Method for organic waste hydrolysis and acidification and an apparatus thereof

Abstract

The invention relates to a method and an apparatus for hydrolyzing and acidifying homogenized organic waste fed into a closed and gas tight reactor using enzymatic bacteria under thermophilic conditions where water may be added to said reactor and the content of the reactor can be mixed and subjecting during hydrolysis and acidification an adequate part of a suspension formed in the reactor toi. a separation step isolatinga permeate comprising an aqueous solution of soluble carbon, volatile fatty acids (VFA) and valuable nutrients, an organic slurry comprising an aqueous solution of insoluble organic solids rich in enzymatic thermophilic bacteria and non-hydrolyzed organic solids, and the remaining part of soluble carbon, VFA and valuable nutrients, thereafter toii. a recirculation step re-feeding said organic slurry into the reactor for further hydrolysis and acidification.

Claims

1. A method for obtaining a permeate in aqueous solution from a homogenized organic waste wherein the obtained permeate comprises low molecular weight fatty acids with a C1-C6 carbon chain and valuable nutrients selected from the group consisting of: nitrogen in the form of ammonium (NH4-N) or nitrate (NO3-N), phosphorus in the form of phosphates (PO4-P), potassium, calcium, magnesium, sodium, sulfur, boron, cobalt, copper, manganese, iron, molybdenum and zinc, comprising the steps of: i. feeding the homogenized organic waste into a closed and gas tight, mixed reactor, ii. hydrolyzing and acidifying the waste in the reactor under thermophilic and microaerophilic conditions utilizing natural enzymes released by bacteria present in the waste, iii. separating the hydrolyzed and acidified waste obtained in step ii into the permeate; and an organic slurry rich in thermophilic bacteria, iv. re-feeding the organic slurry and a suspension formed in the reactor into the reactor for further hydrolysis and acidification, v. discharging the permeate from the reactor for further use, vi. discharging spent solids contained in the suspension from the reactor when the concentration of fixed solids in the suspension reaches a value of 40 to 50 m/m %, vii. measuring temperature, redox potential, pH, and fixed solid concentration in the reactor, viii. adjusting head space pressure in the reactor to a constant equilibrium by feeding gas, formed during hydrolysis and collected in a pressure adjustment means, from said pressure adjustment means into the reactor when pressure drops in the reactor due to removal of the permeate and/or spent solids from the reactor, ix. adjusting the pH in the reactor to a value between 6.0 to 6.8 by addition of acid when the pH value rises above 6.8 or by addition of alkali when the pH value drops below 6.0, x. maintaining the temperature in the reactor between 60 to 65 degree Celsius by a means for cooling and heating to ensure thermophilic conditions therein, xi. maintaining microaerophilic conditions in the reactor by adjusting the redox potential in the range of (300) mV to (200) mV by adding air or oxygen thereto, xii. adding water to the reactor separately when releasing the permeate to ensure a 1:1 ratio of the homogenized organic waste fed into the reactor, and the permeate and/or the spent solids released thereof, and xiii. ensuring a hydraulic detention time of the waste of up to 24 hours.

2. The method according to claim 1, wherein the organic waste is obtained from the group selected from wastewater sludge, food processing waste, commercial waste, agricultural waste, organic municipal solid waste, animal manure, industrial by-products selected from the group of condemned meat, manure and gut contents, catering waste from households or restaurants, former food, waste blood or feathers, or a mixture thereof, organic waste with a high content of carbohydrates, lipids and proteins.

3. The method according to claim 1, comprising the step of separating the permeate from the hydrolyzed and acidified waste by filtration.

4. The method according to claim 1, wherein the pressure adjustment means is a gas balloon.

5. The method according to claim 1, carrying out the feeding of the homogenized organic waste and/or the adding of the water continuously, semi-continuously or discontinuously at a 1:1 ratio.

Description

LIST OF DRAWINGS

(1) FIG. 1 shows a block diagram of a preferred embodiment according to the invention having two cycle loops, one for the separation of the permeate and one for the removal of spent solids.

(2) FIG. 2 shows another preferred embodiment according to the invention having one cycle loop only. FIG. 2 is also a block diagram.

(3) TABLE-US-00001 List of reference numbers Elements referred to Number Separation means 1 Removal means 2 Aspiration means 3 Pressure adjustment means 4 Filter 5 Release opening 6 Passage opening 7 Means for heating and cooling 8 Means for pH adjustment 9 Feed pipe a Reactor b Recirculation pipe c Aspiration pipe d Removal pipe e Recirculation pump f Recirculation pump g Recirculation pipe h Adjustment pipe i Release pipe j Water pipe with valve k Mixer m

(4) Arabic numbers refer to claimed elements while elements known to the public are marked with letters.

