The Fate of Plant Pathogens and Seeds During Anaerobic Digestion and Aerobic Composting of Source Separated Household Wastes

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<ul><li><p>This article was downloaded by: [University Of Maryland]On: 16 December 2014, At: 09:45Publisher: Taylor &amp; FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK</p><p>Compost Science &amp; UtilizationPublication details, including instructions for authors andsubscription information:</p><p>The Fate of Plant Pathogens and SeedsDuring Anaerobic Digestion and AerobicComposting of Source SeparatedHousehold WastesJaak Ryckeboera, Stef Copsa &amp; Jozef Coosemansaa Laboratory of Phytopathology and Plant Protection, KatholiekeUniversiteit Leuven, BelgiumPublished online: 23 Jul 2013.</p><p>To cite this article: Jaak Ryckeboer, Stef Cops &amp; Jozef Coosemans (2002) The Fate of Plant Pathogensand Seeds During Anaerobic Digestion and Aerobic Composting of Source Separated Household Wastes,Compost Science &amp; Utilization, 10:3, 204-216, DOI: 10.1080/1065657X.2002.10702082</p><p>To link to this article:</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (theContent) contained in the publications on our platform. However, Taylor &amp; Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor &amp; Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.</p><p>This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &amp;Conditions of access and use can be found at</p><p></p></li><li><p>204 Compost Science &amp; Utilization Summer 2002</p><p>Compost Science &amp; Utilization, (2002), Vol. 10, No. 3, 204-216</p><p>The Fate of Plant Pathogens and Seeds During Anaerobic Digestion and Aerobic Composting of </p><p>Source Separated Household Wastes</p><p>Jaak Ryckeboer, Stef Cops and Jozef CoosemansLaboratory of Phytopathology and Plant Protection, </p><p>Katholieke Universiteit Leuven, Belgium</p><p>Anaerobic digestion is becoming a more common method for treatment of organicwastes. Little is known, however, about the effects of this process on the fate of plantpathogens and seeds. Therefore, the fates of the plant pathogens Plasmodiophora bras-sicae, Heterodera schachtii, Meloidogyne incognita, Ralstonia solanacearum, tobacco mosa-ic virus (TMV) and tomato seeds were followed during anaerobic digestion of sourceseparated household wastes. With the exception of TMV, all test organisms were de-stroyed to below detectable limits within one day of anaerobic digestion at 52C. Twodays of anaerobic digestion did not reduce the concentration of TMV. However, twodays of anaerobic digestion followed by 19 days of high temperature composting at58C reduced the concentration of infectious TMV particles by a factor of almost threeorders. Anaerobic digestion followed by 12 days of composting at 68C was evenmore effective. Although TMV concentrations were not eliminated entirely, we con-clude that short-term high temperature anaerobic digestion followed by high tem-perature composting is a highly efficient process for the eradication of detrimentalagents from solid wastes.</p><p>Introduction</p><p>Anaerobic digestion is a common method for treatment of organic wastes. Howev-er, little is known about the effects of anaerobic digestion on survival of plant pathogens(Williams 1979; Bollen and Volker 1996). Whereas heat is thought to be the main inacti-vating factor of pathogenic agents during high temperature composting, which is a pre-dominantly aerobic process, toxic agents seem to play the major role under anaerobicconditions in compost piles, especially at lower temperatures. Unfortunately, data con-cerning the identity of the toxic agents are lacking (Bollen 1993). According to Bollen andVolker (1996), pathogens may be more sensitive to toxic agents under low redox poten-tials. These authors also illustrated the effects of anaerobiosis on the destruction ofpathogens during farm-scale composting of flower residues. They determined that theoxygen content of the air at depths of 30 and 70 cm inside a large, compact and poorlyaerated heap at the end of a 32-week composting period, was 14 and 1%, respectively.Surprisingly, even at sites within the heap where temperatures did not exceed 35C, rel-atively heat-resistant pathogens such as formae speciales of Fusarium oxysporum weredestroyed. Two pathogens known for their resistance to adverse conditions in soil, i.e.F. oxysporum f. sp. dianthi and Sclerotium cepivorum, were eradicated within a few daysof treatment under these low oxygen tensions at temperatures of 32-35C (Turner et al.1983; Bollen 1993; Bollen and Volker 1996). Furthermore, Horiuchi et al. (1983) observedthat infectivity of Plasmodiophora brassicae in galls on turnip (Brassica rapa) was lost afterone day of exposure to 45C under (semi)anaerobic conditions. The