KR20210027204A - An apparatus andmethod for improving dewaterability of digested sludge by sludge curing - Google Patents

Abstract

The present invention discloses an apparatus and method for improving dewaterability of digested sludge discharged during an anaerobic digestion process for high concentration organic waste. The method for improving dewaterability for digested sludge is carried out between an anaerobic digestion process of converting organic waste into sludge and a dehydration process for the sludge. The method is characterized by comprising a sludge aging step of reducing the concentration of organic acids in the sludge by introducing the sludge into a reaction tank and then maintaining the sludge at a predetermined aging temperature and aging time while stirring. Accordingly, the method can improve the dehydration efficiency of solid-liquid separation at the subsequent stage, as well as chemical and biological treatment efficiency for wastewater composed of dehydrated filtrate.

Description

Sludge aging device and method for improving dehydration of digested sludge {AN APPARATUS ANDMETHOD FOR IMPROVING DEWATERABILITY OF DIGESTED SLUDGE BY SLUDGE CURING}

The present invention relates to an apparatus and method for treating digested sludge discharged in an anaerobic digestion process for high-concentration organic wastewater or waste (hereinafter,'organic waste') such as food waste, drinking water, and manure, and in particular, dehydration of digested sludge It relates to an apparatus and method for improving sex.

In general, anaerobic digestion of organic matter containing a high concentration of nitrogen can be explained by the following formula (1). In this anaerobic digestion process, based on the total molecular weight of organic matter (MW 285. 4), 70% is _{converted into biogas (CH 4} ,CO ₂ ) by anaerobic microorganisms (methanogenic bacteria), and 8 of the total molecular weight in this process % Is multiplied by microorganisms, of which only 2. 8% of nitrogen is used for microbial growth. 17% bicarbonate ions (bicarbonate, HCO ₃ ^-) are converted into the digester buffering capacity (buffer capacity), and contributes to the measure of bicarbonate alkalinity (bicarbonate alkalinity) of, is generated during hydrolysis of nitrogen could be used to multiply the total molecular weight It accumulates in the digester in the form of a concentration _{of NH 4} ⁺ -N as 5%. In this case, when the total molecular weight organic 1kg, the bicarbonate (bicarbonate, HCO ₃ ^-) suitable amount for a unit of is about 0. 212kg / m ^3, translates it to the alkalinity unit is a 0. 172kg CaCO _3.

In general, anaerobic digestion of organic matter containing a high concentration of nitrogen can be explained by the following formula (1). In this anaerobic digestion process, based on the total molecular weight of organic matter, 70% is produced as biogas (CH ₄ , CO ₂ ), and 8% is _{involved in microbial growth (C 5} H ₇ O ₂ N), of which 2. 8% is growth in the microorganism, 17% bicarbonate ions (bicarbonate ion, HCO ₃ ^-) are converted to contribute to the digestion buffer capacity of bicarbonate alkalinity (bicarbonate alkalinity) scale (buffer capacity), 5% could not be used for the growth is Accumulates in the digester in the form of NH ₄ ^{+ -N concentration.} In this case, when the total molecular weight of the organic matter is 1 kg, the amount of bicarbonate ions generated per unit volume is about 0.212 kg/m ³ , and when converted into alkalinity units, it becomes 0.1 172 kg CaCO ₃ .

The most important concern is the pH range between 6. 0 and 8. 0 in the digester or system for performing anaerobic digestion. However, from the above chemistry (1), it can be seen that as the total molecular weight of the organic matter increases, the generation of alkalinity increases, and accordingly, the pH may be out of this range. 1, the digester in such a pH range of biological response result of the organic material CO ₂ and HCO ₃ ^- can be described in relation to (bicarbonate ion). Referring to FIG. 1, _{it can be seen that the pH of the digester changes according to the concentration of CO 2} in the gas and the bicarbonate alkalinity in the liquid, and from this, the buffer capacity of the digester rather than the effect of pH It can be said to be more important. Buffering action in the digester means a beneficial effect of alleviating the impact against the pH change in the digester in such organic overload, and these buffer action is bicarbonate ion (bicarbonate ion, HCO ₃ ^-) generated after the organic matter is decomposed by Alkalinity, ie bicarbonate alkalinity, can be described. In general, the buffer capacity of the digestion tank (buffering capacity) is because the more increasing the concentration of organic matter entering the bicarbonate alkalinity increases whereby the pH is stable, but known to also receive less adverse effects, bicarbonates (bicarbonate, HCO ₃ ^-) rather haejimyeon excessive It is important to be aware that it can have adverse effects on the digester.

0로 거의 없기 때문에 화학식 (1)에서는 미분해 유기산의 농도가 표시되어 있지 않다. 소화조 내에서 운전시간 경과에 따른 유기산 농도는 일반적으로 300 mg/L 이하(최대 500 mg/L as CH₃COOH)에서 유지됨을 의미한다. 즉 상기 화학식 (1)에서 알 수 있듯이, 유기물의혐기성 소화과정에서 생성되는 것은 미생물이 유기물을 섭취하고 분해하면서 생성되는 바이오가스와 미생물 증식이다. 이 두 가지를 제외하면 ammonium (NH₄ ⁺)과 bicarbonate(HCO₃ ^-)의 생성이 뚜렷하게 나타남을 알 수 있다. 결국 화학식 (1)은 미생물에 의해 유기물이 완전하게 섭취되고 분해됨을 전제로 것이다. When referring to the above formula (1), nitrogen that cannot be used for microbial synthesis remains in the digested sludge in the form of _{NH 4} ^{+ in a liquid state.} The reason why nitrogen (N) was not synthesized in microorganisms is because the amount of nitrogen is higher than the amount of biologically degradable organic matter, which is expressed as a low C/N ratio. The organic matter put into the digester is the production of biogas (CH ₄ , CO ₂ ) produced by the microbial activity, and nitrogen is used for cell proliferation as the microorganisms ingest and decompose the organic matter, and the microorganisms proliferate, and nitrogen that cannot be used for microbial growth is NH ₄ ⁺ is in the form stored in the digester, the organic matter is decomposed by the microorganisms eventually bicarbonate (bicarbonate, HCO ₃ ^-) in the digested sludge, the filtrate is left in the form of. On the other hand, if the digester is not installed to have an appropriate treatment capacity, the concentration of undecomposed organic acid should be indicated in the above formula (1) because volatile acids can be accumulated without decomposition, but if the treatment capacity of the digester is properly designed The change in the concentration of organic acids in the digester with the progress of operation is dC/dt

