Assessment of Disintegration of Compostable Bioplastic Bags by Management of Electromechanical and Static Home Composters

sustainability

Article Assessment of Disintegration of Compostable Bioplastic Bags by Management of Electromechanical and Static Home Composters

Lorenzo Maria Caﬁero 1,* , Margherita Canditelli 1, Fabio Musmeci 1, Giulia Sagnotti 2 and Riccardo Tufﬁ 1

1 Department for Sustainability, ENEA—Casaccia Research Center, 00123 Rome, Italy; [email protected] (M.C.); [email protected] (F.M.); riccardo.tufﬁ@enea.it (R.T.) 2 Technical Assistance Unit, Sogesid c/o Ministry of the Environment, Land and Sea, 00147 Rome, Italy; [email protected] * Correspondence: lorenzo.caﬁ[email protected]; Tel.: +39-06-3048-3332

Abstract: Interest in small scale composting systems is currently growing, and this in turn raises the question of whether the compostable bags are as suitable as in industrial composting facilities. In this work the physical degradation percentage of compostable lightweight bioplastic bags in two types of composter was examined. The main goal was to understand whether the mild biodegrading conditions that occur in electromechanical or static home composters are sufﬁcient to cause effective bag degradation in times consistent with the householders’ or operators’ expectations. Bags, which complied with standard EN 13432, were composted in a number of 600 L static home composters, which were run in different ways (e.g., fed only with vegetables and yard waste, optimizing the humid/bulking agent fraction, poorly managed) and a 1 m3 electromechanical composter. Six months of residence time in static home composters resulted in 90–96 wt% degradation depending on the man-

agement approach adopted, and two months in the electromechanical composter achieved 90 wt%. In the latter case, three additional months of curing treatment of the turned heaps ensured complete

Citation: Caﬁero, L.M.; Canditelli, M.; physical degradation. In conclusion, in terms of the level and times of physical degradation, the use Musmeci, F.; Sagnotti, G.; Tufﬁ, R. of compostable bioplastic bags appeared promising and consistent with home composting practices. Assessment of Disintegration of Compostable Bioplastic Bags by Keywords: composting; electromechanical composter; static home composter; compostable bioplastic Management of Electromechanical bags; physical degradation and Static Home Composters. Sustainability 2021, 13, 263. https://doi.org/10.3390/su13010263 1. Introduction Received: 4 December 2020 With over 6 million tons of organic waste collected and treated using recycling op- Accepted: 25 December 2020 eration (composting and anaerobic digestion) in 2017 [1], Italy achieved a satisfactory Published: 30 December 2020 performance level among European countries in terms of organic waste management [2].

Publisher’s Note: MDPI stays neu- One important contribution to this achievement was compostable bioplastic bags for tral with regard to jurisdictional clai- the separate collection of organic waste. In fact, compostable bioplastic bags decrease ms in published maps and institutio- the contamination of the final product (i.e., compost) with macro or micro fossil plastics nal affiliations. resulting from the use of conventional, not biodegradable, plastic shopping bags and save a not negligible portion of the organic waste with fossil plastics, which is removed by sorting systems [3]. Bioplastics represent an emerging sector: 2.11 Mt of bioplastics were produced Copyright: © 2020 by the authors. Li- throughout the world in 2019 and the global production capacities are predicted to reach censee MDPI, Basel, Switzerland. approximately 2.42 Mt by 2024 [4]. Flexible packaging remains the largest application field This article is an open access article for bioplastics, accounting for 43 wt% of the total bioplastics market in 2019 [4]. distributed under the terms and con- In Italy, the separate collection of organic waste must be done with reusable containers ditions of the Creative Commons At- or with industrially compostable bags that are certified in accordance with UNI EN 13432- tribution (CC BY) license (https:// 2002 [5] and national legislation [6]. Furthermore, in 2011, single-use plastic bags at creativecommons.org/licenses/by/ cash registers, followed by single-use fruit and vegetable plastic bags (whose thickness is 4.0/).

Sustainability 2021, 13, 263. https://doi.org/10.3390/su13010263 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, 263 2 of 17

below 50 microns) in 2018, were banned in Italy and replaced with compostable bioplastic bags [6–8]. Recently, the possibility of treating organic waste in small-scale composting facilities has raised quite a lot of interest [9], especially in order to serve those geographical areas where remote and small communities (islands, mountain villages, etc.) lie away from the main logistic routes. In these cases, the municipal waste management companies have to employ costly waste collection and transportation systems; however, community and home composting of organic waste could be a cheaper and more sustainable alternative. Then, the use of compostable bioplastic bags could be a hygienic alternative that replaces standard waste bags in home and community composting too. It must be said that, in spite of the shared name, industrial, community, and home composting involve different process intensities. Therefore, although the biodegradability of compostable bioplastic bags in industrial facilities is well ascertained, this is not the case in small scale composting installations [10]. The different conditions in home and industrial composting may lead to a significant difference in biodegradation of bioplastics. For example, Rudnik and Briassoulis [11] studied the degradation behavior of polylactic acid (PLA) plastic under home composting conditions in an 11 month period: PLA showed a very slow degradation, which was attributable to the process temperature, which was lower than that of the industrial-scale trial, which could be carried out with a higher temperature range. Needless to say, the low effectiveness of home composting is accepted by householders when the undigested residues come from garden or kitchen waste, but it could cause complaints when packaging is still found not to have completely degraded in the static home composter, especially when that packaging is expected to be “compostable”. Community composting comes between home and industrial composting [9]. In Italy, this practice is encouraged and legally defined [12,13] as “composting of the organic fraction of municipal waste collectively carried out by numerous domestic and non-domestic users to produce compost for use by the contributing users”. The process is carried out using electromechanical composters (ECs) provided with forced air circulation, periodic turning of the organic mass, and temperature monitoring, which ensure that the bio-oxidation stage is accomplished. Generally, ECs are classified on the basis of the number of chambers and turning system [9]. In any case, ECs should be provided with an open space in which the curing phase be completed. Partial, stabilized, organic matter put out by the EC is arranged in a heap under a roof cover and periodically turned. The review paper of Bruni C. et al. [14] concerning the spread of community composting confirmed that this practice is at its beginning and mentions just some experiences out of Italy, two in Spain, two in Ireland, and one in Lithuania. The ECs used in that case had an input capacity from 10 to 26 t y−1 and a reactor volume from 0.5 m3 to 2 m3. The use of compost as a microbial community and an aggressive ambient for the biodegradation or disintegration of different bioplastics has been extensively studied during the past decade, and biodegradability of bioplastics can be strongly attributed to the environment conditions (such as temperature, pH, and moisture content) and to the chemi- cal structure of the polymer [15]. However, the large majority of these studies were carried out in a controlled composting environment using a laboratory-scale test [16–18] and to the best of our knowledge, there is a shortage of specific studies on the degradation of compostable bioplastic bags under home and community composting conditions that sim- ulated a real process (without controlling the organic waste feed, loading the composters gradually, etc.). Furthermore, although most municipalities or composting associations pro- vide guidelines for home and community composting, the establishment of a standardized process remains very challenging because these kinds of composting are not professional waste management activities, but practices carried out on private premises, or they are not organized and therefore very difficult to monitor. This study was undertaken to get a better understanding of the feasibility of composting single-use, lightweight, compostable, bioplastic bags (the single-use bags for fruit and vegetables) in home and community composting facilities (static home composters and Sustainability 2020, 12, x FOR PEER REVIEW 3 of 17

