Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
Disposing waste at a landfill is no longer a preferable method of waste handling. Instead, waste is recycled, reused and further processed to extract materials and energy. Sweden is putting effort to develop ways of incorporating the waste back into the material and energy cycle. Plants require various nutrients to germinate and grow in the same way as humans need vitamins and minerals to be healthy. The most important nutrients for plants, both aquatic and inland, are nitrogen, potassium and phosphorus. Phosphor mineral, such as apatite, is a finite, non-renewable resource. From current world-wide sources, this mineral is expected to be depleted in the next couple of hundred years. According to the United States Geological Survey (USGS, 2012), if production and consumption remain at current levels, notable phosphorous reserves will be exhausted in 350 years. These estimates may change as phosphorous becomes more valuable. As prices for this resource rise, extraction of costlier phosphorous will become economically attractive, expanding supply. While the resource is limited, technical and economic forces will determine how much phosphorous is available in the long term. Phosphorus exists in both the manure and chemical fertilizers. These are used with the purpose of improving the soil conditions for the plants. The nutrients supplied to the soil can be inaccessible for the plants to take up. But by symbiosis with mycorrhiza, plant roots have a better chance of absorbing phosphorous. If the phosphorous supply to soil is excessive, plants are unable to take it all up. Excess phosphorous can then dissolve or bind to fine soil particles, and get flushed into rivers, lakes, oceans and groundwater. In large amounts, phosphorous can lead to eutrophication of water bodies, which in turn leads to unwanted algae growth. This water becomes cloudy and poor in oxygen, which leads to death of fish and aquatic life. It is therefore important to ensure that phosphorous spread to the water system is limited. The phosphorus that has already been extracted needs to be managed efficiently as to minimize the effects on the environment. The remaining reserves require prudent management to ensure this vital resource is not wasted. Large amounts of phosphorus currently end up in urban waste, mainly in sludge and ashes. Reusing ash and sludge to arable and forest soil brings responsible recycling of phosphorus one step closer to realization. This is vital in order to ensure phosphorus fertilizers for future generations. The objective of this work was to use various residues as phosphorus fertilizers and evaluate their impact on phosphorus availability to plants in soil. This report discusses the possibilities and limitations of using waste such as, sludge and ash from sewage treatment plants and incinerators, as soil fertilizers. The experiments were conducted at the Environmental laboratory at the research group of Waste Science and Technology, Luleå University of Technology, LTU. In order to carry out the experiment, grass and herb seeds were sawed on different soil mixtures: one with just soil, another soil mixed with two different ashes, a third was soil mixed with sludge, and two synthetic compounds, CaK2P2O4 and CaKPO4, mixed with the soil. The evaluation methods used in this experiment were leaching test (liquid to solid ratio (L/S) 2), sequential extraction, phosphorus extraction and plant analyses. The results of the measurements show that the plants are capable of transforming phosphorous into an available form. The results of the sequential extraction, most notably the exchangeable fraction, show that phosphorus concentrations are greater in the rhizosphere soil, versus the concentration in the bulk soil. The conclusion of the experiments is that the roots are able to make some of the unavailable phosphorus available. This means that the plants get an enhanced supply of phosphorus from the different materials. Although it is acknowledged that pH has a great importance for phosphorus mobility and accessibility in soil, it did not have any significant effect on the uptake of phosphorous by the studied plants Bio-ash was the byproduct that resulted in the most available phosphorus for the plants followed by the two synthetic materials, CaK2P2O4 and CaKPO4. Despite of that, the highest biomass of plants was measured in soil that was amended with sludge. This indicates, that other factors, such as availability of N, K and micronutrients, amount of organic matter and soil pH are no less important for vegetation growth than available phosphorus.
2012. , 49 p.