Since it is almost zero, the concentration of the undissolved organic acid is not indicated in the formula (1). This means that the organic acid concentration in the digester over the course of operation time is generally maintained at 300 mg/L or less (maximum 500 mg/L as CH ₃ COOH). That is, as can be seen from the above formula (1), what is produced in the process of anaerobic digestion of organic matter is biogas and microbial proliferation that are generated when microorganisms ingest and decompose organic matter. With the exception of the two ammonium (NH ₄ ⁺⁾ and bicarbonate (HCO ₃ ^-) it can be seen that the generation of markedly appears. In the end, formula (1) assumes that organic matter is completely ingested and decomposed by microorganisms.

Therefore, the evaluation of the operating efficiency of the digester can be made through the evaluation of the amount of organic matters decomposed and converted into bicarbonate alkalinity, and the amount of organic matters accumulated as organic acids without being completely decomposed. It can be explained through. Equation (2) is an equation established through the concept of alkalinity of the organic acid and bicarbonate of the general formula (1).

BA: Bicarbonate Alkalinity, mg/ℓas CaCO ₃

TA: Total Alkalinity, mg/ℓas CaCO ₃ , Titration Method.

VA: Volatile Acid, mg/ℓas CH ₃ COOH (Distillation Method, Standard Methods)

In Equation (1), the unit of an organic acid (volatile acid) is mg/L (as CH ₃ COOH), but it can be expressed in mg/L (as CaCO ₃ ), which is a unit of alkalinity, and its conversion value is 0. 71 (US Environmental Protection Agency (US EPA), 1979). In relation to the concentration of organic acids in anaerobic digestion facilities, there is a slight difference, as in the case of Korea, as 4,000mg/L is set as a guideline, but according to the US Environmental Protection Agency (US EPA), organic acids when operating digestion tanks by planting digested sludge The concentration should be maintained below 300 mg/L (as CaCO ₃ ), and it is recommended not to exceed 500 mg/L (as CaCO 3) at the maximum. On the other hand, in the operating condition the incoming organic matter is fully decomposed prior bicarbonate as in the formula _{(1) (bicarbonate, HCO 3} -) only is displayed. In this case, since VA = 0, Equation (1) can be expressed as BA = TA.

Based on the above equation (1), the operating efficiency of the digester is evaluated according to the organic acid concentration standard proposed by the US Environmental Protection Agency as follows. By the time of initial driving an organic acid concentration in the anaerobic digestion tank sikjong to _{300 mg / L (as CH 3} COOH) or less microorganism (digested sludge) and then after continuous operation to inject an organic material is an organic acid concentrations below _{300mg / L (as CH 3 COOH} ) If maintained, it can be seen that the organic matter has been fully anaerobic digested or energized, indicating that it has been properly operated. On the other hand, if the organic matter is not properly digested and the organic acid concentration is _{increased even when the concentration of organic acids exceeds the maximum 500mg/L (as CH 3} COOH), the operation of the digester can be considered to be deteriorating. The operating efficiency of this anaerobic digester can be understood in terms of treatment of sludge and is related to the dehydration of sludge.

In more detail, the degree of accumulation of undecomposed organic solids in the digester can be determined by analyzing the organic acid concentration based on Equation (1). That is, by looking at the organic acid concentration in connection with the digested sludge dehydration, it is possible to evaluate how the increase in the organic acid concentration affects the operation of the anaerobic digestion facility. To this end, the dehydration properties were compared and analyzed using the main equation for calculating the _{specific resistance value (r s} ) representing the degree of dehydration of digested sludge. Dehydration can be evaluated by a specific resistance value, and is calculated from Equation (2) below.

Here, r _s : resistivity value (cm/g), P: applied vacuum pressure (dynes/cm ² ), A: filtering area (cm ² ), μ: viscosity of filtrate (g/cm sec) (at the same temperature Viscosity of pure water is used), W: weight of solid substance per unit filtrate volume (g/cm ³ ), b: slope of straight line obtained from the correlation between t/V and V (sec/cm ⁶ ), t: time (sec) , V: represents the volume (mL) of the filtrate, respectively.

In Equation (2), the weight W of the solid substance per unit filtrate volume is calculated by dividing _{the total solid mass of the sample by the volume of the filtrate (V f) until the filtration type changes rapidly according to Equation (3) below.} .

Here, TS: total solid matter, V _o : volume of initial sludge (mL), V _f : volume of filtrate (mL) at the point out of the linear relationship. In this case, it is reasonable to use the suspended solids concentration rather than the total solids (TS) concentration, but the TS concentration was not significantly affected because the soluble solids (DS) was less than 5% of the total solids (TS) concentration. It was used as it is.

Using this equation, when the organic acid concentration is _{maintained below 300 mg/L (as CH 3} COOH) in the anaerobic digestion facility of organic waste, the specific resistance value of 64 digested sludges was measured, and the anaerobic digestion of organic waste such as food The results of the analysis by measuring the specific resistance values of 10 digested sludge samples with an organic acid concentration of less than 4,000 mg/L (as CH3COOH) and significantly exceeding 4,000 mg/L (as CH3COOH) at the facility are shown in Table 1 below. volatile acid concentration and the specific resistance of digested sludge in anaerobic digester.

