds (VOCs) resulting from the sterilization process are removed in a dryer. The particles cause problems when introduced into a waste treatment stage such as a regenerative thermal oxidizer (RTO), but if the waste stream is introduced from the dryer into the RTO (somewhat Are introduced from the sterilization unit), these problems are avoided. Another advantage is that the size of the RTO can be minimized, because the gas in the sterilization stage is replaced by leaking air required for efficient operation of the dryer.
[0023]
Excess heat associated with sludge drying is recovered and can be used for purposes associated with the method of the present invention or the apparatus for performing the method. The recovered heat can be used to heat the production space and / or heat the ammonia scrubbing step. This achieves a very efficient energy use.
[0024]
The process of the present invention is performed continuously, but batchwise or semi-continuous operation is also possible.
[0025]
According to a second aspect of the present invention, in an apparatus for treating sewage sludge or a similar organic sludge according to the first aspect of the present invention,
Means for drying the sludge to substantially the desired dry solids content of the product;
Means for adding an alkaline additive to the dried sludge;
Means for initiating the sterilization and / or stabilization of the mixture and producing the product without subsequent drying by aeration, holding the mixture and the added alkaline additive. Is provided.
[0026]
The means for holding the dried sludge and the added alkaline additive can comprise a first-in first-out (FIFO) hopper.
[0027]
The apparatus of the present invention can further be provided with a means for dewatering the sludge before further drying the sludge, which means can be constituted by a belt press apparatus, and the apparatus can be constituted by a multi-stage belt press.
[0028]
The means for drying sludge can be constituted by a thin film dryer, and the dryer can be constituted by a horizontal one-pass indirect heating type thin film dryer.
[0029]
The device according to the invention can furthermore be provided with at least one storage means for containing lime, the lime being used as an alkaline additive or part thereof. The lime can be powdered or atomized.
[0030]
The apparatus of the present invention may further be provided with conduit means for removing gas from the means for holding the mixture and introducing the gas to the sludge drying means. This allows the traditionally required leak intake means to be replaced by a dryer.
[0031]
The apparatus of the present invention further comprises heat recovery means for recovering excess heat associated with the drying of sludge and directing the recovered excess heat to a target location so that the recovered excess heat can be used for purposes associated with the method or apparatus. Can be provided. The apparatus of the present invention can further be provided with an ammonia scrubber system that is heated using the recovered excess heat.
[0032]
The drying means can also perform a complete sterilization of the sludge.
[0033]
According to a third aspect of the present invention there is provided a dry sludge produced by the method of the first aspect of the present invention. Such products have a high dry solids content (> 50%) and high nutrients. The product can also be used as artificial topsoil and as an agricultural fertilizer.
[0034]
(Best Mode for Carrying Out the Invention)
Hereinafter, a method and an apparatus according to the present invention will be described with reference to the accompanying drawings.
[0035]
FIG. 1 shows an embodiment of the method according to the invention. In this method, liquid sewage is introduced from a location indicated by reference numeral 10 and dewatered using a belt press system 12 to produce a sludge cake. Generally, the sludge cake has a dry solids content of about 27%. After dehydration, the sludge cake is transported to the dryer 14 by a transport system (not shown). The transport system can consist of known means such as a belt conveyor and discharge plow and infrared moisture sensor and weighing system for continuous monitoring. Optionally, the first part can be placed in a blender into which raw waste such as cut grass can be introduced.
[0036]
The dryer 14 takes a sufficient amount of time to produce dry sludge of the desired dry solids content, which is substantially the desired dry solids content of the product, Dry the sludge at a suitable dewatering temperature.
[0037]
It is advantageous to discard raw waste in this way for a number of reasons. Raw waste generally has a very high water content of 80% and is therefore very bulky. In the United States and other countries, raw waste cannot be landfilled, but municipalities provide collection services as so-called "yard waste." Raw waste, in particular, requires a composting device, which increases disposal costs other than collection costs. Such devices are expensive to operate and at the risk of foul odor complaints. The present invention provides a more convenient way to dispose of raw waste. Also, the dry portion of the raw waste (about 20% of its original weight) provides benefits to the end product because it is rich in organic matter and nutrients such as N, P.
