Possibilities of composting disposable diapers with municipal solid wastes

Effect of diaper waste on composting of household wet biodegradable waste in a decentralized system

Due to changes in lifestyle and improved economic status, the use of diapers is also increasing in developing nations. Hence, there is a need to develop an eco-friendly system for the disposal of discarded diapers which is termed diaper waste (DW). In the present study, the co-composting of DW with household wet biodegradable waste (HWBW) was performed in a compartmentalized rotary drum (CRD) (total capacity = 160 L, number of compartments = 4) under passive aeration conditions. For the co-composting runs, 1 kg of HWBW and DW mixture (mass ratio = 100:0, 90:10, 85:15, and 80:20) was added in four individual compartments daily for 10 days. During the process, the highest temperature of ~ 50-56 °C could be achieved in different compartments for a duration of 2-8 days. The compost yield (i.e., below 4 mm size material) was ranged 10.4-13% after 55 days of composting and the mass of DW was reduced by ~ 61-68%. A mixture of 15% DW and 85% HWBW can be suggested as the best combination for the co-composting process. Based on the "Dewar test" results, the samples recovered after composting could be categorized as "stable". The pot results showed an improvement in the growth of Vigna Radiata when 10% compost sample was mixed with soil whereas with 20% compost in the soil-compost mixture, the plant growth was adversely affected. Hence, co-composting of DW with HWBW can be a feasible proposition which can produce a good quality compost.

Adult incontinence products are a larger and faster growing waste issue than disposable infant nappies (diapers) in Australia

The environmental issues relating to disposable of infant nappies have received considerable attention. However, adult absorbent hygiene products (AHPs) receive less attention, despite having comparable or greater environmental impact. Here we quantify and compare current and future flows of continence related AHPs entering waste streams from both infant and adult populations. Importantly our study accounts for current waste management and landfilling practices across Australia and the environmental implications of AHP disposal. Absorbent hygiene product use from infants and adults was modelled from 2020 to 2030 for Australia, and it's predicted that AHP waste generated by adults will account for between 4 and 10 times that of infants by 2030 due to an aging population. Our results indicate that 50% of used AHPs end up in landfill with both leachate and biogas collection, the remainder going to landfills without biogas collection or without both leachate and biogas collection, based on the most recent national data set, which is over a decade old. The average composition of used absorbent hygiene product (including 60% urine and faeces by mass) is estimated to contain 20% non-biodegradable material, which may complicate the biodegradability of absorbent hygiene products in landfill. Without additional regulatory incentive, the current waste management practices in Australia are likely to continue, with absorbent hygiene products typically entering landfill as municipal solid waste, rather than industrial composting or recycling facilities. More accurate estimation of environmental implications from these disposal pathways requires further work including biodegradation experiments currently unavailable in the literature.

End-of-life management of single-use baby diapers: Analysis of technical, health and environment aspects

Single-use baby diapers belongs to an important group of products used in the parenting journey because of their high performance and convenience. Single-use baby diapers are normally thrown away after one-time use, resulting in a waste management problem. The goal of this paper was to better understand main environmental concerns of different types of diapers and address how to reduce them, with a special consideration of waste management strategies and user behaviour practices. Furthermore, health and environmental hazards potentially associated with materials included in diapers, or substances formed from diapers during the waste treatment stage, are also analysed (e.g., phthalates, pesticides, dioxins, pesticides). Three main types of baby diapers have been analysed: single-use baby diapers, reusable baby diapers, and biodegradable single-use diapers. Each type of diaper comes with technical characteristics and environmental concerns and challenges, which are discussed in this paper to support the development of measures for the safe(r) and sustainable design, use and end of life management of baby diapers.