(5) In the following examples are presented to show some details of the method and means according to the present invention without the intention of limitation.

EXAMPLES

(6) The examples below use a b closed and gas tight reactor for biodegradation of organic solids under thermophilic conditions (60 to 65 C.) in less than 24 hours as shown in FIG. 1 or 2, where said b reactor has the following parameters: capacity: 800 l, material: stainless steel, average detention time of the organic slurry: 10 hours and
the following elements attached: m mixer, 8 water jacket, 1 pipe with 5 porous ceramic membrane filter mounted into it, having a pore size of 0.1 m, a 6 release opening, a j release pipe attached to it and two 7 passage openings, a feed pipe, d aspiration pipe with 3 self-aspirating injector having a valve, k water pipe, at least one h recirculation pipe, at least a g recirculation pump, 9 pH adjustment pipe e removal pipe with a 2 valve and 4 gas balloon attached to an i adjustment pipe.

Example 1Method for Hydrolyzing and Acidifying Organic Waste Cyclically Fed into a Reactor and an Apparatus Thereof

(7) Waste activated sludge from a municipal wastewater plant received at a dry solids concentration of around 15 m/m % is pre-treated (homogenized) first by diluting it using tap water to a concentration of around 5 m/m % dry solids and then using a grinder with a 1 mm sieve to bring the particle size of the solids down to 1 mm.

(8) After pre-treatment the homogenized fresh non-hydrolyzed water-diluted organic slurry is fed to the b reactor cyclically every two hours through the a feed pipe. The slurry remains for 8 to 12 hours in the b reactor. When the concentration of fixed solids in the b reactor is higher than 40 m/m %, spent solids are removed from the b reactor using the 2 valve attached to the e removal pipe. The remaining sludge is recycled to the b reactor through the c recirculation pipe of a first cycle loop.

(9) Hydrolyzed and acidified sludge leaving the b reactor through the h recirculation pipe of a second cycle loop is agitated by the g recirculation pump and is pressed through the 5 membrane filter attached to the h recirculation pipe.

(10) Soluble carbon, VFA and valuable nutrients are discharged from the 5 filter continuously in form of a permeate through the 6 opening of the 1 pipe mounted to the h recirculation pipe of the left cycle loop.

(11) Slurry unable to pass through the 5 filter is recycled back to the b reactor through the h recirculation pipe attached to the 7 passage opening of the 1 pipe.

(12) Pressure variation inside the b reactor is maintained to a relatively constant level using the 4 gas balloon. During the course of hydrolysis and acidification the evaporating gases, vapors are collected in the 4 balloon. When the pressure drops in the b reactor the content of the 4 balloon helps to keep the headspace pressure in the b reactor constant.

(13) Temperature of 60 to 65 C. is maintained using the 8 water jacket mounted on the external wall of the b reactor.

(14) pH inside the b reactor is initially set to a value of 6.5 by adding acid through the 9 pH adjustment pipe and kept in the range of 6.0 to 6.8 without adding chemicals.

(15) Microaerophilic regime inside the b reactor is maintained using the 3 self-aspirating injector mounted onto the d aspiration pipe to maintain a redox value of around (250) mV inside the b reactor.

(16) Table 1 enlists the parameters of samples of sludge slurry (before entering the b reactor) taken on three different days:

(17) TABLE-US-00002 TABLE 1 Samples of slurry before fed to the reactor COD DS tCOD sCOD VFA (mg/l NH4N (kg/day) (%) (g/kg) (mg/l) acetate) (mg/l) Sample 1 50-60 3.90 43.0 2800 656 465 Sample 2 6.52 71.7 3800 226 216 Sample 3 5.62 61.8 3200 100 150

(18) Table 2 shows the results achieved concerning the permeate corresponding to the slurry samples of Table 1 fed into the b reactor:

(19) TABLE-US-00003 TABLE 2 Permeate characteristics VFA sCOD NH4N (mg/l) (mg/l) (mg/l) Sample 1 2339 6000 900 Sample 2 2387 10000 1420 Sample 3 3239 12600 1340

(20) Checking the data of the permeate the results show clearly that the process significantly improves the hydrolysis and acidification of the organic solids. Table 2 shows a 3.5 to 30 fold increase in performance measured in terms of the VFA present, soluble carbon present and valuable nutrients comprised in the permeate.

Example 2

(21) A variation of the method and apparatus described in Example 1 is presented in FIG. 2 where the b reactor has only one cycle loop.