Anaerobic digester volatile acid conc'n
(mg/L as CH ₃ COOH) specific resistance, r _s
(10 ¹³ m/kg) number of samples sewage
sludge less than 300 1. 0 ~ 6. 5
(avg. 5. 0) 64 organic wastes
(food-waste, etc) less than 4,000
over 4,000 50 to 200 10

In a properly operated anaerobic digester of sewage sludge, it is desirable to maintain the organic acid concentration below 300 mg/L (as CH ₃ COOH), and at this time, the specific resistance (r _s ) value indicating the dehydration index of the digested sludge is 1. 0 ~6. It was in the range of ^{1 to 10x10 13} m/kg (average 5. 0x10 ¹³ m/kg), which represents the dehydration property of general anaerobic digested sludge at 5×10 ^{13 m/kg.} However, in the case of digested sludge with an organic acid concentration of about 4,000 mg/L or _{much more than 10,000 mg/L (as CH 3} COOH), the specific resistance (r _s ) indicating dehydration is 50~200x10 ¹³ m/kg, compared to the average value. It shows a deteriorated value from 10 to 40 times. In fact, the amount of polymer used in the digested sludge dewatering process discharged from the anaerobic digestion facility of organic wastes including food is used 10 to 50 times more than the amount used to dewater digested sludge in general sewage treatment plants. From Table 1, it was evident that the increase in the organic acid concentration adversely affected the dehydration property.

chner funnel test) 외에 이를 보정하는 CST(capillary suction time)을 측정하여 서로의 상관관계를 통해서 보정되었으나, 여기서 세부적인 내용은 제시하지 않았다. 이 두 가지 탈수성 측정 방법은 모두 Standard Method에 등재되어 있다. In any case, it does not matter what criteria the organic acid concentration is determined in the guidelines for anaerobic digestion, but it is clear that the organic acid concentration should be recognized as a major factor influencing the operating efficiency of the anaerobic digester. In particular, the presence of organic solids in the anaerobic digester without decomposition and the increase can be judged using the organic acid concentration as an index. This is because the acetogenic activity of the acid-forming bacteria is increased. Eventually, the increase in organic acid concentration should be recognized as a major factor that adversely affects the operating efficiency of the anaerobic digester, and this result was found to have a very close correlation through dehydration analysis. Method of measuring the dewaterability (dewaterability) as r _s BFT (B for the calculation of the (specific resistance value)

In addition to the chner funnel test), CST (capillary suction time) to correct this was measured and corrected through correlation with each other, but details are not presented here. Both of these methods of measuring dehydration are listed in the Standard Method.

Specifically, when it is designed and operated under the following conditions, it can be operated as an optimal energy facility by deriving all the advantages or advantages of the operation of an anaerobic digestion facility.

First, the efficiency of the anaerobic digestion process should be understood first in terms of the treatment of anaerobic digested sludge as shown in Equation (1), rather than in terms of wastewater treatment applied to the rear end of the digester. The amount of microorganisms that are proliferated through complete decomposition of organic waste and ingestion will have a great influence on the amount of dehydrated cake generated for digested sludge.In this case, the moisture content in the dehydrated cake is reduced to a minimum, and the sludge is stabilized by reducing odor and killing pathogenic bacteria. And safe treatment is the main purpose of the anaerobic digestion process. In order to achieve this purpose, dehydration of digested sludge is of paramount importance, and the organic acid concentration in the anaerobic digester must be maintained below _{300mg/L (as CH 3 COOH).} If the organic acid concentration in the anaerobic digester is _{increased to exceed the maximum 500 mg/L (as CH 3} COOH), the condition of the digester gradually deteriorates and dehydration becomes worse. The amount of cake increases. Here, if you check how much the amount of dehydrated cake increases due to an increase of 1 to 2% moisture content in the dehydration process of the anaerobic digested sludge of food waste, it is recognized that the amount of dehydrated cake that is increased at this time can make biogas production insignificant. It should be. It is clear from this that the recent phenomenon in food energy facilities is that the condition of the digester deteriorates, that is, as the organic acid concentration increases, the amount of polymer used in the dehydration process increases exponentially, from 10 times to even. Sometimes exceeds 30 times and 50 times. For this reason for safe sludge treatment, the US Environmental Protection Agency (US EPA) recommends that anaerobic digestion plants _{operate with organic acid concentrations below 300 mg/L (as CH 3} COOH).

Second, the digested sludge filtrate discharged from the digester must be able to maintain the organic acid concentration under the optimum condition, up to 300 mg/L (as CH _{3 COOH).} This is because dehydration properties must be good so that the quality of wastewater treatment can be maintained under stable conditions. Nevertheless, at 4,000 mg/L of organic acid concentration determined by the guidelines of the Ministry of Environment/Environmental Sciences in Korea, dehydration is deteriorated and the concentration of undecomposed organic matter as well as the nitrogen concentration is high, making it very difficult to maintain the emission limit set by the law. For this reason, operating costs may also be excessive. As such, although most anaerobic digestion facilities in Korea have a lot of difficulties in operating wastewater treatment facilities after digestion, discussions on anaerobic digestion and wastewater treatment are neglected while focusing only on the production of biogas rather than economic feasibility.

Lastly, it is generally mentioned that the production of biogas produced in anaerobic digester is the greatest advantage, but the amount of dehydration and dehydrated cake is related to the treatment of the sludge discharged through the anaerobic digestion process rather than the production of such biogas. It should be considered first. In other words, the best value can be provided through anaerobic digestion facilities only when the production of biogas is performed under the condition of the above two conditions.

Therefore, in an anaerobic digester that operates stably, all of the above three points must be met. It is desirable to maintain the organic acid concentration of the digested sludge dehydration liquid, that is, the organic acid concentration in the digester under the optimum condition of 300 mg/L (as CH ₃ COOH), and if the sludge is stably treated in this state, the amount of dehydrated cake will be reduced. It is reduced to a minimum, and along with reduction of odor and killing pathogenic bacteria, the amount of biogas produced can be maintained stably and the value can be increased.

