Impact of hydrothermal process on the nutrient ingredients of restaurant garbage

ISSN 1001- 0742Jourma of Enwirnmental Sciences Vol. 18, No. 5, pp. 1012- 1019, 2006CN 1-2629/XArticle ID: 1001-0742(2006)05-1012-08CLC number: X705 Document code: AImpact of hydrothermal process on the nutrient ingredientsof restaurant garbageREN Lian-hail2, NIE Yong feng'", LIU Jian-guo', JIN Yi-ying', Sun Lu'(1. Department of Environmental Science and Engineering, Tsinghua University, Beijing 00084, China. E-mail: rth0l@mailstsinghua.edu.cn; 2.Departiment of Chemical and Environmental Engineering, Beijing Technology and Business University, Beijing 10037, China; 3. Department ofEnvironmental Engineering, China Agricultural University, Beijing 100094 ,China)Abstract: In order to recover the nutrient resource from restaurant garbage, a complete trial with 2 factors on 5 levels of experimentswas crried out. The temperature and heating time are the main factors infuencing on hydrothermal process (HP) by which improvesthe degradability and digestibility of the restaurant garbage favorably to make animal feeds or frilier The results showed thevariation of protein, saccharide, and oil in the garbage. It showed that protein dissolved and liquefied during hydrothermal process,which made organic nitrogen in solid phase transfer to liquid phase. After heating at 180C for 60 min, organic nitrogen in liquid phasebegan to transform into ammonia. It also showed that hydrothermal process could promote the dextrinization, dissolution of the starchand its hydrolysis to reducing sugar, due to that starch in the restaurant garbage decreases and reducing sugar increases. When thetemperature reached 140C, the reducing sugar started to decrease due to chemical reactions. The cllulose was stable at 100- 180C.The floatable oil increased markedly in the hydrothermal process. The suitable condition for de-oil was observed at 160C heating for80 min. Furthermore, the extraction of grease from the solid phase accords with first-order reaction dynamic model.Keywords: restaurant garbage; hydrothermal process; protein; saccharide; lipidal, 2003; Miyazaki and Morita, 2005). To make clearIntroductionwhat reactions take place and how to control them, isThere are plenty of nutrients such as protein,important for the resource reclamation from restaurantcarbohydrates and grease in the restaurant garbage.garbage. However, few reports on it were publishedThe structure of the nutrient ingredients and theirpresently. .occurrence have great influence on the disposal of theIn this work, the influence theory and procedurerestaurant garbage and its recycle, e.g. if the garbageof the hydrothermal process on the main nutrientshas a high nutrient value, we can consider to make itincluding protein, carbohydrates and grease in thefeedstuff for animals after proper treatment; if therestaurant garbage were studied to investigate theirorganics are high, the garbage could be made intovariation generalization during this process. Theorganic fertilizer after biochemical stabilization; ifresults are expected to be favorable for optimizing thethere is a more occurence of grease in the garbage, thhydrothermal process of the restaurant garbage and forgrease could be extracted out to prepare biologicalconstructing the systematic hydrothermal theory.fuel, and so on. Therefore, it is very important for the1 Experimental materials and methodsdisposal of restaurant garbage and the popularizationof the treatment process to determine how to make the1.1 Test samples of restaurant garbagenutrients change in a proper way from the garbage. LaiThe test sample of restaurant garbage was taken(2001) and Urbano et al. (2003) found that thefrom the 9th Canteen of Tsinghua University. Itshydrothermal process markedly influenced thphysico-chemical properties are shown in Table I. Ofphysicochemical properties of protein, carbohydratesthese, the true protein, starch, raw cellulose, reducingand grease. During hydrothermal process, pathogenssugar, raw fat and floatable oil content were measuredare removed, while the nutrients such as protein,on the dry basis of the restaurant garbage.saccharide, and oil also change (Lai, 2001; Urbano elTable 