Technical References & Research: All The Science Behind Waste Free '23
At Waste Free ’23, we are dedicated to tackling the global waste crisis with innovative, evidence-based solutions. We believe that strong scientific research is the cornerstone of effective and sustainable waste management practices.
Our methodology is not simply based on good intentions; it is informed by rigorous academic studies on waste processing, environmental impact, and so on. This commitment to transparency and scientific backing ensures that our solutions are not only effective in eliminating waste but also have a positive impact on the environment and the well-being of communities.
Articles on..
Plastic Processing
Investigation of Gas Release from Recycled Plastic Shopping Bags during Melting at Low Temperatures (Eberhard et al., 2023)
Parts of the Abstract: Recycling plastic is an excellent way to reduce the environmental impact of its production and use. In a circular economy, recycling of recycled plastic is necessary. Most plastic bags are made of thermoplastic, like high-density polyethylene (HDPE) with a melting point of 130°C, and low-density polyethylene (LDPE). In contrast, recycled plastic bags are made up of many different unknown substances. In this study, the melting of used plastic bags containing 80% unknown recycled material was investigated. FTIR analysis showed that the bags consisted mainly of HDPE.
The bags released small amounts of toxic phthalates. The results show that melting recycled plastic bags for remoulding is promising if safety precautions that ensure sufficient ventilation are utilised.
“Styrofoam Recycling – Smart Business Idea” (Warm Heart, 2023)
Parts of the Abstract: Warm Heart has developed a simple, replicable system to recycle Styrofoam and convert it into useful products like Styrofoam cement bricks. The project provides opportunities for individuals to build a sustainable business while helping clean the environment. The process involves collecting Styrofoam, grinding it into small “fuzz” particles, and mixing it with cement to create lightweight, durable bricks. These Styrofoam cement bricks can be used for building walls, roofs, and insulation. Warm Heart emphasizes that the system is low-cost and can be started with minimal investment, making it accessible to many communities.
Recommendation: Warm Heart recommends using Styrofoam cement bricks for non-load-bearing walls, roof insulation, and external applications. They suggest creating a brick-making machine to increase productivity and to follow safety guidelines, particularly regarding fire safety.
Toilet Waste Processing
Urea recovery from stabilized urine using a novel ethanol evaporation and recrystallization process (H. Marepula et al., 2021)
Parts of the Abstract: Urea is a raw material in the production of various chemicals and is a key nitrogen-based fertilizer. The conventional process to manufacture synthetic urea operates at high temperatures and pressures and is therefore energy intensive. The aim of this work was to investigate the feasibility of recovering and purifying urea crystals from human urine using a novel ethanol evaporation and recrystallization process that exploits the solubility differences of urea and impurities in water and ethanol. This approach could provide an alternative method to produce urea that operates at atmospheric pressure and low temperatures (< 30°C).
Nitrogen Recovery With Source Separation of Human Urine—Preliminary Results of Its Fertiliser Potential and Use in Agriculture (Viskan et al., 2018)
Parts of the Abstract: The growing demand for food and the increasing costs of cultivation are posing a challenge for agriculture. Diminishing phosphorus reserves, as well as the energy intensive method of producing nitrogen fertilisers are drivers for more intensive reuse of different organic fertilisers, such as manures and excreta. Source separation and fertilisation with human urine can be one option for nutrient reuse. Urine contains all the main nutrients as well as micronutrients in soluble form, but it also contains chemicals, like pharmaceuticals and hormones. The aim of this study was to examine the efficiency and safety of the use of source separated human urine as a fertiliser for barley (Hordeum vulgare).
Pharmaceuticals and hormones were found from the urine, but apart from progesterone, all of them presented extractable values in soil below the detection limits, and they were not detected in measurable amounts in barley grain at the end of the growing season. These results suggest that source separated urine could be an efficient fertiliser in crop cultivation.
Pyrolysis of Dry Toilet Substrate as a Means of Nutrient Recycling in Agricultural Systems: Potential Risks and Benefits (Bleuler et al., 2020)
Parts of the Abstract: Biochar is increasingly being applied as a soil amendment in agriculture. Biochar is typically produced from plant biomass and contains relatively low amounts of plant nutrients (e.g., N, P, and K), thus providing limited fertilizer value. Human excreta contains plant nutrients that could be recycled to create sustainable agricultural nutrient cycles. This study investigated the potential of biochar derived from a dry toilet substrate as soil amendment.
[Contd.] Based on these results, it is recommended that urine separation should be considered for biochar of excreta, which could reduce salt stress while maintaining concentrations of “fixed” or bioavailable nitrogen.
