Recent Technology for Recycling of Used Diapers Waste

The purpose of this paper is to provide information related to waste technology processing. The study was conducted using a literature review technique. This review provides an in-depth discussion of the impact and the recent breakthrough in improving problems arising from the generation and disposal of soiled diapers. Various technologies were highlighted, especially the safer use and cleaner technology, such as biodegradation and composting to maximizing recycle process at a cheaper cost. Moreover, pyrolysis shows an opportunity to improve the efficiency of the recycling process used diapers. Finally, recycling is achievable with an economic incentive if the costs of a series of complicated processes are lower than the value of the end product. Therefore, the best technology for recycling that becomes a big consideration. The consideration of which process to use may vary from national and industrial outlook in terms of rate of return, total cost, and environmental. The challenge of recycling is to reduce the cost of waste treatment while providing high-quality final products and need to focus on developing practical and environmentally friendly recovery methods.


Introduction
Baby's growth is always increasing. According to statistical data, the baby birth rate in 2021 is 0.49%, an increase from the previous year to 72.29 (Sembiring, 2021). According to (Morganti & Febo, 2017), daily use of diapers is 7,000 pcs per 2 hours, in addition, (Sugiarto, 2018) states that babies use diapers about 6,000 diapers during their 2 years of life. To meet the demand for diaper usage, the industry attempt to increase their production. It is indicated by many industrial players, especially in Indonesia, which produces baby diapers with various brands (Sugiarto, 2018); Ghahremani Nahe et al. 2022). Great needs will produce big waste (Prasetyo, et al., 2021) (Remigios, 2014. Handling that is not optimal for used diapers will make waste treatment problems never stop. In dealing with this waste, throwing it directly into a landfill (Davidson, 2022) or burning it (Davidson, 2022) (Ntekpe, et al., 2020) are often chosen by parents. Disposing of the waste directly does not solve the problem, it even creates new problems in landfills related to environmental health, such as cholera (Remigios, 2014). Likewise, with burning, the burning process of wet or damp used diapers along with other household waste will not destroy the waste completely (Remigios, 2014). Burning result leaves incomplete burn marks in the end, which in turn creates new waste and air pollution by producing CO and Chlorine (R, 2007).
The purpose of this review is to provide a snapshot of several technologies that can be used to recycle used diapers. The study was conducted using a literature review technique that aims to provide information related to waste technology processing from several kinds of literatures in support of the circular economy program

Diaper Knowledge
The ritual of using diapers for babies has survived for centuries with methods and materials depending on the habits, culture, and geographic location of the people in it (Krafchik, 2016). Parents use diapers as swaddling so urine and feces can accommodate. Using cloth is considered, inefficient, and makes parents switch to using disposable diapers (Ramdani, et al., 2021). Currently, the development of the diaper industry is already massive (Davidson, 2022), it showed by the release of various brands and types of diapers, using adhesive as well as pants models (Sugiarto, 2018). The use of diapers is unlimited in all circles. From birth, babies already use diapers to accommodate urine and feces (Ramdani, et al., 2021). Even for the elderly, the use of diapers has also become normal (www.texus.com, 2016).
Diapers also experience many modifications and developments over time, such as waterproof materials and keeping the skin dry along night (Helmes, et al., 2014). The changes also led to the invention of more modern diapers to biodegradable by addition of petrolatum and stearate, chlorine-free, latex free, more absorbent (keep dry), and free of fragrance ingredients. Some industries combine fabrics with materials to reduce harm to the environment.
Diapers are designed with polymer material that contains cellulose, polypropylene (PP), polyester, and polyethylene (PE) which are arranged in different layers to optimize the absorption process of urine and feces, especially for baby skin health (Counts, et al., 2017). PP is usually used for the top layer in contact baby's skin, PE is used for the next layer, cellulose fluff pulp is used as the base absorbent and core tissue along with superabsorbent polymer and elastic material is used at the waist which is adjustable, adhesive material for tie all materials together (e.g. Fig. 1) (BAHP, 2017).