Phosphorus circular economy of disposable baby nappy waste: Quantification, assessment of recycling technologies and plan for sustainability

This study assessed the potential for minimizing human excreta bound phosphorus (P) loss through used disposable baby nappies, an area that remained unexplored for nations. Accordingly, it performed a substance flow analysis to assess the national P loss through used disposable baby nappies in the case of Australia. The analysis revealed that approximately 308 tonne P is lost through used baby nappies to landfills in Australia in 2019, which is nearly 2.5% of the overall P excreta as human waste. Although the quantity seems small in percentage term, it could result in the loss of a significant amount of P over several years, as assessed 5452 tonne P over the 2001-2019 period, which is concerning in the context of anticipated future global P scarcity. The review of peer-reviewed literature on available technologies/methods for recycling disposable baby nappy waste indicates that there are some technologies for recycling P particularly through co-composting with food and other organic wastes, while the majority of these are still at the lab/pilot scale. There are also various recycling techniques with purpose ranging from energy recovery to volume reduction, generation of pulp, hydrogel, cellulose, and polymer as well as to increase yield stress and viscosity of concrete, however, these are not effective in P recovery. The study implies that compost made of nappy waste can be used as fertilizer to produce bamboo, cotton, and maize plants to supply raw materials for producing biodegradable nappies, hence, to close the loop. The various product and system design options e.g., designing for flushing, designing for disassembling the excreta containing part, and designing for community composting suggested in this study could be further researched for identifying best suitable option to achieve P circular economy of disposable baby nappies. This study also recommends necessary interventions at various stages of the nappy life cycle to ensure sustainable management of phosphorus.

Synergistic effects of CO2 on complete thermal degradation of plastic waste mixture through a catalytic pyrolysis platform: A case study of disposable diaper

Consumption of diverse plastics has posed an environmental threat because their disposal practices, landfilling and incineration, release toxic chemicals and microplastics into all environmental media. Indeed, heterogeneous matrix of plastic wastes makes them hard to be disposed. As such, this study aimed to introduce an environmentally benign/reliable disposal platform for complete decomposition of plastic wastes. Pyrolysis process was adapted to convert plastics into syngas, and a disposable diaper (DD) was used as model plastic waste, because it is composed of a variety of polymeric materials. Pyrolysis of DD resulted in the formation of gaseous products and pyrogenic oils, composed of (oxygenated) hydrocarbons. Nonetheless, reactivity of CO₂ as an oxidant in pyrolysis of DD was negligible. To impart the strong/desired reactivity of CO₂, Ni-based catalyst was adopted. Ni catalyst enhanced H₂ and CO formations 4 and 15 times more than pyrolysis without catalyst at 700 °C under CO₂. The value-added syngas production was originated from the reduction of polymeric waste, and its derivatives including aromatic compounds. Thus, CO₂ offered a strategic means to produce value-added chemicals and reduce aromaticity of pyrogenic products. The observations could offer an innovative way to control the fate of toxic chemicals derived from plastic pyrolysis.

Waste management and environmental impact of absorbent hygiene products: A review

Absorbent hygiene products (AHP) have received much interest due to the notion that their end-of-life (EoL) stage has high environmental impacts. Since the use of AHP will continue to rise in the foreseeable future, information that helps with a reduction in the environmental impacts of AHP through their life cycle is needed. This research presents an estimation of AHP in municipal waste, and it also reviews and discusses waste management options, available treatments at bench, pilot or full scale, and life cycle assessments (LCAs) available in the literature. Municipal waste of countries belonging to the Organization for Economic Co-operation and Development contains on average 2.7% of baby nappies, 4.8% of adult nappies and 0.5% of sanitary pads (in weight), whereas that of Latin-American countries have 7.3%, 3.3%, and 0.9%, respectively. Management options for AHP waste in developed countries are landfilling and incineration, while in developing countries AHP are disposed of in dumpsites and landfills. Most LCAs identify significant environmental impacts in the production of raw materials, while EoL scenarios involving incineration and landfill were found to have a significant contribution to global warming potential. Substitution with alternative products has been suggested as a way of decreasing environmental impacts; however, their use frequently causes a trade-off on different impact categories. Municipalities could use a wide range of policy tools, such as extended producer responsibility systems, bans, levies, ecolabelling, or a combination of these, to reduce the environmental and economic burden of AHP waste.