Meanwhile, the concentration of organic acids in most anaerobic digesters installed in Korea is based on 4,000mg/L (as CH ₃ COOH) in accordance with the guidelines provided by the Ministry of Environment/Environmental Science Institute. However, the dehydration at this time is not good. When the organic acid concentration of the digested sludge discharged from the digester is increased above the appropriate concentration, the moisture content of the dehydrated cake discharged from the dehydrator increases, and the amount of dehydrated cake is increased. If the amount of dehydrated cake is increased, the economic value of the biogas obtained as a by-product may be largely lost, and the quality of the wastewater deteriorated due to poor dehydration will have a great influence on the overall economics of the system. In order to solve these problems, it is necessary to re-stabilize the organic acid concentration in the anaerobic digester to _{less than 300mg/L (as CH 3 COOH) so that dehydration can be maintained properly.}

The present invention was devised in consideration of the limitations of the conventional treatment of digested sludge discharged from an anaerobic digester for high-concentration organic waste or dehydration (wastewater) treatment, and organic acids in digested sludge discharged through the anaerobic digestion process for high-concentration organic waste. By maintaining the concentration below 300mg/L (as CH ₃ COOH) preferably to improve dehydration, it is possible to improve the efficiency of chemical and biological treatment for wastewater composed of dewatering filtrate as well as improving the dehydration of sludge at the subsequent stage. It is to provide a device and method.

The subject matter of the present invention related to the above problem is the same as described in the claims below.

(1) As a method for improving the dehydration properties of the sludge by performing between the anaerobic digestion process of treating organic waste and converting it to stabilized sludge (microorganism) and the dehydration process of the sludge, the sludge is curing A method for improving dehydration of digested sludge comprising a sludge aging step of reducing an organic acid concentration in the sludge by maintaining it at a predetermined aging temperature and aging time in a state accompanied by agitation after introduction into a reactor).

(2) The method further comprising a screen step of filtering solid foreign matters (organic solids of a fibrous system that are not decomposed or very slow, organic residues other than microorganisms) from the sludge before introduction into the reaction tank. (1) Method for improving dehydration of digested sludge.

(3) The method for improving dehydration of the digested sludge of (1), further comprising the step of adjusting the flow rate of the sludge introduced into the reaction tank according to the concentration of the organic acid in the sludge.

(4) The application of the aging temperature to the sludge in the reaction tank is provided along the side wall of the reaction tank and the heat medium is refluxed therein by a coil jacket; improving dehydration of the digested sludge of (1), characterized in that Way.

(5) The method for improving dehydration of digested sludge of (1), further comprising removing struvite from the sludge at a later stage of the aging step before the dehydration step.

(6) The step of removing the struvite is a method for improving dehydration of digested sludge of (5), characterized in that the step of removing the struvite is performed by a screen filtration method or a floating sludge removal method.

(7) The method for improving dehydration of digested sludge of (1), wherein the reaction tank is provided in a single or parallel plural along a process line for sludge treatment.

(8) In the sludge aging step, the organic acid concentration is mostly removed so that methanogenic bacteria can dominate.

(9) The method for improving dehydration of digested sludge of (1), wherein the aging temperature is 35°C.

(10) As an apparatus for improving the dehydration properties of sludge by being installed between an anaerobic digester for converting organic waste into sludge and a dehydrator for the sludge; A reaction tank in which the sludge is introduced and accommodated, a lower inlet and an upper outlet for the sludge are provided, and a biogas discharge port is provided at the top; A distributor for injecting the sludge into the reaction tank through the inlet; A stirrer for circulating and mixing the sludge in the reaction tank; A coil jacket provided along the sidewall of the reaction tank and through which the heat medium is refluxed; And a pressure control means for controlling the pressure inside the reaction tank.

(11) The operation of the agitator is controlled to stop while the sludge to be treated is injected and supplied into the reaction tank by the distributor.

(12) The sludge aging apparatus of (10), further comprising a plurality of baffles provided at predetermined intervals along the inner wall of the reaction tank.

According to the invention. The organic acid concentration in the digested sludge discharged through the anaerobic digestion process for high-concentration organic waste is preferably 300mg by additionally performing sludgecuring, a kind of biological treatment, on the digested sludge discharged from the anaerobic digester for high-concentration organic waste. By maintaining it below /L (as CH ₃ COOH) to improve dehydration, it is possible to improve the dehydration efficiency of the solid-liquid separation at the subsequent stage, as well as the chemical and biological treatment efficiency of the wastewater composed of the dehydration filtrate. The method and apparatus according to the present invention can be usefully applied to anaerobic digestion facilities with poor dehydration properties in existing facilities regarding organic acid concentration, food waste, food waste water, combined treatment of livestock manure and food waste water, livestock manure, etc. It is applicable to all facilities that apply anaerobic digestion system, including.

1 is a graph showing the effect of a change in bicarbonate alkalinity on pH and CO _{2 production in an anaerobic digester.}
Figure 2 is a process chart related to the digested sludge treatment according to an embodiment of the present invention.
3 is a structural diagram of a sludge aging device according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail through examples. Prior to this, terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventors appropriately explain the concept of terms in order to explain their own invention in the best way. Based on the principle that it can be defined, it should be interpreted as a meaning and concept consistent with the technical idea of the present invention. Therefore, the configuration of the embodiments described in the present specification is only one of the most preferred embodiments of the present invention, and does not represent all the technical spirit of the present invention, and various equivalents that can replace them at the time of filing of the present invention It should be understood that there may be variations and variations. On the other hand, in the drawings, the same or similar reference numbers are given to the same or equivalent, and in the entire specification, when a certain part "includes" a certain component, this is another component unless otherwise stated. It does not exclude excluding, but means that other components may be further included.

FIG. 2 is a process chart for digested sludge treatment according to an embodiment of the present invention, and shows that a dewatering process is continuously performed at a subsequent stage, including a sludge curing process. In this case, the dehydration process can be understood as a kind of pretreatment process for chemical/biological treatment of the dewatered filtrate wastewater. 3 shows a structural diagram of a sludge aging device according to an embodiment of the present invention used in the sludge aging process. In the present invention, the sludge aging process and apparatus are basically an anaerobic digestion process in which organic waste is treated and converted into sludge (microorganisms), and a solid-liquid separation process in which digested sludge is separated into a dehydrated cake and a dewatered filtrate (wastewater), that is, a dehydration process. Scheduled to be provided in between.