[0038]
The dried sludge is conveyed from the dryer 14 to the mixer 16 by means such as a conveyor belt, where the alkali additive from the silo 18 is added and mixed with the sludge. The mixture is conveyed to the sterilizer 20. The sterilizer 20 can be constituted by a first-in first-out hopper. At the end of this process, the end product 22 of the eutrophic element is discharged using a belt conveyor device.
[0039]
Excellent results have been obtained when the alkali additive is CaO, but the invention is not so limited, and other alkali additives containing one or more components can be used.
[0040]
Due to the drying of the sludge, it is very advantageous that the sludge / alkali additive mixture is already very dry. This is because a further drying step with all the attendant disadvantages (eg drying) is not required. When the alkaline additive is added to the dried sludge, it is considered important that the sludge is still fairly hot (about 40-60 ° C. or higher) after the drying step. It is believed that the drying process transfers the large amount of heat required for sterilization, which allows for sterilization using relatively small amounts of alkali additives. In contrast, relatively large amounts of the alkaline additive according to the prior art methods of EP 0 283 153 and GB 2 276 876 may be required in part because of the need to generate a germicidal heat pulse from ambient temperature. It is. In these prior arts, this is achieved by an exothermic reaction between the alkali additive and water, which further necessitates expensive alkali additives.
[0041]
It is also advantageous that the sludge itself is partially or totally sterilized by the drying of the sludge itself. The result of the partial sterilization is that relatively small amounts of CaO are required for sterilization (stabilization). The result of the overall sterilization by the drying process is that only the alkaline additive is required to perform the sterilization. This raises the pH of the dried sludge to 12 or more for more than 2 hours, and then for an additional 22 hours, as required by US EPC Regulation 503.33 (b) (6). Achieved by maintaining the pH above 11.5.
[0042]
It should be noted that the addition of CaO allows further drying due to the exothermic reaction with water, but this is not necessary for further drying. Generally, the amount of CaO required is less than or equal to 25%, preferably 20%, and most preferably 15% by dry weight of the dry sludge (or sludge / raw waste mixture). Another benefit is that the sterilization process can be relatively short, and is shorter than one day. The sterilization process can take up to 5 hours, 4 hours or less, and even about 2-3 hours or less. Generally, the mixture is held for about 15 hours for sterilization to ensure that the mixture is maintained at the sterilization temperature for 12 hours or more. However, the present invention recognizes that shorter sterilization times and temperatures are possible. During the sterilization / drying process, a pH of 12 or higher and temperatures up to about 70 ° C. are obtained. It is believed that sufficient sterilization can be achieved at pH below 12 and / or below about 70 ° C. Therefore, the present invention is not limited in this regard. Another benefit of the present invention is that the relatively small amount of CaO in the end product and drying of the end product can reduce the amount of end product made for a given sludge input. Yet another benefit is that the pH of the product drops rapidly as CaO is consumed, since no excess CaO is used.
[0043]
Generally, after the addition of the alkali additive, the temperature of the dried sludge in the insulated reaction vessel rises and is maintained uniformly at a temperature of at least 65 ° C. for up to 5 hours, during which time the pH of the Is maintained at 12 or more. During the next 24 hours, the pH of the product will be higher than 11.5. As a result, the conditions of the EPA rule 503.33 (b) (6) can be satisfied, and the product can be stabilized. It should be noted that in general, the stabilization step is not performed completely in the sterilizer. Rather, the stabilization process is continued after the product exits the sterilizer.
[0044]
The present invention has been found to work particularly well when the CaO is in powder or fine form. This may be due to the larger surface area available in the reaction associated with the sterilization process.
