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  • Author: Zbigniew Wzorek x
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Phosphorus recovery from waste - methods review

According to sustainable development principles, searching for alternative phosphorus sources, especially possible ways of its recycling from waste, should be treated as a preferential problem of the phosphorus industry. The ways admitted as most important are:

- phosphorus recovery from municipal and industrial sewage and from sewage sludge,

- utilization of phosphorus from manure

- management of waste from meat industry

The forecasts elaborated at the end of the last century, indicate that over 50% of the world phosphorus resources in use today will be depleted during the next 60 - 70 years. That fact contributes to increase of market prices of phosphorus products.

This work presents possible directions for the recovery and management of sewage sludge, meat meal and manure as a phosphorus source for chemical industry.

Manufacturing of phosphoric acid from hydroxyapatite, contained in the ashes of the incinerated meat-bone wastes

The results of the investigations concerning phosphoric acid manufacturing, by the extraction method, from the ashes containing hydroxyapatite, obtained through the thermal treatment of bone sludge have been presented. The incinerated bone sludge with ~ 16% P content and the minimal amount of impurities can be an alternative source for phosphoric acid production. The process consists in two stages. In the 1st stage, reaction of hydroxyapatite with phosphoric acid resulting in monocalcium phosphate formation in the solution obtained is carried out. The tests revealed that overall hydroxyapatite dissolution in phosphoric acid takes place when the concentration is 37% H3PO4. In the 2nd stage monocalcium phosphate is converted into calcium sulphate using concentrated sulphuric acid at the recommended temperature of 95°C. The principles of the technological idea of the process of phosphoric acid manufacturing from HA-containing ashes, obtained by bone wastes incineration, as well as a preliminary economic analysis for the production of 10 000 t/year of food-grade phosphoric acid have been developed.

The influence of thermal processing of sewage sludge on the usage properties of the formed ash

The influence of sewage sludge incineration temperature on the formed ash constitution was examined. The comparative extraction tests of two differently prepared ashes (laboratory and industrial) were carried out in order to verify if the parameters of sewage sludge incineration influence the extraction selectivity of phosphorus compounds. The laboratory ash (Alab) were prepared from sewage sludge incinerated at 950°C on a laboratory scale while the industrial ash (Aind) comes from thermal utilization system of the sewage sludge at the Gdynia Sewage Treatment Plant, which uses fluid-bed furnace incineration at 850 - 900°C. It was found that the temperature and the conditions of the sewage sludge incineration process have an effect on the usage properties of the formed ash. Despite the twofold lower Fe content in the industrial ash than that of the laboratory one, its content in extracts after phosphoric acid leaching is 4.7 times higher. The lower values of PO4 3- leaching degree from the industrial ash than the laboratory ash were observed, as well as a decrease of extraction productivity.

A chemical method of the production of "heavy" sodium tripolyphosphate with the high content of Form I or Form II

Sodium tripolyphosphate STPP is used in laundry detergent as a detergent "builder". The paper presents the chemical method of obtaining "heavy", i.e. with higher bulk density granulated sodium tripolyphosphate. The bulk density of sodium tripolyphosphate was increased by preparing a mixture of the dried sodium phosphates, the recycled subgrain of STPP and water in specific proportions and calcining this mixture for 1 hour at 400°C and 550°C (to obtain a proper STPP form) in the chamber kiln. This method allows producing the granular sodium tripolyphosphate with high bulk density (1.04-1.07 kg/dm3) and a high content of Form I or Form II, respectively.

In vitro tests of dense hydroxyapatite materials

The paper presents the results of the calcining process of deproteinised and defatted bone pulp called bone sludge. The calcining process was performed in two stages. The first step of the calcining process was realized at the temperature of 600°C in a rotary kiln. In the second stage the obtained bone ashes were calcined at five different temperatures from 650°C to 950°C for 2 hours in a chamber kiln and in air atmosphere. The products of the calcining process were characterized by the XRD method. Calcium content was determined by titration whereas the contents of total phosphorus and acid-soluble phosphorus - by the spectrophotometric method. The X-ray analysis confirmed that hydroxyapatite is the main component of the calcining products. Calcium and phosphorus contents were kept at the level of 40% and 17.5%, respectively, which corresponded to the Ca/P ratio of not stechiometric hydroxyapatite. In vitro studies, in the simulated body fluid, Ringer liquid and distilled water were realised. The measurements of pH value of SBF and Ringer fluid were realized. Additionally electrical conductivity as well as pH for distilled water where conducted. The goal of these tests was to evaluate chemical durability of dense hydroxyapatite materials.