Sustainable production of diapers and their potential outputs for the Pakistani market in the circular economy perspective

One of the challenging issues of any country's agenda today is the management of solid waste in the circular economy and eco-efficiency perspective. In this context, there has been much debate about the disposal of diapers, but the current research lacks data for developing countries. Furthermore, the research lacks quantification of data, in terms of output products generated through sustainable waste management practices particularly for diapers. Thus, this research aims to develop a quantitative study based on Life Cycle Assessment (LCA) and Life Cycle Costing Analysis (LCCA) which help to evaluate the overall eco-efficiency of various disposal methods by taking into account their net input and resultant monetary value, in the context of Pakistan. To cover limitations of LCA approach, results have been compared along with the expert's opinion using the well-known multi-criteria method Fuzzy logic and Technique for Order of preference by similarity to ideal solution (TOPSIS) technique. Human health and environment have been used as end-point indicators. The main research result points out that incorporating small scale incineration plants along with recycling using Thermal Pyrolysis Hydrolysis (TPH) plants can help to sustainably dispose-off diapers. The results also indicate the importance for policy makers and industrial sector to find solutions to facilitate implementation of circular economy principles for diapers. In fact, the recycling of diapers using waste-to-energy technologies is a significantly eco-efficient alternative for the Pakistani market, which can be pivotal for Sustainable development and initiation of a circular economy model.

Effect of pH on the Economic Potential of Dark Fermentation Products from Used Disposable Nappies and Expired Food Products

Used disposable nappies constitute a waste stream that has no established treatment method. The purpose of this study was the assessment of the dark fermentation of used disposable nappies and expired food products under different pH values. The biodegradable part of the used disposable nappies was recovered and co-fermented with expired food products originating from supermarkets. The recoverable economic potential of the process was examined for different volatile fatty acids exploitation schemes and process pH values. The process pH strongly affected the products, with optimum hydrogen production at pH 6 (4.05 NLH2/Lreactor), while the amount of produced volatile fatty acids was maximized at pH 7 (13.44 g/L). Hydrogen production was observed at pH as low as pH 4.5 (2.66 NLH2/Lreactor). The recoverable economic potential was maximized at two different pH values, with the first being pH 4.5 with minimum NaOH addition requirements (181, 138, and 296 EUR/ton VS of substrate for valorization of volatile fatty acids through microbial fuel cell, biodiesel production, and anaerobic digestion, respectively) and the second being pH 6, where the hydrogen production was maximized with the simultaneous production of high amounts of volatile fatty acids (191, 142, and 339 EUR/ton VS of substrate respectively).

Characterisation Study of Various Disposable Diaper Brands

Seven disposable diaper brands that are commonly used in Clermont, Kwa-Zulu Natal (South Africa) and some frequently found along river bodies (due to illegal dumping) were characterised through proximate analysis, thermogravimetric analysis (TGA), ultimate analysis and analytical pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). A novel approach entailing separation of the diapers into two fractions, interior (constituting mainly biomass fibres) and exterior (mainly constituting non-biomass polyethylene), assisted in assessing thermochemical conversion of the disposable diaper’s potential as well as likely threats to the environment. In a comparison of the volatile matter between the two fractions, the exterior fraction is more combustible (due to a higher volatile fraction). Hence, it is more suitable for energy recovery. The present study investigates the use of pyrolysis to manage disposable diapers to potentially recover pyro-oil, pyro-gas and pyro-char. In this primary investigation, it was observed that each disposable diaper brand reacts differently to constant heating. However, the proximate and elemental analysis also highlights the likely negative environmental threats, such as that the high volatile content can potentially release dangerous permanent gases such as chlorine and cobalt into the atmosphere after the diaper is disposed of illegally and in landfill.