The Impact and Technology Processing Soiled Diapers The Impact of Disposal Soiled Diapers
According to several studies, throwing diapers into the environment is more dangerous because they create huge amounts of waste (Meseldzija, et al., 2013). (Davidson, 2022) stated, that as much as 20 billion pcs or more of 3.5 million tons of used diaper waste will end up in landfill every year. This amount is worth more than $71 billion/ year by 2022. Meanwhile, the decomposition process of ingredients such as wood pulp and cotton takes 5 months, and 500 years for absorbent gel materials and plastic in diapers (Meseldzija, et al., 2013).
There are several problems that arise as a result of throwing away used diapers into the field. The greatest impacts are related to exposure to pathogens (health impacts) and environmental aesthetics, pollution, and exposure to chemicals (Ntekpe, et al., 2020). Used diaper accommodates baby's urine and feces becomes a breeding ground for pathogenic microorganisms. Microorganisms can transfer to humans (Ntekpe, et al., 2020) and disturb health in the long term (Colo`n, et al., 2013). According to (ENVIS, 2016) diseases that can be caused by this waste such as; cholera, typhoid, hepatitis, cryptosporidiosis, ascariasis, polio, and schistosomiasis. Meanwhile, the residential environment which piles up used diaper will cause water pollution, typhoid, skin infection, vomiting, sore throat, stomachache, and malaria (Ntekpe, et al., 2020).
Other problems that arise when used diapers are dumped on the ground is methane gas emission (odor) and the emergence of leachate that permeates into the soil caused by organic waste from diapers (Colo`n, et al., 2010). Besides, the combustion process carried out pollutant to the atmosphere, the main gas produced is dioxane, N2O2, CO, NOx, HCl, HF, SO2, CO2, H2O, and dust that can cause the greenhouse effect (Riber, 2007).
From an aesthetic view, placing soiled diaper -filled dirt carelessly along the road or living area cause an unpleasant smell and attracts flies to perch. Not only flies, but they are also attracting dogs to tear the trash (Ntekpe, et al., 2020).

Landfill
In many developing countries, a common method to treat solid waste is to dump it on a land (Khoo, et al., 2019). Indonesia itself has a policy toward landfills as containers for collecting waste. Landfill technique for solid waste is open dumping managed by the City/ Regency Government (Asisten Deputi Telematika dan Utilitas, 2013).
The Landfill itself has weaknesses, including methane emission, water pollution, use vast land, the unpleasant smell which is generated if landfill method is not managed properly. According to (Satyanarayan & Chandra, 2014), landfill is an effective technique if integrated with a solid waste management strategy.
One problem with storage waste in landfill is producing leachate, leachate is a liquid that has percolated through the layers of waste material (Satyanarayan & Chandra, 2014). Leachate may be composed of liquids originating from groundwater, precipitation, consolidation, and the diaper itself (Satyanarayan & Chandra, 2014).
Good Landfill built by making a hole in soil to hoard waste gradually (K., 2015), (Withgott & Manning, 2006) has attempted construct solid waste landfill scheme (e.g. Fig. 2). First, landfill is coated with dense polyethylene to prevent the percolation of leachate, then the solid waste is loaded into the soil pile (Khoo, et al., 2019). Next, waste is buried until reaches the limit. Waste of used diapers could degrade until about 500 years (Meseldzija, et al., 2013).

