Phosphorus as phosphate and nitrogen as ammonium or nitrate are the main nutrients in wastewaters and agricultural sludges. They runoff easily to waterways and cause eutrophication in water bodies. However, ammonium and phosphate could be precipitated simultaneously and used as recycled nutrients. In this research, dolomite calcined at 650 °C, 750 °C, or 950 °C and commercial MgO were used as precipitants in simultaneous phosphate and ammonium removal from synthetic (NH4)2HPO4 solution and agricultural sludge. Calcination at 750 °C was the preferred option as dolomite was decomposed to MgO and CaCO3 for optimal struvite precipitation. Molar ratios of 1.1–1.6:1–2:2 (Mg:P:N) were employed in the experiments. Very robust ammonium removal was obtained with MgO (57%), dolomite 650 °C and dolomite 750 °C (75%). MgO removed almost all phosphate, while dolomite 650 °C removed 65%, and dolomite 750 °C removed 60% (70% from agricultural sludge). Some part of the phosphate was adsorbed, most likely by CaCO3, during dolomite precipitation. Struvite was the only identified reaction product in all samples after 24 h of precipitation. Calcined dolomite had great potential in ammonium and phosphate precipitation from both synthetic waters and agricultural sludges and the precipitates could be used as recycled fertilizers.
The European Union's circular economy strategy aims to increase the recycling and re-use of products and waste materials. According to the strategy, the use of industry waste materials and side flows is required to be more effective. In this research, a chemical precipitation method to simultaneously remove ammonium and phosphate from the reject water of anaerobic digestion plant using calcined paper mill sludge and fly ash as a precipitant, was tested. Paper mill sludge is a waste material formed in the paper-making process, and fly ash is another waste material formed in the power plant. Objective of this research was to test whether these industrial waste streams could be used as low cost precipitation chemicals for ammonium and phosphate removal from wastewaters and whether the precipitate could be suitable for fertilizer use. Results indicated that calcined paper mill sludge had high removal efficiency for both ammonium (97%) and phosphate (73%). Fly ash also had good removal efficiency for both ammonium nitrogen (74%) and phosphate (59%) at 20 ± 2 °C. The precipitates contained high concentrations of nitrogen and phosphate and could be used as a recycled fertilizer. Other possible mechanisms for the removal of phosphate and ammonium were considered.
Five separate work packages associated with sinter production and quality have been undertaken and during the project great number of planned operational test were accomplished at each participating sinter plant. The first work package, burn-through management across the sintering strand, has been investigated by all partners. The effects of individual feeder gate position changes on bed height and to burn-through point have been established, but the combined sensitivities show large variations in the case of Corus UK. An algorithmic control system would not be appropriate. Video images of burning sinter at the discharge have been analysed and showed the effect of gate changes, but interaction with other zones is apparent. Due to problems with invariant correlation between feeder gate positioning and burn-through profile, it was not possible to complete the feeder gate controller in a closed-loop scheme at HKM. Manual management has been used to optimise the utilisation of the feeder gate system. Rautaruukki has implemented burn-through profile control across the strand and has found that it has good possibilities for stabilising the sintering process. However, equipment on the feeder gate system was permanently damaged. A new feeder gate system has to be redesigned and rebuilt before any further actions are possible with this control. All partners have taken part in the second work package. Corus UK has modelled the existing manual rules for waste gas temperature control and them have been found to be good in practice. Otherwise at HKM and Rautaruukki, burn-though point measurement has been implemented, used in strand speed control and found to improve production rate and sinter quality. Sinter and waste gas temperatures have been found to be useable in a cascade control scheme. The control is in continuous use at Rautaruukki's sinter plant in Raahe. A strand speed controller has been developed on the basis of a simulation model at HKM. The advantages of the controller are to allow the personnel to ensure an optimum and constant burn-through point, and to raise the production rate and the quality of sinter. Optimization of restart strategy led to significant advances with respect to all relevant criteria. Developing of an on-strand permeameter was the third work package. Corus UK has developed an on-strand permeameter making use of air and gas flows to the ignition hood, pressure in the ignition hood and windleg suctions beneath the ignition hood. The roll feed hopper control has been improved by means of a special control algorithm which employs a dynamic model. The aim was to stabilise the sinter mix flow rate and improve permeability. The on-strand permeameter also referred to as a measuring pallet has been implemented at the sinter plant of HKM and shown to be reliable in long-term operation. The on-strand permeameter provides unique information about actual conditions in the sinter process on the strand. Rautaruukki has developed and implemented an on-strand permeameter, which for the most part works correctly. At times there seem to be too many disturbances in the degree of sinter bed compression. Fluctuations in the degree of compression cause fluctuations in the input variables of the permeameter. This permeability management system makes use of the rate of change of several sintering process input variables and their interactions with the aim of optimising production rate.
The European Union’s circular economy strategy aims to increase the recycling and re-use of products and waste materials. According to the strategy, the use of industry waste material should be more effective. A chemical precipitation method to simultaneously remove phosphorus and nitrogen from synthetic (NH4)2HPO4 solution and the liquid phase of anaerobic digestate using fly ash as a precipitant was tested. Fly ash is a waste material formed in the power plant process. It mainly contains calcium oxide (CaO) and magnesium oxide (MgO). Saturated precipitant solution was prepared from fly ash, which was added in small proportions to (NH4)2HPO4 solution during the experiment. Fly ash’s effectiveness as a precipitant was compared with that of commercial CaO and MgO salts, and it can be observed that fly ash removed as much ammonium and phosphate as commercial salts. Fly ash sufficiently removed ammonium nitrogen and phosphate from the liquid phase of anaerobic digestate, which led to the formation of ammonium magnesium hydrogen phosphate hydrate, struvite (NH4MgPO4·6H2O), and calcium hydroxide phosphate, monetite, CaPO3(OH). In this study, we have shown for the first time that fly ash can be used to manufacture recycled, slow-release fertilizers from anaerobic digestate.
Currently, recycling and re-use of materials is extremely important due to the diminishing of natural resources.The objective of the European Union's circular economy strategy is to increase recycling and the use of industrial waste materials and side streams as secondary raw materials.In this study, a chemical precipitation method to simultaneously remove ammonium nitrogen and phosphate from the liquid phase of anaerobic digestate using calcined paper mill sludge was studied.Papermill sludge is a waste material that forms in the paper-making process.In addition, commercial calcium oxide (CaO) was used as a reference precipitant.The suitability of the formed precipitate's composition for recycled fertilizer use was also considered.The study results indicated that calcined paper mill sludge was as effective precipitant as commercial CaO in the removal of ammonium nitrogen and phosphate from the synthetic wastewater.In addition, the results indicated that calcined paper mill sludge removed efficiently phosphate from the liquid phase of anaerobic digestate, which led to the formation of hydroxyapatite, Ca 5 (PO 4 ) 3 (OH).In this research we have shown, that calcined paper mill sludge can be used to produce recycled, slow-release, solid fertilizer.Another possible reaction, such as adsorption was also considered.