Meanwhile, the process including the sludge aging process of FIG. 2 and the sludge aging device of FIG. 3 ultimately set the amount of solid organic matter in the digested sludge discharged through the anaerobic digestion process for high-concentration organic waste, and the organic acid concentration, preferably 300 mg/L ( AsCH ₃ COOH) is related to improving dehydration by optimizing it in the range below, and accordingly, in this specification,'dehydration improvement' method and device in some cases for the entire process or device employing the corresponding aging process and device. Was referred to as In addition, in the specification, the discharged through the anaerobic digestion process is classified as'digested sludge', and the aging process according to the present invention is classified as'curing sludge'. It was used interchangeably in the manner of naming it as'sludge'.

Sludge treatment process for improving dehydration (Fig. 2)

Based on FIG. 2, a sludge treatment process for improving dehydration will be sequentially described step by step. As described above, the sludge treatment process for improving dehydration in FIG. 2 is a aging process at the front (A: curing process, (a) to (e)) and a dewatering process at the rear (B: pretreatment process, dewatering process, (f). ) to (k)) are shown as a series of continuous processes.

(a) Sludge introduction step : The sludge discharged from the anaerobic digester (not shown) is stored in the sludge storage tank (01). For any type of construction method, the treatment facility after the digestion tank starts from the sludge storage tank (01), and a stirring device using a motor or an underwater stirrer is installed to maintain a constant concentration while controlling the flow rate and transferring it to the screen facility (02). .

(b) Screen step : A certain flow rate is sent from the sludge storage tank (01) to a screen facility (02) of a predetermined size, for example, about 3 mm to sort out foreign matter. Although not shown in the drawing, the filtered foreign matter 26 is dehydrated using a screw press through a screw conveyor, and the dehydration filtrate is transferred back to the sludge storage tank 01, and the foreign matter is sent to an armroll box. .

(c) Flow rate control step : The sludge from which foreign substances have been filtered through the screen facility (02) is transferred to the sludge flow rate control tank (03). In the case of sludge with high organic acid concentration due to the presence of organic solids, re-stabilization through sludge aging must be made within a predetermined time. The flow control tank 03 considers the concentration of organic acids in the sludge and is introduced into the reaction tank for sludge maturation at the rear stage. It plays a role of regulating the flow rate of. On the other hand, if the pretreatment for organic waste is not satisfactory, a large amount of organic solids may be introduced into the digester.In this case, although not shown in the drawing, installation of a screw press in front of the screen facility and the process of controlling the flow rate may additionally be required. .

(d) Sludge aging step : The sludge passed through the flow control tank (03) is introduced into the reaction tanks (04, 05) for aging. The detailed configuration of the reaction tanks 04 and 05 for the sludge maturation and the apparatus including the same is shown in FIG. 3 and will be described later. ^{In addition, the capacity of the reaction tank based on the treatment of 100 m 3} (100 m ³ /day) per day in the sludge maturation using the reaction tanks (04,05) may be summarized in a separate table as described below based on the effective volume. In this sludge aging process, a plurality of reaction tanks 1 (04) and 2 (05) can be configured in parallel for continuous treatment, and in this case, each reaction tank (04, 05) is divided by 50% to be treated and operated. It can be designed to do. The aged sludge is discharged to the aged sludge storage tank 06 through a weir (weir) 33.

The sludge aging process is a process of improving the dehydration properties of the sludge by maintaining the sludge introduced into the reaction tanks 04 and 05 at a predetermined aging temperature and aging time while stirring. As the main process conditions according to the use environment, sludge stirring, temperature and time may be considered. For example, the stirring speed may be 30 to 40 rpm, the temperature may be 35°C, and the time may be 24 hours.

The reason for such sludge aging is to stabilize (re-stabilize) the sludge, but fundamentally optimize the _{organic acid concentration to less than 300 mg/L (as CH 3 COOH) through dominance of methanogenic bacteria among anaerobic microorganisms.} This is to improve the dehydration property and improve the solids separation efficiency while additionally obtaining the conditions to obtain a stable water quality suitable for chemical/biological treatment of the dehydrated wastewater. More specifically, in the case of digested sludge discharged through the anaerobic digestion tank according to the conventional method, the dehydration property deteriorates due to the high concentration of organic acids maintained by the organic solids even after digestion, which is a major cause that makes wastewater treatment of the dehydrated filtrate difficult. . In the case of the digested sludge filtrate, the higher the concentration of organic matter (organic acid) caused by the remaining organic solids, the lower the dehydration property. As described above, in the present invention, the relationship between the organic acid concentration and the dehydration property was established through data. The specific resistance value, which is an indicator of appropriate dehydration for general digested sludge, ^{is known in the range of 1 to 10 × 10 13} m/kg, and as shown in Table 1 above, the specific resistance, which is an indicator of dehydration of digested sludge after anaerobic digestion of sewage sludge. (Specific Resistance, r _s ) value is 1. 0~6. It appeared within the range of general dehydration in the range of 5 × 10 ^{13 m/kg.} These are all specific resistance values measured when the organic acid concentration is maintained at an appropriate level of 300 mg/L (as CH ₃ COOH) or less (maximum 500 mg/L). Conversely shown in dehydration castle Table 1 of digested sludge, if one or otherwise maintained in the organic acid concentrations from anaerobic digestion _{4,000 mg / L (as CH 3} COOH) level, such as food waste exceed _{4,000 mg / L (as CH 3} COOH) Together, the results were very deteriorating. This is directly related to the amount of polymer required for dehydration, which greatly increases the operating cost.The increase in moisture content of the dehydrated cake increases the amount of cake generated, and the odor caused by the formation of _{NH 3 due to the high alkalinity remaining in the filtrate.} Occurrence of occurrence, so that proper sludge treatment cannot be performed, and pathogenic bacteria due to organic matter may be generated. Summarizing based on these results, if the organic acid concentration _{is optimized to a maximum of 500 mg/L (as CH 3} COOH) or less through the sludge aging reaction tank (04,05), as shown in Table 1, the dehydration cake can be In addition to contributing to lowering the moisture content, the use of chemicals such as polymer coagulants can be significantly reduced, and stable water quality for wastewater treatment can be secured and supplied, which can greatly contribute to the economic improvement of the anaerobic digestion of organic wastes.