foregoing suggeststhat some fungi may be highly sensitive to anaerobic processes. </p><p>It has been determined that plant pathogenic bacteria are highly sensitive to anaer-obic digestion. For example, Clavibacter michiganense is destroyed by fermentation at35C in less than seven days (Turner et al. 1983). </p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity O</p><p>f M</p><p>aryl</p><p>and]</p><p> at 0</p><p>9:45</p><p> 16 </p><p>Dec</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>Furthermore, plant pathogenic nematodes such as cysts of Globodera rostochiensisand G. pallida are also sensitive to this process (Williams 1979; Turner et al. 1983;Heinicke 1989). Turner et al. (1983) showed that the population of viable juveniles ofGlobodera rostochiensis decreased 1,000-fold during 26 h of anaerobic digestion at 35C.Viability of cysts was completely lost within seven days. </p><p>Data concerning the fate of plant pathogenic viruses are lacking. Furthermore, lit-tle is known about inactivation of seeds through anaerobic digestion. Jeyanayagamand Collins (1984) reported that survival of seeds of Sorghum halepense and of Panicumdichotomiflorum in the temperature range of 35C 1C is influenced by digestion time,the species and dormancy of the seeds. Dormant seeds were less sensitive and seed ofP. dichotomiflorum was more sensitive than that of S. halepense.</p><p>In conclusion, thermal death is assumed to be the most important cause of eradi-cation of plant pathogens during composting (Hoitink et al. 1976; Ylimki et al. 1983;Yuen and Raabe 1984; Bollen 1985; Lopez-Real and Foster 1985; Herrmann et al. 1994;Bollen and Volker 1996), while in contrast, pathogen kill during anaerobic digestion atmesophilic temperatures is often attributed to toxic conversion products or to directbreakdown of pathogen structures by microorganisms (Lopez-Real and Foster 1985;Bollen et al. 1989; Bollen and Volker 1996). Unfortunately, the contribution of factorsother than heat in sanitation during composting or anaerobic digestion is difficult toquantify. Therefore, temperature and time should be considered as the most reliableparameters for prediction of inactivation of pathogens and seeds (Bollen et al. 1989). </p><p>Anaerobic digesters that are operated continuously pose potential problems whenthe feedstock contains infected plant materials. Turner et al. (1983) reported that a smallpercentage of the fresh material leaving such reactors has not been sanitized. For exam-ple, in a continuously fed digester system running with a hydraulic retention time of tendays, statistically 10% of the influent will pass straight through the system. Therefore,pretreatment and/or follow-up treatment with chemicals or heat treatment should beperformed. The obvious solution to this problem is to treat the digested material furtherthrough high temperature composting. This, to our knowledge, has not been tested. </p><p>The objective of this research was to investigate the fate of TMV, Plasmodiophorabrassicae, Heterodera schachtii, Meloidogyne incognita, Ralstonia solanacearum and tomato(Lycopersicon esculentum L.) seeds during anaerobic digestion of source separatedhousehold wastes (also called vegetable, fruit and garden wastes, referred hereafter asbiowastes) in small-scale digesters. Modified German BioAbfV-norms (LAGA-Merk-blatt 1994; BioAbfV 1998; Ryckeboer 2001) were used as the basis for this research, asdescribed further. </p><p>Materials and Methods</p><p>DRANCO Process</p><p>The anaerobic digestion process used in this work was based on the DRANCOprocess (De Baere et al. 1986; Baeten and Verstraete 1993; Gellens et al. 1995; De Baere2000). The DRANCO process is a solid phase (25-35% solids) fermentation process. Thefull-scale reactor is designed as a vertical plug flow reactor that operates at 52C. In thesereactors, organic loading rates of 20 kg Chemical Oxygen Demand (COD) per m3 reactorper day are obtained. Fresh biowastes blended with a small amount of digested residue(inoculum) enters the top and leaves the bottom of the reactor with retention times of 16to 21 days. The digestion phase is followed by an aerobic composting phase of one tothree weeks (De Baere et al. 1986; Baeten and Verstraete 1993; Gellens et al. 1995; De Baere</p><p>The Fate of Plant Pathogens and Seeds During Anaerobic Digestion and Aerobic Composting of Source Separated Household Wastes</p><p>Compost Science &amp; Utilization Summer 2002 205</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity O</p><p>f M</p><p>aryl</p><p>and]</p><p> at 0</p><p>9:45</p><p> 16 </p><p>Dec</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>2000). Due to this continuous feeding process with fresh wastes, a small amount of freshwaste necessarily leaves the digester after having been treated