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mengistu et al environ syst res 2017 6 5 doi 10 1186 s40068 017 0079 4 research open access comparative effectiveness of different composting methods on the stabilization maturation and ...

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               Mengistu et al. Environ Syst Res  (2017) 6:5 
               DOI 10.1186/s40068-017-0079-4
                RESEARCH                                                                                             Open Access
               Comparative effectiveness of different 
               composting methods on the stabilization, 
               maturation and sanitization of municipal 
               organic solid wastes and dried faecal sludge 
               mixtures
                               1*                    1                  1                       2                      1
               Tesfu Mengistu , Heluf Gebrekidan , Kibebew Kibret , Kebede Woldetsadik , Beneberu Shimelis  
               and Hiranmai Yadav1
                Abstract 
                Background:  Composting is one of the integrated waste management strategies used for the recycling of organic 
                wastes into a useful product. Composting methods vary in duration of decomposition and potency of stability, matu-
                rity and sanitation. This study was aimed to investigate the comparative effectiveness of four different methods of 
                composting viz. windrow composting (WC), Vermicomposting (VC), pit composting (PC) and combined windrow and 
                vermicomposting (WVC) on the stabilization, maturation and sanitization of mixtures of municipal solid organic waste 
                and dried faecal sludge.
                Methods:  The composting treatments were arranged in a completely randomized block design with three replica-
                tions. The changes in physico-chemical and biological characteristics of the compost were examined at 20 days inter-
                val for 100 days using standard laboratory procedures. The analysis of variance was performed using SAS software and 
                the significant differences were determined using Fisher’s LSD test at P ≤ 0.05 level.
                                                                               +     −    +    −
                                                                            NH         NH
                Results:  The evolution of composting temperature, pH, EC,     4, NO ,    4:NO  ratio, OC, C:N ratio and total volatile 
                                                                                     3         3
                solids varied significantly among the composting methods and with composting time. The evolution of total nitro-
                gen and germination index also varied significantly (P ≤ 0.001) with time, but their variation among the composting 
                methods was not significant (P > 0.05). Except for PC, all other methods of composting satisfied all the indices for 
                stability/maturity of compost at the 60th day of sampling; whereas PC achieved the critical limit values for most of the 
                indices at the 80th day. A highly significant differences (P ≤ 0.001) were noted among the composting methods with 
                regard to their effectiveness in eliminating pathogens (faecal coliforms and helminth eggs). The WVC method was 
                most efficient in eliminating the pathogens complying with WHO’s standard.
                Conclusion:  Turned windrow composting and composting involving earthworms hastened the biodegradation 
                process of organic wastes and result in the production of stable compost earlier than the traditional pit method of 
                composting. The WVC method is most efficient in keeping the pathogens below the threshold level. Thus, elimination 
                of pathogens from composts being a critical consideration, this study would recommend this method for compost-
                ing organic wastes involving human excreta.
               *Correspondence:  tesfata.menge@gmail.com 
               1 School of Natural Resources Management and Environmental Sciences, 
               Haramaya University, P.O.Box 138, Dire Dawa, Ethiopia
               Full list of author information is available at the end of the article
                                              © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License 
                                              (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 
                                              provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, 
                                              and indicate if changes were made.
                        et al. Environ Syst Res  (2017) 6:5 
               Mengistu                                                                                                          Page 2 of 16
                 Keywords:  Composting, Faecal coliform, Faecal sludge, Helminth egg, Municipal solid waste, Maturation, Sanitization, 
                 Stabilization, Vermicomposting
               Background                                                      substances or pathogens they may contain (Garcia et al. 