[0045]
The present invention has also been found to work particularly well when drying sludge using a plug-flow base or FIFO (first-in first-out) horizontal one-pass thin film dryer. Such a dryer is manufactured, for example, by Buss-SMS GmbH (Hohenrainstrasse 10, Pratteln, Switzerland). The Buss-SMS dryer (type D-0100) is very suitable for continuously drying sludge to a drying rate in the range of at least 50-60% dry solids content. Also, it is relatively easy to achieve sterilization and / or stabilization temperatures because the dried sludge is introduced into the alkaline additive mixing stage while still hot (about 60 ° C.). Horizontal thin film dryers such as the Buss-SMS dryer (Type D-0100) include feed pumps with variable speed drives, conical feed hoppers and agitators, condensers and condensate receivers, liquid rings. By providing a pump (for discharging non-condensable vapors) and heating means, it can be integrated into the system. The dryer blades extrude the sludge through the dryer (in a substantially horizontal direction in the case of a horizontal thin film dryer) while at the same time ensuring that the sludge is spread thinly and repeatedly over the dryer wall. The wall is indirectly heated by heating means, which can be constituted for example by a thermal oil heater or a steam boiler. However, other types of dryers can be effectively used instead of the thin film dryer.
[0046]
However, an advantage of the thin film dryer is that the sludge can be uniformly dried at a minimum sludge temperature of 100 ° C. and a minimum residence time of about 4 minutes. Such conditions are more than sufficient to effect a complete sterilization of the sludge. In this case, the added alkali is simply used to stabilize the dried and sterilized sludge. A ceramic surface can also be provided in the dryer to monitor the drying temperature.
[0047]
In many mixing trials, various combinations of sludge drying rate and CaO mixing ratio were used. Sludge drying rates with solids content in the range of 50-59% were used. 5-14% CaO was added. The drying rate of the final product was constantly only slightly higher than the drying rate of the sludge before mixing. For example, sludge with a dry solids content of 51% treated with 14.1% CaO gives a product with a dry solids content of 56.4%, while a product with a dry solids content of 5.3%. A sludge with a dry solids content of 59% with CaO added gave a product with a dry solids content of 65.1%.
[0048]
The products in these trials all had good or very good quality, which was evaluated using a number of criteria: granularity, stickiness, odor and moldability. FIG. 2 shows the temperature profile of the dry sludge / CaO mixture over time. In this case, a dry sludge with a dry solids content of 57% was mixed with 8.7% of powdered CaO. The results of two other trials under these conditions are shown. Excellent heat pulse profiles were obtained for at least 17 hours when the elevated temperature was maintained. After the sludge was mixed with CaO, a pH of 12.2 was measured. Satisfactory results are obtained at low and / or low pH, but the combination of high and high pH results in excellent sterilization and stabilization.
[0049]
All steps can be performed continuously or almost continuously. Individual or multiple belt presses can be used to ensure a constant or near constant flow of the dewatered sludge cake. Similarly, multiple dryers and mixers can be used to ensure continuous throughput. The sterilization (and / or stabilization) step can be performed continuously using a first-in first-out hopper or similar device. Since the sterilization (and / or stabilization) phase is relatively short, the sterilization (and / or stabilization) can be performed in one pass through the hopper. In other words, the material need not be recycled through the hopper, but can be used to remove small amounts of ammonia and volatile organic compounds (VOCs) from the finished product.
[0050]
Ammonia released during the sterilization (and / or stabilization) stage can be removed using an ammonia scrubber. However, since part of the complete disinfection of the first part is achieved during drying of the first part, the amount of ammonia released is reduced. Dry sludge also generally offers the benefit of reducing the potential for malodor generation. Since this "pre-sterilization" of the sludge is not performed at high pH, substantially no ammonia is released during this step. Even if malodorous compounds such as volatile organic compounds, hydrogen sulfide and many mercaptans are made, they can be easily processed using biological filters, scrubbers or regenerative thermal oxidizers. For this reason, the present invention has the advantage that the problems associated with malodor can be significantly reduced.
[0051]
FIGS. 3 to 5 show a device according to the invention with an emergency backup function which can be operated continuously and which can sufficiently meet the requirements of the regional metropolitan authorities.