1 Physico-chemistry properties of restaurant garbage (% (w/w))templMoisture'True protein'Starch'Raw cllulose' Reducing sugar'Raw far'Floatable oil fromgartbage"' X 10*Average6.5879.0121.7512.510.1415.2427.61Note: * Data measured on dry weight basis of the restaurant garbage中国煤化工1.2 Hydrothermal treatment test on restaurantfeeds.MH.CNMHGenutrients resourcegarbagein tht ICsudulanl gavage 1u11y， here treated theIn order to make the treated products intorestaurant garbage hydrothermally according to theFoundaion item: The Cross Project from Beijing Govenment (No. 2004536);. *Corresponding authorNo.5Impact of hydrothermal process on the nutrient ingredients of restaurant garbage1013experimental arrangement as shown in Table 2, toBefore each test, the hydrothermal reactor wasinvestigate the effects of temperature and heating timewashed for three times with double-deionized water.on the content of nutrients such as protein, saccharide,The restaurant garbage sample 600 g was fed into theand lipid. The structure of hydrothermal equipment isairprofed reactor and 300 ml water was added andshown in Fig.1.the reactor was heated up to a prescribed temperature.Table 2 Hydrothermal experiment conditionsHeating time,Heating timc,Temp,CNo.Temp,CcTemp.,C .min10020101200081606(4014098C60128(135021180148024C15236C16241725pressure was released and treated sample was takenr口→Safety valveout. The treated sample was dewatered for 30 min bycentrifuging at a speed of 3000 r/min to obtain thesolid phase and water-oil mixture. The solid phase ofthe treated sample was dried in a vacuum drying ovento get the absolute dry sample for the measurement.。 RestaurantThe water-oil mixture was separated by a separatorygarbage.Garbageflask. Then the protein, starch, raw cellulose, reducingoutletsugar and raw fat in the solid product were measured,while the pH, the organic nitrogen, ammonia andfloatable oil content in the liquid phase wereFig.1 Diagram of hydrothermal equipment for restaurant garbagemeasured. Here the floatable oil amount should be1. temperature contolle; 2. hea-conducting oil; 3.packing washer; 4.temperature sensor; 5. manometer; 6. body of the hydrothermal reactor;converted to the amount on the basis of per weight7. heaing cordunit of dry garbage. The measurement methods areshown in Table 3.The time was noted as a starting point, and then1.3 X-diffraction tests of the starchduring the course heating temperature was recordedThe starch sample was food grade, bought fromfor a prescribed period. When time was over, thShenyang 5th Chemical Agent Factory in China. InTable 3 Measurement methodsItem .Measurement methodMethod resourceOrganicsPotassium dichromate methodGB 9834-88True proteinKjeldah's methodsMAFIC.LABMETH-004-2001AmmoniaNash reagent colorimetric methodGB 7479-1987StarchEnzyme-colorimetric methodGB/T 16287-1996Reducing sugarDireet assay method中国煤化工85Raw clluloseGravimetric methodMYHCNMH(5194Raw fatSoxhlet methodGB/T 6433- 1994Floatable oilVolumetric method1014REN Lian-haiet al.Vol.18order to investigate the effect of hydrothermal processsulfate, then was scanned by a Fourier transformon the co-structure of the starch, we compared theinfrared spectrometer (Bruker Company), the bariumX-diffraction spectra of the hydrothermally treatedsulfate powder was used as background material forstarch with its origin state at wavelength of 1.5406Xthe infrared scan. In order to investigate the impact of10' nm (D/max1200 X-difactometer, Rigakv Com-the hydrothermal process on the oil, the infraredpany, Japan). The nickel filter sheet was used. Thediffuse reflection spectrum of the waste oil wasscanning scope of 20 was from 4° to 60°. Thecompared with that of the clean oil used to cook in thescanning velocity was 10%/min.restaurant..4 Infrared spectral analysis of the lipid in the2 Results and discussiongarbageThe waste oil sample taken from the restaurantThe experimental results are shown in Table 4.garbage was purified and mixed with the bariumTable4 Results of experimentsTrueOrganicOrganic nitrgen Ammonia inReducingRaw fat inFloatableStarch,Noprotein, nitrogen in solid in liquid phase, liquid phasc,sugar,cellulose, solid phrase,dw%dw% phase, dw% X 10* Ww% X 10* ww%dW%X 10^ dw%21.563.45240.1492.1110.2116.110.2426.301.5224.383.90259. 