Evaluation of the biomedical properties of hydroxyapatite obtained from bone waste

The method of obtaining hydroxyapatite by thermal treatment of deproteinised and defatted bone pulp called bone sludge was presented. The products of the calcining process were characterized with X-ray diffraction (XRD) and Fourier transformed infrared spectroscopy (FT-IR). The calcium content was determined with titration, whereas the contents of total phosphorus - with a spectrophotomertric method. X-ray investigations confirmed that hydroxyapatite was the main component of the calcining products in the calcining process. The FT-IR spectra confirmed that all organic substances were removed during the calcining process. On the basis of the research into physiological liquids the propensity to resorption of hydroxyapatite bioceramic was evaluated.

Thermal utilization of mixtures of bone waste

The results of a research related to the physico - chemical properties of the mixture of bone - waste and their ingredients have been presented. The mixtures was made up from waste: bovine bones, pork bones, bone sludge and bone meal. The content of the individual waste in the mixtures was selected on the basis of the heat of the combustion of the mixture and the amount of the waste produced in a meat processing plant. The heat of the combustion has been determined by the calorimeter, the content of phosphorus by spectrophotometric method, calcium by titration and phase composition by X - ray diffraction.

The investigations confirmed that pork bones have the highest heat of the combustion 17 MJ/kg because of a big amount of fats. The analyzed waste has contained on average 16.5 wt % phosphorus and above 30 wt % calcium. X - ray diffraction method has proved that in bone waste one phase - hydroxyapatite occurs.

Analysis of sodium tripolyphosphate production processes with a cumulative calculation method

Sodium tripolyphosphate - one of the condensed phosphates is an important ingredient in various types of cleaning substances and a food additive. The paper presents a comparison of different variants of STPP production with the application of the cumulative calculation method. The material balances of the processes were taken as the basis of the analysis. The method of the process analysis as shown in the cumulative calculation determines the influence of the emissions of dust and gas pollutions originating from a particular production process, as well as wastewater and solid wastes resulting from it, upon the natural environment. It was proved that the solution of the production STPP with the dry one-step method has the lowest impact on the environment among the three assessed solutions.

Increasing the bulk density of STPP - influence of the process parameters

The new requirements that were placed on STPP, like high bulk density, the proper relation of Form I and Form II and suitable physicochemical properties, resulted in the development of the present production methods. The paper presents the research results on increasing the bulk density of STPP by a chemical method. In the introduced method the solid sodium phosphate from spray drying and sodium orthophosphate solution, after acid neutralization, were rubbed together. Such an operation changes the physicochemical properties of the dried sodium phosphate before calcining, which results in increasing the bulk density of STPP to a level of 0.80 kg/dm3. The dependence of STPP bulk density on process parameters such as: sodium orthophosphate solution to solid sodium phosphate mass ratio, temperature of dosed sodium orthophosphate solution, as well as the calcining temperature of mixtures were analysed.

Waste release from meat processing

The aim of our work is model solution management of waste from meat industry, which would lead to zero waste production with the use of cleaner technology. The process will allow to obtain semi-finished products to be then reused for both meat industry and energy recovery. The model will include thermal utilization of meat, meat-bone and other meat industry waste. The ashes with strictly specified properties containing phosphorus components will be used as a potential raw material for the production of phosphoric acid and salts used in meat production. The new technology is going to be developed in one of the biggest meat factories in Poland - DUDA-BIS in Sosnowiec. The strategic aim of the factory is meat processing with zero waste. That would help to avoid problems with meat waste transport and the expensive utilization of waste to meat-bone meal. The reuse of suitably processed meat waste in meat production will permit to lower production costs. This model will satisfy the requirements of BATNEEC - Best Available Technology No Entailing Excessive Costs. This procedure is advantageous also because in the EU market there are 18 million tons of meat by-products1, 2 per year.

Regardless of how the utilization problems could be solved, suitably processed meat industry waste can be treated as a potential substitute for phosphoric raw materials. According to the forecast, 50% of phosphoric raw material deposits used at the moment will be exhausted in the next 60 - 70 years. As a result a necessity for a new source of the raw materials has arisen.