(e) _{Sturuvite removal step: MAP (magnesium ammonium phosphate, MgNH 4} PO ₃ ) is produced in an anaerobic digester that converts high-concentration organic waste into energy, which is also called'struvite'. From the human body, it is a substance that causes urinary tract stones, but in anaerobic digestion systems, it is a substance that causes a problem of clogging the pipe at the top of the digester or the rear end of the dehydrator. Its specific gravity is higher than that of water, but as the operating period increases, it is produced in the form of porous particles and usually floats in the water in a floating state. It is easily soluble in acid, but hardly soluble in neutral or alkaline conditions. Since digested sludge is mainly in the neutral and alkaline range, struvite can be easily removed (separated) from the aged sludge by using these properties.

Such struvite may be generated not only in the anaerobic digester but also in the above-described sludge aging reaction tanks 04 and 05, and a process of removing it may be added along with the sludge aging process. To this end, the aged sludge discharged from the aged sludge storage tank 06 is transferred to the struvite removal device 07. The struvite removal device 07 is composed of a 2 to 3 mm screen facility and may be operated in a manner of filtering or removing struvite particles having a porosity of 2 mm or more. The filtered porous struvite particles are not shown in the drawing, but are sent to an armrollbox through a screw conveyor. The collected struvite can be used for cell synthesis as components of nitrogen and phosphorus fertilizers. In addition, struvite also contains magnesium, which can increase the value of the fertilizer obtained as a by-product. However, since it is a fertilizer (material) obtained from waste, it is important to increase the purity as much as possible, and it may be essential to consult with the user.

On the other hand, in general, it may take several months after the start of operation to confirm the generation of struvite in the anaerobic digester. Although it is not easy to check with the naked eye, if the sludge is discharged from the digester or reaction tank (04,05), it can be checked through the scale generated in the dehydrator or the downstream pipe in the dehydration process. In other words, it is possible to check with the naked eye in a situation where the dehydration ability is lowered due to clogging (clogging) inside the pipe and the pipe must be dismantled. Since struvite formed in this way is a porous crystal, it floats in a floating state and floats on the top of the digester with sludge, and after a long time, some of the struvite hardens and has the strength of concrete. If the upper manhole of the digester has not been opened or inspected for a long period of time (more than 10 years), such a layer of scale can form 0.5 to 1 m above the surface of the upper sludge beyond the effective volume above the sludge layer. For this reason, if the manhole at the top of the digester is not opened and inspected at least every two years, a hammer or rock-breaking equipment may be used to remove it. However, since these porous struvite particles begin to be produced as very small particles and become larger than 2 mm, in the present invention, the struvite removal device 07 operating in a screen method or a floating sludge removal method is used to enable removal. . However, it may be difficult to remove porous particles of 2 mm or less by the screen method, and even with the floating sludge removal method, it may be difficult to completely separate struvite.

(f) Coagulant mixing step: The sludge from which most of the struvite is separated while passing through the struvite removal device 07 is transferred to the mixing tank 08, and according to the amount and concentration of the sludge, a polymer (polymer coagulant, 23) Is mixed. Meanwhile, a part of the aged sludge from which struvite has been removed may be transferred to the sludge stabilization tank 17 through the pipe 18 and stored, and then used if necessary. The sludge stabilization tank 17 is provided with a pipe 20 for planting microorganisms in the sludge aging reaction tank and transferring them to the flow rate control tank 03.

(g) Centrifugal separation step: The curing sludge mixed with a polymer (polymer coagulant, 23) is discharged to the dehydrated cake 24 by a decanter, a centrifugal dehydrator, and the rest is suspended solids ( SS (suspended solid) is discharged as a dehydration solution (25) of about 4,000 mg/L. Here, the dehydrated cake is transferred to an armroll box via a belt or screw conveyor for final disposal (or composting).

The capacity of the dehydrator (09) is the aged sludge supplied from the aged sludge storage tank (06), the recovered sludge (recycled sludge), which is recovered from the sludge (14) and the sedimentation tank (12) recovered from the pressure flotation device (10). It is preferable that the amount of sludge 15 and polymer (polymer coagulant, 23) added is 1. 5 times or more as a treatment amount than the combined flow rate, but it is desirable to be able to dewater 2. 0 times in preparation for an emergency situation considering the safety factor. . This is because the concentration of solids in the system is reduced when the amount of solids discharged from the dehydrator 09 to the dehydration cake 24 is greater than the amount including the amount circulated.

The pipe through which the dehydration filtrate is discharged from the dehydrator 09 uses a pipe for preventing struvite attachment or is arranged in parallel, but is arranged and installed to enable periodic washing. That is, because smaller and finer particles of 2 mm or less that are not completely removed by the struvite removal device 07, for example, that are not removed by a screen method, may be attached inside the pipe installed at the rear end of the dehydrator 09. , In order to minimize the adhesion of these fine struvite particles, periodic cleaning using the pipe cleaning device 25, or installing pipes in parallel to operate continuously, or pipe made of a material that does not adhere to the struvite Choosing can be important.

On the other hand, in the state that no polymer (polymer coagulant, 23) is mixed, the curing sludge is injected into the dehydrator (09), and the planting species of the concentrated sludge is sent to the sludge stabilization tank (17) to flow control tank (03). It may be used together through the conveying pipe 20, and in order to remove foreign substances contained in a large amount during the initial planting of microorganisms, the pipe 21 conveying through the screen equipment 02 may be used.

(h) Pressurized flotation separation step: After dehydration in the decanter (09), a centrifugal separator, the dehydrated filtrate of about 4,000 mg/L of SS discharged to the filtrate is transferred to the dehydration filtrate tank (09-01), and then a pressurized flotation device ( In 10), the SS is concentrated to a higher concentration, and the concentrated solid 14 is returned to the mixing tank 08 for re-dehydration.

(i) Degassing step: The wastewater treated in the pressurized flotation device 10 is discharged from the filtrate layer at a concentration of about 400 mg/L of SS, and a degassing tank 11 degassing the air adhering to microorganisms during the pressurization process. Is transferred to. This is the step of removing air that interferes with precipitation due to buoyancy.