This study was undertaken to get a better understanding of the feasibility of composting single-use, lightweight, compostable, bioplastic bags (the single-use bags for fruit and vegetables) in home and community composting facilities (static home composters and EC, respectively) in the real management of the food waste produced by a canteen. This feasibility was expressed as the total physical degradation of compostable bioplastic Sustainability 2021, 13, 263 3 of 17 bags at the end of the composting process.

EC,2. Materials respectively) and in the Methods real management of the food waste produced by a canteen. This feasibility2.1. Experimental was expressed Setup as the total physical degradation of compostable bioplastic bags at the end of the composting process. 2.1.1. Community Composting 2. Materials and Methods 2.1. ExperimentalIn this work, Setup two types of ECs were used. The Joraform JK5100 EC (see Figure 1) is 2.1.1.equipped Community with Composting a shredder at the feed hopper, a double chamber with a total volume of 2 m3,In and this a work, turning two types system of ECs consisting were used. Theof an Joraform internal JK5100 rotating EC (see Figureshaft 1coupled) is with peripheral equippedblades. withFresh a shredderorganic at waste the feed mixed hopper, with a double bulking chamber agent with awas total continuously volume of fed into the first 2 m3, and a turning system consisting of an internal rotating shaft coupled with peripheral blades.chamber Fresh for organic the wastefirst mixed15 days; with bulkingafter that, agent wasthe continuouslymaterial was fed into transferred the ﬁrst into the adjacent chamberchamber, for thewhich ﬁrst 15allowed days; after it that,to be the transforme material wasd transferred for a further into the 15 adjacent days without coming into chamber,contact whichwith allowedfresh material. it to be transformed The aeration for a further and 15 turning days without were coming electronically into controlled, but contact with fresh material. The aeration and turning were electronically controlled, but thethe temperature temperature inside inside the chamber the chamber was not. After was a fewnot. days After the testa few was stoppeddays the for test was stopped for reasonsreasons that that will bewill explained be explained in the Section in the 3.1. Section 3.1.

FigureFigure 1. The1. The Joraform Joraform JK5100 electromechanicalJK5100 electromechanical composter (EC). composter (EC).

The SustEco, model BigHanna T60, which is shown in Figure2, is an EC that has no internalThe mechanical SustEco, components model inBigHanna motion and T60, is continuously which is fed. shown It consists in Figure of a single 2, is an EC that has no 1internal m3 rotating mechanical cylindrical chamber. components A fan ensures in motion air ventilation and throughis continuously the organic matter fed. It consists of a single inside1 m3 therotating composter cylindrical and the exhaust chamber. air is sent A tofan a biofilter ensures for odorair ventilation removal. The through the organic composter has three thermocouples installed at three points along the axis of the cylinder, whichmatter monitor inside the the temperature composter of the and composting the exhaust organic matter.air is sent On the to opposite a biofilter side of for odor removal. The thecomposter feeding system, has anthree exit holethermocouples allows the partially installed stabilized at organic three waste points to come along out the axis of the cylin- andder, not which accumulate monitor in the chamber.the temperature Semi stabilized of the compost composting continuously organic comes out matter. of On the opposite the EC as a result of overflow and is moved to a heap, where it undergoes a curing stage forside a number of the of feeding weeks. system, an exit hole allows the partially stabilized organic waste to comeThe out input and capacity not of theaccumulate two ECs is 25–30 in the kg day chambe−1 (up tor. 10 Semi households stabilized of 4 people compost continuously each)comes and out the fillingof the grade EC isas 60–70%, a result which of correspondsoverflow toand a holdup is moved of 350–450 to a kg.heap, where it undergoes a 2.1.2.curing Home stage Composting for a number of weeks. TheThe EuroSintex input capacity (Eurosintex of srl, the Bergamo, two ECs Italy), is “Angolo 25–30 Verdekg day 800”−1 (up model to of 10 static households of 4 people homeeach) composters, and the whichfilling has grade an octagonal is 60–70%, basis, and which a volume corresponds capacity of 1200 to La was holdup used of 350–450 kg. (Figure3). Air oxygen passed through holes drilled in the side walls and through a pallet, on which the composters were mounted. Sustainability 2020, 12, x FOR PEER REVIEW 4 of 17

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Figure 2. The BigHanna T60 EC.