Pretreatment of used disposable nappies: Super absorbent polymer deswelling

Typical used disposable nappies usually consist of nonwoven fabrics, Super Absorbent Polymer (SAP), and organic material, namely fluffy pulp, urine and/or excreta. Currently, this waste stream is being disposed to landfills causing many environmental issues. An alternative management method could be the valorisation of the biodegradable material through anaerobic digestion, and the recycling of plastics and SAP. Pretreatment of nappies is mandatory to separate SAP and plastics from the organic material. The aim of this work was the development of a process to minimize SAP's volume, as this component can swell up to 1500 times its own mass by water absorbance, thus hindering any further biological process. CaCl₂, MgCl₂, and a range of CaCl₂/MgCl₂ combinations were tested against their deswelling efficiency on SAP, residual reagent concentration and reagent cost. The mixture of 20% CaCl₂ and 50% MgCl₂ (w/w) of SAP was concluded as the suitable combination of salts achieving a final SAP volume reduction of 92.7% with low residual cation concentrations and minimum cost. The physicochemical characterization of nappies' hydrolysate that took place to estimate its adequacy as substrate for anaerobic digestion resulted to a COD:N ratio within the acceptable range for a subsequent anaerobic digestion processing.

Assessment of Used Baby Diapers Composting in Bolivia

Solid waste open dumping in developing countries is a global concern. To move towards sustainable development, mixed waste should be reduced, and recyclable waste recovered. The aim of the current research was to find appropriate solutions to disposable used baby-diapers recycling in Bolivia since it is a waste fraction widely produced and commonly disposed of in open dumps. Composting of the organic diaper hydrogel was assessed in five trials, adding components available locally: cow dung, activated bacteria, and Californian red earthworms (Eisenia fetida). It was observed that about 60 days were globally required for biomass decomposition with cow dung, activated bacteria, and earthworms, and more than 70 days for the treatment of the substrate mixed only with manure, while the diaper hydrogel did not degrade without cow dung. This research is the first that attempted to treat disposable used baby diapers with the vermicomposting process. In general, the outcomes of the research are promising: vermicomposting with cow manure can be a recycling option for disposable used baby diapers, introducing appropriate practices toward a circular economy in developing regions.

Offensive waste valorisation in the UK: Assessment of the potentials for absorbent hygiene product (AHP) recycling

Offensive human waste refers to non-hazardous waste that contains body fluids from non-infectious humans, comprised of post-consumer Absorbent Hygiene Products (AHPs), swabs, dressings, bedding, gloves, and other materials. While this waste category requires more stringent handling, storage and disposal measures than general waste, its non-hazardous nature suggests that there are opportunities for waste valorisation. An inventory of 200 offensive human waste bags collected from various healthcare institutions in South-Eastern England show that about 76% of the waste is comprised of AHPs, most of which are adult incontinence pads and child nappies. Mixed plastics comprised of predominantly HDPE represent 9% of the waste. To evaluate the potentials for offensive human waste valorisation, small-scale separation tests involving artificially-soiled nappies and associated mixed plastic packaging wastes have been performed. Findings suggest that about 50% of the total superabsorbent polymer is recoverable from fluff pulp fractions, recoveries of which are unaffected by the presence of ionic species typically present in human waste. On the other hand, recovery of mixed plastic packaging is more challenging. Overall, however, findings suggest that viable AHP recycling is possible if recyclate materials are targeted towards non-food related markets outlets such as the construction and land remediation sectors.

Historical perspectives on contemporary human-environment dynamics in southeast Africa

The human communities and ecosystems of island and coastal southeast Africa face significant and linked ecological threats. Socioecological conditions of concern to communities, governments, nongovernmental organizations, and researchers include declining agricultural productivity, deforestation, introductions of non-native flora and fauna, coastal erosion and sedimentation, damage to marine environments, illegal fishing, overfishing, waste pollution, salinization of freshwater supplies, and rising energy demands, among others. Human-environment challenges are connected to longer, often ignored, histories of social and ecological dynamics in the region. We argue that these challenges are more effectively understood and addressed within a longer-term historical ecology framework. We reviewed cases from Madagascar, coastal Kenya, and the Zanzibar Archipelago of fisheries, deforestation, and management of human waste to encourage increased engagement among historical ecologists, conservation scientists, and policy makers. These case studies demonstrate that by widening the types and time depths of data sets we used to investigate and address current socioecological challenges, our interpretations of their causes and strategies for their mitigation varied significantly.

