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Resource recovery reduces the need for extracting natural resources for raw materials in manufacturing or production processes and reduces the amount of waste going to landfills, while also encouraging better design for Remanufacturing business models and recycling processes. Thus resource recovery and recovering value from waste are a core framework in the Circular Economy and Biobased Economy.
This case study considers the following innovations in Resource Recovery: nutrient recovery, brewing waste food, and chicken feather fertilizer.
Agricultural productivity usually requires the addition of fertilizers like nitrogen and phosphorus. Yet, their presence in wastewater and runoff systems is the reason for algal blooms in freshwater systems. Phosphorus is a mined resource that exists in just a handful of places worldwide, and the cost continues to rise. Conventional methods of removing phosphorus and nitrogen from wastewater do not enable society to take full advantage of these elements as co-products of the wastewater treatment process. There are restrictions due to the presence of heavy metals or even economic hurdles related to the conventional extraction of phosphorous and nitrogen —whether extracted from struvite, sludge, or ash.
Through liquid phase extraction and early removal of elements such as phosphorus in the wastewater treatment process, nutrient recovery enables full lifecycle management of essential substances in limited supply while preventing freshwater pollution. Using a combination of aerobic digestion and nutrient recovery techniques, valuable nutrients can be extracted from wastewater.
Struvite Precipitation removes or digests phosphorus from wastewater at an earlier stage through the formation of struvite, an effective, slow-release fertilizer with a relatively low content of contaminants, which is easily harvested. Struvite is considered a promising alternative to mined phosphorus (P) fertilizer. Ammonia stripping is another process that enables the gas to be extracted from liquids or solids. This procedure can take place inside an anaerobic reactor and generally occurs in two phases. The first procedure is the aeration phase, in which dissolved air passes by a filter panel, helping oxidizing bacteria to thrive, as they convert ammonia into nitrite. Through closed-loop flow, the alkalinity inside begins to drop until the process is ready to go to the second phase. The second procedure is the mixing step. This time, without dissolved oxygen, it happens when remaining substances are mixed until they become nitrogen gas, which can then be used as a fertilizer. Run-on ammonia and nitrite, this process does not require external carbon fuel sources.
Selective Compound Removal can also be used to recover phosphates, fluoride, or heavy metals from wastewater through Ceramic Membranes. (See our stories on Zero Liquid Discharge and Closed Loop Water Filtration for more on using Nanofiltration to treat wastewater for reuse.)
Brewing Waste Food
Most animal feed is a considerable expense for farming systems; adequate and good-quality feed supplies are some of the most significant factors in farm management. Consequently, the production of animal feed from agro-residues may represent a massive cash return as the need for animal feed is nearly entirely stable. It can be derived from a variety of sources, including byproducts from fruits, vegetables, sugar, starch, grain, oil, and byproducts from distilleries and breweries.
The waste from the alcohol-making process, known as Brewer's Spent Grain (BGS) or dried distillers' grains with solids (DDGS ), especially DDGS from the Scotch malt whiskey industry but also from beer, can be used for animal feed applications. Anaerobic digestion by microbes break down and digest DDGS waste, and the resulting product can then be fed to bigger creatures such as worms and larvae, which are, in turn, then fed to fish. Aquafeed has been shown to hold substantial economic value as it is less expensive than other protein and energy sources like soybean meal, in addition to improved feed consumption, feed efficiency, and growth. With rising interest and investment in aquaculture, the closed-loop system of aquaponics is a sustainable way to cultivate fish using the detritus from the fish tank in hydroponic plants, cleaning the tank and feeding the plants at the same time.
High in fiber and protein, BGS and DDGS can even be suitable for human consumption. Yeast extract has been around since 1902, but more recent innovations include using spent grains for plant-based milk, in flour to produce pasta and bread products, as well as to creating snacks, veggie burgers, and even in meat products.
Chicken Feather Fertilizer
Recent studies have shown that poultry feathers are loaded with keratin protein and amino acids, two high-quality components for nitrogen-enriched organic fertilizer. Instead of releasing poultry feathers into the environment in the form of waste, an environmentally-friendly, cost-effective procedure to recover keratin reintegrates the material into the chain as a nutrient-rich organic fertilizer with excellent outcomes for plant growth.
Converting chicken feather waste into fertilizer is expected to reduce the amount of carbon dioxide released into the atmosphere while stimulating the use of low-impact, renewable, organic matter as a nutrient source for crop health.
The most common method of feather waste management is through steam pressure cooking. This technique consists of placing poultry feather (quills and barbs) waste into a supercritical carbon dioxide system at 600 °C (the processing time is variable according to the number of feathers), which leads to the formation of well-shaped carbon microspheres and ammonium bicarbonate ((NH4)HCO3). Additionally, nutritional elements for plant growth, such as nitrogen, phosphorus, magnesium, potassium, and sodium, were recovered in the final product, providing soil deacidification capabilities. A technology appplication that could take advantage of the material harvested from chicken feather is Nitrogen-fixing Bacteria Coating
This technique requires a significant amount of energy, resulting in high production costs. An alternative technique involves combining feather waste with calcium oxide treatments and brown coal in a rotational reactor to produce mineral-organic fertilizer. This process has the potential to lower our agricultural dependence on fossil fuel-based products and offer new business opportunities in the sustainable and organic fertilizer markets.
Opportunities and Challenges
Resource recovery is a growing market, and the demand is high from both an environmental and economic perspective. Scalability of nutrient recovery is possible due to the potential applications in anaerobic digestion plants, which are already used across the globe to treat organic waste streams. However, for nutrient recovery to be fully deployed in the wastewater treatment sector, the reuse of previously unused waste could be integrated back into the chain.
By contrast, one of the most significant constraints in scaling-up PHA production is the cost of the carbon source metabolized by the microorganisms. However, cheap and renewable carbon substrates, notably residues from aquaculture, agriculture, and industrial waste, are currently being researched worldwide. Algae shows excellent potential as a Biofuel, and production of PHA polymers from algae as a byproduct may be possible and even enhanced through genetic engineering techniques such as CRISPR. In the future, water treatment plants from cities and industries could also be transformed into raw-material providers to create bioplastics and reduce waste. This would add even more value to these facilities and help close the loop for urban dynamics unfamiliar with returning materials to their source.
Reusing waste materials such as struvite, spent grains and chicken feathers drastically changes the whole basis of production and growing crops. Without harming the environment, organic waste could become a self-sustaining, renewable source to a business model, such as the Hyperlinked Supply Chain, for example, that is economically, ecologically, and socially sustainable. Eventually, it could help society develop a new mindset condemning and completely eliminating toxic fertilizers from farms.
All in all, bringing value back to discarded items through resource recovery helps close the loop, while expanding the range of resourceful means to provide sufficient supply to meet the rising demand of a globally growing population.