(j) Settling step: The wastewater degassed in the degassing tank 11 is transferred to the settling tank 12. SS about 400 mg/L of wastewater is settled in the sedimentation tank 12 and returned to the mixing tank 08, and about 80 mg/L of symbolic water is transferred to the final process equalization tank 13 for wastewater treatment. . This is a step for separating and removing fine suspended matter through precipitation.

(k) Equalization step : In the leveling tank 13, it is a process to supply stable wastewater quality to the next process by always maintaining a constant concentration.If used for a long time, accumulated solids may contaminate the next process, so periodically washing water ( 29), but the process water used for cleaning at this time is returned to the mixing tank 08 through the pipe 16 so that the SS concentration can be finally removed from the pressure flotation device 10. The wastewater that has gone through the equalization step is purified through a subsequent chemical/biological treatment (30).

Structure of sludge aging device (Fig. 3)

The structure of the sludge aging device according to an embodiment of the present invention will be described based on FIG. 3. 3 shows a longitudinal sectional structure diagram of a sludge aging device 300 according to an embodiment of the present invention, and the sludge aging device 300 of FIG. 3 is used in the sludge aging step of FIG. 2 (d), and is shown in FIG. Identifiers 04 and 05 represent the reaction tanks of the sludge aging device 300.

The configuration of the main part of the aging device 300 used for sludge aging according to the present invention is as shown in FIG. 3, and the aging device 300 is anaerobic that is converted to sludge (microorganism) by treating organic waste. As a device installed between the digester and the dehydrator for the sludge to improve the dehydration properties of the sludge, the sludge is introduced and accommodated, and a lower inlet 31 and an upper outlet 33 are provided for the sludge, and the upper Reaction tanks (04, 05) provided with a biogas outlet (38); A distributor 32 for injecting the sludge into the reaction tanks 04 and 05 through the inlet 31; A stirrer 34 for circulating and mixing the sludge in the reaction tanks 04 and 05; A coil jacket 36 provided along the sidewalls of the reaction tanks 04 and 05 and for refluxing the heat medium therein; And a pressure regulating means 39 for controlling the pressure inside the reaction tanks 04 and 05. In this case, the operation of the stirrer is preferably controlled to stop while the sludge to be treated is injected and supplied into the reaction tank by the distributor. In addition, the aging device 300 may optionally further include a plurality of baffles 35 provided at predetermined intervals along the inner wall of the reaction tank.

The main configuration and operation contents of the aging device 300 will be described in more detail with reference to FIG. 3. For complete mixing and efficient biological reaction, four baffles 35 in each 90° direction, and a stirrer (30-40 rpm, 34) made of a motor and an impeller are provided. Existing digested sludge in which the high concentration organic acid remains is injected through the inlet pipe 31 and the distribution device 32 to the lower end of the reaction tanks 04 and 05. In this case, while the digested sludge is injected into the reaction tanks (04, 05), it is preferable that the agitator (34) in operation is automatically stopped, and in this state, the injection of digested sludge is completed at once and the amount of digested sludge injected at the same time. The amount of digested sludge re-stabilized as much is discharged to the aged sludge storage tank 06 through a weir 33 provided through the upper discharge port. At this time, the organic acid concentration is based on 300mg/L (as CH ₃ COOH). After all of the existing digested sludge remaining high-concentration organic acid is injected into the aging device 300, the agitator 34 may be operated again until the time the sludge is injected the next day, and this process is repeated. In the reaction tanks (04, 05), for optimal biological reaction, a hot water 361 is introduced into the coil jacket (36) and refluxed while maintaining a preset temperature such as 35°C and heating the inside of the reaction tanks (04, 05). When the temperature of the high-temperature heating medium 361 falls and is converted to a low-temperature heating medium 362, the reaction tanks 04 and 05 are maintained at a constant temperature by heating to a high temperature through a boiler again. In addition, sludge outlets 27 and 28 are provided at the bottom of each of the reaction tanks 04 and 05 to remove foreign substances accumulated in the reaction tanks 04 and 05 used for sludge aging or cope with an emergency situation. It was made to be transferred to the aged sludge storage tank (06) through the discharge ports (27, 28) using a pump. At this time, a pressure control device 39 is installed so that the gas pressure inside the sludge aging reaction tanks 04 and 05 does not fluctuate as much as possible. Biogas generated in the sludge aging reaction tanks 04 and 05 is stored in a gas holder (not shown) through a pipe 38.

Regarding the installation of the reaction tanks 04 and 05 of the aging device 300 according to FIG. 3, the reaction tanks 04 and 05 are ventilated a lot and allow fresh air from outside to flow in, and for this purpose, frequent inspections are required. need. Even if the reaction tanks (04, 05) are installed underground, it is desirable to avoid the installation of closed rooms and to ensure good ventilation, and to install the upper part so that it can be exposed to the open space above the ground. Appropriate access roads and spaces are required for vehicles to enter and supply drugs, or to load or unload or transport waste. The operation of this system requires adequate space and equipment for periodic sampling, and through analysis of the sampled wastewater, it is always necessary to check whether there is a problem in the operation of the system and that the operation is working properly.

Examples of the capacity of the sludge aging device

Table 2 below shows "Curing reactor capacity (m ³ ) to 100 m ³ /day treatment standards".

Volatile Acid
(mg/L) Capacity (m ³ ) Note 2,000 250 - 4,000 500 - 6,000 750 Under 6,000 mg/L conditions, if the anaerobic digester is not shut down, the volatile acid concentration will increase to more than 10,000 mg/L. 10,000 3,000 Under 6,000 mg/L conditions, if the anaerobic digester is not shut down, the volatile acid concentration will increase to more than 10,000 mg/L. 20,000 3,000 Under 6,000 mg/L conditions, if the anaerobic digester is not shut down, the volatile acid concentration will increase to more than 10,000 mg/L.

