1. Introduction
More than 380,000 tons of waste are produced on a daily basis in Korean municipalities. Solid waste generation has increased in certain areas as a result of changes in consumption patterns and the life cycles of consumer products, some initiated by recycling efforts. Research indicates that over 90% of parents use disposable diapers since they are comfortable, hygienic, cost-effective and convenient (2017) [
1]. According to a life-cycle assessment of disposable diapers for babies and toddlers aged between 0 and two years, 5.87 diapers are used per child every day, which are sent to landfills or incinerators [
1,
2,
3]. Out of the 240,000 tons of used diapers generated each year in Korea, 141,000 tons (58%) are produced at daycare centers [
2,
4]. The percentage contribution of diapers to the overall weight of trash in general grew gradually to 2.1% in 2002 and is expected to reach 3.6% in 2020 [
1,
3,
5].
Most diapers are basically composite materials that contain plastics (such as polyethylene, polypropylene, etc.), cellulose fibers and super-absorbent particles, all of which are valuable resources [
1,
4]. However, all of them are incinerated or sent to landfills since they are targets for waste charges. According to the Act on the Promotion of Saving and Recycling of Resources (1993), in order to restrict the generation of waste and to prevent the waste of resources, the Minister of Environment imposed fees and collected expenses incurred from the treatment of discarded goods, materials and containers [
1,
4]. Disposable diapers are one of the items subject to waste charges since they are likely to cause problems in the management of waste [
1,
6,
7]. Currently, diaper waste is collected in waste bags and transported to the nearest resource-recovery facilities, where it is buried or incinerated without going through the process of separation [
4]. Diaper waste is disposed of on a daily basis and its environmental impacts include land use, methane production and the leaching of organic compounds into the soil and groundwater [
8,
9,
10,
11]. In 2011, Deloitte conducted a study comparing the environmental performance of Knowaste’s Absorbent Hygiene Products (hereafter, AHP) recycling process to the standard UK disposal practice—namely, controlled landfill or incineration with energy recovery. The AHP process, (1) diverts AHP waste from the standard waste-disposal avenues, and (2) produces materials that can be reused to manufacture other products. Compared to landfill and incineration, AHP’s diaper-recycling process generates up to 71% fewer carbon emissions, based on an annual capacity of 36,000 metric tons of AHP waste; therefore, a recycling plant could save 22,536 metric tons of greenhouse-gas emissions per year [
12].
Along with the environmental effects, technology, social acceptance and economic feasibility also need to be taken into account in promoting the recycling of diaper waste. Regarding technology, various methods for the treatment of diapers have been investigated, such as biodegradation by activated sludge and composting, followed by recycling [
4]. Composting can be difficult to handle at municipal facilities due to several problems that can be encountered such as workers’ health and safety issues [
4]. One alternative solution is recycling technology that has already been developed and is in use in many countries such as The Netherlands, the UK and Japan. Knowaste technology is one of the methods, producing 70,000 tons/year in the Netherlands and 36,000 tons/year in the UK. The Knowaste facility has announced closure of its West Bromwich facility in the UK. Currently, the Knowaste site in the UK is no longer operational although the company is seeking an alternative site in the London area. Proctor and Gamble were also investing in diaper recycling technology in Europe and investigating the factors that influence the sustainability of diapers using life cycle assessment. Total Care, a Japanese recycling company, produces 5000 tons/year with its own technology [
13,
14,
15,
16,
17,
18].
A number of studies on policy acceptance by the public have been conducted in Korea. Mok (2006) surveyed to ascertain perceptions of the acceptability of diaper recycling. The results showed that 73% of respondents were in full agreement with participating in diaper recycling and 90% of them would do so if proper collection methods were put in place [
4,
17,
18]. In 2014, the Ministry of Environment researched the methods for diaper recycling. They analyzed collection, recycling cases and policy, then proposed collection and treatment systems. To determine the social acceptance for diaper recycling, a survey was conducted of 400 consumers using diapers. These results showed 75% of respondents in agreement with diaper recycling and 98% of them saying they would do so, if proper collection methods were employed. However, 46% of them were concerned about aspects of the collection process and sanitation matters [
4,
18].
To achieve economic feasibility in diaper recycling, the collection and transportation of diaper waste—which account for much of the cost—need to be optimized. To that end, we analyzed the results of the Scottish AHP collection trial held in 2012. The analysis included background facts, the method of the collection trial, the selection of participants and the monitoring of the trial. This review was reflected in the design of the disposable-diaper collection trial in Korea. According to research by the Korean Ministry of Environment (2014), diaper collection would be economically feasible with an optimized recycling process. However, it was difficult to secure reliable results since there were not enough data on the costs of collection and transportation, which account for much of the total cost. Therefore, it was necessary to conduct a collection test on diapers to identify unforeseen problems and cost-related factors during the collection. Thus, this study was intended to identify problems with collection and to forecast costs by performing a collection trial on daycare centers with large quantities of diapers. By discovering the factors that would improve the system and reduce the cost, this paper contributes to the economic efficiency of diaper recycling. Further, a more economically efficient diaper recycling system will appear through the monitoring of the diaper-disposal behavior of the participants. In the following section, the basic information regarding the collection trial in Scotland will be presented first; then the collection trial in Korea will be laid out in detail.