A comparison in product-value potential in four treatment strategies for food waste and faeces – assessing composting, fly larvae composting and anaerobic digestion (Lalander et al., 2017)
Parts of the Abstract: Municipalities are expected to provide solid waste management, which is funded by tax revenue or/and waste treatment fees. In many low- and middle-income countries, municipalities struggle to provide an adequate level of service, and in these places, the informal sector plays a major role in the collection and treatment of solid waste. In contrast to the plastic and metal fraction, the organic fraction is not managed by the informal sector, primarily because it has low or no financial value and treatment would cost more than the possible revenue. If the organic fraction could be converted to valuable products, the treatment could bear its own cost and this could act as an incentive to collect and treat this fraction. In this study, the potential product value generated through four treatment strategies treating food waste and faeces was compared in a Swedish context: (i) thermophilic composting; (ii) black soldier fly treatment (BSF treatment); (iii) anaerobic digestion (AD); and (iv) BSF treatment followed by AD (BSF + AD).
In places with an existing AD plant, BSF treatment + AD strategy is the most economically viable. In places where no such plant exists, BSF treatment is likely to be the most economically favourable treatment.
Carbon footprint of processing city market waste for animal feed with Black Soldier Flies in Kampala, Uganda (Pishgar-Komleh et al., 2022)
Summary: The study by Wageningen University assessed the carbon footprint of processing city market waste into black soldier fly larvae (BSFL) in Kampala, Uganda. Results showed that BSFL production emits 3.1 kg CO2eq per kg of dried larvae but avoids 9.7 kg CO2eq, yielding a net reduction of 5.2 kg CO2eq. BSFL can replace soybean meal and fishmeal in livestock feed, enhance local feed production, and improve organic waste management. The study recommends efficiency improvements and further research to optimize BSFL production’s environmental and economic benefits
Nitrogen and Phosphorus Availability of Biologically and Thermochemically Decomposed Human Wastes and Urine in Soils With Different Texture and pH (Krounbi et al., 2018)
Summary: Human waste contains nitrogen (N) and phosphorus (P), which are vital for plants. The study compared three methods to sanitize human solid waste (HSW): thermophilic composting (60°C), torrefaction (200°C), and pyrolysis (300°C, 500°C). These methods affect nutrient availability differently in soils with varying textures and pH levels. Composting released more nitrogen, while higher pyrolysis temperatures increased phosphorus availability but reduced nitrogen. Adding urine to pyrolyzed waste improved nitrogen levels while keeping phosphorus high, although it caused slight soil acidification.
Findings:
- Composting improved nitrogen availability by 15–25%.
- Torrefaction increased nitrogen availability by 40–57%.
- Pyrolysis (500°C) provided the highest phosphorus availability, 41–106% more than composting and 84–165% more than torrefaction.
- Combining urine with pyrolyzed HSW enhanced nitrogen availability by up to 486 kg N/ha and phosphorus by up to 81 kg P/ha.
Recommendations: Using sanitized HSW, especially with urine, is effective for increasing soil fertility. However, the balance between nitrogen and phosphorus availability should guide the choice of treatment method.
“Waste-to-Carbon: Is the Torrefied Sewage Sludge with High Ash Content a Better Fuel or Fertilizer?” (Pulka et al., 2020):
Summary: This study explores whether torrefied sewage sludge (waste heated to high temperatures) is better used as fuel or fertilizer. The researchers tested sludge with a lot of ash, using different heating temperatures and times. They found that the sludge doesn’t work well as fuel because the ash lowers its energy value. However, it contains nutrients like nitrogen and phosphorus, which can improve soil health. Torrefied sludge can be a good fertilizer, meeting quality standards in Poland.
Recommendations: The study suggests focusing on using torrefied sewage sludge as a fertilizer. It’s better for recycling nutrients into agriculture, especially in areas needing sustainable waste management and soil improvement.
Enhancing the Nitrogen and Phosphorus Content of Faecal-Derived Biochar via Adsorption and Precipitation from Human Urine (Koulouri et al., 2024)
Summary: This research shows how human waste can be turned into a useful fertilizer for plants. The scientists used biochar (a type of charcoal made from faeces) and combined it with human urine, which has lots of nutrients like nitrogen (N) and phosphorus (P). They found that soaking the biochar in stored urine helped it absorb nitrogen, and adding magnesium oxide (MgO) made phosphorus stick better. This created a fertilizer that could be easily separated from the urine. The process worked well and recovered over 98% of the phosphorus and a lot of the nitrogen. This method is simple, low-cost, and could help farmers, especially in places without big waste treatment systems.
Recommendations: The study recommends using this method to recycle human waste into eco-friendly fertilizers, which can improve farming and reduce pollution.