[0052]
FIG. 3 shows the preliminary sludge dewatering stage, in which the sludge is dewatered by the belt press 30 and conveyed through the conveyors 32, 34, 36, 38, 40, 41, 42, 43. . The water content is monitored by the infrared scanner 48, the in-line weigh belt system 50 and on-line, and the continuous data thus obtained is used for controlling the whole process. Although not limited to this figure, generally the dewatered sludge has a dry solids content of about 27%.
[0053]
FIG. 4 shows the step of further drying the sludge after the dewatering step. Conveyor belts 52, 54 transport the dewatered sludge cake to storage bottle 56. Next, the screw feeder 58 and the feed pump 60 convey the dewatered sludge cake to the dryer 62. After drying, the conveyors 64, 66, 68 convey the dried sludge to the mixing zone (shown in FIG. 5). Infrared moisture sensor 64 and weigh belt system 66 can continuously monitor the water content. An ultrasonic level sensor 68 provided in the storage bottles 58 can correct the amount of dewatered sludge cake to be supplied to each storage bottle 58 as part of an automatic process control system.
[0054]
FIG. 5 shows the mixing stage of the dry sludge and the alkali additive. Silo 70 stores lime, and other silo 72 stores inert added alkali material such as powdered combustion ash (PFA). The purpose of the PFA is to raise the pH to the desired value without imparting the reactivity provided by the lime. The screw conveyor 74 supplies lime and optionally supplies a desired amount of PFA to a mixer 76 such as a continuous plowshare mixer. The dried sludge transported by the conveyor 68 (FIG. 4) is transported to the conveyor 78 and the storage unit 80 having a capacity of 100 tons. Next, a weigh belt conveyor 82 transports the dried sludge to one or more discharge plows 84, from where the sludge is delivered to a mixer 76 where it is mixed with the alkaline additive. An infrared moisture sensor 86 and a weighing belt system 88 are provided for the aforementioned purpose.
[0055]
After mixing, the mixture containing the alkali additive and the dried sludge is conveyed by the conveyor 90 to the sterilization section shown in FIG. As shown in FIG. 6, another conveyor 92, 94, 96 transports the mixture to a sterilization unit 98, which is a first-in first-out (FIFO) hopper. The mixture is conveyed along a FIFO hopper and discharged from the end opposite to the inlet end using a discharge screw feeder 100. Thereafter, the mixture is recirculated to FIFO hopper 98 using conveyors 102, 104, 106 or discharged onto conveyor 108. Recycling is not required for all drying steps, but is done to remove volatile species. The product is then removed from the apparatus using conveyor 108 and storage belt conveyor 110. Infrared moisture sensor 112 and gravimetric belt system 114 can provide monitoring of the water content and weight of the final product.
[0056]
FIG. 7 illustrates how surplus energy or waste energy can be used for various effective support processes, particularly exhaust gas treatment. A thermal oil heater 120 is used for heating the thin film dryer 122. The oil in the unit 120 is heated by burning the oil supply 124 or the gas supply 126. Excess heat from this process is used to heat a thermal oil or water heat exchanger 128. Next, heat exchanger 128 is used to heat the gas passing through the ammonia scrubber system (indicated generally by reference numeral 130). As a result, heat not recovered is eventually lost from the heater stack 132.
[0057]
In a similar manner, heat from the regenerative thermal oxidation unit 136 (described in more detail below) is recovered using a water heat exchanger 136 (otherwise this heat is lost to the atmosphere via the stack). ). Hot water from heat exchanger 136 can be used in ammonia scrubber system 130.
[0058]
The hot water provided by the heat exchanger can be used for other purposes such as process cleaning, space heating and general hot water service equipment, instead of supplying it to the ammonia scrubber system, thereby providing the traditional The expansion of the water heating means can be eliminated or reduced.
[0059]
During drying of the sludge in the thin film dryer 122, the sludge is maintained at a high temperature of 100 ° C. or more for about 3 to 5 minutes. In addition to the evaporation of water, steam is created to which certain amounts of various gases and volatile organic compounds (VOCs) trapped in the original effluent sludge can be added. These volatiles need to be sucked out of the dryer 122 while maintaining a very slight negative pressure in the dryer 122, which introduces leaked air into the dryer 122 in a manner detailed below. It is achieved by doing.