Thermal Method
The thermal method could distinguish becomes 2, that is incineration and pyrolysis (Khoo, et al., 2019). Incineration is often considered the fastest way of handling household waste, but this method becomes the main problem in an environment (Nidoni, 2017). Incineration could save land utilization (Dursun & Maaroof, 2016) (Patil, et al., 2014) and the most interesting thing is that this process could reduce the volume of waste up to 80-95% (Patil, et al., 2014) compared to landfills, but produce new forms of solid waste of about 30% of the actual volume (Das & Kuity, 2021).
Burning waste can create heat, electricity, or other energy forms, which can be used for heating buildings directly (Ignatyev, et al., 2014). Combustion requires a temperature of about 800°C to avoid odor due to incomplete combustion (Patil, et al., 2014) and to ensure the burning process is complete to prevent the formation of dioxins and carbon monoxide (Nidoni, 2017).
The incineration technique is more competitive if the produce calory (heating value) is not less than 2000 kcal (8370 kJ/kg) (Dursun & Maaroof, 2016) and suitable if applied to some waste characteristics (e.g., Table  2). The weakness of incineration is generated air pollution residue, including the particulate material usually in the range of 2% to 5% of the original waste on wet basis (Nidoni, 2017), emission of dust, sulfur, and nitrogen compounds as well as dioxins (Krepsztul & Rydzkowski, 2019).
In sum, the operation of combustion includes volume reduction, energy recovery, and minimization of hazardous material (Dursun & Maaroof, 2016), which must be equipped with some devices for cleaning the exhaust gases (e.g. Fig. 3) (Krepsztul & Rydzkowski, 2019).
Pyrolysis is usually used to produce coal, biofuels, solid gases, and process water. Pyrolysis can be divided into 3 types; slow, intermediate, and fast, different in temperature, heating speed, and time of vapor residence. However, the disadvantage is high cost of investment and the determination of suitable and effective reactors (Krepsztul & Rydzkowski, 2019).
It can be concluded that pyrolysis has the potential to treat used diapers (Khoo, et al., 2019). When used diaper materials from waste can't experience a biodegradation process, recycle process by utilizing heat energy can be an alternative (Krepsztul & Rydzkowski, 2019).

Recycling
Recycling is a technique that separate organic and inorganic component like plastic. Recycling is a complex process, including collecting, separating, and sterilizing (Khoo, et al., 2019). A number of companies in the world have been able to recycle used diapers, like Knowaste (United States), Total Care System (Japan), and Livedo operation (Japan) (Tkac, et al., 2018) (LiveDo, 2020. The initial process is carried out by separating the attached faces for the next treatment as (e.g. Fig. 4)   The used diapers are stored, then shredded into small pieces, sterilized or heated, and the last is separated for reclamation of plastic materials and paper fiber (Tkac, et al., 2018). According to (Tkac, et al., 2018), used diapers are able to produce some products to be reused as construction materials, soil conditioners, RDF solid fuel, recycled pulp and 80% of urine can retreated biologically. Cellulose material can be made as cardboard and paper, and absorbent (SAP) can be processed into animal urine absorbent pads (e.g. Fig. 5).

Fig. 5. Recycle product by used diapers waste.
According to (Ichiura, et al., 2020), the pulp cannot be recovered by a conventional method, moreover, the recovered pulp did not meet the requirement of regulation for use in diaper manufacture. So, it required better recycling techniques to recover pulp to be reused.
The separating process is an important step in recycling plastic and pulp material in diaper waste. This separation is difficult because the SAP materials swell due to absorbing urine, a technique than can be used is centrifugal separator (Ichiura, et al., 2020). Furthermore, (Ichiura, et al., 2020) says, oxidation by ozone can be used to recycle disposal diapers.