Torrefaction Processing for Human Solid Waste Management (Serio et al., 2016)
Summary: This study looks at how to handle human solid waste during long space missions. Scientists tested a process called torrefaction, which gently heats waste to 200–250°C without air. This heating makes waste safe by killing bacteria, removes bad smells, and turns it into a dry material that doesn’t grow germs. It also recovers water from the waste and shrinks its size by 50%. NASA plans to use torrefaction in their waste system for space missions, such as trips to Mars. The dried waste can be recycled into useful things like fertilizer, radiation shields, or even fuel. This method uses less energy and helps keep astronauts safe while managing waste more sustainably.
Recommendations: Torrefaction could be a great way to manage waste in space. More research is needed to improve its design and test faster heating methods like microwaves.
Introducing Urine-Enriched Biochar-Based Fertilizer for Vegetable Production: Acceptability and Results from Rural Bangladesh (Sutradhar et al., 2021)
Summary: This study tested how urine-enriched biochar fertilizer can improve vegetable farming in rural Bangladesh. Biochar is a special kind of charcoal made from natural materials like wood or leaves. When mixed with urine, it becomes a nutrient-rich fertilizer for plants. Farmers in this project used cow urine because it was socially acceptable, while human urine was seen as impure.
The results were great—vegetable yields increased by 60%, especially for cabbage and kohlrabi. Farmers liked that the fertilizer was cheap, easy to make, and made their vegetables taste better. However, getting enough cow urine and biochar materials was sometimes a challenge. Women found the fertilizer particularly useful because it reduced their need to buy chemical fertilizers from markets. Most farmers said they would continue using it.
Recommendations: Urine-enriched biochar can help small farmers grow more vegetables, save money, and improve food security. It’s a low-cost, eco-friendly fertilizer that could be scaled up in Bangladesh and similar areas.
Food & Other Organic Waste Processing
A comparison in product-value potential in four treatment strategies for food waste and faeces – assessing composting, fly larvae composting and anaerobic digestion (Lalander et al., 2017)
Parts of the Abstract: Municipalities are expected to provide solid waste management, which is funded by tax revenue or/and waste treatment fees. In many low- and middle-income countries, municipalities struggle to provide an adequate level of service, and in these places, the informal sector plays a major role in the collection and treatment of solid waste. In contrast to the plastic and metal fraction, the organic fraction is not managed by the informal sector, primarily because it has low or no financial value and treatment would cost more than the possible revenue. If the organic fraction could be converted to valuable products, the treatment could bear its own cost and this could act as an incentive to collect and treat this fraction. In this study, the potential product value generated through four treatment strategies treating food waste and faeces was compared in a Swedish context: (i) thermophilic composting; (ii) black soldier fly treatment (BSF treatment); (iii) anaerobic digestion (AD); and (iv) BSF treatment followed by AD (BSF + AD).
In places with an existing AD plant, BSF treatment + AD strategy is the most economically viable. In places where no such plant exists, BSF treatment is likely to be the most economically favourable treatment.
Carbon footprint of processing city market waste for animal feed with Black Soldier Flies in Kampala, Uganda (Pishgar-Komleh et al., 2022)
Summary: The study by Wageningen University assessed the carbon footprint of processing city market waste into black soldier fly larvae (BSFL) in Kampala, Uganda. Results showed that BSFL production emits 3.1 kg CO2eq per kg of dried larvae but avoids 9.7 kg CO2eq, yielding a net reduction of 5.2 kg CO2eq. BSFL can replace soybean meal and fishmeal in livestock feed, enhance local feed production, and improve organic waste management. The study recommends efficiency improvements and further research to optimize BSFL production’s environmental and economic benefits
Greenhouse Gas and Air Pollutant Emissions from Composting (Nordahl et al., 2023)
Summary: This study by Nordahl et al., published in Environmental Science & Technology, reviews the greenhouse gas (GHG) and air pollutant emissions from composting processes. The authors analyze 388 emission factors from 46 studies, focusing on CO₂, CH₄, N₂O, NH₃, and VOC emissions. The study highlights that CH₄ is the largest contributor to the 100-year global warming potential (GWP100) for yard waste composting, while N₂O is the largest for nitrogen-rich wastes like manure. Effective compost pile management, including aeration, can reduce CH₄ emissions but may increase NH₃ emissions. The review underscores the need for balanced landfill diversion goals with local air quality and odor concerns from composting facilities. The authors call for more standardized measurement techniques to improve data accuracy and support policy decisions.
Recommendations: To optimize composting’s environmental benefits, the study suggests:
- Improved management practices to minimize CH₄ and NH₃ emissions.
- Further research to refine emission factors and understand the impact of composting conditions and waste characteristics.
- Consideration of non-GHG emissions and their health impacts in surrounding communities.