               As in many other cities of the developing countries, the        1993). Application of raw wastes may inhibit seed germi-
               rapid urbanization and high population growth of Dire           nation, reduce plant growth and damage crops by com-
               Dawa (Ethiopia’s 2nd largest city) have resulted into a sig-    peting for oxygen or causing phytotoxicity to plants due 
               nificant increase in generation of wastes from domestic         to insufficient biodegradation of organic matter (Brewer 
               and commercial activities, posing numerous questions            and Sullivan 2003; Cooperband et al. 2003). Moreover, 
               concerning the adequacy of the current waste manage-            the reuse of untreated faeces for agricultural purposes 
               ment systems, and their associated environmental, eco-          can cause a great health risk, because a great number of 
               nomical and social implications. A report by Beneberu           pathogens such as bacteria, viruses and helminthes can 
               et al. (2012) depicted that, despite the great efforts made     be found in human excreta (Gallizzi 2003). Therefore, 
               by the Dire Dawa city municipality, it has been hardly          the management of urban solid wastes involving human 
                                                                               excreta for recycling in agriculture should necessar
               possible to meet the ever-increasing waste management                                                                      -
               service demand of the city adequately and effectively. The      ily incorporate sanitization, stabilization and matura-
               per capita waste generation rate of the city is reported        tion aspects to minimize potential disease transmission 
                                 −1                                            and to obtain a more stabilized and matured product for 
               to be 0.3 kg day     and the city generates an estimated 
               quantity of 77 tonnes of solid wastes per day (Commu            application to soil (Carr et al. 1995).
                                                                          -
               nity Development Research 2011). The same report indi-            Composting and vermicomposting are two of the best-
               cated that, as there is very limited or no effort to recycle,   known processes for biological stabilization of solid 
               reuse or recover the waste that is being generated; waste       organic wastes by transforming them into a safer and 
               disposal has been the major mode of waste management            more stabilized material that can be used as a source of 
                                                                               nutrients and soil conditioner in agricultural applica
               practice. It has been observed that the indiscriminate                                                                     -
               dumping of wastes into the landfill is resulting in unex        tions (Lazcano et al. 2008; Bernal et al. 2009; Domínguez 
                                                                          -
               pectedly faster filling up of the city’s sanitary landfill      and Edwards 2010). Composting involves the accelerated 
               which would, thus, likely be abandoned in the near future       degradation of organic matter by microorganisms under 
               than anticipated 30 years (Beneberu et al. 2012).               controlled conditions, in which the organic material 
                 In addition to the municipal solid wastes (MSW), the          undergoes a characteristic thermophilic stage that allows 
               human excreta also constitute a significant component           sanitization of the waste by elimination of pathogenic 
               of wastes generated from Dire Dawa city. Faecal sludge          microorganisms (Lung et al. 2001). Vermicomposting, on 
                                                                               the other hand, is emerging as the most appropriate alter
               (FS) accumulating in the commonly used on-site sanita                                                                      -
                                                                          -
               tion systems are periodically collected and dumped indis-       native to conventional aerobic composting (Yadav et al. 
               criminately into its well-engineered sludge dewatering          2010) and it involves the bio-oxidation and stabilization 
               and drying bed. The faecal sludge, after being dried in the     of organic material by the joint action of earthworms and 
               beds, since it has no purpose in Dire Dawa, was observed        microorganisms (Lazcano et  al. 2008). More recently, 
                                                                               combining thermophilic composting and vermicompost
               to be excavated from the drying beds and disposed in the                                                                   -
               landfill site. It is, therefore, of paramount importance to     ing has been considered as a way of achieving stabilized 
                                                                               substrates (Tognetti et al. 2007). Thermophilic compost
               establish economically viable, environmentally sustaina-                                                                   -
               ble and socially acceptable method of waste management          ing results in sanitization of wastes and elimination of 
               for the sustainable development of the city.                    toxic compounds while the subsequent vermicomposting 
                 Bundela et al. (2010) suggested that agricultural appli       reduces particle size and increases nutrient availability 
                                                                          -
               cation of organic solid wastes, as nutrient source for          (Mupondi et al. 2010).