Impact of carbonatation lime addition on composting of vegetable oil refining sludge

The aim of the present work is to evaluate how the vegetable oil refining sludge produced by the agro-food industry could be composted using carbonatation lime and green waste as bulking agents. To achieve this goal, three windrows were prepared with different mixtures: windrow 1 contained oil sludge and green waste (20:10 on a wet mass basis) while windrow 2 contained oil sludge, green waste and carbonatation lime (20:10:10, on a wet mass basis). The composition of windrow 3 was: oil sludge, green waste and carbonatation lime (20:10:20, on a wet mass basis). The results showed that the use of carbonatation lime for composting vegetable oil refining sludge was able to regulate the high acidity of the sludge and thus to obtain an optimal pH value for the launching and maintenance of the composting process. The addition of carbonatation lime also gave better reduction of microbial activity without any negative effect on composting. The compost prepared with oil refining sludge (49% fresh mass), carbonatation lime (27%) and green waste (24%) exhibited the best quality with C/N ratio and pH values within the norm NFU44-051. These promising results could be a sustainable solution for the valorization of both oil refining sludge and sugar carbonatation lime.

Pilot trial on separation conditions for diaper recycling

By utilizing laboratory-scale tests, the optimal separation conditions for diaper recycling were identified, and then, these conditions were validated by a pilot trial. In this research, we determined the mass balances derived during various processing steps and identified the most feasible procedures to use for separating each material in the output flow. The results showed that drum screening was not able to remove all the fiber and super absorbent particles (SAP) in the plastic-rich fraction and that cellulose enzyme treatment can be a good solution. To achieve better separation of fibers and SAP, slot screening followed by a cleaner is a potential option. A feasible diaper recycling process was recommended based on these results. This process involves screening and enzymatic treatment for the plastic fraction, and screening, cleaning, and thickening for the fiber fraction. Treatment procedures were also proposed for the SAP fraction and rejected materials.

Biohydrogen production from used diapers: Evaluation of effect of temperature and substrate conditioning

This research assessed the viability to use disposable diapers as a substrate for the production of biohydrogen, a valuable clean-energy source. The important content of cellulose of disposable diapers indicates that this waste could be an attractive substrate for biofuel production. Two incubation temperatures (35 °C and 55 °C) and three diaper conditioning methods (whole diapers with faeces, urine, and plastics, WD; diapers without plastic components, with urine and faeces, DWP; diapers with urine but without faeces and plastic, MSD) were tested in batch bioreactors. The bioreactors were operated in the solid substrate anaerobic hydrogenogenic fermentation with intermittent venting mode (SSAHF-IV). The batch reactors were loaded with the substrate at ca. 25% of total solids and 10% w/w inoculum. The average cumulative bioH₂ production followed the order WD > MSD > DWP. The bio-H₂ production using MSD was unexpectedly higher than DWP; the presence of plastics in the first was expected to be associated to lower degradability and H2 yield. BioH₂ production at 55 °C was superior to that of 35 °C, probably owing to a more rapid microbial metabolism in the thermophilic regime. The results of this work showed low yields in the production of H₂ at both temperatures compared with those reported in the literature for municipal and agricultural organic waste. The studied process could improve the ability to dispose of this residue with H₂ generation as the value-added product. Research is ongoing to increase the yield of biohydrogen production from waste disposable diapers.

Treatment of the biodegradable fraction of used disposable diapers by co-digestion with waste activated sludge

The results presented in this paper are part of a project aimed at designing an original solution for the treatment of used disposable diapers permitting the recycling of materials and the recovery of energy. Diapers must be collected separately at source and transported to an industrial facility to undergo special treatment which makes it possible to separate plastics and to recover a biodegradable fraction (BFD) made up mainly of cellulose. The methane yield of BFD was measured and found to be 280 ml CH4/g VSfed on average. 150 kg of dry BFD can be retrieved from the treatment of one ton of used disposable diapers, representing an energy potential of about 400 kW h of total energy or 130 kW h of electricity. As the treatment process for used diapers requires very high volumes of water, the setting up of the diaper treatment facility at a wastewater treatment plant already equipped with an anaerobic digester offers the advantages of optimizing water use as well as its further treatment and, also, the anaerobic digestion of BFD. The lab-scale experiments in a SBR showed that BFD co-digestion with sewage sludge (38% BFD and 62% waste activated sludge on volatile solids basis) was feasible. However, special attention should be paid to problems that might arise from the addition of BFD to a digester treating WAS such as insufficient mixing or floating particles leading to the accumulation of untreated solids in the digester.