9095.218.5417.052.1227.194.35255.48105.467.6229.210.4321.982.3130.634.90304.95114.685.9828.330.3224.063.85322.05120.335.1329.30.2316.46 .22.193.55305.1714.059.3318.03026.212.4526.004.16365.32141.06.5230.150.1724.073.5231.445.03334.54176.104.2549.640.2220.473.83361.47190.073.1166.610.0117.951022.00389.10211.042.5653.150.1514.78122.943.67315.75115.518.6965.420.1925.115.0412368.69157.025.2370.860.2522.066.141:21.50 .3.44437.40193.003.6468.590.3117.917.031418.382.94527.85214.0665.320.2114.357.3214.252.28516.67243.001.5650.1710.607.4123.563.77191.68217.4369.560.3023.384.11!26.444.23376.72244.624.2165.210.3719.967.781828.814.61445.26260.0353.541.0514.2110.701921.133.38441.46307.001.0335.349.3913.172010.631.70443.94363.000.6635.150.345.577.53228.064.49143.13337.076.019.641.647.342225.384.06303.95378.003.0225.5316.589.3114.382.30310.48393.851.1418.153.5610.10248.381.34186.45523.610.3515.322.965.66257.001.12210.47646.000.277.9115.521.965.582.1Impact of hydrothermal process on thchan| 中国煤化工inPig2. If itprotein in the restaurant garbagecontircarbohydrates andAs one of the main nutrients in restaurantlipidsMYHC N M H Ghe liquid phase, thegarbage, protein in the product is significant for theprotein content in the product relatively increases andrecycling of the treated garbage. At the beginning ofit gets 31.44% as the highest value at 120C for 60the hydrothermal process, the protein in the garbagemin. Then, the protein absorbs water and swells toNo.5Impact of hydrothermal process on the nutrient ingredients of restaurant garbage1015make the auxiliary bond of the spherical peptide chainjoins chemical reaction besides solution. In fact, whilebreak because of being heated. Hence, the originthe protein dissolves, it also hydrolyzes to formfolded parts of the peptide chain were loosened andmultipeptide, dipeptide and amino acid. The aminomore readily affected by the digestion enzymes.acid further hydrolyzes to form organic acid, NH: andConsequently, the digesting efficiency of the proteinCO2 (Wand and Wang, 2003; Schieder et al., 2000).and the biological effectiveness of the essential aminoThis reaction leads to the loss of the nutrients whichacid in the product are improved which benefits fodose harm to make the treated garbage into feedstuffthe treated product being made into feedstuff (Han,or fertilizer.2003a). Subsequently, the organic nitrogen content inthe solid phase decreases while the organic nitrogen in50 CtF120C-士140C女160-*- 180liquid phase increases, as shown in Fig.3. Then the40 Fmain changes of the protein are solution and liquation.30 -The heating time when the protein content begins to20年decrease at 100, 120, 140, 160 and 180C were 80, 60,60, 60 and 20 min respectively. When it gets 180Cand the heating time reaches 60 min, the organicnitrogen concentration in liquid phase begins toHeating time, mindecrease and the ammonia in liquid phase begins toincrease which indicates that, at present, the proteinFig.2 True protein Vvs. heating time; 1000T. 100C曾800800r. 120C AT. 140C600600p一C400402000204060801001000r. 180CT. 160Cr TN in liquid phrase600 oOrganic N in liquid phraseAmmonia in liquid phrase-0- Organic N in solid phrase204060 80100°0204060 80 100 "Fig.3 Ocurrence of the nitrogen in the garbage at dfferent temperatures2.2 Impact of hydrothermal process on thevariation of temperature. This indicates that almost nocarbohydrates in the restaurant garbagecrystal structure occurs in the gelled particles oThe hydrothermally treated starch was observedstarch. The formation of the gelled particles are thecompared with the raw starch through SEM (scanningtangling of multi-molecules simply resulting from theelctronmicroscope) pictures by Americanhydrogen bonds among several points in the starchA2MARY21000B SEM, as shown in Fig.4. It showsmolecular chains. The hydrogen bonds do not occurthat the hydrothermal process makes the particles ofamong long molecular segments. Generally， thestarch selling and the SEM drive to be fuzzy whichchemical structure of the gelled starch particlesindicates gelling took place. Then the variation of thebehaves similarly to that of raw starch, while it losescrystal