as little as two days. </p><p>In this research small-scale digesters with a content of 2 to 6 liters were filled withDRANCO digester inoculum (= predigested biowastes) and incubated in a hot air ovenat 52C. Inocula of plant pathogens and tomato seeds were prepared and incorporat-ed into these digesters according to the German BioAbfV-norms (LAGA-MerkblattM10 1994; BioAbfV 1998). In all experiments, a controlled quantity of pathogen inocu-lum or tomato seeds was added to an excess quantity of DRANCO digester inoculum(weight ratio pathogen inoculum/digester inoculum between 1:10 and 1:100) to es-tablish optimum digestion conditions (C/N ratio of feedstock: 15-40; pH in reactor: 7.5-</p><p>9; concentration of NH4-N inreactor: 300-2000 mg/kg etc.)in the small-scale reactors.The methane gas, convertedto normal conditions of pres-sure and temperature, wasquantified with a gas meter orwater column (Figure 1). TheDRANCO digester inoculumoriginated from a 40-literanaerobic digestion-unit thathad been fed in batch-mode(= discontinue) with bio-wastes and diapers and di-gested for two to three weeks(Ryckeboer 2001).</p><p>BioAbfV-norms</p><p>The German BioAbfV-norms describe how the hygienic safety of composting anddigestion processes must be evaluated. German regulations also specify that facilitieswhich process biowastes under controlled aerobic (composting) or anaerobic condi-tions (fermentation) must meet the BioAbfV-norms before the end product is com-mercialized. Direct process validation must be performed within twelve months aftera new biowaste treatment facility has been started up and the tests must be performedon a regular basis. The norms prescribe the use of TMV, P. brassicae and tomato seedsas indicator organisms for evaluation of phytohygienic safety. These test organismsare rather resistant to conditions that prevail during composting. Based on the resultsof test bioassays the phytohygienic safety of the compost is then predicted (LAGA-Merkblatt M10 1994; BioAbfV 1998).</p><p>Experimental Design</p><p>Several preliminary experiments were performed to determine the time requiredfor eradication of P. brassicae, H. schachtii, R. solanacearum or of tomato seeds duringanaerobic digestion at 52C. In a second series of experiments, destruction of theseorganisms as well as that of TMV was investigated. The effect of anaerobic digestionon survival was examined in several experiments. In follow-up experiments, how-ever, the effect of anaerobic digestion followed by forced aerated composting wasdetermined as well, which is how the full-scale DRANCO process operates.</p><p>Jaak Ryckeboer, Stef Cops and Jozef Coosemans</p><p>206 Compost Science &amp; Utilization Summer 2002</p><p>Figure 1. Schematic of lab-scale DRANCO digester.</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Uni</p><p>vers</p><p>ity O</p><p>f M</p><p>aryl</p><p>and]</p><p> at 0</p><p>9:45</p><p> 16 </p><p>Dec</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>Tobacco Mosaic Virus</p><p>Inactivation of TMV was tested by mixing tobacco leaves harvested from Nicotianatabacum cv. Samsun plants infected with TMV with DRANCO digester inoculum ata weight ratio of 1:10. The mixture was then loaded into a digester. Control samplesconsisting of a 110-g mixture of TMV-infected tobacco leaves and DRANCO digesterinoculum (1:10; w/w) were stored at the beginning of each experiment at 21C, ex-cept for in one short-term experiment where samples were stored at 4C. Three di-gesters were used per treatment and several types of anaerobic digestions were per-formed as described below. </p><p>TMV-infected tobacco leaves used in these experiments were excised at the six-leafstage from Nicotiana tabacum cv. Samsun plants grown in a heated greenhouse withphotosynthetic illumination (SON-T; 16-h photoperiod) at 21 to 22C. Two or threelower leaves were thinly dusted with carborundum powder (500 mesh; Sigma AldrichChemie GmbH, Steinheim, Germany). The extract of pressed TMV-infected tobaccoleaves mixed with 0.05 mol/l phosphate buffer (pH 7), was carefully applied to car-borundum-dusted leaves using a glass spatula. TMV-infected leaves displaying mo-saic symptoms were selected three weeks after inoculation for use in this work(BioAbfV 1998; Ryckeboer 2001). </p><p>In a first short-term experiment, TMV-infested samples were digested for 72 h. Forpractical reasons controls were stored at 4C. In later experiments, a minimal digesterretention time of two days was simulated followed by an aerobic composting periodof 19 days. During the normal transition from anaerobic to aerobic composting, the ma-terial leaving the DRANCO digester is dewatered with a screw press. The press waterfrom our experiments, therefore, was collected also and analyzed for TMV-titer. Thepressed solids we...</p></li></ul>