Characterization of the pyrolytic solid derived from used disposable diapers

This paper confirms through physical and chemical analyses the possibility to reuse the solid pyrolytic residue derived from used disposable diapers (UDD), heated at different temperatures ranging from 500, 700 and 900 degrees C as a soil amendment. With an increasing pyrolytic temperature, the pH, electrical conductivity, available P2O5, exchangeable K+ and cation exchange capacity tended to increase; however, total-N and exchangeable Ca2+ and Mg2+ decreased. The pyrolytic diaper solid produced at 500 degrees C had a high volatile matter (60.22%) and low ash content (19.10%), which can negatively affect crop growth and productivity when added to soil. Heavy metal concentrations were less than the maximum allowable limits according to Japan standards. The surface of the pyrolytic diaper solid was coarse, porous and heterogeneous with higher temperatures. Hydrogen-containing functional groups, such as OH, C-H, N-H and CH2, decreased with increasing pyrolytic temperature. Based on these results, we concluded that the pyrolytic product derived from UDD at higher temperatures offers a potentially effective soil amendment option.

Performance of compostable baby used diapers in the composting process with the organic fraction of municipal solid waste

In modern societies, disposable diapers constitute a significant percentage of municipal solid wastes. They have been traditionally landfilled or incinerated as only limited recycling processes are being implemented in some parts of Europe. With the implementation of separated collection systems for the organic fraction of municipal solid wastes (OFMSWs) and the need to preserve the environment, compostable diapers have appeared in the market to avoid the main environmental impacts associated to non-biodegradable disposable diapers. In this study, a full-scale composting of door-to-door collected OFMSW with a 3% (w/w) of compostable diapers has also been carried out. Previously, lab-scale experiments confirmed that almost 50% of carbon of compostable diapers is emitted as CO2 under aerobic controlled conditions. The results obtained at full-scale demonstrate that both the composting process and the final end product (compost) are not altered by the presence of compostable diapers in crucial aspects such as pathogenic content, stability and elemental composition (including nutrients and heavy metals). The main conclusion of this study is that the collection of the OFMSW with compostable diapers can be a new way to transform this waste into high-quality compost.

Solid waste generation and decomposition using compost bin technique in Pulau Pinang, Malaysia

Solid waste comprised of a grass clippings mixture was decomposed using a locally-made compost bin in Pulau Pinang, Malaysia, to eliminate challenges associated with improper waste disposal. Bulk density, pH, moisture content, nutrients content, nitrogen (N), phosphorus (P), potassium (K), iron (Fe), zinc (Zn), copper (Cu) and carbon/nitrogen (C/N) ratio were determined over 77 days. A 34% reduction in compost bin volume was observed and bulk density and pH were also reduced from 732 to 482 kg m(-3) and 7.82 to 8.41, respectively, indicating fairly good performance. The final moisture content and C/N ratio were 44.06% and 14 : 1, respectively, and the results also showed that the presence of nutrients and heavy metals in the final compost were within acceptable limits for use as a soil conditioner. Final concentrations of N, P and K were 347 mg kg(-1), 510 mg kg(-1) and 14.8 g kg(-1) and for heavy metals, Fe, Zn and Cu were 5308, 300 and 20 mg kg(-1), respectively, which considerably assisted in the decomposition process. Processed waste materials from the bin were shown to be excellent organic fertilizers with over 75% germination index for seeds grown into bean sprouts in 72 h. An improved bin design to eliminate greenhouse gas emission into the environment is suggested.