structure of the starch is investigated bythe noticeable crystal diffraction peak in the physicalX-diffraction spectrum analysis, as shown in Fig5.structure. It shows the variation of the starchThe diffraction peak of the raw starch in the curve ismolecular chains on the physical arrangement and thesharper which indicates the gelled starch has certainfeatu| 中国煤化工n bonds between thecrstallinity. However, the diffraction peaks of themoloYHC N M H Gsacaride dretly,hydrothermal treated starch at 110, 140 and 180Cinthe curvebecomelow and flat which have noo the carbohydrates such as starch must benoticeablecharacteristicdiffractionpeak.hydrolyzed into low-carbon saccharides to beFurthermore, this trend does not change with thetransferred into the humor of animals and plants. It1016REN Lian-hai el al.Vol.188. Raw starchb. Treated starch with hydrotbermal processFig.4 SEMs of the starch particles amplifed by 1000 times1000Raw starchr. 110C00 t004002000410 20350 606 10203040Degree, 20r. 140CT. 180C800000 F600”6100Fig.5 X-diffraction curve of the starch treated with hydrothermal process under dfferent temperaturemeans that low-carbon saccharide content in theattacked by the lone pair electrons on the N in theprocessed products plays an important role in itsamino group nucleoplillcally to lose H2O and closeddissolving and digesting performance. During thechain to form a kind of spicy substance-hydrothermal process, the reducing sugar in theglucosamine. This results in the decrease of theprocessed product mainly comes from the hydrolysisreducing sugar and the loss of amino acids whichof the carbohydrates, especially from starch in themakes the nutrients value of the products decreasegarbage. With the temperature rising and the heating(Henle, 2001; Slot, 1997; Marrtins, 2001). The SEMtime increasing, the starch swells, dextrinizes andof the hydrothermal treated starch is shown in Fig.8.hydrolyzes to reducing sugar, the starch content in theIn the picture of the starch treated at 140C, theregarbage is therefore decreases as shown in Fig.6.appears brown dots partially which indicates theMeantime，the content of reducing sugar in thereducing sugar from starch hydrolysis has happenedproduct starts to increase as shown in Fig.7. However,maillard reactions with amino acids at thiswhen the temperature reaches 140C ，the reducingtemperature. Furthermore, this kind of colorationsugar in the garbage starts to decrease. This is mainlyreaction happens much more heavily as the brownbecause the reducing sugar reacts chemically to formdots中国煤化工tintheSEMoftheother substances， wherein, one of the importanttreat_strates the nutrientschemical reactions is maillard reaction between theareMYHCN M H Gperature. Therefore,reducing sugar and amino acids. The C- in thein order to avoid the loss of the nutrients effectively,open-chain carbonyl radicals in reducing sugar arethe temperature should be controlled below 140C.No.5Impact of hydrothermal process on the nutrient ingredients of retaurant garbage10172(9o- ◆20min + 40min. 士60 min.￥-80min-*-100min. 120C15_ 140C- 160C180C昂1(50 F30米208010012014016r,cHeating time, minFig7 Reducing sugar vs. temperatureFig.6 Starch content Vs. heating timea 140Cb. 180CFig.8 SEMs of the treated starch with hydrothermal process amplified by 400 timesThe variation of the cellulose in the garbagewith that of the clean oil used to cook in the restaurantduring hydrothermal process can be seen from the dataas shown in Fig.9. The absorption peak of the C=0in Table 4. Under the experimental conditions, thedouble bond in the clean oil ocurs on the point ofcellulose is relatively stable.1740 cm' as shown in Fig.9a, while the absorption2.3Impact of hydrothermal process on thepeak of the C=O double bond in the hydrothermalvariation of the lipids in the restaurant garbagetreated lipid generates red shift and appears on the2.3.1 Infrared spectrum analysis of the hydro-point of 1540 cm' as shown in Fig.9b. This indicatesthermal treated lipidsthat the hydrothermal process enabled the chemicalAccording to the methods described in sectionchanges of the molecular structure of the lipid. The1.4, the infrared spectrum of the lipid taken from thechemical reaction involved