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This paper presents the results of a pot experiment aimed at the assessment of the fertilizer value of struvite, a precipitation product obtained from a liquid fraction of the digestate. The effects of struvite (STR), struvite + ammonium sulphate (STR + N) and ammonium phosphate (AP) treatments were examined on maize and grass cultivation on silty loam and loamy sand soil. The crop yields were found to depend on both the soil type and experimental treatment. Crop yields produced under STR and STR + N exceeded those under the control treatments by respectively 66% and 108% for maize, and 94% and 110% for grass. Crop yields under STR + N were similar or greater than those under the AP treatment. The nitrogen recovery by maize and grass reached respectively 68% and 62% from the struvite and 78% and 52% from AP. The phosphorus recovery by maize and grass reached 7.3% and 4.8%, respectively, from struvite (i.e., STR and STR + N), which was lower than that from the AP (18.4% by maize and 8.1% by grass).

Biogas is an alternative source of energy for fossil fuels. In the process of transforming organic materials into biogas significant amounts of valuable digestate are produced. In order to make the whole process sustainable digestate should be utilized this is a constraining factor in the development of the biogas industry. Consequently, there is an on-going search for new technologies to process digestate, allowing to broaden the range of possible ways of digestate utilization. One of such possibilities is technology of nitrogen (N) and phosphorus (P) recovery from the anaerobic digestate. In this study results of physicochemical analysis of materials flowing through the farm-scale bio-refinery producing struvite (STR) and ammonium sulphate (AS) are presented. Struvite was precipitated from the liquid fraction of digestate (LFDS). Ammonia was bound by sulphuric acid resulting in obtaining ammonium sulphate. The STR obtained was of medium purity and contained other macronutrients and micronutrients that further enhanced its agronomic value. The P recovery effectiveness, counted as the difference between the Ptot content in the material before and after STR precipitation was 43.8%. The AS was characterized by relatively low Ntot and Stot content. The Ntot recovery efficiency reached 43.2%. The study showed that struvite precipitation and ammonia stripping technologies can be used for processing digestate however, the processes efficiency should be improved.

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Abstract--The objective of this paper is to show that for the optimal design of an energy system, where there is a trade-off between exergy saving during operation and exergy use during construction of the energy system, exergy analysis and life cycle analysis should be combined. The two methods are often used separately, but a limited number of studies has been carried out in which they are combined in some way. An exergetic optimisation of a heat exchanger has been carried out on the basis of the life cycle analysis method in this paper. The optimisation takes into account irreversibilities due to frictional pressure drops and the temperature difference between the hot and cold stream and irreversibilities due to the production of the materials and the construction of the heat exchanger. As an example of this type of heat exchanger, a water to water heat exchanger in a city heating system has been selected. The influence of the configuration of the heating system, including the energy conversion, on the optimisation of the heat exchangers has been shown. The analysis of the heat exchanger in which exergy analysis and life cycle analysis are combined gives the design conditions of the heat exchangers which lead to the lowest life cycle irreversibility. © 1997 Elsevier Science Ltd. Heat exchangers Exergy analysis Life cycle analysis

This paper presents the results of a pot experiment aimed at the assessment of the agronomic and economic effectiveness of ammonium sulphate from an agro bio-refinery (Bio-AS). The Bio-AS was obtained by means of the ammonia stripping process from effluent after struvite precipitation from a liquid fraction of digestate. The agronomic effectiveness of Bio-AS in a pot experiment with maize and grass in two different soils, silty loam (SL) and loamy sand (LS), was investigated. The fertilising effect of Bio-AS was compared to commercial ammonium sulphate fertilizer (Com-AS) and control treatment (without fertilisation). The crop yields were found to depend on both soil type and nitrogen treatment. Crop yields produced under Bio-AS and Com-AS exceeded those under control treatments, respectively for SL and LS soils, by 88% and 125% for maize and 73% and 94% for grass. Crop yields under Bio-AS were similar to those under the Com-AS treatment. The fertilizer use of Bio-AS affected the chemical composition of plants and soil properties similarly as Com-AS. This suggests that Bio-AS from a bio-refinery can replace industrial ammonium sulphate, resulting in both economic and environmental benefits.Energies 2019, 12, 4721 2 of 15 ammonia (NH 3 ), nitrous oxide (N 2 O), and hydrogen sulphide (H 2 S) to the atmosphere [8,9]. Due to intensification of animal production observed in EU agriculture, the European Commission regulated the use of organic fertilizers in the Nitrates Directive adopted on 12 December 1991. It aimed at water quality protection across Europe by prevention of pollution of the ground and surface waters with nitrates from agricultural sources and by promoting the use of good farming practices. One of the major restrictions was the limitation of the amount of nitrogen applied, taking into account the crop needs, all nitrogen inputs and soil nitrogen supply, as well as the maximum amount of livestock manure to be applied (corresponding to 170 kg nitrogen per hectare per year) [10]. The Dutch government negotiated special derogation allowing use of 250 kg·N·ha −1 in organic fertilizers under the condition of more efficient use of nitrogen from animal sources, which is included in the Dutch Manure Policy [11] and also encompasses regulations limiting the use of P from organic fertilizers. Many studies report considerable farm-gate N surplus for dairy farms per unit area, for example 138 kg N ha −1 year −1 in Sweden, 223 kg·N·ha −1 ·year −1 in the Netherlands, and 240 kg·N·ha −1 ·year −1 in Denmark [12]. So far, the dominant method of processing of animal waste has been anaerobic digestion. The process results in the production of biogas and digestate [13]. Biological conversion of organic compounds during anaerobic digestion considerably reduces the odour as compared to untreated manures [14][15][16]. Both the nitrogen and phosphorus content in the digestate are comparable with untreated manure; however, in contrast to livestock manures, the digestate is characterized by the presence of the nutrients in solub...