2.1.2. Home Composting The EuroSintex (Eurosintex srl, Bergamo, Italy), “Angolo Verde 800” model of static home composters, which has an octagonal basis, and a volume capacity of 1200 L was used (Figure 3). Air oxygen passed through holes drilled in the side walls and through a FigureFigure 2. 2.The The BigHanna BigHanna T60 T60 EC. EC. pallet, on which the composters were mounted. 2.1.2. Home Composting The EuroSintex (Eurosintex srl, Bergamo, Italy), “Angolo Verde 800” model of static home composters, which has an octagonal basis, and a volume capacity of 1200 L was used (Figure 3). Air oxygen passed through holes drilled in the side walls and through a pallet, on which the composters were mounted.

FigureFigure 3. 3.The The Eurosyntex Eurosyntex Angolo Angolo Verde Verde static static home home composters. composters. 2.1.3. Compostable Bioplastic Bags The compostable bioplastic bags used in the experimental work are made of a patented biodegradable and compostable starch and polyester-based plastic, sold under the trade- markFigure Mater-bi 3. The Eurosyntex (Figure4 ).Angolo These Verd bagse static are home manufactured composters. by Industria Plastica Toscana Sustainability 2020, 12, x FOR PEER REVIEW 5 of 17

2.1.3. Compostable Bioplastic Bags Sustainability 2021, 13, 263 5 of 17 The compostable bioplastic bags used in the experimental work are made of a patented biodegradable and compostable starch and polyester-based plastic, sold under the trademark Mater-bi (Figure 4). These bags are manufactured by Industria Plastica Tos- cana(Florence, (Florence, Italy). Italy). They They comply comply with with UNI UNI EN EN 13432:2002, 13432:2002, are are marked marked with with license license No. No. 16 16issued issued by Novamont,by Novamont, and and bear bear the followingthe following labels: labels: “ok compost”, “ok compost”, “Vinçotte “Vinçotte for foods”, for foods”,“CSI High “CSI performance”. High performance”. A single A bag single has handles,bag has handles, weighs about weighs 5 g,about is 21 5 cm g, wideis 21 andcm wide37 cm and long, 37 andcm long, has a and thickness has a thickness of less than of 50less microns. than 50 microns.

FigureFigure 4. 4. CompostableCompostable bioplastic bioplastic bag bag used used in in the the experiments. experiments. 2.1.4. Measuring Instrumentation 2.1.4. Measuring Instrumentation The main parameters (temperature and moisture) of the composting process were The main parameters (temperature and moisture) of the composting process were periodically monitored, in order to check whether any undesired anaerobic phenomenon periodically monitored, in order to check whether any undesired anaerobic phenomenon had occurred. had occurred. In the case of the EC, the temperature measurement was made using thermocouples In the case of the EC, the temperature measurement was made using thermocouples embedded in three different zones of the cylindrical chamber: the inlet, middle, and embedded in three different zones of the cylindrical chamber: the inlet, middle, and outlet zones. The system made 12 measurements per day (one every two hours) for outlet zones. The system made 12 measurements per day (one every two hours) for each each thermocouple. thermocouple. The temperature of the organic matter in the heaps and static home composters was measuredThe temperature using TC Direct of the T-typeorganic thermocouples, matter in the heaps recording and static the mean home value composters taken fromwas measuredthe three differentusing TC points Direct (oneT-type at thethermocoup center, twoles, at recording the edge the of themean organic value matter), taken from 1 m thebelow three the different surface, points on a daily (one basis. at the center, two at the edge of the organic matter), 1 m belowThe the moisturesurface, on of thea daily organic basis. waste was monitored by taking three 200–300 g samples everyThe two–four moisture weeks of the from organic the middle waste ofwas the mo chamber—thenitored by taking samples three were 200–300 placed g insidesamples an everyoven attwo–four 105 ◦C untilweeks their from weight the middle remained of the constant. chamber—the The pH samples measurements were placed were inside made anusing oven a Hannaat 105 Instrument°C until their pH-meter, weight model remained 8424, constant. on samples The at thepH endmeasurements of the composting were madeprocesses. using Samples a Hanna of Instrument 10 g, which pH-meter, had been homogenizedmodel 8424, on and samples milled usingat the a end laboratory of the compostingcutting mill processes. (IKA, model Samples M20) wereof 10 addedg, which to 100hadmL been of homogenized distilled water, and stirred milled for using 15 min a laboratoryand left to cutting rest for mill 30 min. (IKA, The model pH of M20) the suspensionwere added was to 100 then mL measured. of distilled water, stirred for 15The min aerobic and left stabilization to rest for 30 of min. the compostThe pH of was the determinedsuspension was by means then measured. of a respiration testThe in compliance aerobic stabilization with the UNI/TSof the compost 11184-2016 was determined standard methodology by means of [ 19a respiration]. The test testwas in performed compliance by with a Costech the UNI/TS 3024 respirometer. 11184-2016 standard An extensive methodology description [19]. of The the scientiﬁctest was performedapparatus wasby a reportedCostech by3024 Adani respirometer. [20]. The An compost extensive was description considered of stable the scientific when its −1 −1 apparatusdynamic respiration was reported index by (DRI)Adani was [20]. less The than compost 500 mg was O2 consideredkg SV h stable. when its dynamic respiration index (DRI) was less than 500 mg O2 kg SV−1 h−1. 2.2. Methods 2.2. MethodsThe experiments were carried out at ENEA Casaccia Research Center, which has a dailyThe catering experiments service were that carried generates out aboutat ENEA 150 kgCasaccia of kitchen Research waste Center, from meal which leftovers has a dailyand fromcatering the operationsservice that of generates cleaning vegetablesabout 150 kg and of preparing kitchen waste the food. from A meal breakdown leftovers of andthe workfrom the is illustrated operations in of the cleaning diagram vegeta in Figurebles5 and. preparing the food. A breakdown of the work is illustrated in the diagram in Figure 5. SustainabilitySustainability2021 2020,,13 12,, 263 x FOR PEER REVIEW 66 ofof 1717