[0060]
The steam is sucked from the dryer 122 by a fan (not shown) that discharges the steam into the steam condenser 140. Two waste streams are created, a condensable waste stream and a non-condensable waste stream. Condensable waste streams, consisting primarily of high BOD and COD contaminated water, are returned by pumps 142, 144 into the primary sedimentation tank of the on-site sewage treatment process. Alternatively, the condensable waste stream can be pumped to the head at the system inlet. In any case, the condensable waste stream is diluted by the mass flow through the sewage treatment process, and thus is treated before it is finally discharged as final effluent. The final effluent is pumped by pumping station 146 as cooling water through heat exchanger 148 to cool the condensable waste stream.
[0061]
The non-condensable waste stream contains various gaseous substances and organic compounds that should not be discharged to the atmosphere, and is removed through the regenerative thermal oxidation unit 134. Fan 150 directs the non-condensable waste stream into oxidation unit 134.
[0062]
Each sterilization unit 152 is provided with a fan 154 for removing gas generated during sterilization. Such gases include steam, ammonia, and VOC. The fan 154 can remove fine particles such as alkali powder or dry sludge particles that would otherwise cause problems in the oxidation unit.
[0063]
Conveyor 156 and sludge buffer bottle 158 form part of the post-dry sludge treatment process. Conveyor 156 and buffer bottle 158 are ventilated to remove the generated water vapor condensates and VOCs by maintaining the enclosure under slight negative pressure. Another advantage of such ventilation is that, if necessary, some cooling of the dry sludge can be achieved before storing and mixing with the alkaline additive.
[0064]
Another feature of this system is that the exhaust gases from the sterilization unit 152, conveyor 156, and buffer bottle 158 can be supplied to the dryer 122 to provide the leak air required by the dryer 122. Since the environment within the dryer 122 is saturated with moisture, any particles and gases fed into the dryer 122 are blended in the sludge drying process, thereby providing a dryer discharge stream and condensability through the condenser 140. And the non-condensable waste stream ultimately treats the fully blended vapor effluent. This eliminates the need for the regenerative thermal oxidation unit 134 to process the particles. Also, since only a single non-condensable waste stream requires treatment, the gas throughput required to handle the oxidation unit 134 is minimized.
[0065]
All steps are automated and controlled by computer. The computer can control the generation rate and throughput of dewatered sludge, the number and throughput of operating dryers, the sludge temperature profile in each dryer, the addition rate of dry sludge and alkali additives, and can be obtained by various sensors. The process can be adjusted online based on process information such as water content, bottle level and weight. To obtain other information for performing this online control, for example, a temperature sensor can be used. Thus, all important process control data can be displayed, recorded and stored to satisfy any required control report data.
[0066]
The systems shown in FIGS. 3-6 are designed with extra capacity to handle abnormally high flow rates and / or component failures. For example, only seven belt presses are used for average throughput, but this number can be increased to 10 for peak operation. Similarly, only three dryers and two disinfection units are used during average loading, two each during standby. Such a plan is not a limiting constraint on the present invention, and those skilled in the art will readily appreciate that many other modifications of the system are possible and that such modifications are indeed necessary. It is preferred depending on the exact nature of the processing. The apparatus described in connection with FIGS. 3-6 can handle an average sludge throughput greater than 155 US short dry tons per day at a time, up to 50% greater peak flow. It has sufficient spare capacity to allow for emergency equipment coverage at any throughput. The device of the present invention can operate continuously 24 hours a day, 365 days a year.
[0067]
Because the costs associated with the present invention are inexpensive, and because the present invention can provide an effective and consistent sealable product (i.e., a high quality dried sludge product), the apparatus of the present invention can be used within 4-5 years. Operation will return the invested capital.
[Brief description of the drawings]
FIG.
3 is a schematic flow chart illustrating a method according to the present invention.