                                                                                 Composting methods differ in duration of decompo
               plants and as soil conditioner, is the most cost effective                                                                 -
               municipal solid waste (MSW) disposal option because             sition and potency of stability and maturity (Iqbal et al. 
               of its advantages over traditional means, such as land          2012). Due to the ecological and health concerns of 
               filling or incineration. Though, human wastes are a rich        human wastes, extensive research has been conducted to 
               source of organic matter and inorganic plant nutrients          study the composting process and to evaluate methods to 
               and therefore used to support food production, their use        describe the stability, maturity and sanitation of compost 
               without prior stabilization represents a high risk because      prior to its agricultural use (Brewer and Sullivan 2003; 
               of the potentially negative effects of any phytotoxic  Zmora-Nahum et al. 2005). Although several studies have 
               Mengistu et al. Environ Syst Res  (2017) 6:5                                                                         Page 3 of 16
               addressed the optimization of composting, vermicom-               and Wuta (2013). The shredded MSW and dried faecal 
               posting or composting with subsequent vermicomposting             sludge were then mixed manually in a 2:1 mix ratio. The 
               of various organic wastes (Dominguez et al. 1997; Freder          earthworm species (Eisenia foetida) were obtained from 
                                                                            -
               ickson et al. 1997; Ndegwa and Thompson 2001; Tognetti            Haramaya University. Matured earthworms and their 
               et al. 2005, 2007; Lazcano et al. 2008; Mupondi et al. 2010),     cocoons were brought to Dire Dawa, where they were 
               information on the effectiveness of the different com             made to be multiplied (reared) for about 4 months using 
                                                                            -
               posting methods on biodegradation and sanitization of             cow dung as medium.
               mixtures of MSW and dried faecal sludge (DFS) is scant. 
               Moreover, regarding the sanitization efficiency of the dif-       Composting treatments
               ferent composting techniques, controversial reports have          The methods of composting tested were: turned wind-
               been presented in different literatures. Several researchers      row composting (WC), pit composting (PC) (a compost-
               reported the effectiveness of thermophilic composting in          ing method commonly practiced by farmers of the study 
               eliminating pathogenic organisms (Koné et al. 2007; Vin           area), vermicomposting (VC) and combined windrow 
                                                                            -
               nerås 2007; Mupondi et al. 2010). However, a few studies          and vermicomposting (WVC). The composting was done 
               on composting of source-separated faeces claimed that a           in outdoor but under shade condition. Three replicates of 
               sufficiently high temperature for pathogen destruction is         each of the four composting methods were made being 
               difficult to achieve (Bjorklund 2002; Niwagaba et al. 2009).      arranged in a completely randomized block design. Each 
               Similarly, in vermicomposting, some studies have pro-             composting pile was covered with a layer of dry grass 
               vided evidence of suppression of pathogens (Monroy et al.         (5 cm) to prevent excessive loss of moisture.
               2008; Rodriguez-Canche et al. 2010; Eastman et al. 2001), 
               while others (Bowman et al. 2006; Hill et al. 2013) dem-            a)  Windrow composting: In the thermophilic compost
                                                                                                                                              -
               onstrated the insignificant effect of vermicomposting in                                                             3
                                                                                      ing, the homogenized feedstock of 1  m  volume 
               reducing Ascaris summ ova as compared to composting                    (~275 kg dry weight) was heaped into conical piles 
               without worms. The effectiveness of vermicomposting for                              2
                                                                                      in about 1 m  area after being wetted with water to 
               pathogen destruction was still remaining unclear due to                50–60% (Maso and Blasi 2008).
               conflicting information in the literature (Hill et al. 2013);       b) Pit composting a homogenized feedstock with the 
               the present scenario thus, calls for further exploration.              same moisture level as in ‘a’ was filled in a pit with 
               Accordingly, the present study attempted to investigate                dimension of 1 × 1 × 1 m (length width and depth).
               the comparative effectiveness of four different methods of          c)  Vermicomposting: Vermicomposting was performed 
               composting viz. windrow composting (WC), Vermicom
                                                                            -         in vermicompost bed measuring 1  ×  1  ×  0.3  m 
               posting (VC), pit composting (PC), and combined wind-                  (length, width and height respectively) framed with 
               row and vermicomposting (WVC) on the stabilization,                    bricks where the walls and bottom of the structure 
               maturation and sanitization of mixtures of MSW and                     was lined with polyethylene sheet. In order to drain 
               dried faecal sludge.                                                   the excess water, the bottom of the polyethylene sheet 
               Methods                                                                was made to have tiny holes. Mature earthworms (E. 