FigureFigure 5.5. BreakdownBreakdown ofof thethe work.work. Sustainability 2021, 13, 263 7 of 17

2.2.1. Community Composting and Curing The ECs were started during the first few days of June, and fed daily with 20–30 kg of kitchen waste and 2 kg of bulking material. The start-up alone entailed feeding in 30 kg of wooden pellets. After one month, when the temperature was about 40–50 ◦C, six bags, containing 1 kg of food waste each, were loaded. After a few days, the test with the Joraform JK5100 was interrupted for reasons that will be explained in Section 3.1. Food waste and bulking material continued to be loaded for 72 days. At regular time intervals (every day in the first week, then twice a week until the end), bags inside the chamber were inspected visually in order to monitor the state of degradation. These observations were documented with photographic pictures. During this period the semi-stabilized compost coming out from the composter was put onto the heap. Some considerations about residence time are needed. Preliminary tests ascertained that the organic matter did not always spend the same time inside the composter. It was observed that not less than twenty days were needed before withdrawal at the output. On the other hand, the upper end of this time range was uncertain and could last tens of days. For example, the supplier declared a treatment time of four to seven weeks was needed to obtain an “environmentally friendly peat compost” [21]. However, previous experiments [22] ascertained that a cured compost can only be obtained following a subsequent curing stage of a number of months in a turned heap. The only operating time that can be mentioned with respect to the EC is the time it takes to reach the “overflow” level, which was estimated to be not less than twenty days. In the case described here, the loading time was chosen for reasons of expediency, as it was necessary to come to a compromise between the minimum time necessary to reach the “overflow” level and the reduction in the daily load as a result of the canteen closing during the summer holidays. On this basis, it was decided that the composter should be emptied after 60 days of loading (overall 72 days, including 12 days of stoppage in the middle of August due to summer holidays). Therefore, the processing time of a single piece of bag inside the composter cannot be more than 72 days. Overall, the EC was loaded with 590 kg of organic matter and 76 kg of bulking agent. After 72 days, the EC was completely emptied and the semi-stabilized compost from the EC and from the partially formed heap and the residual bioplastic fragments were mixed together and put on to a new heap in order to complete the curing process. Once a week, the heap was turned to allow an exchange of air and watered to adjust the moisture content if this fell below 40 wt%. As described in Section 2.1.4, the temperature was monitored daily. The curing lasted three months, until the temperature inside the heap reached a steady value, close to room temperature. The stabilized condition was confirmed by means of a respiration test (Section 2.1.4).

2.2.2. Static Home Composting Static home composting was carried out between June and December, with three composters operating in order to reproduce the variability of operating conditions under which home composting might be carried out by a private householder. The first composter, which was identified with the name “Correctly Managed Composter” labelled as CMC was fed every day with 2 kg of kitchen waste and 0.2 kg of bulking agent. The second composter, which was named “Fed with Vegetables Composter” (FVC), again maintaining the weight ratio between the organic fraction and the bulking agent to 10:1, was fed every day only with vegetable scraps, with an average quantity of 1 to 4 kg per day, in order to stimulate an increase in temperature as much as possible. The third composter, which was identified with the name “Poorly Managed Composter” (PMC), was fed every day with just 2 kg of kitchen waste, which did not undergo any preparation, to which dry leaves or plant cutting were added, as necessary. The organic matter in the CMC was periodically turned and watered. Moreover, in the FVC, from time to time, if necessary, freshly chopped grass was added in order to bring about a rapid increase in temperature and sustain the biodegradation process. A bottom layer made up of dried branches and leaves (about 25 kg Sustainability 2021, 13, 263 8 of 17

weight) was prepared for all the three composters, and cured compost was added as the inoculum (about 11 kg weight) to the CMC and FVC. Bags were added in accordance with what is reported in Table1.

Table 1. Timetable of the insertions and withdrawals of compostable bioplastic bags during home composting campaign.

Date (Elapsed Time) Introduction of Compostable Bioplastic Bags 1st day 5 empty compostable bioplastic bags added to each static composter. 3 empty compostable bioplastic bags added and 2 compostable 15th day bioplastic bags ﬁlled with 1 kg of kitchen waste added to each static home composter. Compostable bioplastic bag fragments examined after completely 45th day emptying the static home composters 2 empty compostable bioplastic bags and 2 compostable bioplastic 85th day bags ﬁlled with 1 kg of kitchen waste added to each static home composter. End of the test: the static home composters were completely emptied 175th day and the compostable bioplastic bags fragments examined

2.2.3. Recovery of Compostable Bioplastic Bag Fragments On emptying any of the composters (after 72 and 45 days for the EC and the static home composters, respectively) and at the end of the composting process, all the organic matter was screened using a sieve of 5 cm and subsequently using a sieve of 2 mm in accordance with the criteria established by the ISO 16929 test method pass level [22,23]. Any bioplastic bag fragments larger than 2 mm were taken apart, cleaned of any organic particles stuck to them by means of sonication in an ultrasonic bath, dried at 40 ◦C, and weighed.