FIG. 2
It is a graph which shows the relationship between elapsed time and temperature of the dried sludge / lime mixture.
FIG. 3
4 is a view illustrating a preliminary sludge dewatering step.
FIG. 4
4 is a view illustrating a step of further drying sludge.
FIG. 5
4 is a view showing a step of mixing sludge and lime.
FIG. 6
1 is a view showing a sterilization and stabilization stage of a sludge / lime mixture.
FIG. 7
It is the schematic which shows a heat recovery / waste disposal apparatus.

Claims (28)

In a method of treating sewage or similar organic sludge to produce a sterilized and dried product,
Drying the sludge to substantially the desired dry solids content of the product;
Then adding an alkaline additive to the dried sludge to sterilize and / or stabilize the sludge to produce a product without subsequent drying by aeration. 2. The method according to claim 1, wherein the alkali additive is added to the dry sludge in a mixing ratio of sludge dry solids of less than 25% by weight, preferably less than 20%, most preferably less than 15%. Method. 3. The method according to claim 1, wherein the alkali additive comprises lime. The method of claim 3, wherein the lime is powdered or atomized. The method according to any one of claims 1 to 4, wherein the drying of the sludge is performed by a thin film dryer. The method according to claim 5, wherein the drying is performed by a horizontal one-pass indirect heating type thin film dryer. Method according to any of the preceding claims, wherein the sludge is dried to a dry solids content of greater than 50%, preferably in the range of 52 to 65%. The method according to any one of claims 1 to 7, further comprising a step of dewatering the sludge before further drying the sludge to form a dewatered sludge cake. The method according to any one of claims 1 to 8, wherein the drying of the sludge is performed by partially sterilizing the sludge. The method according to any one of claims 1 to 9, wherein the drying of the sludge is performed by completely sterilizing the sludge. The method according to claim 1, wherein the product is continuously discharged. The method according to claim 11, wherein the sterilization of the mixture is performed in a first-in first-out hopper. 13. The method according to claim 1, wherein the gas is removed during sterilization and is introduced into a dryer used for drying sludge. 14. A method according to any one of the preceding claims, characterized in that the excess heat associated with the drying of the sludge is recovered and used for purposes associated with the method or an apparatus performing the method. . The method according to claim 14, wherein the recovered heat is used for heating the ammonia scrubbing step. The continuous method according to claim 1. An apparatus for treating sewage sludge or similar organic sludge by the method according to any one of claims 1 to 16,
Means for drying the sludge to substantially the desired dry solids content of the product;
Means for adding an alkaline additive to the dried sludge;
Means for initiating the sterilization and / or stabilization of the mixture and producing the product without subsequent drying by aeration, holding the mixture and the added alkaline additive. . 18. The apparatus of claim 17, wherein the means for holding the dried sludge and added alkali additive comprises a first-in first-out hopper. 19. The apparatus according to claim 17, further comprising means for dewatering the sludge before further drying the sludge. 20. Apparatus according to any of claims 17 to 19, wherein the means for drying the sludge comprises a thin film dryer. 21. The apparatus according to claim 20, wherein the dryer is a horizontal one-pass indirect heating thin film dryer. The device according to any one of claims 17 to 21, further comprising at least one storage means for containing lime, wherein the lime is used as an alkaline additive or a part thereof. 23. The device according to claim 22, wherein the lime is powdered or atomized. 24. Apparatus according to any one of claims 17 to 23, further comprising conduit means for removing gas from the means for holding the mixture and introducing the gas to the sludge drying means. The method further includes a heat recovery unit that recovers excess heat accompanying the drying of the sludge and guides the recovered excess heat to a target location, and can use the recovered excess heat for purposes related to the method or apparatus of the present invention. Device according to any of claims 17 to 24, characterized in that: 26. The apparatus of claim 25, further comprising an ammonia scrubber system that is heated using excess recovered heat. 26. Apparatus according to any of claims 17 to 25, wherein the drying means is capable of performing a complete sterilization of the sludge. A dry sludge produced by the method according to any one of claims 1 to 16.

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