The Effects of Two Organic Soil Amendments, Biochar and Insect Frass Fertilizer, on Shoot Growth of Cereal Seedlings (Carroll et al., 2023)
Summary: This study explores the effects of two organic soil amendments—biochar and insect frass fertilizer—on the shoot growth of cereal seedlings. Conducted through a series of greenhouse trials, the research assesses how these amendments impact the growth of four cereals grown in Ireland: barley, oats, triticale, and spelt. The findings indicate that low quantities of insect frass fertilizer, particularly from black soldier fly waste, significantly enhance shoot growth and nutrient concentration in these cereals, especially in low-nutrient soil conditions. However, excessive application can reduce growth or cause seedling mortality. Conversely, biochar did not show consistent positive or negative effects on shoot growth, suggesting limited potential for its use as a growth-promoting agent but potential benefits for carbon sequestration in soils.
Recommendation: Insect frass-based fertilizers appear beneficial in low-input and organic cereal production systems, while biochar’s utility may lie more in carbon storage than in enhancing plant growth.
Black Soldier Fly Biowaste Treatment – Assessment of Global Warming Potential (Mertenat et al., 2019)
Summary: Cities in low- and middle-income countries face significant challenges in managing increasing amounts of waste, especially the organic fraction. Black Soldier Fly (BSF) biowaste treatment is an attractive option, offering a solution for waste management and a protein source to meet rising global demand for animal feed. This study assesses the global warming potential (GWP) of a BSF waste treatment facility in Indonesia using a life cycle assessment (LCA) approach. The results indicate that direct greenhouse gas emissions from BSF treatment are 47 times lower than those from composting. Additionally, the overall GWP of the BSF treatment facility is half that of a composting facility per ton of biowaste. The study suggests that BSF biowaste treatment is an environmentally beneficial alternative with low direct GHG emissions and potential for significant GWP reduction.
Recommendations: To further reduce environmental impacts, the study recommends improving residue post-treatment processes and considering renewable energy sources for electricity needs in BSF facilities.
Participatory Trials of On-Farm Biochar Production and Use in Tamale, Ghana (Steiner et al., 2018)
Summary: This study tested whether biochar (a type of charcoal made from burning organic materials like rice husks) can help farmers in Ghana improve their soil and grow better crops. Farmers worked with researchers to make biochar using simple stoves and added it to their soil. The results were amazing—lettuce yields increased by 93% because biochar made the soil healthier and held more nutrients. Farmers said it was easy to make biochar, and the stoves paid for themselves in just a few months. The study found that having enough materials, like rice husks, is more important than fancy equipment. Farmers’ involvement in the process made the project more successful.
Recommendations: Biochar is a great, affordable way to improve soil and grow more food. Helping farmers get the materials and tools they need should be the focus.
Potential of Duckweed in the Conversion of Wastewater Nutrients to Valuable Biomass: A Pilot-Scale Comparison with Water Hyacinth (Zhao et al., 2014)
Summary: This study compares duckweed and water hyacinth, two aquatic plants, in their ability to clean wastewater and turn nutrients into useful materials. Over a year of testing in China, researchers found that both plants removed nitrogen (N) and phosphorus (P) from wastewater well, but duckweed provided better-quality biomass. Duckweed produced high levels of protein, starch, and other valuable compounds like flavonoids, making it useful for animal feed, bioenergy, and even medicine. Water hyacinth grew faster and removed slightly more phosphorus but had more fiber, making it harder to use for practical purposes like food or fuel.
The microbial communities in the plants’ roots also played a role. Duckweed had more nitrogen-fixing bacteria, which improved its ability to recycle nutrients into biomass. Meanwhile, water hyacinth had more bacteria that removed nitrogen by turning it into gas, which made it less efficient for nutrient recovery.
Recommendations: Duckweed is a better choice for wastewater treatment because it turns nutrients into valuable products while being easier to use than water hyacinth. It is especially promising for areas needing sustainable waste and resource management.
Enhancing Agricultural Yield Using Organic Waste-Based Fertilizers (Koulouri et al., 2024)
Summary: This study looked at how combining biochar made from faeces with urine can create a powerful organic fertilizer for farming. Scientists found that soaking biochar in stored human urine helped absorb nitrogen, while adding magnesium oxide (MgO) improved phosphorus recovery. These nutrients are essential for healthy plant growth.
The research showed that using this mix as fertilizer could boost soil health and help farmers grow more crops. The method was simple and worked well, recovering more than 98% of phosphorus and a lot of nitrogen. This approach also helps manage waste sustainably.
Recommendations: Farmers in rural areas could use this fertilizer to recycle human waste and improve crop yields. It’s affordable and a great way to protect the environment.
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