3. Results and Discussion 3.1. Experiments with the ECs As revealed in Section 2.1.1, the experiment with the Joraform JK5100 was interrupted after a few days because of clogging of the internal moving components caused by the bags wrapping around them. As a result, it was decided to stop the experiment and this EC model was judged inappropriate for the treatment of bioplastic bags. The experimental work was therefore accomplished by the BigHanna model T60 EC and Figure6 shows the trend of the temperatures in three different zones of the chamber and the moisture content during the bio-oxidation phase. During the ﬁrst 30 days, the moisture content of the feed was always more than 40 wt% with a maximum of 55 wt% on the 25th day. These high values went back to fresh fruit and vegetables, which contain a lot of water, typically consumed in the Mediterranean diet during the warm season. As observed in previous experiments, in case of management the EC, this moisture level appeared to negatively affect the evolution of the temperatures in the three chamber zones, especially in the case of the outlet zone, where the temperature fell from 63 to 45 ◦C in 18 days. In the following days, the introduction of extra pellets made it possible to reduce the excessive moisture to 30 wt%, and, consequently, to increase the temperatures. In the middle days of August (corresponding to the range of the 40th–49th days of the experiment), the research center was closed for the holidays. In this period, the temperatures fell again, reaching a minimum of less than 30 ◦C. When the research center re-opened, the organic mass looked dryer and, indeed, the moisture content had decreased to 30 wt%. When the loading of kitchen waste was regularly resumed, the temperatures in the inlet and in the middle zones rapidly increased again, but the temperature in the outlet zone remained almost constant. Generally speaking, despite the research center’s closure, the trend was good with temperatures always above 40–45 ◦C, with peaks close to 70 ◦C. Sustainability 2021, 13,Sustainability x FOR PEER2021 REVIEW, 13, 263 9 of 17 9 of 17

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Figure 6. Temperatures and moisture content of the organic waste during the experiment time in Figure 6. TemperaturesFigure 6. Temperatures and moisture and content moisture of the organiccontent waste of the during organic the waste experiment during time the in experiment the BigHanna time model in T60 the BigHanna model T60 EC (T1, inlet zone; T2, middle zone; T3, outlet zone). EC (T1, inletthe zone; BigHanna T2, middle model zone; T60 T3, EC outlet (T1,zone). inlet zone; T2, middle zone; T3, outlet zone). In the middle days of August (corresponding to the range of the 40th–49th days of In the middle Figuredays 7of shows August some (corresponding pictures taken atto various the range times of during the 40th–49th the bio-oxidation days of phase, the experiment), the research center was closed for the holidays. In this period, the tem- which help to clarify the general trend of the process. the experiment),peratures the research fell again, center reaching was closeda minimum for the of holidays.less than 30In °C.this When period, the the research tem- center As can be seen in the sequence of pictures in Figure7, the compostable bioplastic bags peratures fell again,re-opened, reaching the organic a minimum mass looked of less dryer than and, 30 °C.indeed, When the the moisture research content center had de- re-opened, theappeared organic in mass and disappeared looked dryer from and, the organic indeed, mass, the and moisture were subjected content to thehad movement de- of creasedthe rotating to 30 cylinder. wt%. When Then, the a mechanical loading of stresskitchen contributed waste was to regularly the bioplastic resumed, disintegration the tem- creased to 30 wt%. When the loading of kitchen waste was regularly resumed, the tem- peraturesas well as thein the aggressive inlet and environment in the middle established zones rapidly inside theincreased EC. The ag compostableain, but the bioplastictempera- peratures in theturebags inlet in appeared theand outlet in intactthe zone middle until remained the zones 14th almost rapidly day andconstant. increased the ﬁrst Generally large again, compostable speabut king,the tempera- despite bioplastic the bagre- ture in the outletsearchfragment zone center’s appeared remained closure, on almost the the 18th trend constant. day. was On good the Generally 23rd with day temperatures thespea ﬁrstking, compostable alwaysdespite above the bioplastic re-40–45 bag°C, search center’swithfragment closure, peaks was theclose foundtrend to 70 in was°C. the outputgood with material temperatures coming out ofalways the EC. above From this40–45 day °C, onwards, with peaks closecompostable toFigure 70 °C. 7 bioplasticshows some bags pictures that were taken open at vari or partiallyous times broken during were the bio-oxidation seen in the chamber phase, Figure 7 showswhichand more somehelp or to lesspictures clarify big fragmentsthe taken general at werevari trendous found of times the in process. the during output the material. bio-oxidation phase, which help to clarify the general trend of the process.

(A) The 1st day: a compostable bioplastic bag immersed in (B) The 4th day: a compostable bioplastic bag immersed in

the organic waste. the organic waste.

(A) The 1st day: a compostable bioplastic bag immersed in (B) TheFigure 4th 7.day:Cont. a compostable bioplastic bag immersed in the organic waste. the organic waste. Sustainability 20212021,, 1313,, x 263 FOR PEER REVIEW 10 of 17

(C) The 9th day: a compostable bioplastic bag filled with (D) The 14th day: a compostable bioplastic bag emerges food waste. near the composter outlet.

(E) The 18th day: a large compostable bioplastic bag frag- (F) The 23rd day: the first compostable bioplastic bag ment, which was temporarily removed. fragment found in the output material from the composter.

(G) The 24th day: a compostable bioplastic bag containing (H) The 26th day: a fragment of compostable bioplastic bag food waste appears broken, having lost its content of hu- film found in the middle section of the composter. mid fraction near the input section of the composter.

(I) The 30th day: a compostable bioplastic bag containing (J) The 35th day: a compostable bioplastic bag film found food waste appears open. in the output material from the composter.

Figure 7. Cont. Sustainability 2021, 13, x FOR PEER REVIEW 11 of 17

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(K) The 40th day: a compostable bioplastic bag film found (L) The 72nd day: fragments of compostable bioplastic in the output material from the composter. bags mixed with organic material during the screening. Figure 7. Sequence of pictures illustrating the evolution of the degradation of compostable bioplastic bags in the EC.