5. Conclusions
Currently, disposable diapers are subject to waste charges and thus sent to incineration or landfill, although they can be recycled. In addition, since disposable diapers contain a considerable amount of valuable and recyclable resources, the collection/transportation system and recycling process should be optimized to introduce the policy of diaper recycling. To that end, practical technology and collection efficiency should be secured. More related research work is required due to the lack of reliable positive studies. The economic feasibility of diaper recycling was analyzed by the Korea Environment Corporation in 2006 and by lawmaker Eun Su-Mi’s office in 2012. The costs of collection and transportation accounted for 15–52% of the total and their studies provided hope for attaining economic feasibility. In this regard, this study conducted a diaper waste collection trial to find the difficulties with collection and also identify the relevant cost factors for suggesting optimal methods. First, the results of the Scottish AHP collection trial in 2012 were examined. In it, the most important factors were the opt-in rate, which refers to the rate of participation and the service of providing containers and recycling sacks to the households, since these factors resulted in the highest rates of collection. Moreover, engagement programs, including informative brochures, contributed to promoting the service to the public. A number of the participants said that they believed the recycling of diaper waste would contribute to environmental protection and the creation of better products. As a result of providing the service for six months, the most optimized area, with weekly collections and a collection rate of 75–86%, showed an average collection cost of £1100/ton.
Applying the method showing the highest efficiency in the Scottish trial, containers and 30 L sacks, the Korean trial targeted daycare centers for the quantity of diaper waste they produce. The residential areas in Korea are inconvenient for large vehicles to move in and many residential areas do not contain large apartment complexes. Therefore, daycare centers, especially ones that could be easily accessed by collection vehicles, were selected as the targets considering both their large quantity of waste and transportation convenience. Since the Korean collection trial could not last long due to the limited budget, publicity/education on the necessity of recycling was barely provided for the participants; thus, a lot of mistakes were made during the process of collection. Furthermore, there was a difference in quantity between the expected and actual amounts collected due to an unexpected number of children who spent shorter times at the daycare centers and participants who were confused about the location for diaper disposal and days of collection. Therefore, to expand the target groups and increase the scale of the collection in the future, education and publicity activities should be arranged in advance. At the stage of collection, participants primarily utilized the indoor collection boxes and then put the airtight boxes into waste bags before placing them outside the buildings. The level of satisfaction with the use of the indoor collection boxes was high and the daycare centers also made efforts to reduce the bad odor on their own. The trial lasted for six weeks, with a collection frequency of three times a week and the collection rate was less than 50%. Since the trial ended only two weeks after the participants had become competent with the routine, the results were not cost effective. The reasons why the collection cost per ton was high in the Korean case are as follows: (1) it took some time for the participants to reach a full understanding of how to use the service and follow the directions closely but the period of the collection trial was rather short; (2) the collection companies were not capable of dealing with diaper waste only, meaning a lack of efficiency in the collection and transportation system and (3) the limited number of participants, leading to a small quantity of collected waste, could not achieve economies of scale.
Under current Korean waste regulations, diapers cannot be collected with municipal waste or food waste. If cost-efficient diaper collection is secured through this study, it will be possible to treat it like other types of municipal waste through the amendment of regulations. To promote the recycling of diaper waste as a policy in Korea, a trial needs to be carried out in a wider area by obtaining funding from the Ministry of Environment. It is still meaningful that this trial successfully identified the collection and transportation factors. However, the collection frequency of three times a week and requirement of many worker hours compared to the small quantity of waste resulted in an excessive cost of collection. Therefore, the new trial should be conducted twice a week targeting the daycare centers in the rest of Nowon-Gu or all of Seoul to analyze the economic feasibility of the project. In fact, this study can suggest the most optimized model for collection efficiency after evaluating various scenarios regarding collection cost for the daycare centers of Nowon-Gu. Using this result, the cost by setting the variables of collection quantity, collection frequency and fuel efficiency was calculated and the options when applying the results of an extended application throughout Seoul was identified. It is more correct to say that the scenarios in this study are optional application by collection method. The various options were intended to see what was appropriate in Korea, not to compare Scottish and Korean cases on the same views. In addition, mid to long-term plans should be laid to expand the collection trial to apartment housing areas and other provinces. To increase participation in the trial, the role of citizens in environmental protection should be emphasized and public awareness should be enhanced with regard to the need to reduce the costs of waste treatment and the consumption of energy and resources. Furthermore, participant behavior regarding diaper-waste discharge should be monitored to validate the collection model, all of which will contribute to establishing a more socially acceptable diaper-recycling system.