                                                                                      foetida) were introduced at the recommended stock
                                                                                                                                              -
               Experimental site, wastes and earthworms utilized                      ing rate of 250 adult worms per 20 kg of bio-waste 
               The study was carried out at Dire Dawa, a city in East-                (Padmavathiamma et al. 2008). The moisture content 
               ern Ethiopia located at 9° 6′ N, 41° 8′ E and at an altitude           of the material was maintained between 70 and 80% 
               of 1197 m above sea level. The Municipal solid organic                 (Maso and Blasi 2008).
               waste used in this study was obtained from a door-to-               d) Combined windrow composting and vermicompost-
               door waste collection service provided by the Sanita-                  ing: Thermophilic composting of the wastes was done 
               tion and Beautification Agency (SBA) of Dire Dawa city,                in same manner as in windrow composting and the 
               in which the wastes were collected from various loca-                  piled substrate was allowed to be composted until 
               tions in the city. The dried faecal cake which was about               the temperature was dropped to mesophilic phase. 
               to be excavated from the drying bed and dumped to the                  After the completion of the thermophilic phase (15 
               landfill site was collected from the dumping site. The                 days after the initiation of the process), the subse-
               garbage receives mixed organic and inorganic domestic                  quent vermicomposting continued using earthworms 
               wastes, upon arrival to the composting site; the wastes                (E. foetida) as described under vermicomposting 
               were spread flat on the ground and sorted manually into                (Mupondi et al. 2010).
               organic and non-organic fractions. All the compostable 
               components were shredded manually into small pieces of              The pilled heaps in WC were turned and mixed 
               particle sizes ranging from 3 to 5 cm as described by Pisa        every week while the substrates in other methods of 
                       et al. Environ Syst Res  (2017) 6:5 
               Mengistu                                                                                                     Page 4 of 16
               composting were left intact. The moisture content of each    used (Zucconi et al. 1981). A 10 g of screened compost 
               pile was checked every week and adjusted accordingly.        sample was shaken with 100 ml of distilled water for an 
               The compost mass in WVC received the same treatment          hour, then the suspension was centrifuged at 3000 rpm 
               as WC and VC during the thermophilic and mesophilic          for 15 min and the supernatant was filtered through a 
               phases of composting respectively. The temperatures in       Whatman No 42 filter paper. Number 2 Whatman filter 
               each heap was measured daily with a temperature probe        paper was placed inside a sterilized petri dish and wet
                                                                                                                                     -
               from randomly selected places (centre, bottom and top)       ted with 9 ml of the extract, 30 tomato seeds (Solanum 
               throughout the process.                                      esculentum L.) were placed on the paper. Nine ml of dis-
                                                                            tilled water was used as a control and all experiments 
               Compost sampling and analysis                                were run in triplicate (Wu et al. 2000). The petri dishes 
               Sampling procedure                                           were kept in the dark for 4 days at room temperature. 
               To evaluate the various physical, chemical and biological    At the end of the 4th day, the germination index (GI) 
               transformations of the compost, representative samples       was calculated using the following formula (Selim et al. 
               were collected from four different points of the com-        2012).
               post pile (bottom, surface, side and centre) of each pile at    
               every 20 days (20, 40, 60, 80 and 100 days). All the sam
                                                                       -         GerminationIndex %
               ples were sealed in plastic containers and transported                                ( )
                                                                                       Seedgermination % × rootelongation %
               immediately to the laboratory using an ice box. Up on                                     ( )                    ( )
                                                                                    =
               their arrival to the laboratory, the samples were stored in                                 100
               a refrigerator at 4 °C until they were analysed. Physico-    Faecal coliform analysis
               chemical and microbial analyses were carried out at Har
                                                                       -    For the determination of faecal coliforms in the ini-
               amaya University following standard procedures.              tial raw materials and in the composts the procedures 
                                                                            described by Mupondi et  al. (2010) were employed. 