As can be seen in the sequence of pictures in Figure 7, the compostable bioplastic bags appeared in and disappeared from the organic mass, and were subjected to the movement of the rotating cylinder. Then, a mechanical stress contributed to the bioplastic disintegration as well as the aggressive environment established inside the EC. The compostable bioplastic bags appeared intact until the 14th day and the first large compostable bioplastic bag fragment appeared on the 18th day. On the 23rd day the first

compostable bioplastic bag fragment was found in the output material coming out of the (K) The 40th day: a compostable bioplastic bag film found (L) The 72nd day: fragments of compostable bioplastic EC. From this day onwards, compostable bioplastic bags that were open or partially in the output material from the composter. bags mixed with organic material during the screening. broken were seen in the chamber and more or less big fragments were found in the FigureFigure 7. 7.Sequence Sequence of of pictures picturesoutput illustrating illustrating material. the the evolution evolution of of the the degradation degradation of of compostable compostable bioplastic bioplastic bags bags in in the the EC. EC. In the middle of September, 72 days after the beginning of the test, the EC was emptiedInAs the canas middle shown be seen of in September, in Figure the sequence 8, 72 and days allof after thepictures theorganic beginning in Figuremass of (the7, the the organic test, compostable the ECmass was still bioplastic emptied in the aschamberbags shown appeared inplus Figure the in 8 organic,and and disappeared all mass the organic forming from mass theth (thee heap) organic organic was mass, massscreened and still were inusing the subjected chambera 2 mm plussieve.to the theForty-threemovement organic mass ofsample the forming rotating fragments the cylinder. heap) were wasThen, found screened a me withchanical using a total astress 2 mmweight contributed sieve. of Forty-three3.22 tog, the which bioplastic sample was fragmentsequivalentdisintegration wereto slightly as found well more withas thethan a totalaggressive 10% weight of the environment ofinitial 3.22 30 g, g which introduced. established was equivalent A insidedifference the to slightlywasEC. no-The moreticedcompostable thanin the 10% shape bioplastic of theof the initial bags fragments 30 appeared g introduced. collected intact until Alittle difference theby little14th was inday the noticedand first the 72 in first days the large shape of dailycom- of theloadingpostable fragments in bioplastic comparison collected bag little tofragment those by little fragments appeared in the ﬁrstcollected on 72the days 18th on of theday. daily last On loadingday the when23rd in comparison daythe ECthe wasfirst toemptied.compostable those fragments The formerbioplastic collected had bag rounded fragment on the edges last was day while found when the in thelatter the EC output were was “fibrous” emptied.material comingand The elongated former out of had the in roundedshape.EC. From edges this while day onwards, the latter werecompostable “ﬁbrous” biop andlastic elongated bags inthat shape. were open or partially broken were seen in the chamber and more or less big fragments were found in the output material. In the middle of September, 72 days after the beginning of the test, the EC was emptied as shown in Figure 8, and all the organic mass (the organic mass still in the chamber plus the organic mass forming the heap) was screened using a 2 mm sieve. Forty-three sample fragments were found with a total weight of 3.22 g, which was equivalent to slightly more than 10% of the initial 30 g introduced. A difference was no- ticed in the shape of the fragments collected little by little in the first 72 days of daily loading in comparison to those fragments collected on the last day when the EC was emptied. The former had rounded edges while the latter were “fibrous” and elongated in Figureshape. 8. Emptying of the composter and screening of the output material in search of compostable Figure 8. Emptying of the composter and screening of the output material in search of compostable bioplastic bag fragments. bioplastic bag fragments.

TableTable2 2summarizes summarizes the the mass mass balance balance between between the the overall overall ingoing ingoing and and outgoing outgoing organicorganic materialmaterial duringduring the the 72 72 days. days.

Table 2. Mass balance of the compostable bioplastic bags introduced into the EC after 72 days.

Compostable Bioplastic Bags Amount Weight Loss Compostable bioplastic bags initial weight (g) 30 - Residual compostable bioplastic bags weight after 72 days (g) 3.22 89 FigureResidual 8. compostableEmptying of the bioplastic composter bags and weight screening after 148 of th dayse output (g) material n.d. in search of compostable 100 n.d.:bioplastic not detected. bag fragments. The trend of the temperatures with reference to the curing process is reported in FigureTable9 from 2 thesummarizes middle of the September mass balance to the between ﬁrst days the of Decemberoverall ingoing (the 72nd and andoutgoing the 148thorganic day material respectively) during inthe comparison 72 days. to the ambient temperature. For 20 days, the temperatures were between 50 and 60 ◦C, where the periodic turning and watering of the heap was essential in order to reactivate the heap and maintain high temperatures. Sustainability 2021, 13, x FOR PEER REVIEW 12 of 17

Table 2. Mass balance of the compostable bioplastic bags introduced into the EC after 72 days.

Compostable Bioplastic Bags Amount Weight Loss Compostable bioplastic bags initial weight (g) 30 - Residual compostable bioplastic bags weight after 72 days (g) 3.22 89 Residual compostable bioplastic bags weight after 148 days (g) n.d. 100 n.d.: not detected.

The trend of the temperatures with reference to the curing process is reported in Sustainability 2021, 13, 263Figure 9 from the middle of September to the first days of December (the 72nd and the 12 of 17 148th day respectively) in comparison to the ambient temperature. For 20 days, the temperatures were between 50 and 60 °C, where the periodic turning and watering of the heap was essential in order to reactivate the heap and maintain high temperatures. In- deed, as theIndeed, cold season as the approached cold season approachedand the aerobic and potential the aerobic ran potential out, the ran effect out, of the these effect of these ◦ operations operationsbecame less became effectiv lesse, until, effective, on the until, 148th on day, the the 148th temperature day, the temperature fell below 30 fell °C. below 30 C.

Figure 9. TemperaturesFigure 9. Temperatures of the heap of measur the heaped measuredduring the during curing the stage. curing stage.

All the organicAll the material organic again material underwent again underwent 2 mm screening 2 mm and screening no larger and residual no larger residual compostablecompostable film fragments ﬁlm fragmentswere found were (Table found 2). (TableIn conclusion,2). In conclusion, the physical the physical degrada- degradation tion of the bagsof the was bags complete. was complete. Figures relatingFigures to the relating characteristics to the characteristics of the final ofproduct the ﬁnal are product reported are in reported Table 3 and in Table 3 and show completeshow aerobic complete stabilization. aerobic stabilization.