might be saponification ashydrothermal treated restaurant garbage was comparedthe C=O double bond still exists.a. Clean raw lipidb. Hydrotbermal treated lipid30 F0FWN6(信4(220b4000 3000 2000 16004000 3000 2000 1600 1200800 400Wavenumber, cm'Wavenumber, cm-'Fig9 Comparison of Infared spectrum of the hydrothermnal treated lipid with that of its raw state2.3.2 Impact of hydrothermal treatment on thequic中国煤化工and floats there infloatable oil in the restaurant garbagecontseparated simply byThe oil in garbage exists mainly in five kinds ofgravYHCNM H Ged, emulifed andstates including floatable， diffused, emulsified,dissolved oil have smaller drops in size and bind withdissolved and inside solid oil. Of these, the floatablewater tightly that are separated much harder. As foroil occurs in large drops and if being held sill, it risesthe inside solid oil, it always combines with the solid.1018REN Lian-hai et al.Vol.18garbage in solid state so that can not be separatedwhich means the raw fat (RF) content in the soliddirectly at all. Therefore, the content of floatable oilphase decreases as shown in Fig.11. The RF content inshould be the critical factor for the de-oil performancethe treated garbage varies regularly along with theof the garbage (Han and Hou, 2000).heating time. We make an assumption that theThe content of floatable oil in the restaurantextracting course accords with first-order reactiongarbage varies according to the heating time anddynamic model which can be witten as the followingtemperature as shown in Fig. 10. Hydrothermal processequations:makes the content of floatable oil tend to increase.Furthermore, the higher temperature enhances thedCE = KCep(1)dfloatable oil increases more quickly. At present, theCRF = C,exp(-KI)(2)molecular mobility (Mm i.e, the rotating mobility andtranslating mobility of the molecule) of the garbage is.Where, CRe is the raw fat content in the garbagestrengthened and its diffusing performance of watermeasured in % when heating time is t. Co is the initialand lipid is improved. Because of the chemicalraw fat content in the garbage measured in %. K ispotential difference between the interior and exteriorextraction rate constant of lipid measured in min"'.l is .of the solid phase in the garbage, water goes insideheating time measured in minutes.and the fat is extracted outside to form floating oil. Atthe temperature range from 100- 120C, the content4(100公* 160of floatable oil increases continuously. When the)上. 140Ctemperature and heating time reach 160C and 80 min。2respectively, the floatable oil content per unit weightof garbage reaches the highest level as 131.7 ml/kg.15一After that, floating oil content begins to decrease. That0tmeans that the lipid inside the solid phase hasextracted completely and continuous heating will20400 8010promote the chemical reactions of lipid. For example,Heating time, minlipid would hydrolyze into free fatty acid anFig11 Raw fat content vs. heating timeglycerine. Additionally， the glucose from thehydrolysis of starch will esterify with fatty acid andUtilizing Origin Sofware to edit Equation (2),forms monoester, diester and triester with HLB valuewe fit the extration of raw fat in restaurant garbage(hydrophilia-lipotropic balanced value) range fromIwith heating time. The results are listed in Table 5.0 16, which helps oil and water form O/W typeTable 5 shows that rate constants of lipidsystem (oil-in-water type and water is continuousextraction rises with the increase of heatingphase). It makes part of floating oil convert intotemperature and they are well relevant at differentemulsifying oil, which multiplies the difficulty oftemperatures as all the correlation coefficients areseparating oil from water (Han, 2003b). In conclusion,greater than 90%, which ilustrates that the extractionthe suitable condition for de-oiling of the restaurantof solid grease from interior accords with first-ordergarbage is that the temperature and heating time arereaction dynamic model. According to Arrhenius160C and 80 min, respectively.Equation as follows:E。200. 100lnK=-D_ +InA4(3)RT+ 120150or光160C-米180CE。、00K = Aexp(-where, A is the constant measured in min'; R is thegas constant which equals to8.31 X 103 kJ/(K .mol);8100T is absolute temperature measured in K. E。