                                                                            Aseptically weighed 10 g samples of either waste mix
               Physico‑chemical analysis of compost                                                                                  -
               Moisture content was determined as weight loss upon          ture or fresh compost were added to 90 ml of distilled 
               drying in an oven at 105 °C to a constant weight (Lazcano    water previously autoclaved at 121 °C for 15 min and the 
               et al. 2008). Total nitrogen (TN) and organic carbon (OC)    suspensions were then mixed using a blender to ensure 
               were determined using dried compost samples which  thorough mixing. Additional serial dilutions were made 
               were ground to pass through a 2-mm sieve as described        up to 10−6
                                                                                       . A 0.1 ml aliquot of each dilution was plated, 
               by Pisa and Wuta (2013). For the determination of total N,   in triplicate, in appropriate media-Violet Red Bile Agar 
               samples were decomposed using concentrated H SO  and         (VBA) (Vuorinen and Saharinen 1997). The plates were 
                                                               2   4        then maintained in an incubator at a constant tempera
               catalyst mixture in Kjeldahl flask and subsequently, N con-                                                           -
               tent in the digest was determined following steam distilla-  ture of 44 °C for 24 h. For each of the treatment samples 
               tion and titration method (Bremner and Mulvaney 1982).       the numbers of faecal coliforms were expressed as log  
                                                                                                                                    10
               Organic carbon was estimated by dichromate wet diges-        CFU (colony forming unit) per gram of fresh sample and 
               tion and rapid titration methods as described by Walkley     average values were calculated.
               and Black (1934). Total volatile solids was determined as 
               weight loss on ignition at 550 °C for 4 h in a muffle fur
                                                                       -    Helminth eggs recovery
               nace as described by Lazcano et al. (2008). Ammonium N       The determination of helminth egg in this study was 
                   +
               NH
               (   4–N) was determined from 0.2 ml aliquot of 0.5 M         done based on the US EPA protocol (1999) modified by 
               K SO  extract of the filtrate after colour development       Schwartzbrod (2003). The analysis was carried out in 
                2   4                                              −
                                                               NO           triplicate for the initial raw waste and compost samples. 
               with sodium nitroprusside, whereas, Nitrate N (     3–N) 
               was determined in a separate aliquot (0.5 ml) after colour   The concentration of number of eggs per gram of dry 
               development with 5% salicylic acid using a spectropho        weight of sample was computed according to the follow
                                                                       -                                                             -
               tometer (Okalebo et al. 2002). Analysis for pH and electri-  ing formula (Ayres and Mara 1996):
               cal conductivity (EC) were performed in extracts of 1:10               Y     M
               (w/v) compost: distilled water ratio as described by Nde
                                                                       -         N=C × S,
               gwa and Thompson (2001). The C:N ratio was calculated 
               using the individual values of OC and TN.                    where N = number of eggs per gram of dry weight of 
                                                                            sample, Y  =  number of eggs in the McMaster slide 
                                                                            (mean of counts from three slides), M = estimated vol
               Compost phytotoxicity test                                                                                            -
               For determining compost phytotoxicity, a modified  ume of product at final centrifugation, C = volume of the 
               phytotoxicity test employing seed germination was  McMaster slide, S = dry weight of the original sample.
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...Mengistu et al environ syst res doi s research open access comparative effectiveness of different composting methods on the stabilization maturation and sanitization municipal organic solid wastes dried faecal sludge mixtures tesfu heluf gebrekidan kibebew kibret kebede woldetsadik beneberu shimelis hiranmai yadav abstract background is one integrated waste management strategies used for recycling into a useful product vary in duration decomposition potency stability matu rity sanitation this study was aimed to investigate four viz windrow wc vermicomposting vc pit pc combined wvc treatments were arranged completely randomized block design with three replica tions changes physico chemical biological characteristics compost examined at days inter val using standard laboratory procedures analysis variance performed sas software significant differences determined fisher lsd test p level nh results evolution temperature ph ec no ratio oc c n total volatile solids varied significantly among...

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