Composting with Zeolite
Natural zeolite is incorporated into compost to significantly reduce heavy metal uptake by plants. Zeolite is also used to combat odors produced by waste and manure composting.
Composting is a process that converts organically bound nitrogen to ammonium nitrate and ammonia, both of which are plant-accessible nutrients. It also kills pathogens, dries manure, and kills weed seeds. Ultimately, the goal is to produce high-quality compost that can be used as a bio-based soil amendment.
Methane and nitrous oxide are two greenhouse gases produced during the composting process. Scientists have concluded that both gases are more potent than carbon dioxide.
Studies have demonstrated that aluminum silicates can reduce emissions by up to 100% percent.
Natural zeolite has two methods of holding cations such as ammonium. The first method is absorption, made possible by the mineral’s high surface area and porosity. The second method is by cation exchange. Natural zeolite can sequester nitrates, sulphates, and hydrogen ions, which can prevent methane and nitrous oxide production during the composting process.
Remediating Soil & Solid Waste Compost with Natural Zeolite
The incorporation of untreated or Mg-modified natural zeolite in municipal solid waste compost has been shown to reduce the heavy metal concentration of corn plants growing in the remediated soil.
A primary negative result of municipal waste composts is the contamination of soils with heavy metals. Management of the composted soil must be conducted before any land application in order to prevent heavy metal uptake by plants. Total uptake of Pb, Cu, Mn, Zn, Ni, and Cd was studied in corn plants, grown in remediated soil, with and without the addition of different natural zeolites.
A greenhouse experiment tested the potential effects of composts containing natural zeolite on the distribution of heavy metals in corn plants. Natural zeolite was added to the municipal solid waste at the starting of the composting process at 5%, 10%, and 15% by volume. The solid waste was processed to a size less than 60mm. The waste was mixed with zeolites at different ratios and the composting process was performed for two months. The compost was mixed every three days.
Manure Composting and Odor Reduction
Zeolite also aids in the process of manure composting and acts as an odor control agent because of its ability to absorb and adsorb liquids, gases, and suspended matter. Both properties work together to combat odors linked to manure composting. Ammonium in liquid and solid wastes is constantly undergoing conversion to ammonia gas. Zeolite controls odors by absorbing moisture from waste and adsorbing the ammonia produced by microbial activity on the liquids.
Researchers have identified three main benefits that zeolite provides to manure composting and odor reduction efforts. First, it promotes nitrogen retention in animal waste by adsorbing ammonia. Manure mixed with zeolite serves as a high-quality fertilizer because plant-available nitrogen is retained and returned to the soil. Second, zeolite controls the moisture content in excrement through its water absorption properties. Finally, zeolite purifies the methane gas produced by the anaerobic digestion of manure.
A study by Bernal examined the level of ammonia loss from several straw-slurry mixtures placed into a composting simulator. Then, researchers passed air through the composting materials and finally, funneled the spent-air stream over a zeolite sample. Results indicated that between 53 g kg – 82 g kg of zeolite retained 80 percent of nitrogen in manure compost. Bernal concluded that covering composting materials with a combination of straw and zeolite is a highly effective method to reduce ammonia emissions.
Meisinger also conducted a study that examined the ammonia volatilization of on-farm slurry. The results indicated that adding 6.25 percent zeolite to barn-stored dairy slurry reduced ammonia emissions by 55 percent when compared to the untreated slurry. Also, soluble phosphorus levels in the slurry were reduced, which has positive environmental implications.
A study that examined the use of zeolite in the anaerobic digestion of pig wastes found that utilizing zeolite doses of 8 and 12 g l improved digestion performance, mainly due to the ability of zeolite to reduce ammonium through ion exchange. Results suggested that zeolite had a positive impact on the toxicity of ammonia, the level of methane produced, and regulated the acidity of pig waste
References
Untapped potential of zeolites in optimization of food waste composting - M. Waqas, et al.