is activa-tion energy measured in kJ/mol.Fig.10 Floatable oil per unit weight of garbage Vs. heating timeAccording to the results shown in Table 5, weuse中国煤化工-ion (4) and fit the2.3.3 Kinetic analysis on the extraction of lipidsrateCre (T) as shown infrom the restaurant garbage in hydrothermalFigMYHCNMHGre:A=64.07,E。=process30.17 KJ/mol; the correlation coefficient is 96.6%Lipids in the solid phase of the garbage extractswhich demonstrates that rate constants of lipidout continuously during the hydrothermal process,extraction and heating time accords with ArrheniusNo.5Impact of hydrothermal process on the nutrient ingredients of restaurant garbage1019Equation. Thus, with Equations (2) and (4), the lipidcellulose under the experimental conditions is stable.extraction of treated restaurant garbage can beDuring the hydrothermal process of the restaurantpredicted at any temperature between 100C andgarbage, the floatable oil content increases which1809 during hydrothermal process.indicates that the de-oiling performance of the garbageis improved. The suitable condition for de-oiling ofTable 5 Rate constants of lipid extraction under differentthe restaurant garbage is that the temperature and thetemperaturesheating time are 160C and 80 min respectively.Temperature,KCorrelationAditinally, the extraction of inside solid lipids fromrrorCmin'coefficientthe garbage accords with first-order reaction dynamic000.0044+0.00050.9374model. And the relationship of the extraction rate200.0055土0.00060.9418constant to the temperature accords with Arrheniusequation.1400.0086士0.00080.9618Acknowledgements: The authors are indebted to600.0145士0.000.969Beijing Municipal Management Commission for their800.0237士0.00270.958support.References:0.03 [Han Z X, Hou T M, 2000. Technologies for determination ofphysicocmical properties and content of oil in wastewater[J].Environmental Protection of Chemical Industry, 20(6): 38--43.Han J Q, 2003a. Food chemistry (M]. Beijing: China AgricultureUniversity Press. 109- 112.《0.01Han J Q, 2003b. Food chemistry [M]. Beijing; China AgricultureUniversity Press, 186--188.Henle T, 2001. Maillard reactions of food proteins: chemical, nutritional353 373393~ 413 433 45and functional aspects[J]. Nahrung-Food, 45(3): 149.T, Kai H M, 2001. Efectshydrothermal treatment on thephysicochemical properies of pregelatinized rice flour []. FoodFig.12 Rate constants of extraction vs. temperature (T)Chem, 72 (4): 455-463.Marrtins s, 2001. A review of maillard reaction in food implications tokinetic modeling []. Trends in Food Science & Technology, 113 Conclusions(9/10); 364- -373.Hydrothermal process makes the protein in theMiyazaki M, Morita N, 2005. Effect of heat-moisture treated maizestarch on the properties of dough and bread [J]. Food Res Int, 38restaurant garbage dissolve and liquefy. Inhydrothermal process, the organic N transforms fromSchieder D, Schneider R, Bischof F, 2000. Themal hydrolysis (TDH)solid phase to liquid phase. When the temperature andas a pretreatment method for the digestion of organic waste[J].the heating time reach 1809C and 60 min respectively,Water Sci Technol, 41(3): 181-187.Slot Marek, 1997. Conditions of the milard reaction: Modelling of thethe organic N starts to translate into ammonia.proess[]. Inzynieria Chemicznai Procesowa, 18(1): 81-82.During the hydrothermal process, the starchUrbanoAranda P,omez-Vllalva E et al, 2003. Nutritionalswells, gelatinizes and hydrolyzes to reducing sugars.evaluation of pea (Pisum sativum L.) protein diets after mildThe gelling simply results in the change of thehydrothermal treatment and with and without added phytase[J]. JAgr Food Chem, 51(8): 2415- -2420.physical structure of starch. The hydrolysis leads toWang Z J, Wang w, 2003. Experimental study on thermal hydrolysisthe decrease of the starch in the garbage and theand anacrobic digestion of sewage sludge [J]. China Water andincrease of the reducing sugar. However, when theWastewater, 19(9): 1- -4.temperature reaches 140C, the reducing sugar starts to(Received for review October 19, 2005. Accepted February 27, 2006)decrease because of the chemical reaction. The中国煤化工MYHCNMHG