Composting
Composting technique of used diapers can be conducted by adding organic materials (Colo`n, et al., 2010) which shows beneficial results. Composting process is capable kills harmful pathogenic bacteria (Colo`n, et al., 2013) (Colo`n, et al., 2010. Tables (e.g., Table 3) shows the composition of a used diaper (Colo`n, et al., 2010). In composting operation, several aspects must be considered in relation to superabsorbent polymers (SAP) in diapers. In contact with urine, SAP takes a gelatinous form, called hydrogel. Although urine is an organic substance, the presence of SAP would make it difficult to separate it in composting plant (Colo`n, et al., 2010). On the other hand, (Ramdani, et al., 2021) stated that SAP shows the ability to control soil moisturizer and can survive until 18 days from the first watering. It is caused by the ability of absorbent to be swelling.
Composting process is an alternative to the processing used diapers without producing pollutants (Valdemar, et al., 2014) and can be combined with the incineration process or pyrolysis (Khoo, et al., 2019). Research shows that soil derived from used diaper composting can be used for plants, such as tomatoes (Valdemar, et al., 2014), this is because the soil from used diaper composting can increase the C/N ratio (Valdemar, et al., 2014), P (Phosphorus), and K (Potassium) (Prasetyo, et al., 2021). The end compositions from the composting process uses and without using diapers can be seen (e.g., Table 4) below (Colo`n, et al., 2013) (Colo`n, et al., 2010.

Biodegradation
Biodegradation is a decomposition technique utilizing enzymes from microorganisms, such as bacteria or mold (Khoo, et al., 2019). Many baby diapers originated from non-biodegradable materials (Hirsh, 2019), such as plastic made from polypropylene/ polyethylene, and polyacrylate polymer. Carbon is a strong polymer only could break down with microbe's help (Colo`n, et al., 2013) through the process of enzymatic (Grover, et al., 2015) secretion. As the consequence, disposable diapers are not easy degraded.

Conclusion
There are millions of tons of used diapers being disposal and dumped into landfill yearly and Indonesia still haven't implemented any technology to recycle them. One of the main reasons is the lack of central administrative agencies, waste recycling facility and cost-effective diaper recycling method. Recycling is a complex process which require technology, facilities, and equipment to recycle. The collection and separation of used diapers are an important consideration for the recycling management. It should start from citizens as a source of wastes.
Many methods can be applied to manage used diaper waste. Table below (e.g., Table 6) shows a comparison a every method that has been presented above. Talking about the best treatment, it depends on the requirement, cost, facilities, policy, and ability.  (Patil, et al., 2014) Could reduce the volume of waste up to 80-95% (Patil, et al., 2014) Produce new form solid waste about 30% of the actual volume (Das & Kuity, 2021) Generated air pollution residue (Nidoni, 2017), emission of dust, carbon monoxide Pyrolysis Reduce the greenhouse effect and more ecological for the environment (Krepsztul & Rydzkowski, 2019) High cost of investment and the determination of suitable and effective reactors (Krepsztul & Rydzkowski, 2019).

Recycling
Almost all constituent is reusable to produce other product A complex process, include collecting, separating, and sterilizing (Khoo, et al., 2019) Need another process to convert effectively (Ichiura, et al., 2020).
The presence of SAP would make it difficult to separate it in composting plant (Colo`n, et al., 2010). It needs separation layers of the used diapers to degrade. Composting without separation could degrade until about 500 years (Meseldzija, et al., 2013) Biodegradation Using microorganisms for the decomposition process such as bacteria or mold (Khoo, et al., 2019). Degradation process could conduct with aerobic or anaerobic (Khoo, et al., 2019).
Must consider these parameters (Pressure, presence of certain microorganisms, pH, humidity) to determine whether polymers can be converted into other substances easily (Ignatyev, et al., 2014). It requires cost (Khoo, et al., 2019) and facilities support (Nowak, et al., 2011) While the recycling used diapers will reduce the volume of waste, the recycling process consumes natural resources and generates other forms of solid waste (Khoo, et al., 2019), pollution like emission and water pollution. Finally, recycling is achievable with an economic incentive if the costs of a series of complicated process are lower than the value of the end-product. Therefore, the best technology for recycle that become a big consideration.
Every method has their advantages and weakness and so far, there has no consensus on what the best process for recycling diapers and absorbent polymer is. In fact, the consideration of which process to use may vary from national and industrial outlook in terms of rate of return, total cost, and environmental. The challenging of recycle is to reduce the cost of waste treatment while providing high quality final product and need to focus on developing practical and environmentally friendly recovery methods.