Table 3. GeneralTable 3. figuresGeneral relating ﬁgures relatingto the cure to thed mass cured after mass treatment after treatment in the in theEC. EC.

ParametersParameters Cured Heap Cured Heap pH pH 7.8 7.8 Moisture (wt%)Moisture (wt%) 45 ± 0.2 45 ± 0.2 Final appearanceFinal appearance Granular, Granular,earthlike, earthlike, Odour OdourAgreeable Agreeable −1 −1 DRI (mg DRIO2 kg (mg SV O−1 2hkg−1) SV h ) 461 461

3.2. Home Composting Table4 shows the mass balance and all the parameters measured for each composter after six months. Following the different management approaches, 358 kg was loaded into the CMC, 448 kg into the FVC, and 265 into the PMC. The yield in “compost” considered as the residual mass minus the bulking agent and the inoculum, divided by the overall quantity of food loaded was 8 wt% for the CMC, 20 wt% for the PMC, and 24 wt% for the FVC. These results demonstrate that, when supported by a sufﬁciently high room temperature, the process was effective. The lower yield of the FVC was due to a remark- able moisture content bound to the vegetable input, which in some way greatly reduced the biodegradation process. This was conﬁrmed both by the temperature trend, which we comment on further, below, and by pH and moisture analysis on the last day of the experiments. Considering the pH, all the examined composts showed values above 8 and it was observed that the treatment needed additional curing times. The moisture of the CMC, of 50 wt% fell to within the range recommended by Italian Environmental Protection Sustainability 2021, 13, 263 13 of 17

Agency [24], and for the remaining two composters the values exceeded 75 wt%. In the case of PMC, this was an indication of a weak activation of the aerobic process, which did not increase the temperature, allowing the water content to evaporate. The appearance of the organic material removed from the three composters at the end of the experiments was the most signiﬁcant indication of which composter had been used: in the CMC, the product appeared grainy and powdery, mulchlike, and gave off an agreeable odor of mold and earth; the material removed from the FVC was dark, very humid and lumpy, and had an odor like that of rotten fruit; ﬁnally, the PMC looked heterogeneous with large lumps of sludge-like material mixed with granular mulch, while the smell was pungent and similar to rotten fruit.

Table 4. General ﬁgures relating to the management of the three static home composters.

Parameters CMC FVC PMC Total loaded food fraction (kg) 292 377 258 Total loaded bulking agent (kg) 55 60 7 Inoculum, i.e., cured compost (kg) 11 11 0 Watering (kg) 55 16 0 Total loaded amount (kg) 358 448 265 Total withdrawn amount (kg) 89 162 58 pH 8.4 9.2 8.7 Moisture (wt%) 50 ± 20 75 ± 3 73 ± 3 Appearance Mixed mulch and cuttings Dark, very humid Mixed sludge Odor Agreeable Rotten fruit Pungent smell/rotten fruit

Figures 10–12 below show the temperature trend for the three composters. The ex- Sustainability 2021, 13, x FOR PEER REVIEW 14 of 17 perimental work, which started at the end of the spring season, beneﬁtted from the warm environmental temperatures of June–September, which were well above 25 ◦C.

Figure 10.Figure Trend 10.of temperaturesTrend of temperatures in the correctly in the correctlymanaged managedcomposter composter (CMC). (CMC). For the CMC, the difference between the average and ambient temperature remained For the CMC, the difference◦ between the average and ambient temperature remained aroundaround 5–10 °C, 5–10 andC, maximum and maximum temper temperatureature managed managed to achieve to achieve very veryhigh highval- values, even 20 ◦C, well above the ambient temperature. It is interesting to note maximum temperature ues, even 20 °C, well above the ambient temperature. It is interesting to note maximum peaks of 50 ◦C, with ambient temperatures near to 10 ◦C. This indicates that there was temperature peaks of 50 °C, with ambient temperatures near to 10 °C. This indicates that a well-established composting process in the CMC. there was a well-established composting process in the CMC. In the FVC (Figure 11), the average temperatures during the June–August period were well above those of the CMC in the same period. Around the end of August, a temperature decreases due to the high moisture content of the vegetable-rich feed, followed by a rapid increase when 10 kg of finely chopped grass was added, was seen.

Figure 11. Trend of temperatures in the fed with vegetables composter (FVC).

In the autumn period, unlike the CMC, we noted a progressive decrease following the ambient temperature trend with no upturn. The temperatures stabilized at around 20 °C in the October–November period. Sustainability 2021, 13, x FOR PEER REVIEW 14 of 17

Figure 10. Trend of temperatures in the correctly managed composter (CMC).

For the CMC, the difference between the average and ambient temperature re- Sustainability 2021, 13,mained 263 around 5–10 °C, and maximum temperature managed to achieve very high val- 14 of 17 ues, even 20 °C, well above the ambient temperature. It is interesting to note maximum temperature peaks of 50 °C, with ambient temperatures near to 10 °C. This indicates that there was a well-established composting process in the CMC. In the FVC In(Figure the FVC 11), (Figure the average 11), the temperatures average temperatures during the during June–August the June–August period period were were well abovewell above those those of the of CMC the CMC in the in the same same period. period. Around Around the the end end of August,August, aa temperature temperaturedecreases decreases due due to to the the high high moisture moistu contentre content of theof the vegetable-rich vegetable-rich feed, feed, followed fol- by a rapid lowed by a rapidincrease increase when when 10 kg 10 of ﬁnelykg of finely chopped chopped grass wasgrass added, was added, was seen. was seen.