Due to the excessive organic acid concentration in the existing anaerobic digester, the polymer concentration (0. 2 ~ 0.6%) and the amount used in the dehydration process are the polymer concentration (0. 02%) used for dehydration after anaerobic digestion of sewage sludge. It is very high and large compared to the amount used. The capacity for sludge maturation required to reduce the use of these chemicals and improve wastewater treatment efficiency is as follows. The organic acid concentration discharged from the digester is based on 4,000 mg/L in Korea, and the sludge aging capacity that can meet these standards is about 600 m ³ . The time required for this was based on 24 hours. Of course, there is also initially required adaptation period of at least about 10 days, while the acid concentration maintained in 300 mg / L or less is NH ₄ ⁺ -N concentration in the fermentation reaction tank to a concentration similar to the concentration of NH ₄ ⁺ -N existing digesters Until you get close.

Sludge aging again biologically stabilizes the concentration of organic acids including organic solids that are not properly stabilized in the anaerobic digester. When the organic acid concentration is less than 4,000 mg/L (as CH ₃ ^{COOH) in the digester that treats 100 m 3} /day per day, the capacity of the sludge aging device needs to be about ^{600 m 3.} However, it must be recognized that the anaerobic digester's operating condition worsens when it is discharged above 4,000 mg/L (as CH ₃ COOH), and that even if it is temporarily restored and stabilized, it may deteriorate periodically. In addition, if the organic acid concentration exceeds 6,000 mg/L (as CH ₃ COOH) and continuously rises, it is very difficult to control the organic acid concentration without stopping the operation of the digester. ₃ COOH) to 20,000 mg/L (as CH ₃ COOH) is also increased. In the case of a digester whose organic acid concentration continuously exceeds 6,000mg/L (as CH ₃ COOH) based on 100 m ³ /day per day, the capacity of the aging reactor is not significant, so the capacity of the aging device is larger. Needed.

As described above, according to the present invention, digestion discharged through the anaerobic digestion process for high-concentration organic waste by additionally performing sludge curing, a kind of biological treatment, on the digested sludge discharged from the anaerobic digester for high-concentration organic waste. By maintaining the organic acid concentration in the sludge preferably below 300 mg/L (as CH ₃ COOH) to improve dehydration, the dehydration efficiency of solid-liquid separation at the subsequent stage, as well as the efficiency of chemical and biological treatment for wastewater composed of the dehydration filtrate are improved. Can be improved. The method and apparatus according to the present invention can be usefully applied to anaerobic digestion facilities with poor dehydration properties _{as a guideline on organic acid concentration is applied at 4,000 mg/L (as CH 3 COOH), etc.} It is applicable to all facilities that apply anaerobic digestion system including wastewater, combined treatment of livestock manure and drinking water, and livestock manure.

The above description relates to specific embodiments of the present invention. As described above, the above embodiments according to the present invention are disclosed for the purpose of explanation and are not understood to limit the scope of the present invention, and those of ordinary skill in the art will not depart from the essence of the present invention. No, it should be understood that various changes and modifications are possible. Accordingly, all such modifications and changes may be understood to correspond to the scope of the invention disclosed in the claims or their equivalents.

01: digested sludge storage tank
02: screen equipment
03: flow control tank
04,05: Sludge aging reaction tank
06: aged sludge storage tank
07: Struvite removal device
08: mixing tank
09: Decanter
10: pressure flotation device
11: Degassing tank
12: settling tank
13: Equalization tank
14: recovered flotation sludge
15: recovered sediment sludge
16: return of washing water
17: sludge stabilization tank
18: Transfer of aged sludge for stabilization
19: Concentration and transfer of sludge for planting
20: Sludge pipe for planting
21: Transfer pipe when foreign matter increases
22: Struvite waste
23: polymer flocculant
24: dehydrated cake
25: pipe washing device
26: foreign matter
27,28: sludge outlet
29: washing water
30: chemical/biological treatment
300: sludge aging device
31: inlet
32: divider
33: outlet (weir)
34: stirrer
35: baffle
36: coil jacket
361: high temperature heating medium
362: low temperature heating medium
38: biogas outlet
39: pressure control valve

Claims (12)

As a method for improving the dehydration properties of the sludge by being carried out between the anaerobic digestion process of treating organic waste and converting it to stabilized sludge and the dehydration process of the sludge, after introducing the sludge into the reaction tank, stirring is accompanied. A method for improving dehydration of digested sludge comprising a sludge aging step of reducing the concentration of organic acids in the sludge by maintaining at a predetermined aging temperature and aging time in one state.
The method of claim 1, further comprising a screen step of filtering solid foreign matters of a predetermined size or more from the sludge before introduction into the reaction tank.
The method of claim 1, further comprising adjusting the flow rate of the sludge introduced into the reaction tank according to the concentration of the organic acid in the sludge.
The method of claim 1, wherein the application of the aging temperature to the sludge in the reaction tank is performed by a coil jacket provided along the side wall of the reaction tank and in which the heat medium is refluxed.
The method of claim 1, further comprising removing struvite from the sludge at a rear stage of the aging step before the dehydration process.
The method of claim 5, wherein the step of removing the struvite is performed by a screen filtration method or a floating sludge removal method.
The method of claim 1, wherein the reaction tank is provided in a single or parallel plural along a process line for sludge treatment.
The method of claim 1, wherein in the sludge aging step, the concentration of the organic acid is removed so that the methanogenic bacteria can become dominant.
The method of claim 1, wherein the aging temperature is 35°C.
As a sludge aging device installed between an anaerobic digester for converting organic waste into sludge and a dehydrator for the sludge to improve the dehydration properties of the sludge;
A reaction tank in which the sludge is introduced and accommodated, a lower inlet and an upper outlet for the sludge are provided, and a biogas discharge port is provided at the top;
A distributor for injecting the sludge into the reaction tank through the inlet;
A stirrer for circulating and mixing the sludge in the reaction tank;
A coil jacket provided along the sidewall of the reaction tank and through which the heat medium is refluxed; And
Sludge aging device comprising a; pressure control means for controlling the pressure inside the reaction tank.
11. The sludge aging apparatus according to claim 10, wherein the operation of the stirrer is controlled to stop while the sludge to be treated is injected and supplied into the reaction tank by the distributor.
The sludge aging apparatus according to claim 10, further comprising a plurality of baffles provided at predetermined intervals along the inner wall of the reaction tank.

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