Sustainability 2021, 13, x FOR PEER REVIEW 15 of 17

In addition to the warm season, the better ratio of kitchen waste to bulking agent also probably contributed to the high temperature reached by these two composters in comparison to those reached by the PMC. Figure 12 shows the trend for the PMC. During the June–August period, the composter temperature remained equal to the ambient temperature, in the October–November period, the process reached a high level of activity, achieving maximum peaks even higher than 45 °C. In none of the composters, did the interruption due to the research center closing for Figure 11. Trend of temperatures in the fed with vegetables composter (FVC). the summerFigure holiday 11. Trend influence of temperatures the evolution in the fed of with the vegetablestemperatures. composter (FVC). In the autumn period, unlike the CMC, we noted a progressive decrease following the ambient temperature trend with no upturn. The temperatures stabilized at around 20 °C in the October–November period.

Figure Figure12. Trend 12. ofTrend the temperatures of the temperatures in the poorly in the poorlymanaged managed composter composter (PMC). (PMC).

Table 5 showsIn the the results autumn relating period, to unlike the resi thedue CMC, amounts we noted of the a bags progressive in the course decrease of following the initial removalthe ambient after two temperature months of trend experiments, with no upturn. and at the The conclusion temperatures of all stabilized of the at around experiments20 after◦C six in themonths October–November of treatment. period. In addition to the warm season, the better ratio of kitchen waste to bulking agent Table 5. Physicalalso probablydegradation contributed of bags during to the the high two temperature removals of reached bag residues by these (after two 2 composters in months and 6 months, respectively, from the beginning of the test).

Compostable Bioplastic Compostable Bio- Composters Time Period of Degradation Bags Introduced Plastic Bag Resi- Type Experiments Rate (wt%) Bag Number Weight (g) dues Removed (g) First emptying (1st– 10 50 24.0 52 45th day) PMC Whole set of experiments (1st– 14 70 3.7 95 180th day) First emptying (1st– 10 50 7.6 85 45th day) FVC Whole set of experiments (1st– 14 70 7.2 90 180th day) First emptying (1st– 10 50 11.3 77 45th day) CMC Whole set of experiments (1st– 14 70 2.9 96 180th day) Sustainability 2021, 13, 263 15 of 17

comparison to those reached by the PMC. Figure 12 shows the trend for the PMC. Dur- ing the June–August period, the composter temperature remained equal to the ambient temperature, in the October–November period, the process reached a high level of activity, achieving maximum peaks even higher than 45 ◦C. In none of the composters, did the interruption due to the research center closing for the summer holiday inﬂuence the evolution of the temperatures. Table5 shows the results relating to the residue amounts of the bags in the course of the initial removal after two months of experiments, and at the conclusion of all of the experiments after six months of treatment.

Table 5. Physical degradation of bags during the two removals of bag residues (after 2 months and 6 months, respectively, from the beginning of the test).

Compostable Bioplastic Time Period of Compostable BioPlastic Bag Degradation Rate Composters Type Bags Introduced Experiments Residues Removed (g) (wt%) Bag Number Weight (g) First emptying 10 50 24.0 52 PMC (1st–45th day) Whole set of experiments 14 70 3.7 95 (1st–180th day) First emptying 10 50 7.6 85 FVC (1st–45th day) Whole set of experiments 14 70 7.2 90 (1st–180th day) First emptying 10 50 11.3 77 CMC (1st–45th day) Whole set of experiments 14 70 2.9 96 (1st–180th day)

During the first two months, the best performance was achieved by the FVC with a 85 wt% degradation rate, whereas the PMC achieved 52 wt% and the CMC 77 wt%. If we consider the whole process, which lasted six months, where a total of 14 bags, corresponding to 70 g, was added to each composter, the best performances were achieved by the CMC (96 wt%) and the PMC (95 wt%), whereas the FVC stopped at 90 wt%. This disap- pointing performance of the FVC may have been due to an excessive moisture content (and subsequent fall in temperatures) of the organic mass, which was not evaporated because of the insufficiently high ambient temperatures from September onwards. Conversely, the high temperature reached in the PMC in the second part of the test, achieved a degradation activity on the bags which resembled that of the CMC. In any case, it seems from these results that four months in the warm season is enough to complete the degradation of the compostable bioplastic bags. Unlike the test with the EC, domestic composting degraded the bags into a few rather large fragments, without clear fraying phenomena. Finally, it is important to point out that although the complete maturation of the produced composts was not confirmed, the mass balance showed a mass reduction of organic waste of 92, 76, and 80 wt% for the CMC, FVC, and PMC respectively.

4. Conclusions This study looked at the suitability of single-use lightweight compostable bioplastic bags for collecting organic waste intended for treatment in static home composters and ECs. To this end, the physical degradation of compostable bioplastic bags was evaluated under mild composting processes with the following results: • The EC provided with inside moving parts was unﬁt, as the bags caused clogging and the risk of jamming. Sustainability 2021, 13, 263 16 of 17

• Thanks to the good aerobic conditions reached during the process, the EC degraded the bags up to 90 wt% of the initial amount introduced in 72 days, and the subsequent curing process completed the physical degradation of the residual fragments. • Composting carried out by static home composters is greatly dependent on the external ambient temperature and operating conditions. In any case, a degradation of 90% to 96% was achieved, regardless of whether or not the composter was managed carefully. To conclude, these compostable bioplastic bags can be used to collect organic waste and can be treated by home and community composting, even when the composters are poorly managed. However, it is important to stress that in this study a few bags were added to a large mass of organic waste. In order to replicate a more realistic situation, we set up new experiments where all organic waste will be collected in compostable bioplastic bags and sent to composters. Finally, the compost that will be produced will undergo agronomical and ecotoxicological tests. Experiments are in progress.

Author Contributions: L.M.C. and M.C. conceived and designed the experiments; M.C., L.M.C., R.T., and F.M. carried out the experiments and analyzed the data; G.S., R.T., and L.M.C. wrote the paper. All authors have read and agreed to the published version of the manuscript. Funding: We appreciate the support of Novamont SpA who funded this research and provided compostable bioplastic bags for the experimental work. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. Data Availability Statement: Data is not publicly available, though the data may be made available on request from the corresponding author. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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